Connecting two lines (or blocks) to the same D-ring in a backstay adjuster system

A

anastas

.
Apr 27, 2022
14
Beneteau 310 Toledo
Hi all,

I am working on a custom 24:1 backstay adjuster.
The important constraint is that I want to use the two existing D-rings on the boat and NOT add another one.
I will be using the attached design (see attached figure).

I will need to connect two pieces in the port D-ring
(one is the triple block and the other is the end of one of the lines).
I am concerned about chafing issues.

The question is the following:
Is there a piece of hardware that can "separate" the two attachments?
I am thinking of a triangle-like piece that has three holes: one connects to the D-ring (through a shackle)
and the other two lines are connected each to a different hole so that they stay apart from each other.

If there is such a hardware I would consider buying it instead of custom making it from steel...

thanks in advance,
Achilles
 

Attachments

D

dlochner

.
Jan 11, 2014
12,342
Sabre 362 113 Fair Haven, NY
I'm curious, how are the lower D rings connected to the transom? There will be a lot of force applied to them.
 
Scott T-Bird

Scott T-Bird

.
Oct 26, 2008
6,216
Catalina 320 Barnegat, NJ
Sounds like a custom fabrication is in order. 24:1 - wow! I'd be careful about what you can load just by hand but I guess you have figured that out. Do we assume that the D-rings are original attachments for the split backstay?
 
A

anastas

.
Apr 27, 2022
14
Beneteau 310 Toledo
No problems with the D-rings.
They were holding the original bridal of the backstay.
They are super strong and made exactly for this reason.
 
Johnb

Johnb

.
Jan 22, 2008
1,450
Hunter 37-cutter Richmond CA
Consider using fiddle blocks and soft shackling the lower one to the D ring.

Always assuming you are willing to home brew standing rigging.
 
Last edited:
JRacer

JRacer

.
Aug 9, 2011
1,350
Beneteau 310 Cheney KS (Wichita)
Search for a "triangle plate". Schaeffer makes some of those. Typically used in split backstays. Probably some others have them.
 
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DougM

DougM

.
Jul 24, 2005
2,242
Beneteau 323 Manistee, MI
I don’t understand why you need the double attachment at the top of the setup.
Attach the multi part block directly at the top and at the lower backstay attachment and eliminate the longer section of line. It will change the mechanical advantage slightly thats all.
 
Scott T-Bird

Scott T-Bird

.
Oct 26, 2008
6,216
Catalina 320 Barnegat, NJ
DougM said:
I don’t understand why you need the double attachment at the top of the setup.
Attach the multi part block directly at the top and at the lower backstay attachment and eliminate the longer section of line. It will change the mechanical advantage slightly thats all.
Click to expand
That top block doubles the mechanical advantage ... eliminating it changes it from 24:1 to 12:1. I can see why he includes it.
 
Last edited:
shemandr

shemandr

.
Jan 1, 2006
7,396
Slickcraft 26 Sailfish
Continuing from JRacer, is this what you are describing?

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Note that at a certain tension the rig doesn't get much more tight but the boat starts to bend.
 
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A

anastas

.
Apr 27, 2022
14
Beneteau 310 Toledo
@JRacer and @shemandr :
Although these plates are designed for a different application
(attach backstay to two split backstays)
they will probably work for me at the D-ring attachment.
They provide a separation of about 2 3/4 to 3 1/2 in so they are sufficient.
THANKS!
 
jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,297
CAL 35 Cruiser #21 moored EVERETT WA
It sounds like you feel you need a lot of backstay force. You feel the D Rings are able to handle the applied force of your new rig and the forces involved sailing the boat. I am not sure that type of backstay force was designed/considered for the rig.

I would be concerned with the designed strength of the D rings and their backing plates.

You can tell from this image they are designed to be used for the back stay. Even so, as you tension the rig you will be adding bending force to the mast which in turn will increase the forces throughout the boats rig. Be sure to release this force when the boat is at rest.

1658938866393.png
 
JRacer

JRacer

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Aug 9, 2011
1,350
Beneteau 310 Cheney KS (Wichita)
FYI, on my 310, the backstay adjuster is the factory setup and provides sufficient leverage to apply the backstay as much as is needed. Inside that tube is a multi-part rigging that provides the needed purchase to apply the backstay. Mine was a little "sticky" so I took mine apart last season and cleaned it all out and took the twists out of the line and it works well now.
 
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A

anastas

.
Apr 27, 2022
14
Beneteau 310 Toledo
@JRacer: I hear you. Ours was completely shot: we couldn't even take it off of the D-ring;
we had to use a angle grinder to cut it off...
When I opened it I saw a couple of the blocks being broken.
My assessment was that it was a 10:1 purchase system, although I may be wrong.
My idea is to use the proposed design with either triple or double blocks so that I get 16:1 or 24:1 purchase.
I also appreciate the point that @jssailem is making.
 
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D

dlochner

.
Jan 11, 2014
12,342
Sabre 362 113 Fair Haven, NY
Is the goal to achieve higher backstay tension or to make it easier to get backstay tension? With increased purchase it would be easier to reach excessive tension. On hydraulic adjusters there is usually a gauge that indicates the amount of pressure to prevent over loading the back stay, with a line tensioning system there isn't one.

How far back are you trying to move the mast head? Remember for every inch of movement you will have to move 24 inches of line. Moving that much line will slow things down.
 
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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,297
CAL 35 Cruiser #21 moored EVERETT WA
dlochner said:
Remember for every inch of movement you will have to move 24 inches of line. Moving that much line will slow things down.
Click to expand
A corollary to that is - to move the inch it will be 24 times easier.

I have a 6-1 mainsheet rig. There is a lot of line in the cockpit when the boom is centered on the boat.
 
DougM

DougM

.
Jul 24, 2005
2,242
Beneteau 323 Manistee, MI
Scott T-Bird said:
That top block doubles the mechanical advantage ... eliminating it changes it from 24:1 to 12:1. I can see why he includes it.
Click to expand
I guess what I was trying to note in a roundabout way is that 12:1 on the Bene 31 should be more than sufficient for backstay adjustment.
I wish I had done a setup like that on my 323 when I owned it.
 
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Scott T-Bird

Scott T-Bird

.
Oct 26, 2008
6,216
Catalina 320 Barnegat, NJ
DougM said:
I guess what I was trying to note in a roundabout way is that 12:1 on the Bene 31 should be more than sufficient for backstay adjustment.
I wish I had done a setup like that on my 323 when I owned it.
Click to expand
Yes, it may be ... if the original set-up was 10:1 or something similar, I'd be more than an little concerned that 24:1 is over-doing it (as @shemandr indicated). You made a good point.
 
dmax

dmax

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Jul 29, 2018
1,097
O'Day 35 Buzzards Bay
Scott T-Bird said:
That top block doubles the mechanical advantage ... eliminating it changes it from 24:1 to 12:1. I can see why he includes it.
Click to expand
The top block doesn't provide any mechanical advantage, it is 1:1 as it is anchored - to make it 2:1 you need to add a block at the top of the block-and-tackle assembly, circled in red here:
backstay.jpg
:
 
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