Wave-Piercing, Pitching damping or marketing?

Thanks Tom. I followed the "foils,no foils" debate on the Aussie A class forum. Unfortunately, most of that debate(something like 6 of 8 pages) was lost a year or so ago. I don't remember ever reading how long that foils had been legal and am not sure it was ever mentioned.
I'll do the research you suggested.
-------------
EDIT: In doing research tonight I discovered this head on pix of Glen Ashby's(former world champion at least twice and 2nd in this regatta) boat showing a clearly canted in foil-the only purpose for which I would assume is to develop a small amount of vertical lift with angle of heel. Scroll down -you'll see it . There is a question and comment there as well that seems to say the matter is undecided -whether or not this violates the "no hydrofoils" rule. Anybody know anything more up to date?
Catsailor.com: Pete Melvin Wins the A-CLass Worlds
Address:http://www.catsailor.com/forums/show...b=5&o=&fpart=1
---------------
EDIT #2: ANSWER
Again, thanks Tom-its been very interesting learning about this! I found the answer here where you suggested:
hydrofoil rule 2006
Address:http://www.a-cat.org/id93.htm Changed:4:09 PM on Monday, January 29, 2007
Apparently, the inward cant angle depends on the length to beam ratio of the hulls and the length of the board. Just for the heck of it I tried the rule on a set of hulls with an 18/1 length to beam ratio and came up with a max inward cant angle of about 15° on a 3' board and 11° on a 4' board.

[Triman]

Thanks RG for your answer; as I can see, you are developing a very complete concept; I would very pleased to train together and test the boats! Unfortunately is Switzerland a bit to far from US. If you have new informations (and pics) about your very nice boat, please post it. I'm now at the moment at the swiss Champ. in Silvaplana, near St. Moritz (very cold, rainy and shifty conditions!), so you can see every kind of boats from the marstroms to the Niels Bunkenburgs Nikita with round daggerboards, through Flyer mkII and Scheurers S5. About daggerboards, as i can see from the pictures, yours are straight, whilst trend is to have cantered daggerboards; that's of course not really to promote lift (it is always a simmetric profile), but to have it orthogonal to the water when both hulls are in the water (cantered hulls) and to have a little drift in the gusts. What are your reflection about that?
About hydrofoils on A-Cat: the international Ass. (IACA) promoted 2 years ago a task force to decide about that; they can't accomplish the task because the first problem couldn't be solved: to define what an hydrofoil is (it is much more complicate as what it seems!!). So we have at the moment a regulation that you can find on the IACA site (http://www.a-cat.org/), wich says that foils must be simmetric, and they can't not exceed boat BWL and can't be more near than 1,50 m; that is a limitation to cantered boards, and gerally, to hydrofoils.

[Retired Geek]

Triman....personally I don't see that canting the boards provides any benefit and probably increases the hull pitch rate a bit when you look at all the forces in play when sailing in a chop. Also don't see any good reason to allow drift in the gusts if your able to turn that into boat speed.
RG

[bobdarbygso]

RG

I'm curious how you approach the design displacement of a vessel such as an A-Cat given that the cat weighs 75kg with a moveable ballast (crew) of 75kg.

With 5 to 6 degrees of heel needed to fly one hull the rig must also be generating about 10kg of downforce so the lee hull is going to displace about 160kg versus 75kg with both hulls in the water in light air. In rough terms, can one assume that the one hull flying waterline corresponds with the extreme point of the bow and the bottom of the transom for the LR2?

Thanks
Bob

[MalSmith]

Originally Posted by bobdarbygso

RG

With 5 to 6 degrees of heel needed to fly one hull the rig must also be generating about 10kg of downforce so the lee hull is going to displace about 160kg versus 75kg with both hulls in the water in light air.

Bob

The downforce from the rig can be ignored because it is counteracted by the upforce from the centreboards etc which are also heeled.

Mal.

[bobdarbygso]

At low angles of heel the lee board is vertical and the other is canted at about 10 to 12 degrees so that may well be the case but it doesn't substantially change the problem described; a change in loading from 75kg to 150kg or perhaps 175kg in the case of heavy crew.

This raises one other question; how effective is the windward board when the hull is flying? Is ventilation (perhaps wrong term) of the board a problem?

Thx,
Bob

[Retired Geek]

Bob,
I you go back thru the thread to the first pic's of the boat, DWL is where the hulls were joined...which is the extreme nose of the bow with the transom in the water a bit. In reality, with the boat trucking along the hull rides slightly higher than this. When on both hulls, both the bow and the transom are out. As for the weather boards, the tip chord is so small that they don't appear to have any problems and Ian tells me that he can't tell the difference between having them in or out of the water, although I'm sure that they still produce some drag.

[bobdarbygso]

RG

Thx
Bob

[kach22i]

Originally Posted by MalSmith

Another practical, but more obscure example of wave piercing hull forms can be found in the amas of traditional Polynesian proas. These are usually made from solid logs with a specific gravity of about 0.5, which gives a 50/50 volume distribution above and below the waterline. It has been speculated that one advantage of this, apart from simplicity of the solid log construction, is that the resulting wave piercing nature of the ama reduces torsional loads on the aka structure by minimising movement due to independent pitching of the ama, which would wear out the structure more quickly.

It makes sense that for good wave piercing properties the volume distribution should be about 50/50 above and below the waterline, since the upward buoyant force of the fully immersed hull section will then be equal to the downward weight force when the section is fully airborne. Our findings from tank testing that we got better performance with less than 50% volume above the waterline in the bow region were probably due to the practical restriction that we had to have significantly more that 50% volume above the waterline from about 20% LWL aft of the stem.

One interesting observation from the tank tests was that for a conventional bow, the average running trim in waves was a few degrees bow up, whereas with the wave piercing bow, the average running trim was closer to zero. From this one could speculate that the improved average running trim may result in lower average hull resistance.

Mal.

Great stuff, I enjoyed the perspective.

[Retired Geek]

Originally Posted by MalSmith

It makes sense that for good wave piercing properties the volume distribution should be about 50/50 above and below the waterline, since the upward buoyant force of the fully immersed hull section will then be equal to the downward weight force when the section is fully airborne. Our findings from tank testing that we got better performance with less than 50% volume above the waterline in the bow region were probably due to the practical restriction that we had to have significantly more that 50% volume above the waterline from about 20% LWL aft of the stem.

Not that we design according to such ratios but it peeked my interest to see how our design compared... on total volume ours is 36.1% below DWL, Flyer is 30.7% and our hull has only 84.9% of a Flyers volume.

Originally Posted by MalSmith

I think that an effective wave piercing bow could be defined in very broad terms as a bow shape for which the enclosed volume above the waterline is less than the volume below the waterline, for at least 20% of the waterline length aft of the stem.Mal.

At 150mm aft of the bow we are almost the same at 36.3% and Flyer is much lower at 25.36% while our section area is at 88.1% of flyers. Waterplane for the first 150mm is 115.7% of section area for Flyer while ours is at 222.8%.

Section area at the transom is also interesting, we are at 8.1% and Flyer is at 22.5%, while our section area is just 29.5% of Flyers.

With all that said I doubt you can read much into or infer much from these numbers...ultimately its the forces in play that count...the trick is being able to calculate them.
RG

[Retired Geek]

Has been a while coming, but we finally got some GPS data off the boat, at times the wind was 10-12 knots and very shifty, but the average was 8.2 with the lows around 3 knots and the highest gust at 14.8 knots. Not a particularly good day for results but it will give you an idea of whats possible. (see the polar)

[Retired Geek]

forgot to mention the outer dashed and shaded area represent max speeds and vmg's and the inner darker shaded area and dashed lines represent averages over 500m of distance.
RG

[Retired Geek]

A couple more screen caps from the GPS trace from today, set to 101m averages
RG

[Daniel Gut]

I sail an A cat (Scheurer G5) weigh 90 kg and cast a fair sized shadow. Wind resistance increases exponentially with increased wind velocity, I believe there is substantial room for improvement in the aerodynamic characteristics of the large lump of ballast at the business end of the trapeze wire, who in 15 knots of wind probably has more wind resistance than his boat. Keeping the boat flat when the breeze gets up helps keep that lumpy ballast in the turbulent wind affected by the water and waves, once you get higher up, you the windward hull daggerboards and rudder get into the stronger more laminate air and that must be slow.

Is the LR2 entered at the worlds in the US?

@ Triman; Were you a spectator or sailing in Silvaplana?

Regards from Zurich
Daniel
SUI 208

[Retired Geek]

Hi Daniel,
your right about the lump on the end of the trapeze, and their may be some sort of advantage to clothing similar to what downhill skiers use, but I doubt that it will change your uphill VMG that much. The other alternative would be an aerodynamic "body bag" but I'd guess that would be a pain to wear and quite dangerous if you fell in the water. Attached section is a midships slice thru a couple of older designs at normal AWA's uphill, this I think can provide some advantages, but I know that it doesn't produce enough of a gain to change the VMG's by more than a few 10ths of a knot.

Right now we will definitely have 2 LR2's at the worlds, possibly 3.
RG