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Old 03-25-2009
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Adjusting mast rake on masthead rig?

Hi,

On my 31Ft '79 Dufour sloop I have masthead rig with the backstay terminating with a turnbuckle on the reinforced transom. My mast stands pretty straight without any rake on it at all. I don't do any adjustment to it and would like to know how much improvement I would gain if i'd fit a split adjustable backstay? In addition to that, I use my roller furled jib/genoa halyard to hoist it up and secure it but do not use it to do any adjustment/trimming while sailing. How much improvement can you get by fiddling with jib halyard while sailing on the masthead rig i described above?
I'm not a racer but like to go faster that I am currently if possible.

regards/petar
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Old 03-25-2009
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Petar: Others will check me if I am mistaken, but I don't think there's any point to a split/adjustable backstay on a masthead rig with independent headsail. Maybe if you were hanking the genoa onto the forestay, a backstay tensioner could have some small influence on luff tension, but in general adjustable backstays are for fractional rigs, and more for bending the mast than for raking it. Mast rake is usually set at the dock; a backstay tensioner w/ fractional headsail pulls back on the top of the mast, causing the spar to curve forward and removing draft from the mainsail in high winds.

With a masthead rig, all you're going to do is tighten your forestay a touch. No impact on mast rake or sail draft.
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Old 03-25-2009
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Bob

Thank you, and yes mast bending backwards is what I had in mind when I asked the question. I suspected I would get this response but just wanted to check.

regds/Petar
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Old 03-25-2009
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Quote:
Originally Posted by Petar View Post
Bob

Thank you, and yes mast bending backwards is what I had in mind when I asked the question. I suspected I would get this response but just wanted to check.

regds/Petar

The mast bending is something you should be concerned about. I light winds you want to bend the mast back for the main and flatten the genoa. In heavier winds - shake it out. A split backstay works much like a purchase system does for your vang or main. Just means the level of effort is split .. However, if you have running back stays - you do not want a split backstay as you are adding more complexity to your setup.

Depending on type of boat - the rigging determines what you can do. On mine I can rake the mast, and also bend it port or starboard vias the running backs to totally control the sail shape of the main and genoa. If you do not have runing back stays - a split backstay will actually give you more finite control of shape (but only if you go the route of analyzing it - most cruisers do not). Typically if you have running backs - a split back is useless. If you do not have such - they may be advantageous as you will have a 2:1 purchase system - but you'll have to adjust your sailing accordingly...
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Quote:
Originally Posted by artbyjody View Post
The mast bending is something you should be concerned about. I light winds you want to bend the mast back for the main and flatten the genoa. In heavier winds - shake it out.

Hnh? Not according to everything I've ever seen, read, or heard. Usually in light winds the backstay is loosened to straighten the mast and slacken the forestay, in the interest of maximizing draft and sail drive. In high winds, the backstay is tensioned hard to bend the mast (on a fractional rig, not a masthead), flattening the main and depowering the boat. See Giulietta's video here.

With a masthead rig like the OPs, there's no point to constant backstay tension adjustments.
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Old 03-26-2009
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Jody—

The mast isn't going to bend much on a masthead rig.
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Old 03-26-2009
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Ditto SD's comment that the mast will not bend much on your boat, more in my opinion because you have a large section mast akin to a telephone pole, as opposed to a tapered mast section design to promote bend.

That said a backstay adjuster is still a valuable performance tool, even if its ability to bend the mast is limited...it provides the ability to control the fullness of the jib and the straightness of the forestay, and can materially affect the ability of the boat to sail close to the wind. A split backstay arrangement is of no matter, just shorten the backstay and add a Sailtec if you want the benefits of an adjustable rig.
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If your yacht has a keel stepped mast, or, if deck stepped, you have a baby stay, tightening the back stay will induce some modest mast bend, even in a sizable section. This will not have an appreciable effect of the main but it will have a sizable effect on the head stay and the sag of the foil, which, on most keel boats, is the objective of tightening the back stay. The same holds true with a deck stepped mast without the baby stay. The head of the mast moves aft tightening the head stay, limiting the jib's ability to sag to leeward in heavy air.

The easiest back sty adjuster to add to a boat of your size is made by Harken:



See: Harken Tech Corner: Backstay Adjusters

The foregoing are effective and relatively inexpensive. You have absolutely nothing to gain by splitting the back stay. You could shorten the back-sty and go with a mulit-part block system as well but from my viewpoint, the solid adjusted cranked with a winch-handle is more reliable and can't get away from you.

As wind strength comes up, one tightens the back-stay incrementally from neutral trim and moves the sheet lead aft to flatten the jib. Tightening the foot of the main and the main halyard flattens the main while the traveler is eased to leeward to reduce the twist in the leach and resulting heeling moments.

FWIW...

s/v HyLyte
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Adjustment

Hi Petar,

To answer your question about how much your boat's sailing might improve by adjusting some stuff, consider trying this out. First, go sailing on a day with 10 knots of breeze or so and get the boat on a close hauled course. Sail as close to the wind as the boat will and record some things: boat speed, apparant wind angle....then go forward and sight up the forestay and determine how far the headstay is sagging while still on this course. If the sail is scalloping just behind the furler, lightly tighten the halyard to remove the scallops. Imagine the distance between a drum tight stay and yours in the middle. It may be a few inches. Back at the dock, loosen the halyard and then use the backstay turnbuckle to take most of the play out of the forestay and go back out sailing in the same conditions. Set up the halyard again with no scallops. All other things being equal, the boat should sail a little higher and perhaps a little faster. Remember, there is a reason all the race boats, even those with tree trunk masts and masthead rigs, invest in adjustable equipment....it provides more speed and control. I'm guessing on a boat like yours, you will really see a difference and appreciate the flrxibility an adjustable backstay will provide. Before deciding how to do this project, consider posting a picture or two of the transom setup now and I'm sure you will get some good advice. If you swim some off the boat, the centerline backstay with built in adjuster provides an easy handhold when climbing up the ladder!
121Guy
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