Floor/stringer repair: how far?

Today I started what I thought would be a relatively simple floor patch. I had a soft spot under the observer seat that I cut out, revealing some rotted wood. The wood located between the motor and battery box is rotted on the port side, mostly outwards of the main stringer.

Good news: Ive cut the fiberglass back and have found good wood. Only the board closest to the motor absolutely needs replacing- all the others span both main stringers without any rot. I think anything outside the main stringer can be replaced with foam and glass. Also, all the foam is dry. My boat must be new enough that its all closed cell. Most importantly, the main stringer feels solid.

Bad news: Since the foam didnt absorb any water, it had to go somewhere- my secondary stringer on the port side is rotted as far as Ive dared to cut back. Outside the 1'x3' area that was soft, the floor is solid. All the foam surrounding it is dry. I still havent found where that secondary stringer dries up (if at all) and Ive already come across one perpendicular piece that is rotted as well.

Question: Where do I go from here? Obviously I need to do something with the rotted stringer- can it be fixed or is replacing the only option? Seems a shame to tear in real deep since the foam is still dry.

You're killing me with these pictures. I'd inject the secondary with GitRot or whatever... perhaps drilling holes along the secondary through the floor further back to inject it. Let it dry out and glass her over. I have no experience with this at all but I think tearing out the whole floor is extreme.

That method will work fine and is a good plan IMHO. You may find water between the foam and hull. If so, you need to let it dry out and then find the source of water intrusion. Look for cracks in the fiberglass at 90 degree bends and corners (bilge area). Repair as necessary.

I know everyone loves pictures, so I thought I would give a quick update with my progress.

After finding the rot, the first thing I did was remove the wood between the pylon and battery box.

Then I cut back the fiberglass over the rotted stringer until I found decent wood. Then I started removing the foam surrounding the stringer.

you should have covered the carb before you made the mess, now you'll have some of the foam in your carb.

79, youre right- the motor is a real mess. Everything about this job is messy and rather unpleasant. Ill make sure I blow out the flame arrestor.

Joe, Ive got some GT40p heads, a Weiand Stealth intake and a Cam Research camshaft waiting to be installed. I think that work will be much more enjoyable!

TRBenj,

Your floor repair looks like a mirror image of what I am going through on my 89 SN right now. I started out repairing a couple of soft spots on the port side of the boat, but then found the wood had rotted out under the driver seat and that I had water in the foam on the starboard side of the boat between the primary stringer and secondary stringer.

One thing I noticed in your pictures, is the perpetual wet spot in the bilge, just behind the bulkhead. I too had this. I finally had to take a look, and removed the battery box and dug the foam out. The top of the foam was dry, but the bottom few inches was totally saturated. The bulkhead was leaking water into the bow of the boat. The joint between the bulkhead and hull had cracked, and the caulking around the battery box hose had failed.

I don't know if it something you have to repair, but I thought I would point it out. I have questioned myself on it many times, but once I started there was no going back. There was really no wood in the bow that was harmed by the water as the level was below the stringers. However, the water does seem to wick its way around. It has turned out to be the hardest part of the repair though. It is still ongoing, but I should be done in about a week.

Mark

Mark,

I reached my hand down under the battery box and there is some standing water there. The foam I could touch doesnt seem too bad- so Im hoping that Im OK. I want to pull the battery box to see the condition of the foam towards the front- any tips on how to get it out? Ive cut it out from the fiberglass floor and seperated the top edge from the foam. Still stuck in there- Im afraid if I force it out Ill crack it since its only fiberglasss. Any hints you can provide would be appreciated!

Tim,

On my boat, the battery box had four small nails in the top edge, two in the front and two in the back. I was able to use a small pry bar and work under the edge to lift the heads. I was then able to pull them out.

The foam has a pretty strong hold on the battery box. I had to dig a fair amount of it out, around the box, to free it up enough to pull the box out. I mostly worked on the left side, digging down to the bottom of the box, then was able to rotate the box toward the left to pull it away from the foam on the right. In the process of removing the foam, I destroyed the vent hoses. I am not sure if there is any way to do it without damaging the hoses. They are very thin and brittle, and they run right next to the battery box.

Your getting into the same situation that I was in. I ended up removing most of the foam in the bow, digging a tunnel up to where the vent inlets are, so that I could replace the vent hoses. I also cut an access hole next to the vent inlets so that I could work from the top.    If your careful, you may be able to splice in new sections of hose and not have to go to the same extreme that I did.

Hope this helps,
Mark

I kind of wish I wouldn't have pull mine out. But I did have a lot of water in the bow that extended to about a foot in front of the battery box. Also, one of the vent hoses was in the wet foam and it had deteriorated to nothing more than black dust and rust.

I am doing the same with my bulkhead plus I am going to use a thru-hull fitting in the bulkhead for the drain hose. I think the fitting will maintain a better seal.

Three layers at the stringers is probably plenty depending on the weight of material used. Remember, the first should be narrow and each subsequent layer wider so each layer is getting glued to the hull and not just the first layer. You should start with mat, but it does not really matter what you end up with since you are not apply a final finish coat.

Yes, overlap the butt joints slightly and stagger joints on subsequent layers. Since you are doing a large area, you might consider using a paint roller to apply the resin. First coat the foam, then lay the dry glass then saturate with resin until soaked. Apply second layer dry, roll on the resin until saturated. Use your grooved resin roller to force out air bubbles. Do not press so hard that you force out the resin or air will get back in. Repeat for each layer, rolling each second layer. You need a minimum of 1/8" thickness of the floor over foam. I would go a bit thicker, especially at high traffic areas.

Do not worry too much if the floor is not very level, you can always mix up some thicken resin as a fairing compound to level it out. Simply trowel it on. Don't worry about getting it perfect as the carpet will hide a lot of imperfections.

Don't forget to taper the edges of the existing (old) floor on a 12:1 taper to receive the new fiberglass. Walk the layers up the taper or up the sides of the boat.

Tim,

US Composites has a FAQ that answers your question. Yes, you can do multiple layers but need to wait 15 to 20 minutes between them.

http://www.shopmaninc.com/faq_foam.html#7

Update: This weekend I made a little bit of progress. I coated the stringer and flooring with epoxy resin prior to installing. I dried out the area underneath the battery box, made a new drain for it, then sealed up the bulkhead with 3M-5200. I then fiberglassed the new stringer in with 3 layers of glass (mat/cloth/mat). I also glassed the bulhead in place. I then poured the foam and trimmed it flat with an angle grinder. Its starting to look like a floor again! All that is left is to glass everything down. Many thanks to DavidF and marks for all the great tips and advice! Pics:

Thanks DavidF! Youre right- the 5200 makes a nice fillet for the glass on the bulkhead. Its secured in there a lot better than it was from the factory, so I think its good to go. The only other critical area in the bilge that I can think of is where the main stringers meet the hull- thats really the only other joint, right? Good call on the fasteners. On the screws in the rear, I predrilled the holes, filled them with epoxy, screwed everything down and then coated the top. I plan on doing the same for the screws on the front floor section (1 at a time).

This project is taking me a little longer than I would have liked, but its coming out pretty decent, I think. I sure dont want to be doing this repair again any time soon!

Absolutely amazing. All the more reason to fly out there for a ride one of these days!