Unweighting the keel during repairs - SailNet Community
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post #1 of 16 Old 01-16-2014 Thread Starter
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Unweighting the keel during repairs

Our Albin Ballad is sitting on the hard for three or four years, undergoing an extensive top-to-bottom refit. Among the tasks are removal and retabbing of the major bulkheads, pulling up & re-bedding the cabin sole, and a bit of structural glassing near the mast step strut and the aft end of the keel/hull transition, where some sloppy repairs indicate a past grounding. (Here I ought to mention the Ballad has an integral fin keel, lead ballast in bottom 30".) All interior furniture is getting rebuilt, too.

Anyhoo, the boat sits on its keel with plenty wooden shoring and some tiedowns to resist Wyoming winds. As commonly happens, boat sitting on keel rather than keel hanging from boat creates a bit of a hump in the cabin sole & some minor distortion in the hull shape versus same boat in watery mode.

Should I take steps to unload the keel before fitting the replacement bulkheads and re-glassing the keel areas? If so, how best to simulate the hull's natural shape? Slings? Cradle? One of our tasks will be adding a couple floor stringers athwart the keel sump, & I'd hate to build distortion into the repair due to the upward thrust of the keel.

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post #2 of 16 Old 01-16-2014
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Re: Unweighting the keel during repairs

Had the same issue for my stringer rebuild a while back.. finally determined the only/best way for me to feel 'right' about it was to have the boat afloat.

If the boat is flexible enough to 'hog' over the keel then if the hull is wholly supported on stands the keel may 'sag' the middle portion. It's always tough to know that you've actually got the proper shape when sitting on the hard.

This does raise some caution flags if the water is especially cold and condensation might form to interfere with the bond.. so far it seems I've gotten away with it.

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post #3 of 16 Old 01-16-2014 Thread Starter
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Re: Unweighting the keel during repairs

Good points, Faster. Alas, the nearest likely body of water is 1000 miles from us. I could build a big tank & float the boat in the back yard. Girlfriend has been pining for a swimming pool....

There isn't any appreciable hogging, or distortion fore-and-aft, ala the 'Catalina Smile' in reverse. Rather, the cabin sole humps up slightly between the settees, side-to-side. The hull-to-keel transition is 1" of solid glass; I'm not worried about strength. But the bilge turn is seeing roughly a 7300# difference from tension (afloat) to compression (a-hard). I wonder if we could alleviate maybe 2000# of the hull's 3800# via jacks or slings or cradles, whether that would get rid of most of the hump?

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Re: Unweighting the keel during repairs

I guess I'd try jacking the hull up until the 'hump' in the cabin sole goes away and hope for the best??

My worry would be that you 'lock in' a false form with your repairs/structure, which would immediately be 'stressed' when the boat's lifted and launched - perhaps to point of cracking then and there.. could be an anxious moment.

Ron

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Re: Unweighting the keel during repairs

That's exactly my worry if we do the repairs with the keel pushing upwards. While it will be hard to reproduce floating form perfectly via slings or cradles, just approximating normal keel dangle has to be better than what we have now, when perhaps half the total boat weight is concentrated on the keel/hull transition zone.

Dunno if jacks between keel sump and deck underside would help any?

One possibility would be to weld up a gantry just aft of the companionway out of some 4" Sched40 and an I-beam across the top. I kinda want to pull the Penta MD6 out of this beast anyhow, and that would be a useful way to lift it in and out. Fat lifting sling and two chain hoists to the corners would unweight most of the keel; a second gantry at forward lifting points could do the whole boat. Would also make it easy to lift it onto a transport trailer when the time comes to move it; unloading that sucker with a 20,000# forklift was not a stress-free day.
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post #6 of 16 Old 01-16-2014
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Re: Unweighting the keel during repairs

If you were clever you could probably figure out the total weight of the boat in the water, and then raise the hull on land until the boat weighed the same which would in theory be at least pretty close to the force on the hull from the keel.
That makes sense in my mind, but likely not once I hit the Post Quick Reply button

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post #7 of 16 Old 01-16-2014
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Re: Unweighting the keel during repairs

Consider that when the boat was built, the keel was NOT pulling down on the hull. The hull was laid up, finished, and then the keel bolted on or dropped in. Or, the keep was attached at some point during the build, and the boat then sat on it.

So I'd suggest generous jackstands or cribbing, until you feel the whole alignment is "natural" and then expect that yes, it will change when the boat is floated. As it did when built.

It's an imperfect world.
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post #8 of 16 Old 01-17-2014
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Re: Unweighting the keel during repairs

bobmcgov

My suggestion is that you get in touch with Peter Jacobs. He has this blog:
........ Mostly About Boats
that covers a recent complete restoration of a Ballad in his driveway from an abandoned wreck in a field to an as new boat. He not only knows the Ballad very well but is a retired engineer. He previously had a Vega which he did a large amount of exceptional work on. I actually talked to him today in the marine store I work at. He is easygoing and approachable.
There is a link here to his email just below his picture: https://www.blogger.com/profile/06549321574020928322
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post #9 of 16 Old 01-17-2014
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Re: Unweighting the keel during repairs

Bob,

Did the distortion only happen after you pulled out the bulkheads? Any boat oughtta be engineered to sit happily on its keel without bending, but bulkheads and stringers (and settees and other cabinetry) may be a big part of giving the glass "skin" that strength.

If you're using the old bulkheads as templates, can you just adjust the jackstands till it's "right," i.e. the new bulkheads fit? Barring that, I think your theory about unloading some of the weight and seeing if the glass flexes back to natural is the way to go.

My only similar experience is, the trailer bunks put big creases in the (thin and floppy) aft quarter skin of my friend's Siren 17 this summer, after trying to haul her out with a load of water in the bilges (no we didn't know the water was there!). Bad enough to break the tabbing to the bunks that run aft under the cockpit and form the only internal bracing. After I patched the leak that let the water in and splashed her, the glass relaxed back to "true".
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post #10 of 16 Old 01-17-2014
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Re: Unweighting the keel during repairs

Quote:
Originally Posted by bobmcgov View Post
Our Albin Ballad is sitting on the hard for three or four years, undergoing an extensive top-to-bottom refit. Among the tasks are removal and retabbing of the major bulkheads, pulling up & re-bedding the cabin sole, and a bit of structural glassing near the mast step strut and the aft end of the keel/hull transition, where some sloppy repairs indicate a past grounding. (Here I ought to mention the Ballad has an integral fin keel, lead ballast in bottom 30".) All interior furniture is getting rebuilt, too.

Anyhoo, the boat sits on its keel with plenty wooden shoring and some tie downs to resist Wyoming winds. As commonly happens, boat sitting on keel rather than keel hanging from boat creates a bit of a hump in the cabin sole & some minor distortion in the hull shape versus same boat in watery mode.

Should I take steps to unload the keel before fitting the replacement bulkheads and re-glassing the keel areas? If so, how best to simulate the hull's natural shape? Slings? Cradle? One of our tasks will be adding a couple floor stringers athwart the keel sump, & I'd hate to build distortion into the repair due to the upward thrust of the keel.
I would assume the sagging took 3 or 4 years to get to where it is now. And it will have to be a slow process to undo. If the sag can determine and measured how far it is sagging by measuring the hump inside. Maybe a straight edge across the settees then measure down to the top of the hump. This will get you in the ball park as to how much you need to evenly lift the hull. I would lift the hull in small increments, like 1/4" at a time. You may need to add additional supports, like twice you have now, on the hull to lift so there is no damage or distorting of the hull with the lifting. 1/4" even lift and let it rest for a month or so, then lift it another 1/4" and let sit of a month. Do this until the measurement you took of the hump is gone. 1" hump will take you 4 months. Hot weather will also help, I would not try to lift the hull in cold weather. And hot weather will greatly help.

IMO it will take time to fix this, and by rights just as long as it took to disfigure. But it is hard to say it took 6 months with the boat incorrectly supported or 4 years to disfigure. And at what point was the boat unsupported correctly. Was the boat moved during the 4 years. Was is stored on the soft ground? Are your wind tie down too tight and pulling the hull down? Is the hull dis-formed where the supports are supporting? Are there humps at those locations.

Good luck, hope this helps!

Eric
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Last edited by Delta-T; 01-17-2014 at 09:49 AM.
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