I have a question about setting prebend on rigs (B&R and others) were you can’t bend the mast once you are underway. The three choices are straighter than, more bent than or follow the luff. If you bend it more than the curve of the luff, then when you raise the sail it will automatically be flattening it I suppose? By the same token if you set it straighter than the luff it will allow greater depth. If you go straighter will this make it difficult to move the draft all the way forward?
Mast prebend
- Thread starter Quoddy
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For the most part bendy masts like my J24 (it moves a good 6" with the backstay)are done with a sail desgin in mind that is made to take advantage of were the mast bends to crontol sail power until a reef is required
On a J24 the mast has to be set for who built the sail as ideas have changed over the years and right now there setup straight were in the past you might have 2"+ of prebend
Your not going to be able to do much without knowing how the mainsail was built
For the most part bendy masts like my J24 (it moves a good 6" with the backstay)are done with a sail desgin in mind that is made to take advantage of were the mast bends to crontol sail power until a reef is required
On a J24 the mast has to be set for who built the sail as ideas have changed over the years and right now there setup straight were in the past you might have 2"+ of prebend
Your not going to be able to do much without knowing how the mainsail was built
The rig on our Hunter 260's is not at all like the bendy rig on a J 24. Our Hunter supplied Doyle sails should have been designed around a specific set of parameters. I can't remember the formula offhand but you are looking for 3 3/4 inches of prebend measured at the midpoint between the masthead and the goose-neck. I set mine with the mast upright with no tension on it. I use a measured stick taped to a boat pole to measure. Selden recomends doing it with the mast on horses. Once you pull the pre-bend you can snug up the shrouds. Selden has a booklet of info and hints that is must have reading for anyone with a mast. I got my copy by begging at a boat show, but I think the information is available on their web site. Yes, I know our masts are not Selden but their information is the best I've found out there. US Spar has pretty much nothing.
http://www.seldenmast.com/_download.cfm?id=6740&download=9445082&filename=595-540-E.pdf
The link above will get you Selden mast's Hints and Advice booklet.
http://www.seldenmast.com/_download.cfm?id=6740&download=9445082&filename=595-540-E.pdf
The link above will get you Selden mast's Hints and Advice booklet.
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Quoddy...
when I was rigging the mast on the Hunter water ballast boats our dealership sold, the mast was first set up on sawhorses as mentioned and the pre-bend set according to the Hunter directions to the dealer that came with the boat. When stepped, we tried to achieve a measurement of a dropped halyard end at the boom of no more than six inches back from the mast. Sam's dimension should be spot-on for your purposes.
when I was rigging the mast on the Hunter water ballast boats our dealership sold, the mast was first set up on sawhorses as mentioned and the pre-bend set according to the Hunter directions to the dealer that came with the boat. When stepped, we tried to achieve a measurement of a dropped halyard end at the boom of no more than six inches back from the mast. Sam's dimension should be spot-on for your purposes.
Also consider that the shape will be differnt up wind than off the wind.
Off the wind the sail is across the mast and there is no bend effect.
Generally this is good, because you like flatter up wind than broad reaching.
This is a MAJOR adjustibility factor on cats with rotatable masts (rotating the mast makes the sail full, de-rotating makes it flat). Typically they are pre-bent but not "bendy." The only strong reasons for prebend are to take advantage of these effects.
Up wind the sail is fore-aft and the bend sucks fullness from the sail.
Off the wind the sail is across the mast and there is no bend effect.
Generally this is good, because you like flatter up wind than broad reaching.
This is a MAJOR adjustibility factor on cats with rotatable masts (rotating the mast makes the sail full, de-rotating makes it flat). Typically they are pre-bent but not "bendy." The only strong reasons for prebend are to take advantage of these effects.
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