Ken Smith
ADMIN
Posts: 289
sail often, travel light
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« Reply #1 on: December 26, 2007, 07:49:35 PM » |
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Squire:
There is not one good answer. On the DN archives, aka Collective Wisdom [www.dnamerica.org then link to archives and collective wisdom and follow the index], there are excellent discussions on just that issue (shroud length and tuning). So let me provide some baseline advice, read the archives, and be ready to change. Remember the objective is to get a much power as possible with the boat controllable. This will change with wind strength, depower in heavy air and power up in light air, but the mast still must bend in light air. More rake is depowered, less rake is powered up. More forestay tension (all stays get tight) for heavy wind, less forestay tension in light air to promote mast bend.
There are several variables that affect your best shroud length: Mast stiffness - stiffer masts need to be raked aft to bend, soft masts need to be more upright. Boat geometry - a short nose requires the mast to be more upright, and the longer nose, forward of the front runner pivot (such as shown in the yearbook) requires more rake. Your weight - heavy allows you to rake less, light weight, more. Plank stiffness - something should bend. if the plank won't, rake more and make sure the mast does. And Hardware - is your hound near minimum height, what are you using for side stay adjusters and forestay adjusters, hound hardware, shrouds tie in on outer or inner bolt at the plank? I presume you are about to get some wire cut. Take your adjusters to the guy with the crimper so he can measure pin-to-pin.
Ron's tuning guide presumes his boat (similar to that in the yearbook plans), one of his masts (near minimum hound height), and and average guy. He recommends, in my copy, 136 inches for the side shrouds, hole to hole, ie, from hound pin to plank pin. The forestay has to be adjustable and tight, very tight, with the side stay lengths you pick. If you use multi-hole side stay adjusters, I would suggest making the shroud length hole-to-hole 136, adjustable down to 135 and up to 139. This range will more likely than not suffice any tuning you end up with. [with a short-bow boat, heavy boat and skipper, soft plank or the other factors above, make the range extend more, favoring shorter for more rake and mast bend and longer for more power]. Quarter inch length changes are significant!
Fore stay length needs to be adjusted to follow. With the shroud length set, the forestay should be able to be made tight enough to bend the plank so the side stays remain tight when you stand on the plank.
See the archives. Paul Goodwin has some excellent discussions on tuning.
Hope this helps.
Ken
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