Which one is more hydro dynamically efficient at moderate speeds up to 20-30 knots for moderate light vessel?

Planing or Hydrofoil ?

I am considering to upgrade my power catamaran with hydrofoils similar to moth foils.

It will be very interesting to find out what is minimal HP required to lift such boat

almost 5 meters long 110 kg boat + 150 kg crew + 30 kg motor = 290 kg

Above the water on hydrofoils or get planing (on specifically designed planing surface)

I have 3 motors available for tests:
- 6 HP Suzuki
-Tohatsu 18 HP
- Electric 2 x 1.1 KW 24 V

Apparently for windsurfing at moderate speed there is no obvious advantage to have hydrofoils.

Here is some test done by amateur Frenchman some times ago:

gerard.delerm.free.fr/clair/b_page2a.htm

Hydrofoiling is based on area and speed so you don't need big speed to get airborne, when you double the speed, the lift quadruples so a small increase in area and speed can make all the difference.
Hydrofoils are smoother, quieter and just way cool to ride.
High aspect foils like on the Moths are highly efficient but lower aspect foils give a more stable ride.

landyacht said...
what is the water like where you will take the boat?
logs?weed?sandbars?

Broadwater in Gold Cost is mostly free of floating rubbish but shallow and sandbars could be tricky to find.
My concept is to have hydrofoils lifted for launching, but design in general should protect crew in the case of foils catching something in the water.

For that same reason I would prefer rather to use hydrofoil to sail economically with smaller motor at relatively low speed - up to 30 km/h ,
not to push the speed with bigger motor well above.
At this moment the speed is 20 km/h with 6 HP and 31 km/h with 18 HP.
I wonder if 6 HP will be enough to rise the boat on foils ?

mate you seem to be keen to reinvent the wheel at every turn.
Hydrofoils so not practical on so many levels not the least of which will be transport and draught of boat.
Add countless manhours of tuning and reinventing wheel and you will still be behind.

How many hydrofil passenger ferries do you see around anymore ? none. thats because of real practical reasons. they were everywhere in the 60's. Now they are all cats. .

it's actually very hard to beat a displacement cat (what you have) for efficiency. Modern designers like shionning, crowther etc make fast displacement powered catamarans that are very easily driven. there are even some solar electric ones, but they are of course, pox....

FormulaNova said...

myusernam said...
How many hydrofil passenger ferries do you see around anymore ? none. thats because of real practical reasons. they were everywhere in the 60's. Now they are all cats. .

I've wondered about that. When they retired the last Sydney hydrofoil I wondered why, in that it seemed so much faster.

Are they difficult to keep running or something else?

The old hydrofoil ferries were a blast but extremely inefficient. Can only guess at the fuel they chugged thru. We used to LOVE that wake when windsurfing. Also reminds me of how when we were kids we would jump into the prop wash of the ferries when they were leaving the wharf at Manly in summer. Try that these days! i Gen


The OP asks about hydro dynamics and wants to know if his displacement displacement hulls will plane, um NO.

I think at this stage the real question is why does the OP want to foil; fun, ride, efficiency or just the sheer hell of it. Kind of like those suspension cars but on water. YAY I'M UP YAY I'M DOWN YAY I'M UP YAY.......!!! Once you figure that out the water is less muddied.

Beaglebuddy said...
All I know is this guy has a hydrofoil working at 8 knots on a 5.3

That looks like a genuine 8 knots too. That's pretty damn impressive.