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bumperdocks

Moving shrouds for mast head kite.

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Have any of you guys moved shrouds to the top of the mast from like 2/3 up?  Im looking to put a mast head assym on my c-lark, and just wondering how hard it would be to do it and get the right stuff for the shrouds and spreaders.  

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I'm no engineer on whether or not this is a good idea but why not, sounds like fun.  It's easy to add new holes for shrouds.  You only need two t-ball backing plates, four stainless rivets, anti-seize, and two much longer shrouds with t-ball end fittings.  Trace out the oval hole that the t-ball fitting needs to pass through, dill a hole as large as you can and either finish enlarging the hole with a round/flat file combo or a dremel. Check the hole against the backing plate often so it doesn't get too big. Once the hole is correct, drill two holes for the rivets, put the backing plate on the inside, brush a little anti-seize all over the fitting, rivet in place.  Repeat.  

T-ball backing plate options

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2 hours ago, bumperdocks said:

Have any of you guys moved shrouds to the top of the mast from like 2/3 up?  Im looking to put a mast head assym on my c-lark, and just wondering how hard it would be to do it and get the right stuff for the shrouds and spreaders.  

In 505 some add upper shrouds with separate spreaders to handle the (near) masthead spinnaker.

If you move the main shrouds, you will cpmpeltely fuck up teh way the mast is supported.

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Not a good idea. The typical dinghy rig relies on the free top mast to give gust control. A masthead rig would be very unpleasant to sail. 

What you need to do is to duplicate the twin spreader rig seen on modern skiff types.
Firstly you're going to need a second set of spreaders very close to the hounds, with a good degree of sweep back and probably much the same length as the standard ones. From there a couple of different arrangements are used. The 49er runs cap shrouds from the mast through these spreaders and direct to the gunwhales. Other skiff types run these shrounds through the normal spreader tips and down to the mast again. Quite possibly there are other arrangements too. 

The other thing you may run into is that typically these rigs run with a lot of prebend, and this would mean a different or at least recut mainsail. 

So this is what to try that probably won't totally destroy the boats sailing characteristics. Whether its entirely a good idea I am unconvinced. 
 

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3 hours ago, JimC said:

Not a good idea. The typical dinghy rig relies on the free top mast to give gust control. A masthead rig would be very unpleasant to sail. 

What you need to do is to duplicate the twin spreader rig seen on modern skiff types.
Firstly you're going to need a second set of spreaders very close to the hounds, with a good degree of sweep back and probably much the same length as the standard ones. From there a couple of different arrangements are used. The 49er runs cap shrouds from the mast through these spreaders and direct to the gunwhales. Other skiff types run these shrounds through the normal spreader tips and down to the mast again. Quite possibly there are other arrangements too. 

The other thing you may run into is that typically these rigs run with a lot of prebend, and this would mean a different or at least recut mainsail. 

So this is what to try that probably won't totally destroy the boats sailing characteristics. Whether its entirely a good idea I am unconvinced. 
 

The 505 apprach is easiest. The upper is diamonds off swept spreaders just above hounds.

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In this day and age of synthetic rigging, a bit of 2mm SK 99 has a BS of 600kgs, and a bit of 2.5mm Dyform has a BS of 690kgs.

We used to use 2.5mm 1:7 on the 18teens as cap shrouds, so I suggest you go look for 2-2.5mm SK99, its so much simpler.    After the initial creep, which you can take out by pre loading with your car and a suitable tree, elongation is also less than wire at these sizes.

The top spreader can be swinging, again they where common back in the 1980's on all the skiffs, as long as you have enough tension in the wires/ropes they will self align.

And it not all that big a span, so the 5o5 solution would also be OK, I assume the section is alloy, it could probably take a spin halyard 800-900mm up without cap-shrouds, especially if your going to use a symmetrical spinnaker, is more than likely more than enough.

If your thinking of a asymmetric spin, then your up for a fair bit more load, so couple of strips of alloy riveted to the side walls, in the 29er we use 2 substantial bits of Carbon each side.

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Here is a thread I made in 2013 on the topic. Note I can't see the photos but the one I used in making the thread turned out to be of Mike Holt's boat (World Champ) and he weighed in, so you are getting the very most experienced help here: Julian Bethwaite and Mike Holt!

 

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I added upper diamonds to facilitate a MH asymmetrical kite. I used 3mm sk99 and pre-loaded similar to JulianB's suggestion. To allow for mast dynamics upwind, I automated the system with the spinnaker halyard so the uppers engage downwind, but go slack when sailing upwind. Boat is a Vanguard Nomad with an aluminum selden Gamma section. 

I have not reinforced the mast, but after using this set-up a few times, it would be a good idea.

 

 

 

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Garth, that's a bloody good idea, if you had the caps, going through a furell and then attached to the sheave carrying your spin halyard, you end up with 2:1 tighten your caps, and if you think about the angles, its likely to be more than enough to counter-act the spinnaker loads.

Nice and simple, love it.

Of-course swept back spreaders are possibly one step simpler again, and hold the mast head up (to windward) so to speak!

                          jB

 

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On my IC(A) I had to add all to make work, all carbon spreaders, dyneema shrouds, on seperate system engaged when going downwind, with bungee take up system, just as Sir Rob intended. Works brilliant!

 

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