20' flat bottom river jon.

Howdy been reading up a bit.

I would like to build a river boat that is shallow draft, I fish White River in Arkansas and my old 20 aluminum river boat is getting to the point, well I tighten the rivits monthly and have installed abildge pump if that tells you anything. Beside the metal allow condensation in humid weather. so with that in mind here the idea

I am wanting to build a boat kind of like this one.

http://www.supremeboats.com/207.html

There are four of five companies building boat up here i North Arkansas but at $4400.00 and up it just seems like a lot of money for something I can build and build to my specs.

Requirements are

Up to 25 HP.

42 to 48 inch wide.
20-21 ft long.

Shallow draft.

We have anywhere from no water to 8 generators from Bull SHoals Dam all last summer, currently one generator or two is average and I currently have a 4 stroke Merc 15 on the aluminum boat.

The reason for so narrow is that we have rock to go between and some of the other rivers have some really tight twist not just bends but twist. and I want to be able to put my 4 hp 2 stroke Yamaha on it to fish restricted water

Anyway what weight cloth? matting? Resins?

Thanks John

 

I built a boat just like this 5 years ago, only 14 feet long and not as fancy. Spent $500 in resin alone. I wanted it lite so used foam core and very little fiberglass. Used it for 2years as work boat. Sunk it after water got into core and it became too heavy to really use and my choice of lite was causing all kinds of problems. Next time I will buy a used hull and fix rest of boat myself.

Honestly...My guess is you going to spend $2500 in materials alone to build a substandard boat. Either buy a new one for $4k or buy used one for less.. Also there might some aluminum Job boats that will do job nicely.

 

Nothing wrong with going narrow, though I would try to go 48 inches rather than 42. The slenderness of the hull will give you greater speed and efficiency with the smaller motor, especially when just putt-putting around.

Can't help you on the fiberglass. I prefer aluminum myself, especially in a river where you may hit hidden obstructions from time to time. If you go whole hog and put a tunnel in a boat of that size, you should be able to run through four inches of water when on plane. Tunnels come with a whole 'nother set of design issues, though, so don't do it if you aren't sure.

Number of generators doesn't tell us much since they can vary greatly in the amount of water they put out. Discharge in CFS (cubic feet per second) is a much better measurement, as is change in vertical elevation of the water level where you do most of your boating.

 

Why not use wood construction? It will be much cheaper to build, will build more quickly, will have inherant bouyancy, is quieter, is more tactily pleasing, etc....

All the boats used on your river in the distant past were wood. They did not drown any more people than the current aluminum or fiberglass ones. If you anticipate hitting a lot of rocks or drifts then make the bottom thicker than normal and/or sheath it with Dynel.

 

I'm building a similar one, but not so long, from plywood. I don't anticipate spending any money on resin or glass tape or any of that stuff (although I might tape and epoxy the chine seams if I really can't get it 100% watertight any other way).

Of course, it might sink like a stone. But I can swim, and it won't have cost me very much to find out that it was a bad design :/

 

Sounds like a fine Idea to me!
I'd use a decent 5/8"-3/4" plywood (preferably marine grade though, with enough epoxy, it won't matter so much), draw up the pieces you'll want (or I can do it for you, If you'd like...for a small fee), cut 'em all out & screw or nail it all together in the shape you're wanting.
Now, cover all of the seams & screws with fiberglass tape (I'd go with about 6" wide) & give it a nice, even coat of epoxy over the whole thing. Inside & out (or polyester resin, which is MUCH cheaper).
Last, I'd give it about 3-5 layers of Dynel...and use resin to "glue" each one to the hull. The Dynel is VERY resistant to abrasion, so it'll let your boat survive a few encounters with rocks before it bites it!
Then ad paint, an voila! a boat!

Notes:
1. With Dynel, you'll want to use some form of pressure (vacuum bagging, books on a board, or something) to keep the fabric from expanding once you've added the resin to it.
2. I'd recommend at least 2 pieces of plywood sandwiched & "glued" together with some epoxy/polyester for the stern...give a more stable mount for your motor.

 

Thank you for the idea.

Yes it would be cheaper to buy a used boat, but building boats has been my blood. Started when dad built his first boat back in the late 1950's and I was a small kid.

Most of the time you just slide over rocks. The river can rise from no generation to 8 to 10 feet very quickly.

What I don't like about the current boats sold, is the rear sets down in the water more than I like, I have used the Supremes and a couple other brand and when someone is running part throttle throwing a wake it will wash over the back end, plus none have any flotation.

I have thoughts of building one from pink or blue insulation board over a wood frame and using a resin to glass it in. I don't know what resin would work for Polystyrene foam .

What Epoxy would work with this resin. I am willing to use epoxy where the main strength is needed if will also work with the resin used on the rest of the boat.

I had thought about a tunnel of sorts but since I am not an engineer, I figured I might be into more than I can do.

Also I have been experimenting with vacuum bagging a bit. I am also a taxidermist and do some fish, and have made fish fins and bagged the mold using the shop vacuum for the suction power, really helps on the fins and air bubbles.

John

 

The shop vac isn't what most in here will recommend for vacuum bagging a major project, but for this design, since weight isn't going to be a critical factor, it should work at least well enough to keep the expansion of the Dynel under control.

I wouldn't recommend using ONLY that insulation board for your boat. If you wanted to include it for (slight) stiffening, and for flotation that's great, but I'd recommend sandwiching it between a couple layers of wood veneer (or 1/8"-1/4" ply) at least, as the insulation board WILL NOT hold up to the first rock that scrapes it...it just doesn't have any shear strength or compression strength. Now, I'm right now working on building a little "tinkering" catamaran (4'10"x9'4") out of 1/8" "hardboard" over pour-in-place foam, with plenty of epoxy & glass over the outside to keep the hardboard from EVER being exposed to water. The foam will actually be providing a LOT of the structural strength of the finished boat, but it would be useless without the wood sheathing it, to disperse the energy/pressure from impacts & abrasions over a wider area on the foam.

I hope I made sense to you here. I don't like to ever tell people they have "bad" ideas, just try to find a way to make their ideas workable for 'em...if I can

 

Having a wake wash over the transom is definitely a bummer. The boats with that characteristic are either poorly designed or overloaded near, or on, the transom. The usual problem lies in the psyche of the great American boater. He puts too big a motor on too small a boat. Modern outboards of ten HP or more will weigh near 100 pounds, then upwards to several hundred pounds. In your case you are using relatively skinny boats. Skinny boat, heavy motor, bad news.

One can mitigate the problem with a slight change in the boat design while leaving it narrow. Bring the motor inboard from its' usual place. How can I explain.?....... Try this.... Imagine a conventional boat with the transom at the extreme back end as is common. Now take your saw and cut about 16" out of the middle of the transom, do not cut the sides of the boat. Continue sawing at the bottom. Cut a 16" notch in the bottom that goes forward 2 or even 3 feet. Put some sides on the notched out portion and attach a motor board to the front of the notch. You can think of this in a different way, like this. Let us say that the transom is 48" wide. Build two boxes that are 16" wide and 2 or 3 feet long. Bolt those boxes to the existing transom so that the bottom of the boxes are in line with the bottom of the boat and the outer sides of the boxes are in line with the sides of the boat. What you have done is added some bouyancy to the back of the boat and the bouyancy is behind that heavy motor where it needs to be. Of course the tops of the boxes are to be closed. Using these example dimensions ( 16 wide x 15" high x 24" long), you will have added 400 + pounds of potential stern bouyancy. Swamping will be far less likely.

You can see this system on a number of boat designs. I am thinking of one named "Sneakeasy" , a design by Phil Bolger. You can probably Google up some pictures of that boat. One of the additional advantages is that the boats seem to get up on a plane more quickly. Best of all they do not point the bow skyward when the boat is in the hole just prior to popping up. That pleasing feature could be useful when running in shallow water.

It may be worthwhile to look at Sneakeasy as a possible design for your particular use. It is built of ply and it is one of the most simple boats to build. That is because it has plumb sides and you can frame it with an ordinary carpenters square as a tool. I think that boat as drawn is about 24 feet long. It has a pointy front end, it has some rocker foreward which is useful for sliding over rocks and drift. That boat is designed to use smaller motors, say from fifteen to twenty five HP. It will go like a bat out of hell, even with the smaller motor.

 

I had figured to sandwich the foam. But then also thought about just a plywood boat with the wood sandwiched between glass and resin layers.

I took a trip guiding two other men both smaller than me they were in the 15--190 lb range, a 20 hp 2 stroke mercury jet motor the day before Thanks giving and several times we too water over the rear of the gunwales.

interior is this one.
http://www.supremeboats.com/207.html

Hull outside was this one.
http://www.supremeboats.com/L42.html

empty draft is 2 inches, with 150 lb motor and me at 250 plus gear its a lot more..

Some owners have added oak sider near the rear to avoid water.

I have twpo motors only about 35 lbs difference one is 4 stroke 15hp Mercy prop and a 25Hp 4 stroke prop Yamaha. the 15 is my choice less fuel used.

We use what is called a spider chair, sets on four legs and you can move them around at will to distribute weight.
John

 

Hmmm...looking at the L42, it doesn't look like it has much freeboard ANYWHERE. I'm thinking you'd be pretty happy it you moved the CG fore a bit (by increasing the angle of the bow...I.E. meets the water sooner...which also gives you more usable space aboardship)
I also like messbout's idea Re: stern extensions either side of the transom/motor mount to carry some buoyancy aft.

I think by combining a more blunt bow, higher gunwhales (for more freeboard) and the stern extensions, you'd get a VERY err..."river-worthy" boat that you could enjoy.

Also, what speeds (max) are you wanting out of your boat? Are you just wanting to tool around a bit at 8-10knots, or are you wanting to be able to jump up on a plane & fly at >15 knots? A boat that performs well at 20kts won't do as well at 10kts. One that's designed for 10kts will be downright dangerous at 20kts!

 

The L42 is a bit erratic at wide open throttle on a 20hp 2 storke Merc jet motor. My main motor is going to be the 15hp 4 stroke merc, elect start weighs about 130 lbs.

I think maybe 12" stearn extensions might work. But the blunt bow I dont think will work.

Reason for this is some of the rapid we run going up river have 2 to 3 ft. standing waves.

I have no idea what the top speed would be.

I think the speed on a lake is going to be different than the speed on the river, and then the more water that is flowed the faster the water passes over the hull and while the land speed may not be more the flow rate over the hull can triple.

More freeboard! I think thats a must, one reason is there are some people that run bassboats on the river with lots of water and they dont get them up on plane, throwing large wakes!

John

 

Are you sure the sneakeasy has any rocker in it? I have the bolger plans for the sneak.
looks like shes perfectly flat bottom?
Im not perfectly sure. But pretty sure.
I think with the weight of motor and operator ..the sneak sits down in the rear an inch or two.
and runs on plane like that. Please correct me if im wrong.
thanks
Peabody

 

Peabody; I think sneakeasy has some rise in the forward bottom but not in the aft bottom. Actually I dont know for sure. Bolger did seem to like a lot of upward curve near the forward part of the bottom. I would think that a good idea for the river boat that Taxidermist wants.