Hi,

I have a Parker 275 (Ardea) and have just fitted Dyneema for my lifting keel to replace wire. I've used Marlow Excel D12 Max SK78 - 7mm with a
Stainless Steel Thimble Eye Splice, supplied by Jimmy Green. This is the spec. others have used (though not everyone uses a thimble eye). Now I've read more about it, I wonder why we are using 7mm, when 5mm should be plenty strong enough, any comments on this would be interesting, but this is of secondary interest to the concerns below.

Anyway, I am seeking advice from others who have used the same material. This is how I set things up: I tied a clove hitch onto the winch drum and fitted the end of the Dyneema using the metal plate and bolt on the rotating outer face of the winch, as specified by Dutton Lanson. Then I wound the rest of the Dyneema onto the drum as tidily as I could, using hand tension. This was done with the boat on the hard, the keel in the almost fully wound up position and supported on blocks. However, when I increased the load by starting to pull the keel off the blocks, the part of the rope under tension pulled deeply into the coils that were wound onto the drum. I also noticed that when tension was released the Dyneema jumped off the sheave that is attached to the boat and next to the winch housing and had to be re-positioned by hand

I have two concerns: -

1. that under load the coils will tighten onto each other in a disorderly fashion once the keel is being used regularly and this might cause chafing or problems with the fee movement of the Dyneema.

2. that the Dyneema might jump off the sheave and become jammed in normal use.

I know others have used this arrangement, so I would be interested to know what your experience is and whether these concerns are justified in practice.

Jake

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Jake,
I changed Flamingo's keel wire to 8mm Dyneema two years ago, some observations:
When looking at the figures we need to consider SWL, not breaking strain.
If the keel gets slightly jammed I would guess that it's effective weight could be doubled.
The outer of my first Dyneema got damaged, jammed in the sheave and the winch broke it easily.
I'm now looking at the Dyneema that I fitted last year and thinking does it need replacing already, £20 every year.
Wire seems to work well.
The advantages of Dyneema, it's quieter and easier to handle.
I haven't decided but I may go back to wire.

Hi Phill,

Thanks for replying. The boat is still out of the water with the keel on a block, so I have an opportunity to abandon Dyneema and use wire again without no added expense for getting the keel in the right position to make the change. Your experience gives a nudge in that direction. Just one thing though, your Dyneema must be different from mine, mine has no outer sheath, it looks like tightly woven webbing all the way through.

Another point, the wire I have just replaced with Dyneema is 6mm 7x19 s/s wire, which has a SWL of 432 kg. This is quite a stiff wire and it has a tendency to begin to splinter, which is definitely not a good thing. I had a serious problem with this in the past when the wire frayed, jammed and then released suddenly allowing the keel to crash to the bottom - not much fun!

There are other wires with the same SWL that are supposedly resistant to abrasion and more flexible, e.g. on this website:

http://www.mainco.co.uk/breaking_loads 

What specification wire have you used in the past?

Jake

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Jake,
The wire that I removed came with the boat when I bought it. It had a number of kinks and broken strands. It certainly looked like 6mm 7/19. The second lot of Dyneema I used has a much more tightly woven outer which seems less prone to snagging but it is definitely an inner and an outer, and it's 8mm. I wouldn't steer you either way, I changed to Dyneema because I thought it would be better and I'm about to go into my third season with it. I just think that there are pros and cons to each. One thing I did do was to build a transparent acrylic window into the cover above the winch so that it is easy to monitor the condition of the Dyneema on the drum.
It would be interesting to get some other thoughts.
Regards

Phill

I have used D12 dynamo for the last few seasons - I've not had any problems with it jumping off sheaves. The wire I replaced was 6mm 7x19. The wire becomes tightly coiled and tends to get fractured strands as the winch drum has such a small diameter, the wire also pulled in through the bottom turns that could not be wound on the drum with enough tension.

With the Dyneema I too put a clove hitch on the winch barrel, then lead the tail out through the drum flange and around to be secured with the plate and screw as for the wire. I wind the Dyneema on under as much tension as I can manage, and endeavour to get all the twists out of the Dyneema before attaching it to the keel. Do you think that jumping the sheave might be associated with twists in the line? I think that my sheaves have little clearance at the sides for the Dyneema to go astray in any case. The Dyneema does pull in through the lower turns on the winch drum, but while it might change the line from being perfectly circular in places it does not appear to cause abrasion of the outer strands.

The 8mm Dyneema I used gives a greater factor of safety than the 6mm 7x19 s/s FSWR, the more recent Marlow D12 7mm has the same BL as the 8mm I started off with. I use an anchor bend onto the keel shackle, I felt that there was insufficient length to my first sheave for a splice not to thicken and stiffen the Dyneema where it passes over the first sheave with the keel fully up.

I've been completely happy with the Dyneema performance. In contrast the wire was not so good. The winch drum also suffers from less abrasion and corrosion with the Dyneema.

I'm currently looking at replacing the awful Dutton Lainson winch with something more unobtrusive and also kinder to the line.

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