svonmiller

Greetings,

I'm doing a transom/stringer rebuild. I'm not sure the term for these is stringers, since they don't look like your typical stringers to me. They butt up against the transom and there is a steel bar that bolts onto them, and the motor mounts are on that bar.

They appear to be dimensional 2x4s. But, they're not like your normal 2x4, with rounded edges. At least not like the kind I see at Lowes. They also look like much harder wood than the soft pine you find at Lowes. I've also read in many places here that you don't want to use dimensional lumber for stringers.

So I'm curious if anyone knows what to replace this wood with? Some sort of higher quality 2x4? They don't appear to be laminated together either.. I mean they come apart pretty easily. Of course they're very rotted so that may be why.

Thoughts?

glassdave

This is one of those times where you may need to think outside the box a bit. There are like a gazillion different ways manufacturers fabbed in stringers and liners and many times they missed the mark. I would probably seriously consider abandoning whatever method that was in there and just gut it in favor of a traditional stringer system. That kinda looks like a liner or partial liner kinda thing. If its to involved to re do the whole thing i would laminate up my own lumber to replace whats there, stacked marine plywood or something like that. Definitely try to not use dimensional lumber and also no treated lumber either.

svonmiller

Well the only thing I'm concerned about is matching the strength. I don't know enough to know how much of the structural strength is coming from the wood and how much is coming from the glass. The lag bolts on the engine mount frame thread right into that wood. So I need something that can thread in there too. I'm not opposed to boxing it up like a normal stringer, but I'd be afraid that it wouldn't be strong enough. Or am I just over-thinking it? I suppose one thing I could do is laminate 3/4 ply until I reach that width. I built a really big sailboat rudder that way one time.

Oh, and PS... glad you answered Dave because I've got another question for you - I read in a post by you that you don't use PPG single stage below the water line. What do you use (on a trailered boat that doesn't stay in the water)?

Thanks for the advice!

glassdave

truth be told a conventional stringer system is stronger then what you have there. The lagged in motor mounts on stacked dimensional lumber is very weak when compared to even the simplest through bolted L bracket, standard Merc mount and a standard stringer.

I'm still try'in to figure out what ya got going there? Looks like that wood thing is right under the motor? Is that a boxed in stringer on the outside and were all the mounts just lagged? So there is a steel bracket that spans these things and holds the motors?

your ok with using Concept on a trailered boat its just not good for submerged extended full season use. I do prefer to salvage as much gel as possible on the running surface though, no paint on that if ya can help it.

svonmiller

It's one long steel bar that the front engine mounts of both engines bolt on to. Here's a couple of pics with just the starboard engine out:

svonmiller

I drew on this to help illustrate it:

glassdave

hmmm . . . . never seen nothin like that before . That looks more like some of the methods commonly used in non performance type applications. If you are going to run the boat in the same manor as most of us on here i would seriously consider a more traditional method of stringers and mounts. Not a big fan of mild steel in the marine environment.

Again if re engineering the whole thing is impractical you could re engineer whats there a bit. Use the stacked laminates described above and dont be afraid to change something that doesnt look quite right. Beef up areas that need it and look ahead at what some of those components might cause on down the road. That cross bracket where it bolts to the actual pedestal mounts looks like it could generate a bit of torque that may tear things up if not kept in check. The biggest problem i see is all of it is lag bolted (not good). Switching to a stringer system would allow you to through bolt everything.

svonmiller

I get that a lot with this boat :-) Actually I would very much prefer a through-bolting system. And I can core the holes with resin, which I can't do with lag bolts. A lot of this rot came from those bolts I think.

I'll probably stick with that steel cross member, but replace the wood with 1 1/2" wide stringers (laminate two 3/4 ply). It looks like most BBC setups just mount to 1 1/2" stringers. That should be strong enough, right?

Per the "what wood to use" thread, I'm going with regular ABX ply. I'm using epoxy, just because I'm used to it and have a comfort factor. I continue to see conflicting opinions on using 1708 with epoxy with the stitched backing. That's what I want to use, but you and others have me really re-thinking it.
These guys swear by that combination: http://www.boatbuildercentral.com/

Thanks for the advice! I'm sure I'll be posting more when I get a configuration figured out to see what everyone thinks.

svonmiller

Oh, the reason I want to use 1708 and epoxy is because I already have a lot of both, saving me a significant amount of cash.

glassdave

Yea i think IMP was known for this kinda stuff

1708 can be used in an epoxy system but the labor to get it in pretty much doubles and you loose some strength in the process. Anyone that tells you otherwise lacks even a basic knowledge of how these systems work and how to actually maximize the benefit of using epoxy in the first place. 1700 wets out and drapes SOOO much easier and i doubt you'd use more then half a dozen yards or so, its worth a thought. You have quite a bit of contours you will need to deal with and the extra ease of the fabric without the mat really comes in handy. If you do choose to use the 1708, not sure if you do it this way, but cut all your patterns and fit them dry then wet them out on a piece of plywood or hard surface outside the boat, balancing the laminate with a yellow squeegee then install them. Because of the long work times i will wet out all the patterns for a given area and roll them up individually then place them on a large pan or something. Take 'em all in the boat and roll 'em out . . . . . piece-o-cake This is only for 1708 though, 1700 you can lay in dry and brush wet the laminate. 1700 also requires you handle cut patterns with care, it is easily deformed. Something else to keep in mind is with 1708 you need to place it with the mat side out, contrary to use with esters. The mat is the weak link so it would be better to have at least two bi ax layers in the stack up against the stringer unobstructed. (that theres my own thought on 1708 w/epoxy )

Good idea getting rid of the stacked stuff and putting a stringer where that block is. The outside could easily be converted to an open top and you could through bolt all of it.