Wooden gantry crane to lift hull from keel

[mait]

I wonder if anyone has built a wooden gantry crane to lift the hull from the keel. My new boat is 36ft and near 6 tons. 2.5tons of this is lead keel, the hull itself is approx 3.5 tons. I would use 4 chain hoists in each corner as close to vertical posts as possible.
If anyone has done something similar please share your experience

[RaymondR]

No reason it would not work well and probably no more work than building a cradle.

[RogerC]

Might be easier to excavate under the keel while it's in a cradle.

[mait]

Originally Posted by RogerC

Might be easier to excavate under the keel while it's in a cradle.

Good idea! Maybe even dont need to excavate. I have trailer with three removable crossbeams under the keel. I can fit 2 big hydraulic car jacks between the crossbeams, remove the crossbeams and drop the keel.
Any arguments against this?

[tkeithlu]

Yeah. Instability. You'll be lifting the trailer frame about a meter. Either you start on a solid surface (concrete) and crib it very well on all four corners, or you risk the whole thing "capsizing," which would spoil your whole day, if not your whole life. Lifting from above is bunches safer than pushing up from the bottom.

[Nicholson58]

I have watched keels dropped several times in Trinidad. It is amazingly quick and efficient using the travel lift and good crew with adequate prep. Bolts pre loosened. Cradle ready for the boat. Cradle, temporary support for the keel. The boats were typically lifted free in less than an hour. If it was a simple re-bed, the job was done completely in a day. If it was long mess and repair job the boat is moved to a low cradle appropriate for the necessary work. The keel can then be dealt with in the open. Travel lift time usually less than a half day.

If you build your own, there is the expense plus the danger your boat will grow roots.

[jimbunyard]

Originally Posted by mait

Good idea! Maybe even dont need to excavate. I have trailer with three removable crossbeams under the keel. I can fit 2 big hydraulic car jacks between the crossbeams, remove the crossbeams and drop the keel.
Any arguments against this?

Wouldn't worry too much about stability, but you need four jacks or a boatload of blocks and the patience of Job.

What I would worry about is if the hull can stand the forces imposed on the four points supporting 3000 lbs each when you remove the keel supports. Even if the hull stanchions are situated at main bulkheads, I'd be a little leary of concentrating those loads at only four points.

What you could do is remove the tires or let the air out so that the keel supports are resting on the ground, remove the mounting bolts and then lift the hull while the keel remains resting on the crossmembers on the ground.

That'd get you down to 1750 per point, better but I'd still want the load spread out more, especially if the existing supports are not at the main bulkheads.

A lot depends on the nature of the repairs you're doing...

[jakkum]

I welded scaffoldong Pipes on steel carwheels and used 4 chain hoists

[Cadence]

I believe you would be far better off jacking the hull up away from the keel. Safer as long as you block and shim as you jack.

[RaymondR]

Take it from one who has spent a professional life time lifting and jacking things up your idea with four posts well buried and straps under the hull and chain hoists on each post is the safest and most secure for both yourself and the vessel.

[Lionshooter]

I have done it with 4 posts, 2 crossbeams, and 4, 5-ton hydraulic jacks.

[chrisr]

don't automatically assume that keel and hull will seperate easily

we tried to take the keel off one of my race boats years ago. would not drop off

tried lashing keel down and lifting hull with travel lift, but lifted so hard it got to the point we were worried about damaging the hull...still would not seperate.

as we only wanted to check keel bolts and seating were all ok (and that the keel was not going to fall off), we decided that it was all ok afterall...

cheers,

[mait]

Thank you for your input, everybody. After reading all the replies I decided to undertake the job outside. This way I can support the keel on the ground, lift the hull with a crane truck and use boat cradle and extra stands to support the hull above the keel while prepping the surfaces to re-bed the keel.

[Cadence]

Originally Posted by mait

Thank you for your input, everybody. After reading all the replies I decided to undertake the job outside. This way I can support the keel on the ground, lift the hull with a crane truck and use boat cradle and extra stands to support the hull above the keel while prepping the surfaces to re-bed the keel.

Probably a good decision!

[mait]

I finally chose another way to remove the keel. I do not encourage anybody to do this like I did, there are certain risks involved.

With the boat standing on the cradle (trailer in my case) I started lifting the hull (nuts from the keel bolts removed of course) with a hydraulic jack. I placed the jack just in front of the keel and used a piece of timber between the jack and and the hull. I supported the hull with car stands in front of the keel and just behind the keel (the boat has a longish fin keel).
So I jacked the hull 1cm from the bow, adjusted the side supports accordingly, then let it sit on the car stand. Reposition the jack aft of the keel, raise the hull 1cm, adjust, support... repeat many many times. The keel didn't drop easily, I had to use some force. But I managed to raise the hull from the keel about 15cms which gave me enough room to work on the surfaces etc.

I also made a video:
https://youtu.be/sEUHgi_ZYQQ

All in all the job was no mission impossible. Now the keel is back where it belongs, properly re-bedded with epoxy resin to get matching surfaces and later sealed with Sikaflex. That means I had to raise the hull and then lower it back onto the keel several times. Would have been easier with 2 jacks but I had only one and it was doable.