Repairing Foam Filled Stringers

[jrodp]

I have removed the deck/floor of my 78 MonArk and found the stringer system appears to be a one piece, all fiberglass and foam filled stringer system. I cut part of the top off one of the stringers off where it was broken from a seat mount and the foam is all wet and I assume the stringer is full of water. See the attached pics.

Any suggestions on the best way to cut the tops off the stringers to get the foam out and also how to replace the fiberglass tops I cut out? Should I cut the entire length of the stringer or just a few sections of each, enough to get the foam/water out? Should I save the pieces I cut out and use them to put back in and glass over somehow?

I have never done any fiberglassing before but after reading through some of the rebuilds on this forum, and watching some videos, I believe I can handle it....with a little assistance maybe.

 

[zool]

If I had to do it, I would grind all the tops, sides, and areas adjacent to the stringers clean 1st. Then cut out the caps in sections at the top of the sides, leaving the rounded edge with the cutout cap sections and leaving a foot or so between cutouts intact to maintain integrity. Clean out all the old foam and crud. Then lay the cutout cap sections back in place and glass in the whole stringer system with 1708/poly resin or 1700/epoxy. Then drill holes along the stringer tops to pour in 2 part foam til it weaps out the holes, then glass in the holes and ur done.

 

[Scott Danforth]

if there is no wood in the stringers, you just need to remove the foam

so in that case, use a 3" cup brush on the end of a drill extension, grind the foam up with a cup brush, and vac out with the shop vac.

 

[jrodp]

I took Zool's advice and cleaned then cut the caps out of a few sections of the stringers and cleaned out all the old wet foam. After having to take a break from the deck to replace the transom, I am ready to start repairing the stringers.

I know this is a bit of a contentious question, and has been debated a lot, but I am wondering what the current thoughts are of using a hybrid solution of a few strips of the pink or blue foam insulation (from Lowes or Home Depot), cut to fit inside the stringer sections and laying on the hull, and then use the pour in foam on top of that? Has anyone used both together like that? The old foam that was inside the stringers was not solid and had lots of empty spaces. I was thinking the strips of the foam insulation would at least provide some filler in places where maybe the expanding foam didn't fill out.

 

[Scott Danforth]

I know this is a bit of a contentious question, and has been debated a lot, but I am wondering what the current thoughts are of using a hybrid solution of a few strips of the pink or blue foam insulation (from Lowes or Home Depot), cut to fit inside the stringer sections and laying on the hull, and then use the pour in foam on top of that?

its best if the foam can attach to the fiberglass. the strength is as a composite member.

by putting in the strips of foam, first, it will dissolve a bit, however it will not be adhered to the inside of the fiberglass. so you will be promoting cracking vs resisting cracking

 

[JASinIL2006]

I think you'd be better served by just trying to do a better job foaming the stringers than the factory did. Trying to pour foam around the pre-cut foam boards would be a real pain, not to mention you would be robbing your boat of much of the strength of this type of stringer as Scott suggested.