Renewing Spreaders

[alec]

After unstepping the mast I noticed I had a bent spreader. I was advised that I should renew both which I have done. The most cost effective option was stainless steel.

As holes have to be drilled at the mast end , I was wondering if there is any special procedure in doing this. Also, I believe there is a way for marking shrouds so that the spreaders do not sag.


Any suggestions would be gratefully received.

Regards,

 

[William_H]

You don't give any clues from your bio as to what kind of boat you have so this is mostly guess work.
Stainless Steel would be unusual for spreaders from weight consideration. Every extra kilo of SS would represent the effect of 5 kilos on the bottom of the keel for righting moment. However people happily put radar antennae reflectors and other antennae at the top of the mast believing that the righting moment will still be adequate.
"Holes at the Mast end" I have a friend with a 20 ft keel boat where the spreader had a piece of Aluminium tubing about 25mm diameter passing right through the mast into each spreader. The new mast crumpled after just a few hours sailing because of the large hole in the mast. The spreader attachment should be via a plate on the surface of the side of the mast with no larger holes than that for rivets to hold it in place.
Now spreaders come in 2 styles or functions, On a mastheaed rig the shrouds are usually set abeam the mast and the spreader's function is to improve the angle of shroud at the top and all pressure on the shroud is pressing into the mast in a straight line. I always thought that the shroud should be free to run on the end of the spreader so that it takes up it's best position without bending pressure downwards or upwards on the spreader. The shroud should be captured by a piece of lock wire or similar to stop it falling off the end of the spreader.
Now on a mast head rig the spreaders are usually swept aft by about 15degrees and the shrouds also go to chainplates aft of abeam the mast. The aft sweep of the spreaders means that as the shrouds are tightened they actually push the tips of the spreaders forward. This pushes the middle of the mast forward. This is balanced by the intermediate shrouds pulling aft usually to the same point as the chainplates for the top shrouds. This enables the middle of the mast to be steadied in the fore and aft without having a baby forestay as in a mast head rig.
So this means that the spreaders must not only hold the top shroud out to improve the angle of pull but must also be strong in holding it's sweep back. This is more or less important depending on the height of the mast and the inherrent stiffness of the mast in the fore and aft direction. So on a tall slender mast it really matters while a short mast less than 7metres that has a dimension like 10cms from fron't to back the mast is probably stiff enough to support itself in the middle without aft swept spreaders.
With aft swept spreaders they are usually made thin from top to bottom but wide in the fore and aft direction to stop bending (forward). ie made from 6mm thick Al plate. The attachment of the base is also critical and will often be in the form of a plate wrapped around the front of the mast with the spreader or spreader base welded to the plate. The rivets at the back of the mast are most critical as the tendency is for the plate to peel off as the spreaders are pressed forward. Many years ago I lost a mast (fractional) because the rivets in the aft end of the plate (aluminium I think) let go allowing one spreader to swing forward and the middle of the mast crumpled back.
The plate had a bolt right through the mast which held tangs for the intermediate side stays this held but just a little peeling effect was enough to allow the start of failure when pressures increased to fold the mast.
So your spreaders may be simple or very critical and here I have been talking a boat around 22 ft long larger boat means more critical spreaders so get as much advice as posssible. But first tell us what type it is. olewill
PS why did your spreader bend and in what direction?

 

[alec]

Many thanks for the very concise and interesting response.

The boat is a conventional heavy/med displacement long keeled , single spreader masthead rig. The mast is 32 feet with no baby stay but fore aft lowers

The spreader was bent in the fore and aft plane probably due to a clout when drying out against a wall.

Regards,

 

[oldharry]

Interesting and informative William, and thanks. Uk boats seem to be rigged slightly differently in many cases, as the spreaders are not usually given a backward sweep, and the main shrouds are installed in line with the foot of the mast. I this situation the spreaders not only give the shroud a reasonable angle at the masthead, but support the centre of the mast from bowing. The Lower shrouds provide further support against bowing forces, and also allow precise adjustment of the the curvature - or lack of it - of the middle section of the mast undewr the load from the sails. In a 'normal' crusing boat masthead rig, the aim is usually to acheive an absolutely straight mast, easily verified by looking up the luff track. High performance racing machines of course have their own demands, and often require the masthead to be raked back by varying amounts according to the conditions etc.

For and aft lowers allow this mid-mast adjustment to be made with fair precision.

Spreaders do need to be mounted to load spreading plates, as the one thing that guarantees mast failure is excessive point loading which will collapse the mast section and allow it to crumple under load. Through bolting is common, but with a spacer internally to preserve the shape of the mast - again fairly critical for it to retain its strength.

Finally, any stainless fittings attached to a mast MUST have insulating material between them and the ally mast, as salt water will rapidly set up severe corrosion if the two materials are not separated, and will result in early failure. Various suitable compounds are readily available.

 

[alec]

>Spreaders do need to be mounted to load spreading plates, as the one thing that guarantees mast failure is excessive point loading which will collapse the mast section and allow it to crumple under load <

Thanks Old Harry another nice post.
Following on from the above – While I was out and about today I managed half an hour in a Town Centre library and found ‘The Rigging Handbook’ and looked under ‘spreaders’.

I quote “ All is well until we get to the spreaders, which are horizontal instead of bisecting the angle formed by the shrouds. This is the single most common flaw in rigging. If it is horizontal, the shroud will act to push it’s outboard end down. This leads to an excessive buckling load on the spreader. To fix this, cast off the outboard seizings and tap the ends up to the proper angle” unquote..

Perhaps you might be able to help on this. Does this mean that our spreaders should in effect tilt upwards when at rest, at right angles to the shroud ? I will certainly start looking at other boats now. I presume under load, they become horizontol ?

Also, I have a mast plate as you have mentioned riveted to the mast holding a ferrule type arrangement which the spreader slots in. This has two holes to take the through bolt to hold the spreader. Following the above, do I need to drill the holes in the spreader in a particular fashion to position the spreader and do the bolts need to be loose – ish to allow for movement ?.

Many thanks for any ideas or comments.

Regards,

 

[William_H]

Hi Alec and well done oleharry I wouldn't disagre with anything oeharry says except perhaps the idea that normal is common and highly tuned racing boats are unusual. It didn't occur to me that high point loading on the wall of the mast would be a problem but of course you are right and possibly in the case of mmy friends mast that is why the tube through the middle but did it have a spacer tube as well? I will ask. Yes tips of the spreaders should be adjusted upward so that the pressure in the end of the spreader is in perfect column compression.
I just don't reckon there is so much difference between racing and cruising when it comes to rigs. I certainly think my rig with large main and small jib (no inner forestay) which you would call a highly tuned racing rig is ideal for cruising especially single handed. I would not want a masthead traditional rig for any purpose. I will grant however that long keels have attractions for cruising over fin keels which can be a bugger in a seaway.
Anyway not trying to argue just point out that modern rigs are good. regards olewill

 

[john_morris_uk]

IMHO I don't believe that shrouds should normally be free to run in the spreader ends. I do not believe that they will normally find their 'natural correct position'.

Furthermore on nearly all rigs, the spreaders should 'bisect the angle' of the shrouds. This is easier to draw than to explain! Also the idea of the shroud 'moving down to a horizontal position' as the boat sails and pressure comes on fills me with horror!

One way that a rigger showed me to find the correct place for the spreader to be attached to the shroud was to bring the shroud down close to the mast and then mark the exact point on the wire where it passed the root of the spreader. You then take the shroud out to the end of the speader and fix the spreader at this point.

On a wooden boat we had once, with a wooden mast, and wooden spreaders, I used a bulldog grip beneath the spreader end to ensure that the spreader was held 'up' at the correct position. I can't remember a modern spreader that didn't have the facility to lock itself onto the spreader.

There was a time when riggers didn't appreciate the forces involved, and you will sometimes see older boats with 'horizontal spreaders'. If they survive it is a tribute to their over engineered design.

 

[oldharry]

Yes, the spreaders do need to be angled up, and no they should not be free to move in any direction. The spreader should bisect the angle formed by the shroud as it passes over the end of the spreader. It is easier to set this up than to describe it, but here goes!

With the mast laid flat on the ground, set the bottom of the shrouds at the same distance out as they would be on the boat. Now set up the spreaders so that the angle between the shroud wire and the spreader is the same above and below the spreader. This varies according to how far up the mast and how long the spreader is, but usually gives the spreader around 10 degrees upward tilt. Making sure the wire above the spreader is tight, lock the spreader to the wire in the correct position. The tiny amount of 'give' when you actually tighten the rigging screws should make no appreciable difference.

I find it quite astonishing how many smaller yachts, under say around 24 ft Loa keep their masts up with 'droopy spreaders'. It is not unusal to see them well below the horizontal, and probably doing more harm than good!

Any such boat has a serious weakness in the rigging, and is at risk of dismasting in a blow.

John Morris is quite right, that some older boats were actually designed and rigged with horizontal spreaders, with total disregard to the actual function of the spreader - and that they have survived reflects simply on the strength built in: ("well guv' we 'ad to beef them up like that, the early ones kept busting you see....!").

Oh and William, I wasn't meaning to single out 'racing machines' as being exceptional (well not much anyway!) other than that modern 'bendy' rigs are less common on heavy dispalcement long keelers of the kind Alec describes as his.

Single handing my masthead rigged Eventide would be considerably less effort if I did convert it to 3/4 rig, I agree; but she is so well balanced - steering with 2 fingers even in a F5 - that I am reluctant to mess about! But the big roller jib can be hard work! /forums/images/graemlins/ooo.gif

 

[VicMallows]

Slightly off topic ... but since we've got the experts here....

I need to renew rigging this year, and anticipate difficulting shifting the cast alluminium spreader clamp pieces from the end of the spreaders (couldn't shift them 10 years ago when had mast down to go through the canals). Any particular suggestions? (Kemp (=Selden) mast c. 1984).

Thanks, Vic

 

[john_morris_uk]

Its probable not much help, but the last time I tried heat, oil, etc etc and in the end I took the spreaders into the riggers with the shrouds attached and they gave them me back detached. (I thing they used rather more heat than I'd been willing to try...)

 

[sailorman]

lay the cap shroud along the mast pull tight towards the heel, mark the "spreader root" on the shroud.
afix cap shroud to spreader out-board end @ the mark made & the spreader will be raised slightly @ the out-board end. perfik job

 

[oldharry]

Re removing ally fittings from spreaders - lots of heat. If that doesn't work, take them to the local riggers. That would be the best chance of shifting them without damage - if they can be shifted at all! The riggers would be better placed to source replacements if they have to be cut off.

 

[oldharry]

[ QUOTE ]
Anyway not trying to argue just point out that modern rigs are good. regards olewill

[/ QUOTE ]

Just following through your thoughts Olewill:Modern rigs obviously have the benefit of detailed computerised research, and are naturally going to be more powerful than more traditional designs for a given sail area. However they do tend to be more complex, and to need a lot more skill to get the best out of fine tuning to the prevailing conditions.

A modern competitive racer can have 20 or more bits of string for the crew to play with, while a trad cruiser can get away with just three or four!

Cruising boat rigs where performance to the nth fraction of a knot is not critical tend nowadays increasingly to come somewhere between the two, being anywhere between a basic set up where mast rake is about the only possible adjustment, through to some quite complex mast tuning arrangements. Most cruising boats fall somewhere between the two and rig complexity depends on whether the designer was thinking of a solid seaworthy 'go anywhere' cruising boat which can be safely handled short handed, or a hybrid which will give success 'round the cans' with a crew of gorillas, while providing a degree of comfort and safety for the owners annual holiday cruise, minus the gorillas. The two are by no means mutually exclusive, but the stripped down out and out racing machine, whether a quarter tonner or a toy for Tracey E to break another record in is a totally different beast altogether!

Its best likened to the range of difference available between the family car for mum and the kids to go shopping on saturday /forums/images/graemlins/crazy.gif and the latest 200mph+ Formula 3 monster on the racetrack /forums/images/graemlins/cool.gif

 

[alec]

Many thanks Old Harry for all your help and advice. Thanks to everyone else too.

Regards,

 

[alec]

>shifting the cast alluminium spreader clamp pieces from the end of the spreaders <

I had the same problem with this project. I found spreader ends very expensive to buy and difficult to obtain.

The spreader diameter and metal thickness have to match perfectly. This can be hard to do - as I found out.

My solution was to stand the spreader ends in diesel for a week. It worked.


Best of Luck,

 

[VicMallows]

Thanks Alec and OldHarry.

I'll try both heat and diesel as necessary. I guess if all fails I could go with a swageless terminal at one end and thread the new wire through the 'hole' in the spreader end rather than removing the split end from the spreader.

Vic