Anyone using synthetic steering cables?

[merrydolphin]

I owned and extensively cruised my KP 44, great boat. Yes, the cables were a bit circuitous. We did have cable problems. Where the cable attached to the chain was improperly done. Repaired with the correct chain shackle. I did find that the boat did have a bit of a heavy helm due to cable runs but OK otherwise. When I was sailing it we didn’t have the option of anything else. But would think that would work. And good on you for re-routing the run to the rudder.

[Fore and Aft]

Gilow I think I solved the problem!!
Cheers

[GILow]

Originally Posted by Fore and Aft

Gilow I think I solved the problem!!
Cheers

Don’t joke, I’m actually making just that. The KP44 is notorious for the rudders failing and I can’t build a new one until next summer, so I’m making an emergency rudder very much like what you’ve drawn.

[GILow]

Originally Posted by merrydolphin

I owned and extensively cruised my KP 44, great boat. Yes, the cables were a bit circuitous. We did have cable problems. Where the cable attached to the chain was improperly done. Repaired with the correct chain shackle. I did find that the boat did have a bit of a heavy helm due to cable runs but OK otherwise. When I was sailing it we didn’t have the option of anything else. But would think that would work. And good on you for re-routing the run to the rudder.

Hi MD. Good to hear from you again.

The old cable route was pretty torturous. Like a few things in the KP44, I think good engineering design took a back seat to the interior layout and trying to cram too much into the space available. Getting rid of the aft bathroom was absolutely transformative, plus it left the crazy cable setup hanging in space.

Matt

[Fore and Aft]

Matt why not just bolt this to your transom.
Cheers

[GILow]

Originally Posted by Fore and Aft

Matt why not just bolt this to your transom.
Cheers

Geez, that’s a bargain! Tempted.

[s/v Jedi]

Information posted in this thread isn’t exactly correct.

Dyneema, let’s assume you use Amsteel Blue which is affordable SK75/78 and easy to work with but has no heat treatment or anything special. So it’s kind of the worst case when it comes to stretch. Samson prefers to call it elongation.

There are different kinds of elongation. These need to be addressed separately:

1. Constructural elongation. This is the braid getting tighter when pulled. It is mostly eliminated with heat treatment but of course when you splice that, you reintroduce it so for either case you need to pre stretch it. I normally first splice an eye to one end (regular splice, no Brummel lock), then stretch it to determine length. Next I put a regular eye splice in the other end (these splices are done in a couple of minutes as they are super easy) and tighten it again to check length. Now you can measure how much longer/shorter it needs to be and adjust one or both splices. Always go for maximum length of the tightening mechanism (turnbuckle, lashing) so you have maximum adjustment for more tightening.
When you stretch the line, it is set and constructional elongation is eliminated until you flap it around a bit, but it will get back to the same length when re-tightened. Note that when the size is correct, I recommend to add lock stitches to the splices because it’s easy and quick to do and prevents the splice from moving when not tight.

2. Elastic elongation. This is the real stretch. It is mostly eliminated by tensioning the line. For example, you tension the steering line to 20% of breaking strength. This will stretch it by 0.7% so a 10 meter line will stretch 7cm doing this. The turnbuckle or lashing must be able to absorb that 7cm.

After that, there is no play in the system. Except when a large force tries to move the rudder. This will turn the wheel a bit, because one side is stretched a little more under the added tension, while the other side springs back under reduced tension. Let’s say this force results in another 10% of breaking strength on the Dyneema. This makes it stretch to 30% of breaking strength which is 0.96% instead of 0.7% so that adds 2.6cm.
The other side was pre tensioned to 20% and now becomes 10% which is 0.46% so 4.6cm instead of 7cm which means there is no slack in the system.

Even when this would result in slack in the system, it means the rudder system must have been designed to cope with those larger forces and you can pre tension to a higher load. If you need to go up to 30% to prevent slack in the cable then I recommend to go up to the next size instead.

To put some real numbers on this: a 6mm Amsteel Blue has a minimum breaking strength of 3,500kg. So 20% pre tension is 700kg. I don’t think many will need to go up to 8mm where 20% is 1,120kg.

I think 10% pre tension is what may be required at most.

To conclude: there is no play at the steering wheel, this is a myth or possibly an incorrect installation. Pre tension is required for steel cables as well.

Then there is creep. Creep is a stretch over time. This means you need to re-tighten periodically. Think once a year during the yearly check of the steering system.
You can eliminate creep by choosing a different fiber. A Vectran rope like Marlow Excell V12 eliminates creep. The negative is that it quickly deteriorates with UV exposure, which may not be a problem for a steering cable.

[Ambler]

Hi Matt, I have had my dyneema steering cable on for 5 years now and sailed from Hobart to New Cal via Coffs and back to Hobart via Bundaberg. I hadn't consulted anyone on its use prior to fitting so made up a spare dyneema cable in case.
The biggest advantage for me was I had to use smaller diameter sheaves than stainless cable would have allowed. It took about 6 months for the stretch or creep in the cable to stabilise.
I placed turnbuckles at the cable chain junctions and a cleat at the quadrant, that way when the turnbuckles ran out of adjustment I took another turn on the cleat and started again with almost full adjustment. I can adjust them whilst underway easier than accessing turnbuckles on the quadrant.
Give me call if you need finer detail

[s/v Jedi]

Let me add this: if at all possible, I recommend to use a lashing instead of a turnbuckle. I found a super easy way to do lashings:

You need to prep the attachment points. For the spliced Dyneema (Vectran) add a low friction ring into the eye splice. At the other end, the quadrant, use a shackle.

Use 6mm Amsteel Blue for example, breaking strength 3,500kg.

For the lashing you will need 2.5mm (7/64”) Amsteel Blue, breaking strength 650kg and 2.2mm (3/32”) Lash-it, breaking strength 290kg

Now measure the maximum length of each loop of the lashing, before tightening it. Let’s say this is 50cm.

A loop has two legs so is twice as strong as the material that is looped. So a loop of 2.5mm Amsteel Blue has a breaking strength of 1,300kg. We need to match 3,500kg so 3 loops is perfect. We need to tighten the primary lashing so make it 2.5 times 50cm = 150cm after splicing and pre stretching. Splice one eye to the low friction ring of the steering cable and the other just an eye splice.

Now we do a secondary lashing with Lash-it (another Samson product, available on Amazon but make sure to get the thicker of the two diameters). The reason to do this is because Lash-it miraculously holds knots. It has a different construction and the coating feel different too (but also Samthane). To match the 2.5mm Amsteel two loops is more than enough but I always do 2.5 or 3 loops. Take a piece and tie one end to the empty eye of the 2.5mm Amsteel with a tiny bowline.

Now lash the 2.5 turns of the primary lashing. The eye with Lash-it should just come through the low friction ring. Lash the secondary lashing between quadrant and the eye of the 2.5mm Amsteel. After one turn tighten the whole lashing. You will be surprised how well this works. Add more turns and tighten more. Finish with half hitches around just the lash-it secondary lashing. I often use a splicing needle designed for paracord (Amazon) here because the lashing becomes tight and hard as steel, making it difficult to pull the lash-it through.

I know this sounds complicated but it isn’t. It’s super quick and works brilliantly. Also, the 2.5mm Amsteel Blue is very affordable on Amazon as it’s used for camping.

Attached a picture of this lashing between a large low friction ring and a pad eye. It has more turns because it’s a much higher load running backstay with the tail made of 8mm Amsteel Blue.

Edit: in the picture the Lash-it is also half hitched around the whole lashing. This was done after tensioning to get the primary lashing equalized so that all loops are equally tight. The only reason for wrapping around the whole lashing is that this is a dynamic setup with a lot of movement when the running backstay is pulled forward to store it when not in use. Totally not needed for a steering cable.

[Benz]

^^@Jedi,
The Lash-it is grippier because it's an 8-carrier braid instead of the usual twelve, which makes it more nubbly. If you're really fiddly, you can splice it with a fine piece of doubled leader wire. You have to taper the bury tail first to get it to fit, but it makes a tidy splice you can girth hitch for a the deadend of the lashing.
It's my favorite product for small seizings because, as you noted, it will hold knots better than other Dyneema twines.

[s/v Jedi]

Originally Posted by Benz

^^@Jedi,
The Lash-it is grippier because it's an 8-carrier braid instead of the usual twelve, which makes it more nubbly. If you're really fiddly, you can splice it with a fine piece of doubled leader wire. You have to taper the bury tail first to get it to fit, but it makes a tidy splice you can girth hitch for a the deadend of the lashing.
It's my favorite product for small seizings because, as you noted, it will hold knots better than other Dyneema twines.

It’s also an asymmetrical braid. Some strands have more sub-strands than others. I tried to pull a simple bowline knot out but couldn’t.

[coopec43]

I can't vouch for the accuracy of this formula for calculating rudder loads but it was posted by "Scottie" on YBW and I know I used it some years ago when installing Helen's chain and cable steering system. Of course a yacht has to have a large safety margin as you wouldn't want a cable to break when surfing down a wave.

The formula is far easier to use than it looks. (see the example they give)


When the torque necessary to manoeuvre a boat is not specified by naval architect nor
by the shipbuilders yard, it can be calculated as follows:-
It must be known that the torque necessary to manoeuvre a boat depends on:
• the speed of the water flowing on the surface of the rudder at a certain angle;
• the rudder size;
• the total sweep of rudder (& a part of the boat) when rudder shaft is not perpendicular;
• the compensating surface;
Torque calculation for a maximum speed about 25 knots:
T = S x [(0.4a) -b ] x V
2
x k
T = Torque in kgm
S = Total surface space of the rudder in m
2
(h x a)
h = Height of the rudder in m
a = Width of rudder in m
b = The value of the compensation in m
V = Speed of the boat in knots
k = Coefficient according to the total angle of rudder
- Port to starboard 50° k = 10.84
- Port to starboard 60° k = 13.01
- Port to starboard 70° k = 15.89
- Port to starboard 80° k = 17.80
- Port to starboard 90° k = 19.52
Straightening according type of boats:
- For boats equipped with jet engine T x 1.3
- For power boats with two engines and one rudder T x 0.5
- For sailboats T x 0.5
- For twin rudders T x 2
Example: Assume a rudder with a height of 0.5m(h), an overall width of 0.35m(a) and a
balance of 0.10(b). Maximum boat speed = 22 Knots. Port to starboard = 70°.
The maximum torque on the rudder blade is given by:
T = S x (0.4a-b) x V
2
x 15.89
T = (0.5 x 0.35) x ((0.4 x 0.35) - 0.10) x 22
2
x 15.89
T = 0.175 x 0.04 x 484 x 15.89
T = 53.9 Kgm Assuming twin rudders maximum steering torque = 107.8Kg

[coopec43]

Originally Posted by s/v Jedi

2. Elastic elongation. This is the real stretch. It is mostly eliminated by tensioning the line. For example, you tension the steering line to 20% of breaking strength. This will stretch it by 0.7% so a 10 meter line will stretch 7cm doing this. The turnbuckle or lashing must be able to absorb that 7cm.

After that, there is no play in the system. Except when a large force tries to move the rudder. This will turn the wheel a bit, because one side is stretched a little more under the added tension, while the other side springs back under reduced tension. Let’s say this force results in another 10% of breaking strength on the Dyneema. This makes it stretch to 30% of breaking strength which is 0.96% instead of 0.7% so that adds 2.6cm.
The other side was pre tensioned to 20% and now becomes 10% which is 0.46% so 4.6cm instead of 7cm which means there is no slack in the system.

Even when this would result in slack in the system, it means the rudder system must have been designed to cope with those larger forces and you can pre tension to a higher load. If you need to go up to 30% to prevent slack in the cable then I recommend to go up to the next size instead.

To put some real numbers on this: a 6mm Amsteel Blue has a minimum breaking strength of 3,500kg. So 20% pre tension is 700kg. I don’t think many will need to go up to 8mm where 20% is 1,120kg.

I think 10% pre tension is what may be required at most.

To conclude: there is no play at the steering wheel, this is a myth or possibly an incorrect installation. Pre tension is required for steel cables as well.

.

I don't follow your post!

Are you suggestion your steering cables should be pre-tensioning to 700KG (A Honda Civic weighs 1300KG ) What an incredible strain on all your sheaves. Any cable (Dyneema or steel) will keep stretching until it breaks. Pre-tensioning is not the answer.

If the steering cable stretches too much, go up a size or two. That is why the experienced rigger who designed my steering system said since my steering cables are 3m long I should go for 10mm instead of 8mm cable to reduce stretch.

Now where am I going wrong?

Understanding Stretch in Wire Rope and Cable
https://blog.strandcore.com/blog/und...rope-and-cable

[GILow]

Originally Posted by coopec43

I don't follow your post!

Are you suggestion your steering cables should be pre-tensioning to 700KG (A Honda Civic weighs 1300KG ) What an incredible strain on all your sheaves. Any cable (Dyneema or steel) will keep stretching until it breaks. Pre-tensioning is not the answer.

If the steering cable stretches too much, go up a size or two. That is why the experienced rigger who designed my steering system said since my steering cables are 3m long I should go for 10mm instead of 8mm cable to reduce stretch.

Now where am I going wrong?

Understanding Stretch in Wire Rope and Cable
https://blog.strandcore.com/blog/und...rope-and-cable

For a guy so incredibly accomplished as to build his own boat, I would have thought the concept of pretensioning was obvious.

Where am I going wrong?

[GILow]

Originally Posted by Ambler

Hi Matt, I have had my dyneema steering cable on for 5 years now and sailed from Hobart to New Cal via Coffs and back to Hobart via Bundaberg. I hadn't consulted anyone on its use prior to fitting so made up a spare dyneema cable in case.
The biggest advantage for me was I had to use smaller diameter sheaves than stainless cable would have allowed. It took about 6 months for the stretch or creep in the cable to stabilise.
I placed turnbuckles at the cable chain junctions and a cleat at the quadrant, that way when the turnbuckles ran out of adjustment I took another turn on the cleat and started again with almost full adjustment. I can adjust them whilst underway easier than accessing turnbuckles on the quadrant.
Give me call if you need finer detail

Like your brilliant solution to my rudder travel problem four years ago, your cleat idea is now firmly on my list.