DA dum... DA dum... DA dum... DA dum
SHARRRK SHAAARRRK!! SHARR oh, wait... never mind... sorry.
Here's how to easily turn a remote control boat into a shark fin to scare your friends at the beach. This is a good project for people who like making a mess and for people who like seeing their friends scream.
For this project, I used the following materials.
Cardboard and masking tape (for molds only)
Spray foam insulation
Step 1: The Boat Lid
This step is optional and will probably be unnecessary or difficult with some boat models. The top of the boat I got on Amazon had some large speedboat features on it that I suspected would get in the way of the shark features, so I decided to create a new lid for it before commencing with the shark fin build. I traced the original lid on a piece of acrylic and cut out the shape with a band saw. The new lid had a bonus benefit of being more rigid than the original and easier to seal to the boat with foam rubber tape.
Once your new lid is cut out and inserted, cover the rest of the top surface of the boat with painters' masking tape.
Step 2: The Mold
The first step in carving the shark fin is to make a mold for the spray foam. This is a pretty crude process, so the mold can be pretty crude. The basic goal is to minimize wasted foam, so just an outline of the base of the fin will suffice. I lined the mold in plastic wrap to act as mold release.
Step 3: Spray
This part is pretty simple. All you need to do is fill the mold with expanding spray foam. Remember, the expanding foam expands, so you won't need quite as much as you might think.
Note: I tried to use styrofoam the first version of this boat, but the epoxy I used for the fiberglassing melted the whole thing. Remember, to test your material combinations before going forward with a build.
Step 4: Carve
The shark fin will probably look more like a giant shoe than anything remotely resembling a marine animal, so there's a significant amount of shaping to be done. Start with a hand saw and carve the hulking mass of foam into a rough shark fin shape. Next, use a rasp and sand paper to refine the shape to something you are satisfied with.
Step 5: Fiberglass
Fiberglass is great. It is a great way to put a hard shell foam models. If the object you are fiberglassing is really important I suggest using marine epoxy and marine grade fiberglass. If it's just a shark fin prank you are working on, the inexpensive stuff you can get at Home Depot or Lowe's will do just fine.
Before you begin, remove the boat's lid (with the shark fin attached) from the rest of the boat.
Start by cutting the fiberglass so that it drapes reasonably well over the shark fin. Next, mix up your epoxy and drizzle it over the entire shark fin, and smooth it in over the whole fin.
Step 6: Sand
Fiberglassing results in a less than perfect surface finish, so significant sanding is usually necessary. An orbital sander with two or three progressive grits will be sufficient to do all of the sanding.
Step 7: Paint
At last it is spray paint time. It turns out Montana makes a paint color called 'Shark', so I can't help but recommend that particular color. I'm not sure how accurate the hue actually is, but it must be close enough. I suppose any shade of grey will probably do just fine though (actual shark color may vary).
Step 8: Scare
Now it's time to scare your friends in the water. The boat probably won't move as quickly or steer as well as it did before the fin addition, but if your experience is anything like mine, it should work pretty well.
I recommend being careful about your location of choice. Creating a large amount of panic is probably not a good idea.