18'x60" John Boat Build Idea

Joined
Jul 13, 2016
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Hello. I have been researching how to build a wooden john boat. I have came up with the design i want to do. I just want to get everyones opinion. Here we go...

A typical piece of plywood is 48"x96"
For the bottom of this boat i need:

4 pieces 48"x60"
1 peice that is 24"x60" ( could leave this piece out and just make it 16'x60" total

Normally the would be put end to end instead inplan to put them side to side.

This would give me 4 seems to join together. I dont want to scarf the joints though.
My thought was to join the pieces together using 2x12's with gorilla glue and screws to start.
There would also be a 2x4 running lengthwise on the edge. This would also add support for those four seems.cplus it gives me something to fasten the walls too. They will be 24" cut height. They will also be angled out about 15 degrees should give me a width of 80".

On the underside of the flat bottom there will also be five pieces of wood probably 1x2's maybe something beefier though. Indont know what these are called.

The transom will be made of 2 pieces of 3/4 plywood sandwhiched together.

At each corner of the boat there will be a 4x4( already have them). This will give me a good anchoring point for the transom and again the sidewall.

I dont know about the seats yet.

Everything will be wrapped in glass. The underside of the bottom moreso than anything else.

I hope that wasnt to complicated i tried to discribe it the best way i could.
I dont have any plans or offical drawing just my doodles. I would plan on a huge motor. Max at 35 or so.
 

jbcurt00

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Staff member
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Oct 25, 2011
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24,829
Framing lumber you've chosen is too heavy.

2X12s are much more then you'd need as are the 4X4s and both would make the fiberglass work more difficult then it needs to be.

Google:
Homemade
Home built
Scratch built
Plywood DIY

and Jon boat.

You'll get a few hits and I bet at least 1 will have a link to an 18X5 Jon boat w free (or inexpensive) plans available. I bet at least 1 Popular Mechanics/Science magazine from the 50s/60s had a plan you could use too. There are lots of free boat plans available online.

What are you planning (and where) to use it for? Fishing?

Flat bottom Jon boat w benches and a storage box or 2?

Plan to have flotation foam in it?

Epoxy resin and cloth?
Polyester resin and mat + cloth?

Longitudinal (fore~aft, front~back) stringers are inside the boat, and run the length of the boat. Chines or runners would be on the bottom.

Lateral (port~starboard, right~left) ribs run across the width of the boat.

Good luck w your project
 
Joined
Jul 13, 2016
Messages
18
Three compartments for foam.
Epoxy and resin
The 4x4 are just the to secure the transom to the sides and the bow to the sides. Ive looked at the free plans and the way theey discribe it is just not enough to get a screw into. Most of the olans involve just glueing and glassing it together.

I'm planning on taking it on just lakes.
im supposed to be getting a free trihull. Its a '76 l
It is in bad shape. Need new floor, transom, has no motor, windshield, seats.
Supposed to come with the trailer and titles.

Im just trying to figure out if a large john boat build would be worth it over restoring the trihull.
 

sheboyganjohn

Senior Chief Petty Officer
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Aug 2, 2005
Messages
753
Go to Spira International website. He has not only a ton of boats to build but a bunch of building info. He specializes in boats built from basic construction lumber with simple joints. You can also go through my dory build. All the framing is 2x4 with a 3/4" bottom hull and 1/2" sides. Transom is built of 2x4 and 2x8 with a single 3/4" skin on it. Runs +40 mph with 4 people and has 500 lbs of motor on the back. if that holds up you should be good. For the joints use the same thickness plywood backing that is glued and screwed in place that overlaps minimum. 5x the thickness. so a 1/2 ply, have the board 5" wide 2 1/2" on either side of the joint. Wider is better but you eventually hit the point of diminishing returns and are then just wasting epoxy and wood.
 

jbcurt00

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Oct 25, 2011
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Dont forget, the boat has to float every ounce of its own weight too.

For an 18X5 Jon boat, 2X4s and 4X4s are too much weight. Can you even buy non-pressure treated 4X4s?

PT wood is heavier then non-PT wood and the treatment can cause poor adhesion w the epoxy and glass.

Stitch and glue would be sufficient for holding together a Jon boat you also encase in epoxy and glass.

I built a small wooden boat, 12ft X 3ft, and to futher reduce weight I used 5/8 X 5/8 chine logs instead of the suggested 3/4 X 3/4. Once I glassed over the seams and corners, its plenty strong enough.

Not suggesting you use 5/8s chine logs, but 2X4s arent necessary.

Your 18X5 Jon wont need to be nearly as beefy as a 23ft Center Console dory to be safe and reliable.

If you are using epoxy and glass, IMO 1X1s would be sufficient for the chine logs. But actually 1X1s, not whats sold as a 1X2 ripped in half, which gives you 2 3/4 X 3/4 boards.

I'd probably also use rib frames out of 1/2 or 5/8 ply
 
Joined
Jul 13, 2016
Messages
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After it is built i plan on a 9.9hp max. I know that is small and it wont have alot of speed but several of the lakes around me are HP restricted. I could make a smaller boat but i want something i could take the family out on two. I figure it should be able to hold 6 people. Me, wife, 4 kids.
 

Small Saddle Wedgie

Seaman Apprentice
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Feb 8, 2014
Messages
42
I downloaded a boat plan (Building a Flat Bottom Jon from Plywood).
I've tinkered with the plans, viewed several finished products that were built from the plans.
I've narrowed it down to an 1860 with a 2 foot hunt deck on the rear and a Slightly Dropped (slightly) Transom.

The plywood will be 1/4 Exterior.
The joints will be scarfed for Strength and Durability.
I will Polyester Glass all of the joints and the entire bottom (After the 1x1 Chines are applied and shaped).

I am ribbing the inside, and then foaming, and adding a second 'removable' deck shell that will be a walking surface.

The seats will be removable and cleated so they can be replaced by either Decks (For fishing) or Gun Boxes for Duck Season, or .... (?).

I am building a 22HP Predator Engine with a Long tail, Mud Motor.

I'm a researchaholic, so feel free to ask me why I'm doing anything, I'll do my best to explain myself and my thinking.

This is also my first boat build from scratch, so I'm also always up for the comments and corrections from those who've paved the way before me.
 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
If you want to put 6 people in the boat, you'll need to make her 16' long and 5' wide. Epoxy works much better on Wood boats like this.
 
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