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17-10-2018, 09:09
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#16
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Marine Service Provider
Join Date: May 2017
Location: Southern Ontario Canada
Boat: Goderich 35
Posts: 29
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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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17-10-2018, 09:12
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#17
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Registered User
Join Date: Sep 2014
Posts: 236
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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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17-10-2018, 10:00
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#18
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Registered User
Join Date: Oct 2008
Boat: Custom cutter, 42'
Posts: 701
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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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17-10-2018, 10:17
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#19
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Registered User
Join Date: Oct 2015
Posts: 2,007
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by boatman1
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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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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17-10-2018, 11:05
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#20
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Registered User
Join Date: Mar 2016
Location: New England. USA.
Boat: McCurdy & Rhodes Custom 46
Posts: 1,474
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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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17-10-2018, 15:23
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#21
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,602
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by aquafacts
Look at Edsons conduit and cable system - eliminates pullies, alignment issues and simplifies installation ! or
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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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17-10-2018, 15:43
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#22
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Registered User
Join Date: Sep 2014
Location: Toronto summer rest somewhere else
Boat: Outremer 45/pdq36
Posts: 1,169
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by coopec43
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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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.
__________________
“Growing older but not up”
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17-10-2018, 16:37
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#23
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,602
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by dfelsent
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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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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17-10-2018, 16:56
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#24
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Registered User
Join Date: Oct 2008
Boat: Custom cutter, 42'
Posts: 701
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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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17-10-2018, 17:46
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#25
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Registered User
Join Date: Mar 2016
Location: New England. USA.
Boat: McCurdy & Rhodes Custom 46
Posts: 1,474
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by coopec43
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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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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17-10-2018, 18:22
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#26
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,602
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by dfelsent
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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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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17-10-2018, 18:49
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#27
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Registered User
Join Date: Mar 2016
Location: New England. USA.
Boat: McCurdy & Rhodes Custom 46
Posts: 1,474
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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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17-10-2018, 20:03
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#28
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,602
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Re: Sheaves for yacht cable steering
Quote:
Originally Posted by Pauls
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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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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17-10-2018, 20:37
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#29
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,602
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Re: Sheaves for yacht cable steering
Looks like it needs further research.
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