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Old 14-11-2008, 11:07   #16
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I am replacing all but masts and booms on a 47 foot ketch, ouch$$$. New chain plates old tangs. everything in between, pin to pin will be new. I am not a rigger but wonder if you talk with someone more knowledgeable about a compression post under the main if you like that idea....Just a thought.
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Old 14-11-2008, 11:32   #17
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Hi Amgine,
You're talking about a mizzen staysail. They are wonderful but you don't need a dedicated stay to use them, just a substantial luff on the staysail and an extra halyard on the mizzen mast. They add a lot of power in light winds when on the beam. I really loved flying mine when the wind was right.
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Old 14-11-2008, 14:35   #18
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It may come as a surprise to some but many of the tube sections being manufactured today are the same as the sections of 25-30 years ago and some might argue that the quality of the aluminum is not as good as it was in the early to mid-80's. Hence an "Up-grade" might not be. Increasing the mast height can be accomplished by adding a few feet of extrusion to the bottom of the mast, which is a fairly routine matter, but one needs to take a hard look at how that changes the rig's geometry as, without an attendant increase in the length of boom, the aspect ratio of the main is increased--leading to more difficulty trimming--and the center of effort is rasied changing stability and sail carrying capacity, which obviates the advantage of increased sail area. Moreover, an additional spreader and added intermediate shroud may be required, increasing complexity and weight in the upper 1/3rd of the rig.

Further, one needs to think long and hard before arbitrarily changing the design of a rig, and particularly lightening a rig with a thinner extrusion. For example, some believe that substituting a carbon fiber spar for aluminum is an improvement that makes for a "stiffer" boat and allows one to remove ballast--presumably creating a faster boat as well for a given sail area. Unfortunately, however, an unintended consequence of same is a radical reduction in the yacht's moment of inertia and radius of gyration which leads to significantly reduced roll damping and much faster roll periods, so much so that a yacht can easily become unmanagable--if not unindurable--in even moderate seas. A friend of ours spent rather a huge amount of money to re-rig his mid-80's Swan with a Carbon fiber mast and high tech fiber rigging--and chopped 1200# of ballast off his keel--only to discover that he'd made his boat all but unmanagable in conditions that the yacht had previously handled with aplomb. (Similar to the changes that were made to the recently lost "Freefall".) After two seasons he admitted his mistake and spent another fortune to return the yacht to its original condition.

FWIW...

s/v HyLyte
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Old 14-11-2008, 15:15   #19
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Two changes, not one..

While in general I'm in agreement, your acquaintance made two changes - replacing the spar & reducing ballast - not one change. I'm fairly sure WestSail42 is only interested in making considered changes which are suggested by NA/Riggers/Sailmakers after examining the situation pretty carefully, and that it would not include reducing ballast.

Yes, reducing the mass of the rig aloft can reduce the inertia enough to be significant, but not usually. Especially if you're also increasing the length of the stick. The benefit of the carbon fibre mast is that the weight savings is noticeable although not likely to be dramatic with a boat whose mast is 50 feet and would likely be as over-engineered as the aluminum one was. With no other changes such a mast should give a slight stiffening, enough to require examining the wire and chainplate strength but probably not an issue.

But that's why you consult the pros before committing yourself.
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Old 14-11-2008, 16:06   #20
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Amgin--FWIW I'm a registered structural engineer (now retired). That's what I did for too many years--and particularly dynamics. Roughly 75% of a yacht's roll stability comes out of the rig. Even a modest change can have significant effect on stability, and natural period, and it may be the latter of the two that is the more important. Moreover, I believe I did say "arbitrarily", no?

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Old 14-11-2008, 16:41   #21
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I should add, parenthetically, that adding another 5' to the mast on a Westsail 42 is not that remarkable a change and if the same section is used, will actually increase the I. It will not appreciably increase the area of the main but will raise the CE by a few feet, and may require the addition of upper spreaders et al as previously noted to get a fair shroud angle. (I, for one, am not an afficianado of spreaders.)

FWIW...
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Old 14-11-2008, 21:04   #22
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You're clearly more expert than I, but the Swan 46 from that time frame had 11,400 lbs ballast on 8.2 feet of keel while I cannot find a mast measurement quickly but the I is 62', even throwing in an additional 10' and assuming the point of oscillation is at the keelbolts I think that's going to be a butt-heavy mast to hold 75% of the inertia.

On yet another hand, this isn't about modifying an existing boat which is fully rigged and working... it's about giving our personal advice to someone who is in a position to rethink the rig for a 30-year old design before it gets finished.
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Old 15-11-2008, 05:17   #23
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Amgin--

I don't want to belabor this discourse and this shall be my last comment on the matter. However, for the record, the yacht I sited was a Swan 651 which my old notes indicate had a displacement of about 75,000 lbs with a mast height of 100+/- feet. Approximately 7% of the yacht's displacement was in the rig yet it accounted for approximately 65% of the yacht's mass moment of inertia (incremental contribution to "I" being dependant upon the square of the disposition from the selected roll axis.) If you wish to pursue the matter further, I refer you to CA. Marchaj's tome, "Seaworthyness"--particularly pages 214-220, inclusive, for a more articulate exposition than my own.

With regard to the significance of the foregoing to the original enquiry, there is none. My supplemental observations were digressionary. Returning to the enquiry, from an admittedly cursory perspective there would seem to be little gain for the cost of replacing the rig with a more "modern" substitute and, in every case, one must keep in mind the law of unintended (and often unrecognized) consequences.

FWIW...

s/v HyLyte
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Old 17-11-2008, 07:25   #24
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Thanks for the replies. Yeah, "splicing" a section was something I had not considered. And, stepping the mast at the keel instead of the deck would be an option.

What I might do is walk into my local riggers shop and ask "How much does 50 feet of aluminum mast with this approximate cross section cost these days?"

His response may prompt the decision right then and there ;-)
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Old 17-11-2008, 07:28   #25
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42:
Keep in mind that the deck stepped spar will require a stronger section than a keel stepped spar. Theoretically anyway. Often times if you "round up" the moments you end up with the same section anyway. But there is a chance you could use a lighter section if you keel stepped it and that could save some money on the extrusion.
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Old 17-11-2008, 08:27   #26
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Experience from another 42

R,

We've now been offshore twice with our boat. Not a lot of exp but something that has effected me more than I thought was the shrouds. We have the 55' spar with the double spreaders and the cutter rig. We also have the designed boom for the boat. What effect me most is the double spreader rig. The lower shrouds have such an angle that I have learned to hang on and swing inboard. It's just weird; but I figure it's nothing that anyone would have really considered.

A second observation is from a friends Westsail 43. He has the tall rig too and he followed Kern's (Primary sailmaker for westsails) recommendation and cut I believe a foot and a half off of the boom and went with the "Super Yankee" that Kern pushes. After a 1 1/2 of full time cruising he is really happy with what he's done.

We have a Genoa and a Yankee. I don't know what size Yankee (I think it's about a 90% or so and we felt the Genoa was just to damn big and we replaced it with the Yankee. Sailing from Marathon to West End Grand Bahama's we carried full sail all the way with 20 - 25 kts wind the entire way. Great sail.... Lumpy ride.

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