Foiler Design

[mad engineer]

Doug,

As a concept it sounds good, but it raises afew questions in my mind:

With the present moths, what is the span of the main lifting foil?

If the foil were to be retactable, how wide would the hull have to be?

Would the loss in performance due to the increased width of the hull be less than that by having the foil always extended?

CHeers,

Mad

 

[Doug Lord]

Moth foil span ect.

I just looked up the data I have for John's foils and the span is 800mm with a 120mm chord.
I'm not sure what the tradeoffs would be -thats where serious design work would have to be done. Perhaps a combination of changing the aspect ratio of the foil and designing the hull specifically for light air sailing would work.
The Moth foil loading is light compared to David Luggs I14 but about the same as the RAVE at takeoff.
I know(at least I think I know) that this concept will work on a larger canting keel equipped boat.
Juggling the factors involved is where the real fun is going to be; I'm not sure this idea will work for a Moth but it's definitely worth looking at.

 

[Wardi]

The current Moths weigh about 100Kg all up including skipper.
They are using two 800x120mm foils and lift in 6-8 kts windspeed on a reach and 10-12 kts upwind. Top speed seems to be around 18-22kts

The Miller sailboard foiler weighs perhaps 10Kg lighter but only has one lifting foil approx 500 x 80mm with liftoff at 12 kts windspeed and top speed of approx 30-35 kts.

What I understand from Miller is that big foils take off at slower boatspeeds, but interestingly the takeoff occurs at about the same windspeed, it is just that the small foils are going faster.

I conclude that if the displacement hull can give high speed, then it is best to use small foils

I feel the Moths foils are perhaps double the size really necessary.
It would be good to have some analysis of this to find the optimum area.

My own Moth experiment is using a single foil about 1000x80. The aim is lift off in 8-10kts, top speed 25-30kts. The total foil surface area is the same as for a standard centreboard, hence I do not expect any reduction in light wind performance.

This is why I do not think it is necessary to have retracting foils. It is more important that they can feather and run neutral so they provide as little drag as possible in dislacement sailing.

I figure the only way to find out is to build one, but it would certainly be useful to have some design analysis to optimize areas.

Doug seems keen to commercialise a bifoiler arrangement, but I feel it is far too soon. Best to have some furious development within an open design forum first, eg Moth class, to come up with an allround good solution first.

 

[National3434]

More Qs for Wardy and others

I have been following your discussions for the last few days and reviewing some the original postings that brought this thread about. I sail a (UK) National 12 which is a 2 man development class but with enough rules to keep it reasonably accessible to sail.

Anyway I am really enjoying the good stuff you are doing and would like to cheer on the likes of Wardy, John Illet and Astevo who have moved into the hardware phase!

One question for Wardy. You say that your main foil is in the normal centrboard slot. Is that a daggerboard slot, and where is it in the boat (rel to transom, say). Where do you position yourself fore and aft rel to the centreboard to get the precise control of the canard you speak of?

A more general question. Miller's setup (what a great idea!) uses a supercavitating foil section that happens to work very well in tracking the surface but is poor when fully immersed for both lift and drag. What is it that makes a foil good at suface tracking (rather than surface diving/ porpoising)? Is it the sharp leading edge (and what radius is sharp), the under camber, the flat back, the percent chord of max thickness or just the angle of incidence? Are there sections that work well both immersed and in surface tracking/wave slicing?

Good Sailing (to those in the southern hemisphere!)

 

[Rohan]

have just been following the post on a few topics recently and thought i would give my 2 cents on sailing with foils in varous conditions and what i think we need to work on next.

the sensor device i don't think will ever be fast enough to control the height of the boat in chop, as you are just going way to fast and the boat is too close to the water's surface to make the adjustments quick enough. in flat water it works great, but it is not often we sail in those conditions and plus i think we should be aiming to develop something that works in all conditions, so therefore i am only focusing on foiling in difficult sailing conditions at the moment, as the rest is easy.

here is a summary of what i have found...

- it is ideal to set and forget, especially in a moth.
- the simplier the better.
- a good rig makes a big difference. sail must be flat and fast with minimal leach twist.
- rudder trim tab adjustments are minimal (in fact i have even gone out with the trim tab disconnected in lumpy conditions, and still found it ok to use) but i think are still necessary to use.
- sailing downwind in waves (+0.3m) cause the biggest problems because the boat keeps wanting to lauch up when sailing into them.
- moving body weight, sail trim and making small adjustments on the rudder by anticipating the boat's pitch and yaw is far more effective than any automatic trim device for ride height at this stage. in addition you steer the boat to a course that is going to give you the most water underneath the boat (don't sail into a trough).
- when foiling in +15 knots, remove all packers from the lower rudder fitting to lift the transom and force the bow down.
- there is a huge advantage to be made when sailing upwind when foiling in waves, and probably more so than downwind.
- when foiling upwind, you need to don't need to hike as hard because you are able to get more righting moment when higher out of the water.
- you need to sit a fair way back and sheet off initially to get air upwind, but once foiling you can sail quite high into the wind as there is less drag forcing you down.
- once foiling upwind, you can sit back and ride on 'cruise' mode (with high angle of attack) or move weight forward and trim the rudder at the same time to pitch the boat down and go faster with a smaller angle of attack.
- max speed is about 20 knots at this stage with what i am using.
- foiling speed is exactly 10 knots in about 7 knots of wind.

possible improvements to be made include:

- less drag on main lifting foil by tapering the ends and maybe little winglets at the end to reduce tip vortex.
- move mast position aft.
- wider centerboard near top of case to make light wind sailing better.
- ???? (maybe you ask the questions and i'll tell you if it will work on the water in all conditions)

wardi - are you going to the nationals with your boat? robo will have his boat up there with foils but won't be using it? garth is interested in borrowing it, but not sure about going yet. would be good to have another foiler to race against. i think this will be the most exciting part of foiler moths... the on-water action!

people love watching just me sail, imagine a whole fleet of them? it would be unreal!!! can't wait to see what happens.

keep up the posting and development and let me know if you want me to test something on the water with my boat.

cheers

rohan

 

[Wardi]

Tom,
The centreboard slot is just a standard dagger board in the normal position.

It so happens that this coincides pretty closely to the centre of gravity of the hull and rig.
This means that sitting in the normal upwind sailing position the boat is nicely balanced when foiling. Moving your weight aft just a little aft of the centre of balance enables you to unload the foil and easily control the balance. I think this would be the case on most boats, but it will depend on the relation between the centre of gravity and the centreboard position.

The surface tracking canard does not have to be a supercavitating shape, but it helps. Miller gives the reasons in his article at www.foils.org
For displacement sailing, it will be necessary to use a normal foil shape. This is what I am using currently and it seems to work OK.

 

[Wardi]

Rohan,
It is very good that you contribute this information and thoughts.
Interestingly Miller uses his canard foiled sailboard in big chop and ocean swells and at high speeds. The canard tracks the surface very well. In gusts and at high speed the canard is kept down on the wave surface, overcoming the problems you have mentioned. This is one reason this arrangement appealed to me compared with the sensor system I had previously.

I would really like to know what happens if you reduce the foil area. Perhaps if you just use a normal T-rudder instead of the new one. :idea:

For your interest, here is very recent quote from Masa the Japanese Moth guru on his second foiling experience:

"Sun 23 Nov Sailing on KAMAKURA bay watched Flying Moth at sailing club, friends and everybody surprised mate ! Inside KAMAKURA BAY was 8 to 12 knots & Bloody Flat water & wide 400m ! So cool mate !

Out side was 14 to 16 knots & waves I had try but about 100m & lots of capsize Only 100m & too much lift

Sat & Sun, I met lots of sailing friends on the water & Nippon Cup (ISAF Grade 1 match race) Racing on HAYAMA just
front of Hayama marina Semifinal & Final Peter Gilmor(AUS) won & 4th was Dean Barker (NZL) Lot of specterboat stay
around Start & Finish Line I had close to Gilmor boat when just After last race finished & Flying just front of them 15 knot, too much lift may be 50m ) Whooooooou !!!!!! Shout & Cheer ! everywhere (Too much) I have to more practice!

Everybody interesting watched Flying Moth Sailing !!! Jury boat close to me & Hallow say Someone follow me I met lots of sailing Friends on the water Whooooooou !!!!!! Shout & Cheer ! everyfriends

& met famous photographer with moth sailor drive power boattoo He want to take photo Flying but I don't know take Good one, Im Beginner yet Nobody know my sailing Plan on last weekend but Unbelievable !!!

Feeling is not speedy but Bloody Faster No spray ! Bloody Quiet ! So Smooth ! Fast is Fun mate

Nobody Stop Foil Moth Sailing! "

 

[Rohan]

my apologises to john in my last post and any others that may have got confused about the control wand that john uses on his foiler system.

it is important that we have it to adjust the main foil and it works very well, but what i meant is that in heavy air and waves, it is important to just lock it off with maximum tension, as there is no need to create any more lift than necessary as the boat powers up so fast. so therefore the wand that we use is still important in heavy air and waves, but sail trim, rudder trim and body weight tend to take over to control boat height once the wind kicks in.

to let you know how successful john's foils have been also, after a lot of training and use of them on the bay here in melbourne recently, we had a mixed fleet race last night in about 8-12 knots, and i ended up winning the race by lap from the majority of the fleet and beating the two 14's that were there by a leg after 3 triangles (60mins of sailing).

i didn't think the conditions were that ideal either, so the potential here is incredible. also passed an A class on a reach in about 12 knots with about 0.5m waves the other week. i couldn't even foil clear of the water in those conditions, but still went quick enough.

went out again tonight after work and was about 5-8 knots/flat water, so i powered up the boat as much as possible and found that i could still foil upwind and on the reaches. didn't have the GPS on board, but was doing more than 12 knots at times.

was interesting to note that i had a small bit of seaweed wrapped around the centerboard at one stage while foiling and the whole boat had this wierd vibration. didn't know what was going on til i saw it there. large jelly fish are the worst tho have hit a few of these at moderate speed and it hurts.

am keen to see some pics of your configuration too wardi. can you send me some to put on the web?

 

[Doug Lord]

Flying

Rohan, that was inspirationl stuff you posted -really capturing the allure of foiling.
I have an off the wall question for you: do you think it would be physically possible to 'JUMP" the Moth intentionally-- landing safely? It would be something done just for the hell of it but I'm not sure the foils wouldn't just ventilate and the boat crash; any comments?
What do John and Ian think on this subject?

 

[Wardi]

The sailboard guys in Hawaii are placing airchair foils under sailbards for just this purpose.

The airchair arrangement is pretty slow and heavy and requires a lot of balance...only one foil in the water, but could be a lot of fun.

The racing foil arrangements we have today on Moths are built for speed and would probably break if intentionally jumped!

The bifoiler arrangement would probably crash if jumped, but the unifoiler seems to crash land in a controlled fashion.

Is this just for thrills?

 

[Doug Lord]

Thrills without spills

You betcha: for the pure unadulterated fun of it AND to provide a possible marketing "gimmick" for a mass produced foiler. You see windsurfers jumping all the time-even on relatively flat water.
The rc models I've tested jump and re-enter seamlessly but at the model Reynolds numbers it is apparently nearly impossible to ventilate a foil. So the testing will have to be done on an actual boat. John are Rohans foils strong enough to take jumping and re-entry? Rohan, have you accidently jumped?; do you think this could be done? Safely? I'm going to try it on my 16' foiler in a couple of months....

 

[John ilett]

I would'nt recomend jumping them unless they were design to do so. But then, Garths and Rohans have both left the water often enough and suprisingly always re-enter without major problems. They may cavitate on re entry but I guess that only softens the blow.

 

[National3434]

Wardi, thanks for your reply about C/B position. How are the trials going?
And thanks, Rohan for your experience summary. It is indeed inspirational!
About the Y foil, I think I follow why it works on a windsurfer heeled to windward (climb to windward with the vertical part, foil off the horizontal part) but does that not lead to lateral instability? i.e. if you get caught heeling to leeward at speed the foil will keep on turning you over? (is this why Miller is worried about forces in his ankles?) Presumably yours does not do that? Dihedral rather than anhedral would seem to be a good thing from a stability point of view. Would anyone like to comment? Or share experience?

General Qs for those who are doing it:

What happens with tacking & gybing: can you stay foilbourne? Is gybing downwind now faster than straight running? How does the Miller system work in sea waves on a Moth?

Cheers
Tom

 

[Rohan]

sorry, have not looked at this in a while. too busy working, training, racing, triming sails and trying to buy a house!

about jumping on the foils, i have done this many times, but are unintentional as it usually happens when foiling downwind into the back of a wave and the boat springs up into the air as the sensor wand induces too much lift. have not got it on video yet as i would love to see what it looks like. the bigger the wave, the harder the crash. but so far, have not had any damage tho. have learnt to control this now tho.

went out tonight in about 10-12 knots with 0.5m waves and was just mucking around on the foils, no GPS, but i know i was getting up to +18 knots as the only sound the boat makes is a wind whistling through the tramp lacings. the higher the pitch, the faster the boat speed! i remember my first few times when doing +15 knots on the foils and i was **** scared. now i only want to go faster and break 20 knots. i know i can do it, just need flat water.

also worked out tonight, that a change in body weight backwards by as little as 20cms, makes all the difference to foiling upwind. it is critical tho to move the weight forward once the boat is foiling tho, otherwise you'll launch up.

to answer tom's questions about tacking and gybing, yep, can tack and gybe on the foil. just need to make sure the boat is flat or slightly healed in the direction you want to go with minimal tiller movements.

and yes i am totally comfortable with tacking downwind now and on the same angles as the cats. can drive it deep if i get +15 knots, but i really do need that flat water.

 

[Olav]

Thanks to all who have given so much useful and detailed information about the different foiler concepts!

I'm about to build a new Moth (my 2nd homebuilt) that features the Miller system with a V front foil to avoid any movable parts (the design of the boat is finished and the foam bulkheads have been cut out by now).

Although Wardy says he uses the standard centrecase on his scow (which is really encouraging!) I still wonder if I should use a 2nd case aft to increase the distance bertween the front foil and the main wing to improve ride stability. I think that's what Miller himself mentioned in his brilliant article.

Or what about raking the board aft??? I have to admit I'm a bit worried about major changes of the LCE position...

A first screenshot of my design can be seen in the Student Design Gallery and I welcome any comments! I will upload a lines plan soon...

All the best,

Olav Nehls - GER-1038