Keel bolts and plywood

Apr 11, 2017
Catalina 27 WA
Hi everyone. I have something of a project in my bilge and I'm looking for input.

I bought hull 3688 last fall (27, '77). She's in good shape - no evidence of the smile - lots of work done by earlier owners. She does have rusty keel bolts, however, and I'm working on identifying the source of a trickle that runs into the bilge from aft. (She's an outboard btw)

I have done a bunch of reading and I'm given to understand there's probably a piece of plywood under the glass bottom of the bilge that needs to be chiseled out and glassed back over, but that procedure seems dependent on being able to take the nuts off the keel bolts, which I don't expect I can do with the current state of them.

I was planning to do a keel bolt retrofit using either lag bolts or the windowing method, but I need a plan to tackle the whole project in the right sequence to avoid having to undo and redo things later. If I remove the plywood from the bilge and re-glass, it's going to lower the floor of the bilge and I'll not be able to tighten the existing nuts down on the new surface - so now what?

I could remove as much of the plywood as possible and build up the glass around the bolts to meet them at their current height? Or is there something else I should be doing?

Has anyone dealt with this confluence of factors before?

Grateful for any advice.

Sep 8, 2014
Catalina 22 Swing Keel San Diego
I hope your boat is on the hard to tackle this job (sounds like it is anyway).
- To remove the rusty keel nuts, first hit them with a wire brush as much as you can to get loose rust off. A wire wheel on a drill is handy but space could be tight down there. Then liberally apply penetrating oil spray(PB Blaster). You have to let it soak for days, keep applying daily. This works for some, but in the worst cases you'd need a cutting wheel on a dremel tool to make a side cut in the nut. I hope you don't have to take that measure.
- the lag bolts into the keel do not buy you much strength and is considered a 'bandaid' repair. The better option is to sister new keel bolts that threaded into the keel. To determine your strategy you need to know what condition your original bolts are in, so the nuts have to come off and keel needs to come off. If the old bolts are completely destroyed you will be glad you have done a full keel drop, new bolts, and re-bedding.
- yes, when you remove the rotten plywood core you are essentially lowering the floor of the bilge... BUT, you should replace that same thickness with a few layers of G-10 board epoxied into place. 1/8" G10 sheet is way cheaper to buy and cut than 1/4" thick, you'll just have to cut more layers. 1/4" can be cut on a bandsaw. Those layers plus some fiberglass cloth that extends up the sides of the stub make the structure WAY stronger and the nuts should seat at the same level (roughly).

This is a pretty big job but not out of the realm of DIY capability. If you plan ahead and have the right resources available its not crazy expensive either. Search "Catalina Keel Stub plywood" and you should find a ton of pictures on Google images.