How to Build Your Own Hull - the Lost Foam Method
There are a lot of kits out there, and more are cropping up every day. Having said that, the odds that a kit of the exact boat you're looking to add to your fleet being available every time is slim. You can chalk up one to the small hobby and move on to another boat, or you can get up and do something about it yourself.
Building your own hull is actually a pretty straightforward exercise and the shape of most submarines lend themselves well to a technique called the Lost Foam Method. In a nutshell, you build your model out of foam, lay up epoxy and cloth on the exterior, cut it in half, pull out the foam, and you're left with a perfect (well... perfect-ish) fiberglass shell.
With the help of some excellent videos put together by my good friend Dwayne Hill up in Quebec, Canada, I wanted to take a few minutes and run through the process, start to finish. The boat in the pictures and video is a completely scratch-built model of the Russian Kilo Class in 1/48 scale.
View the videos at the links below, and read on for a description of each step:
Video Five: Sail and periscopes
Materials and Tools Recommended:
-Two-part epoxy resin (West System)
-Fiberglass cloth (West System)
-Large scissors
-Disposable brushes
-Closed cell construction foam (Styrofoam brand by Dow Corning)
-Steel or fiberglass rod - 3/8" diameter and 6" longer than your model
-Razor saw or hacksaw
-Acetone
-Pencil or fine marker
-Masking tape
-Safety glasses
-Utility Knife
-Access to a band saw or jig saw (optional)
-Rubber gloves
-Hot glue gun
-White glue
-Automotive body filler
-Automotive scratch-filler
Section One: Do Your Research
Any project requires planning, and building your sub is no exception. The biggest asset you'll have at this point is a good set of blueprints, ideally one that includes loftings, or cross-sections of the hull at given stations along the hull. This will allow you to create the foam block outlines when you start cutting foam. Also ensure that you have the rights to use the plans from the original owner.
Now that you have plans, you should decide what scale you're going to build in. Big boats are easier to work on and behave better on and under the water, while they also are harder to transport and store. Larger components such as props, pumps and seals may be harder to find and cost more as well. I'd highly recommend going with a standard scale such as 1:32, 1:48, 1:72, or 1:96. If you're lucky, you'll be able to find off-the-shelf detail parts that will make your life easier down the road during detailing.
So, plans in hand, now you need to take them to the local print shop and get them blown up to 1:1 scale for the boat you're building. This will make things much easier when you need to measure out distances and sizes.
Section Two: The Foam Part of Lost Foam:
What you'll want next is to find your foam. Closed-cell construction foam is ideal for this purpose, cheap, easy to find, and easy to work with. It is typically sold in 4'x8' sheets in thicknesses of 1" and 2". Ideally, your stations from your drawing will coincide nicely with the thickness of your foam sheet. If not, you'll need to cut sections of foam to match your drawing or else extrapolate at a mid-point. Styrofoam product by Dow Corning is what I use.
Now that you have your foam, you need to transfer your drawing templates to them. You take your drawing and make one copy of each of the station outlines. Number them from #1 at the bow through all of the sections until you have all of the templates marked out clearly. That done, you secure the templates to the foam with spray adhesive or white glue.
The next step involves cutting the foam along the outline of the templates, using them as a guide. Modern subs are a great project to start with due to how easy the basic shapes are. Most are circular in cross-section, and you can mark and drill the center of your circle to press a rod through for perfect alignment and strength in the next steps.
To cut the styrofoam, you can use a very sharp utility knife, but if you have one, a scroll saw or band saw makes quick work of this stage.
Beginning at either the bow or stern, begin stacking the discs of styrofoam onto your alignment rod, adhering them together as you go. I find that hot glue works well for this, setting up quickly and with a nice, strong bond.
This is where things start getting exciting, as your project now looks like a submarine and not just a pile of foam sheet! What you have at this point is a submarine-ish shaped object that consists of stepped discs. What we need to do now is knock the edges down and blend them one into the other.
If you're working on a boat that has a perfectly cylindrical cross-section, a great time-saver is to rig up a cheap lathe using a power drill and the rod that you previously inserted down the length of your boat for alignment. You'll need to build a simple mount for the drill using pipe clamps and 2x4's. By powering up the drill, you end up with a lathe that turns your boat quickly about its center-axis. You can use your utility knife to shape the edges together roughly, then progress to a rasp or other coarse file to further blend the edges. As you get closer and closer to the correct shape, progress to finer and finer files, ending with sandpaper for a smooth finish. If your boat is not perfectly circular, you'll be stuck doing things manually, unfortunately.
Section Three: Laying Up your Shell
If you've managed to come this far, you're probably pretty happy. You've got a submarine-ish looking thing on your bench and you can already envision what it will be like to run under the waves of your local pond. Congratulations! You've likely come further than 75% of the dreamers who undertake these projects.
The next step is to create your hard shell that will become the hull of your submarine.
You'll need to get some good quality two-part epoxy such as that from West System. You'll also need some fiberglass cloth (not the matte, the cloth!). Cloth is specifically designed for use with epoxy. Also note that I've stipulated epoxy and not polyester resin, which is what most people are used to seeing and using. Polyester resins will attack your styrofoam plug, melting it into a pile of goo and effectively killing all of your hard work. Don't use it. Epoxy is more expensive, but much easier to work with and it smells much better as well!
Lay out your cloth and cut it to shape, aiming to get the upper or lower half of the hull in one sheet, if possible. Note that curved sections like the bow or stern may require you to slit the cloth so that it can be overlapped without wrinkling. Preparation at this point will save hassles as you're wetting out the cloth. Cut enough to cover the half of your model in 3 layers.
Begin by wetting down the entire upper (or lower) half of your plug with properly mixed resin. A 2" disposable brush is perfect for this. Once you have a layer of epoxy on the plug, carefully lay out your cloth over it and press it down firmly to keep it in place. Saturate the cloth with more resin, watching closely for any trapped air beneath it. If you find a pocket of trapped air, dabbing at it with the brush will force it out through the cloth.