Evolvement of foiling sailboats over the last 70 years

Fig. 1 — 2 — 3 — 4 + 5 — 6 — 7 — 8 — 9 + 10 — 11 — 12 — 13 + 14 — 15 + 16 — 17 — 18 — 19 — 20 — 21 — 22 — 23

 

I think that supports my point that the clever development of UpTip foils is not that they happen to be able to breach the surface. WRT the GC32, the question (that cannot be answered) is "would it have been faster with a foil optimised for that higher speed that did not break the surface?"

That is not my experience, for example Hydroptere's foils (not technically a V) are >90 degrees; Flying Dolphin Vs are >>90 degrees. Generally there is a tradeoff between efficient flying (horizontal foil) and gradual reduction in lift (steeply sloping foil).

 

Have searched for images of Flying Dolphin hydrofoils, but haven´t found any. Are there any drawings to see the complete set of foils?

 

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Aside from being called "full flying DSS" the Quant 17, 23 and other foils of the type are called "Q Foils" by the designer(Hugh Welbourn).

 

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Angel, the Hobie Trifoiler, Dr.Sams Rave, SKAT and Osprey all use foils designed to have the windward foil pull down to increase RM. Kettermans Trifoiler uses "feelers" sticking out in front of the boat to change the angle of the whole foil while Bradfields trailing wand system moves the flap on the foil to change the effective angle of incidence of the foil. Bradfields main foils are set with an AOI of +2.5 degrees(flap neutral) and the flap moves 20 degrees up and 30 degrees down.
My Fire Arrow Test model and WOLF use a wand controlled mainfoil that works like Bradfields foil system.
All of these foils are capable of generating substantial downforce. As an aside some are also capable of breaking the boat: Dr.Sam had a "Never Exceed" speed limit for the Rave. If it was exceeded disaster could happen and did at least once breaking the massive aluminum crossarm!
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Ketterman--DLA

Here's what Greg Ketterman says about his foil system:

"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."
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* On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.("feelers")

 

Thanks for the info Doug !

 

This is in addition to what the "other Doug" said.

You do not want to allow the windward foil of a surface-piercing foiler to get negative lift. Surface-piercing foils are self leveling as long as they are lifting upward. Flying higher causes a reduction in foil area that reduces the lift. But when they are lifting downward, flying lower causes an increase in foil area that increases the downward lift and pulls them ever lower, without limit.

Here's a sequence showing what happened one time when I allowed Broomstick's windward foil to get negative lift. (Not shown is the broken foil that resulted.)

 

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More info on Gordon Baker's Monitor, she was mentioned in several posts on page #1 of this thread.

‘‘ The 1950's hydrofoil, using a mechanical computer they sailed at 30 knots. . . . . ’’

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Video info (click away the ‘‘save as’’ window that appears)​

 

Speaking of how foilers have evolved, ladder foils don't seem to be in favor these days.

My early days of foiling (1974) soured me on that configuration...


Incidentally, the mast & sails on this boat were the same ones I used on Broomstick 30 years later.

 

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I think some doubters are confused by what is not said: the set up did not include the fact that the Artemis boat was not oriented exactly parallel to the flow of the current which allows the wingsail to have a proper angle of attack with the apparent wind to get started.

 

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Doug, that is really cool! Thanks for showing it!

 

Any boat that has a downwind VMG greater than the true wind speed ought to be able to sail upriver on a calm day.
I'm pretty sure a Moth could do it. Here's some measured polars, showing VMG ~17 knots on a day where the maximum recorded gust was about 13 knots.

 

The key here is that these are maximum speeds, not sustained speeds.

Moths do sail DDW for a short time when gybing, and directly upwind when tacking (if the crew is good enough to manage foiling tacks). It's common during a gybe for the sail to stop filling and flap briefly as the boat goes through the apparent. However my experience of sailing a Moth for many years is that they cannot sustain foiling directly down wind (DDW) in any conditions. If that was possible, they wouldn't bother to tack downwind.

 

You don't have to sail DDW for any extended periods. I'm assuming the boat would sail at its angle for max VMG & gybe when necessary.