[Gregory Manning]

I have owned A142 for 23 years and in that time have had the rudder control cables break four times. On the first occasion my co-owner and a friend were positioning from Gairloch to Ullapool and on a lee shore when the break occurred.  It was only due to their quick action and ingenuity that the boat was not lost.  After that I mounted the emergency tiller to hand in the rear cabin.  The cable that failed was galvanized steel spun over a natural fibre core and appeared to be original.  I made up my own cables from some wire rope I had which I found about to fail while moored one day a couple of year later.  I checked the blocks, replaced two and adjusted their angle to ensure a fair run. The next failure was coming into Whitehills in the dark with a N’ly wind and swell.  We had dolphins playing in our wash but the enjoyment was short lived when with two cable to go we only had one rudder cable attached.  About three yaers ago I took professional advice and had 5mm cable made up with 7 X 19 stainless steel but imagine my horror when at the beginning of last season with a week to go to launch I found these to be held togther by only a few remaining strands.  Having replaced them I was happy that all was well until a week ago when carrying out a routine check I found some broken strands on cables that had only done one season, and a short one at that.  The only other relevant factor is that A142 is in a swinging mooring with the helm lashed so there is constant fretting as she swings.

I have received the following advice and suggestions.

1. The stainless steel case hardens with use so might not be the best material and using galvanized wire rope might be  better.

2. Have new cable made form 6 X 36 SS

3 Have cable made from dyneema.

4 Just use terylene rope.

Does anyone have any suggestions, comments or ideas?

Topic

[JimSumberg]

Greg,

This is an interesting challenge. A couple of points:

• Judging from the materials in the archive, reports of failed steering control cables seem to be quite rare (and I don’t imagine that is because they have always been replaced in a timely fashion).
• Over the years, many other boats must have been kept on swinging moorings, so that in and of itself is unlikely to be a major factor.
• Have you considered the potential role of the tension under which the cables are kept? Could too little or too much tension be part of the problem?

Jim

[Gregory Manning]

Thanks Jim,

I have considered tension as a factor.  I have made sure they are never overtightened although I have had them tighter than I have them now.  I have have two colleagues one a licensed helicopter engineer and the other a fellow pilot who has an HND in mechanical engineering.  We are all used to working on, or doing prefight inspections of yaw control cables on helicopters which are kept tight.  We are all scratching our heads as to the reason for my problem.  The professional rigger I use says that the cables and blocks I have should allow a 180 degree change of direction and I only have 90.

I think the cables may be too thick but they are approved by the rigger man.

Thanks again for the thought.

Greg

[Mike Dixon]

Greg,

Tempting fate here, but I have never had a cable fail.  Twice, on different boats, I’ve had the pulley blocks pull out of the adjacent woodwork which in effect gives the same result as a failed cable.

On all three boats, T4, A31/4  and A1 have had s/s cables.  None were oversized; none were over tensioned.  In fact there was always a bit of play in the system, which is fine as long as it’s not too sloppy.

Agree with Jim – I doubt whether working to and fro whilst on a mooring is an issue.

Don’t have an answer as such, but to my mind, any cable needs to be as flexible as possible.  Also check the provenance as I’ve heard anecdotal evidence from more than one source that s/s from China is not up to much.

Mike

[Gregory Manning]

Thanks Mike,

I am using TS Rigging of Maldon who I think rigged the Cutty Sark so have been assuming that they would be using quality cables but I note the reference to cheap Chinese.  I have 5mm 7 X 19.  I have more play in the system for the last season than before.

I can understand my first few failures as one was original and I used the wrong spec cable for the next two but I am on my second 7 x 19.

Tis a mystery!

You have me thinking that perhaps I should changed suppliers.

Aye

Greg

[JimSumberg]

Greg, Last week I moved Helene to a swing mooring off Wrabness, about half way between Manningtree and Harwich. There is plenty of water and it moves quite fast. Over a couple of days it became very clear that when the rudder is left fully down it is much less active — quiet even — compared to when the blade is lifted. So my question to you — Do you raise your rudder when the boat is left on the mooring?

Jim

 

 

[Gregory Manning]

Jim,

Thanks for the feedback and I do see the sense in what you say.  Alas I do have a potential problem with the depth of water at LWS so I do bring the rudder up when moored.  It may not be a problem but I can not risk damaging the rudder if it does come into contact with terra granite.

Aye

Greg

[Trevor Thompson]

Greg,

I have never had any problems with my steering control cables. I suspect that they are original. I have used them for 25 years without any problems. They are still in good condition with no broken strands.

There may be an issue in that you say that you lock the helm when on a swinging mooring and that the rudder is raised. My understanding has always been that you should NOT do that, particularly if the blade is raised. With the rudder raised natural movement of the boat can place an enormous strain on the system – such as when the wind opposes the tide. A shock cord which allowed the tiller to move would be much kinder to the rudder system.

I don’t know that this would be the cause of your problems – but it might have a bearing on the problem.

On the other hand I have frequently had to replace the uphaul and downhaul wires which pass over extremely small sheaves.

Trevor

[Trevor Thompson]

Oh – I forgot to mention that Calista is kept on a mooring where there is 1M at low water springs, so she is always left with the blade raised, and the tiller totally free.

Trevor

[Trevor Thompson]

I have just carried out a few rough calculations.

 

If the tiller is 1 metre long.

If you can exert a pull about the same as your weight on the tiller about 220lbs or 100Kg.

The torque on the rudder stock is T = F x L.

This is T = 100 x 1 = 100Nm

If the arm at the bottom of the tiller stock is say 3″  or 75mm long – just a guess I haven’t measured it.

Then the force on the wire is F = T / length

Wire force = 100/0.075 = 1333Kg.

If we use 5mm stainless wire it has a safe working load of 1448kg. I think the breaking load is 14210kg.

So I reckon that at the most the helmsman can apply a load which is just within the safe working load.

However on a mooring, when the blade is raised, and the helm locked, that safe working load will regularly be exceeded by shock loads as the boat swings between wind and tide. It clearly isn’t reaching the breaking load of the wire – or you would come back to the boat to find a broken wire.

If anyone is unsure about the force that a raised rudder can exert on the helm try motoring backwards, with the blade raised. Hold that tiller centrally and firmly or you will lose control of the tiller.

I think this is the cause of your problems.

Check my calculations and take measurements to see how far out I am – but I think my values are in the correct order of magnitude.

Trevor

 

[Trevor Thompson]

My last post contained errors. The errors don’t change the outcome but for anyone with a vaguely scientific background there are glaring. So to correct it (I tried editing the post but the system wouldn’t do it.)

the 100 kg that the helm can apply to the tiller has to be converted into a force in Newtons

F = m x g so F = 100 x 9.81 = 981N

The torque on the TILLER stock is T = F x L = 981 x 1 = 981 Nm

The force on the wire is 981 / 0.075 = 1308N

The safe working load for the wire was given in kg – as if a weight was hanging on the end of the wire.

So that force on the wire of 1308N can be converted to a weight using F = m x g transposed to m = F / g

So m = 1308 / 9.81 = 1333.33 kg.

That is 92% of the safe working load for the wire.

Why have I calculated this? I think I have established that a helms person cannot apply enough force to overload that wire – but they could get close to its safe working load. This applies whether the blade is up or down. If it is up you cant apply enough force to exceed the wires safe working load – the rudder blade will control the tiller not you.

The situation is very different with the tiller held still by ropes. The raised rudder blade can exert sufficient force on the wire to exceed the wires safe working load.

My conclusion remains as per the last post. Repeatedly exceeding the safe working load of the wire is bound to reduce its working life and lead to premature failure.

 

Trevor

[Gregory Manning]

Thanks Trevor,

 

I am sure that the fact that I have the rudder up and on a swinging mooring is the cause of the problem.  Alas I dare not leave it down.  I will try replacing the wipstaff lashing with a heavy duty shock cord as a temporary measure.  This will reudce the strain on the cables but likely increase the amount of movement.  My intention is to replace the cable with dyneema but need to source and make up the cable replacement in the fullness of time.

 

Aye

 

Greg

[Trevor Thompson]

Greg

“Alas I dare not leave it down” – I didn’t suggest you should – leaving it up isn’t the issue.

“likely increase the movement” – why do you think this is an issue? I suggested that you let it move freely. It won’t do any harm.

I have always tried to discourage Atalanta owners from redesigning the boats. I would be very cautious about changing to rope. The pulleys are designed for wire – it isn’t as simple as just replacing wire with rope. Beware the unintended consequences of “improving” the design. The system works as designed – my strong advice is to leave it as it is.

The solution to your problem is to allow the tiller to move freely when you leave the boat on its mooring with the rudder blade raised. I have been doing that for 20 years. It isn’t an issue.

 

Trevor

[Gregory Manning]

Trevor,

As I mentioned, my first failure was of cable of the original spec, that is galvanized wire spun over  a naturel fibre core. Having stainless steel cables is therefore not original and the original spec is no longer available.  It has been suggested that the ss case hardens with repeated flexing which could be a factor in the problem.  Changing back to a galvanised cable even without the fibre core might be an option which I could try.  I am also guessing that the blocks have been changed too.  I changed two of them due to excessive wear.

Thanks again for the input, all welcome.

[Author]

Replies