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Old 11-04-2016, 21:39   #1
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Four And After Play In Spreaders N Pumping Mast

I have a 1978 Cal 39.
at the dock with sails down, i am getting fore and aft mast pumping. i dont get it at anchor, so I think it's only when the wind from the beam(90 degrees fron bow. )
i went up the mast and noticed the spreaders have play when moved fore and aft. maybe about !/4 inch.

i tuned rig to:
uppers 15% break
lowers 9%
backstay 15%
forestay is roller furling so im not sure how to test.

my questions are
should spreaders have any play and what is an acceptable play if any?
why is mast pumping and any ideas on how to keep the mast from pumping.

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Old 12-04-2016, 03:19   #2
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Re: Four And After Play In Spreaders N Pumping Mast

See ➥ Mast Pumping - Is This Normal?

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Old 12-04-2016, 04:23   #3
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Re: Four And After Play In Spreaders N Pumping Mast

GordMay's linked post covers a lot of it. But there are some other things which you can try too.

But regarding your question, if your spreaders are attached to the mast via a single, vertical bolt, though them, then yes, a small bit of play is normal. And in spreaders which are more firmly affixed to the mast, to a small degree, they flex & bend, as the mast tune changes. And or when the boat passes through each wave, etc.

They pretty much have to have some range of motion, regardless of their design, or material, as both the rest of the rig, as well as the boat flexes, when any outside force acts upon it, or the rig is tuned. Such as when a racer cranks on 18" of bend in a mast that's the same length as yours, via a hydraulic backstay. In order to de-power the main.

As to some simple things to try:
- Add some tension to your lowers, so that their tension is on par with the uppers. As 15% in any stay isn't a high load.
- Add another 5% to your backstay too, if you like.
- Lead your topping lift forward to a strong foredeck fitting, a good bit aft of the stem, & crank on a few hundred pounds of tension.
- Make sure that your furling line is strong, and, well cleated off. And then crank some tension onto you jib sheets when docked.

Or if you don't have a headsail up, have a sailmaker make you a very strong, flag sized "sail" (normally used to stop racer's headstay foils from fluttering/sailing - tell them this part, & about your problem, when they're taking the order to make it).
Then run it up the headstay, with a halyard, a stout downhaul, & a "sheet" attached to it. And tension things as you would on a furling headsail as delineated above.

Also, I don't know if you have a baby stay or not. But most of them are detachable at the deck level. So if you have one, & yours is, then lead it forward, & tension it a bit.

There are other, more complex "fixes", but really, it's a non-problem. As every mast has it's own particular harmonic frequency. And when the wind manages to hit it right, then it gets the rig moving, due to this.
But it's not a danger to your rig, assuming that you have all of your cotter & ring pins properly in place.
Worst case, it might throw your rig a tiny bit out of tune from where it currently is. But even that's unlikely.

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Old 17-04-2016, 11:40   #4
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Re: Four And After Play In Spreaders N Pumping Mast

my spreader has a two bolt mount. and when i move it fore and aft there is quite a bit of play. im suspecting elongated mount holes. i have a good video of the spreader
moving fore and aft. is there anyway to paste it to forum?
also can spreader be repaired and if so where should i send it?
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Old 17-04-2016, 12:13   #5
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Re: Four And After Play In Spreaders N Pumping Mast

Our spreaders are somewhat free to move fore and aft (our spreaders are the straight style, not swept).

The mast is pumping when the extrusion is ("too") fine (and/or) lowers are not spread enough, not many enough, not tight enough or (back to square A1) the panels between the spreaders are too long.

I have seen plenty of racing masts pumping on IOR mostly boats. How we stopped this was most of the time by hoisting a loop round the mast with a free halyard all the way to mid mast and then making a temp soft line extra 'stay' - most often run to the bow. This nearly always stopped the dance.

Jib foils pump too at times and my fellow racers hoist an empty foil tape to stop this. This works as a flow spoiler. I think this may work too on the mast but I have never tried. Should not be difficult to make such a tape on a home sewing machine of any sort. Pink dacron is said to be best.

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Old 09-07-2017, 15:00   #6
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Re: Four And After Play In Spreaders N Pumping Mast

This Response might be a bit dated, but you might still be interested.....

From the Cal 39 owners manual:

Upper shroud tension- 1500-1600 lbs.
Forward lower tension- 400 lbs.
Aft lower tension- 100 lbs.
Back stay maximum tension- 4000 lbs.

" The figures are meant as a guide line only, and the mast should be tuned to remain reasonably straight under sail, both athwart ship and fore and aft."

Never experienced any mast pumping on our 39 with std. rig, but there is a bit of play in the spreaders.


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