16 FT Plywood Hull

I want to build a simple, flat bottom, vertical stem, plywood boat with fiberglass over the hull exterior. It will be a steam sidewheeler, having a fully loaded displacement of 1200 pounds, design speed is 5 KTS. It will be trailered, and used in fresh water.

Does 1/2 inch plywood, with frames 16 inches on center seem OK? What is the best way to approach this project, with respect to framing, seams, type of resin, fiberglass cloth, etc.

Thanks in advance for any help.

 

"Seems OK" doesn't cut it when boats are involved. I would suggest you calculate the actual loads: in particular how the weight of the boiler is to be distributed, how wave loads will affect it, and what the righting moment curve will look like (steamboats tend to have a very high CG). The calcualtions are not horrendously difficult, and some software tools can help you out. Look through older threads for recommended books, and read some before you start. Enjoy!

 

1/2 Plywood Hull

I have done hull strength calculations, and the hull is good with respect to bending moments with both bouyancy and wave action. As a matter of fact, all of this would be OK with a 1/4 plywood hull.

But I think there would be the potential problem of punching a hole in the hull, either dropping something heavy inside the boat, or hitting a submerged object. Of course, one could always imagine hitting a very ridgid object and punching a hole in heavy plywood too. I plan to have floorboards inside the boat, 1 x 4 or similar, and no high heels allowed.

What I am asking is if the 1/2 plywood is normal for this general size of boat. In typical plywood construction, how big do runabouts get before they use greater than 1/2 inch plywood? What thickness of fiberglass and resin is typical in this type of application? Planing runabouts have much bigger horsepower, and higher loadings in a planing condition.

With respect to stability, the design I envision has a high metacenter, even though the beam is fairly small (4ft-9in, to leave enough room for a trailerable boat with sidewheels) The boiler will be fairly light weight (watertube rather than firetube), and mounted low in the hull, the paddle shaft will pass over the boiler.

 

1200 lbs on 16' seem pretty heavy. Is it really deep?

 

Hull is 23 inches deep midship. Draft is 5.35 inches at 1200 pounds in fresh water.
Draft/Displacement Calc:
0 0
1 120.9405042
2 327.0497914
3 573.6310721
4 840.1919974
5 1109.7132
6 1380.961754
7 1653.937658
8 1928.640914
9 2205.07152

 

A commonly used "ballpark" guidelie for hull planking thickness in wood is one quarter inch thick for every 10 feet of length. This is generally considered a minimum. Plywood can often be slightly lighter than this. You would likely be fine with three eights plywood, but there is no harm in using half inch since no one in his right mind is going to try to lift a boat this heavy by hand.
I hope the bottom of the hull will be 4' 9" beam or close to it for the sake of stability.
Sounds like a fun boat.

 

1/2 Plywood on little steamer.

Thanks for the reply, just the answer that I was looking for. I think I will use 1/2 inch plywood for the sides and bottom.

Fred Rosse

 

Finally got this little steamer into the water in October 2010! Boat is built heavy, frames on 16 inch centers, 5/8 marine plywood bottom, 1/2 sides, with 10 oz. fiberglass exterior coating, 8 gallons of epoxy. Build can be seen on the NEWSTEAMBOATINGFORUM.net