gybing center boards

[Paul B]

Originally Posted by Gary Baigent

He said the system worked well but later it was outlawed by IOR so he didn't pursue it any further.

It was not outlawed under the IOR. As I mentioned earlier, a gybeing keel was used during the 1984 OTC.

Using a gybeing keel did incur a MAF penalty. IIRC it was something on the order of 1% per appendage.

[philSweet]

There seems to be a consensus forming that any benefit is utterly and entirely due to drag phenomena, with the proviso that some other stuff like VCR is bound to get affected. Another interesting effect is that, as the hull is rotated (and sails retrimmed), the heeling force will decrease and the pitching force will be more nose down. The first is a rather small effect, but would work to offset the increase in heeling moment arm caused by the lower VCR. The second one might well be an issue in a multihull. Although it would be less than when reaching under similar conditions. But the "death zone" might shift a bit.

The discussion about flopping it the other way when headed down wind has me completely baffled. There is no difference downwind. It's still all about drag. Meaning lift has nothing to do with it. We still want to go as fast as possible. And the faster we can go, the higher downwind we will want to point, not deeper.

[warwick]

Possibly for sailing down wind what is meant by heading down to obtain more VMG.
Some one posted a thread with the speed vectors compared to VMG, where you may be able to find the cross over point.

[Gary Baigent]

Quoting philSweet -
"And the faster we can go, the higher downwind we will want to point, not deeper."

Maybe you should rethink (give it 15 seconds) or rephrase that statement.

[warwick]

Gary, by faster do you mean to your destination rather than boat seed through the water as referred to by PhilSweet? in terms of VMG does it apply to direction or speed.

[philSweet]

Gary,

If boat A is doing 0.8 (true) windspeed and is at its max downwind VMG heading and boat B is doing 1.2 wind speed and is at its max VMG heading, which is sailing deeper. (Yup, that's all you need to know to answer the question if the boats are at all comparable). Deeper meaning relative to true wind (which is probably where we are looking at things differently)

You don't need two different boats, just look at any polar and compare the best downwind angle as wind speed increases. Boat speed as a fraction of windspeed will decrease. And you will be obliged to sail .......

[Gary Baigent]

Warwick, of course, yes, first boat to the bottom mark means sailing as low as you can at the greatest speed you can achieve ... and maybe, not saying it is true, never tried it, (never had a twin asymmetric boards monohull and this is probably just a silly theory) but if you could use the windward asymmetric foil to move you lower yet still retain the same speed as the other boats (who have their leeward foils down as per normal, windward one up, which continually lifts them higher, especially during gust acceleration) ... then you will be first to mark. But you have to consider drag and also ventilation if the boat heals during gusts.

[HASYB]

silly theory part whatever.
About/around the above statements; it probably be double dutch but I give it a try anyway.
If you are on a broad reach there can be situations that the sails actually overpower/overcome the forces of the hull going to leeward and are propelling/driving the hull to windward. (eating their way into the wind)
In that situation one can lower the windward board and gain going (more) to lee, if that's what you want.

Cheers,

[philSweet]

If you are on a broad reach there can be situations that the sails actually overpower/overcome the forces of the hull going to leeward and are propelling/driving the hull to windward. (eating their way into the wind)

It's a good point and one I hadn't thought about. The (wrong) board would keep the hull aligned with the course and perhaps reduce drag. But that is never the fastest point of sail and It would only happen on fairly slow boats that could get their sails positioned to do that.

edit: I guess if you can surf for minutes at a time, that would be another situation where this could come about.

[HASYB]

Originally Posted by philSweet

It's a good point and one I hadn't thought about. The (wrong) board would keep the hull aligned with the course and perhaps reduce drag. But that is never the fastest point of sail and It would only happen on fairly slow boats that could get their sails positioned to do that.

Well, I never thought about it either, just experienced it.
Let me reassure that you are faster than similar vessels on the same course.
If you experience the phenomena the sails are very efficiently providing lift.
Further I don't think there are wrong boards, just use the one that is most relevant.
Sailing isn't just science, there are just to many variables to consider to it being static. Sometimes even magic takes part.

Cheers,

[philSweet]

I was being silly when I called it the "wrong" board. I didn't feel like spelling "counterintuitive" before my coffee. We should probably come up with a name for this. Wallying is already taken. Wilburing, maybe? I don't much care for "negative leeway".

[HASYB]

yeah, I'm also feeling sorry for being pedant.

cheers,

[Gary Baigent]

How about "positive leeway?"
It is lee-bowing in reverse. All kayakers know this. Is a basic. The difference aboard your twin foiled mono is that your "wrong" asymmetric is taking you to leeward, yet the rig is breathing properly and you're sailing at the same speed as the opposition and not rounding up in gusts. This is just pure conjecture. Need to ask the Open 60 and VO70 crews whether they have ever tried it out.

[Corley]

Heres the scanned extract from Yachting World it doesn't go into any further detail in the article.

[Doug Lord]

Originally Posted by Corley

Heres the scanned extract from Yachting World it doesn't go into any further detail in the article.

=========
I wish there was more on it but thanks very much! There is the theoretical discussion then there is the proven practical application as shown by Banque Populaire V.