Foiler Design

First a statement - I know absolutely nothing about foiling or foilers so expect some stupid statements. However, I may be representative of many sailors who love the idea of foiling if it were simple enough.

So here is my tuppence worth...

If I were to sail a foiler, and sell a foiler, I would want it to be as easy to rig and launch and maintain as any other dinghy.

Also, when sailing, I would be looking for speed - but a low take-off speed at the sacrifice of top end speed would certainly be an advantage.

From my standpoint, and what I understand from the discussions so far, the neatest solution does appear to be the canard mono-foiler.

Having said that, I will now attempt to explain my understanding of the concept so that some one can tell me if I have understood it correctly.

1) There is a fixed foil on the centreboard, with a positive angle of attack.

2) There is a small foil at the bow (canard foil). This could be fixed, but much shallower than the main foil.

3) As the boat accelerates, more lift comes from the foils (front and rear).

4) Eventually, the boat is going fast enough to lift onto the foils completely, and will rise until the front foil breaks the surface and planes.

5) From this point, as the boat continues to go faster, more lift is generated from the main foil on the centreboard. This causes the boat to rise.

6) Since the front foil is planing, the boat actually pivots about the front foil, causing the angle of attack of the main foil to decrease.

7) The reduction in angle of attack will reduce the lift giving a self-trimming craft.

Have I got the theory correct?

If so, it sounds much better to me than sensor cables and wands and moving parts. Also, since the sail is trying to push the bows down, and you can balance this by moving behind the main lifting foil, it would seem to give greater ultimate pitching stability.

It would also be a great help if some one could explain in simple terms the reasons why an inverted Y foil would help.

CHeers,

mad

 

Good summary

G'day mad engineer,
You have summarised the "canard monofoiler" very well and even appreciated som of the benefits of its simplicity!

When in displacement mode, the idea is to have no angle of attack on the main lifting foil so there is minimal drag. In fact it should act just as a centreboard.

The canard is given an angle of attack, which can be fixed as in the case of the Miller sailboard, or adjustable in the case of my Moth dinghy foiler.

As the canard lifts, it in turn gives an angle of attack to the main foil, which then lifts until it reaches a height set by the length of the canard strut. The whole unit then flys in a stable manner as you describe.

The reason for the inverted Y foil is given in detail by Rich Miller in his excellent article at www.Foils.org

Basically, a deep Tee foil centreboard will work quite OK as this is what I have used to date....but it is not the most efficient arrangement and can also give some problems. The inverted Y can solve these problems for the reasons

1) Side force can cause ventilation down the vertical leg of the Tee and a crash.
2) As the Tee gets closer to the surface it can kick out sideways in gusts and if heeled, the tip can clear the surface and ventilate resulting in a spill.
3) The Tee is on the centreline and limits stability somewhat.

The idea of an inverted Y foil is to tilt it to leeward so that one fin is horizontal and the other vertical. This results in:
a) The vertical leg from the hull takes no side load at the surface and hence solves the ventilation problem.
b) The arm of the Y running horizontal gives efficient lift and does not broach the surface, so no spills.
c) The leg of the Y which is nearly vertical runs deep and provides efficient resistance to leeway.
d) The centre of lift is well to leeward and provides a big increase in stability.

The only downside is the need to tack the foil 30 degrees to leeward. While easy to do, it would be nice for this to happen automatically. This is the bit I am working on right now.

In the end a deep running simple Tee may still be the best compromise for simplicity as it can be applied to any existing craft with a standard centreboard case. The only real addition then is the canard, which is a very simple affair, cheap and easy to make and attach to the boat. Ideal for skiff dinghies.

Ian Ward

 

ian ive worked out a way around the need to unroll the foil or the canard.
if you build the canard with generous dihedral it has the same effect as rolling the board to windward (as miller does) with out the need to have the main foils tacking. sure you have to sailed heeled to windward but we do that anyway
the only negative is that it may have a tendency to pivot upward when the canard is disengaged, you can get round this by building the hinge of the canard above the absolute bottom of the canard surface, also by having the pivot point along way forward(20%) rather than the 25 or 30% you might otherwise have. I've got most of it worked out and building starts next week.
andrew

 

Now we are getting some positive ideas and action! Thanks for the input Astevo!

I think it will be good to test this out. The reason it is not used by Miller, is that he needs to have minimal lateral resistance in the canard, so he can steer in a conventional way on a sailboard.

In a dinghy we have the luxury of a rudder, which I have found works really well and will enable you to get away with a dihedral V or curved "banana" canard.

Miller heels his board 30 degrees to windward and I think you will only get 10-15 degrees on the Moth going upwind, but it will still be beneficial.

One way to overcome the problem with the pivot point for the canard is to pivot it from below, such as for a kite.

Perhaps if you get the angles right, you can have a fixed canard...move forward in light weather and aft whenever you want to foil. This way there are no moving parts at all and it makes the transition to foiling automatic and smooth.

 

:idea: One more comment:

An interesting observation is that the once the main foil lifts the boat, you are already at the stern!. Just moving your weight aft a little balances the forward thrust of the rig, preventing nosediving and unloads the canard.

Interestingly the fastest types of boats such as skiffs and sailboards all have this same arrangement when planing fast, ie: the crew moves aft until they are at the stern of the boat, so that they can balance the loads and prevent nosediving. In these craft, it is necessary to move a long way aft, because initially moving your weight also moves the centre of bouyancy aft, so you then need to progressively move even further aft to keep the boat in balance. ie: the centre of bouyancy chases you aft, reducing the effect you are trying to achieve. Finally when the stern is reached, the centre of bouyancy can no longer move further aft and it is then possible to easily balance the hull.

It is fascinating that a single main foil allows this condition to be achieved without moving from your normal hiking position at all. This is why Tee foils on rudders are a bad thing. It is also one reason why this is a better arrangement than a bifoiler with centreboard and rudder foils, which has similar limitations to normal boats. It would be very nice if it were possible to achieve this same effect on planing hulls.

Ian Ward

 

simplicity ?

I just wanted to stand up for the T foiler with regard to simplicity compared to the Y foiler so far.
The Y foiler or canard foiler has three appendages of which two (possibly one) are adjustable being the canard and the main Y foil which is cranked to leeward on every change of tack.
The T foiler has two apendages and a number of moving parts which so far have been very relaible. The sensor mechanisms are fully automatic so the sailor just sails the boat like any boat. The sensor wand and cable remain on the boats from week to week as there is no need to remove them.

I also had a thought for the canard foiler to have a crucifix style T foil so as there would be some vertical component below the horizontal foil. This would solve the leeway slip when you get too high. The foil could also rake forward to prevent air flow down the foil.

 

i get the feeling we are actually going somwhere with this now,

i think the canard system is the most simple whilst sailing along as it requires no input from the skipper in terms of pitch control. also i like the fact that the entire canard can be disengaged for light air and the main foil has zero angle of attack when the hull is in the water. extra bonus is ive sourced everything i need and its cost me $15 with all the stuff found in the shed including an old whale tail rudder.

how much difference in height are you using between the two foils? im thinking that the main foil should be neutral at about 150mm underwater. im not sure if the foil is going to ventilate like crazy if it gets too close to the surface.

 

The T foiler has no input from the skipper for pitch at all, the rudder flap is only occasionally tuned as you would other systems. The main foil flap can also be disconected from the cable whilst sailing to reduce drag.
In short the Tee foiler is more complex, but it is that detail that makes it easy to sail.

 

Re: Fly!

When I was in college, I worked on the design of a flying hydrofoil dinghy using actively controlled fully submerged foils. The sensor problem is not that difficult - take a look at the ultrasound sensors that were originally developed for the Polaroid self-focusing cameras. It's also not a slam-dunk decision as to whether to measure the height of the hull above the water, or to look up at the water surface and see how deep the foils are. And today the computational part of an active control system is not a problem, either - you could do it with a PDA.

The bigger problem is how to actuate the system and how to power the actuators. Electromechanical actuators are heavy and the batteries to power them would be even heavier. The beauty of mechanical feedback as used by Sam Bradields' wand, Hook's planing floats, and Greg Ketterman's similar rotating amas is that the power for the actuators comes from the same hydrodynamic forces that are acting on the height sensors.

I think it should be raced against non-foiling boats. This will encourage the development of an all-round design. Racing on a provisional basis, with the results from the foilers being either handicapped or not counted for the most important awards, would be OK. Provisional racing has been used in various classes to allow the class to experiment and generate a consensus as to whether the class wanted to go that way.

The Rave has gone the mass-market one-design route and I think one reason it hasn't become more popular is because it's a bit of a dog when it's not foiling, compared to existing beachcats. The Trifoiler is an example of a production-engineered version of a one-off speed machine. Besides being expensive, it also suffers from poor performance when not foiling, and it takes a fair wind to get it to foil. Each of these have advanced foiler development but don't really fit with how most people really use their boats.

It's just a reality of physics that a slender displacement hull has the best performance in the wind range that many if not most people experience. If we always raced in the trade winds, foilers would be more viable. But that's not the case.

If a foiler is to be truly successful, the foils have to offer benefits when not flying. Along with considering how to fly the boat, we also have to look at what compromises are made now in hull design to handle a wind speed range and what performance gains there might be by optimizing the hull for the light wind range. Minimizing the wetted area of a dinghy that would otherwise have a planing hull shape is one example.

 

John,
I do not see this as a competition between different foil systems, simply a forum for open discussion on ideas and developments.

Speaking as the first person to have built and sailed a bifoiler dinghy using Tee foils, I know the problems you have overcome and I have to congratulate you on your excellent effort in getting it to work reliably in a wide range of conditions. I also think it is excellent that others can now buy a set of foils and go sailing with minimal effort.

The mono or unifoiler design is being developed to overcome some of the limitations I discovered with the bifoil arrangement.
The intention is not to discredit or downgrade the bifoiler, simply to explore going one step further in the development.

As Astevo indicates, to experiment with a unifoiler is simpler and cheaper.

While I am currently trialling the inverted Y foil canted to leeward, there are reasons for this which I have explained, and it is on an old wingless scow, not a skiff Moth, so I need the extra leverage.

You are correct that a fixed Tee centreboard may be more than adequate for the purpose and far simpler to build and operate.

You are also correct that I have 3 foils, but one is a simple conventional rudder, so the only complexity is the canard,which can be a fixed foil also. Even making it adjustable is very cheap and simple. I intend to place some photos on the moth website.

Another future possibility is to turn the canard into a dual purpose foil and make it a rudder, steering from the front and remove the aft rudder. Back then to two foils.

Ian Ward

 

Tom,
I agree entirely with your comments about Rave and Trifoiler. I sailed a Trifoiler, which first got me going on foil development with its excellent performance in a breeze, but in the light, they are a real dog. This is what prompted me to place foilson Moths because it is obvious that a small, lightweight craft with good light air performance is an ideal platform for foils.

We can definitely do better in the light winds. Although it will be hard to improve much on the current skiff Moth which has minimal surface area. Perhaps a little more stability for ease of handling.

On the height sensing, I am sure that a very simple mechanical system will win out every time, but it is always interesting to see what can be done with electronics.

Ian Ward

 

Ian, as an open forum on design the information spoken should at least be correct so as not to create a web of misinformation. I just needed to correct others misunderstandings when comparing the pros and cons of these designs.

 

As I understand the current Moth rules, any foils that pierce the water have to do so within the static waterline beam, and you can't change foils during a regatta.

But is there any reason foils cannot be retracted out of the water if they stay with the boat? This would make a big difference as to the size and type of foils to consider.

 

Tom,
There is a lot of discussion right now within the Moth class about the rules relating to foils, which is probably best done within the Moth website. www.moth.asn.au

There is no current restriction in the Moth class rules on foils, their size, location or deployment. Currently some sailors are removing their lifting foils in light weather in order to reduce drag and win regattas.

This appears unfair to the sailors of conventional boats, who are prevented by the rules from switching hulls during the series to suit the conditions. It is therefore being proposed that whatever foil are used, they should be used in all conditions.

I happen to agree with this concept, as I think it will ultimately lead to the development of a better all round solution.

In the meantime, foils are allowed, with the exception that Trifoilers are considered to constitute multihulls, and hence wing mounted foils are not allowed. I think, this is fair too and this has resulted in the development of the bifoiler.

While the moth class has yet to debate and decide what they want from a a foiler, I think the end result should be something simple, practical, cheap, easy to rig & launch, (not a contraption) gives a smooth transition from displacement to planing, gives good performance across the entire wind range with foil deployed, be stable, easy to handle.
It should also not detract from the tactical nature of competitive sailing (ie: not just a high speed drag race to each corner of the course) and should require a good level of skill and judgement to sail well.

I know this is a long list and seemingly difficult to achieve, but I think we are steadily getting there. Any ideas on how best to achieve this, would be most appreciated.

 

Flying Now

In my humble opinion I think the system that is closest to being able to be "presented" to the world is a mainfoil with wand altitude control that would retract in lite air and a rudder T-foil.
I absolutely believe that Ians work is promising but the fact is the twin foil boat has had a lot more time and has proven to be reliable and relatively simple to sail. Again, I think if a hull was designed that allowed for the main foil to retract flush with the bottom using a daggerboard WITHIN the main foil vertical strut for light air lateral resistance with a hull only slightly wider than present the nail would be hit on the head.