Steering sheaves / pulleys

[Rowglide]

So I am piecing together my "System" to install a pedestal / wire rope /quadrant steering system on my boat.

I am now looking at sheave /pulleys. I intend to use 1/4" wire rope so 6" pulleys, not 4". I can build my own blocks and support plates but need to get sheaves.
Other than Edson and Lewmar who are crazy expensive, is there a source for wire rope pulleys?
I see a lot of newer boats have aluminium pulleys are these durable or do they corrode crack?

[coopec43]

I am building up my sheaves for a 43ft yacht I am building. I am using 4 in. pulleys but with rope (Dyneema?). Like you I found Edson and Lewmar prices a joke.

I question your decision to use 1/4 in. wire rope because when I was thinking of using 6 mm the rigging people said it was definitely too light for a 43 ft yacht and said I should be using 8 mm. But he then measured my pulleys and said they would take 10 mm and that would be even better. (There was no question in there minds)

I am using ss plate for the pulley holders and ss round bar for the axles, ss washers and split pins (bought on eBay) Buying 3 M of rod was quite cheap and far, far cheaper than industrial bolts. My pulleys are cast iron with brass bushes.

I bought my pulleys from a crowd that supplies industry. Make sure you work out how many you want and buy them all together because if you just buy one they'll want an arm and leg too.

I just did a search on "pulleys sheaves Kingston Ontario" and came up with quite a few hits. Maybe you should google "wire rope sheaves pulleys" as well

https://www.google.com.au/search?q=p...w=1080&bih=573

I got mine from a crowd like Acklands Grainger

https://www.acklandsgrainger.com/en

https://www.grainger.com/category/bl...ves&sst=subset

Clive

[Jim Cate]

What is the finish on those cast iron sheaves? Looks almost like they are some sort of plastic!

Jim

[coopec43]

Originally Posted by Jim Cate

What is the finish on those cast iron sheaves? Looks almost like they are some sort of plastic!

Jim

No. It is just yellow paint.

[roverhi]

6mm/1/4" 7x19 302 wire has a breaking strength over 6,000#. Working load on the cable is probably measured in hundreds of pounds not 1,000s for normal steering of the boat. If the load was to approach the breaking strength of the wire would worry about it destroying the steering components and/or pulling the sheaves away from whatever they are affixed to.
I'm not an engineer but increasing the wire diameter would seem to be false security

[coopec43]

Originally Posted by roverhi

6mm/1/4" 7x19 302 wire has a breaking strength over 6,000#. Working load on the cable is probably measured in hundreds of pounds not 1,000s for normal steering of the boat. If the load was to approach the breaking strength of the wire would worry about it destroying the steering components and/or pulling the sheaves away from whatever they are affixed to.
I'm not an engineer but increasing the wire diameter would seem to be false security

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.

[Rowglide]

Thanks for the engineering,
Clive, I have 2 concerns with the iron pulleys, am I being snowed by a love of bronze or is iron a perfectly suitable material?

1- any corrosion will be very abrasive, will abrade dyneema
2- Are the bushings really brass or are they bronze? again a corrosion concern

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.
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

[blubaju]

Originally Posted by Rowglide

1- any corrosion will be very abrasive, will abrade dyneema
2- Are the bushings really brass or are they bronze? again a corrosion concern

abrasive is a problem when things SLIDE on each other, a rope on a sheave should not slide. But your paint will be gone soon, even if Epoxy paint.

My Catamaran 43' has sheaves made from nylon and I use sleeveless DYNEEMA 6mm ropes. Dyneema is extremly forgiving, splice them yourself

[sainted]

Harken sells seaves. Garhauer may as well. You'd have to build cheeks for them, but it looks like your planning to anyway.

In addition to strength, low friction is necessary to achieve good steering feel. The edson stuff may be expensive, but it will last forever and perform great.

[jkishel]

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.

Correct, the force on the rudder could be several thousand pounds, but the force on the wire rope itself is much less. The resultant force on a spade rudder turned hard over is located several inches aft of the centerline of the stock and the quadrant is much larger than that. For example, with an 18 inch radius quadrant and a resultant located 2 inches aft of the stock centerline, the mechanical advantage is 18/2 or 9. With 3751 pounds on the rudder per the previous post, the load on the wire rope would be 3751/9 or about 417 pounds.

The breaking strength of 1/4 inch 6/19 wire rope is around 5000 pounds. this may seem like a lot for a 417 pound design load, but with an appropriate safety factor and strength reduction due to u-bolt clips and chain connections, this could be about right.

[stormalong]

Originally Posted by coopec43

I question your decision to use 1/4 in. wire rope because when I was thinking of using 6 mm the rigging people said it was definitely too light for a 43 ft yacht and said I should be using 8 mm. But he then measured my pulleys and said they would take 10 mm and that would be even better. (There was no question in there minds)
Clive

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.

[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.

[billgewater]

For what it is worth.... a problem I encountered using 4 inch steel pulleys with galvanized steel cables was that unless the alignment of the cables was perfect, the wire can abrade on the pulley groove. I have had to replace my steering cables once due to this problem. Replacing the cables was actually cheaper than altering the pulley arrangements. Making the pulley mount "flexible" actually may not completely resolve this problem because the pulley may want to hang in a vertical plane which may not actually be the plane that the cable wants to lie in. Or the flexibly mounted pulley may want to "fall over" depending on the mounting arrangement. I assume the problem may be related to the fact that the steel industrial pulleys are actually quite heavy.

[coopec43]

Originally Posted by Rowglide

Thanks for the engineering,
Clive, I have 2 concerns with the iron pulleys, am I being snowed by a love of bronze or is iron a perfectly suitable material?

1- any corrosion will be very abrasive, will abrade dyneema
2- Are the bushings really brass or are they bronze? again a corrosion concern

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.
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

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 3700lds equates to 46ilb 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 boltsare steel and they don't rust because they are painted. (I never have to check the "V"belt pulleys for corrosion!) 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



Clive

[coopec43]

Originally Posted by jkishel

For example, with an 18 inch radius quadrant and a resultant located 2 inches aft of the stock centerline, the mechanical advantage is 18/2 or 9. With 3751 pounds on the rudder per the previous post, the load on the wire rope would be 3751/9 or about 417 pounds.

The breaking strength of 1/4 inch 6/19 wire rope is around 5000 pounds. this may seem like a lot for a 417 pound design load, but with an appropriate safety factor and strength reduction due to u-bolt clips and chain connections, this could be about right.

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