Stringer replacement report - UPDATE

C

cliffpaul2

Junior Member
I pulled my burned up motor a few months ago and I'm working on putting a remanufactured long block together.  In the process, I figured I should check out the stringers that the motor mounts on.  A buddy came over and we started by drilling a hole between the old mounting holes, and the wood was dark and soft there.  The next step was to cut a strip out of the fiberglass on top, which exposed even more soft (rotting) wood.  So the cutting continued:
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The next thing we did was cut a cross section about 15" forward from the transom, and my worst fears came true:
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These things are a total loss. Luckily, these pieces are fairly short (they stop at the first bulkhead), so we completely removed both of them, and will start from scratch.  

I bought a beam remnant at the lumber yard that I think is perfect.  It is a product called "glue lam", which is basically several 2"x4" boards stacked on top of each other and glued together to form a beam.  They are cured before they are glued, so there shoudn't be any warping later.  The piece that I bought had been exposed to a little rain this winter, but it was wrapped with plastic, so it held up pretty well.

Here is the question:  Should I cut the new stringers should to fit tightly between the transom and the bulkhead? When I removed the old stringers, I noticed that they were both about an inch too short.  Was this intentional?  I don't think they shrunk after they were glassed in.  They look like they were installed that way, because on both ends there was a gap where they attached and there was an indentation where the fiberglass cloth had been contoured around it.  Maybe this is a structural thing that I don't understand?  Maybe this allows the stringers to expand?  Any ideas?

Note:  The stringers that I removed were made of two 2"x8" boards that were nailed together.  As you can see from the photos, this put the mounting screws right in the seam between the boards.  I think this is a really poor design, because the worst rot was between them.  You can also see that from the cross section photo.  However, most of my rot came from the bottom, so I think there were some voids in the fiberglass too, and too much water in the bilge (the previous owner didn't even have a bilge pump installed!).

Thanks in advance for your advice.
 
Re: Stringer replacement report and question

I can't help you on the stringer question, but I wanted to say GOOD JOB tackling such a project.

The "wise guys" will be along soon and help you out.
 
Re: Stringer replacement report and question

I would cut them to be barely snug. kools can telll ya how to glue them in prior to glassing. When I had mine done I had a 1" hole drilled thru each one. My cockpit drains were on the outside of the stringers and wouldn't let water drain to the garboard drain. Water would finally spill over, but it got sucked into the fiberglass and stringer  (fiberglass ain't waterproff.) Be sure to predrill the stringer for the motor mount bolts. and seal them with 5200
 
Re: Stringer replacement report and question

The beam sounds nice, but what kind of glue?? If it isn't a water proof glue holding it toghter it will be junk in short order!!

if was me I would make up a new stringer and seal with resin before all the way around before putting in place.

I aslo would make it a pretty tight fit!

Keep up the good work!!
 
Re: Stringer replacement report and question

I replaced part of a stringer, it was fairly easy.  If you're not removing the whole stringer, make sure you scarf the joint.  I used thickened West System to bond everything and then laminated with 2 layers of 1.5 oz mat and 1 layer of 24 oz. roven.  The work was really not very hard except I had to cut a hole in the deck for access to the other side of the stringer.  I used douglas fir to make the stringer.  I would shy away from laminated woods not intended for marine use because moisture can break down the glue.  Doug fir is cheap, I paid $16 for an 8' 1x8. I don't know about the gap to the transom. I see that a lot but I also see people putting knee braces against the transom in order to strengthen the boat.

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Re: Stringer replacement report and question

Those stringers look fine! Even if the wood completely rotted out the shell of the glass around the wood is plenty strong enough to support the deck and the hull. So just replace the section of wood your going to lag bolts into.

This is how oceanmaster and the old seacraft stringers are built.

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as long as the glass hasn't delaminated from the hull you don't need to worry.
 
Re: Stringer replacement report and question

BiG...While I love that last picture you posted, it scares the devil out of me at the same time. Thats some major surgery being done.
 
Re: Stringer replacement report and question

Yep I be looking for a new boat at that stage of the game!!
 
It's been a while, but I've completed the stringer replacement project. I used one of the old ones as a template and cut two new stringers. I shaped them with a belt sander until they fit almost perfectly, coated the bottoms and the ends with resin for protection from water seapage, gave it enough time to harden, and then dropped them into place. Before I did, though, I scrubbed the hell out of the bilge area. This was not only long over due, but necessary to allow the fiberglass and paint to stick later. I measured about twenty times and adjusted the stringers until they were perfectly centered. Then I cut a couple of spacers to hold them the right distance apart. From the other side of the first bulkhead I drove a couple of screws into the end of the stringers to hold them in place.

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Then the first batch of fiberglass went on. We did the ends first, again to help hold them in place. Then we laid a long piece that wrapped the entire stringer and extended about 6 inches on both sides.
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It took several sessions with drying and grinding time in between, but the result was pretty good for a couple of amateurs! We put some reinforcement on both ends and along the top of the stringer, and two strips of heavy weave along the inside of each stringer right at the point where the motor will be mounted. We're not sure if there's any structural benefit to doing this, but what the hell. We had some extra materials!

I sanded the entire bilge area so that I would have a good surface for the "Bilgekote" paint that I bought at West Marine. I applied two coats of bright white (an upgrade over the grey that I used to have), and it turned out great!

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It took a long time, but I'm glad I did this. Since the motor was out anyway, it was a really good opportunity, and it was definitely needed.
 
It's really simple work, just labor intensive.  It doesn't take any really special skills.

Don't be affraid to use that grinder to rough things up where you want the fiberglass to stick. Fiberglassin on top of the bilge paint puts a lot of faith in the bond between the paint and the hull.
 
Cliff, that's quite a project and a job well done 8) ... the Bilge Coat REELY highlighted a good job ;) ...thanks for the pix and hope we see more on the engine install ;D ...
 
Perty work Cliff ;) You are now the subject matter expert and will be called upon any time a board member has this issue. Congrats on your new appointment as V20 Stringer Repair SME!
 
Cliff, looking really good there buddy.

I'm not sure I agree with the sentiment that anybody can pull this off or that it's altogether easy. I know it would be quite a task for myself and I hope I never have to do it. But if I do, I now know where to go for good info on how to do it.

Thanks for the tutorial and pics.

Steve
 
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