7:1 to 8:1 conversion

Hi,

Please look at Annapolis Performance Sailing ... catolog 2011/pg56 ....

You will find in the upper left corner a pic of a Harkin

Quad Block/ part#H2631 that you can use as your

Boom Block

. Combine that w/ a Harkin part# H2687 (pg57) for your

Bottom Block" and you will have a 8X1 Mainsheet Stack.

Now, I like Lewmar Blocks and have used them for my 7X1 Mainsheet Stack .... but I do have a 8X1 Mainsheet Stack using the Harkin Quad Block since I have been unable to locate a Lewmar Quad Block .... I set the 8X1 Mainsheet Stack up for use on my P19MX to control the mainsail leech ... but ... I found out that there is a big difference between a 7X1 vs 8X1 in the amount/length of mainsheet line that you need to take-in or ease-out. For me it is generally too much ... and I went back to just using the 7X1 systems ...

Harry
H18Mag/P19MX

Interesting idea, but you better verify the load rating on the single upper block. I'd be concerned about pulling the becket off the upper block where you're attaching the triple to the underside of it. The becket is generally intended as a tie-off point and would typically only see the load from one

throw

of the line. In the configuration you've drawn, the becket will see seven times that load.

sm

sm

I would add a block on the inside, probably a 40mm Harken, on the top becket where you currently end the line. Then add a tie point by creating a loop of 3mm dyneema through the center of the bottom 3 blocks, and attach the end of the line there. Working inside keeps all the loads down, except for the external block fittings, which are designed for the high loads.
Also, you should reeve the line with the top and bottom blocks perpendicular to each other, not parallel. That makes it easier to avoid crossings

I like your idea, it's also easy to test with an existing block. Regarding paralell blocks, I've found that there's more friction with the blocks perpendicular. Crossings is not such a big issue but I never thought that was the reason for using them perpendicular, I'll be testing that too.

Regarding load, what do you think is a reasonable value of total load? (or single segment load)?

Loads on the inside are exactly the strength you pull on the line for the line end, and double your pull for the internal block - unless you are a gorilla then several tens kg max. Loads on the outside are 7 - 8 times your pull.
That's why if you mount the block externally it see's much greater loads and will be prone to break

Right. The question was how much do you think we normally pull

Several ten kilograms

shoot...you should try the 10:1 on F18s.

I presume you mean 30 kg or so? I bet it's not quite that much - probably more like 20kg...I bet we surprise ourselves with how low it really is. I've been wanting to do a bench test to see what I pull single and double handed - I would be very interested in some tested information on that.

I think you're probably right, and Ive been wondering the same. My guess is that the final schlepp out on the wire, with both legs and upper body, is aaround 30

or the new 12:1 on the Wildcat.

Hi,

Are those F18 Mainsheet Stacks (10X1 or 12X1) straight singular ratios ... or ... are they a type of

cascade

system like those developed by Mr Greg Scase for Tornadoes and marketed by Harkin that have two ratios such as 6X1/12X1 that effectively mean they have a

macro

and

micro

modes.

Harry

There should be enough room to add an 14-16 inch pigtail between the boom and the upper blocks, that will allow you to shorten the mainsheet by at least 8-10 feet when using an 8-1 you can do the same thing with a 7-1.

Well, get you a market (hanging) scale, tie it to the sheet and pull away. Some have a max indicator needle, too. What's that... about $12 USD total?

But being the jakemister you are, you've probably spliced a load sensor into your mainsheet and have it wireless transmit to your wrist computer

I don't suggest modifying an existing block system.

Upgraded

an 8:1 system to a 9:1, but the existing block hardware was not beefy enough to handle the loads, found out the hard way 3 days into Tybee.

Checking the numbers, it seems that the limit may be on the sheave rather than the becket:

Safe working load for H002, H004 and H076 is 227, 454 and 544 kgs respectively.

454 is 2 times 227 but 544 is not 3 times 227, so I guess the limit is on the sheave for the first two and on the structure for the third one. Probably too much guessing on my analysis, but 227 kg for the single block seems close enough to the 30 kg pull anyway. But on the other hand, not close enough to 1100 kg breaking load, so I would probably try it anyway... Plus, much of the pull tension is lost in friction, so effective loads are actually a lower.

Oops... my previous message was entered before reading samc99us's, who is contradicting me with solid proof.......

On a N20 or F18?

10:1 system I've used on the N20 was just like this: http://www.harken.com/OneDesign/tornado.php

I haven't seen a cascading setup (per here: http://www.catsailor.com/forums/ubbthreads.php?ubb=showflat&Number=185848) on an F18 but somebody's probably tried it.

N20, but I suspect the leech loads are pretty similar these days on the F18 high aspect ratio mains.

Any diagram, for harken quad stack main block?

I have the 5 block on top with a triple and a double on a becket on bottom . Using a tapered main it works great for me.

line route for 8-1 main block

Nice! Thanks for that picture, worth a thousand words. Now I've got to pull mine apart and re-do it right!

Y/w

thanks ,now on to nacra rudder system non pivmatic..pull down line to cam cleat on rear beam continuous line,,schock cord up through rudder control arm?Sound right any decent picture will help possable upgrade;;

Not so fast ....

Study that diagram closely on how to weave/thread the mainsheet line .... now, if you rotate the single block attached to the camcleat 90*, so that it is orientated ACROSS the axis of the triple and quad blocks, there is a way to weave/thread the mainsheat line w/ no crosses .... so it will operate cleanly ...

Can you fiqure it out??? (Hint: At one point, you will need to thread the mainsheat from the extreme outboard sheave on the Quad Block, down and through the Single Block, and then back up to the other outboard sheave on the Quad Block ...)

Try it ... it works really well, but you need to actually see it/play with-it ... to apprieciate how it works

Note: It works best if the Single Block is the same size sheave as the Triple and Quad Block's sheaves ....

Harry
H18Mag/P19MX

This statement suggests that an increase in purchase means necessarily an increase in max load applied. Is that really true? Don't we want to actually lower the pull to acheive similar results? Therefore more pulleys should mean lower load and not higher, except at the connections in both ends, where the total load is applied.

That's assuming that the goal is to distribute the load rather than apply more total tension. Maybe I'm wrong there.. Still, we are talking about a 10 to 15% increase in purchase, which comes with a decrease in overall efficiency because of the higher friction, therefore, the total tension is increeased in less than that. Would that be enough of an increment to break the blocks? If not rearranging blocks too differently (like the single block suggested in the first post) I think it shoudn't