shroud tension

[surekandoo]

I've bought a s/h Loos rigging tension gauge to set my rigging up this season

My boat has a fractional rig,. Upper shrouds are parallel with the mast i.e. not swept back, and there are two sets of lowers, one set going forward, and one set swept back. The uppers are fastened through the deck to the main bulkhead, the lowers are fastened through the deck and connected to rods which themselves are connected to the backs of the internal seating down each side of the main cabin. The forward lowers are just connected through deck with no additional internal support structure.

The port forward lower ONLY is showing early signs of pulling through the deck although in the current tension doesn't seem excessive. This has happened over winter while the boat has been ashore, so may have had a "clonk". Who knows. Anyway I will " plate" the anchorage internally and reset the tension.

How do I set the rig up?

I understand about getting the mast vertical from side to side using the main halyard, and also using it to set the mast rake.

What I don't understand is setting the relative tension of the forward & aft lower shrouds.

Can anyone help please?

 

[VicS]

There is an excellent guide on the Selden website which will probably answer all your questions

See http://www.seldenmast.com/files/595-540-E.pdf


Its a big file so may take a moment or two to download.

 

[neilf39]

Are you sure it is fractional? I haven't come across a fractional rig where the uppers are not set back on swept back spreaders, or with forward lowers. Are you sure it is not a masthead rig. Anyway similar to the Selden guide is the Kemp one from their site and covers fractional and masthead.

 

[mrming]

Are you sure it is fractional? I haven't come across a fractional rig where the uppers are not set back on swept back spreaders, or with forward lowers. Are you sure it is not a masthead rig. Anyway similar to the Selden guide is the Kemp one from their site and covers fractional and masthead.

Fractional rigs with inline spreaders do exist and they usually have running backstays (and checkstays if they're a certain vintage of racer).

With regard to tension / tuning, the Selden guide is indeed the business. If however you have a chainplate pulling out, I wouldn't be winding in any tension until you've repaired it and preferably identified the cause of the failure.

 

[VicS]

Are you sure it is fractional? I haven't come across a fractional rig where the uppers are not set back on swept back spreaders, or with forward lowers. Are you sure it is not a masthead rig. Anyway similar to the Selden guide is the Kemp one from their site and covers fractional and masthead.

The Selden guide covers fractional rigs with in line spreaders with forward and aft lowers

 

[William_H]

It seeems likeOP rig is more of a mast head rig with forestay only slightly down from mast top. ie 7/8 or so. In any casae the 4 lower shrouds amkes it's set up more akin to a mast head rig. The lower shrouds are set primarily to locate the middle of the mast in both fore and aft and sideways directions. Slight middle forward is usual. The staic tension of the lowers are set to whatever you think a reasonable thing. I would er on the low side to limit static loading on the hull.
Never under estimate the importance of the lower shrouds. They take a lot of load when sailing and any failure will result in broken mast. Those forward lower shrouds should have been treated in the same way as the aft lowers. ie carry the load down through the deck into the hull or structure. You can beef up the deck but a far better way is to add a stay wire from the chain plate under the deck and take that down to a chain plate bolted to the structure. A turnscrew or similar is a convenient way to take the load way from the deck. In fact pull the deck down. If your chain plate is a U bolt then this can be replaced with a saddle for the shroud through bolterd to another saddle underneath for the extra stay wire. good luck olewill

 

[oldsaltoz]

We set the stays by monitoring the slack on them when to leeward, then make an adjustment, tack and do the same thing.

Finally check the mast for bend to one side or the other and adjust again if needed.

Not scientific I know, but we broke a rig and won a lot of races.

Good luck and fair winds.

 

[wklein]

Without looking its impossible to say with any certainty (although description was excellent) but i would say the aft lowers are designed to be opposed more by the backstay than the forward lowers. You should slacken off the forward lowers put on the for prebend then pull it out with the aft lowers until you have roughly 1 fore and aft mast length of prebend a tight forestay. Then tighten up the forward lowers to snug everything up.

 

[Rigger Mortice]

I read your post, thought "this sounds familiar", checked your profile and, sure enough, we have the same boat!

Mine had/has the same problem with the forward lowers. They are not supposed to be very tight but, at some stage, they had been overtightened. I've put hefty backing plates on but I do little more than tighten them up to take the slack out. AFAIK they are simply there to prevent the mast from "pumping"; to make sure that it doesn't bend back in the middle when, say, a gust hits the genoa or spinnaker or if the backstay tensioner were to accidentally release. i.e. they are there for insurance. Other than that all the tweaking is done on the uppers and aft lowers (and of course the backstay when underway). Both uppers and aft lowers need to be pretty tight (Sorry, I can't remember my settings). Yank the backstay tight first. Then start on the uppers. When the mast is about right laterally and rakewise then start on the aft lowers. Then tighten uppers and aft lowers in rotation, checking that the mast is straight when you look up it. A bit at a time until it is all tight. Then slacken off the backstay.

If you see the forward lowers going obviously slack when you are underway then tighten them up a little. If you see the uppers or aft lowers going slack then tighten them up a lot.

The 720 has slightly unusual rigging in that the spreaders are inline and not swept back.