Initial considerations of scratch building:
Build light, or build heavy? Well...
Neither! Build right.
If light: You can of cause add dead weight if it ends up being too
light, but why not use the need for weight on bigger batteries? Or
If heavy: You can (maybe) add enough floatation material to keep it on
the surface, but remember that the engine has to move the total mass of
the sub when it sails, regardless of the volume of foam inside, not to
mention the rudders. They have to be able to turn the sub, not just
cause the water to make funny noises behind your sub.
During construction, keep an eye on weight, and buoyancy. Make a spread
sheet, and enter the actual numbers as you go along. This will help you
see of you are aiming for buoyant neutral, or if you need to watch
construction weight in either direction.
As mentioned earlier, the main hull is simply a plastic tube. Go to your local hardware store and look for a tube that’ll
fit your needs, and app. 0.2” (5 mm) in material thickness. If you cannot find any with these measurements, then pick the one closest to. If you want to recalculate the length so that the length-width ratio still fits, then do like this:
Real sub's length:
Real sub's width:
Ratio = 560 / 42 = 13.33 (read as “One unit wide, gives 13.33 units long”)
So, if you get a pipe that is slightly wider, then you can use the above given formula to get your new planned
overall length. The main hull pipe extends from right below the sail
dive plane, and all the way back to right before the missile deck ends,
just like shown on the illustration below:
Once you’ve got the length in place, and have cut out the piece needed for the main hull, you need to decide on how you will build the bow
and aft section. The choices are:
The "mold" method: Here
you first build a master in plaster, wood, clay or any other material
that you like working with. You then make a mold from that, and in that
new mold, you build your finished hull using resin (Epoxy) and all.
The only advantage when doing only one hull, is the fact that
it'll be easier to sand the master hull to a smooth surface, as it is
not made of epoxy.
The disadvantages are that unless you plan to build more than one
hull, then it's too much work with too little advantages.
The "Inside and outwards" method:
Here you take your pipe as described above, and
build two mock-up's of the bow and aft section directly in extension of
the tube ends. Simply build it up in wood, plaster, clay or any other
material that you like working with, but build it a bit smaller so it'll
fit when the resin (epoxy) is applied, and not before. (E.g.. the
diameter measurements should be app. 2 x 1/4" smaller than what you want
to end up with. Then apply wax, duck tape or something else that the
resin will not glue to, and apply layer after layer, mixed with fiber
cloth, and sand it along the way, until you have the thickness you like.
The advantage is that you save a step this way, and save on the
materials used for building the hull compared to the mold method.
The only disadvantages are: This approach takes a lot of
sanding before you have a smooth surface, and it's hard to make another
hull if you should loose the first one.
Common for both:
You need to mix the resin with silica thickener
in order to prevent it from running, running and running as you apply
it. You also need to start and finish with one or two layers of resin
with out fiber cloth in order to have a good surface both inside and
outside. Also, the
choice of resin (Epoxy) is important! Please read
this important information before buying!
Based on the above I choose to go with the
"Inside and outwards" method. What we want to end up with is something like this (only more detailed):