2 person pontoon boat

i am wanting to build a small pontoon boat, and i have never built a boat before or fiberglassed anything, but i do have construction skills i have built many things just none that float and my stuff is usually built from steel. it will be for 2 people and powered by an electric trolling motor or two. pontoons will be 10' and it will be 4'-5' wide(still deciding width). what is the thinest plywood i could get by with. i am wanting to keep it as light as possible. it will be used in a small lake for fishing shallow water. the design i am going to use will be very simple,square pontoons with 45 degree angle in front and flat in the back. i was going to build an internal frame from 2"x2"s would this be the best way to go about it? i was going with 16"x16"x10' pontoons would this be a suitable size to carry 2 people, a few rods and reels and a tackle box. also fiberglass and epoxy where is a good place to get some and how heavy of cloth should i use. i am wanting to build it for my dad for christmas b/c his got squished last winter in when an ice storm crushed his barn. a boat kinda like this one is what i am going for. the 4th pic is my design, its very simple and hopfully easy to build and strong.

any input would be greatly appreciated!!!
MR

 

This is similar to the first boat I built. It held 2 adults(about 300 # total + gear). It was lightweight and only 8 feet long x 6 feet wide. 10 feet long would be better. Each hull was 2 feet wide and 1 foot high. It was all 1/4 inch plywood. There was more shallow slope on front end though.

 

I have built 3 boats of plywood, a 15 foot stitch n glue dory, an 8 foot scow, and a 12 foot rowboat (square stern, pointy bow).
The dory was made from ¼ inch marine grade (okume) plywood with 1X2 sheer clamps, and it is a very strong, rigid boat.
The 8 foot scow was made from underlayment with 1X1 sheer clamps and it is strong and rigid. (It weighs about 25 pounds, so I can carry it on my shoulder a mile to the river).
The row boat was made from ¼ plywood from Lowe's, with 1X2 frames. It is way too floppy, and I'll have to fix it somehow or throw it away. One sheet of ¼ inch plywood weighs about 30 pounds, so you can figure the weight of the boat by the number of sheets you use to make it.

The point being, you can make a nice rigid structure from plywood, and you can make a poor one. To make a rigid one, you need to study boatbuilding technique. Generally, you need to bend plywood panels to make them stiff, and boatbuilding is the art of bending wood into a boat shape. Or, you could just say “screw it” and make it out of 1 inch ply!

Regarding plywood, Marine grade has no internal voids. So it bends in fair curves, and it won't collapse in a sharp curve. Underlayment has almost no voids, but the face layers are extremely thin and they will peel off if you try to glue it to something them bend it. Construction grade plywood will collapse, doesn't bend fair, and rots quickly. But if you are going to design your own boat, it'd be worthwhile to make the prototype out of the cheap stuff.

I used glass over the dory and the scow. Fiberglassing the plywood will not make it any stronger, but it will vastly improve scratch resistance. I've smacked some pretty good size rocks with my dory and not punctured the glass. I got my epoxy and glass from West Marine, but they are about the most expensive place you'll find. I've heard good things about Raka (raka.com) but have not used them myself.

Regarding pontoon size, here is how I figure how much weight a hull will support. One pound of water takes up about 28 cubic inches of space. So if you want to support 300 pounds, you need to displace 300 X 28 cubic inches of water or 8400 cubic inches of water.

Using your pontoons, if they are 16 inches square, for each inch of length, they displace 16 X 16 inches, or 256 cubic inches. 10 feet of length is 120 inches, so 120 X 256= 30,720 cubic inches of total displacement for each pontoon. Divide that by 28 to get your displacement in pounds, and viola: each pontoon displaces about 1097 pounds. That should be plenty!

There are some details, such as whether 16 inches is the inside or outside diameter, how far a pontoon will sink if a lot of weight is moved forward or aft, how wide the pontoons need to be separated for stability...

I hope this helps.
Chip.

 

thanks kayaker
this does help. i think i am going to use 2x2 lumber for a internat frame (for structural support) and then fiberglass the whole thing with 6-7 oz cloth. i was going to sure exterior grade plywood that has all voids filled and that has been sanded smooth.

 

Muddin redneck, Kayaker50 gave you good advice. I just wanted to make clear to you that with the boat, the passengers and gear all weighing 1100 pounds, your pontoons will only be about 8" deep in the water. It would take about 2200 pounds for the pontoons to be fully submerged. Like K50 says, that should be plenty!

Also, it would be very easy to make the bows in a curve instead of the abrupt 45 degree angle. If you came straight down, or with a slight angle for a few inches and then started the curve, it would look a little less boxy. All the edges and corners will have to be rounded over for the fiberglass. A 1/4 " roundover bit in a router is the minimum, 1/2" is better. A few watertight compartments in each pontoon would be easy to do also. Good luck.

 

thanks sam
i was going to round all the edges. using agles instead of curver just seem easier to build. as for the fiberglassing i am unsure of what type of resin/epoxy i should use. and since i have never fiberglassed anything i a very nervous about the working time i have with the epoxy and hard hard it will be to make it look good. i guess there is only one way to find out the difficulty level of it and that is to just dive in and do.

 

Practice with some small pieces. You can learn a lot from 6" square pieces of cloth and a little bit of resin. Put one on a flat piece of scrap ply, wet it out and use a plastic auto body filler squeegee to work out the bubbles. You'll get a good idea of what you have to do and how long you have to do it and what the results will be. Try one going around a corner. Try overlapping one that's already set up and you'll see what problems arise and what you can do about it.
With what you're doing you can do small areas at a time and come back, sand down the edges and do a little more, it won't effect the final outcome. What your trying to get is waterproofing and some abrasion resistance and durability against weathering of the plywood.
You'll also get to practice itching and scratching.

 

Sam thanks for all the info i really appreciate it. do you know what kind of resin/epoxy i should use for this project?

 

I haven't been involved with fiberglass for awhile, some one else could tell you particulars. You couldn't go too wrong with West System stuff. Look through their site, if for nothing else tha "how to use the product" part. They have written guides and videos there for free.

http://www.westsystem.com/ss/