Flat bottom alluminum boat building ?

This is much easier than the boat forums on this sight. I am going to build a 18' flat bottom I have a 20' custom made coast guard bow boat now. I need one more boat for the place I hunt. I am going to build a flat bottom because I don't need the handling it is more for the simplicity. I do have one similar to look at to build off of, but there is a few questions in mind. I have one piece 5' wide for the bottom of the boat. Will that have to get smaller when I go towards the front of the boat and how much? It seems that I will have to do that to match the degree of angle for the sides. Any help or pictures etc. will be appreciated.

 

i have recently put lots of thought into designing a flat bottom aluminum boat about the same size you are planning. you won't HAVE to get skinnier as you get more towards the bow, but i would suggest you do. i like the idea of being able to bounce off trees and stumps, so i prefer a more pointed nose, it should also make it a little more aero- or hydro-dynamic.

let me ask you, do you plan on using one big peice of aluminum, cut it and fold it to create the sides, and bottom in one peice?

 

Thanks for the reply. No I will have one piece for the bottom and weld the sides down. Yesterday I actually went as far as buying some 16 gauge steel and making a 2' boat. It worked out well. I got measurements off of the other flat bottom boat that I have access to and made this one in proportional to that on. I have another question after my little boat build yesterday it looks to me that the rake of the front will determine the height of my sides. This might be common sense but I did not realize this until yesterday. I think I really want to do this boat build. For me it will be just start and I am sure there will be more questions as I go. Have you built yours yet? It does make it nice to have another boat that is pretty similar to what I am going to build. I would rather have more of a coast gaurd bow, but that looks much more complicated. Where this boat will used it is not that much of a problem to have a flat bottom.

 

Not sure what you mean by a "coast guard bow". Perhaps you are referring to the garvey type where the bow curve is a rounded transition as opposed to the flat foreward transom of the pram type.

There is no problem with building a flat bottomed aluminum boat except..........you will need a lot of framing for the bottom. If you use something like 0.125 thick aluminum, then you will need a honeycomb like structure to keep the bottom skin from panting badly.

 

i like the "coast guard" type too, shuold be able to take on waves a bit better.

and you don;t understand how i am, yes when i say im gonna do something, i sure as hell will do it. but i still gotta go through college and all that bs. i'll be aking baby steps on this build

 

I will use .125 on the whole boat. I decided to go with that gauge because of the rigidness and the ease of welding. I would like to go thinner for the wait but myself would never be able to weld something of that thickness. I have seen the boat builder that has built my big boat and he builds a lighter boat and uses 1/8 witch I think is basically .125 and he runs his 2" braces length ways with the boats and runs them I believe on 1' centers and then puts kickers in between every so often. Do you think that will be enough to get the honey comb effect? Any more knowledge will be appreciated. If and when I start this project I will keep in touch. The way it looks I will probably start here real soon.Another question I have ran into here today is that I can only find 10' long sheets and will have to weld them to get the length that I need. I don't think that will be much of a problem. I am getting a good price on them. Do you know where I can order a 5'x20' long piece that is good pricing so I can at least have the bottom in on sheet? Every place i look to order this they have a minimum or it is priced very high. Sounds like you will have time to figure it all out before you build have fun in school.

 

Since you're in Illinois, you might check out the AAD and Oquawka boats - they specialize in heavy-duty custom aluminum builds.

The 0.125 thickness should be fine for hitting mud, sand and maybe the occasional stumps. I've hit plenty of stumps in 0.010 aluminum boats, but those boats were pretty light and bounced off easily - if you have a heavy boat with thin metal, you run more of a chance of doing damage. If you're running around big rocks, then you will definitely need heavier aluminum. Most of the custom builders use either 0.190 or 0.250 for the bottom and maybe the transom, then do the rest of the boat in 0.125. I believe some of the custom builders on the Columbia River (with lotsa rapids and boulders) are doing some larger boats up to 0.375 bottoms with the rest of the boat in 0.250.

Of course, it also matters what kind of aluminum (alloy) you are using. You might use 5086 for the bottom, 5052 for the sides, and 6061 for the stringers. Check out the Boats Document at marathonmarine.com for a good read.

 

Something you might think about is a used airboat hull. Florida has lots of them for sale cheap, very solid and well built. I have one and it will supposedly repel a 38 caliber bullet. I dont doubt it. Also it has 3/8 polymer on the bottom and I can run over anything without fazing it. I put an outboard on it and it runs well, just a little hairy on turns since it has no keel.