Need some help with replacing keel stringer in 25ft power boat

[vetting]

I tore up the floor in the cuddy cabin and found a rotten keel stringer. It rotted because they did a horrible job of glassing it in and someone nicked a huge hole in it when installing the stand for the table and for a drain. The actual piece of wood only goes as far back as the bulkhead for the step to the main deck. The stringer itself also came to too sharp of a point down its length so it didnt match up with the hull very well and caused the glass over the top of it to be pretty weak since glass came so far in at the bottom. Kinda like an upside down U except squeezed in.

So I cut out the stringer and ground down all of the bad glass....now the boats covered in a 1/4" of resin dust.

So Im looking at how to replace the thing. Should I just cut some pine to match it and then dont make it as pointy (V shapped) on the bottom so it matches the hull better? Should I bed it in PL or PB the whole thing in? I have plenty of epoxy and 1708 cloth.

After some inspection, the hull itself there is full glass as around an inch thick and is in great shape.

 

[Woodonglass]

Re: Need some help with replacing keel stringer in 25ft power boat

Uhmm, typically the Keel stringer is the backbone of the hull and runs from the bow all the way to the stern. Are you absolutely certain that it terminates at the Bulkhead? Pics of it's removal would be very helpful. Never seen a 1" thick hull.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Uhmm, typically the Keel stringer is the backbone of the hull and runs from the bow all the way to the stern. Are you absolutely certain that it terminates at the Bulkhead? Pics of it's removal would be very helpful. Never seen a 1" thick hull.

A complete different section of board runs from that bulkhead to the bilge bulkhead. That board is fine (all underneath a covered deck with no penetrations).

The 1" thick hull is just a guess - have no way of telling without drilling a hole all the way through. The sides of the boat are between 1/2 and 3/4" thick all glass. I found that out when I replaced the bilge pump through hulls. The back transom is a full 3" thick (cored) - found that out when I redid some of the hardware on the back. The chines (think thats what they are called) alone stick out a full inch from the hull, so its a really solid boat.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Here is a picture of the beast - 1989 Cobia 265fc.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Ok I just picked up a few pieces of really clean douglas fir. I'll use the old stringer that I cut out as a template. So the next question is - what should I bed it in with? I know you either need to do it with something soft like PL (wont that take forever to dry and then outgas) or just PB the entire thing in so it makes full contact. If I go the PB route, I have some West 406 and 407 - which one should I use?

 

[Woodonglass]

Re: Need some help with replacing keel stringer in 25ft power boat

Use PB with the 406. Pics of the repair area now that it's all torn out would help

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Here is everything all ground down and somewhat cleaned up. Also there are 2 photos of the new board set in place. Plan on wetting the board out with epoxy until it stops drinking it up. Then set it in PB with 406 and let it set up a bit. Then go over the entire thing with 2 layers of 1708 wetted out with with epoxy. Does that sound right?

Notice the board stops at the bulkhead - that is how the other one was also. On the other side of the bulkhead, another board continues down to the bilge bulkhead. That board is fine and doesnt have any rot....mainly because they didnt poke 20 holes in the thing and didnt set a drain in the floor that drained right through a hole in the glass to the stringer.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Can anyone confirm these are the correct steps?

Plan on coating the board with epoxy until it stops drinking it up - pay special attention to the end.
Wipe down the hull one more time with acetone.
Put down a layer of PB made with 406 on the hull and smush the board into it. For a fillet around the sides.
Let it set up a bit - maybe an hour or so.
Then lay the first layer of trimmed 1708 epoxy glass out over the board and extend it 3 inches onto the hull. Wet it out with epoxy and remove the air bubbles with a squeegee.
Then lay down the 2nd layer of trimmed 1708 epoxy glass over the board and extend it out 6 inches onto the hull. Wet it out with epoxy and remove the air bubbles with a squeegee.
Then let everything set up a bit and go back over with some more epoxy to fill in the weave.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Here is the progress so far.

Coated the bottom of the board until it wouldnt soak any more epoxy in. Cleaned up the hull really well with acetone. Then made about 22oz of epoxy and cabosil. Laid the PB in the bottom on top of a thin coat of unthickened epoxy and then set the board in and made the fillets. Have some milk jugs sitting on top of the board now while the epoxy sets up. Going to lay the 2 layers of glass tomorrow.

 

[Woodonglass]

Re: Need some help with replacing keel stringer in 25ft power boat

no need for 1708 with epoxy. The mat on the 1708 will not breakdown. All you need is some 17oz biax cloth.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

no need for 1708 with epoxy. The mat on the 1708 will not breakdown. All you need is some 17oz biax cloth.

I already have the 1708 cloth. I got it from Raka along with the epoxy - its supposed to be the epoxy compatible kind. So am I ok using that?

 

[Woodonglass]

Re: Need some help with replacing keel stringer in 25ft power boat

Well Alrighty Then!!! Yep, you're fine. Next time as a FYI using mat with epoxy is basically a waste of Resin. It abosorbs the resin but adds very little strength to the mix. Mat is used in Poly resin due to the fact that poly resin has no binders in the resin and becomes very brittle when it cures without the fibers in the mat to help "Bind" it together. Poly contains Styrene to help breakdown those fibers to make this happen. Epoxy does not have styrene but it DOES conain it's own "Binders" within the resinous mix so that when it cures it is hard and does NOT become brittle when it's use by itself. When used in conjunction with woven fiberglass cloth it becomes vastly stronger. Hope this helps explain thing a bit better.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Thanks for the help. So do I have to wait for the first layer to set up a bit before I put on the 2nd layer of glass? I dont mind the extra epoxy that much - the Raka epoxy is priced pretty well at $100 for 6qt of non blushing.

Thanks again for your help with all of my newbie questions.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

Put down 2 layers of 1708 with epoxy tonight. It was already rock solid with the PB and fillets that its bedded in. With the 2 layers of glass and epoxy, the thing will probably last after the boat is long gone. Should I put another layer of epoxy over it yet?

 

[Woodonglass]

Re: Need some help with replacing keel stringer in 25ft power boat

I'd say she's good to go! For a rookie, your glass work looks pretty darn good.

 

[vetting]

Re: Need some help with replacing keel stringer in 25ft power boat

I'd say she's good to go! For a rookie, your glass work looks pretty darn good.

Thanks again for the advice and help. Its a bit easier with epoxy since you can take your time to get the glass conformed to everything. Now onto the rest of the projects so i can get the boat in the water this weekend.