Main Halyard Question

[Andrew Troup]

Originally Posted by roverhi

If the sail requires 500 lbs force to raise, the compression load from the block at the mast head will be 500#s no matter how many purchases there are in the Halyard. The force required in pulling on the lines will be reduced but the load on the blocks/sail will remain the same.

The downforce ('compression load') on the pin of the block at the masthead would be 1000lb, not 500.

Think of replacing the sheave with a horizontal lever, pivoted on the sheave pin, with the head of the sail shackled to one end and pulling down with 500 lb, and the halyard shackled to the other end, also pulling down with 500 lb

It's like two 500lb fatties sitting on a seesaw, and the support pin had BETTER handle 1000lb or there will be tears !

[Andrew Troup]

Expanding that analogy, now think of a seesaw where the pivot pin, rather than being at the midpoint, is one-third in from one end.

And the 500lb fatty on the end nearest the pivot is balanced by a 250lb stripling on the other end.

Now the pin only 'sees' 750 lb, on this "2:1" seesaw.

no?

[thinwater]

Originally Posted by Suijin

Cored lines get most of their strength from the core and the braided cover is largely protective, so those can go a bit longer but you should still replace them if the core gets exposed.

If we are talking about polyester double braid...

No.

First, the line is balanced with about 50% in the cored and 50% in the cover. the splicing method depends on that.

Second, I have pull-tested old polyester (so have others), and typically the cover and core are equally deteriorated. The cover sees UV and the core sees abrasive wear. If you believe this is incorrect or counter intuitive, please break-test some lines and get back to us.

[thinwater]

Originally Posted by DotDun

Since the original discussion was on mast compression, not halyard/luff tension, transmitterdan is correct. If the halyard is cleated on the mast, the mast compression is the same, purchase or not.

No.

Basic engineering statics; the halyard contribution to mast compression is exactly the cleating load, which will be about 55% with 2:1 purchase.

There is a zone of full compression, between the tie-off point and the mast head pulley, about 4 inches long.

Troup had the core of it. I think what Roverhigh is missing is that though the downward force of the purchase is logically the sail luff tension, the load on the masthead is the sum of the purchase loads plus the tail load. With 1:1 the compression is 2x, with 2:1 it is 1.5x, and with 4:1 it would be 1.25x (with a correction for sheave friction, which is material at high purchase). With a lock it is 1x.

[sabray]

I am guessing but for cruising. Xls is getting the same uv exposure as any other line. I wouldn't put a lot behind any halyard after 7 years of sun. So I use xls for halyards .


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[savoir]

Dyneema halyards are a little OTT for any cruising boat, and besides, they cost more than three times as much as a plain polyester product such as XLS. There is no way your boat will respond to the weight saved because it is just too little.

The best bang for the buck in a main halyard rope is New England VPC. It offers high abrasion resistance due to its thick cover combined with only moderate stretch in the Vectran core. In addition you will be able to go down in size from 12mm to 11 mm because of the product's added strength. Currently at Defender 7/16" ( Americanese for 11 mm ) VPC costs $1.74/foot, 1/2" XLS $1.24, while 7/16" Warpspeed costs a whopping $4.20. The additional weight of the VPC halyard over Warpspeed of the same diameter will only be about 1/2 lb.

There are plenty of ropes with higher strength and lower stretch than VPC but all cost big buck$. If you would prefer an all polyester product then the one with the lowest stretch is NE Ropes Sta Set X which in 1/2" size is currently $2.32 at Jamestown.

[conachair]

Originally Posted by Andrew Troup

Expanding that analogy, now think of a seesaw where the pivot pin, rather than being at the midpoint, is one-third in from one end.

And the 500lb fatty on the end nearest the pivot is balanced by a 250lb stripling on the other end.

Now the pin only 'sees' 750 lb, on this "2:1" seesaw.

no?

Like it

As a system of pulleys is basically a system of levers.

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[Andrew Troup]

Thanks conachair.

OK, might as well extend the analogy and see if it can be made to serve for the halyard lock.

Take the simple 1:1 lever analogy, with 500+500 lbs pulling the masthead downwards.

Now imagine the pin to which the head of the jib connects is hollow, and lines up with a suitable hole provided in the mast. Slide a bolt through it, locking the lever, and let the halyard loose.

Do you make it 500 lb only, downwards force? I do too.

I suppose it's like an infinity : 1 purchase, once you lock it.

And notice that the former pivot pin is now doing nothing.

And sure enough, if you revisit the seesaw analogy, a halyard lock is like moving the pivot all the way to the end with the fatty.

The person at the other end now needs to weigh nothing;
The entire weight of the fatty, but no more, is now bearing down on the pivot pin.

[StuM]

> With 1:1 the compression is 2x,

So let's put a jamming cleat on the headplate of the 500lb sail, run the halyard down from the masthead sheave through the cleat. Once the sail is up, lock the halyard in the cleat at the headplate of the sail. Are you telling me that the sheave at the top which is supporting 500lb of sail is subject to 1000lb of downward force? Where is the other 500lb of load coming from?

(Ignoring additional forces from luff tension - obviously once you tension the luff, there will be greater compression loads equal to the tension in the luff.)

[Andrew Troup]

Originally Posted by StuM

> With 1:1 the compression is 2x,

So let's put a jamming cleat on the headplate of the 500lb sail, run the halyard down from the masthead sheave through the cleat. Once the sail is up, lock the halyard in the cleat at the headplate of the sail. Are you telling me that the sheave at the top which is supporting 500lb of sail is subject to 1000lb of downward force? Where is the other 500lb of load coming from?

(Ignoring additional forces from luff tension - obviously once you tension the luff, there will be greater compression loads equal to the tension in the luff.)

What you describe with the jamming cleat on the headboard is analogous to a halyard lock, not to a 1:1 conventional halyard. So no surprise that only 500lb of downforce is fed into the mast.

Your analogy loses sight of the importance of where the halyard tail is cleated. Cleat it to the mast at the masthead, and there is no resulting compression (from the halyard tension) carried in the remaining mast tube.

This also is similar to a halyard lock.

Cleat it on the sail (as you suggest) and the force of the halyard tail cannot be transferred to the mast anywhere, anyhow.

[Matt Johnson]

Whats the life expectancy of a dyneema/ poly halyard. I have some lying around that has a very sun-bleached poly cover (blue which is now a light purple) and unsure if the dyneema core has been effected. Any easy way to check if the line is a total loss?

Matt

[colemj]

Most likely the halyard was sized to fit a rope clutch and not the load it would experience and is oversized for your actual use. This would give it quite a margin for degradation.

If the cover is bad, you can recover it by buying cover material cheaply. We did this a couple of years ago. I got our cover from Annapolis Performance sailing.

Mark

[Cruisin Cat]

Originally Posted by Jim Cate

You might give Emmet Ropes in Tingalpa a call for a quote on various bits of cordage. His prices are WAY lower than Whitworths et al, especially on longer lengths, and he can supply most sorts of modern line. We've used this vendor for some time now and had good luck and good prices.

Cheers,

Jim

Jim,
Thanks for the recommendation on Emmetts Ropes...they certainly seem to know ropes, and as you said, their prices are way under the chandleries, almost down to half for double braid.
Barrie

[Jim Cate]

Originally Posted by Cruisin Cat

Jim,
Thanks for the recommendation on Emmetts Ropes...they certainly seem to know ropes, and as you said, their prices are way under the chandleries, almost down to half for double braid.
Barrie

G'Day Barrie,

Glad that it worked out. I enjoy going out to their shop to pick up cordage. Their business is making things out of rope, not selling rope... things like cargo nets, tugboat fenders, ladders and other interesting stuff. Always fun to poke around and watch folks who can throw in an eye splice faster than you can tie a bowline!

Cheers,

Jim

PS They don't do plastic money, so take cash or a checkbook.