Author Topic: Guesstimations calculations.  (Read 3038 times)

Offline tundratoad

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Guesstimations calculations.
« on: July 12, 2013, 01:33:29 AM »
 :-\OK so I am stretching out the 20 footer into a 24 footer or so I said. Actually it looks like it will only 42 inches longer than the plan called for in the 20 footer which was actually only 19' 6". Since I didn't consider myself smart enough to know if making the boat longer would have any affect on it relative to how Renn oriented things to station 6 I left that alone and put the first two molds where specified in his plan. The aft mold however, I suspected should be shifted a little further toward the transom in an effort to keep the contour or profile proportional to the original design so I moved it back and additional 22 inches to 132 inches (just a wag, had no way of calculating how Renn came up with his mold placement so I thought it looked good there),  aft of station 6. Remember I extended the jig three feet. I hung the transom today and it became quite clear I am going to have a problem  complying with the equal measurement stipulation in figure 12-7, I am not seeing how this could be possible with the mold being where it is, the stringers being the width they currently are, (6 1/4 inches, came that way in the kit I bought, with no instructions).  I can see several options in trying to reach or get close to those measurements being the same but none of them are easy to do at the point and I continue to ask my self what is the value? How critical can it be? I am not sure how much I would be off right now but I would say near an inch maybe a little more. The shelves drooped a good bit when installed because of the added weight I have not installed and additional horse near the transom but it is looking like I should, The question would be, no, there are several questions.
1. should I have put the mold at 110 inches and added another one further aft? 2. If I had done that should the distance of the rise change at station 6 (1") if so 3. what would it need to be? 4. Should the distance be changed at the 110 inch mold from 3/8 to something else 5. and what would the adjustment be at the third mold if one were installed.? And of course 6. should some consideration be given to changing the height of the stringer horse? 7. If a second stringer horse is installed would it be the same height off the jig as the one at station 6? 7.If a third mold were added where would it go? While none of these things are insurmountable they do make things more tedious so I come back to my original question. How critical do you guys consider this to be.

Some things I ruled out. Changing the width of the stringers by more than 1/4 inch at the widest points. Building another transom high enough to get the distance needed, Notching the stringer at station 6 to get it lower so as to match the distance near the transom,

Offline jerry bark

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Re: Guesstimations calculations.
« Reply #1 on: July 12, 2013, 04:39:11 AM »
Here is my thinking:

1  make and install the molds for the forward half of the boat as per the book.

2  the shape of the hull is the same for the rear half of the boat, so if you want to add an extra mold (probably a good idea) do it back there. make it the same as the rear mold, but install it so that the lines of the shelves are fair, use your eyes.

3  make another horse for the stringers if you think you need it, but let the transom and the bow stem guide the shape of the boat. don't go messing around with the stinger dimensions, you can make small adjustments once you have it all set up to get things fair.

4  lots of things could effect the equal measurements of the stringers, every part of this thing will flex to some extent. When i was at this point I added blocks of wood and shims to level and straighten my jig before I set up the molds and began assembly. I had the jig blocked every 6 feet or so. before doing this my jig was too flexible and it made things hard to line up. If I build another skiff I will build a much stiffer jig to start with.

Good luck,
Jerry
Tolman Widebody Skiff built in 2011

Sturgis, Michigan

Offline jim shula

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Re: Guesstimations calculations.
« Reply #2 on: July 12, 2013, 06:57:02 AM »
As Jerry says, use your eye.  The molds are there to define the shear line, so you'll need to spend some time on your hands and knees eyeballing the shear line with the molds set at different heights and at different spacings.  Look at the big picture and don't get too hung up on thinking about spacing specs from the book and how to adjust them for your boat.  The rear shelf location is set in stone based on the stringers setting level on the horse and lining up with the bottom of the transom, but everything between the transom and sta 6 is up to you.

Offline tundratoad

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Re: Guesstimations calculations.
« Reply #3 on: July 12, 2013, 07:45:42 PM »
Thanks guys, Pretty much what I thought would be the response. This is not a grand piano. Things can be adjusted, Not clear to me what is referred to as the "shear line" but in my mind as long as I can get things to follow the contours brought about by the effect of the beam support on the shelves and get the stringers and shelves to mate up to the transom as per the plan and lit looks like a skiff from the side view it may not cart wheel on sea trial. I have the other horse on it I have not put in another mold yet. I have some work to do on the stringers before I am ready to dry fit the bottom so I will work on that when I get back from harvesting me some of those red salmon fish. It has been recommended that I fiberglass the top portion of the stringers before I secure the stringers to the boat. Sounds like a good idea from an ease of application standpoint but not sure what if any affect it might have down the road. Any thoughts/comments.

Offline Dave Wright

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Re: Guesstimations calculations.
« Reply #4 on: July 12, 2013, 08:34:47 PM »
I think someone on the old forum did a 23 foot standard. You might be able to find him there along with boat pix in the yahoo photos section.

Offline Dave Wright

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Re: Guesstimations calculations.
« Reply #5 on: July 12, 2013, 10:25:28 PM »
Here's the 23 foot standard pix, just in case something there might help:

http://groups.yahoo.com/group/tolmanskiff/photos/album/996075035/pic/list

Offline tundratoad

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Re: Guesstimations calculations.
« Reply #6 on: July 13, 2013, 11:19:46 PM »
 :-[ Hmmmm. Nice looking boat and some very nice fish for sure. I feel better about the contour of my shelves having looked at his. I did ad the additional horse as I mentioned, and I was concerned I had altered the curvature too much but I believe I am right with this 23 footer. I found it very strange that he did not have the beam support in place but had the stringers on and the bottom on it as well. If I could, I would ask him if this was just a fit check or were the straps there as part of the assembly process. Seems to be a significant departure from what the plan would call for if he was actually securing the bottom at that particular point.

Gonna have to take a little break from boat building and go get some fish. I am sure I will be back with some more problems in a week or so. 

Thanks a lot Guys
Herb

Offline Dave Wright

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Re: Guesstimations calculations.
« Reply #7 on: July 14, 2013, 08:46:45 AM »
By "beam support" you mean the beam that holds the bow stem in place? I'm guessing he was irritated by the fit of the bow stem and was modifying it. On my old standard I was really irritated by the bow stem fit up.  I had the bow stem temporary tacked to the bottom, completed the bottom 1/4 inch laminations, then fiddled with carving the stem a bit more. Although I figured it was exactly to the books dimensions, I didn't like the fit up and threw it away. I built another with the same results. I was about to abandon the bow stem altogether for a big fillet and glass, but decided to do my own bow stem with inset for bottom plank thickness. I was pleased with the final result.

These boats are nice, and it's great that Renn has given us the design and methods, we in his debt, but that doesn't mean that some tweaks and efficiencies aren't possible here and there. Now on my second Tolman build I'm thinking that the ideal would be to have patterns to precut the side panels just like the bottom panels, then rest the whole thing up on the stringers screw in place per Pfithian's method, and then glass. Who knows.....I'm pretty much doing the Widebody per the book to avoid thinking to much about it.