This instructable will explain how to create a device to attach a small outboard motor to a Hobie 16 and turn it into a very fun cheap cruising boat...
Step 1: Philosophy
Sailing is a great art. Many people see no other way to enjoy the water. The Hobie cat 16 catamaran is a great intermediate sailboat that can be a blast. I have sailed my Hobie several times and I just wasn't having too much fun; I knew what the problem was: it just wouldn't go any old direction you point it. I knew I had to do something, so I set out to convert it to a motor vessel.
Step 2: Get Started
Obviously you will need a hobie cat for this project, craigslist is a great place to find cheap ones, try to find one that is missing sailing implements but has solid hulls (brings down cost) You should spend under $500 with trailer
The first thing I did was think, how would I get a "transom" on a catamaran, the rear crossmember of the cat looks like a good place to start. Basically what the motor mount is is six pieces of steel shaped like the number 4. The mount is bolted through the rear crossmember and the motor clamps onto the rear side of it.
After you have decided what motor you're going to use (I highly recommend the honda 2.3hp outboard, very reliable) It's time to make the mount.
The mount is mainly made of 12 guage 1 3/4"x1 3/4" square mild steel tubing and the end plates that the bolts go through are 1/4" steel plate ("borrowed" from a mower deck). The transom is 3/16" steel plate.
Other ingredients include
2x 1/2"x6" zinc plated bolts
2x 1/2" lock nuts
2x 1/2" wood screws
some scrap wood
2x 175lbs carebiners and some paracord (safety chain)
Once you have collected these materials, you are ready to make the mount
Step 3: Put Things Together
1. Remove the current steering stuff from the hobie cat along with any other sailing implements. (save these in case you want to sail it again someday as this process is easily reversible by removing the mount)
2. Cut your steel to the measurements in the plans, be sure the transom plate that you cut out is plenty wide for your outboard's clamp width. I cut my tubing with an abrasive chopsaw and my plate with a grinder with cutting disc. You may need to lengthen the bottom tube if your motor controls are longer. Be sure to angle the back edge of the bottom tube so the transom plate sits at an angle like in the pictures. IT IS ESPECIALLY IMPORTANT THAT THE DISTANCE BETWEEN THE TWO PLATES IS 2 7/8" otherwise it will be difficult to attach the mount
3. Drill two 1/2" holes in each plate on the hobie side of the mount. (I recommend using bits that aren't gold in color, the gold ones dull quickly.)
4. Drill two small holes in the transom plate for the screws to go through, does not matter where on the plate
5. Cut a piece of your scrap wood (not thicker than 1") the exact shape of the transom plate, except that is must have a channel cut in it to fit around the bottom tube
6. Weld the steel pieces together in the shape in the pictures (If you do not want to or can't weld, you will need to take yours parts to a weld shop to put it together for you.) Understand that this is not a good project to learn how to weld because it could cost you your outboard.
6 1/2. Test your mount by clamping it to a strong table and pushing hard on the transom plate (I sat on mine, don't recommend it), if it holds, you're in good shape
7. Take about two feet of the paracord and tie each end to a carebiner.
8. I highly recommend painting your mount to rust-proof it, 3 or 4 coats of any rustoleum will work fine. I did a metallic blue that I had lying around, but I think the color went well with the blue trampoline of the catamaran
Step 4: Attach Motor and Mount to Hobie Cat
After the paint is very dry, we are just about ready to get cruising. Screw the scrap wood onto the transom plate with the short screws, this wood's function is to facilitate better clamping pressure so the motor clamps do not loosen; it also protects the transom plate. Take your mount and put in over the rear crossmember and mark two holes through the ones already drilled through the plate, then drill these holes through the crossmember and repeat for the underside. Then place the two bolts through the holes (should be a total of four holes for each bolt to go through. You'll probably have to hammer them through because its difficult to line up the holes perfectly.
Once the mount is on and the nuts are tightened, connect one carebiner from the safety harness to shackle on the outboard and the other end to main sheet block eyelet on the catamaran.
Since I used a honda 2.3hp outboard, the fuel tank is inside the motor cowling, if your outboard needs an external fuel tank, I would recommend strapping it to the trampoline of the catamaran.