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Forums / Technical / Mast pumping  
The discussions for this thread include the following:

Posted: 06 Feb 2009 at 9:55pm
Dear Dedicated Dolphinites,
A friend helped me tune my rigging and all seems well when sailing, however on bare poles when the wind is blowing the mast starts pumping a bit causing a mild thumping sound you can feel and hear down below. Anyone else experience this problem? My friend says it is normal on some boats. Any suggestions?
Capt. Thumper
Hull #85

Posted: 07 Feb 2009 at 8:38am
Hi Greg
I have had fore/aft mast pumping happen on my boat, O'day # 12 in strong breezes. We have only one set of lower shrouds and they are in line with the uppers. Setting up mast prebend on a telephone type mast like mine is problematic.

On Yankee Dolphins there are 2 sets of lowers set fore and aft of the mast centerline, and presumably a lighter mast section, so setting up some prebend is a lot easier and should help. This will also flatten out the mid section of the main a bit, usually a good thing for sail performance especially if you have an 'older" main. Probably about 2" prebend. If you have been thinking about a new main you can get your sailmaker (hopefully one experienced with Dolphins) to look at your rig and get some professional advice on mast tuning.

For boats rigged like mine a baby stay could be set up that should stop the pumping and that is what I am considering. The plan would be to reinforce the topping lift block and fastenings and use one of the high strength synthetics as a halyard. In heavy breeze conditions this halyard would serve as a baby stay by being snap shackled to an eye fitting on the deck.

However, that means a setting up a removable wire support below the deck fitting which would be just forward of the leading edge of the house. It would dead ended in a strong fiberglass tabbed base at the V in the hull - unclipped when not in use so it would not 'invade' the V-berth space.

Marionette, #12

Posted: 23 Feb 2009 at 10:00am
As an after thought - regarding the 'baby stay' approach discussion, I should have mentioned that there may be a simple way to set this up without the hassle of setting up a support back up stay below deck for the deck fitting. It would still require, I think, beefing up the topping lift block and its fastening, and going to a low stretch halyard.

Run the low stretch topping lift halyard to a shackle made fast to the forestay fitting. This would be a bit of a hassle when sailing to tack around but not an issue if at anchor or motoring under bare poles. This might still be a reasonable solution for boats with double lowers that, for whatever reason, cannot fix the pumping problem with prebend tuning.

Ron (Marionette # 12)

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