RL24, RL28, and RL34 Trailable Yachts
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Is there a future for foils on the RL24?
One day not too far away, someone will add foils to enhance the performance of an RL24 and the current rules would appear to allow it.

I have watched with great interest over the last two seasons the developments in the moth class, then the massive Americas cup catamarans and their sensational increase in performance, and now much closer to our type of boat a Laser dinghy has increased its performance also.

Foils do have an infinitely better lift to drag ratio than the forward section of a conventional hull, and any boat that can exceed the normal displacement speed for its length should be able to gain an advantage using foils.

A single horizontal foil sliding from a housing that runs across the interior, and is just forward of the keel case and below the water line should add considerable lift to the forward section of the boat and being outboard to leeward then the lift developed would also add to the sail carrying capacity provided that the boat was sailed with little heel.

There would be no problem with nose diving as with the more extreme boats nor would the foil interfere with the accomodation or the outward appearance of the hull.

Is there a future for foils assisting on a RL24? I just wish that I were 20 years younger.

Rob Legg 31-Aug-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Hi Rob
Great idea.
Are you able to do a rough sketch on how this concept would work on a RL 24?
Luke Ratcliff 3-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
I do not envisage a 24 getting up and being totally on foils, but with modern foils developing a lift to drag ratio of up to 20 to 1 at only 11 knots then a single foil to leeward could greatly assist in sail carrying, and also lift the bow sufficiently to assist the boat to plane much earlier'

Naturally there would need to be a lot more work done in refining this proposal, and our measures and the controlling bodies concerned would need to express their approval first

I do think that you will soon see some of the larger keel boats attempting to enhance their performance in this way.

Example: A foil of only 1/5 squ meter (100cm X 20cm width at 11 knots can attain a lift of 200kg with a drag of only 10 kg.
Rob Legg 4-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Geez, Rob. Thank God Dad doesn't mess around on the Internet!
James Shannon 4-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Hi Rob,

That's a interesting idea to try a foil on a RL24.

The thing is most RL's wouldn't seem to get much benefit form a foil of this type unless the wind is blowing 15 - 20 knots or so. With our moderate sail area on the RL's most RL's are under control until then so the foil would be more drag if used.

In order to make this work on a RL in a bigger wind range what other changes would we need to be made to the boat before foils would work in a bigger wind range ?

Dave Pullin 4-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
I had not even considered anything more at this time, as anything that hampered the launching and retrieval from the trailer, or, was a permanent protusion from the hull would detract from the practical usability of the boat.

In the lighter winds the foil would be retracted and the ends would be faired off to the hull, but the configuration may allow one less crew to be required, as when the wind freshens the lift generated to leeward could more than make up for another crew member out on the gunwale, and there would be a definate advantage down wind in that.
Rob Legg 4-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Interesting concept Rob. Got me interested. So you guys, who's going to cut a hole in the bottom of their RL first?
Steve. 28-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?

L/D of 20 is pretty good. Can you point me to a paper which supports such a good value for a low aspect surface ? In the aerodynamics world I wouldn't be seeing anything like 20 ..


John Heddles 28-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
There is a lot of information on the net, and one of particular interest is the actual results of "The full scale US Naval Hydromechanics lab tank tests on a Hydrofoil International Moth". Also worth a look for the basics is "2.972 How the Hydrofoil works" where the claim is made of a L/D ratio of up to 30/1.

When reading the results of the Moth tests keep in mind that the drag factor also includes the 50cm depth of the actual Keel and rudder , If the foil protruded from a hull that would not be a factor.

I feel that foils will be an important issue on sailing boats in the future, not only for keels and rudders, but for assisting in making displacement hulls more efficient
Rob Legg 29-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Thanks for that, Rob. Haven't played with any hydrodynamic work since undergrad days. Will read up and be educated on the current literature ...
John Heddles 30-Sep-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Hi rob thanks for the drawing. Have you got some ideas on the foil shape? If so can you post a drawing ? Do you think the pitch of the foil would need to be adjusted whilst sailing?
Luke ratcliff 8-Oct-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
I would have preferred to have actually tried the whole concept myself before making any reccomendations, but as that is not now possible I can only advise as to what my approach would have been.

NACA did most of the early published work on foils, and I would have chosen a foil that had a good lift to drag ratio with an optimum attack angle of around 5 degrees that was operable up to 10 degrees without stalling, so, NACA section 0015 would be a good starting point.

Note that small changes in shape make a large difference in performance and published shapes should be accuratly followed.

It is interesting to note that "Wild Oats X1" will be sporting a retractable horizontal foil to increase performance downwind in the Sydney to Hobart race this year and on a boat that weighs may be 50 times more than a RL24, their foil protudes less than two meters and is 55 cm wide.
Rob Legg 9-Oct-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Some things I wonder about. First, when the boat heals, does the downward angle of the foil cause the boat to turn leeward? Or at least make it hard to turn up wind, in a last ditch effort to save the boat.
Second issue is that it only seems useful in steady winds. Flying too much sail because of the lift of the foil could also cause one to get knocked down easily before the boat has a chance to accelerate and the foil to actually create lift.
While I had previously thought through this idea, there seems some complications.
One other observation and that is if you are only lifting, would the foil work better to be shaped like an airplane wing, meaning flat on the bottom?

Daveinet 17-Oct-2013    Edit    Delete 
Re: Is there a future for foils on the RL24?
Good question Daveinet.

I see it this way. When the boat heels it normally automatically has increased weather helm because the centre of effort of the sails moves outboard , and the pressure being partially forward creates the need to fight it with the rudder, this in turn slows the boat. This is why well sailed 24s are sailed flat, and you will seldom see them heeled to more than 20 degrees, so, a metere long foil that has its centre only 50cm beynd the hull should create a drag of maximum 10 kg for a benifit of up to 200 kg lift at speed, and down to nil when stoped, whereas, the sails would create much more than that in the opposite direction when the boat is heeled too far.

The end result should be just a reduction in weather helm experienced and an increase in speed.

As with the "Moth class" I would expect that it may require a rather different technique to get the best from the boat, but keep in mind that this is just a theory at this time and would only be proven, or disproven if tried.

It will be interesting to see what happens in the "Sydney Hobart with "Wild Oats".

Re your later question. Actually I know of no true foils that are flat on the bottom, and all have at least some convex shape, as, a flat shape creates much more resistance and turbulence. Have you ever wondered why symmetrical wing sails are so much more efficient?

In the foil we are discussing a symmetrical foil also has the advantage of being stronger, as we are talking about an upward pressure of up to 200kg out from the hull, also manufacture of the foil would be simpler in carbon fibre by making it in a mould that could be used for both top and bottom, then joined together.
R0b Legg 17-Oct-2013    Edit    Delete 

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