Author Topic: Boyancy, MaxLoad, MaxPower + USCG -calculations on Standard 18/20 tutorial style  (Read 790 times)

Offline KenB

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THIS IS, ONCE AGAIN, A GENTILE REMINDER TO TAKE THE FOLLOWING COMMENTS WITH A HUGE GRAIN OF SALT.  JALLII HAS NEVER SHOWN EVIDENCE OF SAWDUST, CURED EPOXY, OR ANYTHING CLOSE THE TYPE OF WORK EVERYONE ELSE ON THIS WEBSITE POSTS.

I HAVE READ THROUGH THE ENTIRE COMMENT AND THERE IS NOTHING OF VALUE IN IT.

AS USUALLY, TAKE CARE THAT THE USEFUL INFORMATION (PROBABLY NOT CONTRIBUTED BY JALLII) IN THIS THREAD NOT BE OVERLOOKED.
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BobC et al - For the record, closed-cell POLYETHYLENE foam does not become waterlogged over time an neither is it degraded by petroleum products such as gasoline, diesel, or oil (or alcohol).  I read that long ago, and personally gave chunks of foam a 1 year test ... soaking in the various liquids (water, gas, oil) in 5-gallon buckets ... foam weighted down to keep it completely immersed and liquids kept topped off as they evaporated.  The foam was evaluated visually (signs of breaking down or loss of flotation) and were each weighed (in grams) before and after the test.  The worst case was with water, and the foam only weighed 3% more after the test ... an insignificant loss of flotation.  My conclusion was that closed-cell polyethylene foam was the way to go for flotation ... the only downside is that it's not available as a pour-in or spray-in foam, but must be cut to fit and glued or trapped in (chambers).

I agree that close cell polyethylene foam as a material is probably if not the best, then at least among the best materials. The problems with that is just as you described the availability and form.

I now bring 3 other prospective candidates to the table.

1. The first one is EPOXY FOAM

Ideal in all ways but price.  It has all the good qualities. Its extremely resistant to water and chemicals. You CAN pour it into cavities. You can regulate its density, that is,  its foaming.  It is ideal when considering compatibility with other epoxy work.  Used a lot in keel structures, surfboards etc...   Also gives some structural strength.  You can even combine it with prepreg work....

I have not calculated the total cost for a boat, but its not a cheap solution.  Probably worth the price in some places as a partial solution.  I will post 2 PDF for this type of material. A Finnish provider is selling it online for  about 200€ / 5 kg resin and about 90 € / 2 kg hardener.  I think its a French product by Sicomin. Density of final product is 170 kg or 250 kg / cubic meter.  This is 2 part epoxy, but with 3 part epoxy foams you can regulate the density. 

2. PVC- foam + other plastic foams
Yes PVC os also available as foam. Similar to polyetylene, but you CAN glue it unlike polyetylene. Similar problems with price and availability.  There are also other plastic foams that have similar properties and problems. Now we have to remember that the floating material need not be hidden. There are some PVC foam products that are glued to internal surfaces of the boat, so that they have a double function as a pleasant internal surface, but still provide some flotation volume. Again the gained volume / price is not great. 

3. In search for a cheap solution for DIY builders
One possibility I have studied is a surprising one. Exstruded Polystyrene or closed cell XPS, is available in large quantities as a building material. That mekes it extremely cheap and readily available as about 2 inch sheet product.  Remember I am not talking about normal polystyrene. Expanded polystyrene is hopeless material that absorbs large amounts of material. XPS is made of the same material, but because of the manufacturing process it has very different qualities. It has closed cell structure. These cells are very small in size, and the surface of the sheet get some additional protection from surface absorption due to how its formed. 

According to a Finnish manufacturer their product has only 2% water absorption due to the extremely tight closed cell structure.  I do not know if there are differences in the manufacturing process in different countries. I have also heard some counterclaims about XPS long term water absorption, but IF you boost the water resistance with a layer of epoxy... 

It most certainly is cheap, but it also has serious problems with chemical resistance. If used with normal polyester products, it literally dissolves into the styrene that is the solvent in polyester. It is also vulnerable to other solvents that are common in a boating environment.  This means that if used, it must be properly protected from chemical exposure. Luckily it does not react to epoxy or polyurethane products.  BUT its very cheap, and you can cover it with a thin layer epoxy + glass layer to harden it against environment. Epoxy is one of the best protections against chemicals. If it is protected from mechanical forces it should be fine. 

I see 2 potential ways to use it.

A. You could build the thickness up to a block, cover it with epoxy + glass and strap it  in its place.  You can easily cut it with a electrically heated resistor wire. Thus you can build up any desired form by stacking 2 inch thick pieces. Just cover the whole thing with thin layer of epoxy and glass to hold it as a block and protect from chemicals.

You could also use it in sheet format for example on the sides of the boat. You could simply glue it to the sides and then cover it all up with either epoxy + glass or plywood using products that do not melt the XPS.  In that case it would be exactly in the sweet spot for floating material. 4-5 cm layer covering the sides gives a considerable amount of flotation. If covered with thinnest, cheapest plywood available, you would never even notice it.

Adding some pool noodles or other flotation material below the decking if needed would probably be enough to complete even the most demanding boat.


Ps. Posting these pdf was a bit problematic. The other one is split in 3 parts
 
« Last Edit: April 18, 2024, 07:27:53 AM by KenB »
best,
KenB

"HOW CHEAPLY CAN A TOLMAN SKIFF BE BUILT AND JUST HOW  MUCH IS SACRIFICED IF COST IS THE PRIME MOVER?"
- Bruce Armstrong   

"I can tell you that either a nice BFT or a big YFT is an absolute riot on a Tolman. The boat is so light it's like the old man and the sea..."
- Dave Nolan (RIP)

Offline KenB

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THIS IS, ONCE AGAIN, A GENTILE REMINDER TO TAKE THE FOLLOWING COMMENTS WITH A HUGE GRAIN OF SALT.  JALLII HAS NEVER SHOW EVIDENCE OF SAWDUST, CURED EPOXY, OR ANYTHING CLOSE THE TYPE OF WORK EVERYONE ELSE ON THIS WEBSITE POSTS.

I HAVE READ THROUGH THE ENTIRE COMMENT AND THERE IS NOTHING OF VALUE IN IT.

AS USUALLY, TAKE CARE THAT THE USEFUL INFORMATION IN THIS THREAD NOT BE OVERLOOKED.
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Renn designed the Standard for moderate loads and moderate power. On page 16 Renn discusses the Standard skiffs and says:
Quote
" I consider 40 to 70 horsepower to be a reasonable power range for open Standard skiffs. My guideline for engine weight for standard skiffs is 300 pounds; if you exceed this you'll probably have a stern-heavy skiff (see next paragraph). So if you're thinking about twin40- or 50-horsepower engines (many owners want to have full planing speed on one engine alone), choose the Widebody, wich can pack all that iron much better. Fifty horsepoweris the mostcommon power for Standard skiffs intended to carry moderate loads, say 3 people and gear. At the top end of the range a 70 horsepower two stroke Yamaha and a 15-horsepower auxiliary, both with 20 inch shafts is a combination that falls within my weight guideline.
I think the Standard skiff is best as an open skiff. Although you can build cabins on them ..." 

If I compare the result to what Renn recommends I notice a major difference.
Renn recommended Max power mostly based on weight, and much smaller numbers.  CFR seems to allow for much more powerfull engines.  USCG boatbuilders handbook and the CFR allows for much more power. Bigger and heavier boats need more power to move them at a reasonable speed. The fact that it is realistic to have power recommendation thats is less than half or a third of the allowed Max HP is a testimony of the quality and purpose of the design.   

Determining MAXIMUM POWER (MAX HP) according to 33 CFR 183 Subpart D

Quote
§ 183.51 APPLICABILITY.
This subpart applies to monohull boats less than 20 feet in length, except sailboats, canoes, kayaks, and inflatable boats, that are designed or intended to use one or more outboard motors for propulsion.

§ 183.53 HORSEPOWER CAPACITY.
The maximum horsepower capacity marked on a boat must not exceed the horsepower capacity
determined by the computation method discussed in paragraph (a) of this section, or for certain
qualifying boats, the performance test method discussed in paragraph (b) of this section.

(a) The maximum horsepower capacity must be computed as follows:
 (1) Compute a factor by multiplying the boat length in feet by the maximum transom width in feet excluding handles and other similar fittings, attachments, and extensions. If the boat does not have a full transom, the transom width is the broadest beam in the aftermost quarter length of the boat.
 (2) Locate horsepower capacity corresponding to the factor in Table 183.53.
 (3) For a boat with a factor over 52.5, if the horsepower capacity calculated in Table 183.53 is not an exact multiple of 5, it may be raised to the next exact multiple of 5.
 (4) For flat bottom hard chine boats with a factor of 52 or less, the horsepower capacity must be reduced by one horsepower capacity increment in Table 183.53.

 
STEP 1 Calculating the FACTOR

Standard 18:
LENGTH =18 feet    BEAM = 81 inch  = 6.75 feet 
==>  Factor 18 = 18 X 6.75 = 121.5

Standard 20:
LENGTH =20 feet    BEAM = 81 inch  = 6.75 feet 
==> Factor 20 = 18 X 6.75 = 135




STEP 2  Determine correct formula and calculate MAX HP


A: If boat has remote steering and the transom height is over 20 inch.

The correct formula for Standard 18/20 is HP = (2 x factor) – 90
Calculate for Standard 18        (2 x 121.5) -90 = 153 HP
Calculate for Standard 20        (2 x 135) -90 = 180 HP

Quote
Renns guideline for Standard skiffs HP range is 40-70 hp.
We can see that CFR allows for a boat of this size to have 2-3 times more HP.
This is a very significant difference. Builders should follow Renns guideline.
The boat is not designed for the much larger power the CFR allows.
Large power requires a boat designed to handle it.

B: If boat does not have remote steering or the transom is lower than 20 inch.

The correct formula for standard 18/20  is HP = (0.8 x factor) – 25
Calculate for Standard 18        (0.8 x 121.5) -25 = 72.2 HP
Calculate for Standard 20        (0.8 x 135 )  - 25 = 83 HP
best,
KenB

"HOW CHEAPLY CAN A TOLMAN SKIFF BE BUILT AND JUST HOW  MUCH IS SACRIFICED IF COST IS THE PRIME MOVER?"
- Bruce Armstrong   

"I can tell you that either a nice BFT or a big YFT is an absolute riot on a Tolman. The boat is so light it's like the old man and the sea..."
- Dave Nolan (RIP)

Offline KenB

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- I recently completed the ABYC standards course; his use of 3D models is not an acceptable method.
- Renn was correct about engine size and weight; the book is right, Jallii is wrong.
- Jallii made numerous arithmetic errors, resulting in Jallii's unsupported conclusion.  When you fix his math, his conclusions are wrong.

Again, none of Jalllii's comments in this thread show any evidence of having started, built, or completed a Tolman Skiff. Or built any kind of boat, for that matter.

Pool noodles and hot glue are more than adequate. On other more informative threads where the math is done correctly, because plywood floats, only the plywood above the gunnels/shelves needs corresponding floatation. This is in contrast to poly/resin/fiberglass boats, where the entire hull is denser than water and needs floatation.
« Last Edit: April 19, 2024, 12:21:48 AM by KenB »
best,
KenB

"HOW CHEAPLY CAN A TOLMAN SKIFF BE BUILT AND JUST HOW  MUCH IS SACRIFICED IF COST IS THE PRIME MOVER?"
- Bruce Armstrong   

"I can tell you that either a nice BFT or a big YFT is an absolute riot on a Tolman. The boat is so light it's like the old man and the sea..."
- Dave Nolan (RIP)

Offline BobC

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BobC et al - For the record, closed-cell POLYETHYLENE foam does not become waterlogged over time an neither is it degraded by petroleum products such as gasoline, diesel, or oil (or alcohol).  I read that long ago, and personally gave chunks of foam a 1 year test ... soaking in the various liquids (water, gas, oil) in 5-gallon buckets ... foam weighted down to keep it completely immersed and liquids kept topped off as they evaporated.  The foam was evaluated visually (signs of breaking down or loss of flotation) and were each weighed (in grams) before and after the test.  The worst case was with water, and the foam only weighed 3% more after the test ... an insignificant loss of flotation.  My conclusion was that closed-cell polyethylene foam was the way to go for flotation ... the only downside is that it's not available as a pour-in or spray-in foam, but must be cut to fit and glued or trapped in (chambers).

I agree that close cell polyethylene foam as a material is probably if not the best, then at least among the best materials. The problems with that is just as you described the availability and form.



Thanks for confirming my suspicions with actual "lab" testing.  LOL  Good info to know. 

I now bring 3 other prospective candidates to the table.

1. The first one is EPOXY FOAM

Ideal in all ways but price.  It has all the good qualities. Its extremely resistant to water and chemicals. You CAN pour it into cavities. You can regulate its density, that is,  its foaming.  It is ideal when considering compatibility with other epoxy work.  Used a lot in keel structures, surfboards etc...   Also gives some structural strength.  You can even combine it with prepreg work....

I have not calculated the total cost for a boat, but its not a cheap solution.  Probably worth the price in some places as a partial solution.  I will post 2 PDF for this type of material. A Finnish provider is selling it online for  about 200€ / 5 kg resin and about 90 € / 2 kg hardener.  I think its a French product by Sicomin. Density of final product is 170 kg or 250 kg / cubic meter.  This is 2 part epoxy, but with 3 part epoxy foams you can regulate the density. 

2. PVC- foam + other plastic foams
Yes PVC os also available as foam. Similar to polyetylene, but you CAN glue it unlike polyetylene. Similar problems with price and availability.  There are also other plastic foams that have similar properties and problems. Now we have to remember that the floating material need not be hidden. There are some PVC foam products that are glued to internal surfaces of the boat, so that they have a double function as a pleasant internal surface, but still provide some flotation volume. Again the gained volume / price is not great. 

3. In search for a cheap solution for DIY builders
One possibility I have studied is a surprising one. Exstruded Polystyrene or closed cell XPS, is available in large quantities as a building material. That mekes it extremely cheap and readily available as about 2 inch sheet product.  Remember I am not talking about normal polystyrene. Expanded polystyrene is hopeless material that absorbs large amounts of material. XPS is made of the same material, but because of the manufacturing process it has very different qualities. It has closed cell structure. These cells are very small in size, and the surface of the sheet get some additional protection from surface absorption due to how its formed. 

According to a Finnish manufacturer their product has only 2% water absorption due to the extremely tight closed cell structure.  I do not know if there are differences in the manufacturing process in different countries. I have also heard some counterclaims about XPS long term water absorption, but IF you boost the water resistance with a layer of epoxy... 

It most certainly is cheap, but it also has serious problems with chemical resistance. If used with normal polyester products, it literally dissolves into the styrene that is the solvent in polyester. It is also vulnerable to other solvents that are common in a boating environment.  This means that if used, it must be properly protected from chemical exposure. Luckily it does not react to epoxy or polyurethane products.  BUT its very cheap, and you can cover it with a thin layer epoxy + glass layer to harden it against environment. Epoxy is one of the best protections against chemicals. If it is protected from mechanical forces it should be fine. 

I see 2 potential ways to use it.

A. You could build the thickness up to a block, cover it with epoxy + glass and strap it  in its place.  You can easily cut it with a electrically heated resistor wire. Thus you can build up any desired form by stacking 2 inch thick pieces. Just cover the whole thing with thin layer of epoxy and glass to hold it as a block and protect from chemicals.

You could also use it in sheet format for example on the sides of the boat. You could simply glue it to the sides and then cover it all up with either epoxy + glass or plywood using products that do not melt the XPS.  In that case it would be exactly in the sweet spot for floating material. 4-5 cm layer covering the sides gives a considerable amount of flotation. If covered with thinnest, cheapest plywood available, you would never even notice it.

Adding some pool noodles or other flotation material below the decking if needed would probably be enough to complete even the most demanding boat.


Ps. Posting these pdf was a bit problematic. The other one is split in 3 parts
 

Offline BobC

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Jalli,

Based on my experience with building stitch and glue, every peice of wood bends slightly differently.  That means that a guy building using Renns given dimensions and marine fir will get one shape, and a guy using stiffer meranti or baltic birch might get a different shape yet.  Renn built backwards for a purpose.  Until you start making sawdust and stitch it together, the line drawings are almost useless and attempting to build a boat stitch an glue from line drawings is yet another challenge.  Additionally, seam taping, thickness of epoxy wet out, layup material etc. may mean that the finished deadrise or chine, or other areas are +/- a couple degrees.

I predict you will have a lot of pretty pictures and 3d renderings with which to go fishing, but paper and print don't hold up well to water.  I made lots of drawings and renderings, but my finished project will not look like any of them.  LOL

Offline jallii

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Jalli,

Based on my experience with building stitch and glue, every peice of wood bends slightly differently.  That means that a guy building using Renns given dimensions and marine fir will get one shape, and a guy using stiffer meranti or baltic birch might get a different shape yet.  Renn built backwards for a purpose.  Until you start making sawdust and stitch it together, the line drawings are almost useless and attempting to build a boat stitch an glue from line drawings is yet another challenge.  Additionally, seam taping, thickness of epoxy wet out, layup material etc. may mean that the finished deadrise or chine, or other areas are +/- a couple degrees.

I predict you will have a lot of pretty pictures and 3d renderings with which to go fishing, but paper and print don't hold up well to water.  I made lots of drawings and renderings, but my finished project will not look like any of them.  LOL

You mention a few things you think is problematic for the use of line drawings 3D models for extracting data for calculations on the boat.

You suggest that the following things are somehow problematic: 
-different plywood types bend with different corner radius
-different "styles" in making the seams result in slightly different thicsknesses in seams.
-slightly different angles
-differently skilled builders achieve different levels of accuracy in following any instructions 

Technically you are right on all of these points, and I agree with you on this, but you would still be missing the point. All these mentioned things, although the mentioned inaccuracies are possible, the scale of them is normally such that it has about zero significance to those things that matter. You would have to be an extremely sloppy builder to make any noticeable deviation.

There might be many other similar things that affect how accurately any linedraving, building instruction by Renn or 3D model corresponds to the actual boat thats done by a non-professional DIY builder. Thats nothing new to boatbuilding. These kinds of problems have been there for decades, even centuries. There even used to be a special group of specialists who did something called lofting. Lofting is a process where the line- or workdrawings the designer has done on a paper, are redrawn to life size for actual boatbuilders to make their parts from. Even a thinnest pencil line has some thickness, and when the inacccuracies in the linedrawing are scaled to some 20 to 100 times bigger real life size, all the inacccuracies are multiplied. It was the lofting process that dealt with these inacccuracies. They used battens and the eye to find the proper lines before the boatbuilders copied their parts from the lofts. A boat that was poorly lofted if allowed to go on has perhaps ugly lines, but the displacement etc similar design features are pretty much the same. The same applies to most DIY builders rookie mistakes. Its hard to be a crappy enough builder for the end result to affect enough to make a difference. The result may not be pretty and perhaps it rides poorly but without holes it will float prettty much the same.

In this project I am only interested in the size of the hole the boat makes in water. I am not yet building some G-code for a a CNC- machine to plot the plywood pieces. Perhaps in the future, but that would require much more work. 

Ps. The problem you mention about your drawings not resembling the final product is probably due to the fact that the process of documenting a product is different than designing something new, even if it was just a part of something bigger. Documenting in 3D is simple when you know the coordinates, but exploring possibilities is a different matter. CAD programs are not like some simple drawing program where you choose the pencil tool and try your way to the best result. In CAD you need to first establish by calculation or other design methods what, why and where you want it. Its much harder to move things around in CAD than it is in a drawing program, so the approach is pretty much the opposite to the try and keep changing method you described. I have plenty of experience with all kinds of hands on approach in designing things when the parts you are dealing with are small enough to handle manually, but when the parts need some tools or helping hands to move them around, its better to first finish the design and move the parts only after you are sure about all the what, why, where and how questions about the piece.  This is where CAD becomes handy, but the simple test and try method is not suitable for CAD. You need to know first. But..... its a joy to feel the size and weight of the material and try it first when the pieces are "humanly" sized. Doing CAD is the new thing for me, not the "making sawdust", but you also need to weld some stainless, aluminum and even plastics, tighten some bolts, lay some glass and paint along with polyester and epoxy if you truly want to be in the business of boatbuilding. 
I like to find out and really understand things. A perfectionist, curious mind cannot stop learning, and picks up many things. I don't claim to be an expert. I'm not an engineer or a chemist by training. I make mistakes. If I manage to make something understandable I am happy. IF you want to build a boat make sure you follow designers instruction. Do your homework and be safe.

Offline Kobuk

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On polystyrene:  EPS and XPS are both extremely common in Alaska, both used extensively in house construction (not to mention XPS being used as the ultimately superior outhouse seat material to prevent frostbite).  I can guarantee that both EPS and XPS do in fact similarly absorb water, and anyone who claims otherwise is either a fool or a liar.  XPS has been (and probably still is(?)) used under-deck by some common commercial aluminum boat manufacturers, and tearing up decks of used boats to get that waterlogged crap out of there is a common occurrence here.  Sorry, man, but you won't find me using any of that crap in any boat I build.
https://www.fishyfish.com/boards/index.php?topic=5536.0
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020

Offline jallii

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- I recently completed the ABYC standards course; his use of 3D models is not an acceptable method.

Please do not post claims you cannot back up with facts. Its hard to be more wrong than the above claim that 3D model is not a valid method. It is totally the opposite. CAD model is the preferred method for most, and for a reason.  USCG document instructing on how to comply with the CFR safe loading requirements specify that there are 3 valid methods to determine the required value of Maximum Displacement value. 



Quote
It is important to note that all three categories of boats in 33 CFR Subpart C covered by this regulation
require that the maximum displacement be found (by any of the three methods described here). This is
the most involved step in the whole process of meeting safe loading requirements.

The three methods mentioned are:
Quote
The three methods discussed to determine boat displacement are a ‘high tech’ figure it out with a
special computer program method, a ‘low tech’ immersion method - with the boat placed into the water
with weights added up until water is about to enter the boat, and a mathematical method (Simpson’s
Rule).



I am pretty sure that the high tech CAD program method is the preferred one for most designers and boatbuilders. You can simply read the numbers from the program. If you think this issue through its very easy to understand why this is preferred method.



The second method available is IMMERSION, but I do not think very many boatbuilders have a suitable pool available for the this method. Try hanging the boat above a pool of water, and filling it with weights (about 6000 kg) until water starts flowing over the gunnels. The method is actually quite demanding....
Quote
The system, as its name implies, consists of placing the boat in a tank or pool of fresh water while it is
suspended level from above by a pair of hoists that permit lowering it into the water, and then adding
weights distributed evenly so the boat immerses with the float plane parallel to the surface of the water.

The third method available is by math and measurement. In short this means that you first measure and calculate using Simson's method the area of transverse sections from a number of longitudinal places.  After this you apply the Simson rules for a second time to estimate the combined volume of the boat.  I don't think many DIY boatbuilders are familiar with these methods, or have the needed skillset even though it is the standard method of estimating boat volume. The math itself is not hard, its just lots of measuring and calculating. The referenced USCG instruction on HOW to do the measurements is on pages C9 to C20.  It takes 11 pages to explain this mathematical estimation method and lots of detailed measurements. It's possible to accomplish good estimates without any special facility, but the math and measurements that need to be taken are pretty intensive. The use of Simpsons rules was the established method to do these kind of estimations in the industry until the CAD method moved the heavy math for computers. I will demonstrate this method in a later post as an example. Can you do it?

Here is a quote from Math24.net https://math24.net/simpsons-rule.html 
Quote
Simpson's Rule is a numerical method that approximates the value of a definite integral by using quadratic functions. This method is named after the English mathematician Thomas Simpson (1710?1761). Simpson's Rule is based on the fact that given three points, we can find the equation of a quadratic through those points.
Here is a video about the Simpsons estimation method itself. https://youtu.be/RTX-ik_8i-k?si=pxnTb0jWvok5EDv1 




Witch one of the mentioned 3 allowed methods would you use. Do you have a facility available for immersion? Can you do the Simson math? The CAD method requires the 3D model that contains the geometry of the boat as the basis for the calculations the program makes.  Of course you can hire a company that uses the immersion method to measure the boats capabilities. I have provided the numbers for free from the CAD model. The modern preferred method for practically everyone that has the possibility.  I think most designers choose the CAD method.

Please read the whole thing yourself. This instruction pdf-file is available as a whole from here: https://safeafloat.com/wp-content/uploads/2021/04/C-Safe-Loading-Final-4-14.pdf   

This post is already too long so continue with the rest and continue with the tutorial stream of posts in further post later.
« Last Edit: April 23, 2024, 01:30:32 PM by jallii »
I like to find out and really understand things. A perfectionist, curious mind cannot stop learning, and picks up many things. I don't claim to be an expert. I'm not an engineer or a chemist by training. I make mistakes. If I manage to make something understandable I am happy. IF you want to build a boat make sure you follow designers instruction. Do your homework and be safe.

Offline GlacierBoats

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I'll stick with closed-cell polyethylene for flotation and just keep it in enclosed areas ... areas that have a drain, whether or not it can be plugged.

Short answer on flotation: The volume of all components in the boat (including windows, motors or whatever), in cubic feet, times the weight per cubic foot of water (approx. 63# for seawater) is the total flotation contributed by the boat and all that's in it.  Subtract from that the weight of the dry boat and you get the buoyancy in pounds. Example? You have a ply/glass/epoxy boat that, with only the wood components on board (no windows/tanks/motors/etc) weighs 4000#.  The boat's weight divided by (approx) 48 lbs/cu. ft says the boat has about 83 cubic feet in wood/glass/epoxy structure.  Total flotation is 83 times 63 lbs/cu ft seater, or about 5250#.  Subtract the boat weight from that and you get about 1250 lbs buoyancy ... the maximum weight of added non-floating components before you go net negative.  You can easily blow that number with tanks, glass, metal components, motors and brackets etc.  In a Tolman or Great Alaskan, adding flotation in the form of closed-cell foam hedges your bets.  If it were me, I'd cut block or sheet polyethylene to fit and fill under-deck spaces with it and perhaps consider compartments under the sheerdeck as well.  Forget the scenario where you capsize and you (and your passengers) try to right the partially-submerged boat ... you and the boys are not going to be heavy enough.  Instead, figure out how to get out of the water and on top of the boat if you can ... better yet, wear your Mustang suit if the conditions are like a washing machine on high ...

Done.

PS: Try to get the weight of of your boat before you install the non-wood items, even if you have to approximate the weight of wood components that aren't yet in the boat ... say 7000# on the truck scale minus 3500# weight of the trailer but add 400# for the weight of the decks that aren't in it yet ... that's just an example, and it results in a boat weight of 3900# for the boat w/decks in it (via calculator).  And BTW, the 48 lbs/cu ft for wood/glass/epoxy is pretty close ... I've weighed lots of assemblies and determined their volume via 3D CAD to figure out the average weight of wood/glass/epoxy boat structures.  It's the magic number that I used for the Great Alaskan CG work and displacement and it nailed it .. right on the money.


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Offline TNeilson

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I appreciate this condensed take estimating buoyancy - a simple and effective approach.

This thread has provided some entertainment, and, no doubt, some useful information, however, I think the ultra-detailed approach being presented is missing the mark.

I would characterize my approach to this topic as follows, and maybe there are others who feel similarly... or not (makes no difference to me)!

- I care about safety of myself and others on the boat I have built.
- I am not a professional boat builder, and never intend to be. Anyone who views a home-built boat as an investment that will provide some monetary return is fooling themselves. Building your own boat is an expense, and if you do sell it at some point, it likely won't be for the money so much as to get it off your hands so you can focus on something else.
- I have a modest interest in the coast guard regulations, but no desire to meet them to the letter. They are designed to regulate a commercial industry that I am not a part of, and I am not subject to these regulations.
- I want to do what I need to be safe enough, within my personal risk tolerance, and within my personal use scenario, but I do not have a taste for doing more than this. What GlacierBoats just presented is a simple road map that will do exactly this.

As I see it, Renn's instructions for building a boat share much more with the one-off skiff building techniques used by fisherman for centuries to build simple, utilitarian craft to work coastal waters and get to and from places and boats than it does with the modern design approach that is being taken here. Those skiffs were built with chine logs sprung around a single mold and the transom, then the topsides and bottoms planked as desired with whatever material was available. Any working wharf you visit in Maine (where I live) will have examples of these boats. No drawings, no calculations, but built based on what worked (or didn't) the last time, and what you need the boat to do. It is orders of magnitude simpler that the "traditional" method of carving a half model, pulling the lines from the model, lofting, and then building to the lofted lines. And it is nearly opposite the modern approach taken by boat designers.

To me, this is the ethos of the Tolman. Can it be done in CAD, reverse engineered to meet all of the USCG requirements and tick all of the boxes? Definitely. Does it need to be? Definitely not, especially when I can do it with minimal effort as part of the build process. Will one method make a safer boat than the other? Highly doubtful.

Sometimes good enough is just that, good enough.

Offline Kobuk

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I appreciate this condensed take estimating buoyancy - a simple and effective approach.

This thread has provided some entertainment, and, no doubt, some useful information, however, I think the ultra-detailed approach being presented is missing the mark.

I would characterize my approach to this topic as follows, and maybe there are others who feel similarly... or not (makes no difference to me)!

- I care about safety of myself and others on the boat I have built.
- I am not a professional boat builder, and never intend to be. Anyone who views a home-built boat as an investment that will provide some monetary return is fooling themselves. Building your own boat is an expense, and if you do sell it at some point, it likely won't be for the money so much as to get it off your hands so you can focus on something else.
- I have a modest interest in the coast guard regulations, but no desire to meet them to the letter. They are designed to regulate a commercial industry that I am not a part of, and I am not subject to these regulations.
- I want to do what I need to be safe enough, within my personal risk tolerance, and within my personal use scenario, but I do not have a taste for doing more than this. What GlacierBoats just presented is a simple road map that will do exactly this.

As I see it, Renn's instructions for building a boat share much more with the one-off skiff building techniques used by fisherman for centuries to build simple, utilitarian craft to work coastal waters and get to and from places and boats than it does with the modern design approach that is being taken here. Those skiffs were built with chine logs sprung around a single mold and the transom, then the topsides and bottoms planked as desired with whatever material was available. Any working wharf you visit in Maine (where I live) will have examples of these boats. No drawings, no calculations, but built based on what worked (or didn't) the last time, and what you need the boat to do. It is orders of magnitude simpler that the "traditional" method of carving a half model, pulling the lines from the model, lofting, and then building to the lofted lines. And it is nearly opposite the modern approach taken by boat designers.

To me, this is the ethos of the Tolman. Can it be done in CAD, reverse engineered to meet all of the USCG requirements and tick all of the boxes? Definitely. Does it need to be? Definitely not, especially when I can do it with minimal effort as part of the build process. Will one method make a safer boat than the other? Highly doubtful.

Sometimes good enough is just that, good enough.
Well said.
https://www.fishyfish.com/boards/index.php?topic=5536.0
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020

Offline jallii

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A few general issues

As I have earlier stated, I am not from US, and not a lawyer. There are some issues that make me wondering about stuff that is NOT stated in the this boatbuilders handbook, but might still be very much relevant on the issues. I point to a few issues...

MAXPERSONS defined as a number and total weight needs to be defined and printed on the PLATE. It affects the flotation calculations. The number is defined with a formula that is based on weight only. The builder can reduce the number if he wants as only the max values are defined. But...USCG handbook does NOT give any detailed DEMANDS about other things that affect this number. At least I have not noticed any. The corresponding EU regulations implied in RCD and the international/local standards adds some other requirements, like having a seat for these persons and something to hold on during heavy seas. USCG simply leaves everything to the the builder to decide. Its like saying "It would be good if you would have seats for those persons you allow for your boat" and deals with the issue as if it was only a matter of weight. Clearly it is not. Of course they can do that, but I see a definite difference in the way this issue is handled in EU. This makes me wonder if there is some other regulation somewhere else that perhaps regulate issues involving passenger safety on some other perhaps on a general general level. Again, I can only deal with the stuff that is written in the handbook and its your responsibility find out if there is other stuff somewhere that dictates more. (like general product safety etc...)

I have a similar concern about MAXHP allowed.  There are definite international standards and agreements that dictate lots of things concerning the ships. One of those things is demands on manouverability. You recently had a ship hit a bridge, causing a major catastrophy, because they lost controll of the ships movements. You boat is basically just a ship thats shorter than 24 meters. The major reason for limits on maximum HP for boats has to do with preventing this loss of control over the movements of the boat due to too big engine. Renns concerns had to do with weight only. I think manouverability is more important. For us there are spesific manouverability test that the boat has to pass with full power, that determine this MaxHP. But... USCG deals only with the width of the transom and length of the boat. A flat bottom, lack of remote steering, low transom height (below 20) cause different formulas, but nothing else. Ability to steer the boat in emergencies, manouverability, ability fot instant emergency stop, strength of the transom.... should also be considered, but no demands on those things in USCG that I have noticed. 

SOME PRELIMINARY INFO

Will post calculations separately
I don't want to go into the practicalities about Hull identification and Manufacturer Certification and the Plates etc. that at least professional builders need to attach to the boat. I dont know what DIY builder should do with these issues. At least the HIN needs to be acquired through different means. There might also be some other mechanism to defione the MaxPersons, Max Person Weight, Max Gear weight, MaxHP allowed, etc... for the boat.

Here is the model for the PLATE, although DIY builders probably cannot attach it without registering as a boatbuilder by USCG. The same applies to the HIN as DIY builder cannot get a MIC code. These things you need to figure out yourself. Here is a bit more info on the matter. https://www.uscgboating.org/library/boating-safety-circulars/BSC70.pdf#basics  or https://newboatbuilders.com/pages/index2.html



Different rules for different types of boats.
There are differences in how MaxHP is calculated that depend on wether the boat has remote steering, flat bottom,... as mentioned earlier.

Similarly there are differences in other calculations. CFR divides boats in 3 categories.

33 CFR 183 subpart F handles Inboard boats, inboard/outdrine boats and AirBoats. In all of these the engine is an integral part of the boat. MaxHP is not even defined. I ignore their calculations. 33 CFR 183 subpart H is about smaller outboatd boats with less than 2 hp power. I ignore this group.

33 CFR 183 subpart G Applies to all boats below 20 feet that have more than 2 hp outboard. This is the subpart Standards belongs to, so all my formulas and calculations have to do with this part. Within this group you either have a permanent or a temporary gasoline tank.  Standard 18 belongs to this group. Standard 20 could be build slightly longer so than 20 feet so that none of the stuff in this thread applies, but perhaps something else. I am handling it as if it is slightly less than 20 feet so that everything applies.

Defining the USCG Plate info.
Even if you cannot attach the PLATE without complying with all the requirements you still need to DEFINE the data that is on the PLATE, because that forms the basis for flotation calculations.

Determining the weight of the boat
The weight of the boat is central to all the calculations I will provide a separate post on how to dtermine the weight of the boat. Although it is based on hydrostatic data from the model 3D it will provide a method to estimate the weight of your boat, provided you have built your Standard the way Renn intended and use the method described.

Deciding flotation material
Different possibilities have different advantages and drawbacks.

Determining the amount and placement of needed flotation material
Determining flotation needs has 2 parts. You need to determining the amount of material needed. After that you need to determine tha placement of the material. I will post the formulas here so that you can understand the calculations and discussion on what to define as PLATE info. The placement of Part 1 flotation material is different from the placement of Part2 and Part 3 placements. This means that all these have to be calculated separately. 

The placement of flotation materials


PART 1  DEFINING BOAT WEIGHTS and MATERIALS.

PART 2  DEFINING ENGINE WEIGHTS

PART 3    DEFINING PERSONS WEIGHT
 
« Last Edit: April 24, 2024, 08:50:46 AM by jallii »
I like to find out and really understand things. A perfectionist, curious mind cannot stop learning, and picks up many things. I don't claim to be an expert. I'm not an engineer or a chemist by training. I make mistakes. If I manage to make something understandable I am happy. IF you want to build a boat make sure you follow designers instruction. Do your homework and be safe.

Offline jallii

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- Jallii made numerous arithmetic errors, resulting in Jallii's unsupported conclusion.  When you fix his math, his conclusions are wrong.

I noticed a TYPO...

Quote
STEP 1 Calculating the FACTOR

Standard 18:
LENGTH =18 feet    BEAM = 81 inch  = 6.75 feet
==>  Factor 18 = 18 X 6.75 = 121.5

Standard 20:
LENGTH =20 feet    BEAM = 81 inch  = 6.75 feet
==> Factor 20 = 18 X 6.75 = 135

The last line should be:
==> Factor 20 = 20 X 6.75 = 135

The math was correct, but obviously the length of 20' standard is 20' not 18'

Thank  you for pointing out the possibility of errors in math, but It would be more helpful if you pointed out where the mistake is if you notice one,
instead of a generalized claim about conclusions. If you think some conclusions are wrong, please point out witch one and why.
This typo is corrected.
« Last Edit: April 24, 2024, 10:32:23 AM by jallii »
I like to find out and really understand things. A perfectionist, curious mind cannot stop learning, and picks up many things. I don't claim to be an expert. I'm not an engineer or a chemist by training. I make mistakes. If I manage to make something understandable I am happy. IF you want to build a boat make sure you follow designers instruction. Do your homework and be safe.

Offline KenB

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1 of 6 math errors. i found 4 more statements that are incorrect, but more than anything, you have a taken a topic and now two threads anyone WHO ACTUALLY BUILDS BOATS must take seriously, and as we say in the US "flooded the zone with shit."

More than happy to back up with CFR as well as the abyc standards.

You made any boats yet? Big words from a poser. Fraud. Post a picture of you working on a boat. Until then, please stop posting in this forum.

- I recently completed the ABYC standards course; his use of 3D models is not an acceptable method.

Please do not post claims you cannot back up with facts. Its hard to be more wrong than the above claim that 3D model is not a valid method. It is totally the opposite. CAD model is the preferred method for most, and for a reason.  USCG document instructing on how to comply with the CFR safe loading requirements specify that there are 3 valid methods to determine the required value of Maximum Displacement value. 



Quote
It is important to note that all three categories of boats in 33 CFR Subpart C covered by this regulation
require that the maximum displacement be found (by any of the three methods described here). This is
the most involved step in the whole process of meeting safe loading requirements.

The three methods mentioned are:
Quote
The three methods discussed to determine boat displacement are a ‘high tech’ figure it out with a
special computer program method, a ‘low tech’ immersion method - with the boat placed into the water
with weights added up until water is about to enter the boat, and a mathematical method (Simpson’s
Rule).



I am pretty sure that the high tech CAD program method is the preferred one for most designers and boatbuilders. You can simply read the numbers from the program. If you think this issue through its very easy to understand why this is preferred method.



The second method available is IMMERSION, but I do not think very many boatbuilders have a suitable pool available for the this method. Try hanging the boat above a pool of water, and filling it with weights (about 6000 kg) until water starts flowing over the gunnels. The method is actually quite demanding....
Quote
The system, as its name implies, consists of placing the boat in a tank or pool of fresh water while it is
suspended level from above by a pair of hoists that permit lowering it into the water, and then adding
weights distributed evenly so the boat immerses with the float plane parallel to the surface of the water.

The third method available is by math and measurement. In short this means that you first measure and calculate using Simson's method the area of transverse sections from a number of longitudinal places.  After this you apply the Simson rules for a second time to estimate the combined volume of the boat.  I don't think many DIY boatbuilders are familiar with these methods, or have the needed skillset even though it is the standard method of estimating boat volume. The math itself is not hard, its just lots of measuring and calculating. The referenced USCG instruction on HOW to do the measurements is on pages C9 to C20.  It takes 11 pages to explain this mathematical estimation method and lots of detailed measurements. It's possible to accomplish good estimates without any special facility, but the math and measurements that need to be taken are pretty intensive. The use of Simpsons rules was the established method to do these kind of estimations in the industry until the CAD method moved the heavy math for computers. I will demonstrate this method in a later post as an example. Can you do it?

Here is a quote from Math24.net https://math24.net/simpsons-rule.html 
Quote
Simpson's Rule is a numerical method that approximates the value of a definite integral by using quadratic functions. This method is named after the English mathematician Thomas Simpson (1710?1761). Simpson's Rule is based on the fact that given three points, we can find the equation of a quadratic through those points.
Here is a video about the Simpsons estimation method itself. https://youtu.be/RTX-ik_8i-k?si=pxnTb0jWvok5EDv1 




Witch one of the mentioned 3 allowed methods would you use. Do you have a facility available for immersion? Can you do the Simson math? The CAD method requires the 3D model that contains the geometry of the boat as the basis for the calculations the program makes.  Of course you can hire a company that uses the immersion method to measure the boats capabilities. I have provided the numbers for free from the CAD model. The modern preferred method for practically everyone that has the possibility.  I think most designers choose the CAD method.

Please read the whole thing yourself. This instruction pdf-file is available as a whole from here: https://safeafloat.com/wp-content/uploads/2021/04/C-Safe-Loading-Final-4-14.pdf   

This post is already too long so continue with the rest and continue with the tutorial stream of posts in further post later.

- Jallii made numerous arithmetic errors, resulting in Jallii's unsupported conclusion.  When you fix his math, his conclusions are wrong.

I noticed a TYPO...

Quote
STEP 1 Calculating the FACTOR

Standard 18:
LENGTH =18 feet    BEAM = 81 inch  = 6.75 feet
==>  Factor 18 = 18 X 6.75 = 121.5

Standard 20:
LENGTH =20 feet    BEAM = 81 inch  = 6.75 feet
==> Factor 20 = 18 X 6.75 = 135

The last line should be:
==> Factor 20 = 20 X 6.75 = 135

The math was correct, but obviously the length of 20' standard is 20' not 18'

Thank  you for pointing out the possibility of errors in math, but It would be more helpful if you pointed out where the mistake is if you notice one,
instead of a generalized claim about conclusions. If you think some conclusions are wrong, please point out witch one and why.
This typo is corrected.
best,
KenB

"HOW CHEAPLY CAN A TOLMAN SKIFF BE BUILT AND JUST HOW  MUCH IS SACRIFICED IF COST IS THE PRIME MOVER?"
- Bruce Armstrong   

"I can tell you that either a nice BFT or a big YFT is an absolute riot on a Tolman. The boat is so light it's like the old man and the sea..."
- Dave Nolan (RIP)

Offline Kobuk

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1 of 6 math errors. i found 4 more statements that are incorrect, but more than anything, you have a taken a topic and now two threads anyone WHO ACTUALLY BUILDS BOATS must take seriously, and as we say in the US "flooded the zone with shit."

More than happy to back up with CFR as well as the abyc standards.

You made any boats yet? Big words from a poser. Fraud. Post a picture of you working on a boat. Until then, please stop posting in this forum.
Ken, you've made your personal opinion about Mr. Jallii abundantly clear.  I think you're safe to give it a rest at this point, eh?
https://www.fishyfish.com/boards/index.php?topic=5536.0
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020