Rudder foils for Mini Transat

[Polarity]

Hi all

This is for a good friend of mine who is brave/foolish enough to race one of those 6.5m (21ft) Mini rocketships across the Atlantic.

His boat is a Proto(type) Mini designed by Finot in 99 and he wants to replace the transom hung rudders and dagger board with lighter and possibly more efficient versions. I'm helping him out by measuring the rudders for him (he's a few 0000 miles away at the moment), he has tried to get the foil spec from Finot but to no luck.

Q. best points to measure to identify the foil profile ? (he's looking at having them made where he is and bringing them back)

Q. Is it likely to be worth developing a new profile (developments in the last 7 years?) and if so what numbers need to be considered.

Any help greatfully received !

Cheers !

Paul
www.express40.com

[Tad]

Paul,

For up-to-date info contact http://www.philsfoils.com

He sometimes posts here and may be along.

Tad

[tspeer]

Originally Posted by Polarity

...
Q. best points to measure to identify the foil profile ? (he's looking at having them made where he is and bringing them back)

As many as possible, especially near the leading edge.

Q. Is it likely to be worth developing a new profile (developments in the last 7 years?) and if so what numbers need to be considered

Possibly. You need to define what the requirements are (lift range, Reynolds number range, structural thickness, etc.) and see how the current section stacks up. Then you can use XFOIL to revise the design to better meet the requirements.

[Phil Locker]

Originally Posted by Tad

Paul,

For up-to-date info contact http://www.philsfoils.com

He sometimes posts here and may be along.

Tad

Thank's Tad. But I promote myself as a fabricator, not a
designer. If someone's looking for cutting edge in foil design
they're best to go to someone specializing there.

As for the Mini, I've done a few sets and none of the designs
I've seen are doing anything unusual with foil sections or
mechanical design. Being a Proto and not a Series, its
likely built quite lightly anyhow. Weigh them and report in...
it might be possible to shave some weight while remaining
strong enough. Also look for weight savings in the tiller,
cassettes (if it uses them) and other associated parts.

Cheers
Phil

[quicksail]

On any raceboat wetted surface is the enemy. Look at reducing the wetted surface by developing lifting rudders and design the foils to have minimum surface area while maintaining enough stirrability of the boat. I find the profiles have changed over the last ten years, moving from eleptical shapes to a more skewed tip. This helps centralize the vortex of the foil to the very tip. Also, with transom hung rudders, consider that lift is reduced in the top quarter of the foil due to surface effects. You may want to reduce surface area in this part of the foil and add it somewhere else where it is more useful.

I like the 00 section as it can take reasonably high angles of attack before stalling, which is good for a rudder. I hope some of this helps. Weight reduction is also very important and should always be considered to when building raceboats.

Cheers