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7:1 to 8:1 conversion #244097
02/16/12 07:38 AM
02/16/12 07:38 AM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Andinista  Offline OP
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Santiago, Chile
I'm thinking to modify my mainsheet system for 8:1. Anybody tried this option?

- Invert upper and lower triple blocks
- Add hihger diameter block with becket
- Connecting hardware must keep all blocks parallel

I have enough room for the additional block.

[Linked Image]

Attached Files
mainsheet.JPG (349 downloads)
Last edited by Andinista; 02/16/12 07:39 AM.
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Re: 7:1 to 8:1 conversion [Re: Andinista] #244106
02/16/12 10:25 AM
02/16/12 10:25 AM
Joined: Apr 2006
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SE Pa. or Chesapeak Bay
HMurphey Offline
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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

Re: 7:1 to 8:1 conversion [Re: Andinista] #244112
02/16/12 11:12 AM
02/16/12 11:12 AM
Joined: Jan 2004
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srm Offline
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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

Re: 7:1 to 8:1 conversion [Re: srm] #244118
02/16/12 11:54 AM
02/16/12 11:54 AM
Joined: Oct 2005
Posts: 49
Israel, Sdot Yam
Opher Offline
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Israel, Sdot Yam
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


Opher
Nacra F20C ISR1
F18 Cirrus ISR2
Sdot Yam, ISRAEL
Re: 7:1 to 8:1 conversion [Re: Andinista] #244119
02/16/12 12:08 PM
02/16/12 12:08 PM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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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)?

Last edited by Andinista; 02/16/12 12:09 PM.
Re: 7:1 to 8:1 conversion [Re: Andinista] #244120
02/16/12 12:17 PM
02/16/12 12:17 PM
Joined: Oct 2005
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Israel, Sdot Yam
Opher Offline
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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


Opher
Nacra F20C ISR1
F18 Cirrus ISR2
Sdot Yam, ISRAEL
Re: 7:1 to 8:1 conversion [Re: Andinista] #244121
02/16/12 12:18 PM
02/16/12 12:18 PM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Right. The question was how much do you think we normally pull

Re: 7:1 to 8:1 conversion [Re: Andinista] #244122
02/16/12 12:23 PM
02/16/12 12:23 PM
Joined: Oct 2005
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Israel, Sdot Yam
Opher Offline
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Several ten kilograms


Opher
Nacra F20C ISR1
F18 Cirrus ISR2
Sdot Yam, ISRAEL
Re: 7:1 to 8:1 conversion [Re: HMurphey] #244123
02/16/12 12:30 PM
02/16/12 12:30 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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shoot...you should try the 10:1 on F18s.


Jake Kohl
Re: 7:1 to 8:1 conversion [Re: Opher] #244124
02/16/12 12:32 PM
02/16/12 12:32 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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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.


Jake Kohl
Re: 7:1 to 8:1 conversion [Re: Jake] #244126
02/16/12 12:41 PM
02/16/12 12:41 PM
Joined: Oct 2005
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Israel, Sdot Yam
Opher Offline
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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


Opher
Nacra F20C ISR1
F18 Cirrus ISR2
Sdot Yam, ISRAEL
Re: 7:1 to 8:1 conversion [Re: Jake] #244132
02/16/12 01:17 PM
02/16/12 01:17 PM
Joined: Dec 2007
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california
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Originally Posted by Jake
shoot...you should try the 10:1 on F18s.


or the new 12:1 on the Wildcat.


Richard Vilvens
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http://www.capricornsailing.com/
Re: 7:1 to 8:1 conversion [Re: Andinista] #244134
02/16/12 01:24 PM
02/16/12 01:24 PM
Joined: Apr 2006
Posts: 699
SE Pa. or Chesapeak Bay
HMurphey Offline
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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

Re: 7:1 to 8:1 conversion [Re: HMurphey] #244135
02/16/12 01:27 PM
02/16/12 01:27 PM
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Hullflyer1 Offline
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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.
Originally Posted by HMurphey
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

Re: 7:1 to 8:1 conversion [Re: Jake] #244136
02/16/12 01:33 PM
02/16/12 01:33 PM
Joined: Dec 2001
Posts: 5,590
Naples, FL
waterbug_wpb Offline
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Naples, FL
Originally Posted by Jake
I 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.


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


Jay

Re: 7:1 to 8:1 conversion [Re: Andinista] #244145
02/16/12 02:31 PM
02/16/12 02:31 PM
Joined: Mar 2009
Posts: 932
Solomon's Island, MD
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samc99us Offline
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Solomon's Island, MD
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.


Scorpion F18
Re: 7:1 to 8:1 conversion [Re: srm] #244146
02/16/12 02:45 PM
02/16/12 02:45 PM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Andinista  Offline OP
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Joined: Aug 2003
Posts: 351
Santiago, Chile
Originally Posted by srm
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


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

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.


Re: 7:1 to 8:1 conversion [Re: Andinista] #244147
02/16/12 02:47 PM
02/16/12 02:47 PM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Andinista  Offline OP
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Santiago, Chile
Oops... my previous message was entered before reading samc99us's, who is contradicting me with solid proof.......

Re: 7:1 to 8:1 conversion [Re: samc99us] #244149
02/16/12 02:55 PM
02/16/12 02:55 PM

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MN3
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Originally Posted by samc99us
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.


On a N20 or F18?

Re: 7:1 to 8:1 conversion [Re: HMurphey] #244151
02/16/12 03:14 PM
02/16/12 03:14 PM
Joined: Mar 2009
Posts: 932
Solomon's Island, MD
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samc99us Offline
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samc99us  Offline
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Solomon's Island, MD
Originally Posted by HMurphey
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


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.



Scorpion F18
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