HYDROFOIL and theThe DEVIL !!! a Ray Vellinga video

[kwokwing]

I suggest that the air propeller has to be tilted a few degrees upward.

[AaronWalkhouse]

Oh, and don't tune up the controls under tow.

The thrust line is totally different and you would end up with a boat that tows well but flounders or stumbles under it's own power.

Once you hit about 40 knots don't try to add more power for more speed. You'd need a bigger boat and costs go up quickly from there.

[AaronWalkhouse]

With the above tweaks your speed may be higher, possibly near the usual 40 knots for that size of boat. Test under tow before using the prop to push her as you may need to beef up a foil. It's safer to find this out under tow because towing stabilizes you and you don't have a prop hitting water near your assets.

A stumble under tow is less likely to hurt the boats if you use a breakaway on the tow line and have alert hands on line releases at each end. Water will bend steel if you let it.

[AaronWalkhouse]

A rudder behind the prop can be confusing as it changes effect on turns once you are up. It puts roll against yaw instead of with it so don't use it if you don't have 3-axis controls.

If you use a joystick or aircraft style yoke then the air rudder is one of your ailerons. Control the water rudder with pedals as usual.

Full three axis control makes sense in a hydrofoil. Familiar flight controls give you stronger control and the ability to instinctively recover from stumbles and unexpected.

[AaronWalkhouse]

Once you are up, thrusting more levelly will help raise the stern but the best angle will still be at least -15° until you are at speed. Directing the propwash up and away from the stern will be more comfortable for riders and bystanders too.

If it's low and close astern you should cage it for safety so try adding elevators behind it, like a plane, instead of tilting it. If they don't cross the hub. propwash won't be noisy. Try a pair at the top and bottom or a single large one high or low.

[AaronWalkhouse]

Moving the prop to the stern will maximize performance. More length from the bow and a shorter mast both reduce leverage. Angling thrust down will eliminate the remainder.

Aiming the thrust at the foil will give it power to lift the bow without much downforce, now very low due to angle of thrust and nil due to leverage. (Do the trig) Less lift v. downforce at the foil reduces drag too.

Result: you leap out of the water at a low speed and can accelerate right away.

[AaronWalkhouse]

The mast is too weak but you surely know that by now. Making it heavier is not the answer but a foot shorter with 2 guy wires from the upper gearbox to either side of the deck will do.  A heavier one would carry more vibration to the hull anyway.

It is also much too long and the high centre of thrust is forcing the bow down too forcefully for your bow foil to overcome the downforce. Angling the prop upwards until you are underway will help.

[AaronWalkhouse]

Match the prop to the motor. Make it much smaller and lighter. Look at props on ultralights for examples.

Higher RPMs will solve your vibration problem.

You don't need a wide speed range so don't worry about performance at speed yet. Pitch it to pull hard on the bench and you'll get enough thrust to get started. Fine adjustments can come later.