Electric Foiler(or foil assist)

Delftship has an export function for Michlet. I use this method.

I have done various manipulation of the Michlet hull table for various reasons but it takes me a bit of time to work it out.

My usual process is to start with Godzilla to optimise the hull for the conditions. I import the offsets into Delftship and clean up the hull to suit how I will build it. Then I export the hull to Michlet to check that my fiddling has not altered performance much.

The attached is a Michlet input file for the V11J hull. The photo shows the boat. It will give you some idea of the translation required. There are explanations around.

If you delete the existing in.mlt file in the folder where you have the michlet exe file and replace it with the attached file renamed to in.mlt it will give you the outline when you run Michlet and you can get the drag data for this hull.

I find the Godzilla element of Michlet to be very powerful and always start with this for a new hull. You only need 4 numbers to specify a hull to start with.

Rick W

 

Terry
You have it partially solved. You only need the other bits of the jigsaw to give it a real chance. The attached might give you a clue to what I am thinking. This blade always trails horizontally with little drag unless it is being swept vertically. (Based on the front mount being vertical of course)

The other thing I learnt with this was its ability to balance through symmetry alone. Out of the water it flopped sideways but once in operation it was very stable laterally with no tendency to twist.

I think you could make a foil from very strong material that is very light (probably CF) and it has a completely compliant mount that releases if the force just exceeds the design load. The foil itself will have very little inertial energy. Maybe even some strategically placed compliant bump strips to give momentary energy absorption. Could be hydrodynamically useful polyurethane winglets for example.

Rick W

 

20kts is a leisurely pace even by comparison with 60mph.

The point I am making is that the specification requires it to take a decent bump. It will not be falling off 20ft waves onto containers at 20kts. However it will be beached at maybe 10kts as it will have a great tendency to glide and unless the controller has an effective reverse it will just glide into the shore. Very easy to do until some experience is gained with its operation.

In fact maybe we need to specify it to have a reverse mode.

Rick W

 

If you spring-loaded the strut on a "T" foil, mounted to the midline of your hull, then upon impact it would get pushed back & up to the hull. Once against the hull, the lifting foil would roughly equate to a vertical plate being dragged through the water/mud/sand & make a fairly effective brake. This idea MIGHT enable the foil to survive log impacts, but it WOULD enable it to survive most groundings & simple stop the boat. In the case of a log (assuming it doesn't break the lifting foil), sand bar, reef, or cabbage-head; the foil would flip up some, clear the obstacle, then (depending on craft speed) either get held up against the hull until the craft slowed sufficiently, or flip back down into a normal operating position. Either way, it would have slowed the craft down enough that you're going to have to build some speed back up before you're likely going to be "flying" again.

 

That is why I preferred the idea of three foils with two main ones either side of the hull. they do not get jammed against the hull.

Also why does the foil have to be rigidly mounted to the strut. It could be a ball joint on the bottom of the strut so it can move freely in most directions. It only needs to produce a vertical force.

Rick W

 

1. If the foil is on a ball joint @ the bottom of the strut it can't give you any righting moment.

2. In your 3-foil setup, you would still have the rear foil.strut swing up into the hull, and the front foils (though not the struts) would still strike the bottom of the hull, unless you mounted them extremely far apart. Also, if the front foils came completely out of the water, they'd have a VERY hard time pushing back down through the surface of the water to return to their operating position, unless you slowed the boat down very considerably (and they'd still act as drag-brakes the whole time they were trying).
I guess that idea would work if you went with 4 foils, spaced widely out to the sides, and made them spring-up, completely clear of the water, once they reached a certain point.

 

Rob
You are not trying very hard.

The front foils have a back stop that prevents rotation as they lock into position. Does not take a lot of thought to work this out. An alternative could be a back plane to provide the necessary moment but this would produce a large counter moment when trying to roll the foils down at speed.

The 'T" foils will only be around 800mm wide. That is 400mm either side of the supporting strut. So at 2m centres that gives 1.2m between tips. The hull is only 500mm wide. So at least 300mm from tip to hull.

Being on a ball joint the foils just trail once unlocked.

The stern "T" foil/combined rudder and drive simply swings up like an outboard. It thrusts against a stop. Swing up provides both foil and and prop protection. Angle could be used for flight trimming if necessary. Same ball joint arrangement of the foil allows it to trail once the rudder strut trails.

You are not showing much imagination.

Would be quite easy to get to speed with both bow foils rolled back and just fold down and lock in to get lift. Could easily be done on the fly.

Remember this boat has a total mass of 200kg loaded. The front foils carry 80kg each. The lift to drag is 30. The drag is less than 30N. That is not much force. Until the foil starts to provide lift (the last couple of degrees of engagement) the drag is considerably lower than 30N.

The foil support system does not even need a dedent or spring. It can be self locking with over-centre action. Might have some sort of bungee just to give a little extra restraint when jiggling around.

Surely you do not expect me to do the whole design!!

Rick W

 

OK Rick,

Most of that sounds fairly plausible except: How are you going to design a foil with L-D of 30:1 with a submerged ball joint, U-joint, or anything similar?
Every time I try to imagine something like that, especially if it's supposed to have 90* forward rotation, I end up seeing MUCH lower L-D ratios...ball joints just aren't THAT graceful underwater, they fairly unavoidably add some drag.

Also, I had overestimated the width of the front foils from your earlier post. You had said 1m foils on struts 2m apart, and I was picturing 1.75m foils in my head...don't ask, it was 3AM here....

 

Maybe the spring-loaded strut in post #32 has a flaw. I assumed it retains lift as it swings back by virtue of the parallelogram linkage, so I don’t see it as a brake the way Rob does. It also eliminates the need for the other foil(s) to cancel lift simultaneously, and maintains speed. However, as Rob pointed out, when it swings back the lift vector applies more torque to the spring-loaded pivot and it may not spring forward again at speed.

However, if the strut is swept back it will tend to glide over obstacles the way a fixed keel does, and if continues down past the foil it should lift the boat over the obstacle allowing a fixed foil to be used. A small winglet(?) partway down the strut will prevent ventilation. It should handle horizontal solid obstacles, but the foil may need a vertical axis hinge to dodge tree stumps which I have added.

I imagine reverse would use displacement mode; slower, like an auto, but perhaps the foils could be sprung loaded in the reverse direction at the hull attachment.

 

AK,

I hadn't thought about parallelogram linkage, but that could be a useful way to reduce the braking that the foil would cause upon swinging up. Then, if it didn't return to its original position, it would still be providing SOME lift, and it would be able to swing back down at a much higher boat speed than the fixed foil on a spring-loaded strut.
Either way, I like your vertical-hinged, swept-back foil design for avoiding stumps. The swept-back foil should be able to self-track very well in all modes except for reverse without the need for a spring that could get fouled or weakened over time. Would you lock the foil in place for reverse mode, or remove/raise it some way? I think it's a good idea, but reverse-mode will give you some hassle. My best spur-of-the-moment idea there would be to have a vertical hole through the front center of the foil, and have a locking-bar that can slide into the hole while the foil is centered to hold it in place for reversing.

Would there be any way to retract your design vertically up near the bottom of the hull for beaching/reversing?

 

The foils did shrink a little when I looked at what was required. My first guess is that one cannot make a foil much smaller than 60mm chord that will carry the load with some margin. So I set this as a limit. With this limit the lowest L/D foil is around the 800mm mark across. My initial guess was 1m. The 60 by 800 can achieve the L/D of 30.

My vertical strut is 10mm wide so I have to devise a compliant connection that can take a vertical force of 800N and horizontal force of 30N when in the locked position. Forces are quite steady so low fatigue cycling. Should not be a huge ask. The joint could be a little thicker without noticeable increase in drag.

Refining the design with proper stress analysis might reduce the chord. At this stage I am still wondering if the 3 tees offer the best solution.

Rick W

 

...OK, while you do your stress analysis and get your chord perfect on the 3-strut setup, I think I'll toy around with my very NON-definite balancing foil idea & see if I can make anything (cheap) that will prove my idea to be a feasible way to balance the thing on only 2...so fewer struts, and (hopefully) less surface drag.
I'll leave the analysis to those of you with more training/equipment than myself...as long as it's only my own life at stake, "trial-and-error" will work for me for now.
I'll let you guys know if I find anything useful in my bathtub tests.

 

Yes, simple is sometimes best. It should be should retract for reverse, I don’t like the idea of foiling backwards! I think for reversing it could just pull up and forward along its own LE until the foil snugs up under the hull although I would prefer some way of getting it completely out of the way for beaching.

 

My idea of a two seater electric foiler. Design weight is 200kg. Total boat weight is 50kg including battery.

Would foil from 14kts. Design speed is 20kts.

Requires 950W motor output at design speed.

Features overcentre locking of front foil beam and tilting stern "T" foil to provide foil impact protection.

Rick W

 

Very interesting ,Rick. Would you use wands for altitude control?