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!

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

Thanks 911. So the tighter the wires, the more power? Is this the case irrespective of crew weight and wind speed?

Correct

Hi Jim!

indiana18

So the tighter the wires, the more power? Is this the case irrespective of crew weight and wind speed?

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.

sm

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tighter diamond wires = straighter mast = more power

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).

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

Hey I'm in Indiana where do you sail ?

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H14
H16
H18
H18
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in812

Hey I'm in Indiana where do you sail ?

From Hobie Beach on Eagle Creek Reservoir mostly, Monroe a couple times a year. You?

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Hm, I don't think it's that simple.

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.

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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From Hobie Beach on Eagle Creek Reservoir mostly, Monroe a couple times a year. You?

Starve Hollow lake and sometimes Monroe

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H14
H16
H18
H18
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Hey Andrew. I'll be back at the causeway one of these days. Miss all you guys!

911hobie

Hey Andrew. I'll be back at the causeway one of these days. Miss all you guys!

let me know if u want to come out sailing - anytime amigo

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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.

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.

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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Jeff R
'88 H18 "Jolly Mon"
'10 C2 USA1193
NE IN / SE MI
cramsailing.com
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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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1998 P18.2
Sailing out of SHBCC, NJ
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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.

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.

CatFan57

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

As I said before, it depends on what school of thought you are using to tune your mast. Modern boats that use pre-bend depower by increasing spreader rake and diamond wire tension and reducing mast rotation. Old-school boats (like the Hobie 18) do the exact opposite - depower by slacking the diamond wires (they may actually be flopping around) and increasing mast rotation.

I don't think you would ever see an F18 depower by loosening the diamond wires.

For the OP, I agree, start with the diamond wires snug and loosen from there if you end up over powered. The honest fact is that the H18 just isn't as sensitive to tuning as the modern boats. You may notice some slight power differences going from the extreme ends of the tuning spectrum, but this is not going to be a night & day change.

Having a functional and powerful downhaul setup is more significant IMO.

sm

makes sense to me, and thanks for the downhaul suggestion.

I have never owned a Hobie 18, but there was one real sweet one at our yard once that was owned by a guy I use to sail with on my NACRA 20... The two of us would have the NACRA singing when the winds were being cooperative, and we both came to the conclusion that it was; as he put it in his southern draw..., "what y'all have dar is ayy NAYSCARR wid saaaiiiiils."

Anyway, as I said, he had a pretty sweet 18 and he kept the diamond wires pretty lose... I had asked about that one day as I have always gone in the opposite direction... Told me he leaned about that at a regatta, that is he went up to the winning boat after the first day and checked it out... said that was the first thing he noticed... and the next day they were the same... lose Said he loosened his up and noticed a vast improvement...and had left that way.

Oh, his boat had a composite mast, my be different for the all aluminum mast..

FWIW...



Edited by JohnES on Aug 22, 2018 - 05:17 PM.

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John Schwartz
Ventura, CA
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CatFan57

I'm not an H18 owner (am the fairly new owner of a P18.2),

Now that I am an 18-2 owner again, I have pulled out all my old notes... glad I didn't trash those old 3.5 Floppys... A good general setting for your diamond wires should be at about 16" above the tang, that is with the mast standing you should be able to squeeze the wires to the mast they should touch at 16"... not as accurate as a Lose gauge.. 14" is about a tight as you want to go, and 20" is as lose as you want to adjust them.

For the spreader rake, about 1 1/4" aft...



Edited by JohnES on Aug 22, 2018 - 05:39 PM.

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John Schwartz
Ventura, CA
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JohnES

I have never owned a Hobie 18, but there was one real sweet one at our yard once that was owned by a guy I use to sail with on my NACRA 20... The two of us would have the NACRA singing when the winds were being cooperative, and we both came to the conclusion that it was; as he put it in his southern draw..., "what y'all have dar is ayy NAYSCARR wid saaaiiiiils."

Anyway, as I said, he had a pretty sweet 18 and he kept the diamond wires pretty lose... I had asked about that one day as I have always gone in the opposite direction... Told me he leaned about that at a regatta, that is he went up to the winning boat after the first day and checked it out... said that was the first thing he noticed... and the next day they were the same... lose Said he loosened his up and noticed a vast improvement...and had left that way.

Oh, his boat had a composite mast, my be different for the all aluminum mast..

FWIW...Edited by JohnES on Aug 22, 2018 - 05:17 PM.

So I tested both tight and loose settings yesterday with a good amount of downhaul. I too have a composite mast. Looser definitely seemed faster. Winds were 10-15. With the wires tight, the boat almost seemed kind of bound up; like it wanted to move faster with the given wind, but just wasn't. With the wires loose, mostly on a beam reach, the windward wire didn't even fully tension under near hull flying speeds. This makes me think the mast doesn't bend a whole lot, but the looser setting definitely felt better. The wind at my lake is hardly ever consistent, but I would like to test w a GPS someday.

Like I said in my original response, you are at the low end of the weight spectrum, so loose diamonds will likely be preferred. If you had 75-100 Lbs more crew weight, you would probably find yourself under-powered with the loose setting.

Also, the windward diamond wire will always have a tendency to go slack under load because the mast is bending in that direction. On any given tack, the leeward diamond wire is what limits the amount of mast bend.

sm

JohnES

Now that I am an 18-2 owner again, I have pulled out all my old notes... glad I didn't trash those old 3.5 Floppys... A good general setting for your diamond wires should be at about 16" above the tang, that is with the mast standing you should be able to squeeze the wires to the mast they should touch at 16"... not as accurate as a Lose gauge.. 14" is about a tight as you want to go, and 20" is as lose as you want to adjust them.

Okay, glad you saved your notes, and thanks for the tip. I have not messed w/ diamond wire tension as yet, but now I will check it.

I also checked my P18.2 owers manual (there's a novel idea, right?), and it says to set tension so the wires touch the mast anywhere from 12" to 20" from the lower attachment point. So your 16" suggestion will give me a more precise point to shoot for as a starting point.

I notice the manual also says: "WARNING: If the diamond wires are too loose the mast could break under high pressure loads."



Edited by CatFan57 on Aug 23, 2018 - 05:11 PM.

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1998 P18.2
Sailing out of SHBCC, NJ
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CatFan57

I notice the manual also says: "WARNING: If the diamond wires are too loose the mast could break under high pressure loads."Edited by CatFan57 on Aug 23, 2018 - 05:11 PM.

I have never seen a Prindle 18 or an 18-2 mast break.... and I have seen them take some abuse.... but there is always a first time... 20" is pretty loose for the diamond wires.... I have found that setting and forgetting has always been the best policy... where are yours set now....

If you're going to start playing with your diamond wires I was going to recommend getting a Loos Gage, but I see they are are $100 plus bucks these days.

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John Schwartz
Ventura, CA
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Dogboy

Like I said in my original response, you are at the low end of the weight spectrum, so loose diamonds will likely be preferred. If you had 75-100 Lbs more crew weight, you would probably find yourself under-powered with the loose setting.

Also, the windward diamond wire will always have a tendency to go slack under load because the mast is bending in that direction. On any given tack, the leeward diamond wire is what limits the amount of mast bend.

sm

Right and right!

JohnES

I have found that setting and forgetting has always been the best policy... where are yours set now....

If you're going to start playing with your diamond wires I was going to recommend getting a Loos Gage, but I see they are are $100 plus bucks these days.

I won't be at the boat til this weekend, so I don't know where mine are currently set. I bought the boat used and never thought to check the existing tension, so this thread is prompting me to check it. I don't have any plans to start playing around with different tensions, so don't think I'll get a gauge. I just want to check it to make sure it's in the appropriate range and equal on both sides, and hopefully set it to a tension that gives lots of power.

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1998 P18.2
Sailing out of SHBCC, NJ
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