mast rake???
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It depends on the boat
but a reasonable rule of thumb is about 1% to 3% of the height of the mast. So if your stick is 30 feet, about 6" will be close.
but a reasonable rule of thumb is about 1% to 3% of the height of the mast. So if your stick is 30 feet, about 6" will be close.
Rake or pre-bend?
Rake and pre-bend are two different things entirely. Rake is the degree that the mast is out of plumb, usually to the aft. Pre-bend is the amount of bend deliberately induced into the mast. Without knowing what boat or type of rig you have, my guess is that you are asking about pre-bend. For general cruising, I've been told about 1" of bend per 10 feet of mast, so that would be 3" for a 30-foot mast. this is roughly the same as 1% of mast height. 3% seems pretty radical to me. My 33.5 mast is just about 50-feet (48'-1/2")so I have about 5-6" of bend. I have a running backstay so I can induce a little more bend when I want it.
Rake and pre-bend are two different things entirely. Rake is the degree that the mast is out of plumb, usually to the aft. Pre-bend is the amount of bend deliberately induced into the mast. Without knowing what boat or type of rig you have, my guess is that you are asking about pre-bend. For general cruising, I've been told about 1" of bend per 10 feet of mast, so that would be 3" for a 30-foot mast. this is roughly the same as 1% of mast height. 3% seems pretty radical to me. My 33.5 mast is just about 50-feet (48'-1/2")so I have about 5-6" of bend. I have a running backstay so I can induce a little more bend when I want it.
Rake moves center of effort aft
More rake moves the draft in the mainsail aft, which will generate more weather helm but also more power. It is a question of balancing the head sail and the main to get the most power without putting the boat into an unbalanced situation where the rudder is fighting you and slowing down the boat. If you have an easily adjustable rig, no reason not to experiment - as long as you don't take the mast so far out of line that it fails in high wind.
More rake moves the draft in the mainsail aft, which will generate more weather helm but also more power. It is a question of balancing the head sail and the main to get the most power without putting the boat into an unbalanced situation where the rudder is fighting you and slowing down the boat. If you have an easily adjustable rig, no reason not to experiment - as long as you don't take the mast so far out of line that it fails in high wind.
Prebend / Luff curve
Check the fit of the mainsail to the mast. If the depth of the mainsail looks reasonable (maybe 20-25%camber) with no backstay tension, how flat does it get at full tension? If you like the shape at both ends of the range your mast pre bend fits the sail. If the draft in your main is always too deep, you can probably stand a little more prebend. If you have little or no weather helm with full sail and 10 knots of wind, try a litle more rake to help your pointing. However, if you are struggling with more than one spoke of weather helm as the wind comes up into the low teens, tighten the backstay adjuster and flatten the main. If you still have more weather helm than you are comfotable with, then you may have too much rake already. If you have no sister ships to look at this would be the trial and error method I'd to get your mast setting right. I should also have said you need to be sure the mainsail is in decent shape so we're not trying to solve blown out main sail problems with mast tuning.
Check the fit of the mainsail to the mast. If the depth of the mainsail looks reasonable (maybe 20-25%camber) with no backstay tension, how flat does it get at full tension? If you like the shape at both ends of the range your mast pre bend fits the sail. If the draft in your main is always too deep, you can probably stand a little more prebend. If you have little or no weather helm with full sail and 10 knots of wind, try a litle more rake to help your pointing. However, if you are struggling with more than one spoke of weather helm as the wind comes up into the low teens, tighten the backstay adjuster and flatten the main. If you still have more weather helm than you are comfotable with, then you may have too much rake already. If you have no sister ships to look at this would be the trial and error method I'd to get your mast setting right. I should also have said you need to be sure the mainsail is in decent shape so we're not trying to solve blown out main sail problems with mast tuning.
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