Jon boat build

[topwater]

just bought jon boat plans from unclejohn.com and getting ready to start building.

16' x 48" - bow and stern decks with a center bench. Largest spance of unsupported floor will be 3.5'.

My quesiton is. . should I go with 1/2" ply for the bottom (i know the bend in the bow will be difficult with 1/2") or will 3/8" ply be sufficent.

Im planning to glass only the seams and paint the bottom with epoxy, inside and out.

Also, is marine ply worth the extra expense?

 

[mike]

Howdy, topwater!

Welcome aboard!

I think most everyone will tell you 1/2" is over-kill and too heavy. If you don't plan to glass the whole thing, marine ply might be worth the extra money. I'm not sure about that, but it will all depend on how well you maintain the paint (or varnish) job on the boat.

Mike

 

[Jimmy W]

Uncle John just calls for using 1/4 inch plywood. Marine plywood would likely be stronger.

 

[seedtick]

depends on how large of a motor you plan to hang off the back

16' X 48" - could take 50 Hp = no place for 1/4" plywood

3.5 ' clear span ? - you wouldnt' put 1/4" on your house roof with 3.5' rafter spans. A 1/4" bottom could be ok as long as you be sure to load it or walk on it only when it is the water otherwise you're likely to crack it

or 1/4" could be ok if you glass both sides

personally, without glass, i'd use 1/2" and have ribs (or some support) closer to 16" apart and not 3.5'

also use marine ply - no question about that in my mind

 

[dawallace45]

I went with 1/2" on my Jonboat because I wanted a large area in the middle open and un-supported , figured if I went with lighter the oil canning would be more than I wanted even with the keel runners I put on

David

 

[oldsparkey]

On the Skiff he suggests 3/8th for the bottom and not 1/4 inch if you are using a motor .... The Jon Boat is wider and longer then the skiff and since you do not plan on glassing it I would suggest the 1/2 inch ply to be on the safe side. Will be harder to get into shape but it can be done.
Or go with the 3/8th and glass it , anyway the bottom of it , to make up the difference. I would glass the bottom on both sides. Especially the inside areas that will get the wear and tear from folks walking around. Epoxied glass will take more abuse then just the epoxied saturated wood.

You could get by with marine ply on the bottom since that takes a beating and normal on the sides , just a thought since I have never built one and have no idea how much wood is needed. I like to use the same wood all the way around.

Chuck.

 

[gbinga]

It depends on the motor, and also how you are going to haul it.

If you are using a trailer, and a good size motor, weight isn't going to be that much of an issue. I'd guess that with anything 20 hp or more, the extra weight from the plywood would be trivial in terms of performance and it would make the boat ride smoother.

If you were carrying it in the back of a truck and running it with an electric, it's a different story. But a 16' x 48" boat sounds like too much hull for that kind of duty.

If you are using a 10 hp, maybe go with 3/8"?

I think it comes down to what size motor, which of course is what Seedtick already said.

GBinGA

 

[topwater]

Appreciate the feedback!!

It will be hauled on a trailer and Im hoping to go with minimum 15hp and possibly up to 25hp depending on what I can find in the used market when Im to that point. Based on the replys I've gotten, Im going to go with 1/2" inch ply on the bottom and 3/8' for the sides.

Now just need some warmer weather so I can get started ;o).

 

[funbun]

Jim Michalak recommends 1/2 in ply for the bottom and 1/4 in for the sides. His boats is 16 x 48 as well. Note: it only has four support ribs. He only recommends about 10 hp, although according to Coast Guard probably allow much more than that. (Honestly who needs more than that anyway?) He also doesn't recommend marine ply, and he only glasses the bottom and chines. This is a hard chinned boat, btw.

If there is any doubt, go down to your local Academy or Bass Pro Shop and just look at how those jon boats are made. A 16 footer usually has about seven ribs or so.

I plan on building a jon boat myself and have looked at different designs. I keep coming back to the one linked above.

 

[islandpiper]

It seems to me that 1/2 ply has three plys of wood......why not use 1/4 ply in two layers, thus having SIX plys altogether. Bend on the first one, epoxy coat it, and the inside face of the second one. Then, after the epoxy cures, coat them again, bend on the second and keep them in contact with drywall screws and backing blocks. Later, pull the screws and dowel the holes.

Personally, I'd never leave the glass off the bottom's outside face? What's the point? There's a lot of trash and sticks and stumps out there.

piper

 

[funbun]

That does sound like a good idea, islandpiper, especially given how easy it is to work with with 5.2mm Lauan. I do worry about the thin vernier of lauan, though. It doesn't seem like plywood at all, but with a hard chinned boat, you'd have nails and screws in addition to epoxy.

 

[islandpiper]

In fact.........set a layer of light glass cloth BETWEEN the two 1/4 plywood sheets and have some real bottom armor for the occasional pesky stump that jumps in front of the boat when your wife is steering. (voice of experience)

piper

 

[funbun]

Wow, piper, that gives me a whole new set of ideas. Thanks, man.

 

[Kayak Jack]

You definitely want a layer of glass on the INSIDE of the bottom too. If a bot gets pinned up on a stump, rock, or other obstacle, it bends the wood upwards and inwards. Glass on the inside surface will help keep it from splitting and breaking.

 

[islandpiper]

Kayak Jack saw the inside of my UJ. I glassed the outside and only taped the seams inside. Now whenever my big bee-hind is in the boat and wave action sets us down on a cypress stump i hear the faint crackling sounds of the inside ply. Further, all those little cracks have been happily drinking sips of swamp, dew and condensation and now require that i put a bottom on the boat or simply make a new boat.

piper

 

[oldsparkey]

You can do the short cut of just epoxy saturate the boat and glassing the seams , then painting it. A lot of folks make them that way and then make a few more to replace them. For the extra ( initial ) cost of glassing it inside and outside it sure costs less them having to repair /replace or even making another to take it's place.

Before you say it , Yes I have made them the way you were thinking about , taping the seams and epoxy saturating the wood but they are paddle craft ...No Motor... on them. Heck I have even just glass the outside on some and not the inside. The ones I want to last are glass encapsulated. A boat does suffer more abuse from hidden objects in the water with a motor on it then one without a motor.

If you laminate the bottom sheets with glass that will offer a lot more protection and don't forget to glass the bottom , better to have the glass get a scratch then just the wood to get a hole.

Paddling we hit a log or something it might be at 2 mph , with a motor you really multiply that speed. This skiff I am making will be glass encapsulated and epoxy saturated since it will have a motor on it at sometime. Probably a 3 hp ( gas or electric) or less since I don't get in a hurray anymore.

I know back in the dark ages they made wood boats from nothing but wood and paint , I have had some and they were good boats and lasted forever , with yearly maintenance. Heck there was one like this skiff I wish I still had today , it was a really great boat.

Chuck.
Just tossing out my thoughts , it is your boat and you know how you want it.

 

[islandpiper]

Chuck, you said, "Just tossing out my thoughts , it is your boat and you know how you want it."

Hey, what's the fun in that? The whole idea here, I thought, was to have all us armchair experts help each other make things OUR WAY with no expense to our selves, no risk, no "essplainin'" to the wife or anything. piper

 

[oldsparkey]

Chuck, you said, "Just tossing out my thoughts , it is your boat and you know how you want it."

Hey, what's the fun in that? The whole idea here, I thought, was to have all us armchair experts help each other make things OUR WAY with no expense to our selves, no risk, no "essplainin'" to the wife or anything. piper

That's the general thought but now and then we need to be nice , after all we want him to have a good serviceable boat to enjoy for years down the river.

 

[islandpiper]

Chuck, he'd have a great boat if he just did everything that you and i and Jack and JEM and seedtick and everyone else suggested. It might weigh in at about 4000 pounds but it would be a great boat. Piper

 

[Kayak Jack]

A flat bottomed boat does a great job of sneaking up into dark waters and inaccessible corners - where more obstacles hide. Now, when a round bottom or even a vee bottom encounters a rock or root, being naturally sloped, it will try to slide off and avoid getting stuck. A flat bottom drills right on until resistance finally overcomes power.

And, if there's a motorized prop driving it, that may take a few extra seconds to get back up on your seat and grab the throttle to turn it in the correct direction. So, a flat bottomed, motor driven boat is probably more likely to get more hung up on an underwater obstacle than any other kind of watercraft.

What all that says to me is at least two things: (1) Glass on both the inside and outside, and (2) Apply graphite enriched epoxy to the outside below the waterline.

Now, not all boaters will agree with that, and frankly, 15 years ago I wouldn't have agreed with it either. But, I didn't get this old by being dumb. I learned these two lessons from other boaters. (Here's an adage to nail up on your wall: "It's cheaper to learn from someone else's mistakes than from your own.")