Electronic Foil Control Systems.


New member
It's not a matter of computing power, much more a matter of a suitable sensor and power for whatever control is used to adjust the height. I can't tell you how many times I've run aground in a Ross 780 (draws 1.8m) and the depth sounder alarm (set at 3.5m) has gone off a few seconds later. We actually run aground less often when sailing with it turned off.

I expect it's a similar problem for any sensor looking for a boundary layer between media. At a speed differential of say 20kn between Moth and wave, the time to respond is extremely short. The bow to foil distance is perhaps 1.2m which will be covered in about 0.1 seconds.

An additional issue is the momentum of the boat—even if you can make instantaneous adjustments (which a mechanical wand does reasonably well), the boat takes time to respond. So the sensor has to be able to look forward and make adjustments in anticipation of surface level changes—sensing at the strut is too late unless fast, large adjustments can be made to (over) compensate for momentum.

And then there's the power to activate whatever control is used (main foil flap, centreboard AoA, pitch, whatever). The forces involved can be quite high, I hate to guess but likely 3 to 5 kg of compression/tension until some physical limit is reached, which might be some device (say a tether or wingbar) or whatever breaks first (probablly a pushrod or fitting but maybe the wand or flap hinge). So the servo providing the movement probaby needs to be able generate the equivalent of 10kg of force more or less instantaneously over perhaps 20 to 30mm (theres' some units here I'm missing, probably Newton metres).

Note that current mechanical devices work just fine in most conditions, it's only when the breeze gets toward 20kn and whips up 1m chop or more that they start to have problems. Even the best height control in the world isn't going to overcome low sailing ability in those conditions.

Very good point!

I agree the main problem is on mechanical side not computing power. How to make servo/actuator powerful and sensitive enough is the key.

Comparing to flight control, just like what you pointed out foiling is much complicated due to boundary of 2 phase media (water and air). So it almost impossible to completely control a foiling dinghy. For a big boat or ship you can almost negate the local wave motion condition due to the ratio of ship's dimension vs wave length. So for dinghy, such as moth, electronic control will be only suppliment to the man-control. It might assist during the take-off phase, or maintain in air for relative calm see condition.

By the way, anyone know of Iphone App could be used for this type of purpose?

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Super Anarchist
despite there being an app for everything, this particular application might be a long shot...unless you program it yourself.


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