Building Pontoons

[Guest625101138]

Originally Posted by muddin redneck

what are some good books or websites on how to stitch and glue a boat together b/c i have not idea what that really means? and i was wondering if i had my floation calculation correct. if my pontoons were 24' long, 18'' wide, and 12'' deep they would hold up 2246 lbs. each(I think).

The idea of stitching is more often replaced with external jigs these days. Rather than wire stitching the cut pieces together, they a formed up in the jig and glued/glass taped internally. This is a photographic explanation using home made sandwich flat panels (boat forming about halfway through):
http://picasaweb.google.com/adventur...nBoatBuilding#
This one uses factory formed sandwich panels but same method of joining the sheets:
My little piece of peace

The same method can be used for joining pieces of ply to form a hull. In your case it is likely to be easier to use stringers in the internal corners rather than glass tape.

What speed are you hoping to get from the boat and what power do you have in mind?

Rick W

[muddin redneck]

for the first time in my life the speed doesnt really matter to me. the boat is going to be used in the mississippi river for a weekend camping out boat for me and my lady and our dog. once i get where im going to spend the weekend it will be anchored and left there, while i run around in a small flat bottom boat. as for the motor i was thinking something small with about a 5:1 gear reduction with about a 13'' prop(because i have one). now the stringers your talking about do you mean use like 2x2 lumber for a frame (internal skeleton of the pontoon so to speak)and nail or screw the to plywood to that and then fiberglass it, or am i waaaay off.

[muddin redneck]

hoy
this boat is going to be in a marina and only trailered in the winter months. i am wanting to camp out on it in the mississippi river.

[Guest625101138]

Originally Posted by muddin redneck

for the first time in my life the speed doesnt really matter to me. the boat is going to be used in the mississippi river for a weekend camping out boat for me and my lady and our dog. once i get where im going to spend the weekend it will be anchored and left there, while i run around in a small flat bottom boat. as for the motor i was thinking something small with about a 5:1 gear reduction with about a 13'' prop(because i have one). now the stringers your talking about do you mean use like 2x2 lumber for a frame (internal skeleton of the pontoon so to speak)and nail or screw the to plywood to that and then fiberglass it, or am i waaaay off.

You are close with the stringer size. I would use even smaller - say 1.5" square. Screwing with stainless screws is better than nailing it. They need to be countersunk for glassing over.

For slow speed up to about 10kts on a 24ft hull the canoe sterns will work well.

You should be able to build the whole thing with a loaded displacement of 1 tonne if you keep the cabin simple. The hulls 24ft long and 16" square section. In plan the hulls would have a gentle curve from maximum beam in the middle coming to a point at stern and bow. If you wanted to get fancy you could taper the sides outwards from bottom to deck but it adds complexity. It is desirable to have a bit of rocker forward so the boat will glide up a beach easier if that is something you are likely to do.

I would be looking around for a good 7 to 10HP outboard rather than trying to put something together just because I have the prop. You could expect 10kts from 7HP. A 10HP will have some reserve at 10kts.

12mm (1/2") ply is quite heavy for this. You could get away with 3/8" but it will not take as much punishment. I would not go down to 1/4" as it will need careful use. With 1/4" it will not be a robust hull unless heavier glass is used.

Rick W

[hoytedow]

Just a quick sketch.

[hoytedow]

[quote=Rick Willoughby;299838]You are close with the stringer size. I would use even smaller - say 1.5" square.

Rick,
What we in the states call 2x2 is actually 1.5x1.5, the reason being rough lumber measure is the source of the name. After planing the size is diminished to 1.5"

[rozerdemit1]

Originally Posted by Rick Willoughby

For fully enclosed pontoons you will get good strength and adequate life from externally sheathed ply with fibreglass cloth. 200gsm cloth is all that is required because it essentially is there to protect the wood from sunlight and mild abrasion. It will hold paint a lot longer than unsheathed ply.

The thickness of the ply will depend on the power and target speed. For displacement speeds up to about 10kts 12mm ply will be more than enough. The best shape will be a canoe style for these speeds. It will not require much power.

This thread gives an idea of how simple it is to construct the hulls:
camping kid build for raft race
In your case the hulls will be heavier, bigger and fully enclosed. Screwing and gluing them is probably easier than stitch and glue for joining. The timber is providing adequate strength. Using simple chine and gunwale stringers with regular bulkheads will be adequate.

Fully enclosed hulls like this will be quite strong.

The deck can simply be made from 12mm ply sheets separated by 100mm bearers. You need to determine how you will connect the deck to the hulls and provide appropriate reinforcing in the hulls and deck to suit. Stainless brackets and bolts work well.

With sheathing you need to round all the corners of the timber to soft curves of say 10mm radius. It is desirable to do as much with a single piece of cloth as you can but you are limited in how far the cloth can be curved before it creases. It is better to overlap with another layer of cloth than allow creasing. There is no need to vacuum bag any sheathing if you do not try to wet out cloth that will hang down. You do not want to try sheathing the complete hull in one go. May be possible to do bottom and sides in one step and then the deck.

This gives some description:
http://www.azom.com/details.asp?Arti...dure_for_Glass

The peel ply is recommended if you want the minimum effort to get a good finish. If you want a nicely faired finish then you will also need to bog up the surface with a fairing filler and sand it smooth. A little time and effort here can result in a high standard of finish.

There are heaps of references on sheathing and stitch and glue. With these hulls you should be able to do full length sheathing. I would probably do each hull in four goes - port side, starboard side, bottom and deck. This will provide double layer on the chine and gunwale. Extra wear layers on the bow are useful for beaching.

If you want to push the hulls into planing regime then you have to look more closely at the hull loads and strength.

With the hulls and deck all fully sealed you will have sufficient buoyancy in any of the three elements to float the weight. Hence very low risk of it actually sinking.

Will take a few hours with cardboard and glue gun to make a model that will give insight into what it will look like and how to build it.

To get the hull sizes you need to determine how much it is going to carry and make an initial stab at the hull weight. This will give the hull volume needed. Each hull should have enough buoyancy to float the entire weight. Stability can be a concern if this is not achieved.

Rick W

Really good answer thanks for sharing this with us,,,,

party tents and marquees

[Boilermaker]

I believe your calculations are for a equal amount of water displacement. If you do not want the pontoons completely submerged you have to calculate the volume of water displacement (gallons)(weight) of how much of the pontoon you would want submerged. Usually half on most pontoon set ups. Just my 2 cents worth. Steve

[joefaber]

Mud - look over the attached PDFs.

just add an eight foot section to the middle of the PM Platfrom boat
and build a cabin based on the PARTI-O boat design.
you'll have the boat you described.
add another 12" to the pontoon height,
keeping the bulkheads proportionate,
will give you LOTS of floatation.

[hoytedow]

Originally Posted by hoytedow

Rick Willoughby,
Good answer, saves me from having to cover it. I used screws and glue since this was my first boat and I had not heard of stitch and glue yet. The hulls were open except for the bows which held air under short foredecks. The motor mount was mounted to the stern crossbeam with heavy angle braces. There was no tent or superstructure since it was used for day trips on the river. It was however very stabile and comfortable within its designed function. I am planning to build another one but right now am short on cash. When I draw up the plans the old fashioned way I may post them but right now it is low on my priority list. P.S. I used 1/4" plywood(approx. 12 mm) and the stringers were 1 by 2s(approx. 36mm by 72mm) softwood.

Correction: metric conversions were twice the accurate number. 12mm should be read 6mm and 36mm should be read 18mm.

Sorry about that.