Halyard Locks reduce mast compression?

I would like to know if Halyard Locks reduce compression on mast.
Southern Spars says that it reduces the mast compression produced by the halyard, but some people said the reduction is up to 50%, is this correct?
If somebody can explain the halyard forces on the mast, it will be welcome.

Thanks in advance
Luis Temperini
Los Angeles, CA

http://www.southernspars.com/index.cfm?sector=4&shownews=34
http://www.snipe.org/list/ListArchive/snipe-list-digestV1-24.txt

 

With a single-part halyard, you have the end attached to the sail pulling down on the mast, and you also have the running end pulling down on the mast. So the total compression is twice the halyard tension. The running part is essentially acting like a bow-string to compress the mast.

With a halyard lock, the tension on the running tail of the halyard is released, so you only have the sail pulling on the mast. Hence the 50% reduction in the compression provided by the halyard.

You can also reduce the mast compression by going to a two-part halyard, with a block on the head of the sail, one end of halyard made fast on at the head of the mast, and the running end tied off on the mast or led aft. In this case, the tension in the halyard is half what it is with the one-part halyard, and you have two halves provided by the sail and one half provided by the running part, so the total compression is 3/4 that of the single-part halyard, for a 25% reduction and no halyard lock.

But the tension from the sail and halyard is only part of the compression on the mast. You also have the shrouds, forestay, other halyards, main sheet, and vang. So halyard locks won't get you to 50% of the total compression.

 

I think it does... The idea is that without one you've got the tension in the luff of the sail and the halyard compressing the mast, while with a halyard lock (also referred to as a skyhook) there is no tension in the halyard beyond the hook so only the tension in the luff of the sail puts the mast in compression. They're relatively common on dinghys, tornados in particular I believe

 

Thank you guys.
It is what I thought, but I was needing a confirmation.
There was no mention about this in the whole forum, so now there is.
Thanks again
Luis

 

I suppose that if the spar is in a static position with no loads other than the main halyard, that analysis is true. On a boat underway, there are a lot of other variables that affect mast compression. If the mast is rigged with side and forestays, the compression from these will be far higher than from halyards. Compression from the side stay alone will, in fact, be equal to the righting moment of the whole boat. When added to compression from the forestay/jib/backstay/mainsheet combination, the compression from these sources make compression from a main halyard trivial.

If the mast is unstayed and it bends aft, as it will do underway, the sail luff will lock itself in the slot and the tension will ease due to mast bend. This is also true for stayed spars.

Compression from jib and spinnaker halyards, unless they have upper locks, will make for more tension translated to spar compression than the main halyard.

External halyards will however, when the spar bends, go out of column and exert more bending moment than either locked or internal halyards.

In other words, it's not a simple answer but halyard tension is not usually a major player in mast compression.

 

I know that halyard locks was used in old 12m S.I. and it's now used in hobie 16 and some other dinghy, do you know wich other boat use it?
In hobie 16 it's almost impossible to reef the main while you're sailing, because of the absurd shape of halyard lock, how is this problem solved on other boats???
if it has been solved.....

thanxs
Mistral

 

Mistral,

I've never seen a commercial halyard lock that looks very good although I have made several for small racing boats.

One is a piece of stainless shaped on the flat like two saw teeth with a slot down the middle. The halyard wire runs in the slot and is fitted with a swaged ball. At the proper location, the ball rides over the first tooth and drops behind it. When you hear and feel that click, release tension and the halyard locks in place. When you want to take the sail down, pull the halyard ball over the second tooth and release it. The ball goes back through a widened hole in the slot at the bottom of the fitting and escapes back under the the teeth and out through another hole at the top. Its all automatic and works sight unseen.

If other balls are swaged at the proper locations for reefing, it works for that also.

Harder to describe than to see. If you e-mail me I may be able to find an old drawing.

The ususal ones seen with a spur on the aft side of the masthead that is supposed to capture a ring on the headboard are a pain in the rump even if you can see them.

 

thanks Tom, i was just curious ) In hobie 16, the boat wich i used to sail 'til few months ago, halyard lock is , brutally speaking, a steel fork riveted to the mast, where you have to stuck the nicopress that close the halyard; this operation is quite annoying when you launch your boat on the beach, but it becomes practically impossible to do while you're on the water,or at least i think so. I was just curious, your experience seems to prove that anyway halyard lock is not a very smart sistem !!!

fair wind
Mistral

 

The most loading is on the headsail ,

so combining a toggle with a halyard lock would make sense.

Tension the sail from the tack with a downhaul.

FAST FRED

 

http://ourworld.compuserve.com/homepages/Chris_AES/halydlok.htm

Has pictures of the mastlock on my 52' cat with an 82' mast, and 1500 sq. ft. main.
Not real convenient at times, but it works.