My Skimmer.

One of the two plans.

features the plans of a small air boat, or skimmer.

Following the instructions given, it will be constructed out of balsa wood. The club was hoping that a number of them would be built by members as a relatively easy project.

When I became the commodore of the club, I wanted to renew interest in the idea.

I decided to promote a styrene foam version instead. This would be much easier, cheaper and quicker to build and I had already used a hot wire to make model aeroplane wings and fuselages.

Various hot wires.

For this I use a 5amp, current limited battery charger and a length of wire. Because the power supply is current limited, it can be connected across any length of suitable wire. I normally use a length of a welding wire. For special shaped cutters I use a stiffer heater element wire. The flexible wire is looped around a suitable ‘handle’ at each end and I use alligator clips to attach the power source.

The main criteria when cutting the styrene are to maintain a good tension on the wire, keep the wire hard against the former you are cutting around and square to it as well.

The latter point is particularly important if you are cutting around a curved shape.

Now back to the skimmer model. First cut and shape two side profiles for the hull, as per the drawing. Then mount these, the width of the hull (165mm) apart, on a base board. Prepare a piece of styrene the required size using a hot wire. See the photo of my jig for doing this. Insert it between the profiles and place a heavy weight on top to hold it down and in position. Then proceed to cut out the styrene hull. It may need some sanding, particularly around the curved bow shape.

I use a hot wire to cut out the equipment recess. Make this from stiff wire the appropriate depth for the hull.

Choose water based, coloured paint, enamel will dissolve the styrene. The paint applies easily. Use a clear packing tape to cover the hull. I have tried a water proof version, however it was thicker and not so clear. Because the skimmer is only in the water for a short time, ordinary tape seems to cope. You may get some condensation under the tape.

Because of the limitations of using rudders to direct the airflow from the propeller and therefore steer the craft, I chose a different approach. The whole motor mounting pylon turns on my model, making it very manoeuvrable. It is well worth the extra effort to achieve this, and my method of doing so is shown in the photos.

Under the hatch cover.

The top pivot is a bolt with two nuts on it. Version I, the red hull, had the steering servo mounted in a hole cut out of the styrene directly under the axis of rotation of the pylon. It formed the bottom support for it. Operationally this was great and easier than organising a linkage from the steering servo. Unfortunately within a short time, the servo suffered water damage. (I probably could have done more to protect it) Version II, the green hull detailed here is more conventional. A short rod sticking out of the hull is the bottom support.

For the motive power, I used the motor/ESC/batteries from a Cessna model. This has now been retrofitted with a brushless motor. (Actually identical to that in my jet boat)

Overall weight is a consideration when choosing a motor and batteries, the lighter the better. My model weighs 450gms (1 lb.)

The propeller guard ring is vacuum formed from 1mm styrene sheet, the plug being shaped on my lathe from MDF board.

The driver will get a tired arm.

The hatch cover and spray shield are from 0.5mm styrene sheet. The driver is cut from scrap styrene with a hot wire. He is sitting on a cardboard seat.

It is very necessary to fit a trim tab to the transom of the hull to correct for engine torque. I used a small piece of brass shim inserted into a cut in the styrene and bent downwards. Without this, at full speed, it needed almost hard right rudder to keep a straight path.

Hoping to get better performance, I have now changed to a brush-less motor.

The following describes how I did it.

Skimmer II

I have found this model fun to sail and it usually attracts attention.

So give it a go too.

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