Need Suggestions on type of Aluminum to Use

[rmbates]

I plan to build a set of cradles to hold a small boat on board a larger boat. Plan to use 1/4" aluminum plate in the vertical position which will be cut in a gently rolling pattern on the top side to match the contour of the small boat's bottom. To the top side of the plate I plan to weld the same plate material in a 2" wide strip for the boat to actually sit on. This will be a saltwater corrosive environment but the finished product will be powder coated or urethane painted. I know 6061 is probably the way to go for the main plate, but wasn't sure if the strip on top could be made from the same alloy and bent & formed to match the rolling contour. Any input would be appreciated. Thanks.

[greywynd]

Instead of 2" aluminum, what about a strip of teflon or similar plastic? Drill and tap the vertical plate, and use some flathead ss screws, countersunk in some to prevent marking/rubbing on the hull.

Aluminum on aluminum, when there will be some vibration/movement, is going to make a mess of things rather quickly.

I recall some threads talking about anodizing marine aluminum...don't recall what exactly.

[rmbates]

Thanks for your response Greywynd. Actually I forgot to mention in my origional post that the top strip of aluminum will be covered in 1/4" neoprene which will cushion and protect the boat's bottom (which is fiberglass). And, even with significant vibration, there shouldn't be any movement between the top strip of aluminum and the supporting plate if I get my welds right. My main concern is whether 1/4" 6061 can be bent to the contours of the supporting plate before welding. Thanks.

[CRAFTBENDER]

5052 H32 is used a lot by boat builders. It forms and welds very good. 5356 is the filler I would use for welding it.

[greywynd]

I haven't done a lot of it, but you can anneal 6061 with an O/A torch. Lite it up, acetylene only, and blacken it with soot. then heat until the soot burns off. (Often do the same for preheating.) You should now be able to bend it.

I would suggest you try a bit of testing first though....

[vicegrip]

5052 H32 is used a lot by boat builders. It forms and welds very good. 5356 is the filler I would use for welding it.

I 2nd this we have a fair sized harbor here for recreational boats.

5052 yealds to nearly any shape.
Consider that the alloy has the strenght of play-dough.
You have to build the strenght into how you use
the various cross-sections.

vg

[usmcpop]

Here's some good info on aluminum in marine applications:

http://www.key-to-metals.com/Article99.htm

[partagas]

We use Alum V-Blocks at work when we have to set our magnets down. The Mags weigh 4 tons when done, so the V-blocks can hold a lot of weight. Making it in that shape would cut down on weight and material. 1 set for the front and for the rear. Good luck.

[Rocky D]

6061 won't hold up in salt water, 5052 is the choice for marine applications, and as stated use 5356 wire.

[Rocky D]

6061 won't hold up in salt water, 5052 or even better 5086 is the choice for marine applications, and as stated use 5356 wire.

[rmbates]

Thanks for all of your replys and suggestions! Let me sum up what I'm planning to do based on what I'm hearing.......

Will use 5052 plate with 5356 filler rod

5052 is relatively weak, but v-shape of the cradle will help with strength issue, and I will add bracing and perpendicular strip of plate to sides, bottom and top. The small boat only weighs 1000 lbs and will have cradle in front and back to carry the load so all should be well.

Time to get cutting and welding. Thanks again!