Crane barge

[rajeshram]

Am designing a barge on which one or more cranes shall be loaded to lift heavy weights over the side of the barge. Can someone who has performed or seen such task performed advise me whether the following is OK-
a. The barge will be moored on spuds. My intention is to allow part of the heel (abt 3 deg) to be taken up by the vessel & part by reaction (2 deg) at the spud walls. Spud wells will be a little bit larger to allow the heel upto 3 deg.
b. In case the reaction is taken by the spuds what is the fixity considered at the base of the spuds (fixed, pinned?).

Regards,
Rajesh

[Ad Hoc]

rajeshram

a) can the spuds take the bending and compression loads and, is the local structure of the hull/spud interface strong/stiff enough to take the loads?
b) Depends upon the grounding of the base of the spud, is it mud, sand, rock etc. But if in doubt, use worse case, simply supported ie pinned

[gonzo]

Sea bottoms are not homogenous. The spuds will settle unevenly. You could have a levelling system to take that into account.

[rajeshram]

I wanted to know from someone with experience on similar operations if the normal way is to -
a. Resist the heel with the spuds or
b. Allow the barge to heel freely & use spuds only to arrest drift of the barge

[gonzo]

You don't want spud wells to allow for 3 degrees each side. That is 6 degrees of total movement. If you have three, and you raise the barge enough, it will settle until the bottom takes enough weight. There may be bottoms that are too soft for that, so you have to assess the situation. Wave action is also something to take into consideration.

[rajeshram]

What is the material strength (sigmay) normally used for spuds (this one extends only abt 4m below keel) for such vessels? What is the normal diameter of spuds used on 40-45m crane vessels?

There is no spud raising or lowering mechanism.- hence there will be some heel before the top of one spud & bottom of the other will touch the deck & bottom of the barge respectively. From this point on, the behaviour is a bit difficult to estimate- the spud could have some deflection after which the spuds will act integral with the barge i:e while one spud digs in, the other will experience tension. In this case, the forces would be axial along the spud with forces calculated as follows -
Heeling Moment = force in each spud x distance between the spuds

Would this logic be right?

[jimm]

I am no expert but a did sleep at a - ha - work on the Lazzara showcase. It is used in intercostal waters of Fl. East and West coasts. The origional 4 spuds (one on each corner was modified to 2 on opposing corners) It has done well for two seasons now. The spuds have a cable system / winch raising and lowering system. They were 20" in dia. 30' long with welded nose cones on the bottom. Like gonzo said I think There is not much slop between spud and sleve 1.5 Deg max.
This application and yours may require greater demands than what I worked on. Much of our information came from Misener Marine in Tampa Fl. They have barges of all types operating all over the world. Contacting them would be a very wise choice, I think.