Looking for some help with diamond wire tension. I usually solo my H18 Magnum and am 250-265lbs depending on the week. Ideally a tension that will perform well in moderate wind. I try to go out any evenings 10+, and we do get some days 15+ towards the end of the summer.
I have the performance manual, but get a little confused with the whole light wind/heavy crew/heavy wind light crew etc and am not really sure where I fall.
Btw, I've been a Beachcat reader for a few years and really appreciate the knowledge you all provide!
H18 Diamond wire tension?
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Posted: Aug 14, 2018 - 02:31 PM
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Posted: Aug 15, 2018 - 08:10 AM
A good all around tension can be accomplished by measuring 18" from the rotator bolt and adjust tension until both wires can be pushed to touch the mast at 18". Tighter from there to power up, looser to power down -
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Posted: Aug 15, 2018 - 08:46 AM
Thanks 911. So the tighter the wires, the more power? Is this the case irrespective of crew weight and wind speed? -
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Posted: Aug 15, 2018 - 09:05 AM
Correct -
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Posted: Aug 15, 2018 - 09:34 AM
Hi Jim! -
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Posted: Aug 15, 2018 - 09:50 AM
A little background info...lay your main sail out on the ground and you will see that the luff (leading edge) is curved. Sail shape is achieved (at least in part) by taking that curved luff and forcing it up a straight mast. This is what induces draft/depth into the sail. As downhaul and mainsheet tension is increased, the mast bends so that it starts to match the luff curve of the sail and so the sail becomes flatter. Since the diamond wires influence how much the mast bends, they affect how much shape is in the sail and thus, how much power the sail generates. So yes, tighter diamond wires = straighter mast = more power.
There are also other factors that influence rig power - downhaul and outhaul tension, mainsheet tension, mast rotation, batten stiffness, sail cut.
At 250-265 Lbs, you are probably going to want to run the diamond wires pretty loose since you're at the bottom end of the crew weight range.
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Posted: Aug 15, 2018 - 10:48 AM
Hm, I don't think it's that simple.
With slack diamond, the mast will bend readily to leeward, depowering. You can get enough tension to ensure it's stiff windward/leeward, while still being mostly straight (fore-aft) -- that'll maximize power. You can then put _more_ tension, and that'll increase the fore-aft bend, depowering (same effect as you get with downhaul). -
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Posted: Aug 15, 2018 - 11:28 AM
I really enjoy pushing it as hard as possible, so trying to avoid anything de-powering. 10-15 mph winds is usually as good as it gets with a few puffs greater.
See what I mean about being a little confused? I've received both "tighter from there to power up" and "run the diamond wires pretty loose" recommendations -
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Posted: Aug 15, 2018 - 12:05 PM
Hey I'm in Indiana where do you sail ?
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Posted: Aug 15, 2018 - 12:17 PM
From Hobie Beach on Eagle Creek Reservoir mostly, Monroe a couple times a year. You? -
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Posted: Aug 15, 2018 - 12:27 PM
OK, there are two schools of thought on mast tuning.
The traditional setup as I mentioned earlier... tighter diamond wires = straighter mast = more draft in the sail = more power. Vice-versa to depower.
The pre-bend setup (what I believe Mr. Langhoff is referring to)... over-tighten the diamond wires to pre-bend the mast along it's fore/aft axis. This basically "gets the mast bend started" so that it bends more front-to-back rather than side-to-side. With this setup everything is reversed and tighter diamond wires = more pre-bend = flatter sail = less power.
The caveat with using pre-bend is that the mast has to have spreaders that are capable of being raked back far enough to induce the pre-bend. The spreaders on a Hobie 18 really can't be raked back far enough to do this, so most Hobie 18 sailors use the traditional diamond wire setup. To induce pre-bend, you also need to put somewhere on the order of 2,000 Lbs of static pre-load on the spreader wires to get the mast to bend.
If you want to experiment with pre-bend on a Hobie 18, be my guest, but from a traditional standpoint, and what most 18 sailors go by tighter diamonds = more power. Looser diamonds = less power.
sm
Edited by Dogboy on Aug 15, 2018 - 12:31 PM. -
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Posted: Aug 15, 2018 - 01:55 PM
Great info thanks Dogboy! This is my second 18 and have spent a good amount of time learning about tuning for speed. Spent all winter wet sanding/reinforcing the hulls. Also brand new sails form Slo Sail (Blue Hawaii pattern) this summer. I'm excited to experiment with these settings. -
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Posted: Aug 15, 2018 - 02:40 PM
Starve Hollow lake and sometimes Monroe
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Posted: Aug 16, 2018 - 07:06 AM
Hey Andrew. I'll be back at the causeway one of these days. Miss all you guys! -
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Posted: Aug 17, 2018 - 11:51 AM
let me know if u want to come out sailing - anytime amigo -
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Posted: Aug 18, 2018 - 01:18 PM
Fair enough, my statement was in general, I don't know Hobie 18 specifics, and a marked with my personal experience: my boat has raked-back spreaders and a very bendy mast, so there's clearly two "depower" configurations for my diamond wires -- slack and taut. -
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Posted: Aug 19, 2018 - 06:56 AM
Also, remember that since the H18 mast isn't pre-bent, you can depower the sail by fully rotating the mast 90deg. This places the major axis of the mast across the boat and the weak axis in line with the sail and allows the mast to bend more easily and thus flatten the sail. Its more/less opposite what I do on the F18 with a pre-bent mast.
Edited by rehmbo on Aug 19, 2018 - 07:56 AM.
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Posted: Aug 19, 2018 - 09:26 AM
I'm not an H18 owner (am the fairly new owner of a P18.2), so I'm just following this discussion to get acquainted with general principles of how diamond wire tension affects performance. So we can have fore-aft bend in a mast, but also windward-leeward (side to side) bend. It's been stated that the spreader design of an H18 does not enable induction of aft "pre-bend" via diamond wire tension, so let's take fore-aft bend out of the equation for now. Apparently we still have the issue of windward-leeward bend to contend with, and Martin_Langhoff said that excessive diamond wire looseness will allow the mast to bend to leeward, which would de-power the sail. But I'm not sure what Martin means by "bend to leeward" in this context. Since the side stays are holding the upper end of the mast from falling to the leeward side, I assume he means that with very loose diamond wires, the center section of the mast will be bowed out to the leeward side, and that that de-powers the sail. If so, I take it from that that there is still some point at which the diamond wires on an H18 (or any other boat) could be so loose as to de-power the sail owing to leeward bowing of the mast(?).
Edited by CatFan57 on Aug 19, 2018 - 02:42 PM.
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Posted: Aug 19, 2018 - 10:31 PM
With low diamond tension, the top of the mast bends to windward. Note that the shrouds don't run to the top of the mast. -
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Posted: Aug 20, 2018 - 10:05 AM
Soaking this all in. Seems with a H18, soloed by a heavy single crew, that "snug" tension seems appropriate. Not really loose but not all the way tight either.
