Light Trow hull?

Hi everyone. I'm new here, and I'm looking for help with building my first boat. I've scoured the internet for plans and finally settled on Gavin Atkin's Light Trow. (http://duckworksbbs.com/plans/gavin/lighttrow/index.htm) In the plans, he calls for 3/8" plywood hull, but I was wondering if, in an effort to use as much materials that i already have as i can, i can use 1/4" ply instead, and possibly even fiberglass over it, too. I was thinking that i might need to put more internal braces than the plans call for if i were to do this, but that really wouldn't be much of a problem as far as i can tell.
Thanks in advance,
Joe

 

Can you use 1/4" ply? Yes. And Possibly even fiberglass over it? You had better.

I looked over the plans and it talks about some fiber glassing, but with 1/4" you will definitely want to. For comparison, with your hands, break a small piece of 1/4" and then 3/8". You will find the 1/4" is very weak, almost frail in comparison.

The number of plies and type make a difference too.

Read over this site about ply strengths.

http://www.plumcreek.com/Portals/0/downloads/productInfo/Y510.pdf

In most cases 3/8" is around 2x as strong as 1/4".

 

I have two suggestions.

1.) Contact the designer, or, failing that,
2.) I would consider putting in stringers, so the length of unsupported panel is cut in half.

I would fiberglass both sides of all the panels. If the plywood is only three ply, fiberglassing both sides is even more vital. This is because you have two veneers going one way and only one veneer running across them, in between them. This makes the plywood about 1/3rd as strong when it is bent across the outer grains.

Fiberglass, with a good bond, effectively adds two thinner veneers. The one on the outside of the bend is more important, strength wise, than the one inside the bend, but the one inside the bend helps too.

 

Okay, thanks guys. I tried contacting the designer about two days ago, just because he said in the little blurb with the plans to tell him if you start it, but he never responded. Does anyone have any experience with this particular boat by any chance?

 

Also, would you recommend fiberglass chopped strand mat or woven cloth? and what weight?

 

Six or eight ounce glass will do. Don't even think of using mat on the exterior of your boat. If you use mat, you will spend half your life trying to get the surface decently level and smooth.

 

Okay. At this rate i might as well just buy the 3/8" ply rather than save a little money. I'd rather have something well mad that i can be proud of than something that i skimped on that doesnt work too good.

 

You probably will save or come out even. I know we didn't discuss it but you will want to use marine plywood. It's a little more expensive but it will last longer.

 

How much is a little more? I'm only 17 working 30 hours a week at $7.25 an hour so I'm on a pretty tight budget.

 

Then I would go with the 3/8 inch and use "AC exterior grade" for a work boat finish. It would probably be cheaper all around.

The plywood will probably be fir and will check like crazy, if not well painted.

The knot holes on the "C" side will have to be facing inward and I wouldn't bother filling them in. Why create more potential rot traps?

The boat will have to be carefully attended to. Not kept in the water, and, when stored on land, stored upside down, so plenty of air can get under the sides.

Given this kind of treatment, it could last a decade or more. It just won't look as pretty as with more expensive materials.

This design calls for at least seven sheets of plywood and is no joke.

It will come out weighing around 300 lbs when fully rigged.

But it ought to be sweet rowing craft and a decent sail boat.

 

Alright thanks again! I'm not really looking for it to be pretty. Only functional, being my first boat and all.