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Mary and Rick; Got to thinking that maybe you would want to publish this exchange on your internet section. I learned this all from you, so either way people set their mast up, you can take credit for it!
Mike---------- From: mike fahle < To:
Subject: Re: H18: mast pre-bend
Date: Friday, January 23, 1998 2:09 PM
However, before I destroy the boat I thought I'd better seek wisdom from this group. Rick White and Mary Wells state (Catamaran Racing: For the 90's) that they have successfully used mast pre-bend on a H18. What I'd like to know, if possible, is:
1. Is pre-bend much used on H18s? Its getting popular - most of the top sailors are doing it. I don't think its the most important thing on the boat by a long shot. I've sailed 10 years without prebend, and started using it in the middle of nationals last year. I didn't notice much difference, but that might be because I was busy Tea-Bagging (dunking the crew on the wire), dropping wet suit boots in the lake, sailing the lifts before the headers, keeping myself covered, tacking through H17 traffic and lots of other stupid stuff. I beat the same people and lose to the same people before and after cranking on the diamonds.
2. Is something likely to break (eg. the bolt going through the rotation arm that anchors the diamond wires, or the mast). I've seen two rotator arm bolts break (one mine). Both were on boats not using much diamond wire tension (mine is what you would call floppy). I think the failures caused by too much diamond tension are the H20 masts that snap near the spreaders. Mike Fahle -- can you comment on this further? -dave (Fort)

Sure, why not. I have written about this before. The Hobie 18 sails are very flat. My experience is that they usually need to be powered up as much as possible as we sail in areas with winds normally 20MPH. I sail with my wife at or close to minimum weight. We are very competitive in wind up to about 25MPH. Because the Hobie 18 class now allows an 8 to 1 purchase on the main downhaul, I find it fastest to sail with no pre bend at all so that the main is as full as it can be when the downhaul is eased. This is desirable downwind until control becomes an issue, and all other points of sail until depowering is required to fly the hull at the desired attitude.
The downhaul at 8/1 does this very effectively, and for that reason, should be rigged to the trapeze wire so that it is readily available to the crew while on the wire. In other words, before you make a change, try to understand the reason and apply that to your situation. You would have to sail in very windy conditions for prebend to be desirable. Even in such conditions, I would keep the mast straight and rake it back because that would provide more control downwind. I can blade out the mainsail with the downhaul, so prebend really adds nothing and reduces the amount of power available tome should conditions call for more power.
Accordingly, I set the spreaders so that they are as far forward as I can adjust them. I set the diamond wires tight enough so that the leeward one is not slack when we fly a hull. This requires a second helm on the boat to steer while I check this. This is to prevent the mast sagging sideways into the slot. I want to keep the slot as open as possible while I sheet the jib as tight as possible so that I can point as high as possible with no backwind. As the wind comes up, I move the jib sheet block back as far as possible to ease the leech and allow me to point higher. At some point, the wind gets strong enough so that point-mode is slower than foot- mode and then we ease the jib sheet a tad and travel the main down appropriately and sail lower and faster.
Summary: Use the available power in the relatively flat 18 main and develop the techniques to harness it, rather than limit it in all conditions. Set the mast up straight, not prebent, and use the 8/1 downhaul to depower as needed. (For Portsmouth sailing, I use a much fuller oversize main with a 16/1 downhaul to sail boat for boat with 20 footers.) Tim Allen is right on target.... more power!
Mike Fahle
Toledo, Ohio (Hard water winning the battle)
P.S. For those of you who just love to prebend your mast, an easier way to tighten the diamonds is to raise the main and apply the downhaul forcefully. This will prebend the mast without pressure on the diamonds so that you can tighten them with little effort.
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