Author Topic: Jon boat with a Tolman Transom.  (Read 174 times)

Offline KenB

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Jon boat with a Tolman Transom.
« on: November 10, 2021, 07:13:01 AM »
Totally hypothetical questions here...

If someone had a 9.9 hp toad motor, or even a new 4s 9.9... and wanted to make a scaled down tolman standard to fit that motor, what would the dimensions be?
- 12'? 14'?   If an 18' standard has a 25' transom and a jon boat has a 20 inch transom, then the jon boat is 14.4 feet.  14 feet feels long for a flat bottom skiff with a 9.9, but the 8° vee should make the jon tolman a little more efficient:


- when I think of those 14 aluminum jon boats, the transom/bottom corner is usually flat, and the bow pops way up before getting on plane...
- using jumbo (22' long, 6' at bottom), widebody (20, 5.5, and standard  (18', 5') numbers plus some math ('show your work' below), results in a bottom around 4.5', but wider is usually better so even going shorter than 14, probably 4.5 is about right.

(Kind of a fun aside... to curve fit I just wiggled the curve around until I thought it fit; mathematically, this process is by definition 'AI,' where machine learning, deep learning, etc are just different tricks for getting the line in the right place. Theoretically, AI is just a statistical method to approximate or curve fit. I did mine in 2 dimensions, while AI can add many more. That said, at least for right now I'm still better at picking out the 3 pictures of a stoplight.)

Other hypothetical topics:
- laminated 1/2 ply transom, but no 2x8
- shorter sides to save weight...
- ... but a spray rail to keep it a tolman. 
- 3/4 ply stringers to make the side seat/box things that jon boats have? Jon boat owners, are these side seats better than the ones that run abreast?
- no shelves, instead 1x3 rubrail, from maybe ipe decking. On the gulls and skiffs I have done, when wood rubrails are PL'd to the sides, they becomes kind of structural.
- no floatation at bow, but maybe a cubby. That 'bow stem to the top of the sides' triangle piece is probably needed.
- 1/2 ply for bottom? poking through other stitch and glue designs, perhaps 3/8 is enough, since both sides get glass. I think 1/4 is too thin for bottom, but maybe ok for sides. But any votes for a 1/2 ply bottom?
- Most controversially, again hypothetically, because of no shelves, maybe one laminated frame amidship, in order to spanish windlass the sides to the transom. The way I have done work skiffs and gulls is to attach the sides to the bow stem, let that cure, then bend the sides around a frame placed amidship, and finally attach sides to transom. On gulls, you can do one side at a time because of the strongback/frame, but with work skiffs you can do both sides at the same time; the spanish windlass! Cut the sides to fit the bottom, then tape all the seams. I use Renn's '2x4 blocks' trick to snug the sides/bottom and sides/transom to fit. On the gulls, the frame is then removed. On work skiffs, I've left the frame in, so I know where to put the bench seat. I actually use thule roof straps instead of a traditional spanish windlass, but anyway I also prefer epoxy and plywood to lapstrakes, too.
« Last Edit: November 19, 2021, 06:58:57 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

Offline KenB

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Re: Tolman Standard Jon Boat? Jon Tolman Skiff?
« Reply #1 on: November 18, 2021, 02:08:46 PM »
Picked up my 9.9 today, $2300. 20" shaft, no tiller. Guess the jon boat is getting a console...

These guys did the side bench seats, too bad its flat bottom.  Could use 8 degrees of deadrise.
https://www.clcboats.com/peeler
- they went with 1/4 ply, then complained about the floor flexing.
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

Offline Kobuk

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Re: Tolman Standard Jon Boat? Jon Tolman Skiff?
« Reply #2 on: November 18, 2021, 02:43:15 PM »
If you really want to venture down this slough you otter check out the boats guys build for the Yukon 800.  That's some crazy stuff.

Just because a floating object is created with stitch and glue construction doesn't mean it should be associated with the Tolman name though, especially a jon boat. IMO, that's cringe worthy, if not outright sacrilege. :o
22' Widebody
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020

Offline jallii

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Re: Tolman Standard Jon Boat? Jon Tolman Skiff?
« Reply #3 on: November 19, 2021, 02:35:05 AM »
The idea to simply scale plans of a 20 -28 foot boat form to some 12-16 foot size will not work as perhaps you would like /or expect it to. Geometrically scaling linear proportions changes other factors to the power of 2, 3 or 4 depending on witch particular we consider.

If you for example change the length of a 20 foot by 6 feet to 14 feet the change would be as a persentage 6/20 = 30%.

However the corresponding:

Bottom surface area has 2 dimensions and the change vould happen in both dimentions.
30% = 0.3  change in 2 dimensions would mean 0.3 times original length multiplied by 0.3 times original breath. So you would need to factor in 0.3 *0.3 = 0.09 = 9 % change in surface area of the bottom. (One of the components of calculating power requirements) 

The total volume of the boat and the displaced underwater volume of water would change in 3 dimensions. So what the boat weighs and how much weight the boat can carry would also change in 3 dimensions and the corresponding change would happen to the power of 3.
0.3*0.3*0.3 =0.027 = 2.7%

The inertia effect of a certain part from a distance of x to the center of mass would change to the power of 4.

The above is an oversimplification of what happens with the intent to illustrate the problems. With the above I have tried to demonstrate the if you change the dimensions of the plans, then whatever is the end result of this operation the boat would not be the same or behave similarly.

Renns designs are exceptional in allowing some variations in length without big changes in the overall characteristics of the boat as a whole, but there are limits to acceptable changes. Go overboard and you are not happy with the results.

If you want a smaller boat its much better to take as a starting something that originally designed to that particular size.  There are plenty of FREE designs available that can be used with stich and glue ply-epoxy building style.

If you have trouble finding I can post a few to the forum that spesifically made for that.

I suggest you start by trying to define what you want from the smaller boat.
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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Re: Jon boat with a Tolman Transom.
« Reply #4 on: November 19, 2021, 07:51:04 AM »
Kobuk - thread name updated. Point taken, but I am not sure I understand the cringe part, can you please explain? At the very least, can you maybe suggest another name?

Jallii - Did you click on my little diagram? I believe the phrase is "a picture is worth 1000 words."   

Fuck it here's my 1000 words... maybe you are just a little dense or something, but my premise is to take the three designs in the book, derive a best fit line as a scaling factor (THE WHOLE POINT IS TO INTEGRATE ALL THE VARIABLES YOU LISTED), and see what the results are. Unsurprisingly, you end up with about the dimensions of the classic aluminum jon boat. So the only part of your reply that is correct, I already did! You are clearly unfamiliar with boat building trends (do you even read wooden boat!?) but micro flats skiffs are a pretty hot design right now, a tangible example of why the rest of your math is wrong. You are ranting about boxes and cubes, but boats are made of curves. I bet that I have downloaded and built more free boats than you have... you get what you pay for. You advice is horrible, and your attitude is toxic! Let's cut to it, how many boats have you designed? How many have you built? I have designed 3 boats, and built over 10. Have you ever spent time talking with Renn about boat design? I have. He didn't write one book, then tell people "go download skiff designs online."  He wrote three books, he designed and built a diesel-based shallow draft tunnel hull. What I took from the conversation but also his writing is that he was constantly tinkering, pushing limits, and exploring common sense ways to address basic boat design in spite of the recreational marine industrial status quo; there is a reason he calls them shelves and not gunnels. Unless you have something nice or helpful to add, maybe contribute to some other thread!  You suggest that I didn't "define what I want from the smaller boat"... in a forum literally called "Free Boat Building Plans." And you are completely wrong about the origins of the skiff... go read the book again. The first chapter. The standard skiff was 16-20 feet, and is based on the classic flat bottom work skiff. The books don't have a 28 foot boat, for exactly the reasons you listed, you clown. Guess what, Im naming this skiff after you. Enjoy the Jallii Skiff!
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

Offline Kobuk

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Re: Jon boat with a Tolman Transom.
« Reply #5 on: November 19, 2021, 10:33:00 AM »
Kobuk - thread name updated. Point taken, but I am not sure I understand the cringe part, can you please explain? At the very least, can you maybe suggest another name?
Sorry, I didn't mean to rub your fur backwards. Maybe I was just being a little AR.

What would Renn say about this?:

I can only imagine...!
« Last Edit: November 19, 2021, 10:48:54 AM by Kobuk »
22' Widebody
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020

Offline Kobuk

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Re: Tolman Standard Jon Boat? Jon Tolman Skiff?
« Reply #6 on: November 19, 2021, 10:37:05 AM »
Go overboard and you are not happy with the results.
I'm going to borrow this quote and make a little placard for my skiff...
22' Widebody
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020

Offline jallii

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Re: Jon boat with a Tolman Transom.
« Reply #7 on: November 19, 2021, 07:08:20 PM »
Totally hypothetical questions here...

If someone had a 9.9 hp toad motor, or even a new 4s 9.9... and wanted to make a scaled down tolman standard to fit that motor, what would the dimensions be?
- 12'? 14'?   If an 18' standard has a 25' transom and a jon boat has a 20 inch transom, then the jon boat is 14.4 feet.  14 feet feels long for a flat bottom skiff with a 9.9, but the 8° vee should make the jon tolman a little more efficient:



Totally unhypothetical answer here...
Starting the design process by fixing the engine power and taking a boatmodel thats designed to be in a totally different size category and scaling it down untill the boat is small enough to be handled by your chosen engine is not a good strategy. A much better strategy is to first define needs (2, 3 or 4 persons... etc) and take as a starting point a boat that resembles the one you want and then modify the design to fit your preferences. If the boat model is designed by a naval architect or an already existing professional build you can get the power requirements etc from the starting point. After your modifications you only need to estimate how much your modifications change the requirements from the starting point. This way you end up pretty close to what you want to. By large scaling you probably end up with something unexpected.

Hope this clarifies.

And YES there are boatdesigns available for free by professional boatdesigners and naval architecs. The design process for a boat includes necessary calculations that estimate desired characteristics. Without this info its not a design its a drawing of a boat.

Both William Atkin and W.D.Jackson were both experienced designers and trained naval architects. You will find many possible starting points on these sites.
http://www.atkinboatplans.com
https://www.diy-wood-boat.com
http://www.svensons.com/boat/

There are free versions available for these designs by professionals because they were originally published in magazines for DIY builders.

For example: 
You were looking for proper length for a jonboat type boat for a 9 hp engine... Here is one.
http://www.atkinboatplans.com/Dinks/Chatterbox.html 

It was actually published many times. There is an article by Mike O'Brien in Boat Design Quartely
The above Atkins site shows you the article content and has a reference to the website of the article publisher: http://www.boatdesignquarterly.com/  It was also published long time ago in MoToR BoatinG-magazine. One of the DIY magazines of the past. Its free if you can get a hold of one of the articles. The above sites have many of those published articles in PDF form.  So you get the drawings and the DIY build instruction with all the necessary information for building the boat in these articles. If you need more you can buy the plans.

Note also: In a proper design you get dimensions, max load, power requirements, expected behaviour and speed with the engine. Buildin material thickness... So its a proper design by a wellknown designer. William D Jackson also built every design he published. His designs are actually quite modern.

Even if the boat structure changes from plank on frame to plywood epoxy, the boat behaves the same if the total weight is about the same.  Most of these original designs have strenghtening frames etc... and very thin plywood as shell. If building from plywood-epoxy with glass on both sides and glued seams you can reduce the framing mostly or in some cases totally. Transverse framing can usually be taken out by compensating with thicker ply and epoxy filled glass on both insode and outside. Avoin reducing longitudinal support structure. Just use a bit thicker plywood and build the same way as you would build a Tollman boat. If you use Renns specs for a standard for material thicknesses, etc. then every boat thats smaller than it should be fine with specs from a standard. To be sure that you have strong enough scantlings, refer to  Dave Gerrs book. Use scantlings for plywood epoxy construction instead of plank on frame construction. This way you modernize the old design. The boat should still behave the way the original did, but you have your wood protected. If you decide to build exactly as old plans indicate, I suggest you still make sure that every wooden part is covered from all sides with glas and epoxy.

So from this boat and some others I come to the conclusion that the rigth answer to the boat length for a 9 hp outboard is about 10 to 12 feet with max 2-3 persons to get a decent speed. Some 14 foot boat with 4 persons migth still work, byt there is a risk of not having big enough engine. Small dimentional differences or the shape of windows etc dont matter. Big weigth differences do matter. A flat bottom has the smallest power requirement. Power demand increases as the V bottom deepens.

NO I do not call mere drawings of boats (even proper line drawings by people that have no clue about the principles that govern the process) as designs. They are mere drawings. Drawings can be good or bad. Bad is more probable by unknown "designers" unless its a drawing of a traditional design.

You are rigth keeping the L/B ratio steady you keep some of the characteristics stable, but in defining the needed power, the weigth of the fully loaded boat (displacement) is more important than LENGTH / BEAM ratio that you have tried to extrapolate. A higher L/B ratio would give a faster boat with same weigth. A beamier boat is slower and power hungry. Deadrise angle has a big effect on power requirements. But it all boiles down to how many HP you need to move your boat. Some think 25-40 LBS/HP is a good general estimate.

The point I tried to explain was that scaling a boat design distorts many things in numerous ways. Most often in ways most people cannot even imagine. Still some things stay the same and even that is a problem. You can Shrink the boat, but you cannot shrink yourself. Same weigth in a different sized boat changes everything. Therefore a different strategy is better.

I am sorry if I offended you somehow. That was not my intention. And I see no positive outcome in a discussion comparing the size of my third foot to yours. For the most part I dont understand you 1000 words, but if I have offended you, I apologize for that.
« Last Edit: November 20, 2021, 07:37:07 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.