17ft aluminium center console boat - Opinions?

Honestly Maxxi it's not intuitive. Just in case you don't know, delftship free is from the same developer as freeship so you can just install it and load up your file, press hotkey alt-D and voila you'll know for sure. No reason not to do it.

And your model looks nice! "Tortured" is just in reference to "tortured plywood" that you can more easily bend into compound curvature. A larger, relatively thinner sheet of metal might be harder to torture into shape, could crumple or something.

 

It is surprising that people can design presentable looking boats, although I wonder how original, and be oblivious of how allowance has to be made for the plating limitations of the material used. Of course you can bend and twist sheet materials, but unless they have inherent "stretch" in them, they will not conform to compound curves, and compound curved areas are not necessarily all curves, like a beach ball, in every direction. Some directions can be straight lines, and that is what the forward portion of your boat is.

 

Ok, I see now what you guys mean. Stress in the material tries to "balloon" the surfaces. That could be eliminated by clamping the plate tight to the framework/bulkheads. Anyway in the bow section of the boat it would not have any effect in planing speed handling or anything else dramatic. We kind of have different thoughts about developable surfaces. I think, for example, this Freeship software is just a good tool to make outrolled sheet plans that you can cut with a CNC machine, and it seems to work quite well. It would be very hard to do those plans without a software like this. For me few mm difference in the real life model compared to the 3D model render doesn't do anything, especially when it is just one of a kind build.

Stiff material with small surface area, like in the model, would not "balloon" much, if any all, propably flexible aluminium in real life size would do it. But if you would cut all bulkheads 1:1 and force/press the hull against them(and weld them together), the hull would be like in the 3D model.



I was going to make a framework like in this pic anyway, so few mm curvation in the hull sheets doens't do any harm. But in this pic you can also see how the lower part of the bottom sheets has curvation. They are welded together in the middle and the force in the material tries to bend it back flat, it's just heavy stress in the material that tries to flatten out. If you have good tooling(clamps) you could force the hull sheets and framing together.

 

Yeah maybe, probably, who knows? But why don't you want to use the software to find out for sure?

 

Delftship doesn't open my Freeship file.

So you mean Freeship doesn't do developable surfaces right?

 

My apologies, I just assumed this would work. Maybe you can export / import as another file type.

 

Did you read this, maxxi ? Similar situation to yours.
Building of Aluminium Boat . Mounting of hull framing structure https://www.boatdesign.net/threads/building-of-aluminium-boat-mounting-of-hull-framing-structure.61901/

 

Yea, I did read it, but totally too much non relevant info there. The whole problem in that thread wouldn't exist if the bottom sheets would have been mounted differently in the first place. This kind of boats have been made tousands and tousands, basic sheet builds. The problem with the curvation is just a issue with the material itself when the material tries to force itself back to flat. But with good supports and tools you can make it perfectly ruled.

Orginally I just wanted to share this build idea here on this forum, so if there is some things that seems wrong when thinking about using the boat, and handling of the boat at higher speed...

 

I am reasonably familiar with these plate alloy boats, and the convexity of the forward bottom sections, is pretty well standard. You will not get the finished product to agree with the lines you have drawn. The straight sections are the preferred shape, but the convexity is what you end up with, using normal techniques. That is only a problem with getting your frames to meet the plating, all over. The actual shape will still be quite functional. But I would not be depending on forcing your plating to meet straight sectioned frames, it may be the cause of some grief. The boat below shows the typical convexity of the bottom forward, of a plate boat.

 

Note the convexity of the forward sections of this boat designed for plywood sheeting. It is not that way because they wanted convexity, but because developability governed what could be done.

 

Forcing the plate to fit 'flat' (straight) frames (and longitudinals ) may probably buckle it.
"Don't force it.... get a bigger hammer"

 

Mr E's first comment that you could not use vertical straight frames in the forward part of the boat is the main point here. The plate will not lay flat against vertical straight frames and
HAVE SMOOTH lines. Clamping and hammering might get the plate against the frame but the boat will not have fair lines.
Your comment about "different thoughts about developable surfaces" In boat building, there are not just opinions what this means. Basically, if you take a plate and want fair lines but with
curvature, it will bend to suit its own curvature, from between where it begins to bend to where it will end up. Then the frames must be made to match. Of course in larger boats, you could roll bend plates to produce compound curves but this hull is not in need of that.

Re the attachment of the aluminum hull construction
We have built many aluminum hulls and I am not sure why you are considering choosing this method of installing many short stringers.
The generally accepted method is to have non interrupted main stringers without welding a bunch of short pieces together, and then adding framing or support between the main stringers.
Mainly to make the boat easier to fit up plus getting rid of all the welding issues throughout the stringer. I don't think that I have ever seen such an interrupted set of stringers in an aluminum hull.

 

This business of forcing the plating to suit the frames, is asking for trouble, in more ways than one, probably, as Barry mentioned, a hull that will look and be unfair, and who knows what stresses built in, that could lead to failures down the track. One of the mass market alloy boat makers in Australia, spent a bomb on stretch-forming equipment, to get away from the limitations of developable surfaces, I'd be confident they would not have done that, if they could have created a boat as drawn by the OP, without it.

 

The stringers in the pic are full lenght, the framing just have notches to fit them.

Anyway, as it has come up several times, the only issue may be that the framework doesn't match the hull 100%. Even if the hull sheets get the curvature it would affect the main measures very little, boat will still look the same as planned. So I still doesn't see the problem here? And the orginal plan was to use framing like in the pic I posted, it can be made to fit the hull, but main reson is to save material and I wouldn't like to weld the hull in Y-direction, only do welds in X-direction. 4mm material would shrink some around the welds anyway, so it would be visible on the outside.