spreader ends replacement, how tight and which material?

[alexlago]

The ends of my mast spreaders are badly damaged and I've asked a lathe to turn new ones...

The guy offered to do that in aluminium, I wonder about electrolysis between the steel cable and the alloy spreader end, wouldn't it be better to turn them in a material like acetal/delrin, or it doesn't matter?

The spreader ends are closed by a small plate, should this plate press firmly/tigthly on the shrouds or is it there just to prevent the cables to pop out of the spreader and I can thus allow some play there?

 

[john_morris_uk]

Yes the plate should grip the wire shroud.

Put some Duralac (Zinc Chromate paste) on the junction to stop the electrolysis and corrosion problem. Wipe the excess off of it will get on your sails.

The spreader should be tilted up slightly to bisect the angle that the shroud makes as it passes through the end (but I expect you knew that.). There’s a trick to finding the correct position of the spreader on the wire if you’re interested.

All IMHO of course.

 

[Spirit (of Glenans)]

There’s a trick to finding the correct position of the spreader on the wire if you’re interested.

All IMHO of course.

Do tell!

 

[john_morris_uk]

Do tell!

Stretch shroud from top of mast down to the base of the spreader and mark the wire (felt tip or tape?) bring wire away from the mast to tip of spreader and fix at the marked position.

It’s what a profession rigger taught me and it’s simple and works beautifully.

 

[alexlago]

There’s a trick to finding the correct position of the spreader on the wire if you’re interested.

yes, I am ! (interested...)

thanks for your answer

 

[Poignard]

Stretch shroud from top of mast down to the base of the spreader and mark the wire (felt tip or tape?) bring wire away from the mast to tip of spreader and fix at the marked position. That is what I have always done
It’s what a profession rigger taught me and it’s simple and works beautifully.

Thereby forming an isosceles triangle, the spreader being the base of that triangle. That is what I have always done.

 

[johnalison]

Thereby forming an isosceles triangle, the spreader being the base of that triangle. That is what I have always done.

It looks like a useful method, but is only an approximation since it won't exactly divide the angle in all rigs, though I don't suppose the difference matters.

 

[Poignard]

It looks like a useful method, but is only an approximation since it won't exactly divide the angle in all rigs, though I don't suppose the difference matters.

I'm sure you're right. But with the setup I have, the spreader is aligned with the socket on the mast so there is no strain.

 

[john_morris_uk]

It looks like a useful method, but is only an approximation since it won't exactly divide the angle in all rigs, though I don't suppose the difference matters.

I’d noticed that too, but I believe that for the angles involved in most set ups it’s so close to the ‘perfect’ position as not be worth bothering about.

 

[William_H]

Of course in a small boat it is not so critical compared to a bigger boat. (ie 24ft +)
Much depends on just how stiff the spreaders are in the up and down at the tip direction. If they are floppy then yes you need to clamp them onto the wire at the correct position. Although as said this is not so critical. If on the other hand if the spreaders are quite robust (tiff) then allow the wire to slide when tensioning. Mine are aft swept spreaders and quite robust so the wire is allowed to slide. I have not seen any concern re different metals ss on ali spreaders. Just keep an eye on it.
Or perhaps some tape or similar around the wire at the contact point. ol'will

 

[PeteCooper]

The spreader should be tilted up slightly to bisect the angle that the shroud makes as it passes through the end.

I have seen this quoted many times but it doesn't match what I see as I wander round the marina. The vast majority of boats, and I have looked at a lot, have the spreader set in a bracket so that it is perpendicular to the mast - and to try to set the spreader to any other angle would not be possible.

The original premise may or may not be true but it doesn't match what I see on many boats.

 

[john_morris_uk]

I have seen this quoted many times but it doesn't match what I see as I wander round the marina. The vast majority of boats, and I have looked at a lot, have the spreader set in a bracket so that it is perpendicular to the mast - and to try to set the spreader to any other angle would not be possible.

The original premise may or may not be true but it doesn't match what I see on many boats.

I think you’re either not looking straight or you’re looking at different boats in different marinas to me. Most boats I see have the spreaders up slightly in an attempt to bisect the angle. Older traditional boats (possibly with lower rig tensions?) often had horizontal spreaders but there are good geometric reasons why spreaders should bisect the angle (and good reasons for the spreader to be fixed to the shroud too).

If you are looking at a modern boat with horizontal spreaders then I suspect it’s been rigged incorrectly.

 

[reeac]

The effect of equal angles at the spreader tips must be to put the spreader in pure compression ie. no bending component which must be the ideal situation.

 

[john_morris_uk]

The effect of equal angles at the spreader tips must be to put the spreader in pure compression ie. no bending component which must be the ideal situation.

Exactly so; and it's what you are aiming to achieve.

Masthead rigs with in line spreaders are easier to understand, but even with swept back spreaders inducing pre-bend, and with lowers controlling the bend in there mast, for the spreader its only compression forces that are desirable.