Intro, and 1/4 inch ply question
October 17, 2019 01:28AM
Hey everyone, The forum I’m from requires a proper introduction so let me make it quick before the cold gets in the garage door.

I’m the ‘shoe, and this is my boat, the wooden shoe

And whiskey tastes good in it.

And every once in a while we catch something for my dog Nuya to lick out of it

Anyways, I’ve already drawn up plans for a modified 12 foot version of Jason’s skiff, and intend to use it on our sandy, woody rivers In northern Michigan were we’ve no can openers to worry about, so durability is less of an issue here. I really just want the lightest boat possible to be able to push over fallen trees and to winch up clay banks when needed on smaller streams.

I was planning on using 1/4 ply side walls, but do you think I can get away with a 1/4 bottom with 2 layers of glass on bottom and 1 layer on top? My biggest concern is it simply won’t hold the weight of two guys and the dog. Any think I should just use 3/8 ply? I’m all ears. Thanks
Re: Intro, and 1/4 inch ply question
October 17, 2019 11:11AM
I'd use 3/8" inch plywood. Or 3/4" inch inch Plascore. 1/4" inch plywood with glass on either side is surprisingly durable and strong, capable of taking big strong hits from blunt objects like big mid-river boulders or protruding logs. It's weakness is sharp hits.

I was trying to gun my 20hp a few years ago, right up onto my trailer. I'd done it many times before. But a gust of wind hit the front end a 1/2 second before I got to the trailer and I hit the sharp corner of the trailer roller. Punched a hole right through the 1/4" inch side panel, which was glassed both sides, albeit with 3.5oz fabric. Would it still have punctured if I had used 10oz fabric? It's hard to say. 3/8" does add a lot in that sharp object context.

....very nice boat
Re: Intro, and 1/4 inch ply question
October 17, 2019 07:41PM
Shoester, Why did you make it so pretty. No one will want to fish from it and will spend the whole time looking at it. Send me your dog and I'll watch him while you float with the 1/4" bottom. He is a handsome little barge dog.

I'm not sure what the cost comparison will be but perhaps 1/4" ply with two layers of Kevlar and double or triple biaxial taped seams would work safely. You could do a drop test to be sure. Make up two 1' square plywood pieces and cover one with fiberglass and the other with Kevlar. Lay them on a bag of wood pellets or something similar and drop a sharpened steel rod from 3'+/- or so and see if it penetrates. You'll have to manipulate the distances(height), weight of the rod and number of layers. Keep raising the rod until one of the pieces fail. Three drops from each height is appropriate.
Might have to resort to the softworn engineer (Sandy) to prove the math. Landscrapers do a similar test to develop compaction tests for gravel before installing pavers.
The goal is two-fold;
1) see if the kevlar covered 1/4 ply is more puncture proof than the fiberglas covered 1/4" ply.
2) then See if the kevlar covered 1/4"ply is more puncture proof than the 3/8" fiberglass covered Ply.

Once the data is in then simply doing the cost analysis will lead you in the right direction.
Re: Intro, and 1/4 inch ply question
December 10, 2019 06:23AM
I heard that typical Ausable Drift boats use 1/4" ply; my ocean going tri uses 1/4 inch ply. If you aren't on a budget, you could consider 1/2" corecell with double 10 on the outside, and single on the inside. Light and easy to work, and you don't have to worry about punctures as they are easily patched.

Just so you know... 3/8 is over 3 times as stiff (27/8), and more than 2 times as strong as 1/4". But it weighs only about 5 ounces more per square foot. So, if you are asking the question, it is probably worth it to go to the heavier ply. These numbers assume similar species, and plies.

If you go with 1/4", one thing you can do is find ply that is 3 evenly balanced plies, and scarf it so that you have joints every 4 feet. That would be the case where the 8 foot side is going across the boat. That is a stronger orientation. Though the effect is relatively minimal compared to what you would get with 3/8". It can make good use of the material, though.
Re: Intro, and 1/4 inch ply question
December 10, 2019 12:29PM
All, is it possible to find an equivalent of durability for 1/2 and 3/4 plascore vs ply similar to what ThomD writes regarding 1/4"vs3/8". I personally find it easy to work with Ply. With my "older guy" eyesight and dexterity 3/8" is much nicer to work with than 1/4. my fear about plascore is that I may end up with un-fair bends and bulges here and there as it doesn't appear to have any inherent directional trueness or stability as does Ply.

Way too nice Shoe!
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