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Block selection help please

1886 Views 10 Replies 8 Participants Last post by sailingdog, May 27, 2009

Flatfendershop

Discussion Starter · May 26, 2009

Hello, I need to see if anyone has a suggestion for application of blocks for my boat. I sail a 1967 Venture 21. The main sail sheet runs through a single block on the starboard gunwale and a double block that is attached to the aft end of the boom. Both of these blocks currently have 1 inch sheaves, and appear to be original (they look like good quality sailing blocks). They are TUPHBLOX from England and are a stainless steel and composite make up.

The sheaves roll fine and seem to be in good shape, but the sheet is not real easy to draw in or let out. I'm getting friction somewhere.

Since I am going to replace the blocks, would it be better to go with a slightly larger sheave? Say a 1 1/2 inch?

I was looking at some Harken Big Bullet with 1 1/2 inch sheave. Is this the sort of block I should be after or would something else be better?

Keep in mind this is an older, simple, fairly inexpensive boat - so I don't need overkill but I do like to stay out when it starts to blow!

Many thanks.
Flat
1967 V-21
Quixotic

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merc2dogs

· #2 · May 26, 2009

Larger blocks generally do pull easier. I'd also see how flexible the line itself is, with my old portager (same setup for the mainsheet) I bought new line that turned out to be so stiff it was a real pain to work with.
For that setup having a more flexible line helps. If it's an older sheet, try washing it (net bag in the washer, hang dry) That's more of an issue if you're in salt though.

Ken.

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negrini

· #3 · May 26, 2009

Dig Harken Inc. as they have an extensive documentation about blocks sizing and recommendation. Very useful !

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Flatfendershop

Discussion Starter · #4 · May 26, 2009

Thanks for the thumbs up on Harken, they seemed to have their ducks in a row.

Ken, I'll check my sheet, it is an older line and has been in the Great Salt Lake, but not regularly. I've never washed it, but will. I'll try a couple of other lines to compare.

What about the sheave diameter, is upsizing 1/2 inch enough to matter? I don't want to go too big and have a big clunky block on the boom.
Thanks for the help.
Flat.
1967 V-21
Quixotic

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christyleigh

· #5 · May 26, 2009

negrini said:
Dig Harken Inc. as they have an extensive documentation about blocks sizing and recommendation. Very useful !

Gather all the info you can from Harken or whomever ...... but buy from Garhauer for a lot less with enough quality that you will never notice the difference.

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radly53

· #6 · May 26, 2009

I ll second the vote for Garhauer blocks. I replaced some last year and Ive been so happy with them I ordered 12 more this year. They arived 3 days after I placed the order.

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zz4gta

· #7 · May 26, 2009

Find out what the load on the mainsheet is going to be. Size accordingly. If you have friction, and its not in the blocks, replace the mainsheet. Also, blocks my run free with no load on them, but bind up or be rough once a load is applied.

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sailingdog

· #8 · May 27, 2009

A few points to make.

First, Harken's sizing guide is excellent.

Second, Garhauer makes some very good blocks for a reasonable price.

Third, mainsheet friction is due to sheet size and amount of rope required. A thinner mainsheet will be faster than a thicker one, a lower leverage purchase will be faster than a higher one....

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Flatfendershop

Discussion Starter · #9 · May 27, 2009

Sailing Dog, I understand all of what you described except "a lower leverage purchase will be faster than a higher one....". Could you please clarify?

I called Garhauer yesterday...yikes! My first impression was not favorable. The lady that answered the phone had all the customer service savvy of one of Marge Simpson's sisters. I sat on hold waiting for someone named "Guido" (all the while my knee caps started to hurt and thoughts of cement boots went through my mind). Well Guido was out for the day, nobody else seemed to have any knowledge of the blocks they sell so I hung up. Saving money is not always what it's cracked up to be.

Anyway, back to leverag purchase...

Flat.
1967 V-21
Quixotic

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tommays

· #10 · May 27, 2009

Well

On a 4:1 you have to pull 4' to move the boom 1' and so on as you go to 6:1 or 8:1

We just changed from a 6:1 to a fancy 4:1/8:1 AND DUE TO THE WAY its not WORKING OUT THE 6:1 MAY GO BACK ON

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sailingdog

· #11 · May 27, 2009

Basically, aside from what TOmmays said about how much line is involved, the more blocks a line goes through, the more friction it experiences. Having four sheaves in a typical 4:1 setup creates less friction than the six sheaves in a typical 6:1 setup. The better the sheaves, the less friction they create.

For dynamically loaded lines, like a main sheet, you generally want roller or ball bearings, which are good at reducing friction, but aren't very good under static high loads. For a halyard, which is primarily a statically loaded line that isn't often adjusted, you usually want sleeve bearing blocks, since the sleeve bearings are generally less likely to deform under a high static load.

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