Centerboard Thunk!

[Robert T. Pierce]

Need some help here. I have a 2002 X that I just put in the water for the first time.

When the centerboard is lowered I hear a thunking sound at the fore end of the trunk in the general area of where the bolt comes thru the hull under the forward galley seat. Seems like it is more pronounced on the port side of the trunk.

I can raise and lower the board without any problem. There are no leaks or cracks anywhere and when the board is in the up position there is no thunking noise at all.

I noticed this at the slip where we get a little power boat wake that come from side to side. Something is wrong in Little China. Anyone have this problem before or suggestions on what it may be?

Thanks

[Don T]

Hello:
Common problem with swing keels. All Macs come with that noise as standard equipment. They don't want to manufacture the system too tight or it will bind up after it gets some growth on it. I decided to go ahead and install nylon shims and cushions to quiet the board but my boat is trailered so it doesn't spend time sitting in a slip. Go to the mods section of this site and look up the "quiet centerboard" post.

http://macgregorsailors.com/cgi-bin/mod ... record=390

[craiglaforce]

I think, I thank, I thunk.
Too much thinking leads to future thunks. (as a past reference).

They all thunk, but you will not think tho don't thorry.

thorry, I mean sorry, I'm just delerious about becoming first officer.

[Robert T. Pierce]

I hope you guys are right. This is pretty loud and you can feel the thunk in the cabin and hear it in the cockpit. The boat slipped next to mine is an X and I rocked it a bit to see if I could get the same response. I didn't. Do you still think this is normal? I am used to a fixed keel boat and this really bothers me. Don't know if the previous owner busted something like the pivot pin or I am just being paranoid. I don't know how anyone could possibly sleep with this kind of noise.

[craiglaforce]

In the slip I leave the board most of the way up so it will not clunk and wear unnecessarily.

At anchor is the problem. The board pretty much has to be down to keep the rolling motion under control, (unless the water is calm).

I bought a couple of rocker stopper and hang them from the stern cleats with a 3 lb weight on each one to help reduce roll and clunking. It helps a bit but still not perfect.

The clunking is pretty loud down below unless you are in calm water.
The other thing to try is setting an anchor sail. I will try setting an old jib tied to a stern cleat and hoisted with the jib halyard and sheeted off to one side. That should stablize things a lot.

[Sloop John B]

Clunk, da clunk, clunk.

Let's you know you're still alive at night sleeping aboard your Mac. If it bothers you, pull the centerboard up real tight and wait until you broad side that fancy yacht moored next to you.

Baloom!

[Mark Prouty]

At anchor is the problem. The board pretty much has to be down to keep the rolling motion under control, (unless the water is calm).

Is it better to anchor with the centerboard down if not in calm waters?

[craiglaforce]

Well, if you put it down it cuts down on the rolling, but then it clunks.
If you pull it up in rough conditions the rolling is intolerable.

Lots of different approaches have been tried all with varying degrees of success.

Bridle from bow to stern cleat to hold boat at an angle.

Anchor from bow eye - really helps boat motion a lot, but the eye might break from shearing sideways pull. So most of us have stopped doing this. At least one bow eye broke as reported a while back (boat was kept on a mooring so it got a lot more of a workout than a fw overnights. .

anchor sail - maybe the best approach.

Rocker stoppers - helps considerably, but not a cure-all.

ANchor with bow and stern anchors mainly to stop the sailing back and forth business- I never tried this for real, although I have simply tossed a stern anchor out to no advantage.

By far the best approach is to find a still calm anchorage.

[Duane Dunn, Allegro]

Unfortunately the clunk is a part of any swing centerboard. Some have found that the pivot hole gets elongated and the clunk gets worse. If this is the case you may want to fill the area with solid epoxy and re drill.

I'm going to try to cure my clunk this week by dropping the board and putting a vee shaped foam block in the upper trunk half way back so when the board is full up it is locked in place. I tried shims last year but this did not cure it.

Other than a solution like that think of it as a feature. It is constant reminder all night that you are still floating and have not gone aground when the tide goes out.

[Chip Hindes]

I have a new anchor riding sail that I haven't tried yet.

In the past, something that has worked for me: Run a loop of line around the centerboard and pull it tightly to one side. You can use the winch, but the line must be fairled (is that a real word?) from well forward or the board will just fold and shed the line. The forward stanchion works.

Warning in advance, it is nearly impossible to do this without actually getting into the water. Although, you might be able to do it from a dinghy.

Another: if you have a buddy or two and the wave action isn't too bad, raft up on a single anchor. This virtually eliminates both rocking and sailing. Lots of fenders and adequate ground tackle are a must, of course.

[dclark]

You don't have a problem until it stops clunking.

[Jesse Days Pacific Star 2]

I am in agreement with all. They all clunk. If we're at a marina that has a lot of wake action and it's clunking, I just raise it and remember to lower it when we leave.

Jesse

[Robert T. Pierce]

You folks make me feel much better. This is my first season with the boat and as I said it hasn't been in the water long. The first few times sailing or at the dock the water was very calm and I didn't recall hearing anything. Yesterday there was a lot of small wake and I couldn't believe what I was hearing. You guys term it as clunking but I thought it was a little more violent so I termed it a thunk as I could feel the board moving in the well. As long as you guys "feel the thunk" too then I am not going to bother hauling the boat out of the water. Was all set to go out yesterday but ended up pulling the board to the up position and ran home to ask you guys. I am very grateful for this site. So one last time...based on what I have described, does clunk and thunk appear to be one in the same in your experience? Thanks!

[Frank C]

. . . and when the board is in the up position there is no thunking noise at all.

The extended board must make noise at anchor or in a slip. The loose fit is a cheaper way to design it, and it helps insure that the extended board will wedge-lock itself under sail, to prevent it from just folding back into the trunk under hydro-pressure.

Unlike others, except when sailing or for very slow docking maneuvers, I always keep the board up. This eliminates the noise when stationary, and of course you shouldn't use the board when motoring anyway.

When anchored, I hang a triple rocker stopper and heavy pendulum from each hip-rail to help control rolling (keeping these as short as possible to prevent fouling the anchor rode). I plan to try an anchor sail this season.

[dclark]

I keep mine in a slip, pay to have it cleaned, and hope not too much starts growing up there. I find the sound of a loose and free mving centerboard quite refreshing.