FOILER 1 Grand Prix

It did perform but was outlawed as a multihull. At the time is was quite successful and faster than the non-foiling moth. Look here for some pictures. http://www.moth.asn.au/pictures.html It would be interesting to know if the two have been raced aginst one another.

Nobody

 

Moth surface piercing foiler

Brett Burvills surface piercing Moth foiler was the first Moth foiler to win a race but sufferd down wind because it had very poor roll stability among other reasons. I'm not sure the two types of foiler ever raced each other but the comparison of both to a seahugger Moth demonstrates clearly the superiority of the bi foil Moth foiler configuration configuration.

 

Doug,

Wasn't that RHough's point. That in the absence of the rules the current moth configuration is not the best. It is the way it is to meet the mono-hull rule. If the rule didn't exist then it would be better to seperate the foils to provide some stability/lateral damping.

Nobody

 

I have sailed both of the foiling moth designs.

The bi foil moth and the surface piercing designs have not raced each other to any extent. In 2003 we had the prototype hydrofoil Prowler sailed by my brother Garth sail against Brett Burvill on his tri foil design. It was not a race day and I can not remember anything significant of that day. The tri foil boat was then put into the West Australian Maritime museum along side 12 metre Australia II in Fremantle.

Brett did win races at the 2000 worlds by the same margins of around 20minutes as did the first winning Bi foil design in 2004 relative to the top non foiling boats.

I think that the main benefits of the bi foiler in comparison would be earlier foiling in low wind and overall ease of handling. The tri foil may have had a higher top speed but was tricky to handle due to the foils passing through waves and especially when gybing. The foil loads would basically reverse as the sail/power changed sides. If you did not have your body in the correct place then the lift would flip the boat pretty quick.

 

Yes they do, the weight of the boat. If they lifted more than the weight of the boat it would be an airplane. If they lifted less than the weight of the boat it wouldn't foil.

No, All the foils are doing is lifting the weight of the boat out of the water. No increase in area needed. If a Moth can foil with 100% of the RM coming from the crew, so could any other configuration. There is no need for any RM from foils.

The total displacement of the boat doesn't change, just shifts from one hull to the other. In Minimum foiling speed operation all three foils would lift. As speed and heeling moment increases more load is shifted to the leeward foil, it doesn't have to be any bigger to support the higher percentage, the lift goes up as the square of speed. Of course it would have to have independent control of the foils.

What forces are involved? Where is the proof? There is no way that the hull and sail can develop a windward directed vector from heel into the wind, if tilting the rig was the key, windsurfers would have good upwind performance. Some angles and speeds? Some data? If there is proof, lets see it.

Don't be dense. In order to limit the RM induced by the weather foil, the foils would not be allowed to generate negative lift. The lower limit would be zero.

 

Is there not a windward vector/lift from the lifting foil when heeled to windward? Doug did not imply that any windward vector came from the hull or rig just that heeling the boat to windward helps which it does. 14 knots up wind is pretty quick.

 

You can see that. http://www.boatdesign.net/forums/showthread.php?t=2447&page=32&highlight=foil

 

"if tilting the rig was the key, windsurfers would have good upwind performance."

Well, I rarely jump in to bolster the case of certain people, but I have to say that windsurfers and foiler Moths in 8 knots+ DO have very good upwind performance. A Div 2 board (the round-bottomed machines designed for triangle racing in the winds we get, rather than the winds we dream of) can best be compared to a non-foiler Moth. The board is 1'9" longer but carries over .7m2 less sail and is of similar all-up weight and greater beam (due to class rules). In light airs, a Div 2 board is basically identical in speed to a non-foiler Moth (ie Mark & Les T.) which IIRC means it would beat a Contender, International Canoe or most other (much longer) singlehanders.

In my experience, above about 7-8 knots, the board starts to move faster upwind and down, and gets to be faster than an International Canoe (probably the fastest upwind non-foiling singlehanded dinghy) with similar or superior height. I think the D2 is always about as fast as a Canoe upwind and normally/often faster, despite being much smaller in hull and rig. That's quick. From 16+ knots a Mistral board is also quicker than a Canoe or (IIRC) Moth or Contender etc upwind.

A modern Formula board is arguably 49er pace+ upwind in a breeze (but is Opti meat in 5 knots) with good height. Even a modern slalom board points like a dinghy in a good breeze and goes VERY well. Finally, even the ancient original Windsurfer (in '80s Mk2 guise) is as fast as a dinghy of similar age but more sail and length (ie Laser) upwind in a breeze.

So boards CAN go upwind. So do foiler Moths, once they are on the foil - and they do it heeled to windward. I don't think any singlehanded dinghy could beat a good foiler Moth upwind when the Moth is foiling and heeled to windward, so it does seem to pay. This comes from seeing a guy who was top 7 or so in the worlds in Canoes against the world Moth champ. It must be said the Canoe sailor was VERY out of practise but still the Moth, when foiling, was much faster.....no comparison.

Exactly how much the windward-raking rig plays a part in this is a very hot topic - guys like real-life rocket scientist Jim Drake (inventor of the Windsurfer and developer of the modern FW board) reckon raking the rig about 15 degrees improves speed, Olympic medallists in D2s and World champs in IMCOs reckon the upright rig is faster, the world FW champ can be seen trying to keep the rig vertical, and in old Windsurfer One Designs the former world champ is as fast as all hell upwind with the rig raked right to windward.

All of which seems to show that (1) boards ARE fast upwind and (2) the effect of windward rake seems very complicated and may vary considerably from class to class. There are also some very smart people who are very good sailors (Wardie etc) who reckon windward raking helps Moths and it certainly seems to in practise. Even before foilers came in, 18s and Moths used windward heel; so do Lasers at times.

 

Moth wins again....

Randy, you could do what you want if you devised a system to disconnect or limit the wand on the windward foil only on a three foil fully submerged system. But even monofoilers need to be able to develop negative lift to control the dynamic response of the boat in waves. So you couldn't eliminate that function on the lee foil
and you would have to have a way to set the limit tack to tack and gybe to gybe.But you're still nailed with three surface penetrations and with the inabilty to heel the boat to weather. You could mount the vertical fins so that they angle outboard so as to mitigate some of the negative effects of boat heel-and maybe benefit a bit from the angled attitude of the lee foil-assuming the windward foil was unloaded. Which it would not be until the crew was at max extension.
But you're much more complicated than a Moth foiler and without the ultimate power of a Rave with a long way for the crew to go side to side with a heavy workload ,while not benefitting from the 'heel to weather ' technique until max RM if then.
I still say the Moth would take it in 8-15 around a course.

 

To restate the question:

What forces make a windward tilted Moth faster upwind?

Not faster than a canoe, not faster than a non-foiling Moth, that is obvious.

If two identical Moths are sailed unwind, both on foils, one is heeled into the wind, the other is not. Is the claim that the heel to windward makes the heeled boat faster?

What is different?

We are not talking about extreme 15 degree to windward heel as seen on windsurfers, Moth foilers heel more like 5 degrees to windward.

The amount of force driving the boat to leeward remains constant, it is a function of the height of the sail plan (the Sail Arm) and the RM (Crew weight x distance off centre).

The leeward force must be balanced by the underwater foil(s). To improve the windward performance something must change.

Since the force remains constant the only way the windward performance could be increased is if the drag is reduced. Does the drag of the foil system decrease with a change in angle?

Work it out.

Vertical lift must = total boat and crew weight.
Horizontal lift (to weather) must = Horizontal force (to leeward) of sail plan.

How does it work?

 

14 knots boat speed? or 14 knots VMG?

Side by side, the Moth that heels to windward is faster than a Moth sailed at zero heel? What windward heel angle gives the best result?

 

Vertical lift from foil and strut = weight - lift from sail
Side force from struat and foil = side force from sail

The leeway angle and foil angle of attack may change as the boat is heeled, but the total forces have to be nearly constant. So the question really should be, "What heel angle produces the least drag?"

I can see two sources of drag reduction from windward heel. The first is lift from the sail rig, which has a much larger span than the foil, so it may be more efficient to offload part of the weight to the rig.

The second source would be an increase in depth to handle the side force. The T foil will have its greatest vertical span when a line conecting the surface chord to the foil tip is vertical. This is especially important when the boat is flying high and there's not much strut in the water. Heeling puts the windward tip of the foil much deeper, signficantly increasing the vertical span. Since drag due to sideforce is inversely proportional to the square of the depth, this is a major factor.

There may be an increase in righting moment, too. It seems feasible to me that the vertical lift on the foil will reduce the leeway until the strut is unloaded. Then you basically have an inclined foil to leeward, like the daggerboard on a trimaran. There's a horizontal separation between the vertical lift of the foil and the hull at the center, much like there is with a trimaran, which would increase the righting moment. Or decrease the heeling moment, depending on how you bookkeep the forces and moments.

 

They do sail heeled to windward about 15 degrees. maybe more.

 

Hi Tom. It would have been to easy to ask that question directly.

The forces being nearly constant part is the point I was trying to make. No magic in heeling to windward.

Although the video and images that I've seen don't show a 15 degree windward heel, John has sailed foiler Moths and I have no reason to doubt him.

The lifting foil is 800-900mm span and the strut has about the same span.

It should be easy to plug some numbers in and see what the drag bucket looks like at zero and at 15 degrees of heel.

Total force has to equal the sum of foil supported weight and windward force. My guesses are that the side loading is about 80 pounds and the vertical loading is perhaps 220 pounds, the foil must create 300 pounds of force.

Note that the maximum force from the sail is limited by RM and sail arm. In a typical Moth that might be 80 pounds of force acting through the AC of the sail. Tilt the rig to windward and figure out what percentage of that 80 pounds of force is up. Subtract say 10% - 8 pounds, now the total load on the foils is 292 pounds instead of 300 ... 2% So the induced drag of the foil system is reduced by 2%

If the induced drag is 50% of the drag total the gain is 1%.

Sorry, I'm not buying.

This is the Australian Champ, Rohan Veal ... Not even close to 15 degrees of windward heel, more like 0 ... :?:

 

The picture shown is Moth class world Secretary Mark Robinson sailing a Prowler. The boats only use the windward heel when sailing upwind. This photo shows Mark reaching.

If the rig carries weight then the foils carry less so the sectional shapes may improve with less positve flap.

Below Rohan and Mark sailing upwind.