Design? Why prebend the mast, with the luff specially designed to match that curve. Why not straight luff ,straight mast?
- Status
Adjustment
For most people it is more of a racing thing The curve allows the mast to control the draft in the sail for different wind conditions I have seen far more foolish things done in the quest for speed like floppy lose head stays
Tommays
For most people it is more of a racing thing The curve allows the mast to control the draft in the sail for different wind conditions I have seen far more foolish things done in the quest for speed like floppy lose head stays
Tommays
Main reason on a cruising boat is to reduce mast pumping
prebend changes the mechanical/structural characteristics (I^3) and dampens the vibratory nature (resident natural frequency) of the mast ('pumping'). Allows the usage of a lighter/thinner mast - weight reduction aloft is ALWAY a good idea on a sailboat. Prebend also resists the reverse curvature of the mast (powering up the main) in the higher wind ranges. Secondly, most sailmakers assume that you have a proper prebend and so most sails are so cut. One of the reasons why you have a local sailmaker come to your boat to do the actual measuring, etc. Prebending pulls sail fabric from the center of the sail towards the mast/bend, making the luff shape a little flatter while reducing the maximum amount of draft .... for a FAST sail that can be sailed with tighter 'slot' for better close-hauled performance. Typical prebends (but consult your mast mfgr.): 3/4" for single spreader ring, 1-1.5" for double spreader rig. So ultimately, prebend on a cruising boat is for SAFETY especially when using a 'thin sectioned' mast that can catastrophically shake the mast in the high wind ranges.
prebend changes the mechanical/structural characteristics (I^3) and dampens the vibratory nature (resident natural frequency) of the mast ('pumping'). Allows the usage of a lighter/thinner mast - weight reduction aloft is ALWAY a good idea on a sailboat. Prebend also resists the reverse curvature of the mast (powering up the main) in the higher wind ranges. Secondly, most sailmakers assume that you have a proper prebend and so most sails are so cut. One of the reasons why you have a local sailmaker come to your boat to do the actual measuring, etc. Prebending pulls sail fabric from the center of the sail towards the mast/bend, making the luff shape a little flatter while reducing the maximum amount of draft .... for a FAST sail that can be sailed with tighter 'slot' for better close-hauled performance. Typical prebends (but consult your mast mfgr.): 3/4" for single spreader ring, 1-1.5" for double spreader rig. So ultimately, prebend on a cruising boat is for SAFETY especially when using a 'thin sectioned' mast that can catastrophically shake the mast in the high wind ranges.
check this site
See the discussion on this site under Resources / reference library / B&R rig tuning tips. The pre-bend in a mast allows, by the use of more stays, a smaller, lighter section of mast. The stays, located at predetrmined engineered stress points, give the mast strength and rigidity. It also allows a deck-stepped mast, which has some advantages of economy, weight, and is easier to step. The pre-bent mast on a B&R rig with no backstay allows for a much larger roach in the mainsail. Pre-bent masts are almost always fractional rigs.
See the discussion on this site under Resources / reference library / B&R rig tuning tips. The pre-bend in a mast allows, by the use of more stays, a smaller, lighter section of mast. The stays, located at predetrmined engineered stress points, give the mast strength and rigidity. It also allows a deck-stepped mast, which has some advantages of economy, weight, and is easier to step. The pre-bent mast on a B&R rig with no backstay allows for a much larger roach in the mainsail. Pre-bent masts are almost always fractional rigs.
Pre-Bend
The masthead rigged Hunter 28.5, 31, and 34's of the mid-late 80's have double spreader somewhat lighter crossection B&R rigs with a split backstay and about 1% prebend. This eliminated the need for a baby stay and provides a light flexible mast capable of having a little more induced bend by adding a backstay adjuster to flatten and de-power the main when necessary. Comparing the PHRF numbers to current fractional rigs without backstayas and you may also be surprised to find the masthead rigs are rated faster. So I'd contend the design was more performance related.
The masthead rigged Hunter 28.5, 31, and 34's of the mid-late 80's have double spreader somewhat lighter crossection B&R rigs with a split backstay and about 1% prebend. This eliminated the need for a baby stay and provides a light flexible mast capable of having a little more induced bend by adding a backstay adjuster to flatten and de-power the main when necessary. Comparing the PHRF numbers to current fractional rigs without backstayas and you may also be surprised to find the masthead rigs are rated faster. So I'd contend the design was more performance related.
My boat is 46 yrs old with spruce sticks and you'd
be amazed at how much pre-bend the mainmast has in it. It's gotta be at least a foot on a 45' mast. I've seen J-boats with less.
be amazed at how much pre-bend the mainmast has in it. It's gotta be at least a foot on a 45' mast. I've seen J-boats with less.
I always thought that
I always thought that the B&R had it's bend set using only the diamonds - not with a backstay.
I always thought that the B&R had it's bend set using only the diamonds - not with a backstay.
Original B&R rigs had back stays
Brian: The original B&R Rigs had a back stay that was split several feet above the cockpit. The specs for these back stay versions was about 1% bend. The bend is calculated on the distance from the boom to the top of the mast. A 50' mast would have about .5 ft (6" of prebend). The link below will guide you to some of the background of the original B&R rigs and how popular they really are outside of the Hunter family of boats.
Brian: The original B&R Rigs had a back stay that was split several feet above the cockpit. The specs for these back stay versions was about 1% bend. The bend is calculated on the distance from the boom to the top of the mast. A 50' mast would have about .5 ft (6" of prebend). The link below will guide you to some of the background of the original B&R rigs and how popular they really are outside of the Hunter family of boats.
Charlie
Thats not pre-bend that's permanent deformation from all that heavy weather sailin you do...
Thats not pre-bend that's permanent deformation from all that heavy weather sailin you do...
- Status