ISAF vs KITE Sailing

[Paul B]

Originally Posted by CT 249

"On the same reach angle in the same wind, Nicorette going twice the windspeed will have the AWA full forward, Code Zero strapped"

And if it's the previous (1999) Nicorette with the original rudder in, the driver will be alternating between going "aaahhhh this is such fun, what a well balanced helm" and then "oooooooooooooohhhh shit" as the rudder loads and unloads as she speeds up and down swells. Never felt anything like that foil for shifting CLR back and forth but I only drove her once.

Well, now we are quite a bit off the original topic of ISAF and Kites.

I need to ask, what was the problem with that rudder and setup? Too much counterbalance? Not enough? Was there something about that foil shape that was causing stall at normal operating angles?

Are you sure it was CLR shifting and not CE?

I'm sure the crew was full pro, so I doubt it was the normal problem of overstrapping the kite on the way down the wave (as the AWA shifts forward), then not enough ease as you decelerate at the bottom (as the AWA shifts back).

By the way, have you ever seen a boat tack through 50 degrees? I know the 18s tack through a pretty narrow angle, I'm guessing in the 65-70 degree range?

[Skippy]

Speaking of 50-degree tacks, is that really where you get max VMG even in an IACC boat? If you fall off just a little, it does wonders for the AWA even at higher speed given equal VMG.

[daveculp]

Originally Posted by Skippy

Speaking of 50-degree tacks, is that really where you get max VMG even in an IACC boat? If you fall off just a little, it does wonders for the AWA even at higher speed given equal VMG.

Absolutely not, Skippy. IACC boats can tack through 50-60 degrees and they can also make good better than the wind speed dead to windward, but NOT at the same time. It's interesting that the "mathematical" arguments here work so quickly to put words into one's mouth, but the facts are (obviously) somewhat different.

FWIW, it is possible to predict the best course for VMG, up or downwind for a given set of circumstances. I don't have my Marchaj with me at the moment, but it's a simple formula; if you have accurate drag angle data on both the hull/keel and the rig. ("drag angle" is the arc tan of the L/D of either the rig or the hull/keel--it is easier to measure than L/D, especially with models or towing full size hulls). Drag angles of both are needed to predict optimal course. The "hook" is that these angles change significantly for most monohull sailboats as their speed increases, due to hull speed limitations on non-planing, non-multihulls. OTOH, understanding the formula--and how it's derived--will help you to better your VMG work in any boat--it can improve your "intuition" at the helm. See Aero-hydrodynamics of Sailing, by Marchaj.

Dave

[usa2]

we should make an IACC thread, cuz if you read the title of this one its something to do with kites....

[SailDesign]

Originally Posted by Paul B

I'm sure the crew was full pro, so I doubt it was the normal problem of overstrapping the kite on the way down the wave

Nicorette uses a KITE? Well, that means we are right on topic, then

Steve "who WAS there..."

[usa2]

ya, but Nicorette's "kite" hasnt been banned by the ISAF...yet

[CT 249]

Originally Posted by Paul B

Well, now we are quite a bit off the original topic of ISAF and Kites.

I need to ask, what was the problem with that rudder and setup? Too much counterbalance? Not enough? Was there something about that foil shape that was causing stall at normal operating angles?

Are you sure it was CLR shifting and not CE?

I'm sure the crew was full pro, so I doubt it was the normal problem of overstrapping the kite on the way down the wave (as the AWA shifts forward), then not enough ease as you decelerate at the bottom (as the AWA shifts back).

By the way, have you ever seen a boat tack through 50 degrees? I know the 18s tack through a pretty narrow angle, I'm guessing in the 65-70 degree range?

Ummm, it was about 4 years ago and I only sailed her a coupla times. I think it was a function of the foil shape for some reason reacting wildly to different speeds, in terms of the Centre of Lift (IIRC) of that particular appendage making the rudder go more or less balanced as the boat accelerated down swells or slowed up the back of them. It was wrong of me to say it was the CLR.

Why it did that, I don't know; isn't that a problem with laminar flow sections or something? AFAIK it is a recognised effect that becomes worse with foils of certain sections; I know of cruising cats with long keels that wander terribly because the C of L or whatever it is wanders up and down a certain % of the foil as speed changes, and when the boat is quite fast down waves and has a long keel the CLR can be moving several feet in a few seconds.

The Nicorette guys had built a new rudder but put the old one back in for farting around. I think I asked them about the reason for the change and that's where my vague memory of the cause comes from. You could definitely feel it on the helm.

It wasn't stalling, it wasn't crew problems. A mate had the same problem with a Jutson rudder on his 10m tri.

I haven't seen a boat go through 50, but I haven't been on an IACC boat and the only one sailing around here is a dog. Dunno about the 18s tacking angles, sorry. It's fairly "normal" from memory.

PS to all; sorry "kite" was just used as Aussie sailing slang term for spinnaker.

I may have a kite sail on a proa in two days time, should be fun.