Masthead multipliers

[Endemann]

I have finally gotten on the site to ask a question. Sorry to tell you that my computer skills put me in limbo when I have to sign in, make up a password, etc. Very hard for a guy who is in the computer generation gap. Can you guess my age?

QUESTION: When you put tension on a halyard, especially with a bendy mast; is there a mechanical advantage of 2:1 that compresses the mast? I ask this as a comparison to a halyard lock, where the tension might be more than the weight of the sail but not doubled due to the fact that the masthead sheave MIGHT be moving downward as a result of the "purchase" created by a masthead block. Can someone answer this for me, I would love to hear from you. Thanks, Fendemann@gmail.com

[Ian McColgin]

There's also halyard stretch. Really, you're over-thinking the hypothetical. You tension the halyard to a final result that inevitably includes whatever the marginal (given modern materials, it was not always such) bend, stretch, sag etc. so it's not a noticable deal. Besides, whatever you can do with a halyard is utterly trivial compared to the compression from shrouds and stays.

G'luck

[Stumble]

End,

There most definatly is a compression load caused by the halyard but as Ian points out it is pretty minimal compared to shroud loads, and masts are designed (even the bendy ones) with this halyard tension in mind. So for the vast majority of sailors there is no issue.

That being said, in very high end long distance racing boats (Open 60's, Maxi Trans-Pac boats, ect...) boats will replace the halyard with either a strap, or special hardware that holds the sail up. This not only reduced compression loads, it also prevents halyard chaff, and reduces weight aloft. But these pieces of hardware are completely unecessary for the average sailor (even the average long distance racer).

Take a look at http://www.southernspars.com/souther...uildpage&p=446 for a primer on the systems.

[allene]

Originally Posted by Endemann

QUESTION: When you put tension on a halyard, especially with a bendy mast; is there a mechanical advantage of 2:1 that compresses the mast? I ask this as a comparison to a halyard lock, where the tension might be more than the weight of the sail but not doubled due to the fact that the masthead sheave MIGHT be moving downward as a result of the "purchase" created by a masthead block. Can someone answer this for me, I would love to hear from you. Thanks, Fendemann@gmail.com

My wife always want to know why I ask a question and I always say because I want to know the answer, not because I think she did something wrong. You asked a question and the answer is yes, there is a 2:1 mechanical advantage in that the mast sees an additional compression of 2x the halyard tension. With a halyard lock, it would be 1x and with a 2:1 halyard setup where the halyard is attached at the masthead, goes through a small block as part of the halyard shackle, then back up to the masthead and down to the mastbase, there would be a 1.5:1 multiplier as the halyard going back down the mast carries 1/2 the load of the sail.

[Brion Toss]

[quote= there would be a 1.5:1 multiplier as the halyard going back down the mast carries 1/2 the load of the sail.[/QUOTE]
I think you mean .5:1, yes?
Fair leads,
Brion Toss

[allene]

Originally Posted by Brion Toss

I think you mean .5:1, yes?
Fair leads,
Brion Toss

Well, I meant that setup with the 2:1 block on the sail shackle puts a compression load on the mast of 1.5 times the load of the main. But that does result in a .5:1 load on the halyard going down the mast. I think it is all relative but I was being relative to the compression load.

Allen

[Endemann]

Thank you all for chiming in on the question of halyards and mast compression.
My most recent boat is a Nonsuch and I love to watch people gape at the swaying masthead when I ask them to sit in the padded pulpit seat. I recently delivered a J 122 that had a gorgeous combination halyard shackle/block and it worked beautifully but I started to wonder about the old compression thing.

Remember when two of the AC boats bent in the middle (one sank) about 8 or 10 years ago?
Now that's compression!! Endemann