Stringer And Deck repair

[oceansswk]

Hello,
I have a 1988 Sport Craft and while I was working on the boat I noticed the fiberglass mat on the stringers was black, I began probing around and I found the stringers where like peat moss. I could not remove the deck without cutting it out, which I did today. Water was seeping out of the stringers once the foam was removed. I am not sure what material is the best, wood, Coosa etc. I read someone said pressure treated plywood is good for the stringers yes or no? Once that decision is made what material do I use to cover the material to encase. I will use epoxy not sure on the proper fiberglass. Do I cut the top of the stringer off and clean out the center or do I cut one side off to replace the core material ? I appreciate any help you can give me. Once the stringers are repaired I need to make a new deck.

[missinginaction]

Hopefully some of the more senior people will post as well and help you out. I'm not sure how large your boat is or what the engine mounting arrangement is, but I'll show you how I solved this problem on my boat. I'll attach some pictures showing the stringer fabrication on my 1973 Silverton. I used epoxy and 1708 biaxle stitchmat. This worked out OK, but PAR has since weighed in and told me that I could have saved some epoxy by using cloth and skipping the mat. I may have overbuilt the stringers, but what the heck, you live and learn.

PAR instructed me to remove the old stringers by using a long sawsall blade and bending the blade slightly so that it can be moved along the inside bottom of the hull. This technique works very well and you'll have the old stringers out in no time. Be sure that you've thought through the whole job though. I made a jig so that I could install the engine mounts exactly where they were originally and of course the stringers as well.

I made my stringers out of a product called Formular made by owens corning. It's just foam insulation and it doesn't absorb water. It isn't strong at all, but that's not the point. Once you coat the stringer with a number of layers of fiberglass and resin you will have a very solid assembly. Books such as Dave Gerrs "The elements of boat strength" will provide formulas that will determine how thick your fiberglass should be. Perhaps some of the more senior members here can give you a quick approximation based on the size of your boat.

Photo 1 shows the stringer being made up on the garage. Photo 2 shows the stringers being installed in the boat. At that point there was only one thin layer of glass on the stringer. This was applied in the workshop. The wooden blocks are installed where the engine beds bolt in, they are there since the foam is not strong in compression and I needed a strong material to clamp to. Photo 3 shows the stringers installed prior to painting. Photo 4 shows the original stringers and the jig I made so that I could install the new engine beds and stringers exactly where the old ones came out. If you study the photo you will see how the jig straddles the engine bay and the vertical pieces of plywood rest on the engine beds. Once the new stringers were ready to go all I had to do was install the jig and I had a guide to aid me in getting the new stringers in the correct location.

MIA

[PAR]

First off, welcome aboard Oceansswk. Can I assume you're from south Jersey?

As you've found out, your stringers are shot. This isn't uncommon and there are many, many previous threads on this site covering the different aspects of replacement. The key question now is, (picture your wife asking this) "will the boat be worth all this trouble when you're done". This can be a difficult question to answer, mostly because you don't know how bad a job this is yet. If the engine, electronics, trailer and hull are in good shape, the boat looks good and has some resale value, then go for it. On the other hand, if it needs an engine, the electrics and plumbing are shot and the whole boat looks like the Russian 3rd Army spent their last payday partying in it, then maybe she's spent and you should look for a different project.

Your choice of epoxy is a good one and all I recommend for the back yard builder. It's stronger, more water tight and easier to work with then the other choices, even though it does cost a little more.

When using epoxy, you don't need nor is it desirable to use mat. Use cloth or knitted fabrics instead.

The trick I told MIA (reciprocating saw) is a good one if you like to save time, but heed the warnings. You can just as easily cut through the hull with a tool like this, as easily as you can the stringers, so watch what you're doing.

Generally, you want to remove the damaged areas, clean, grind and other wise get back to good material, then bond and laminate new stuff in its place. Don't use pressure treated plywood for your stringers. Epoxy doesn't like to stick to the new PT chemicals they're using now. Besides, if you do it right, then you'll be dead the next time this issue comes up on your boat, which is pretty good durability if you ask me.

The first thing you should do is get the boat supported firmly. The trailer works well, especially if the keel area has several supports. You want to be able to walk around inside the boat with many of it's support elements removed, without the hull becoming distorted or warped. This often requires some additional bracing and blocking.

This will get you started.

[oceansswk]

I appreciate the information you both have given me. The boat is a 20 CC motor runs good. I asked the same question about value to a friend of mine who works in the marine industry an he said you could spend 10000.00 or more on another boat and the stringers could also be bad. Now that I have removed the floor and foam it was very poorly build and quality was not job one. There were no drain hole between compartments, matting was not installed on all exposed wood areas, etc. I think the sawsall is a great idea. The lumber industry has pressure microlambs, lvl and all are structural. Then I shopped XL panels from greenwood products very expensive 125.00/sheet. I do not know what to use at this point and would appreciate both inputs. Yes I am from So Jersey. Thank You both

[PAR]

Use dimensional lumber from you local Lowe's/Depot. Clear and straight grained 1 by stock is best. Laminate together if you need bulk.

You've discovered the reason most of these era boats die an early death. Manufactures were attempting to save on everything, resin, mat, labor, etc. The results are clear. You should check the transom also, which also suffers from similar issues, particularly is an outboard.

Use dimensional lumber on the longitudinal stringers. Use exterior plywood for the athwartship stiffeners and of course the sole (floor). Make sure the various compartments that are formed as the stringers and cross pieces go in, have drain holes to let out accumulated moisture at the transom.

See if you can find a Kamco building supply in your area (Trenton?), they'll have marine grades of plywood, which is the best thing for the sole.

Can you post pictures?

[oceansswk]

Hello Par, Thanks for your input. I will take Pictures tomorrow and post. I will see if Kamco is in the area

[AroMarine]

If you are near the shore Nacote Creek Marina in Port Republic and South Jersey Lumbermans in Mays Landing have marine plywood in stock

[oceansswk]

Good Evening Everyone,
I attempted to upload 4 pictures and is was rejected due to size. How do I upload pictures of the stringers. Yes I can go to Lumberman' s for the plywood. I am waiting on prices for epoxy etc. I did remove the stringers on the starboard side to start prepping that.
Thanks

[gonzo]

Mat and epoxy don't work well together. It has a binder that disolves with the styrene on polyester or vinylester resins. Epoxy won't bind properly to the fibers.

[PAR]

As a rule you don't need, nor do you want to use mat in an epoxy matrix.

[Fanie]

I attempted to upload 4 pictures and is was rejected due to size. How do I upload pictures of the stringers.

Download a little program called FastStone Capture, you capture a reasonable viewable picture off the viewing screen. Freeware.

Par has answered the stringer questions so many times he has a standard response he just copy and paste...

[PAR]

This assumes I'm willing to look up one of my previous replies Fanie . . .

[Fanie]

That wasn't what I meant One thing, we are lucky to have you on the forum, your advice is always sound and spot on. Doesn't leave much for the rest of us to comment on though

[PAR]

Now you're just kissing up . . .

[missinginaction]

oceansswk.....

I used to have the same problem. When you go to upload photos note that file size restrictions apply. For instance a jpeg file can be no larger than 2mb.
So you may want to check the size of the photo file you're trying to transfer.

Now, I have a comment regarding the stitchmat. I certainly respect PAR's expertise. That said I also have confidence in Joe Merton at Mertons Fiberglass Supply. Joe recommended that I use 1708 biaxle stitchmat (knytex) to fabricate my stringers. I followed Joes advise and was very pleased with the results.

I 'm confused as I don't understand why this stitchmat (knytex) is considered to be a poor product to use with epoxy. Joe Merton made no mention of compatability issues with epoxy resin systems. It's in the boat and made a very substantial stringer matrix I did some research and found a book called Composites Design Manual by James A. Quinn. In the book it states (with regard to kyntek fabrics) that:

"All fiberglass reinforcement fabric used in composite laminates has a chemical finish.......compatable with the resin matrix with which they are used. This sizing is generally an organo-silane chemistry and is compatable with polyester, vinylester and epoxy resin systems."

I have no idea what an "organo-silane chemistry" is.

Help me out here..I'm just trying to understand opposing views from two respected sources.

Thanks

MIA