Some Foiler Thoughts From the U.K.

[MultiFast Is MultiFun]

I have used the new scanner to good effect this morning and have attached the comments from Nigel Irens on the subject of foils. This is going to upset a number of people but the facts of life are hard.

Be warned a lot of people who know little about foils in the real world will very unhappy and those who know a little still unhappy. The 90 year Sam will agree that Nigel is right and those who support the same rationale thinking. The attachment reveals all.

Chapman has a soul mate across the Atlantic called Sam Bradfield, a Florida-based, 90’s -something professor of hydrodynamics who commissioned British multihull designer Nigel Irens on a project to build a 37ft hydrofoiling trimaran. Bradfield has had his tri up to speeds of 30 knots, although it would not beat a conventional tri of similar dimensions around a course, according to Irens. Off wind speed is blistering, but upwind performance is tamer so far Chapman's experience with 'Ceres' has led him to believe that sailing in a mode of 'flying displacement' - his term for raising the hull aft inches out of the water while still maintaining contact with the surface - is faster than fully foiling for upwind VMG.

Irens believes that whereas an International Moth relies on body weight to keep the boat upright, the forces on a multihull are such that) technology and theories of hydrofoiling are not directly transferable. If it were, we would have seen them on the 60ft ORMA trimarans by now. Irens is one of the leading designers on this cutting-edge circuit, and has also designed Ellen MacArthur's new 75ft trimaran.

Irens picks up on Pemberton's earlier point of the narrow performance envelope of hydrofoils, The ORMA tris have to cross oceans whilst beds sailed single-handed, and Irens believes the risks are becoming excessive with current technology, let alone attaching untested hydrofoils to these untamed beasts. The other issue is cost, and Irens says experimenting with hydrofoiling would send budgets skyrocketing beyond the bounds of most ORMA sponsors.

Instead, the latest generation of 60ft tris has employed curved daggerboards, which apply a combination of lateral resistance (like a conventional centreboard) and horizontal lift. Irens believes it was John Shuttleworth who first. came up with the idea in the 70s, when he was designing fast multis such as 'Brittany Ferries'I Chay Blyth. But the resurgence of interest in the technology has been led by La Rochelle design Marc Lombard. Now the curved foils are becoming must-have technology for the 60s and are beginning to replace straight foils. 'Over the last three years this technology has really come on strong,' explains Irens, who says the curved foils are more versatile. 'When you put a straight foil down at 45 degrees, you get a degree of vertical and horizontal force. You get what you get, but you can't vary the relationship between the two components.'

Irens says that lifting force increases with the square of the speed, so the changing relationship between lift and speed demands different combination of lifting force and later resistance from the foil. This is the beauty of the curved foil. When you push the foil down there is a large lift component, which is useful for light winds. As you pull the foil up, the lift component reduces but the lateral resistance remains. He points out that the aim is not to have the leeward hull clear of the water but merely reduce hull drag whilst keeping the float kissing the surface. The 60s are limited to 11.8 square metres of lifting foil (measured by viewing the foils from above). Irens doesn't want to see these 60s hydrofoiling quite yet. When you realize the that for last year's Route du Rhum across the Atlantic only three out of the 18 tris made it to the finish, he has a point.

He does reckon there is some potential for helping lift the windward hull of the big ocean going cats like 'Maiden II' clear of the surface, but again there are huge safety issues to consider. For the time being, it seems as though the real pioneering work will be left to the small-boat community.





EDIT: Image was added for easier reference.

[Doug Lord]

Open 60's using curved daggerboards have proved extremely dangerous at sea because the curved daggerboard behaves like a surface piercing foil WHEN it lifts the ama clear of the water. Because the curved daggerboards use NO form of altitude control the faster the boat goes the higher it flys. When the ama finally comes clear of the water the air/water interface is right at the area of maximum lift on the foil and ventilation is almost certain to occur. When that happens the tri pitchpoles in an instant-especially those with no rudder t-foils.
On RC models, foils using an altitude control system similar to the one used by Dr. Bradfield on the Rave and on Scat do two thngs: raise the boat clear of the water eliminating wavemaking resistance and develop all the righting moment for the boat-something the curved daggerboards don't do at all.
The "wand" altitude control system on each ama is the key to the development of virtually unlimited righting moment-so much so that the Rave has a warning in the cockpit not to exceed the designed loads.
On rc models this system is far superior to surface piercing foils due to the development of righting moment-something surface piercing foilers cannot do. On models this may be the biggest benefit of foils surpacing even speed. Since the boat gets more stable the faster it goes in both pitch and roll the tendency of small multi's to pitchpole/capsize can be completely overcome allowing great speed with absolute control.
That onlyleaves light air where a foiler using an automatic "wand" system can be a dog since it is commanding max lift from the system yet there is not enough wind so the major by-product in those conditions is drag. The solution is being worked on all over the world and that is to retact the hydrofoils in light air. Using a retractable foil system a foiler can take advantage of foiling conditions and not be disadvantaged in lite air....
In monohulls fully submerged foils using a "wand" altitude control system recently won the Australian Moth Nationals against around 40 other boats showing superior speed upwind and off the wind as well as the ability to tack and gybe while on foils. This was the first time in history that a development class Nationals had been won by a hydrofoil..
On models the most important benefit of hydrofoils-at least on multihulls-is control: they can make a hard to sail boat easy to sail even by a beginner in almost any condition.

[Doug Lord]

Gee, that looks an awfull lot like the above mentioned rig .. Except it appears he forgot the most important part!
Sure would be interesting to get more details, Dick..

[MultiFast Is MultiFun]

It was requested - but the whereabouts of Mike Dann at present put him in England, Australia, or somewhere in between. He doesn't have email.

If I hear anyting I will be posting. Sorry

[Matt L]

Hmm, I recon thats not a wing tip rig, but a gassfiber flexitop, it looks very thin....

[Doug Lord]

You may be right Matt ; it sure doesn't appear to have an adjustable upper outhaul -a key ingredient of the wing tip rig and the angle's kind of high. The sail seems well matched to the spar. Seems to me the tip may rotate but thats hard to say...Sure would like to get the designers thoughts.

[peter]

It looks like an old flexi top rig that the 18 foot skiffs used to use. They went away from using them because they kept snapping.

The other thing it could be is a "quiver tip" fishing rod blank. We have them over here and they are really good for catching small fish.

If you don't know what one is, the top of the "rod" is hollow and the "quiver tip" slips into the end of the rod. You can by several different weights depending on the conditions.

Peter

[MultiFast Is MultiFun]

The hulls looked a bit familiar, and the bow bumper does have a strange look to it. I dug out some of my plans, and hulls really look like something from GHOST TRAIN design.

Seeing as how it is a U.K. design, my guess is that there is definitely some Andy McCulloch influence.

Also, using a scale and a bit of calculation, the cross beams would seem to be in the 30 inch wide range. This also makes sense, since most cat designs sail better when the beam is less than the overall length.

Just my opinion and guess - of course.