I have a tall rig 30 Catalina. It was recently suggested that I adjust the mast by tightening the forward shroud and loosening the aft shroud and tighten the back stay in order to be able to sail closer to the wind. I do both cruising and some racing. What are the pros and cons about doing this?
standing rigging
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Stern face,
If you are who I think you are, don't forget the next time you need to take down your headsail just call on me.
Reef early,
>>ron<<
If you are who I think you are, don't forget the next time you need to take down your headsail just call on me.
Reef early,
>>ron<<
It sounds like
you're being encouraged to induce bend in the mast by moving the center of the mast forward and pulling the top of the mast aft.
If that's correct I'd highly recommend against it.
In theory this will flatten the main by pulling the center of the luff forward thereby flattening the camber of the sail.
Unfortunately, this doesn't work well on all types of rigs in all conditions.
First and and foremost, it's your boat and if you don't know why you're doing it on your particular boat then I wouldn't do it.
Secondly, on your particular boat it's not an adjustment that you can easily make under way and a flatter main may not be what you want in many wind conditions.
Thirdly, that particular adjustment is generally only effective on fractional rigs with tapered, easily bendable masts and easily adjustable backstays. Attempting this adjustment on a masthead rig with a relatively large cross-section mast will likely cause things other than your mast to give way.
Finally, even if you could get your mast to bend I doubt you'd notice a significant change in your pointing ability. There are other adjustments you can make that would be far less prone to damage your boat.
I race on a J-40 with a masthead rig and we don't tension runners or our hydraulic backstay with the intent of inducing bend (we do it, however, to flatten the headstay, which is an entirely different deal.)
Alan, who frequents this board, races a fractional rig and may chime in but a fractional is an entirely different animal as I'm sure he'll tell you.
In short, don't do it just because someone else said it would work. These 'one-size-fits-all' bits of advice are often wrong. A little bit of knowledge is a dangerous thing.
you're being encouraged to induce bend in the mast by moving the center of the mast forward and pulling the top of the mast aft.
If that's correct I'd highly recommend against it.
In theory this will flatten the main by pulling the center of the luff forward thereby flattening the camber of the sail.
Unfortunately, this doesn't work well on all types of rigs in all conditions.
First and and foremost, it's your boat and if you don't know why you're doing it on your particular boat then I wouldn't do it.
Secondly, on your particular boat it's not an adjustment that you can easily make under way and a flatter main may not be what you want in many wind conditions.
Thirdly, that particular adjustment is generally only effective on fractional rigs with tapered, easily bendable masts and easily adjustable backstays. Attempting this adjustment on a masthead rig with a relatively large cross-section mast will likely cause things other than your mast to give way.
Finally, even if you could get your mast to bend I doubt you'd notice a significant change in your pointing ability. There are other adjustments you can make that would be far less prone to damage your boat.
I race on a J-40 with a masthead rig and we don't tension runners or our hydraulic backstay with the intent of inducing bend (we do it, however, to flatten the headstay, which is an entirely different deal.)
Alan, who frequents this board, races a fractional rig and may chime in but a fractional is an entirely different animal as I'm sure he'll tell you.
In short, don't do it just because someone else said it would work. These 'one-size-fits-all' bits of advice are often wrong. A little bit of knowledge is a dangerous thing.
I assume from your description that you have double lower shrouds. Tightening the forward lowers and loosening the aft lowers and adding backstay tension will put some bend in the mast of a masthead rigged boat. I sail a masthead with an "I" dimension somewhat less than yours and I can easily put 2" of bend in the mast by using a babystay and backstay. Bending the mast will help de-power the main but I doubt it will make any difference in your pointing ability. On the other hand, if your helm is neutral, adding mast rake will help you point higher. I don't think you're talking about rake though. It's all about balance. A blanket statement regarding proper mast bend or rake is nearly impossible to make. To make more accurate suggestions we need some additional information from you about the sailing characteristics of your boat and the conditions in which you are trying to improve upon.
What is being described is mast 'pre-bend' quite standard for both masthead and fractional rigs.
For single spreader boats 1/2 to 3/4" forward bowing of the mast is standard set up.
For Multiple spreader boats typically 3/4" to 1" per set of spreaders.
1. Your mainsail was most probably cut to these bowed dimensions, and if the mast is straight-up will be slightly powered-up with with increased draft. .... sail will be less 'fast' and wont point as well in relatively flat water (~1-1.5ft. chop). Such 'power shapes' (increased draft) in the mainsail are for 'blasting' through heavy chop/waves (2nd gear), but not 'fast' . Flat sails with minimum draft are for FAST sailing in flat water (high gear).
2. Mast prebend prevents the mast from being 'excited' at lower windstrength conditions. Mast pumping is an excitation of the natural harmonic frequency of oscilation of the mast - the very same oscilation that makes a guitar string "vibrate in resonance'. Pre-bending radically changes the natural frequency so that it only occurs (intent) at very high windstrength conditions.
Pre-bending the mast is 'standard' rigging tune.
For single spreader boats 1/2 to 3/4" forward bowing of the mast is standard set up.
For Multiple spreader boats typically 3/4" to 1" per set of spreaders.
1. Your mainsail was most probably cut to these bowed dimensions, and if the mast is straight-up will be slightly powered-up with with increased draft. .... sail will be less 'fast' and wont point as well in relatively flat water (~1-1.5ft. chop). Such 'power shapes' (increased draft) in the mainsail are for 'blasting' through heavy chop/waves (2nd gear), but not 'fast' . Flat sails with minimum draft are for FAST sailing in flat water (high gear).
2. Mast prebend prevents the mast from being 'excited' at lower windstrength conditions. Mast pumping is an excitation of the natural harmonic frequency of oscilation of the mast - the very same oscilation that makes a guitar string "vibrate in resonance'. Pre-bending radically changes the natural frequency so that it only occurs (intent) at very high windstrength conditions.
Pre-bending the mast is 'standard' rigging tune.
Rig tuning - prebend
http://www.ballengerspars.com/mtguide5-97.html
http://hallinc469.corecommerce.com/~hallinc469/uploads/Prebend.pdf
http://www.catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=21844
http://www.kempsails.com/index2.php?option=com_docman&task=doc_view&gid=18&Itemid=12
www.ukhalsey.com/sails/onedesign/j22/J-22_Tuning_guide.pdf
..... and you can find identical prebend info from virtually ALL the major sail lofts and also the spar manufacturers. Do websearch = "mast + prebend". Just about ALL mainsails are cut with the expectation that the mast has an approximate amount of forward prebend - ~3/4" per spreader set for a mast head rig, etc.
If you do not prebend, your mainsail will be slightly 'powered-up' (slow) and the boat wont 'point' well .... simply because most ALL mainsails are cut (curved luff, not 'straight') with the EXPECTATION that mast is already properly set/tuned with the proper pre-bend.
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So too headsails are cut with the expectation that the forestay tension is at about 15% of ultimate tension load ... and the sailmaker 'slashes away' a smooth curve (luff hollow) to match the expected sag in the forestay wire --- usually designed for 15% tension and the approximate 'sag' in 15 kts. of windstrength.
Sails dont have straight 'edges', they are 'curved' and your rig needs to be properly tuned (including prebend) so that the rig 'matches' the curved 'sides' of the sails.
http://www.ballengerspars.com/mtguide5-97.html
http://hallinc469.corecommerce.com/~hallinc469/uploads/Prebend.pdf
http://www.catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=21844
http://www.kempsails.com/index2.php?option=com_docman&task=doc_view&gid=18&Itemid=12
www.ukhalsey.com/sails/onedesign/j22/J-22_Tuning_guide.pdf
..... and you can find identical prebend info from virtually ALL the major sail lofts and also the spar manufacturers. Do websearch = "mast + prebend". Just about ALL mainsails are cut with the expectation that the mast has an approximate amount of forward prebend - ~3/4" per spreader set for a mast head rig, etc.
If you do not prebend, your mainsail will be slightly 'powered-up' (slow) and the boat wont 'point' well .... simply because most ALL mainsails are cut (curved luff, not 'straight') with the EXPECTATION that mast is already properly set/tuned with the proper pre-bend.
------------------------------------------
So too headsails are cut with the expectation that the forestay tension is at about 15% of ultimate tension load ... and the sailmaker 'slashes away' a smooth curve (luff hollow) to match the expected sag in the forestay wire --- usually designed for 15% tension and the approximate 'sag' in 15 kts. of windstrength.
Sails dont have straight 'edges', they are 'curved' and your rig needs to be properly tuned (including prebend) so that the rig 'matches' the curved 'sides' of the sails.
I am surprised no one has mentioned or asked how much tension is on the stays currently. Depending on the spar, pre-bend may not be realistic. Some boats have baby-stays that also help to give prebend.
A loos gauge is very helpful. Making sure that there is sufficient backstay tension when sailing up wind to help tension the forestay is probably more important.
I start by tensioning my uppers to 15 percent of the breaking strength of the wire. I then use the main halyard to check that the mast is centered by taking it down to a chainplate on one side then the other. I center the top of the mast by adjusting the appropriate turnbuckle.
I put 10 percent of the breaking strength of tension on my backstay. When I am beating into the wind in strong winds, My backstay tension is about 2000 lbs.
My lower forward shrouds are at 10 percent, my lower aft shrouds about 8 percent. I then sight up the mainsail track to make sure that the mast is in column.
If there is a question of rake, I put a weight on the main halyard and see how far aft the top of the mast is.
A loos gauge is very helpful. Making sure that there is sufficient backstay tension when sailing up wind to help tension the forestay is probably more important.
I start by tensioning my uppers to 15 percent of the breaking strength of the wire. I then use the main halyard to check that the mast is centered by taking it down to a chainplate on one side then the other. I center the top of the mast by adjusting the appropriate turnbuckle.
I put 10 percent of the breaking strength of tension on my backstay. When I am beating into the wind in strong winds, My backstay tension is about 2000 lbs.
My lower forward shrouds are at 10 percent, my lower aft shrouds about 8 percent. I then sight up the mainsail track to make sure that the mast is in column.
If there is a question of rake, I put a weight on the main halyard and see how far aft the top of the mast is.
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