Jib sheet blocks
- Thread starter higgs
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You will need to provide the following information to get your answer.
1. What is the square footage of your headsail?
2. What is the angle that the genoa sheet makes with the deck. Measured from the deck to the sheet forward of the genoa lead block? (This can be roughly calculated if you provide the "I", "J" and "LP" dimensions.
3. What will be the maximum wind speed that the sail will be used in?
Without this information you can't determine the load on the genoa lead block.
1. What is the square footage of your headsail?
2. What is the angle that the genoa sheet makes with the deck. Measured from the deck to the sheet forward of the genoa lead block? (This can be roughly calculated if you provide the "I", "J" and "LP" dimensions.
3. What will be the maximum wind speed that the sail will be used in?
Without this information you can't determine the load on the genoa lead block.
What came with the boat?
If you don't have them, ask someone w/ the same, or a similar boat.
At any rate track track will limit the size of block if they are integral.
Lastly, what is the strength of your sheets? 1/2 " line? 7/16" inch line?
If you don't have them, ask someone w/ the same, or a similar boat.
At any rate track track will limit the size of block if they are integral.
Lastly, what is the strength of your sheets? 1/2 " line? 7/16" inch line?
Sq footage means nothing when comparing a tender boat to a stiff boat. Angle of the lead will change as the sail is furled in heavy air. Max wind speed? Who the hell knows what is going to happen? One certainly wants a block that is strong enough to take a knock down.
I am looking at blocks rated at 3000 lbs. How much load is placed on a typical 35 footer taking a knock down?
I am looking at blocks rated at 3000 lbs. How much load is placed on a typical 35 footer taking a knock down?
There have been a few discussions about wind pressure a while back.
http://forums.sbo.sailboatowners.com/showthread.php?t=74065&highlight=wind+pressure+psf
http://forums.sbo.sailboatowners.com/showthread.php?t=93442&highlight=wind+pressure+psf
http://forums.sbo.sailboatowners.com/showthread.php?t=74065&highlight=wind+pressure+psf
http://forums.sbo.sailboatowners.com/showthread.php?t=93442&highlight=wind+pressure+psf
I've got the answer if you can provide the necessary information needed to calculate it. Sail area is of utmost importance because as the wind speed doubles the forces quadruple. As the wind strength increases and you begin to furl your headstay, the sheet angle changes from maybe 40 to 70 degrees which will dramatically change the load placed on the block. Generally, your highest loads would be realized with your smallest headsail being used in appropriately windy conditions.
Damn, Higgs....... you post a technical question on Sunday evening and don't get the answer you want within a few hours.. and so you make the assumption that no one knows...... Yikes!...... some of the guys take a day off from the forum, I'll bet.
If I had a question like yours I think I would would pose it to a known expert.... such as a tech rep at Ronstan, Garhaurer, Harken ... etc. People who set boats up for a living might have the "rule of thumb" answer we need.... because, like you, I think I'd be unsure in coming up with the data Ted requested.
Give it another day or so for more people to comment.... but I'd still call a tech expert.
If I had a question like yours I think I would would pose it to a known expert.... such as a tech rep at Ronstan, Garhaurer, Harken ... etc. People who set boats up for a living might have the "rule of thumb" answer we need.... because, like you, I think I'd be unsure in coming up with the data Ted requested.
Give it another day or so for more people to comment.... but I'd still call a tech expert.
Higgs:
Have you gone to the Harken website yet? They have sections that provide equipment recommendations for various boat size ranges. Look up the corresponding safe working load for the recommended jib sheet blocks.
Have you gone to the Harken website yet? They have sections that provide equipment recommendations for various boat size ranges. Look up the corresponding safe working load for the recommended jib sheet blocks.
"What came with the boat are blocks that no longer spin easily, making sheeting a lot harder."
I think I would put some effort into getting what I had already had working properly. Seems like you have a pretty decent boat with decent gear already aboard, and that what you have only needs some maintenance, rather than replacement.
I certainly would try that before shopping around for new blocks that could set you back several hundred bucks.
A friend just replaced his perfectly fine gene blocks with these new, extremely sexy looking ones that cut his sheets and 3/4" double braid ain't cheap. He was pretty chagrined as it is a 53' boat and the new blocks cost a whole lot of money!
I think I would put some effort into getting what I had already had working properly. Seems like you have a pretty decent boat with decent gear already aboard, and that what you have only needs some maintenance, rather than replacement.
I certainly would try that before shopping around for new blocks that could set you back several hundred bucks.
A friend just replaced his perfectly fine gene blocks with these new, extremely sexy looking ones that cut his sheets and 3/4" double braid ain't cheap. He was pretty chagrined as it is a 53' boat and the new blocks cost a whole lot of money!
How much tension is in the sheet? On my boat I have 46 power winch and estimate I push on the winch handle with 50 lbs. So that gives 2300 lbs of tension in the sheet on a beat on a windy day. The turning block takes the sheet through 160 degrees or so , call it 180 and this means it sees 4600lbs. So rather than fuss about with how much force the wind/sail combo generates you can look at it backwards and ask how much force you generate.
Now the interesting thing is how much safety margin? New England ropes (I think) has a nice video showing some hi tech line snapping at 20,000 lbs of force hella strong. Same rope snaps with a 200 lb weight (i.e. the arborist) dropped 6 ft so the rope has so little stretch that any shock will generate tremendous forces and break the rope.
So given that knowledge I go looking for rope datasheets and get essentially no joy. SWL is shown generally, stretch sometimes and shock absorption not at all for sailing ropes.
So what to do? You kinda have to trust the experts, those who have done this before many times and have learned what works and what breaks. Harken website had good info, Ronstan web site has good info.
Now the interesting thing is how much safety margin? New England ropes (I think) has a nice video showing some hi tech line snapping at 20,000 lbs of force hella strong. Same rope snaps with a 200 lb weight (i.e. the arborist) dropped 6 ft so the rope has so little stretch that any shock will generate tremendous forces and break the rope.
So given that knowledge I go looking for rope datasheets and get essentially no joy. SWL is shown generally, stretch sometimes and shock absorption not at all for sailing ropes.
So what to do? You kinda have to trust the experts, those who have done this before many times and have learned what works and what breaks. Harken website had good info, Ronstan web site has good info.
You determine the SWL for the existing block and go get a better one that fits your jib sheets. No need to turn this job into a physics calculation.
Sorry I got impatient. I agree this does not need to be a physics equation. I did write Garhauer about this, but they have not responded. I have had trouble communicating with Garhaur in the past. Left several messages for Guido and never got a reply. Anyways, the guys at Obbersheimer's in Buffalo, NY seem to be on top of this. As for maintaining my old blocks as was suggested - and not a bad suggestion - but I want more. The jib is oversized for the winches and I am thinking some ball bearing blocks would help make trimming the big jib easier. New blocks are lot cheaper than a set of big self tailers.
Higgs...
Schaeffer 500 series may be marginal for a 150's load, so would consider their 700 series blocks. Get their (or any maker's) catalog and you'll find all the loading data in their specs.
Schaeffer 500 series may be marginal for a 150's load, so would consider their 700 series blocks. Get their (or any maker's) catalog and you'll find all the loading data in their specs.
Garhauer, like Catalina yachts, doesn't do email too well. That's why they still use telephones. 
Call Guido
While Garhauer may not do email so well - they are great over the phone. Call Guido. My experience with the Garhauer folks:
1. They'll know the answer to your question.
2. They'll have a very high quality product to fit your need.
3. The price will be better than the other brand names.
4. If there's a problem, their customer service is outstanding.
While Garhauer may not do email so well - they are great over the phone. Call Guido. My experience with the Garhauer folks:
1. They'll know the answer to your question.
2. They'll have a very high quality product to fit your need.
3. The price will be better than the other brand names.
4. If there's a problem, their customer service is outstanding.
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