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Old 17-10-2018, 09:09   #16
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Re: Sheaves for yacht cable steering

Look at Edsons conduit and cable system - eliminates pullies, alignment issues and simplifies installation ! or
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Old 17-10-2018, 09:12   #17
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Re: Sheaves for yacht cable steering

Washers/shims on each side of the "cheeks" won't hurt, but most if not all turning block issues will be eliminated if the vector of the compression on the sheave by the cable is perpendicular to the axis of the shaft.
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Old 17-10-2018, 10:00   #18
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Re: Sheaves for yacht cable steering

Cooopec, are you planning on using wire rope? You mention 8mm. Even the most flexible wire rope - 16x36 - will require a much larger diameter sheave than what yours appear to be. Judging visually, they are probably OK for high modulus rope.
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Old 17-10-2018, 10:17   #19
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by boatman1 View Post
Washers/shims on each side of the "cheeks" won't hurt, but most if not all turning block issues will be eliminated if the vector of the compression on the sheave by the cable is perpendicular to the axis of the shaft.
If the load is not perpendicular to the shaft, all kinds of bad things will happen. For one, it forces the cable to slide along the edges of the sheave, wearing away at both.
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Old 17-10-2018, 11:05   #20
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Re: Sheaves for yacht cable steering

For 7x19 stainless wire rope most manufacturers suggest 24:1 sheave to rope diameter ratio.
https://www.loosco.com/resource-libr...ave-diameters/
A smaller ratio than this compromises service life. You end up with broken strands and pigtailing. I've seen this.
With the correct ratio and fair leads the weak link in chain to rope steering is crevice corrosion in the chain.
I have had chain failures from crevice corrosion, and had broken strands from "conservatively sized" wire rope that was in fact too large for the sheaves and was failing early.
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Old 17-10-2018, 15:23   #21
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by aquafacts View Post
Look at Edsons conduit and cable system - eliminates pullies, alignment issues and simplifies installation ! or
I planned to use conduit but the expert on steering big yachts said it was a NO! NO! as as it hides the condition of the wire rope. (He pointed out that plastic coated ss lifelines on yachts has been banned in competition)

My opinion of Edson (and others) who push their gear for high performance yachts is they push the the limits too far. How many of these "state of the art" yachts have to pull out of offshore races in rough weather because of steering failure?

Clive
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Old 17-10-2018, 15:43   #22
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by coopec43 View Post
I planned to use conduit but the expert on steering big yachts said it was a NO! NO! as as it hides the condition of the wire rope. (He pointed out that plastic coated ss lifelines on yachts has been banned in competition)

My opinion of Edson (and others) who push their gear for high performance yachts is they push the the limits too far. How many of these "state of the art" yachts have to pull out of offshore races in rough weather because of steering failure?

Clive
I have had this system on my pdq Since 2003. Steering cable breaks at the ends not in the middle .
The system is a dream as you can make slight adjustments in the diection ie to go through bulkheads and things without the need for pulleys etc.
I steer a 36 foot cat going up wind at 9 knots (flat water ) with two fingers. No friction whatsoever.
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Old 17-10-2018, 16:37   #23
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by dfelsent View Post
For 7x19 stainless wire rope most manufacturers suggest 24:1 sheave to rope diameter ratio.
https://www.loosco.com/resource-libr...ave-diameters/
A smaller ratio than this compromises service life. You end up with broken strands and pigtailing. I've seen this.
With the correct ratio and fair leads the weak link in chain to rope steering is crevice corrosion in the chain.
I have had chain failures from crevice corrosion, and had broken strands from "conservatively sized" wire rope that was in fact too large for the sheaves and was failing early.
I worried about the diameter of the sheave/cable diameter too until I realized the recommended ratio of a minimum of 24/1 was for a constantly spinning sheave as used in industry. That is a complete contrast to sheaves used in yacht steering.

I've been waiting for one of the yacht steering experts I speak to to challenge me about the sheave diameter I am using but they haven't.

But thanks for your advice and I accept I'll have to keep a close watch on it.

Clive
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Old 17-10-2018, 16:56   #24
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Re: Sheaves for yacht cable steering

As I posted earlier, you can go to the more flexible 6x36, but you will still need larger sheaves. This is NOT just for constantly spinning use. Every time you move the wheel you are bending the wire. Too sharp a bend damages it in short order.

Go to the Loos website. They have a table showing minimum sheave diameter for different constructions and diameters of wire rope. Sorry to say but your sheaves are too small for wire rope.

As I posted, you can use high modulus rope, ie spectra, amsteel blue, etc. This stuff is as strong as wire rope and can handle much smaller sheave diameters. Recommended sheave diameter is 8X rope diameter.
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Old 17-10-2018, 17:46   #25
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by coopec43 View Post
I worried about the diameter of the sheave/cable diameter too until I realized the recommended ratio of a minimum of 24/1 was for a constantly spinning sheave as used in industry. That is a complete contrast to sheaves used in yacht steering.



I've been waiting for one of the yacht steering experts I speak to to challenge me about the sheave diameter I am using but they haven't.



But thanks for your advice and I accept I'll have to keep a close watch on it.



Clive


I am far from a yacht steering expert but my experience is that after about 7000-10000 miles 5/16 7x19 cable on 6” sheaves has broken strands and meathooks. 1/4” does not.

Discussions with Edson and with Edison’s former Chief Engineer confirmed that the issue was the diameter ratio.
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Old 17-10-2018, 18:22   #26
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by dfelsent View Post
I am far from a yacht steering expert but my experience is that after about 7000-10000 miles 5/16 7x19 cable on 6” sheaves has broken strands and meathooks. 1/4” does not.

Discussions with Edson and with Edison’s former Chief Engineer confirmed that the issue was the diameter ratio.
Sigh...... It looks like I've got more work to do. (But it is not just pulley diameter)
https://www.maritimenz.govt.nz/comme...nuary-2011.pdf
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Old 17-10-2018, 18:49   #27
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Re: Sheaves for yacht cable steering

I am impressed that you have tackled building a 43 foot boat.
Best wishes on the project!
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Old 17-10-2018, 20:03   #28
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Re: Sheaves for yacht cable steering

Quote:
Originally Posted by Pauls View Post
Cooopec, are you planning on using wire rope? You mention 8mm. Even the most flexible wire rope - 16x36 - will require a much larger diameter sheave than what yours appear to be. Judging visually, they are probably OK for high modulus rope.
Yes you've got me thinking and I just discovered Amsteel (Dyneema?) but I must do much more research. Is this what you are suggesting?

https://www.go2marine.com/product/38...blue-rope.html

Apparently Dynex Dux is another alternative.
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Old 17-10-2018, 20:37   #29
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Re: Sheaves for yacht cable steering

Looks like it needs further research.
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Old 17-10-2018, 22:31   #30
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Re: Sheaves for yacht cable steering

I think I'll use Dyneema SK78 as it has low creep. I don't mind if I have to tension it up a little each year.

"Dyneema and Spectra are both brand names for UHMWPE. The UHMWPE is Ultra High Molecular Weight Polyethylene. The individual fibres are very thin but incredibly long and straight and this provides UHMWPE with its strength. Lots of different ropemakers(eg. Samson) buy the fibres from DSM who license dyneema, and then spin them into lovely braid which we know as Amsteel Blue. Amsteel blue is made from a specific type of fibre called SK75. There are other grades of dyneema too, such as sk78 as used in Samsons AS78 hollow braid.


http://www.samsonrope.com/Documents/...Manual_WEB.pdf

http://www.samsonrope.com/Documents/...AR2012_WEB.pdf

https://www.riggingdoctor.com/life-a...anding-rigging

https://www.ebay.com.au/i/172317479456?chn=ps

https://www.ebay.com.au/itm/105-of-5...qu17:rk:3:pf:0
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