Crossmembers need replacing - advice on material / costs?

[quantum]

Hi all. I just finished the tear down on my 1992 Smokercraft 21ft. Everything is off, and the crossmembers are a little rough. Some are bent, others have a pretty significant amount of surface rust on them where the crappy original elevator bolts go. So, might as well replace them all (12 total), and update all the hardware to SS at the same time!

I have a machine shop in town that can do aluminum or galvanized (originals are galvanized Z channel). Since I am replacing every one, should I go with galvanized again or something different? How about material gauge, any tips? Any particular reason why one is better than the other? About how much should I expect to spend here in the northeast?

They can punch the holes and match the ones I need on each piece, which makes that part easy. I just want to do it right, maybe better than the original, the first time. Plus, this gives me a chance to flip the toons and give 'em a good polish all the way around and replace literally every single nut and bolt on the boat!

Happy Boating!

[GregF]

I used aluminum 2" 1/8" wall square tube on mine. The outer ends are bolted from the inside of the tube and the center part is through bolted through the deck. It makes a very stable structure.
My originals were galvanized and they did not hold up.

[quantum]

I would up going with 16 gauge galvanized. The guy at the shop said he was concerned with the punched holes wearing over time on the aluminum. Plus, the galvanized was cheaper. Total cost was $375 for a dozen shiny new pieces of metal. Took 4 days. Got $15.00 for the old pieces at the scrap yard

I gave him one crossmember as a sample, and numbered the holes. The nasty OEM pieces were all the same with 14 mounting holes on one surface, 5 holes on the top surface (for the elevator bolts), and two 1" grommet holes on the vertical surface to pass wires bow to stern.

Although it sounds like alot, all pieces got the 5 holes on top. Easy. For the bottom, 6 were the same (4 holes), 2 had 2 holes (first 2 up front). 2 pairs of two forming the high hat with the z channel had 10 holes or so for mounting the transom, etc. Instead of drilling, the shop punched all the oval holes, so I have some wiggle room to do adjustments. I thought that wa spretty cool.

I think I have the bolts and washers picked out, it's the NUTS I have a question on! I am using 3/8" stanless steel hex head bolts to attach the crossmembers to the pontoon brackets. I see many people using nuts with the nylon inserts. I think that's fine for rail mounting, etc. But for the crossmembers and transom I was going to use reverable locking nuts, like these - http://www.boltdepot.com/Two-way_revers ... _18-8.aspx

As a matter of fact, I was thinking about using the locking nuts everywhere instead of the nylon inserts (elevator bolts, transom wood, railing, etc.). Does anyone have any thoughts on this? Just looking for a little direction. Is one better that the other?

[rancherlee]

I personally like Nyloc nuts over lock washers when high heat won't be an issue. Either or is fine IMO. I've never had a Nyloc loosen up.

[GregF]

You may get away with galvanized in fresh water, this is what happens in salt water

[quantum]

I appreciate the comments. If its all the same, I'm probably going to use the lock nuts for the structure parts and nyloc for the fence/rails.

I really don't intend on doing any saltwater stuff. But since I can't say 100% what the future holds, what can be done to prevent the rust streaks like in the pic? Should I look into priming/painting them or should I just leave them alone and let nature run it's course? How long do you think these will last, freshwater only?

[Bamaman]

You might want to check with Fastenal for a less expensive source of bolts. They are also the place to purchase rivets in bulk.

Nyloc nuts are usually put on stainless bolts for marine use, and stainless bolts often have finer threads than galvanized threads. If you go nyloc nuts, you'll have to go stainless all the way. I agree with the lock washers, however.

I don't see pontoon boats advertising galvanized crossmembers. Galvanized is just zinc coated steel, and it's very heavy.

Aluminum crossmembers are the way to go--specifically stretching the boat's width to 8' 6". Such crossmembers are easily found @ http://www.custompontoonboatkitsetc.com/id16.html.

[BobG]

I think you should go with a single-piece cast transaluminum (transparent aluminum) with surface texture, so you can see through the deck into the water.

[playcat]

I'm not real keen on mixing dissimilar metals, i.e. stainless steel, galvanized mild steel and aluminum. it might work in fresh water, but if its brackish or a little stray current and something will be dissolving quick!

[quantum]

I think you should go with a single-piece cast transaluminum (transparent aluminum) with surface texture, so you can see through the deck into the water.

They only had 1/4" 4x8 sheets in stock. At best, I'd only be able to bring back a few sunnies, which would do humanity absoluty no good.

I do believe I am going to bite the bullet on this one, and get the crossmembers redone the same way but in 1/8" aluminum like I shoulda done in the first place. In the scheme of things, its not too huge of a hit, just a few hundred bucks (little ouch). In the long term however I think 100% aluminum crossmembers and SS hardware will pretty much last forever and will probably look good as new 10 years from now, no matter what kind of water I dunk it in.

[GregF]

Mine are 22 years old and still good as new in salt water. The original steel ones just rusted away.