Size of Pipe Required to Support Mast Stepping

[Northeaster]

Hi Folks,

I will be adding some 8"x8"x 10' hemlock beams around my existing crib dock (current dimensions are 8' wide x 8' deep x 6' high) before attaching the gangway and floating docks. I would like bolt into position, a steel, or aluminum pipe, that will be high enough, and strong enough to step and unstep the mast on my 30' sailboat. I can easily notch out the existing crib beams and the new ones, to allow something like a 4" or 5" pipe to be sandwiched in between, and therefore fixed to the crib. I would also bolt it to the beams, etc.

the deck stepped mast likely weighs 150 - 200 lbs (30 year old boat with heavy single spreader rig) and is about 34' long, and the deck could be floating about even with the top of the crib, at low tide.
However, the mast step would be about 15 - 20' out from the crib, as it rests in the water, on the flating dock.
Or, at High tide, I could likely bring it in closer to the crib, perhaps temporarily tied inside the floating dock, adjacent the gangway.

I have seen some small marinas where their mast crane is a fairly tall, heavy pipe, with a block and tackle attached to the top, and a rope runs from it to the top of a secondary pipe, which is attached 10 or more ft up the main pipe. This secondary "arm" pipe does the lifting, and is supported by the main pipe.

I would think that the system would have to be about 20' high to be able to lift the mast from above it's halfway point, and be able to swing, or reach out to position the mast for stepping / unstepping each season.

If anyone would care to provide some advice on what size or design of system would be best for this application, I would appreciate it.

If necessary, I could run supporting lines from the top of the pipe / crane, to the base or midway point of a couple of large pine trees which sit 50' back from the crib dock.

I do not need to rig up the whole system now, but want to put an adequately sized pipe in the crib, to be used this fall to unstep!

I am thinking of something like this ship /barge derreck image:

http://myweb.tiscali.co.uk/gansg/9-loads/c-type.jpg

Thanks in advance for all responses!

[Shoalcove]

Why not run around to some of the local clubs and government wharves to see if you can find an existing rig to copy? I would think there is something like that around Chester. South Shore Marine has a mast crane that may provide insight to sizing. I'm not an engineer but would think that you'll want a heavy walled pipe to allow for corrosion. Good luck!

[perchance]

Why not install a short length pipe of a large enough diameter that you can insert your crane pipe into at a later date when you figure out what will work? That way you can finish your crib and work at the crane at your leisure.

[Northeaster]

Shoal - I did look at some of these setups, but they all seem to be built to take masts of much larger boats than mine, so I would like someone with an engineering background to give me an idea what woudl be needed to support lifting a 200 lb weight, outreached approx 20 ft from the base of the "crane".

Perchance - Yes, this is a good idea. I will look at what combinations of pipe will fit into each other. On the other hand, it would then ne rather difficult to raise the smaller pipe up enough, to vertically side down inside the larger pipe.

I did do most of the crib rebuilding this weekend, and decided not to put the pipe in between the crib beams. I will just mount it with heavy hardware, through bolted on the outside of each 8"x8" beam, and likley supported by a large rock, or cemented in between a couple of rocks, at the base, 5 ft down the side of the crib.