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How important are smooth foils

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KnightMare View Drop Down
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Post Options Post Options   Quote KnightMare Quote  Post ReplyReply Direct Link To This Post Topic: How important are smooth foils
    Posted: 11 Mar 05 at 10:33pm
Yeah so annoying, even more annoying when that lake is covered in it. (our 200 open ) soooo horrible.
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I luv Wight View Drop Down
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Post Options Post Options   Quote I luv Wight Quote  Post ReplyReply Direct Link To This Post Posted: 11 Mar 05 at 9:31pm
And if you've got crap lumpy foils - you'll never know how fast you could be going.
But this also may partly explain boat speed difference between the ends of the fleet.
If you have nice foils you can tell when they are not working right ( ie weed!) but the problem in a fleet is deciding whether to stop and clear the weed, or continue at a slower speed without stopping.
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sailor.jon View Drop Down
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Post Options Post Options   Quote sailor.jon Quote  Post ReplyReply Direct Link To This Post Posted: 11 Mar 05 at 9:12am
it must have been annoying for the sailor in the vende globe knowing they had large amounts of kelp or what ever tangled around there keels, and not been able to get it off,
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KnightMare View Drop Down
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Post Options Post Options   Quote KnightMare Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 7:51pm
Yeah do have to argee with the weed thing. soo annoying.
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I luv Wight View Drop Down
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Post Options Post Options   Quote I luv Wight Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 7:42pm
It's amazing the slowing effect ( and sideways drift ) when you get even a small bit of weed stuck on the board - this effect is noticeable when it's only weed on a small proportion of the board length.
So smooth surface ( and of couse the right shape ) is essential.
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Dave S View Drop Down
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Post Options Post Options   Quote Dave S Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 4:38pm

Actually, no. A laminar flow section operating in its laminar flow bucket will have lower drag than a similar turbulent-flow section. One way to illustrate this is to think of all the small-scale movements inherent in a turbulent flow. The energy to create these movements must have come from somewhere, and it is extracted from the kinetic energy of the foil as drag.

The big deal with laminar sections is that they can get a lot draggier outside the laminar flow bucket, so there's a real incentive to keep them within it. With a turbulent-flow section you don't get the same step change (even though it may be more efficient than the laminar flow section outside its bucket) so the incremental cost of imperfections is smaller.

Dave

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Phil eltringham View Drop Down
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Post Options Post Options   Quote Phil eltringham Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 4:19pm
regardless of the type of section the board has a smoothe surface will improve performance.  With a turbulent section a smothe surface will promote a stable lamina sub-boundry layer which will be just as efficient as a a lamina section, or even better, see my posts in the Dinghy Yarns section. 
FLAT IS FAST!
Shifts Happen
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Dave S View Drop Down
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Post Options Post Options   Quote Dave S Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 4:03pm
Originally posted by redback

How do the 14s get ashore and keep their foils so good, or do they refinish them each week?

By being very careful! Actually, it probably makes more difference with our laminar-flow sections because there's a tangible benefit to keeping everything laminar, whereas with a turbulent-flow section (which I assume the production boats have) there's much less downside. But a good 14 crew is super-careful with the foils, and is willing to get very wet in order to avoid pranging them. If you sail in with the board half-way up and jump out when the water's still 4 feet deep you should be absolutely fine. At an unfamiliar venue, use other crews who have already jumped out to gauge the depth.

We do also do a fair bit of sailing in Chichester Harbour, where running aground is much more likely and can happen at considerable speed. Options here are to take less risks when travelling at speed or where you believe the bottom may be hard, and to pay close attention to other boats! It is often better to be twin wiring when you hit the bottom because the board only has to absorb the momentum of a relatively light boat (helm and crew go round the forestay). But 14 boards are pretty well-built so even a big crash just tends to wipe out the bottom couple of inches, which are relatively easy to reconstruct (an hour or two's work).

As an aside, the Ovi 1 14 was (some time ago) sold with a stock 49er board, which was pretty useless. Just about everyone threw it in the attic and had a decent one built, and it made a massive difference!

Cheers,

Dave

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KnightMare View Drop Down
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Post Options Post Options   Quote KnightMare Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 11:45am
Yeah, but it is important to look after your boat, all the way through otherwise when you get good you will have to spend lots of moeny/time to improve the boat enough. Just get sailing and learn how things feel and once you can sail by feel you will know if the foils or anything are getting worse as the boat will feel diferent. PS its also good for when you want to think about tactics to be able to sail by feel.
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Adam84 View Drop Down
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Post Options Post Options   Quote Adam84 Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 05 at 11:38am

Yeah sailing skills are definitely the thing to worry about first but once you get your sailing up to scratch, good boat preparation will win you races.

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