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Old 05-31-2009
sassafrass sassafrass is offline
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nice topic and great info...

i race in one design keel boats some of the time. rig tune is paramount to sucess. so i thought i would chime in a few fine points for those looking for them (like the comment on how to tune your rig for 20 knots).

sailboats have generally two modes upwind. seeking more power, and seeking less power, with a small happy medium in there. there are of course things we do with strings to help with this, however, mast tune is more significant, that is like a coarse adjustment, the strings we pull the fine adjustments.

i would also side with the disclaimers that have been mentioned, but you may want to consider going too much with an adjustment. that is go too far, far enough that you will know it is too far (performance will suffer). then you will know it is somewhere between those values (of too little/too much).

all of this is for uphill travel...

mast position in the boat (fore and aft) is critical. every boat is different in this regard. talk to other people with your boat and see what they have found out. with the butt, partners and forestay length you can control mast rake. if you have too much weather helm with mast rake right, the mast needs to move forward. not enough, mast needs to move aft. this is assuming your are trimming everything right. highier winds we use less rake, that is we shorten the forestay for the same butt position. other boats move the butt around. both work, but forestay length changes other things as well, and i think is generally easier. i don't know the math on degrees, as we measure the forestay length for the adjustment, but i would suspect we vary the rake by several degrees.

optimizing for light air. forstay sag is good in light air as you are trying for max power. you can try the same on the luff of your main by letting it sag off. how much, well you can try too much and then tighten up from there. too much sag will break/bend your mast. don't send me the bill. i would think somewhere around one to one and half mast diameters would be ok. this is what we use. as the wind builds and the boat is not needing as much power you can bring the mast in line. you do this by adjusting the lower/intermediate shrouds.

for high winds, the opposite is true. you will want no forestay sag (impossible), shorter forestay, less rake (butt aft, wedge partners forward). you will want your mast straight side to side, with more prebend. ideally, you will want the top of the mast to fall off some. fractional rigs do this better.

you can adjust some of this with a backstay adjuster, but really you need to get up there and adjust your forestay length/butt/parnter position to optimize your boat for any particular windspeed. most people in crusing, even racing boats will not play with there upper/intermediates/lowers at all. they have a set it and forget it attitude, especially with discontinous rigs. there is nothing wrong with that, in fact a lot of sense. tune for midrange and use other adjustments to keep the boat on its feet/use the engine if there is not enough wind.

downhill is different of course and mast tune is not as critical. you will want to undo as much rake and prebend as possible with your set up. having the mast tilt forward is best. you cannot do this with spartite, but you can with removable fore and aft wedges.

best of luck...
tom
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