Mast Pumping

[Dolce_Vita]

This season, I've noticed a tendency for my mast to "pump" in moderate winds while sitting at the dock.  I have observed the midpoint of the mast, at the spreaders, visibly oscilating in a fore-aft direction.  Vibrates the whole boat.

My shroud tensions were low, so I borrowed a Loos tension gauge and retensioned all the upper and lower shrouds: about 1000lbs on the uppers and 700-800 on the fore & aft lowers.  Still pumps. Haven't touched the fore & back stays.

I'm stumped where to proceed next at this point, but I'm sure the pumping can't be good for the rig.  Anybody else observed this behavior?  How did you fix it?

[Rusty Pelican]

I had it, the mast was pumping in the midsection.
My conclusion was that the mast was under too much compression. could be wrong about the cause.
I fix the problem and have never had the pumping since.
Start off by removing the boom
Loosen uppers, lowers and backstay
position the mast in the center of the mast partner. if you have the mast collar install it
secure the mast in the mast partner with pine wedges, I use about 8 on them
tighten both lowers on each side a little then switch sides. Tighten to Loos setting listed below
open hatch in main salon and eye up the mast track for any bends
Tighten uppers a little on one side then the other. Ditto on the settings
If you tighten one side too much, a bend at the top is visible
tighten backstay. should see a nice bend aft
I have a roller furlng on headstay that can not be adjusted
I you have an adjustable headstay back it off so that the mast has a bend aft
BTW I had a friend that had a P323 he tightened the backstay so much he could not open the cockpit lockers
Go for a sail, adjust, then pin the turnbuckles
I yank my mast every season, and it never pumps even high winds

The Loos I have is the one that you attach to shrouds then pull a string loop to read the numbers. The cheapest model.
If you have my Loos. try 38.5 to 39 on lowers and I think 42 to 45 on uppers and backstay.
These numbers worked for me

Good Luck
BobG

[AnaMeg]

Dolce Vita, did you solve the pumping problem? I have the same phenomena, pumps only at the dock at about 12+ knots of wind. Frequency of pumping is about 6/sec. Shakes the boat a bit and keeps me awake. I don't have a loos or any other way of assessing rig tension and haven't tried anything to alleviate the problem. If you have a solution I'll try it next season.

Geoff

[Dolce_Vita]

Geoff,

  I didn't solve it for the 2012 season, and the mast is now off of the boat for painting, a new step, and a complete rebuild with new rigging.

  My research suggested that improper rake and/or improper bend would cause pumping when the rig tension was increased.  This seems consistent with my experience, as I believe I first noticed this after the first time I tuned the rig.  Prior to that, it was so loose that the shrouds on the downwind side would go totally limp to the point that the spreader would flop around fore and aft.

[AnaMeg]

That's interesting. My rig was new 4 years ago and the yard installed and tuned at the time. I've done nothing with it since. When close on the wind the leeward shrouds remain taught. The shrouds twang as Brian Toss says they should. My mast has a lot of rake... I think. Anyway when I look down the line of masts at the dock mine is more "leaning" than most in the line. The helm is near neutral until close hauled with 15+ knots. Based on this thread and your experience I'm guessing my rigging is too tight.

I've never tuned my rig. I'm a casual sailor; fun tweaking the sail trim but a bit too lazy to sail/stop/adjust repeatedly. I don't have a loos gauge. Perhaps should get one. Or perhaps get a sailor who's really into this to come along and help me.

Next spring when she is in the water I'll try adjusting the tension. Let me know if you find the magic result. Then I can follow your advice and retain my lazy attitude.

Geoff

[admin]

Interesting rigging suggestions from Bill Shaw on this topic - recovered from internet archives of "The Pearson Current" in 1994 (I could not recover the drawing that was referenced):

QUESTION:
I am the owner of a Sublime Pearson 323 (#54). A question I have related to mast pumping. Since we have put on jib roller furling, I have noticed that at times, when no sail is set, the mast has a tendency to pump. I have played with rig tension in order to minimize the pumping.

ANSWER:
As for the mast pump, adding a roller furler will often do this. The big furled sail starts to oscillate and then the mast starts pumping. Try putting a line around the mast at the spreaders. Tie off the lower end way forward, near the stem head fitting with lots of tension. If this works, you can add a small block at the height I’ve drawn here, sort of like a boom topping lift. Sometimes, a line around the furled jib led aft will work.

[Rusty Pelican]

View my previous post on this subject.

One cause is that the forestay & backstay are too tight and the lowers are too loose.
Get a Loos gauge and trim the standing rigging accordingly

BobG

[Captain Bri]

View my previous post on this subject.

One cause is that the forestay & backstay are too tight and the lowers are too loose.
Get a Loos gauge and trim the standing rigging accordingly

BobG

Thanks Bob, great tuning guide!  I really only updated this thread because I found Bill Shaws advice in the internet archives - I think that Bill's advise is only necessary when all else fails with regards to rig tuning. 

I think the P323 naturally has a little lee-helm, hence your advice to rake the mast makes a lot of sense (after setting uppers and lowers).  I also like the rig settings information and would like to publish your guide on the website.

[Rusty Pelican]

Sure