Size of I Beam needed

[boatbuilder]

I must move my 58' steel sailboat from my backyard to a
commercial site 1 mile away. I have movers who can move it but they will require one I beam on either end of the boat to support the lifting of the hull onto the trailer. WHAT SIZE OF I BEAM SHOULD I BE LOOKING FOR TO SUPPORT A 20 TON LOAD CENTERED ON A 16' SPAN???

 

[austim]

Hi, boatbuilder.

The simple answer is that no-one can design the beams without knowing the angle of the slings that your movers propose. ie, what will be the distance from your beam to the hook(s) above? (That will control what compression force is going to be applied, coincident with the vertical plane bending).

Having said that, I would not recommend simple I-beams anyway. Those who know, who have done research on buckling of crane-suspended beams, state "the classical buckling solutions do not apply". (Very helpful that, don't you think).

For some years now, my practice has been to insist that lifting beams for your sort of usage are of a section which cannot exhibit lateral-torsional buckling. ie use tubes of some sort, either circular or square, (or possibly H column sections, bent about their axis of minimum strength).

Once you know the full geometry of the sling arrangements, then we may be able to help you further.

 

[boatbuilder]

I plan to use an 16' I beam with a 1/4" plate welded to one side of the beam (from the top r/h side of the I to the lower r/h side of the I) this should prevent twisting of the beam. The beam will be placed in a horz. plane to the bottom of the boat with the keel (center lowest point) of the boat welded to the center of the I beam (@8') then weld some 3"x1/4" box wall pipe from the I beam to the sides of the boat, say every 2 feet or so. The end that attaches to the steel boat would be attached to a 1' square piece of 1/4" plate which would be welded along the edges to the hull. I am thinking a 1' high I beam might be heavy enough but am not sure. The whole structure will be raised up 6' using 4 heavy heavy hydralic jacks located one at each end of the two I beams (one I beam forward near the center of gravity and the other one at the other end(stern). The plan is to then drive a 11' wide low-boy trailer under the boat, lower the boat onto the trailer, cross chain using the attachments to the I beam and slooowly drive away. Simple! But not so simple if the I beam bends in the middle with the force of 20 tons comming down on it.

Any advice you can offer would be greatly appreciated as I am being forced by a court order to move my boat (those city lawyers just don't have any sense of humor)

thanks

 

[ishvaaag]

I made an study for one 16 ft span loaded by 40 kips at center, slings at 45 deg at compressed flange, assumed load would be hanging. Impact factor 1.3 and safety factor 1.6 required for the studied arrangement W18x86. Your 16" inch is not far the mark I assume with the welded plate. Your actual arrangement seems less stringent in not depending on slings but be supported on the jacks. I also think your bam should be preferably a box, and guide to the displacement of your beams while lifting must be braced strongly enough for not even in the worse nightmare of a impact the outfit tumble.

In any case and since you are risking your boat, why not ask the services of a professional engineer?