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PostPosted: Mon Mar 31, 2014 5:04 pm 
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Hi all,

So I recently bought a copy of the Hobie 18 Performance Manual through Murrays, and found it quite useful for the reference points when it comes to mast rake, shroud tension and the like, but with as much as everybody seems to rave about it, I suppose I was expecting more "trade secrets," haha.

One question I do have is regarding the spreader rake & diamond wire tension. I notice that the Performance Manual is contradicted by Catamaran Racing for the 90's.

Performance Manual suggests:
1) set spreader rake based on the conditions
2) set diamond wire tension either loose to allow mast bend & de-power, or set them tight (based on conditions)
3) set mast rotation to allow more or less mast bend (based on conditions)
4) set downhaul as necessary for conditions

These seem to be contradictory to the pre-bending theory, which I imagine wasn't around when Phil Berman wrote the manual. Loose diamond wires would defeat the purpose of raked spreaders, would they not?

Catamaran Racing for the 90's has me thinking:
1) keep spreaders raked aft (max) regardless of conditions
2) keep diamond wires tight to pre-bend the mast regardless of conditions
3) set mast rotation for smooth entry regardless of conditions
4) downhaul to bend the mast & depower as necessary for conditions

I also notice that Catamaran Racing for the 90's suggests that spreader rake and mast pre-bend theory has been applied to H18's with much success at nationals... Can this be done without modifying the spreaders? And how tight should the diamond wires be?

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PostPosted: Tue Apr 01, 2014 5:13 pm 
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If pre-bend worked on the H-18 mast, that would be the way to go but, it has been my experience that you can't. It will only bend on the minor axis, not the major. Allowing the mast to bend into the slot is not ideal, but it is all we have.

Use the adjustments as outlined in the Performance Manual.

I have also found raking the mast back to be a useful de-powering technique.


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PostPosted: Wed Apr 02, 2014 4:58 pm 
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Well, theoretically speaking, any mast will bend on it's major axis with enough spreader rake and diamond wire tension. I just wasn't sure if it's been done with the H18 without modification. Like I said, in 'Catamaran Racing for the 90's' Rick White claimed "We tried [pre-bending the mast] at Hobie 18 Nationals at Daytona Beach and found it very effective, and safe." (pg. 81)

If it doesn't work that way in practice, then oh well I guess. I can always follow the performance manual, though I don't quite understand why Phil Berman suggests adjusting the spreader rake, if not to pre-bend the mast?

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PostPosted: Wed Apr 02, 2014 5:55 pm 
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I have not found any significant difference in the different spreader settings. There is not much geometry change between the first hole and the last. I don't change my spreader rake any more.

It is fairly easy to see if you can cause pre-bend or not. Rake your spreaders all the way back and then raise your mast. Tighten your diamond wires as far as you dare. Now raise your mainsail and crank your downhaul on as hard as you can. Put your head at the base of the mast and sight up to the top. How much fore and aft bow do you see in the mast? Now let the downhaul off and then loosen the diamond wires to the loosest setting as described in the Performance Manual. Then crank on the downhaul again and sight up the mast. How much fore and aft bend now?

On your next windy day, shove off with the diamond wires fully tight as per the PM. Sail upwind and note how much she wants to heel. Now luff up and loosen the wires to the loosest setting as per the PM (yes, on the water. I always race with the tools necessary to adjust them between races, when the conditions change). You will see a significant difference between the two settings.


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PostPosted: Wed Apr 02, 2014 7:19 pm 
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Okay, that's more in line with what I thought... spreader rake doesn't much matter if you're not pre-bending... and I agree, if they don't rake aft enough, there's no pre-bending to be had. I haven't actually adjusted my spreaders before, I didn't know they were adjustable... the boat's currently winterized, but reading the PM I got a little hopeful, haha.

I have played with the diamond wire tension on the water as well... mine tend to loosen up on me as I sail. But I have noticed the effects you describe. I try to only adjust them shoreside, however, because it's tough to adjust them evenly on the water.

Thanks jim!

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PostPosted: Fri Apr 04, 2014 2:16 pm 
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Has any one noticed the bolt at bottom of mast that anchor the diamond wires bent? Adjusting wires last summer I noticed mine are bent . Plan to order new ones this spring, Ive owned boat for several years and have never played with the tension before last year . That's when I noticed them. Evidently previous owner had them quite tight at one point.


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PostPosted: Fri Apr 04, 2014 7:55 pm 
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I have not had that happen, but I haven't inspected that bolt very closely. I was just reading someone else on here saying that the bolt has actually broken on them underway, instantly de-tensioning the diamond wires. Seeing as this could lead to a broken mast and/or could leave you stranded, I might buy a spare to keep onboard.

I have lost my turnbuckles twice now, as they apparently loosen up on long drives (I trailer mine often, and over distances). I saw in the H18 manual that they recommend tying a string through the holes in the turnbuckles to prevent this, so... lesson learned.

Diamond wire tension plays a pretty key role in allowing you to power up or depower your sail plan, as was kinda discussed above.

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PostPosted: Sat Apr 05, 2014 3:06 am 
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I have broken that bolt twice. I sail with a spare in my tramp tool kit so I can sail to the closest shore and replace it, if necessary.


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PostPosted: Sat Apr 05, 2014 1:45 pm 
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I've managed to break mine also... carry a few spares in the tool box... something that is part of the pre sail check list... though not easy to check, but you can see if it's unusually bent or something...

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PostPosted: Sat Apr 05, 2014 2:28 pm 
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I've also broken the diamond wire bolt (once). Carrying a spare on board isn't a bad idea, however if you sail in salt water, the aluminum compression sleeve will probably be frozen to the bolt which means that you may have to use a hack saw to cut the bolt off of the turnbuckle fitting.

Regarding diamond wire settings, we never adjust this. I keep it pretty snug, maybe able to touch the diamond wires to the mast a foot up from the bolt if you press pretty hard. They aren't so tight that we're inducing any pre-bend. We run pretty high above minimum weight so I want to keep the bottom of the mast rigid. Plus with a 6:1 downhaul and the comptip, we get plenty of bend out of the top 8 feet of the mast to depower the boat.

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PostPosted: Thu Apr 10, 2014 3:42 am 
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The H18 mainsail luff isn't really cut to take advantage of a prebent mast. If you start prebending, (1) you'll put loads on the mast it was never intended to take and (2) you'll probably take all the camber out of the sail which would be fine if its super windy (20+kts), but would leave you under-powered otherwise.

I do sail a different boat with prebend and always looked at prebend like the front chain rings on a mountain bike. Kind of a gross adjustment. The fine adjustment comes from the cunningham/downhaul. Since the H18 dacron sails are pretty stretchy, the regular downhaul and rake changes seem to give an adequate sail power adjustment range.

Having said this, I no longer race my H18, so perhaps the experts can chime in. However, I don't believe any Nationals level guys are doing this.

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