Stringer Replacement

I am replacing the stringers on my boat and came across this photo is this an acceptable way to repair. It looks like they reused existing tabs slid in new material screwed and epoxied.

 

Welcome to the forum.

When you blow the image up, those look to be concrete form nails (double headed), which makes pulling them out easy.

This can be acceptable, but the photo shows what not to do. He's using a mix of PT lumber and CDX plywood. Both of these materials should be avoided, for many well documented reasons. A better grade of plywood is acceptable, but PT lumber isn't. It also doesn't look like he bonded the new stringers in, as I see no ooze out anywhere. He has the right idea, but his techniques and application seems way off the mark. Screwing or nailing the stringers to the tabbing will not do anything, except rip out on the first wave hop.

Also the stringers need to be encapsulated and ideally sheathed, so moisture can't get at it. He also seems to be trying to "beef" her up, when in fact he's just increasing point loading and weight. A better approach would be to use plywood as the stringers, with a simple 1x2 or 2x2 at the top edge to act as a bonding surface, when he puts the sole back on. The stringers could be inserted into the previous tabbing, like shown and well bonded in the process. Then the stringers and the little bonding strip at their tops, encased in goo and fabric, before the sole is bonded down.

If you do a search here for sole and stringer replacement you'll find hundreds of previous posts on this subject.

 

Thank you for your response I plan on using marine ply or coosa board. I will wet it out before installing and wrap with 1708 overlaying tabbing 4 in to encapsulate. I wasn't sure about reusing tabbing would one layer of 1708 be sufficient? Also would epoxy be the best material to bond the stringers to the tabs?

 

You can use either polyester or epoxy. Epoxy sticks better, especially to wood, but polyester can and has been used. No, a single layer of 1708 wouldn't be stiff or strong enough. Measure the thickness of the current tabbing, which is like a few units of heavy roving/mat and mimic this with the replacement fabric. If you do use epoxy, you can skip the mat, as it's not necessary and just a resin sucker. Yes, you can reuse tabs, though most like to add at least an additional layer of biax over it, just for good measure. Coosa costs a lot more then plywood, but is lighter for the same stiffness and strength.

 

Why is pt lumber not good?

 

The new PT lumber has it's pores sealed by the CA treatment, which prevents resins from getting a good microscopic, mechanical bond. You can roughly abate the surface, which does improve this to a degree, but peel strength is still dramatically lowered. If the PT is purchased as CCA (still available, but only commercially), then this isn't an issue. Most folks buying PT, haven't a clue as the the chemical treatment and are getting CA pressure treated stock. This is true in the USA and some other countries, but I'm not sure which other countries.

 

Does that mean it also doesn't glue well?

 

I don't have much data on glued PT, particularly the new CA stuff, except for some of the usual suspects, mostly because I don't use much of it and because most of it is junk wood, I wouldn't employ in a boat anyway. I do know polyurethane is commonly used on land based projects, but as to data about it . . . the APA would be the place to look initially.