Mast measuring........would this work?

[macd]

Easiest method I've used was a digital spirit level borrowed from a builder mate. The level can be 'zeroed' somewhere athwartships known to be parallel to intended sea level, then held against the mast. Dead simple. Also good for setting mast-rake, although a bit of tweaking afterwards is always required.

I've mentioned the device to a couple of riggers who'd never heard of it. Their first reaction was slightly patronising. Then...you could almost hear the gears turning...they began to think it might save a lot of long-winded bother.

When I last heard they cost around £100 but they're the sort of thing that generally comes down in price as sales volumes rise.

 

[macd]

By way of a P.S. on digital spirit levels, check out:
www.laserlevelshop.co.uk/browse.asp...pirit+Levels&gclid=CIuYybHy4ZwCFU0B4wodUF0VIw

 

[dukes4monny]

By way of a P.S. on digital spirit levels, check out:
www.laserlevelshop.co.uk/browse.asp...pirit+Levels&gclid=CIuYybHy4ZwCFU0B4wodUF0VIw

I like this idea too, especially as it gives an easy method for checking rake too.
I'm sure one of my builder buddies will have one that I can 'borrow' ;o)

 

[ytd]

what I have used in the past is to have someone hold a 1m spirit level vertical and then take a photo from the dinghy. Print the photo out and draw lines from the spirit level to get the angle of mast rake. You can also calculate mast length from the 1m length of the level. Good for about 0.1m accuracy

 

[Lakesailor]

then held against the mast.

.....as long as the mast is straight along it's whole length and not just at the bottom.

 

[srm]

The type of laser level which is mounted on a gimbal inside the device will project a line all the way up the mast if you attach it to the mast base.

Indeed it will, and you will be able to watch the mast swing like an inverted pendulum either side of the vertical laser line. Also watch the effect as you move around the boat or someone steps on / off board. Its not going to tell you if the mast is upright relative to the hull though unless you are ashore and have carefully levelled the hull first in a rigid cradle.
(I was working at the masthead while ashore in a cradle and could feel the boat moving as my assistant moved on deck)

 

[srm]

and there is a lot of movement in a rig and distortion in a hull when sailng to windward anyway ( see your lee cap-shrouds slackening).

Unless sailing an old gaffer or aged wooden hull that has to be treated gently I take being able to see lee cap-shrouds (or any lee shrouds for that matter) slackening as a sign that the rig is in serious need of setting up properly. Try squinting up the sail track as you probably have a bend developing with the head sagging off to leeward. Also, if you sail in open water such a slack rig is going to increase the shock loads on mast and wire as you bounce over waves. Lee shrouds may feel slightly slack in strong winds but should not look slack, and the mast should remain straight in the athwartship plane.
This is for masthead rigs, as I have little experience of setting up fractionals.

I once found myself with slack lee shrouds in the middle of the North Sea on passage from Lerwick to Bergen, with the keel stepped mast just starting to move against its deck wedges. The standing rigging was all new, had been set up tight, but 100 miles plus of beam reaching in force 7 gusting 9 had caused it to bed in and show its initial stretch quicker than usual. I do not recommend tensioning rigging in those conditions, but was concerned for the safety of the mast.

 

[Refueler]

Unless sailing an old gaffer or aged wooden hull that has to be treated gently I take being able to see lee cap-shrouds (or any lee shrouds for that matter) slackening as a sign that the rig is in serious need of setting up properly. Try squinting up the sail track as you probably have a bend developing with the head sagging off to leeward. Also, if you sail in open water such a slack rig is going to increase the shock loads on mast and wire as you bounce over waves. Lee shrouds may feel slightly slack in strong winds but should not look slack, and the mast should remain straight in the athwartship plane.
This is for masthead rigs, as I have little experience of setting up fractionals.

A small amount of slack in lee shrouds / stays when mast is under pressure from sails full is acceptable. If you set up too tight you will create compression of deck or strain on keel member. I have a good indicator of mast tension ... if my bog door binds on mast underdeck doubler, then I've set up too tight !

If a newcomer to boating took some posts as gospel and followed the advice, eg. set up their rigging too tight - they could rue the day they ever read the post !!

 

[macd]

.....as long as the mast is straight along it's whole length and not just at the bottom.

Wot you on about Lakesailor? The question was about lateral verticality. Any mast that isn't substantially straight that way ought to be thrown away.

As to fore-and-aft straightness, usually they are until you start putting in pre-bend. That's why I mentioned subsequent tweaking.

Of course I omitted to factor in gravitational effects from nearby Cumbrian mountains, so maybe it wouldn't work in your neck of the woods.

 

[srm]

A small amount of slack in lee shrouds / stays when mast is under pressure from sails full is acceptable.

Which is what I said, feel slack but not look slack. Once the shrouds are visibly slack the mast is able to move and is very probably bending out of line, thus weakening it.

Perhaps I have been very fortunate and somehow only sailed on well designed and built boats since my first offshore passage in 1971. Some have been fairly lightweight cruising multihulls but even these never suffered from visibly slack lee shrouds.

If my bog door jammed under sailing rig pressure I would want to strengthen the structure of the hull not slacken the rig to compensate, as the weakness is still there and will only get worse if the load bearing structure flexes that much.

According to an article on setting up a rig published by Kemp masts many years ago, its almost impossible to overtighten a rig with ordinary hand tools (ie a pair of spanners). However, I do accept that a poorly designed or built hull can be bent by rig tension, though the main danger is the back and forestays not shrouds - after all imagine the hull as a bow, mast as the arrow, and fore stay plus backstay as the bow strings.

 

[sailorman]

plumbbob

heavy winch handle on a halliard