Sailing Dinghy Design

[SailDesign]

"The rudders are moving back as opposed to the idea of putting one under the boat."

Is that for control, or to get the foil lift further aft?

 

[Paul B]

It is probably a bit of both, although the gantrys were used on 18s and 14s more than 20 years ago, long before the foils came about.

As "Another Guest" mentions, the separation between the foils dampens the inputs and helps control. With the rudder foils the crews, rigs, and boards have also moved back, so it would be a benefit to move the rudder back as well to keep the sparation. I don't have the current rule handy here, but I imagine there is a limit to the distance the gantry can extend.

If you read Bieker's writings about the rudder foils he mentions the interaction of the foil's wave with the stern wave, flattening it and moving it back. That is why the foils are full width. Supposedly this fools the wave train into thinking the boat is longer than it is. So moving the rudder back would possibly make the wave train even longer, unless you got it so far aft that you lose whatever interaction the waves have. I imagine they've done some trials to find the point of diminishing return.

The foils are a cool development to solve some known I14 problems, but they probably have a limited use outside this type of boat.

 

[astevo]

with a boat that long i wouldn't have expected the steering to be too twitchy. i guess with the assymetrics you might be able to have a longer tiller, for the same cockpit space, so the helmsman dosent feel like he is being pushed out of the boat by the lee-helm.??? could this be a reason for the gantry?

also given that the foils are mostly liftinng ing the 14s (as opposed to the moths where we have them pulling down) does this mean that the incresed seperation could be there to create a larger nose down moment.

i would have thought the increased aspect ratio would be to reduce drag but, i can see how the foil of full span would hold the stern wave down. this would also be the reason of having the foil being half way up the foil.

this is all assumption based but it seems to make sense,
to me at least.

 

[Tim B]

Be careful not to confuse the 'rudder' (steering, paddle-like thing) with the hydrofoil stuck to it (wing-like stern-wave lowering thingy).

Cheers,

Tim B.

 

[astevo]

tim,
i dont know what you mean.
the two are attached so you cant move one without the other,
ive read through the previous posts again and cant see instances of confusion?

 

[Paul B]

Confusion

Maybe some of what I wrote adds to confusion. I tend to interchange "foils" for all the surfaces. Makes sense in my head, but probably not descriptive enough. From here on I'll attempt to stick to "centerboard" or "Board", "Rudder", and "Foils" to describe the underwater entities ("Foils" being the Hydrofoils on the rudder).

Astevo: on the 14s the Foils are set at a positive angel of attack uphill and negative downhill (to help keep the bow up). There are some slick adjustments through twisting the tiller. I'm sure you have something similar in the foiling Moths.

I posted this information on another board a while ago and someone scoffed at the idea of the wake being smoothed. They were adamant the foils should be smaller and at the very bottom of the rudder. Their quote was something silly like, "If you want to smooth the wake you should drag a sheet of plywood behind the boat."

It is funny to read a Moth perspective. "with boats that long"... The problems the Foils are there to solve are commonly described as being due to how SHORT the I14 is. But I guess when you're at 11 feet and looking up at 14 feet it doesn't seem short.

Anyway, here is an older piece on Foils from Bieker: http://www.i14.org/boat/articles/bieker-rudder.html

 

[Andy]

Hi everybody - nice to see you guys have buried the hatchet at last! Does anyone know how critical the foil sections used in the winged rudders are to control? Although they undoubtedly damp pitching Im wondering what happens when the boat does meet big waves...any ideas?

Also, I think the source of the lines for NZL 32 aren't all that well known. Paul B stated that "The Kiwis "got the cup" in '95 by hiring in the lead designer and the CFD expert from the '92 winner, and worked up an evolutionary design" and "When the Kiwis won the cup they did so by hiring the designer from the previous winner (Doug Peterson), and the 1995 winning Kiwi shape was an evolution of the 1992 America Cubed shape". Although I could be completely wrong, I always understood that The A3 lines were developed from work done by John Bertrands Beach Boys sydicate which Koch 'acquired' (maybe One World wasnt the first...). I think it was Reichel Pugh and ( this im a bit unsure of) Ian Murray (before Spirit of Australia) who were the main men in the design team of the defunct syndicate.

Reichel Pugh then went to A3, but suddenly it was Jerome Milgram (one of the greatest technicians in sailing) who was the talked about guy of the syndicate, possibly because of his dynamometer ideas which were the talk of the town? I always thought the hull lines were credited mainly to Reichel Pugh tho. I suspect that if Peterson had been very influential then Koch would have shelled out to keep him on for '95.

Clay Oliver was with the Kiwis in '92, not A3, and with S&S in '87. The design of NZL 32 was rumored to be mainly Laurie Davidsons, whilst NZL 38 was supposedly mainly Petersons. Which boat was chosen for the Cup? Also, TNZ made a big thing about using the Wolfson tank over (and also to verify/correct) CFD techniques so Im not sure how much primary input Clay Oliver would have had. Certainly Davidson publicly hinted time and again that he had no confidence in Olivers ideas (most notably when the double knuckle bow was a CFD reject but tank success, and then when he left TNZ muttering about the member of the design team who had '...never actually designed a successful yacht'. I actually believe that Oliver is a fantastic technical guru, but that he has been unlucky with the state of the art in CFD not being sufficient to model more radical ideas realistically (the hula came close, but didnt quite hit the mark).

Tempering theory with practical knowledge is an idea many of the contributors to this forum have put forward, and was it not Laurie Davidson who had an advert many years ago showing a picture of the designer looking out to sea with the caption "This is the way Laurie Davidson designs yachts"? I certainly like Lauries 'Old School' approach - supposedly the lines for One World were done in a month, and it certainly wasnt slow (didnt DC amongst others think they were among the best of the hulls, but not sufficiently developed in other areas?). His other boats look good too, if not quite as refined as Farr or R-P. But I never could quite agree with Petersons lines (post IOR) - there was always something slightly ungainly about them (anyone seen the new Bavaria Match 38 versus, say, any IMS 600 (not the 40.7!)).

I'd also hazard the opinion that NZL32 was quite different in section to A3, with A3 seeming to be 'harder edged' at the turn of the bilge than NZL32's rounded sections. Certainly both are narrow for their time, but many commentators and some members of TNZ themselves stated the design philosophies were different. I'll need to look out the back issues of Seahorse et al for further details...

It's not my intention with all this to ignite any more slanging matches, but rather that I feel the history of all this, as well as being very interesting, is obviously incomplete and therefore worth discussion. Maybe if anyone has any more historical knowledge they could share that would fill in some of my gaps (especially about the Beach Boys syndicate) then the moderator of this site could put these ideas up as the start of a new Americas Cup Design 'Family History' thread.

In the meantime, how about some design ideas from other people? If anyone wants to put up something from SDN or similar in 3d DXF format (even some 2d lines from one of the free cad packages would do) then I'll loft them and fair them in Rhino and put them up as a render when I have time. Also, does anyone have any details of aspects other than the hull of a 14, e.g. suitable foil sections, construction details, spar development and specifications, sail design? Lets hear some more!!!


Andy

 

[Andy]

oops I meant to add that Clay Oliver was with Tag in '95, not TNZ. He is the CFD specialist we're talking about, no?

Also, Paul B, I like the look of your 'not quite yet a' 14 - any more details/developments? Could you design a similar boat without looking at the lines of existing boats? This might unearth some interesting discussion about the subtleties of a boat which is in the ballpark but different for whatever reasons you hypothesize. Is this 'free but ballpark' thinking?

Yours philosophically,

Andy

 

[Guest]

Beach Boys

The A Cubed designs did have their genesis in the Beach Boys Syndicate. Doug Peterson was one of the founders of the Beach Boys Syndicate. John Reichel was also an integral part of that design effort.

I don't think it was Milgram who was the "technical" hocus pocus of the Cubans. Was it Calderon? I don't recall, but the word is the yacht designers designed the successful boats.

Koch didn't shell out to keep anyone for '95. He ran the old boats with the girls crew. Peterson went to the team that he thought had the best chance to win.

For '95 I wan't referring to Clay Oliver, but rather David Egan. I believe even Davidson admits to 32 and 38 being mostly Doug's effort. I think he was miffed that NZ brought in this American and gave him the nod when LD thought he could do better.

You really don't believe the OW boats were fully designed in a month? I think something will come out now that the Reeves case is back in the NZ courts.

Peterson has done some really cool boats post IOR, but hasn't done a lot of racing stuff. He makes a lot more dough for less effort doing the production boats like the Sun Legende 41 and the new Bavaria.

Doug's 5.5 meter design from '92 dominated the class for almost 10 years. His MORC designs were lighter and faster than the rest (with a higher rating, of course), but still good enough to win. But the real bread and butter for guys like Doug are the big cruising boats, and the AC contracts.

I should add the disclaimer here that I worked for Peterson for a couple of years and some of my observations could possibly be tinted by that. But I don't think so.

 

[Paul B]

Time Out Again?

It appears that if I start a message and then do some other tasks for a while my connection must time out, and when I do post I show up as Guest.

The above message is mine.

 

[Paul B]

Originally posted by Andy
oops I meant to add that Clay Oliver was with Tag in '95, not TNZ. He is the CFD specialist we're talking about, no?

Nope, I was referring to David Egan.

Originally posted by Andy
Also, Paul B, I like the look of your 'not quite yet a' 14 - any more details/developments? Could you design a similar boat without looking at the lines of existing boats? This might unearth some interesting discussion about the subtleties of a boat which is in the ballpark but different for whatever reasons you hypothesize. Is this 'free but ballpark' thinking?

No more development on that "3D Sketch". Could I design a similar boat? Sure, I suppose, but not as well as Bieker or Morrison. That's why I don't do it for a living. Also, I don't sail skiffs, and as someone else mentioned you really have to be there and do it to know what needs the next tweak.

As I mentioned, I worked for Peterson and know most of the successful designers in SoCal. That experience let me know that I lack the genius required to really be at the top of the game. But it remains a fun hobby.

By the way Andy, my parents are both from Glasgow.

 

[Another Guest]

Someone - I think Andy - asked about hydrofoil shapes. I know that some of the early ones were made from sailboard fins and they worked OK, which may indicate that they don't need any special section or plan form.

Re position of foils; look at the last sentence from my notes from a chat with Grant Geddes ('99 world champ) on foiler v non foiler I 14s.

“The dynamics of the foils are really different upwind. On my old (pre-foil) boat, I’d stand about one metre (3 feet) from the transom going upwind. Now, my back foot is 300 mm (1 foot) from the transom, and my crew is in my old position.”

“When you’re going quite quick and at the back of the boat, the whole boat seems to lift up, and the bow lifts over waves really easily, so you get two advantages. And because it’s one foot off the back of the boat, the foils stops hobby horsing upwind and downwind.”

 

[Phil S]

Most Moth T foils on rudders I have examined have a symetrical section. Few have any adjustment and operate at very small angles of attack until the bow starts to go down. Those who sailed moths when they were introduced say they had a very significant damping affect on hobby horsing. Now every moth has one.

Rohan Veal's article on his foiling moth (maskerading as a report on the Moth worlds in France) published in Australian Sailing and Seahorse, provides some insight into lifting foil design. He has given away what was probably John Illets (Designer and builder of the boat) secret foils section. The foil on the bottom of the centreboard which does most of the lifting is stated as NACA 63412. It has a trimmable trailing edge flap which would change the back of the section at different speeds.

The boat only won two out of 10 races on its foils and that was the same as Brett Burvill did 3 years ago, but the Moth class populace seems to be about equally split as to whether airbourne foiling is really good for the class. If development continues and a foiler eventually wins a major event there may well be a major exodus by those against.

That event would also make most of the discussion here about hull shape almost totally irrelevant.

 

[Doug Lord]

Foiling dinghies

Seems to me that there is a wide open opportunity to create a fast design in the Moth class(less so now in the I14 class) that uses a retractable main foil to allow excellent performance in light and heavy air. I personally hope the Moth class stays the course so evolution can produce the ideal fast boat: good in lite air and full on flying when the wind blows!
I believe this represents an exciting vision for the future-I'm working on an rc test model right now that uses a canting keel and just two foils-as test for a larger retractable foil version....

 

[mad engineer]

I'm not sure it would make the discussions irrelevant, but certainly it might move things in a different direction.

To my way of thinking, if you are building a foiler then you are separating static and dynamic lift, and with the boat flying you are narrowing the operating range of the hull. At face value this would simplify the hull design process.

I've only seen the foilers on the videos on the Moth site, and it is difficult to see much on short clips. I guess the critical factor in the hull design is the lift off speed. Up to the point of flying, the hull needs to be very efficient, beyond that point it is largely irrelevant. If the lift-off speed is at or around hull speed (about 4kts for a Moth), then we have a pure displacement hull, minimum wet surface, plenty of rocker. But if you only get foil borne at 8kts of hull speed, then the hull design in the "forced mode" is still critical and hull shapes may not be that different from the current state of the art - flatter rocker profile certainly, but you could probably still go for minimum wet area as you don't need the flat bottom to provide any lift.