Does 2:1 halyard lessen load on mast head sheave?

[atmartin]

Originally Posted by rhubstuff

Anyone who claims that the sheave takes 100% of the load of a 2:1 halyard purchase must also admit that the tang end takes 0%. This is clearly impossible. The tang takes 1/2 the load, the sheave the other half, regardless of wind loading, weight of the sail, etc. If this were not true, the tang could be removed without consequence.

No one is claiming that the tang makes no difference. If by 'load' you mean force from the head of the sail, in the OP's setup the sheave takes 100%, the tang 50%. Without the 2:1, the sheave would take 200%. So, there's certainly a difference.

Originally Posted by rhubstuff

I think I'll use this as a test question when interviewing crew. I might not want to sail with someone who clearly doesn't know basic high-school level physics and fails to see what is patently obvious.

'Clearly' it isn't 'obvious' based on the length of this discussion. Imagine someone takes a block with a safe working load of 300 lbs and runs it up the main halyard. He takes one end to a winch and ties the other to the bosun's chair. Now he wants to hoist a 200 lbs crew member up on that block. If you follow savoir's thinking a 200 lbs 'load' could never put more than 200 lbs on the block, so haul away! Of course, many of us realize that the block will need to support 400 lbs in this scenario. So, I agree with you, I wouldn't want to sail with such a person either.

Adelie, pizzazz and others have done yeoman's work explaining the physics behind this and it's a shame that some posters don't appreciate that.

[rhubstuff]

Originally Posted by savoir

I'm sure glad you weren't my math teacher.

OK. I just went out to my shop and, using a fish scale and a gallon of paint, proved myself absolutely WRONG!! Always hated math anyway. I get it now, Savoir.

[Training Wheels]

Much respect for admitting your mistake. I've always thought a true measure of a man is admitting when he is wrong.

[rhubstuff]

Originally Posted by Training Wheels

Much respect for admitting your mistake. I've always thought a true measure of a man is admitting when he is wrong.

God, I hope my wife doesn't see this thread.

[LongRange]

This is from the boat moored right next to mine. It reminded me of this thread, and just how much physics is applicable to sailing and boating in general.

[jkishel]

An additional point; as correctly noted in several posts the load on the sheave is twice the halyard tension. The halyard tension required to just raise the sail is equal to the sail weight for a one part halyard and half the sail weight for a two part halyard (one third the sale weight for a three part halyard, etc.). However, as halyard tension is increased beyond that required to just raise the sail (continuing to crank away on the halyard after the sail is up), the sheave load will increase accordingly.