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tuning 5.6 sail for max power to replace 7.5 in light wind
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spennie



Joined: 13 Oct 1995
Posts: 699
Location: Thousand Oaks, CA

PostPosted: Fri Apr 05, 2013 10:43 am    Post subject: Reply with quote

ISOBARS: Did you really say this?

"First and foremost, For any given size, a race sail has LESS low end (light wind) power than any other kind of sail."

Your contention is that a sail that holds a perfect foil shape when underpowered has less power than one that goes flat? Really?

I expect better from you!

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adywind



Joined: 08 Jan 2012
Posts: 201

PostPosted: Fri Apr 05, 2013 11:02 am    Post subject: Reply with quote

spennie wrote:
ISOBARS: Did you really say this?

"First and foremost, For any given size, a race sail has LESS low end (light wind) power than any other kind of sail."

Your contention is that a sail that holds a perfect foil shape when underpowered has less power than one that goes flat? Really?

I expect better from you!

I had the same feeling about 2 and 3 cammed sails and that's why I got rid of them. Don't miss them at all.
For the OP a sail suggestion I think will suit him good. The 7.5 size especially. Check how light it is-stripped down to only what realy matters:
http://www.ezzy.com/sails/2013-sails/2013-ezzy-legacy/
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zirtaeb



Joined: 03 Jul 2009
Posts: 2146

PostPosted: Fri Apr 05, 2013 11:30 am    Post subject: Reply with quote

As said, 5 cam is mid to late '90's.
Those sails were designed for low end power, not high end control like the newer race sails. For most sailors, wind range would fall somewhere between 17-27, depending on tuning. Took KingKong to downhaul for higher winds, as much as NorthIQ's and Prismas, their contemporaries.
DEEP draft, the twist only above the top 2 battens.
Don't speculate. Either say nothing, or have lived thru those sails and know how they perform.
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zirtaeb



Joined: 03 Jul 2009
Posts: 2146

PostPosted: Fri Apr 05, 2013 11:32 am    Post subject: Reply with quote

I"m somewhat surprised Mike Isobars didn't think this thru.
Hi booms, means base forwards, so you can hook in once planing. Base forwards gives you longer board to slog onto a plane, while high booms allows you to pull DOWNWARD on the booms, unweighting your feet, placing weight more forwards at the mast track, so you plane earlier.
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adywind



Joined: 08 Jan 2012
Posts: 201

PostPosted: Fri Apr 05, 2013 2:04 pm    Post subject: Reply with quote

zirtaeb wrote:
I"m somewhat surprised Mike Isobars didn't think this thru.
Hi booms, means base forwards.

Not nesessery unless you have control problems from lifting nose. Mast foot back + boom up+ foot straps back and out= less wetted surface =higher speed=earlier planing maybe?=better upwind=less control
I go this way in light wind and I like it best.
I don't know how it looks like on a flat like a cargo container long board, but on a short board the rocker line starts to curve just in front of the front footstraps. The faster you get the board on its flatter back and stop it plowing the earlier it will plane. The higher boom helps somehow in achieving this.
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isobars



Joined: 12 Dec 1999
Posts: 13292

PostPosted: Fri Apr 05, 2013 4:03 pm    Post subject: Reply with quote

spennie wrote:
ISOBARS: Did you really say this?

"First and foremost, For any given size, a race sail has LESS low end (light wind) power than any other kind of sail."

Your contention is that a sail that holds a perfect foil shape when underpowered has less power than one that goes flat? Really?

I expect better from you!

A race foil is flat, because it's optimized for upwind speed and minimal drag for max top reaching speed when fully powered at beam reaching and above. That "perfect shape" is perfect for those conditions, not for broad reaching or light winds (relative to sail size).

For example, when NP came out with a "race sail" in about 1992, they told PWR Magazine to rig their 5.8 (5.7?) race sail for winds which would normally be considered 5.0-5.2. IOW, rig much bigger than normal, because race sails have no guts at the lower end of their performance range because their foil is so flat for the reasons I gave above. In general, deeper foils with longer chord length favor low-end power (i.e., early planing power) at the expense of high-speed drag whereas shallower foils with shorter chord lengths produce less drag for greater top end speed at the expense of early planing power. Musclecar vs turbo 4-banger. Harley vs Kawasaki.

On top of that, not all camless sails automatically "go flat" when "underpowered". Some do, but that's usually reserved for sails the rider wants to luff when surfing swell or waves (and maybe freestyle?). Many other non-race sails maintain plenty of shape underpowered, especially when broad or beam reaching. It depends on their design and intent, not strictly on the lack of cams.

That's just one of many reasons I so strongly believe that no one should saddle himself with a race sail until and unless he has the first-hand experience, skill, and knowledge to know for a fact it's what he needs and wants to achieve his goals. And partly because many experts here have said much the same thing, I remain convinced until otherwise persuaded.
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isobars



Joined: 12 Dec 1999
Posts: 13292

PostPosted: Fri Apr 05, 2013 4:06 pm    Post subject: Reply with quote

zirtaeb wrote:
I"m somewhat surprised Mike Isobars didn't think this thru.
Hi booms, means base forwards, so you can hook in once planing. Base forwards gives you longer board to slog onto a plane, while high booms allows you to pull DOWNWARD on the booms, unweighting your feet, placing weight more forwards at the mast track, so you plane earlier.

The criteria you gave and I discussed was reduced wetted length, not earlier planing. Now you're saying the same thing I said.


Last edited by isobars on Fri Apr 05, 2013 8:00 pm; edited 1 time in total
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paulf.



Joined: 21 Mar 1996
Posts: 303

PostPosted: Fri Apr 05, 2013 7:08 pm    Post subject: Reply with quote

to give iso some cred, there was a generation of sailworks race sails that were so flat, tall and short boomed that i would rig the 8 when people were on 6.5s, and the 6.5 when the 5.6s came out. to stir the pot, i heard bruce peterson once recommend lowering the boom in light winds, so that the sailor had less leverege to choke off the power in the sail, and go up when overpowered for more control.
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adywind



Joined: 08 Jan 2012
Posts: 201

PostPosted: Fri Apr 05, 2013 7:33 pm    Post subject: Reply with quote

paulf. wrote:
to stir the pot, i heard bruce peterson once recommend lowering the boom in light winds, so that the sailor had less leverege to choke off the power in the sail, and go up when overpowered for more control.

I think I get his point. He probably meant that when your boom is up you will be leaning the rig too much back/closing the gap/ and chocking its power instead of keeping it more upright in light wind. Well, I think I'm correcting this problem with placing the mast foot farther back~130cm from the tail end and using long harness lines 30" and placing them back on the boom 1/3. But I'm realy speculating here about what he meant by that.
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paulf.



Joined: 21 Mar 1996
Posts: 303

PostPosted: Fri Apr 05, 2013 7:49 pm    Post subject: Reply with quote

that is exactly how he described it. get the rig upright and get away from it.
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