Should we impose a sail area/length2 limit?

Not all that difficult to determine, since the formula is stated in the prelude to the charts.

 

single digit SA/D

Well, I can't find it; why would they use a formula not generally used? If anybody has any knowledge of a single digit SA/D formula and the reasons for it's use I'd sure like to hear about it. The "normal" formula produces results in double digits and every time I've seen it used in a boat description this is the one I've seen.

 

Frank B isn't into DLR and SLR, but other dinghy designers of equal skill are - Paul Bieker for example. Andy Paterson refers to the length of the Cherub a lot, and Doug he created the Moth foiler (as well as the skinny Moth) so you must respect him. Without wanting to put words in his mouth, looking at his writings about Cherubs and Moth shape and performance and the way they are restricted in certain conditions by their length, it seems obvious that he thinks that length IS important.

Without wanting to denigrate the Bethwaites, it should be recalled that the last time they actually went head-to-head in a true development class (there were restrictions on new 18 designs which favoured the Bethwaite), they did not dominate for years in the way Bieker did for several years in the 14s, and they were not up against the variety of designers you have seen in 14s and Moths.

In fact, I think the last time the Bs went head-to-head in a development class was '76, when the defending 18' skiff world champ sailed a Bethwaite and lost his title - because, it was said at the time, of the problems getting the Bethwaite boat downwind in a breeze.

I'm not saying the Bs are inferior, merely that other people are probably their equal in understanding design and therefore when people like Paul Bieker say that DLR is important in skiffs, their views deserve at least equal credence.

Finally, if DLR and SLR isn't important, why do the Bethwaites always design such long boats (compared to other Australian classes).

Doug, in the spirit of fairness shouldn't you say that the estimate of a Moth being 15% faster than a 49er comes from (IIRC) ONE Moth sailor's performance in ONE regatta?

Meanwhile the world champ, last time I read anything relevant he wrote, is still normally beaten around the course by Int. 14s. This is in foiling conditions, the chap who runs much of the UK Moth class calculates that the foilers are about Laser Radial speed under about 8 knots.

Which is not saying the foiler is not amazing, great, the fastest singlehanded mono when foiling, perhaps faster than the fastest boards around a course, etc etc etc. But the current detailed estimates of the world champ and the guy who runs the UK class does NOT indicate that the Moth is 15% faster than a 49er all-round.

 

It is the square root of the sail area divided by the cubic root of the displacement (as stated in the first three lines of the prelude.

 

ratios

CT, I was trying to give the person that asked an overview of the various measures that attempt to look at SA andDispl. I have enormous respect for all the small boat designers and read everything I can find that they've written.
Things like Disp/L ratio have no meaning when talking about a Moth on foils. Neither do other ratio's I've looked at since none of them predict the performance that is evident with a foiler Moth. However, they all have some meaning in predicting performance off the foils but that area of the performance envelope is continuously shrinking.
I'm fascinated by whats going on: it used to be that you could pretty much count on increasing speed if you increased length; is that still true? What ratio, formula etc. is there that accurately predicts a foilers performance at differnt lengths? I feel like the answer will be some form of comparitive ratio(formula) that takes into account: 1)foil loading, 2)sq.ft.SA per sq. ft. foil area and 3)Sail Loading(weight divided by sail area) without regard to length. But, then again as the boat gets bigger there may be some RE effects that should be considered by such a "ratio" or "formula". I guess we should discuss that on the Foiler topic after we figure out the effect of pitch on foil loading(ha).

 

SA/D -finally

Soren-I finally read it ! Was staring me in the face but didn't pick up on it-thanks to you and Paul B for trying to show me.
But why would they use that instead of the generally accepted definition?

 

Seems to be your MO, relating to subtleties of things you claim to "research".

 

If you want a sail area-length limit make up a box rule and go race using it.

 

A box rule with SA and Length

When the thread was posted, it was meant to provoke a discussion on the usefulness or not of just that: a modern box rule, as simple as possible, taking into account sail area and length2. With recent technological developments, an upper limit of SA//LWL2 of 1 for upwind would be quite reasonable. SA 225 sqft for a 15 ft LWL boat.Any suggestions?

 

Box rule

Those dimensions are very nearly the same as a 49er. Not sure if that much sail is necessarry when using foils-that depends on two things-righting moment and allup weight.
So maybe a box rule should limit those factors? But ,I guess, that depends on the purpose of the box rule.
Ian Ward has proposed(in an article in Seahorse) a series of different "classes" of development foilers-I think I posted his idea under "foiler design" but I'm not positive. Anyway, his limits are LOA and SA and the purpose is to push foiler development with the fewest restraints possible while providing racing at different levels.
What is the purpose of your box rule?

 

There are limits in our effort to design and control a machine, a sailing craft, a vehicle, or whatever. At any time, technology pushes the limits further off, but there are limits and we must always respect them. I think that, for the time being, we can safely control a sailboat with an SA/LWL2 ratio of 1 at most. (For a foiler we are still at about 0.5 , and there I agree that we had better use LOA instead). Box rules are used succefully in the past (see "open" classes like Open 60), but I always found it curious that we do not have such a simple modern box rule.

 

Box rules are good if the boats that come out of it are fast and efficient. The TP52's are fast (22 knots) and can go to windward very well considering that they are designed originally for a downwind race. The new ORC box rule (proposed) boats will most likely be much slower than sportboats of the same length.

 

Level of control and safety is what I find more important than speed and efficiency, dont you agree?

 

Box Rule

If the purpose of the "box rule" is for boats that race then speed and efficiency will be the most important parameters.
Under your proposed rule is the limit supposed to be total SA-both upwind and down? Curious because stemming from its skiff heritage the 49er while having 228 upwind has got a total of 600 or so off wind.The interesting thing about a foiler is that it does not need the huge spins used by skiffs.

 

First, a yachting organisation puts the limits with safety and control in mind, and then the designer comes up with a fast and efficient plan and at the end here comes our sailor who tries to win and have a fun!
Downwind, I would say a more modest ratio of SA/LWL of 2 (double the upwind area), i.e. 450sqft for a 15 footer. (For a foiler, I think that the sail area should be the same in the upwind and the downwind case.Not sure about this) I, for one, find the 600sqft of the 49ers too much. I wouldn’t like to see sailing degenarating into an extreme sport !