Spreaders angle question......

[dukes4monny]

Hi all, I have read a few articles regarding the angle of mast spreaders in relation to the shrouds. The articles all say that it is important that the spreaders should bisect the shrouds.
On my Jag27 (masthead rig) the spreaders are horizontal and definitely do not bisect the shrouds.......and (from memory) the other JAG27's that I've seen have a similar setup (horizontal spreaders).

Any thoughts / advice?

 

[Swagman]

Don't worry about it.
Our Sparcraft rig is relatively new (well four years anyway) but certainly high tech with 3 sets of spreaders on a 9/10th fractional rig. The spreaders were set up horizontally and it has not fallen down covering 25,000 miles so far.
JOHN

 

[lw395]

If the spreaders do not bisect the shroud angle, there is a net upward or downward force on them, so they need to be strong enough to resist this, and it makes sense to clamp the wire in the spreader tip to prevent the spreader sliding down. It's not a problem if the spreaders are strong enough, but it also puts leverage on the spreader bracket etc. If the rig is standard, and there is no history of failure, it's probably OK!

 

[oldharry]

[ QUOTE ]
Don't worry about it.
Our Sparcraft rig is relatively new (well four years anyway) but certainly high tech with 3 sets of spreaders on a 9/10th fractional rig. The spreaders were set up horizontally and it has not fallen down covering 25,000 miles so far.
JOHN

[/ QUOTE ]
Very different setup to a Jag 27 which is a straightforward masthead rig. Here the spreaders should bisect the shroud angle. If not they become a source of weakness in the rig because they are not under correct compression loading, and may fail. The huge number of rigs one see around with spreaders horizontal or even drooping suggests the incidence of failure is small. But equally the likelihood of failure is going to be at the worst possible moment when things - including yourself - are going to be stressed way beyond normal sailing useage. Leave it and take a chance, or get it right - up to you.

 

[sailorman]

i was told by a rigger to take a line from the mast hd down to the spreader root & mark the lenght, swing the line out to the spreader tip clamp tip in this position.
it gives a very pleasing angle

 

[dukes4monny]

Thanks for all of the replies........a mix of opinions, but I'm erring on the side of altering the spreader angles.
I assume that I will need to get new mounts to rivet to the mast?
I haven't had the mast down yet, so I don't know what fitting method is used at the outer ends of the spreaders, but aren't the shrouds normally free running through them?
Sailorman, you mention actually clamping the tip in this position, is there a special type of clamp for this purpose, or am I looking to change the whole spreader setup?

Thanks again for your help. /forums/images/graemlins/smirk.gif

 

[sailorman]

if its a kemp or selden then there is a lot of play in the mast root fitting
my mast is kemp & no probs

 

[Salty John]

No, the shrouds need to be secured to the spreader tips - there is usually some means of seizing the shroud, two holes through which you run seizing wire, or there may be a clamp of some sort.
On boats with very tall masts, triple spreaders and a narrow shroud base the problem of having the spreader tips bisect the shroud angle is less significant because the shroud angles are much less than they are with a single spreader, short mast, wide shroud base arrangement.
Apart from terminal failure, drooping spreaders leading to spreaders collapsing is the biggest contributor to rig failure.

 

[alec]

Would echo what fellow posters have said about bisecting the angle.

Cable clamps work fine. I have seen distorted shroud root brackets, proving that level and drooping were not aligned correctly. Perhaps older boats can take it better with oversize masts, spars etc but best to get it right.

 

[Bajansailor]

We have a Kemp mast with single spreaders and I have just replaced the cap shrouds.
There is room for a fair bit of 'play' in the socket on the mast where the spreader goes into, ie the spreader tip can move up or down a significant amount.
There are cast aluminium fittings in the end of the spreaders - these have a nut and bolt which when tightened clamp the end fitting to the wire.
I adjusted mine sitting in a bosun's chair, by trial and error using a bevel gauge to ensure that the angle was reasonably well bisected.

 

[sailorman]

use a halliad & do wot i said its very easy so much so i even managed it /forums/images/graemlins/ooo.gif

 

[dukes4monny]

Thanks all, the mast comes down (intentionally) in about three weeks time....watch this space /forums/images/graemlins/cool.gif

 

[VicS]

[ QUOTE ]
it gives a very pleasing angle

[/ QUOTE ] And there was me thinking the "bisect the angle" idea was all based on scientific logic. Purely a question of aesthetics then?

 

[sailorman]

ot at all this method doesn't bisect just a little less than a true bisection
with a double spreader rig each set of spreaders will be a slightly angle & easy to obtain with a halliard as a marker

 

[VicS]

If the width of the spreaders equals the base of the shroud plates, making the lower section of the shrouds vertical, then setting the position of the spreader ends as you suggest will in fact make them bisect the angle the shroud makes over the end.

Interestingly though the often recommended Selden Hints and Advice book says.
"the final vertical spreader angle must always be 6°". The accompanying diagram does show that as 6° from the horizontal. That's rather lower than bisecting the angle on most normal aspect rigs I think. (Trig's a bit rusty though)

 

[alahol2]

Every boat I've had (4) from 20ft to 32ft has had horizontal spreaders with no option to 'tilt' them up. Thousands of boats are sailing around with horizontal spreaders. Should somebody tell the designers/builders/mastmakers about this?

 

[William_H]

If you look at the geometry of the question then the spreader should bisect the angle of the shrouds. However horizontal will give an error of perhaps 3 degrees. This error does not generate a lot of out of column pressure on the spreader or force driving the spreader tip down further out of lie.
A spreader base needs to be robust if only to ensure a long life so they usually have plenty of stiffness strength in the up and down direction.
Likewise the question of attachment of the wire to the spreader tip.
You can attach it but would need to move the clamp everytime you tightened up the shroud. In my experience they need a lot of tightening after the first sail stretches the wire. If you didn't move the clamp you would pull the spreader tip down. back to where you started. So I would leave the wire running in the tip spreader. Acknowledging that it may leave the spreader with out of column forces. olewill

 

[sailorman]

You do what you want I am only STATING WHAT A RIGGER TOLD ME /forums/images/graemlins/tongue.gif & thats hoe mine are set-up /forums/images/graemlins/ooo.gif

 

[DJE]

If the clamp to the shroud at the spreader tip is adequate then this will induce a slight difference in tension in the wire as it passes over the spreader. This difference in tension will result in a vertical shear force at the spreader tip counteracting the downward force due to the mismatched angles. Horizontal spreaders are only a problem if there is inadequate clamping to the wire. Having said that mine are set up to bisect the angle (by matching the distance from the masthead to the root and tip of the spreader) and the clamp acts as back up, and to support the weight of anybody climbing the mast.

 

[oldharry]

[ QUOTE ]
Every boat I've had (4) from 20ft to 32ft has had horizontal spreaders with no option to 'tilt' them up. Thousands of boats are sailing around with horizontal spreaders. Should somebody tell the designers/builders/mastmakers about this?

[/ QUOTE ]

My 24 ft Trident the designer (Alan Hill) specifies spreaders should be up 6 degrees from horizontal. When the mast comes off I shall have a chance to try Sailormans suggestion to see what angle that gives. But it certainly sounds like a move in the right direction, and a whole lot easier than trying to measure 6 degrees.

The function of the spreader in supporting the mast means that if the load is not columnar, then they will be more likely to fail, as they will be wrongly stressed. The fact that many rigs are incorrectly set up does not make it right, and will account for some dismastings.