Steering sheaves / pulleys

[coopec43]

Originally Posted by stormalong

10 MM is way oversize. Is your sheave diameter large enough for 10 MM? The wire will fatigue and break if pulled around too narrow a sheave. You don't have to use Edson but you can use their dimensions to build your own system.

The yacht riggers said that too but they said I'd get a more positive feel at the helm if I used 10 mm.


I agree 7/19 SS cable will break down if the pulleys are too small. I have now decided to go to Dyneema (or equivalent) so I won't have that problem. (I think it is Beneteau 47ft that comes with Dyneema as standard. Maybe other yacht in their range too)


Clive

[coopec43]

Originally Posted by kmacdonald

Bear Sheaves: Wire Rope Sheaves - Bear Equipment Inc.

Make sure you use the correct diameter sheave for the diameter wire you are using. It is CRITICAL to prevent fatigue breaking of the wire.

Thanks for that. Originally I was going to use SS cable but have now switched to Dyneema.


Clive

[coopec43]

Originally Posted by Rowglide

Besides it's a HC43...only time it would ever see 16 knots would be riding down a 60' wave or on the back of a transport truck

That's when you need a strong steering system! Tidal currents can be very strong in places.

Of course if you happen to run aground the stresses on the steering could be enormous too.


Clive

[coopec43]

Rowglide QUOTE If I got 4000lbs of pull on a cable, that would translate to roughly 1/18th of that at the rim of a 36" wheel (sprocket is 2") which would be about 220lbs.
I am a strong man but fighting 200+ lbs at the helm would be tough/dangerous, and more likely to destroy many of the underdeck components.UNQUOTE


I don't know where you got the 200lbs from because you haven't taken the mechanical advantage of the quadrant into account. (According to the article 3700 lbs equates to 46 lb at the wheel)

Did you read the article?

Let's take a close look at how those two fingers turn the rudder. As an example, we'll take a stock, 42-foot cruising sailboat from the pages of Cruising World and see what's involved in steering it.
The fingers rest on the rim of a 30-inch-diameter wheel. Turning the 30-inch wheel turns a 3-inch-diameter sprocket on which rides a chain connected to the steering cables. That's a power ratio of 30:3 or 10:1, so 1 pound of force applied to the wheel rim delivers 10 pounds of force to the steering cable.
The rudder is a partially balanced spade--its stock is set back a short distance from the rudder's leading edge. When the airfoil-shaped rudder is turned a small amount, its center of lift (the point at which the average of the forces on it act) is a little aft of the stock, in this case about 2 inches. The cable turns the rudderstock via a quadrant that has a radius of 16 inches, so the power ratio of the quadrant to this lever arm is 16:2 or 8:1. Combine this with the 10:1 power ratio of the wheel to the chain/cable, and the total power ratio is 80:1. Therefore, two fingers applying a force of 1 pound to the wheel rim deliver 80 pounds of force to the rudder (or counter a force of 80 pounds acting on the rudder).

The bushes would be bronze not brass as I stated.

I thought about cast iron pulleys (sheaves) and decided all the pulleys on my motor are cast iron, the block of the motor is cast iron and all the nuts and bolts are steel and they don't rust because they are painted. (I never have to check the "V"belt pulleys for corrosion!) Cast iron rusts a lot slower than steel. Some yachts have cast iron keels/ballast!


I did research the matter and found other yachts with cast iron sheaves. (

Maybe I will have to watch the sheaves as I will the Dyneema.


Clive

[stormalong]

Originally Posted by coopec43

The yacht riggers said that too but they said I'd get a more positive feel at the helm if I used 10 mm.

I agree 7/19 SS cable will break down if the pulleys are too small. I have now decided to go to Dyneema (or equivalent) so I won't have that problem. (I think it is Beneteau 47ft that comes with Dyneema as standard. Maybe other yacht in their range too)

Clive

I am not an expert here. All I can reference is my personal experience including rebuilding my Edson steering a couple of times.

I would be very wary of dyneema or any rope products because of abrasion. Alignment is critical on any system. Getting that right is easy if the sheave mounts are designed right and I praise Edson for making this easy. Riggers are experienced with stainless for standing rigging and maybe rope-wire halyards. I doubt you will get a more positive feel with thicker wire on a pull-pull steering system, maybe stiffer but not more positive.

The weak link of my steering system has been the chain. I have had SS chains break three times over the years. I had a lot of miles on them. Edson recommends replacing the chain and cable every four years. My chains broke after many miles and many more years than that. I always carried spares. Fortunately my autopilot is on a separate tiller arm and I have come in to port after an ocean passage on autopilot.

[coopec43]

Originally Posted by stormalong

I would be very wary of dyneema or any rope products because of abrasion. Alignment is critical on any system. Getting that right is easy if the sheave mounts are designed right and I praise Edson for making this easy. Riggers are experienced with stainless for standing rigging and maybe rope-wire halyards. I doubt you will get a more positive feel with thicker wire on a pull-pull steering system, maybe stiffer but not more positive.

I'm getting advice from Taskers and feel quite confident of their experience.
My yacht is not a racing yacht but a heavy cruising yacht. I think Rostan equipment is too light and expensive.
Maybe they did say "stiffer" rather than "positive". ( I took it that they meant there'd be less play on the wheel)


Nordic 44 eh? (Must check that out)



Clive

[kmacdonald]

I know this is a little off topic but is close enough. The Edson "adjustable crossed wire idler" (776AL-4AL) sheave assembly was originally made with a steel base that would rust if the pedestal bolts leaked water. The rust would weaken the steel base to the point that the sheaves would bend back toward the radial drive wheel. This would cause the cable to loosen. They have been known to fail completely also. The new version of the "adjustable crossed wire idler" has an anodized aluminum base.
This part was used on a lot of older boats and should be checked to prevent loss of steering in the event of failure. If you have had to re-tension steering cables you very well might have this problem.

[kmacdonald]

Originally Posted by coopec43

Well it depends on the size of boat!

On a 43 ft yacht the loads on steering components could be several thousand pounds

Rudder Loads on the Modern Cruiser
To do their jobs, rudders must cope with enormous forces.

What would we expect the worst-case load to be on our rudder? Let's examine a wipeout at 16 knots, with the rudder hard over and stalled out. Let's assume maximum dynamic loading and the simplest case.
The dynamic load on a flat plate in a stream is expressed as q = dv2A/2g, where d is the density of the fluid, in this case seawater at 64 pounds/cubic foot; v is the velocity in feet per second, so multiply by 1.69 for speed in knots; A is the area of the plate; and g is gravity, conveniently 32 ft./sec.2. This all boils down to q = v2A.
Our rudder only goes to 35 degrees, so the frontal area it presents is A(sin35) or .57A.
At 16 knots, with our 9-square-foot rudder, q = (16 x 1.69) 2 x 9 x .57 = 3,751 pounds.

https://www.cruisingworld.com/how/ru...modern-cruiser


Now look at this chart in the Edson Manual. They suggest the same diameter cable for 30 ft LWL - 70 ft LWL but then there is a rider stating it is up to the naval architect.

Rudder loads and force on the steering cable are two different animals and not the same. Forget the math and copy a well proven Edson design on a similar boat.

[blubaju]

engines run fast, the V-belts remove the rust and polish. Your steering, I asume, should be a little slower, that gives rust the time to build up.

Your steering cables/ropes are usually not in a wet environment, you might use bronce or "marine" brass for your bushings if you do not want stainless ball bearings. But make sure your sliding bearings are made from selflubricating bronce/brass. Ball bearing, you do not want the open type, you want them with gaskets.

Whatever bearing you choose, be sure not to have them hand made, buy stock bearing, once you need to change them you only call your supplier and rest assured, a standard bearing is always cheaper unless bought @marinesupply

For info only, there are many companies:

Sintered Metal: https://www.ames-sintering.com/self-...ting-bearings/

As mentioned, I use Nylon sheaves, hence no extra bearing needed. The mast sheaves with their more static loads are made from Aluminum, the bearing high grade "plastic" from GGB Bearing Technology. All other sheaves ball bearing Aluminum/plastic balls.

Life time: since 2010 only Dyneema shrouds 1x changed for safety, nothing else.

Somebody mentioned the high loads when you hit something, might be a good idea to place a security bolt in your quadrant or splice a piece of weaker rope in the steering cable. It is easier to change that bolt or rope than to repair the whole heck of your ship.

Btw, this is why our rudder stocks are carbon, they do not bend, but break.

Just as example, might not suit your purpose ;-)

Fair winds and following seas!

P.S. left over Dyneema make very good "Soft Shackels", we love them

[jkishel]

Originally Posted by coopec43

The article which I gave the link to says you get mechanical advantage from the wheel as well as the quadrant is 80/1. They went on to say when the force at the rudder is 3700 lb the force at the steering wheel is 46 lb.


Are you saying that is wrong?


Clive

Not at all, that is all correct, I just went one step further to describe the load on the wire rope itself.

[coopec43]

Well I didn't know this.


"With suitable alloying, the corrosion resistance of cast iron can equal to or exceed that of stainless steel and nickel (Ni) based alloy. Since outstanding properties are obtained with this low cost engineering material, cast iron finds extensive use in atmospheres which need good corrosion resistance. Services in which cast iron can be used for its good corrosion resistance include water, soils, acids, alkalis, saline solutions, organic compounds, sulphur compounds, and liquid metals. In some cases, alloyed cast iron is the only economical choice for the equipment manufacture".

Corrosion of Cast Irons | ispatguru.com

[Rowglide]

OK, I neglected to account for the quadrant. So yes there is a further reduction in load to the wheel. If they are correct with 46lbs at the rim, lets say 50lbs at the rim, 18" wheel radius with a 1" sprocket radius. That is 900lbs at the cable in a maximum load situation.
Well within the load range for 1/4" wire rope, no?

[coopec43]

Originally Posted by Rowglide

OK, I neglected to account for the quadrant. So yes there is a further reduction in load to the wheel. If they are correct with 46lbs at the rim, lets say 50lbs at the rim, 18" wheel radius with a 1" sprocket radius. That is 900lbs at the cable in a maximum load situation.
Well within the load range for 1/4" wire rope, no?

Sorry your maths are wrong!


Did you read the article?


If you have a look at the Edson table I posted above you would see what you are suggesting is wrong.



Clive

[Rowglide]

I have read the article and gone over the Edson chart... what am I missing?

It appears to me that the loads referred to in the article are at the rudder post, a twisting action. When you move out from the center of the rudderpost by however many inches of radius on the quadrant, you are reducing the load.

Also, if you look at an 11 tooth Edson sprocket, the radius of the chain center is a hair over 2".

No?

[coopec43]

Why does Edson stipulate ¼ in. cable if the loads are so light?

Of course the yacht must be able to withstand an extreme event like a grounding or a Force 12 Gale.