We have a 36MKII. The mast starts to pump and vibrate strongly at times while the vessel is swinging at anchor or berthed in a marina, in approx winds above 12 knots. It makes the whole vessel shake. We are 3rd owners and just acquired the vessel. We suspect the rig may have been over tightened. Is there any tuning of the rig which may alliminate this problem, or do we need to install an inner forstay, and would this rectify the problem.
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David Johnstone
Hey David, please edit your signature to at least indicate your boat year, rig type, and keel type.
Other owners may observe something different, but with Whimsea we've been up to 30 knots of wind on a mooring and not a peep. One possibility is that you have a "reverse bend" in the mast, i.e., the middle part of the mast is aft relative to the top and base. Head-stay tensioning after the back-stay has been set could cause this, usually in conjunction with the aft lowers being tighter than than the forward lowers. Sailing a boat with a reverse-bend in the mast is not safe.
If you observe a reverse bend, you might try re-tuning from scratch. There are other things that could cause rig shaking and they should all be checked by a rigger. Loose mast partner, step, spreaders, tangs, etc.
Nick Caballero
Retired C36/375IA Mk II Technical Editor
Thanks for your email. We have had a rigger inspect the rigging, and the mast appears not to have a reverse bend, however we will get a rigger to set the rig back to original specs and take it from there. Thank you for your input. Our vessel is a 2006 model, wing keel, furling head sail, 3 blade prop.
David Johnstone
Doing a bit more research I've found this: http://www.c34.org/faq-pages/faq-mast-pumping.html. Also: http://www.boatbanter.com/showthread.php?t=20764. From what I can tell, a smooth column promotes the formation of vortexes and a lack of rigidity allows the vortexes to flex the column. Although more prevalent in other boats, the phenomena of vortex shedding does not appear to be very common in Catalina 36's. If the rig is fine insofar as nothing is loose or broken, then there are two common solutions that have worked in other boats:
Take your spare jib halyard and wrap it in a spiral pattern down the mast. The spiral wrap on a car radio antenna is there for the same reason. All you're trying to do here is upset the vortex generating conditions. It might even require using the halyard to hoist a larger diameter rope for additional disruption. Guaranteed to work if vortex shedding is indeed your problem. You might want to try this first just to verify this is what's happening before trying the next step.
Make sure there is at least some static prebend in your mast. Less likley to work then the spiral wrap. This prebend must be so that the middle of the mast is curved slightly forward relative to the top and base. Correct static prebend is introduced by having the forward lowers tighter than the aft lowers along with proper backstay tension. Note that in a furling mast, bend should be conservative due to the internal construction of the mast and the need to have smooth furling. The idea of correct static mast prebend (aside from the mainsail shape and overall rig safety) is that it adds rigidity to the mast.
Nick Caballero
Retired C36/375IA Mk II Technical Editor
I had the mast pumping Hum problem years ago with my Catalina 30. It only happened at the dock and could be heard only inside the cabin. Outside on deck or on the dock it could not be heard. Someone told me about wrapping the halyard around the mast. I never heard it after that. I don't know if that eliminated the hum or was it just the direction of the wind, but like I said I never heard it after I started wrapping the mast. I never had the problem with the C36.
__/)__/)__/)__Capt Mike__/)__/)__/)__
Punta Gorda Florida
1990 Std WK M35 Hull #1050
I have often wondered whether my boat's rigging is too tight, because the last time it was tuned about 8 years ago the guy used a Loos gauge on it, and he told me later that it was very tight. A Catalina 36 rig is supposed to be loose - so I have heard - but mine is probably 'tighter than a $3 watch' as the saying goes.
I'm sorry I don't have an answer to this problem; in fact I HAVE this problem on my #2109, and I'd sure like to eliminate it. I'll be following this thread carefully. I ask all to keep posting results of their findings.
Larry Brandt
S/V High Flight #2109
Pacific Northwest, PDX-based
2002 C-36 mkII SR/FK M35B
I encountered mast pumping with my C30. Tightening up on the shrouds a bit eliminated it. We've had our C36 for a couple years and have not experienced it. But, a taught spare halyard sometimes hums as well as the turnbuckle brass jackets sometimes vibrate a little in the right wind conditions when at the mooring. The sounds can only be heard inside the cabin.
Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B
We occasionally experience mast pumping at what I though was always at the dock or at anchor until on Monday when for the first time it happened under sail, - upwind,, full main and jib unrolled to about 110% in 15- 20 kts. Rig was tuned beginning of last season. At anchor it only lasts until the boat changes orientation to the wind, it can be irritating when trying to sleep though
Gary Smith
93 MK I, Hull #1231
Std rig; wing keel
M35A Oberdorfer conversion
Semantics check here. Let's say pumping is the middle of the mast visually moving forward and aft. Using this definition, some minor pumping happens when sailing and this is normal. Most pronounced when going upwind, variable moderate breeze, choppy conditions. No amount of rig tension is going to eliminate all pumping when you're talking about the variable forces generated by sails, seas, heeling, etc.
Is the stationary boat issue being described actually pumping, or more accurately a "flutter" or "shake" and more felt or heard then actually observed?
Nick Caballero
Retired C36/375IA Mk II Technical Editor
Our problem is pumping for and aft, shaking the whole vessel, inside and outside and easily observed. Impossible to sleep. We thank you all for your help and will look into it once we return home, as at present on our shake down cruise.
David and Gloria Johnstone
Gloria 2006 Catalina 36 Hull #2291
Wing keel
Home waters: Queensland Australia
David Johnstone
Nick
Shaking accurately describes what we experience both when stationary and recently underway. More felt and heard then seen. Will try the halyard wrap next time it starts up.
Gary Smith
93 MK I, Hull #1231
Std rig; wing keel
M35A Oberdorfer conversion
My boat does it sometimes. I will check the rig tension with loos gauge. Does anyone have the numbers for a mk1 tall rig? I will let you know if it helps. The loos gauge is in the tool loaner program.
Catalina 36 MK1
1984 Hull #306
OK. This is going to hurt my head to think this way but here goes a basic description of whats happening based on a 1976 mechanical engineering degree. The mast is a spring standing on end. Every spring or spring system (include the stays and it becomes a system) has resonate frequencies. Resonate frequencies are frequencies that represent maximum vibration. They are dependent on the spring rate of the system and input frequency (wind blowing on and around the mast). You change the spring rate when you tighten or loosen the stays. There are lots of variables but the only ones that can be intentionally changed is stay and shroud tension. Tune the rig for optimum sailing.
Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B
Tune the rig for optimum 1st sailing and then if it vibrates, either loosen a bit or tighten. Trial and error should be able to minimize the resonate frequencies for your typical wind conditions.
Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B
Just winterized my 2004 with roller main. Put on the cover, which does not provide cut-out for the intermediate stays, so these had to be slackened and looped above the cover. In doing so, notice that in a wind I now get the rig pump. Something I can hear and see. Since the middle of the mast is now unsupported and the long wires are still tight, this allows the middle of the mast to move. This is not a vibration, but a pump that is proportional to the wind. The amount of movement is inches and seems to be the classic symptoms of vortex shedding. So, either the total lack of intermediate tension or the lack of prebend seems to be culprit - both were removed when I slacked the intermediates.
Just received this update from the original poster, David Johnstone: "We have virtually eliminated the mast pumping problem. A rigger inspected the rig and slackened off the aft lowers on both sides, which gave the mast a slight bend. We occasionally feel a slight movement of the rig when at anchor, but nothing like the way it was. His opinion is that the rig has not been set up correctly from new, and that the mast actually comes out of the partners leaning slightly forward. We will pull the mast out next year, renew the rig, and set it up correctly"
Nick Caballero
Retired C36/375IA Mk II Technical Editor