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Does low boom equates to wrong sail design
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isobars



Joined: 12 Dec 1999
Posts: 14322

PostPosted: Sat Mar 29, 2014 12:00 pm    Post subject: Reply with quote

My luff sleeves lay snugly against the mast when fully downhauled.
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manuel



Joined: 08 Oct 2007
Posts: 149

PostPosted: Thu Apr 03, 2014 11:08 pm    Post subject: Reply with quote

Wow so surprised the sails would work being so far out of range. (well apparently they are not!)

So basically we are saying that the boom height doesn't impact the mast's flex curve and therefore sail twist. Or if it does we can't feel it.

However there's an increased force of leverage from the upper part of the sail (above the boom) when boom is lower, no?

When we know how precise our settings can be, how could adjusting this one by a range so great be of little influence?
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swchandler



Joined: 08 Nov 1993
Posts: 5893

PostPosted: Fri Apr 04, 2014 3:08 am    Post subject: Reply with quote

"So basically we are saying that the boom height doesn't impact the mast's flex curve and therefore sail twist. Or if it does we can't feel it."


Speaking for myself, I can't comment whether boom height affects mast flex or sail twist. However, if my boom is too low, my left knee starts bothering while I'm sailing. By raising the boom to the appropriate height that I like, no problem at all with my left knee. Experimentation is your best guide in what's right for you. Also, it should be remembered that we all are a bit different in what we like. There is no single answer for everyone.
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rlemmens



Joined: 09 Feb 2008
Posts: 189

PostPosted: Fri Apr 04, 2014 11:44 am    Post subject: Reply with quote

I used to be a advocate for super high booms. For freestyle it works great and seems to get planing earlier and planing out if tricks easier. That being said, if its windy, or if you're wavesailing, lowering the boom a bit gives more control. Also, since your knees are constantly bending while wave riding, it makes sense to put your boom in a lower position.
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PeconicPuffin



Joined: 07 Jun 2004
Posts: 1221

PostPosted: Sat Apr 05, 2014 8:18 am    Post subject: Reply with quote

What I think you are missing is that your body is part of the rigging. The sail is not something independent of you that you use. If the boom height is not dialed in to your body's geometry "the rig" is not optimally set. And you'll notice that for a sail with 18" of luff cutout, there isn't also 18" worth of clew attachments. The sail and sailor need to be balanced, as do the sail, sailor and board.

In terms of things to be concerned with on one's sail, the odds are overwhelmingly highest that you don't have enough downhaul.

manuel wrote:
Wow so surprised the sails would work being so far out of range. (well apparently they are not!)

So basically we are saying that the boom height doesn't impact the mast's flex curve and therefore sail twist. Or if it does we can't feel it.

However there's an increased force of leverage from the upper part of the sail (above the boom) when boom is lower, no?

When we know how precise our settings can be, how could adjusting this one by a range so great be of little influence?

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Michael
http://www.peconicpuffin.com
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isobars



Joined: 12 Dec 1999
Posts: 14322

PostPosted: Sat Apr 05, 2014 4:52 pm    Post subject: Reply with quote

manuel wrote:
Wow so surprised the sails would work being so far out of range. (well apparently they are not!)

So basically we are saying that the boom height doesn't impact the mast's flex curve and therefore sail twist. Or if it does we can't feel it.

However there's an increased force of leverage from the upper part of the sail (above the boom) when boom is lower, no?

When we know how precise our settings can be, how could adjusting this one by a range so great be of little influence?

My boom height as rigged isn't "out of range"; it's just a bit lower than many people prefer, but still above what some experts use. That makes sense due to my average height of 5'9", my short legs, my preferred harness line length, and most notably my sailing style. I have my cutouts extended lower just to make rigging easier since there's no downside to it.

I'm not (deliberately) implying that moving the boom height away from some theoretical optimum doesn't change the rig's performance characteristics. I am implying, though, that the obvious, in-my-face, moment-to-moment ergonomics trumps some elusive hypothetical sail performance perfection for me. I've extensively experimented with hundreds of sails, a wide range of boom heights and harness line lengths, and a variety of B&J sailing styles, and concluded that I notice ergonomic human factor issues long before I notice rig performance issues when tweaking boom heights. IMO, for me, rig performance changes more obviously from tweaking outhaul tension than it does from tweaking boom height. Tweaking boom height, however, makes BIG differences in my moment-by-moment interaction with the boom.

By definition, the rig's COE height directly affects the sail's pitching moment leverage for any specific boom height. With most sails I've ever used, the COE height is near boom height or maybe even lower, so leverage isn't something I worry about. The only times I notice a sail's leverage over me (not counting operator error exiting a bad jibe or getting creamed by a huge gust when slogging a sinker), is when the COE is high because I have insufficient downhaul or am riding a Sailworks Hucker tuned for max jumping altitude and hang time. OTOH, running my booms a bit below some societal norm gives me MANY ergonomic advantages.

Modest boom height variations probably affect sail characteristics out at some distant decimal point, but a) who's to say what's perfect, b) define "perfect", c) the only person I'm trying to outperform is myself, circa yesterday, and d) any very good sail is inherently better than I'll ever be anyway.
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gary.home



Joined: 16 Feb 2014
Posts: 7

PostPosted: Wed Apr 09, 2014 6:41 am    Post subject: Reply with quote

long ago,... my first board was a bic dufour wing with soft sail.
as I remember, boom height affects leech vs foot tension as the sail loads. I expect that fully battened, non-stretch sails hide this effect (but I strive to use 'near' middle of the cutout in hopes of not hindering the sail design from working as intended)

dunno, but I expect that if there is no combination of boom height (using mfr's cutout), harness line length, and mast base position that works, the sail/board is not compatible.
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isobars



Joined: 12 Dec 1999
Posts: 14322

PostPosted: Wed Apr 09, 2014 9:07 am    Post subject: Reply with quote

No room for personal preferences?
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westender



Joined: 02 Aug 2007
Posts: 634
Location: Portland / Gorge

PostPosted: Wed Apr 09, 2014 10:46 am    Post subject: Reply with quote

A special place to mount the boom for the sail to work right???

Maybe it's different now but didn't it used to be that they would prototype a sail in one size and make it bigger or smaller from the design of one sail?

Testing every sail to determine where the center of the cutout would be because that's where the sail will handle best?? BS.

I can have a fun session even if I'm on the wrong size sail, violating the manufacturers suggestions for wind range.

Set your boom to a height that gives you the most control and let er rip.
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isobars



Joined: 12 Dec 1999
Posts: 14322

PostPosted: Wed Apr 09, 2014 12:23 pm    Post subject: Reply with quote

It's beginning to sound like so many other big debates over small issues, IMO.
Fin size: Some experts (e.g., Robby Naish) prefer the biggest fin that still turns well, while others prefer the smallest fin that doesn't spin out.

Harness Line length: Some experts go much longer, some much shorter, than I prefer.

Mast foot placement: Some (Robby again) pick a spot and don't move it with sail size, others move it fore and aft depending on sail size.

Would you believe some people prefer wave sailing, while others prefer freestyle, racing, speed records, camping on longboards ... crap, even KITING?

Single-bolt mast feet: how detrimental is its offset when tightened?

Slotted fins: I've seen Robby use them.

Sinkers?

Helmets?

Sail colors?

Boom shape?

Drysuit material?
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