Aluminum mast/ladder

[fisherJim]

I want to weld up a new mast for my wood boat using 2" aluminum pipe configured into a ladder.

The rungs would be something smaller, maybe 3/4" or so. The mast/ladder would be about 22 feet high and would be mounted on the top of my cabin of the boat.

My question is this: Should I just weld the rungs to the aluminum pipe or should I drill a hole first and insert the rung and then weld it?

Obivously I am striving for strength and want to do this right. Any insight on this? Tricks? Should I make the rungs out of something else? 1 1/2" I-beam?

Thanks,

Jim

[MikeJohns]

As a triangular configuratiion with 3 uprights and rungs joining the uprights ?

Then you minimize welding and butt the rung up to the upright. The uprights are the tension compression members the rungs are just spacers so interfere with your main members as little as possible.

I hope this helps

cheers

[fisherJim]

Yes it would have two supports going forward and bolted through at the top and at the bottom to the top of cabin or maybe the hull it's self. Cables on the side for added strength. The mast its self would have the appearance of a ladder with two aluminum pipes and the rungs welded in making the ladder configuration.

http://i141.photobucket.com/albums/r45/c_man2/ladder-1.jpg

[LyndonJ]

So is it a mast or a ladder ? You add a lot of windage with all those round tubes up in the free airstream. A stayed mast with attached side rungs might be simpler.

[Moss]

Be sure to check on the effect of all that welding on the temper of the pipe. As a rule of thumb, depending on the alu grade you use, welding reduces the temper in that region to zero, and if you're planning to do that repeatedly all the way up your "ladder", you're creating multiple weak spots.

[Ad Hoc]

If your mast is also a ladder, what is it carrying and how much?
You'll need to work out the static and dynamic bending moments on the ladder of all the eqpt on it, including a crew memeber if that is normal MO for you. Once you work out the loads, the design of structure becomes self evident in terms of scantlings and how to fabricate it.