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Bending masthead-rigged masts

mm2347

.
Oct 21, 2008
238
oday 222 niagara
A past discussion asked if a masthead-rigged mast could be bent aft to trim a mainsail. I just have run across a chapter in "Understanding Rigs and Rigging" by Richard Henderson that addresses the question. The short answer is maybe as it depends on the design of the masthead as well as the rigging. Simply put: If extended lines are drawn above the mast of the forestay and backstay and they meet on the centerline of the mast, the mast will not bend. If the backstay crane is lengthened the extended lines will now meet aft of the mast centerline creating a "bending moment" allowing the mast to be bent aft. A bluewater cruiser would probably want the added strength of a straight mast and lose a little sail trim. The racer would want the best possible sail trim and lose a little strength.
 
Nov 9, 2012
2,499
Oday 192 Lake Nockamixon
I think by now, a racer would (ideally) want a high aspect fractional rig with blade jib, as these have proven the best rig to go to windward. And depending on the course an asym on retractible sprit for downwind work, or maybe a symmetrical for DDW. Depends on the boat's polars.
 

mm2347

.
Oct 21, 2008
238
oday 222 niagara
You're right Brian. Sorry, the example of racer versus cruiser was a poor one. In my case, I'm a primarily a cruiser but sometimes like to race and have found doing so not only is fun but greatly improves my sailing in general. The past discussions of sail trim on this forum included bending the mast but I was not clear in the info given. So the question is: Can I bend my masthead-rig mast to improve my sail trim and is Mr Henderson correct?
 
Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Racy mast-head rigs have been off the market for 20 years. But when they ruled the roost, (think C&C glory days), they used babystays with adjusting tackle to bend the mast.
 
Nov 26, 2012
1,520
Hunter 34 Berkeley
Generally, no. Tightening the backstay on a masthead rig will not bend the mast. For me, the question then becomes: does an adjustable backstay have any value on a masthead rig? It does allow you to adjust the tension on the headstay. Tighter for going to windward and looser for running. How much is that worth? I am not really sure.
 

Ted

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Jan 26, 2005
1,215
C&C 110 Bay Shore, Long Island, NY
There are newer masthead rigged boats that were designed so that increasing backstay tension will induce mast bend without using a babystay. My boat has a triple spreader masthead rig which can easily be bent by only using the backstay adjuster. Proper rig tuning is important to achieve the desired results. There are pros and cons to each design and your preference will depend on how you intend to use the boat. Richard Henderson's answer "it depends....." is correct.
 
Last edited:
Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
There are newer masthead rigged boats that were designed so that increasing backstay tension will induce mast bend without using a babystay. There are pros and cons to each design and your preference will depend on how you intend to use the boat.
Is that how your 110 works? That (as a 2003 design) must be one of the last great masthead racer/cruisers! How does it work? are the spreaders slightly swept aft?
 

Ted

.
Jan 26, 2005
1,215
C&C 110 Bay Shore, Long Island, NY
Is that how your 110 works? That (as a 2003 design) must be one of the last great masthead racer/cruisers! How does it work? are the spreaders slightly swept aft?
Yes, that's how it works on my C&C 110. The hydraulic backstay adjuster easily bends the mast without a baby stay. The lowest set of spreaders are very slightly swept back. The outboard tips do not extend past the backside of the mast. You almost don't notice the swept back angle and the spreaders don't poke the leeward side of the main sail while sailing downwind. The middle set of spreaders are swept back even less. The uppers are not swept back at all.
 
Jan 1, 2006
5,993
Slickcraft 26 Greenport, NY
With triple spreaders I would guess the mast sections are more thin than those classic C&C tree trunks of yore. When I had the Ranger 29 the mast was a beast.
Regarding the backstay adjustment of headstay sag on a masthead boat, I think it is worth a lot. It can turn a cranky over powered rig into a well behaved sailing vessel.
 
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Ross S

.
Oct 20, 2011
120
Precision 21 Great Sacandaga Lake
I thought the advantage of a backstay adjuster on a masthead rig was to control forestay sag.
 
Oct 26, 2008
4,994
Catalina 320 Barnegat, NJ
I agree with Andrew. Adjustable backstay works wonders for reducing forestay sag and eliminating weather helm as the wind gets strong. I adjust mine for conditions every time I'm heading upwind. Then back it off when sailing downwind. So, yes, it is a critical control. No way I would sail without it.
 
Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
I thought the advantage of a backstay adjuster on a masthead rig was to control forestay sag.
Indeed that's the primary function on a traditional masthead boat

On a fract it does that as well has flatten the middle section on the mainsail.
 
Jun 11, 2004
1,203
Oday 31 Redondo Beach
I raced on an masthead Express 37 for most of the 80's and we regularly tightened the backstay to bend the mast and flatten the main (and adjust forestay tension).
 

pateco

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Aug 12, 2014
2,207
Hunter 31 (1983) Pompano Beach FL
How would I choose a backstay aduster for my 1983 Hunter 31 with masthead B&R rig, and Split Backstay? I have seen other H31s with adjusters.
 
Oct 26, 2008
4,994
Catalina 320 Barnegat, NJ
How would I choose a backstay aduster for my 1983 Hunter 31 with masthead B&R rig, and Split Backstay? I have seen other H31s with adjusters.
Very easy install, just choose the parts you want. I did find that the Johnson split backstay fitting has too much friction. I might replace that part someday. The hardest part was crawling into the back to fit the backing plates for the deck-mounted fixtures.
 

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Likes: pateco
Jun 11, 2004
1,203
Oday 31 Redondo Beach
A past discussion asked if a masthead-rigged mast could be bent aft to trim a mainsail. I just have run across a chapter in "Understanding Rigs and Rigging" by Richard Henderson that addresses the question. The short answer is maybe as it depends on the design of the masthead as well as the rigging. Simply put: If extended lines are drawn above the mast of the forestay and backstay and they meet on the centerline of the mast, the mast will not bend. If the backstay crane is lengthened the extended lines will now meet aft of the mast centerline creating a "bending moment" allowing the mast to be bent aft. A bluewater cruiser would probably want the added strength of a straight mast and lose a little sail trim. The racer would want the best possible sail trim and lose a little strength.
MAST BEND AND HEADSTAY SAG
Working with the backstay and a combination of running backstay, baby stay, and/or vang, it is possible to control mast bend and headstay sag separately.

Backstay tension will bend the mast through compression as well as tighten the headstay. The mix depends on running backstay tension. If the runners are tight, they restrict mast bend, and the backstay impacts headstay sag. Looser runners allow more mast bend.


With a stiff mast, backstay tension translates primarily into headstay tension, controlling sag. A baby stay can then be used to add bend. The backstay contributes to bend as well, particularly once bend has been initiated by the baby stay.

Running backstays allow control of mast bend independent of headstay sag. A tight backstay will tighten the headstay and bend the mast. Tensioning the runners will straighten the mast.
 

jviss

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Feb 5, 2004
4,627
Tartan 3800 Westport, MA
Cool discussion. My new boat has a baby stay, a (new) hydraulic backstay adjuster, and a film-on-film mylar main with a lot of curve cut into the luff (I don't know the correct term). I assume that if the rig is set up correctly, I can really flatten that main when it blows up hard; maybe defer reefing 'til 25+ kt.?

But, how to set it up? It's a Tartan 3800 with an Offshore Spars, tapered, aluminum spar, two spreader rig. I don't recall specifics in the manual on pre-bend, etc. (I'm away on business this week and not with the docs or boat).

Thanks,

jv