Replacing Cypress bunks - Big pieces of wood!

[BOAH]

I recently bought a '91 Magic Tilt aluminum trailer. One of the bunks looks like it's been eaten by termites so I would like to replace both of the bunks. The current bunks are 3" x 12" x 10' Cypress. So these are big pieces of wood. I've been calling around and getting Cypress in this size is going to be a chore but can be done for a price. What do you think about using 2 x 12's and bolting them together?

Looking at the Yella wood looks like an inexpensive way to go. Or would it be better to go with a specific type of pressure treated wood?

If I go with the pressure treated wood, are there things I need to be aware of when using pressure treated being in contact with aluminum?

Or should I just keep shopping for the Cypress?

Thanks for your input.

 

[Incorrigible]

Re: Replacing Cypress bunks - Big pieces of wood!

I've used pressure treated lumber on my boat lift for years with no ill effects, but I am in fresh water. I don't believe there will be a difference between Cypress and pressure treated wood making contact with aluminum.

 

[ezmobee]

Re: Replacing Cypress bunks - Big pieces of wood!

If I go with the pressure treated wood, are there things I need to be aware of when using pressure treated being in contact with aluminum?

Yes! This whole aluminum vs. the PT thing is no joke. Don't use it anywhere it will be in constant contact with aluminum. Now that being said, although others may disagree, I am not paranoid enough to worry about the carpeted PT bunks I installed for use with my painted aluminum boat.

 

[BOAH]

Re: Replacing Cypress bunks - Big pieces of wood!

Thanks! I'll bite the bullet and just get cypress.

 

[Incorrigible]

Re: Replacing Cypress bunks - Big pieces of wood!

What's the aluminum vs. PT thing? Very curious? Is this the same in salt water as in fresh?

 

[lncoop]

Re: Replacing Cypress bunks - Big pieces of wood!

What's the aluminum vs. PT thing? Very curious? Is this the same in salt water as in fresh?

Yep. PT wood and aluminum are not friends. The chemicals they use in today's PT lumber reacts adversely to aluminum and causes it to corrode.

 

[jeeperman]

Re: Replacing Cypress bunks - Big pieces of wood!

The PT industry advises not to use any type of PT in contact with aluminum.
But you could cap the wood with vinyl or plastic before putting on carpet.

Aluminum should not be used in direct contact with wood products treated with ACQ (the new, readily available stuff) or CCA (the old stuff, now commonly refered to as marine grade or even below ground use)preservatives.

 

[jeeperman]

Re: Replacing Cypress bunks - Big pieces of wood!

The current bunks are 3" x 12" x 10' Cypress. So these are big pieces of wood. I've been calling around and getting Cypress in this size is going to be a chore but can be done for a price.
Thanks for your input.

Have you contacted the sawmills in your area?
The lumber yards are doing that and then adding their mark up to you.
Might be rough cut, but does that matter to you?

 

[BOAH]

Re: Replacing Cypress bunks - Big pieces of wood!

I did, thanks. Going through the sawmill is a much better way to go. But after all of that, it looks like I need to move the bunks in closer to center. I'm looking at new bunk brackets mounted on two of the frame crossmembers. And since I'm doing that, probably go with 2 x6's set on edge? Maybe double them up?

Any thoughts?

Attached is the current setup.

 

[hungupthespikes]

Re: Replacing Cypress bunks - Big pieces of wood!

Lots of problems to work out. One the springs on the axles need room and mounting on the cross members will limit that. Moving the bunks up with brackets and there only looks like two places to secure bunks and will be at the two ends. How far apart, wood warping problem? Height is another, getting clear of the fenders.
How far in are you moving the bunks?
Had to do the same to the Baja trailer, so went with the sawmill and pin oak. Went over sized on the width so they could stay on the I beams, and with pin oak the trailer would not float when I had to go deep with the trailer, that was PITA, because of river currents. Had to load in stages.
Worked out fine, but only needed an inch or two on the extra width to narrow up the gap.
Good luck
huts

 

[BOAH]

Re: Replacing Cypress bunks - Big pieces of wood!

Here's what I ended up doing. I got 4 2x10 by 12' PT pieces. I cut them down to a little over 11' and then screwed them together with 3" exterior screws. I beveled the top edge to about 12 degrees to match the bottom of the boat the best that I could. The previous crossmember on the front of the trailer was a C channel that I replaced with a 3x3 galvanized crossmember with a V bend in it. I matched up the holes from the C channel and mounted the new crossmember in the same location. I took an old bike tube and cut it to fit between the aluminum frame and the galvanized crossmember so they weren't in direct contact with each other.

The back crossmember on the trailer is 3" lower then the front crossmember so I mounted two 10" brackets on the back crossmember and two 8" brackets on the new front crossmember. I adjusted the width of the crossmembers so that they sit on the outside of the chines(?) on the boat. I then carpeted the bunks and installed a galvanized eye bolt on the back of each bunk for my tie downs. I put the boat on the trailer and I had to move the head bracket up about a foot but using a bathroom scale, I weighed the tongue and it came in at 220 lbs. which is where I want it. I took it out for a two hour road trip for a season ending scallop trip and everything worked great.

I've attached some pictures of the outcome so hopefully this will help someone else. This forum and the people on it sure have been good to me.

 

[brokeboater]

Re: Replacing Cypress bunks - Big pieces of wood!

where did you get the crossmember(s)? both of mine are the aluminum channel and i feel sure they would not be enough to support the weight. how does the new cross member attach to the trailer?

it looks like a very feasable solution. getting the crossmember may be the issue. sorry for all the question but i'm trying to do the same thing to mine this winter.

just re read a previous post that had a pic of the original config of the trailer and answered some of my question.

 

[BOAH]

Re: Replacing Cypress bunks - Big pieces of wood!

I got the crossmember from a local boat supply store. I attached it using the same bolt holes as the original crossmember so I only had to drill holes in the new crossmember.

Hope this helps.

 

[hungupthespikes]

Re: Replacing Cypress bunks - Big pieces of wood!

Sweet !!!
Nice job. Thanks for posting from all of us.
huts

 

[brokeboater]

Re: Replacing Cypress bunks - Big pieces of wood!

thanks for the replies boah.

I just went out and did some measuring. i think i can just replace the aluminum cross members with straight 3x4 galvanized tubing. as long as i keep the clearance between the keel and the cross members the same as it is now it shouldn't matter. to do that would require using 12" lumber if i set it down on the cross member. i might could get by with 10" by raising it up slightly off the cross member. from what i have read, the bunk needs to be as close to being under a stringer as possible.

anyone have an opinion on how much the aluminum channel could support? it is 4" wide and 2" deep, about 1/4"+ thick. just curious if it may be strong enough without doing the tubing. trailer carries a 21' fiberglass cuddy cabin with 200 outboard.