[MHml] Main Halyard

[Rob Denney]

G'day,

Presumably the knot with the big losses we are referring to is the bowline.
Equally presumably, the area where the rope goes round the shackle (the
bight of the knot) is not where the ropes break.

Therefore, if you take two or more turns around the shackle (better would be
a large diameter rod in the head of the sail), and use a knot such as a
fisherman's bend or even a round turn and two half hitches, the standing
part of the rope will not be under any strain so will have 100% of capacity.
The problem is untying it as these knots jam, but it is simple enough to put
a small tapered pin in the knot to enable it to be loosened.

More elementary problems with a jammer at the mast head are: weight in a
really bad place, cost, complexity (2 lines going to the masthead and a
relatively complex mechanism a long way from the tool box), lack of fail
safety (trigger line fouls, breaks or comes undone) and inefficiency when
reefed.  Better and easier is a simple, fail safe catch which works at the
reef points as well as full hoist with the halyard also working as an
engage/disengage trigger.

regards,

Rob

.----- Original Message ----- 
From: "Paul Nudd" <paulnudd at actionpotential.com.au>
To: "Informed discussion of multihull issues" <multihulls at steamradio.com>
Sent: Wednesday, May 16, 2007 8:05 AM
Subject: Re: [MHml] Main Halyard


> I had a ZS jammer on the mast in 1995 and I took it off, mainly because
> I feel that it is important to be able to quickly release the halyard.
> The ZS cannot be released under load, I needed to reload the halyard
> onto the winch then winch the halyard up a little to unload the ZS in
> order to release the ZS and then release the halyard.
> Now I leave the halyard on the s/t winch so that I can drop the sail
> quickly when necessary. It also means I achieve full hoist. When using
> the ZS I lost a few inches to allow the ZS to jamm.
>
> Presumably, using a ZS at the masthead would entail losing a few inches
> of hoist for it to jamm, then to release the ZS the halyard would have
> to be winched up those few inches to release (remotely). Also the ZS
> would fail to the locked (not fail-safe) position. All this is of course
> no big deal on Charleston where a capsize is 'not the end of the world'.
> On many other boats a capsize would be 'the end of the world' - "well
> hardly ever" - "we hardly ever capsize at sea".
>
>
> I once tried a 12mm spectra halyard with a splice but the splice tail
> (14mm?) wouldn't go through the sheave.
>
> I still agonise over to splice or knot to splice as Creighton has sewn
> the seeds of concern over the splice tail working through the 2 sheaves
> (2:1 halyard) and the knot is replaceable and a professional splice
> costs $60
> The 1:1 11mm 1998 vectran halyard failed at the knot after 9 years.
> I will be using 2:1 (half the load) 10mm 2007 vectran which may be
> better than the older stuff, so can I expect a few years out of it with
> a knot at the top. I imagine I was perhaps using 20% of the load
> capacity of the old stuff, thus the failure after 9 years.
> I guess I will be using about 10% of the load capacity on the new
> halyard so if I use a knot it should last 'forever'.
> Alternatively I could perhaps use 2:1 6mm 2007 vectran and use maybe 50%
> of the load capacity and need a splice. If I had a lightweight carbon
> mast perhaps I would be looking for the last bit of weight aloft saving
> and use the 6mm but I have a rather heavy, very strong aluminum alloy
> mast and there are easier ways to save a bit of weight aloft.
> I will leave that to the next owner and just try to turn over a good
> strong reliable package.
> I will continue to maintain the boat to the highest standard but will
> undertake no further development.
> PN
> Ross Hobson wrote:
> > Paul
> > On Charleston we have reduced any stretch to zero by installing spinlock
> > ZS jammer on a remote release at the mast head - even is we manage to
> > strech 10mm dia (8m core) spectra the actual working length is only
> > 300mm
> >
> > We use a 12:1 downhaul
> >
> > It's an easy way of getting around all that rope plus it reduces mast
> > compression
> >
> > I would splice every time - as I said in a prveious email having
> > undetaken the load cell (instron) tests - a knot reduces rope strength
> > at at least 60% and a proper tapered splice only 10-20% reduction in
> > rope strength
> >
> > But you may be using the knowt as a'fuse' so you don't overload
> > things....
> > :-)
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