Unintentional stringer job

[Bill Adkins]

Re: Unintentional stringer job

Eric, first of all I need to thank you far the effort and time you put into answering my questions. I can now see exactly the process and format to repair my boat. I was a tech for 38 yrs and being able to plan out a repair and then do it is more important than people may imagine. I was considered as one of the technical experts that people went to for resolution of performance issues with MB for most of my career so if you ever have need of my expertise please feel free to send a note. You Rock. If your ever in my part of the world, I owe you a beer.
Bill Adkins

 

[lundnisswa]

Re: Unintentional stringer job

What a fantastic description of the work you have accomplished.

I new to this site and am currently undertaking a stringer replacement as well, could you tell me if this is a bad plan,
I have 14' continuous stringers, I have access to Roof Truss grade lumber, I plan on using 2 x 10 lumber for the stringers, planed to a thickness of 1", I am planning on waterproofing these with CPES after they are cut to fit.
I have left 1" of fiberglass channel sticking up out of boat, I have sanded and cleaned these channels and will wipe down with acetone prior to final placement, I am going to put a 1/4"thick strip of urethane foam in bottom of channel so the new stringer does not touch fiberglass. To secure the stringer in place I was going to use epoxy thickened with saw dust or some other thickner, after curing I was going to dress up the side with a new fillet, then lay-up fiberglass up the sides.
OK that was my plan, is it faulty??
Does the Transom end of the stringer get glassed to the transom??

Thanks for any pointers, this easily the most informative site that I have found in my research,
Scott R. in North Dakota

 

[erikgreen]

Re: Unintentional stringer job

What a fantastic description of the work you have accomplished.

I new to this site and am currently undertaking a stringer replacement as well, could you tell me if this is a bad plan,
I have 14' continuous stringers, I have access to Roof Truss grade lumber, I plan on using 2 x 10 lumber for the stringers, planed to a thickness of 1", I am planning on waterproofing these with CPES after they are cut to fit.
I have left 1" of fiberglass channel sticking up out of boat, I have sanded and cleaned these channels and will wipe down with acetone prior to final placement, I am going to put a 1/4"thick strip of urethane foam in bottom of channel so the new stringer does not touch fiberglass. To secure the stringer in place I was going to use epoxy thickened with saw dust or some other thickner, after curing I was going to dress up the side with a new fillet, then lay-up fiberglass up the sides.
OK that was my plan, is it faulty??
Does the Transom end of the stringer get glassed to the transom??

Thanks for any pointers, this easily the most informative site that I have found in my research,
Scott R. in North Dakota

Okay, I'll try to take these in order.

First, the roof truss lumber should work ok, but it won't be as strong as something like plywood nor even something like douglas fir. Most truss wood nowadays is something like "white wood" which is a pretty soft, dry wood, lacking oil or resin which would help protect it. The CPES is a good idea, bear in mind that it's mostly just a thinned epoxy... you may save some $$ by just getting epoxy and applying the appropriate thinner (varies by brand, but usually you can buy generic thinner like mineral spirits at your local store). If it were me, I'd use two pieces of 1/2" ply instead of the truss wood, but it's your call.

You can use the original channels, and if you do cleaning them with acetone is a necessity. Ideally you should grind off the surface glass and resin to make sure of a good bond, but the epoxy will forgive a lot. Also be aware that using the existing channels saves time, but is weaker than making new connections using epoxy and glass. It might not matter for your boat unless you're going to take it on the great lakes or ocean though, and your repair job with epoxy will be stronger than the original.

The foam strip will avoid any hard spots, but that shouldn't be much of a problem if you use dimensional lumber anyway. You could skip the foam and float the lumber on thickened epoxy too, but that's more expensive.

For thickener, consider buying something like wood flour or cabosil or milled fibers... if you use your own sawdust, there's a good chance you'll get some unintended contaminants in it that might make the bond weaker than you want in places. But if you're going for really low cost then your own sawdust is ok.. try to keep it clean, and as dry as possible.

Make sure you coat the whole side of the stringer that goes in that channel with epoxy... you want a continuous bond, not just in spots. The fillet probably won't be needed as the existing channel will do much the same job, but if it looks like the glass you're using won't make the turn, I'd suggest a fillet anyway. Glassing the sides (and if possible top) in is necessary too, I'd recommend a minimum layup of two layers of 14-18 oz roving, applied wet on wet and if possible with the epoxy glue for the channels wet too, and the fillets.... that way you get one big piece of FRP, not multiple mechanical bonds.

The transom end of the stringer gets glassed to the transom using the same layup as stringer->hull. It's just as important (if not more) a joint than the one between the stringers and hull. Consider using a small knee (search other threads here for "transom knee") if you want to reinforce it even more.

All in all, a pretty good plan.

Erik

PS: Do also start a thread here to show your progress

 

[lundnisswa]

Re: Unintentional stringer job

Erik, thanks for the response.

All of your pointers will be well taken, I did start a new Thread, titled Lund Nisswa Restoration.

Just one clarification if I may, I agree on using the plywood for stringers but how do I make a 14' continuos stringer with 8' lengths?

Thanks,
Scott

 

[erikgreen]

Re: Unintentional stringer job

You sister together two 1/2 pieces of ply with the joints at staggered intervals... so eg. you cut the first section of stringer 8 feet long, and the first piece to sister to it 4 feet long. The next 8 footer attaches in front of the 4, and then you finish the other side with another 4. You can reinforce the joints with glass if you like, but it'll be plenty strong. Here's a crude pic:


-----------------======== <-- port half 1/2 ply
=======------------------ <-- starboard half 1/2 ply

As long as you make sure when there's a joint on one side it's solid wood on the other, you're fine.

Erik

 

[erikgreen]

Re: Unintentional stringer job

Time for a quick update after many days.

I did about 2 hours of grinding today, to clean out the last of the old deck, get the existing glass ready for the new starboard stringers, and generally clean up. I had about a half inch of powder all over the bilge. I'm glad I wore a respirator full time.

Tomorrow probably more grinding once I vacuum the dust up, and if all the grinding gets done I'll acetone and glue down the starboard stringers, but I probably won't have time to do the fillets and glass.

I also did find some wet wood (but no rot yet) on the transom where the portside engine mount stringer met the transom wood. I'm thinking I'll take the wet stuff out and overlap a temporary patch on there for now. Since I still have a bit of water under the motor mounts (not in) I think I'll end up taking the motor out next fall and redo the transom and mounts then.

The transom stood a car crash hard enough to snap off the transom plate last summer, so it's solid enough to last a season. One nice thing about Sea Ray's "short" engine stringers design is that It'll be relatively easy to do the transom.. I can leave the main stringers in place and just remove the short ones for the work.

Hopefully I'll make some good progress soon and have some nice pics to post.

Erik

 

[Coors]

Re: Unintentional stringer job

While you have it opened up, spray the remaining wood with anti-freeze.
It will kill anything trying to grow in there.

 

[Lou C]

Re: Unintentional stringer job

Another thing you can do is get some of Smith & Co's Clear Penetrating Epoxy Sealer. It is a thinned epoxy that will flow deep into the wood and the carrrier solvents are so nasty, any rot spores wouldn't have a chance of survival. Mix up a couple of batches (WEAR A FUME RESPIRATOR!!) and really let it soak into the wood. I have used this stuff and it works, it really penetrates and gives the wood a good coating of epoxy. Used it in boat repairs and in reparing rot on my back porch.
www.rotdoc.com

 

[erikgreen]

Re: Unintentional stringer job

Okay, I finally took some more pics.

I've been working to get the second main stringer in and the second aft one... that's done now, and both are glassed in.

I bought a 55 pound box of biaxial glass scraps off ebay... I got roving from the same place before. GREAT deal for $40 plus $40 shipping (heavy stuff).

Here's a pic:

What I got was a big box of 1708 biaxial fabric with 8 oz mat attached... identical to the 1 foot wide "tape" I ordered from US Composites for $55, except I got probably 8x as much fabric for less than twice the price. It's mostly in 2x3 foot rectangular pieces, looks like they are cutouts from hull or some other large fabrication. I use a razor blade and the pictured paper shear to cut it to manageable size.

I had so much I went ahead and glassed in the short ribs, glassed the aft stringers to the transom (layers 1 and 2) and glassed the short ribs to the stringers on both sides. A half gallon of resin later, it all looks pretty good:

I see some trimming in my future.

I'm going to add additional layers tomorrow to the transom/stringer joints and another layer on the main stringers.

Then it's time to fabricate the tank compartment bulkheads, and start gluing/glassing them in. After that I'll glue some cleats along the hull/side joint and at deck level on the transom. Last I'll do the fuel tank mounting and the bilge cleanup.

That'll be it for the under-deck structure... then it's on to the deck.

I'm going to be using 3/4 inch ply for the deck because I've got lots of hatch holes and that'll match the contour of the remaining original deck. Thus I can skip a lot of reinforcement under decks... the original structure didn't have it anyway, it just had foam. I may put a few stiffening planks on the deck underside, I'll see.

Onward and upward

Erik

 

[oops!]

Re: Unintentional stringer job

erik....the picks didnt work on my puter......

 

[oops!]

Re: Unintentional stringer job

ok....got em now....


erik...that looks really, really good.

bet your glad!

juuuuusssstt a little more...then its deck time....wahoo!


giv-er heck buddie !

 

[lundnisswa]

Re: Unintentional stringer job

Man your fiberglassing job looks good!
I would like to see closer pictures especially of inside corners.

So in your most current pictures I am looking at 2 layers of 1708? I notice that you did not go over the tops?
Where you made the turns on the floor looks great, so I am gonna remember what you said about making the fold, put in place, and then work out any imperfections.

You know as I have been grinding along the forward tips of where the stringers were I have ran into what were huge air bubbles, and wrinkles, and sags, the manufacturers QC process must have been slacking, maybe one of those "Friday Boats".

In an earlier conversation we had about Truss Lumber for 12' Stringers, well I did go with that, the wood is absolutely knot free and is indeed douglas fir, they are planed down to thickness and currently drying, if I ever get done grinding I will be in for a challenge trying to make the templates for those 12 foot stringers.

I have the Transom Pattern all ready to transfer to wood but;
The Plywood situation is "Killing Me",,,,,,, I bought Ext A/C grade, but I do not like it, seems very porous, the A-side is Ok, but the C-side has cracks and knot all in it, for 40 bucks a sheet they just are not what I was wanting, it is currently on drying racks too, but I could bring it back if I decide to go with another plywood.
I looked at the birch faced Cabinet grade such as you had used, and man that is some nice stuff, the 3/4 inch had 9 plies, and 1/2" had 6 plies, it stated right on the information chart that it was for interior/exterior applications, I am really having a tough time deciding on the plywood, if I could get marine grade I would just get that and be done with it.

Anyway, thanks so much for inputs earlier.
I went looking for the stubby rollers today but how do I know which style holds up to epoxy, the store clerk certainly did not know.

Lund

 

[erikgreen]

Re: Unintentional stringer job

Man your fiberglassing job looks good!
I would like to see closer pictures especially of inside corners.

Sure, I'll take some tomorrow. Of the neater ones, anyway

So in your most current pictures I am looking at 2 layers of 1708? I notice that you did not go over the tops?

Not yet... when I started the stringers I had a limited amount of 1708, so I put it where it counted most... I'll go back and fully coat the stringers in the next couple days. Yes, 2 layers of 1708.

You know as I have been grinding along the forward tips of where the stringers were I have ran into what were huge air bubbles, and wrinkles, and sags, the manufacturers QC process must have been slacking, maybe one of those "Friday Boats".

Yeah, me too. Makes me relax on my own work a bit (I'm a perfectionist sometimes)... if it held up for 25 years with the odd bubble, then my glass sticking up here and there won't hurt too much.

In an earlier conversation we had about Truss Lumber for 12' Stringers, well I did go with that, the wood is absolutely knot free and is indeed douglas fir, they are planed down to thickness and currently drying, if I ever get done grinding I will be in for a challenge trying to make the templates for those 12 foot stringers.

Cool, douglas fir is good stuff. One nice thing about dimensional lumber stringers is that they tend not to create hard spots.

I looked at the birch faced Cabinet grade such as you had used, and man that is some nice stuff, the 3/4 inch had 9 plies, and 1/2" had 6 plies, it stated right on the information chart that it was for interior/exterior applications, I am really having a tough time deciding on the plywood, if I could get marine grade I would just get that and be done with it.

Anyway, thanks so much for inputs earlier.
I went looking for the stubby rollers today but how do I know which style holds up to epoxy, the store clerk certainly did not know.

Lund

I like the idea of marine grade, but I just can't bring myself to spend $80 a sheet for plywood..... I know it's strong, but if it gets water soaked it's coming out anyway.

The rollers I use are a foam type... in the paint section, they're 1 inch across, white foam that's perfectly smooth, with a handle that's a 3/16 or so wire with a blue plastic grip. I use the ones that are about 7 inches wide, the brand name is "Shur-line foam mini rollers"... they're sold for about $5 for the handle with one roller, and about the same for a refill pack of two rollers. They work great, just remember to pull the roller off the handle before the epoxy hardens.

 

[Coors]

Re: Unintentional stringer job

The cracks and knot hole voids will help any resin stick better

 

[erikgreen]

Re: Unintentional stringer job

The cracks and knot hole voids will help any resin stick better

LOL... so I should use CD-X grade or worse?


Here's some pics from today. First, I found a couple interesting bits in the junk pile. The first one is a cross section of my new stringers, cut when I made a limber hole:

The dark band in the middle is the "peanut butter" glue.

Here's an example of a fillet I removed before I glassed it in... I found I needed more work on the stringers it was attached to than I'd done, so I pulled it out.

Here's the view from the back side... note that the epoxy didn't fail, the plywood did... if I recall right I had to separate this with a sledgehammer:

Here's a couple close-ups of joints I did in biaxial glass. An inside corner, with several layers made up of the glass holding the cross piece to the hull, the stringer to the cross piece, two holding the stringer to the hull... I think that's it. Note how the stitching on the biaxial likes to stick out of the resin.

And here's a view along my starboard stringer, looking forward. Nice even glass. Sorry about the dust... I'll be done grinding belowdecks only when I put the deck on, I think :\

I spend some time today glassing a couple tight corners. I also added one more layer of glass to the outboard side of the main stringer joint. I noticed about half way through that I was using way, way more epoxy than I should have been.

I realized I'd somehow grabbed a much thicker piece out of my "bulk biaxial" box, and that I was glassing something like 30 oz. biaxial onto the stringers. Took about a half gallon of resin for 12 square feet of the stuff, but I got it wet out. Whew.

Next up is bulkhead fabrication.

Erik

 

[oops!]

Re: Unintentional stringer job

I was glassing something like 30 oz. biaxial onto the stringers. Took about a half gallon of resin for 12 square feet of the stuff, but I got it wet out. Whew.

man thats crazy....30 oz...what a pita....

good thing your working smaller sections.......i did 2 24 layers at the same time, 11 feet by 50ins. just about killed me to get it done before it kicked!

this project is looking fantastic erik.

 

[erikgreen]

Re: Unintentional stringer job

Okay, it's update time.

I finally got a camera to use, and I hate posting updates without pics.

I've been busy. Both stringers and all bulkheads are now glassed in, and covered with glass. I put the shelf supports in the fuel tank compartment, glassed in the forward bulkhead at the step-down, made a curved piece of glass for the sump there, and glued it all in place. Pics follow.

First, here's the tank compartment, all glassed in:

Then, I put in the shelf supports for the tank floor. These are 1 inch aluminum angles, drilled for bolts, and through-bolted to the stringers with 1/4" stainless steel bolts and nuts.

I had to think really hard about putting holes in the stringers after going to all that trouble to glass them in and waterproof them. But, I decided it's the right way to go, so I pre-drilled the holes, then filled them with PL construction sealant (more on this in a bit), pushed the bolts in, wiped off the excess, then put more PL under the angle and tightened the bolts. It's never coming off, even if I want it to (!).

After that, I worked on the sump at the step-down to the cuddy. It's basically a semi-circular hole in the deck that leads down to the bilge. I glassed about four pieces of biaxial, fully wet out, onto a plastic bucket in a semicircle, then once hard I used the bucket to scribe the semicircle for the sump. I cut it out with a roto-zip, then trimmed the semicircle to fit the hole and glued it in. I used lots of peanut butter to avoid any leaks. This won't show anyway, especially after I get done coating the bilge soon.

Finally I glued in the forward bulkhead that forms the back side of the sump, and has limber holes for drainage. I also glassed it in to use up the last of my resin... I have more on order, hopefully it arrives soon.

The extra compartment that this forms ahead of the fuel tank will be a forward battery compartment. It's going to bounce the batteries around more than I'd like being ahead of the fuel tank, and I'll have to vent it properly, but it will fit two group 24 batteries or one larger one for powering the side scan, heater, and extra lights. I cut some space out of the step down to get enough for it.

So, assuming all this hardens properly and comes out, I still need to do some shelf rails in the forward battery box, then cut holes for the fuel filler, vent, and fuel line to the engine, and seal those openings.

After that it's a bit of grinding, a thorough cleaning, and I've decided to paint sections of my bilge where there will be storage. I'm going to experiment with pigmented epoxy for this, but I need to get my new epoxy order in first.

I better hurry up, spring's coming

Erik

 

[erikgreen]

Re: Unintentional stringer job

One more thing... the PL cement sealer.

I found out that the "PL Cement crack and mortar sealer" is identical to 3m 5200 in most ways, the differences being pigment (it's gray) and a couple inactive ingredients. Double check the ingredient list if you don't believe me

It hardens like 5200 (slightly soft) is polyurethane (tough) and is cheap ($5/tube).

So I'm using it where it won't show in lieu of 5200, under and around the fuel tank.

I'll be trying PL construction adhesive to put the deck on... should be interesting (also cheaper and neater than epoxy).

Erik

 

[lundnisswa]

Re: Unintentional stringer job

Erik, your boat is looking great, really looking forward to seeing it progress.

Got the message on making sure to resin the entire Transom prior install.

The through hull fittings and engine mount bolts have me trying to decide what to do, I have read about over sizing and filling with resin, then redrill, what do you do, I know I want them sealed with resin thoroughly, and I was going to use 5200 when the bolts go through too, my transom has 11 holes to deal with.

Found the nicest mixing cups today, they have all the ratios marked out, and only .30cents each, I will use them until I gain confidence in the pumps dispensing the correct volume for a 2:1 ratio.

I used a company called John greer and associates for the Resins and Pour Foam, do you know anything about this stuff?

I am building a mock up now to represent a stringer and Bulkhead, need lots of practice with applying the cloth.

How large of a section do you lay up at a time, and how do you know how much resin to mix? I was going to do a 4 foot section first, both sides of stringer, perform fillet then two layers of 1708 overlapped and then one layer 1708 over the top, is the a reasonable area, or is it too much? Got a bunch more acetone today, takes quite a bit to do the serious cleaning required.

I assume by one of your last messages to me, when you said sanding and grinding on the transom, this was so the Resin/cloth has something better to grip to? Do you just Rough Sand it? I seriously scuffed up the inner parts of the Transom with the Grinder, for sandwiching them, but I had not planned on doing that to the exterior of the Ply, or the Stringers for that matter, should I?

One more thing, I am seriously considering using the PL for adhering the Transom wood and the stringer bedding, the 28oz tubes are a bargain, and that stuff really grabs, what do you think?

Sorry for hogging your space, I am charging on here and am finalizing things then doing it, I am fortunate to be semi Retired and have plenty of time and energy.

Thanks again.
Lund

 

[erikgreen]

Re: Unintentional stringer job

Erik, your boat is looking great, really looking forward to seeing it progress.

Got the message on making sure to resin the entire Transom prior install.

The through hull fittings and engine mount bolts have me trying to decide what to do, I have read about over sizing and filling with resin, then redrill, what do you do, I know I want them sealed with resin thoroughly, and I was going to use 5200 when the bolts go through too, my transom has 11 holes to deal with.

Good call. That's the reason most transoms are rotten in the first place, they got drilled into and the holes didn't get sealed.

I tend to use the pre-drill and fill technique for relatively shallow or easy to get to holes... it would have been really hard to use on my stringers for mounting those fuel tank shelves, there was too much chance of wandering with the drill bit.

Just remember the important thing is to keep the water away, or if it gets in to limit its spread. Bear in mind that the main thing that keeps boats in good condition isn't the build or materials, it's the maintenance. Don't be afraid to check on your work next year, and fix anything that's wrong.

Found the nicest mixing cups today, they have all the ratios marked out, and only .30cents each, I will use them until I gain confidence in the pumps dispensing the correct volume for a 2:1 ratio.

I used a company called John greer and associates for the Resins and Pour Foam, do you know anything about this stuff?

I haven't used that company, and I've only poured foam on one boat, not mine. It's pretty simple to use, just be ready to pour when you mix it

I am building a mock up now to represent a stringer and Bulkhead, need lots of practice with applying the cloth.

How large of a section do you lay up at a time, and how do you know how much resin to mix? I was going to do a 4 foot section first, both sides of stringer, perform fillet then two layers of 1708 overlapped and then one layer 1708 over the top, is the a reasonable area, or is it too much? Got a bunch more acetone today, takes quite a bit to do the serious cleaning required.

The strongest stringers will be made by doing one layer at a time.. instead of doing a 4 foot section, consider doing the whole thing in steps... glue in place one time, fillet the next time, glass the first layer next, finish glassing next. It's ideal (and strongest) to work wet on wet epoxy, but if you do the prep between steps (over 24 hours sand and acetone) it'll still be really strong.

I've been typically mixing my resin in batches as large as I comfortably can, which usually amounts to 20 ounces at a time - that's one 16 oz cup of resin and one four oz. measure of hardener. The stuff hardens slowly enough if I keep it in the paint roller tray that I can just mix more as I go and it's still wet on wet.

For my stringers, I used about 20 oz. of epoxy mixed with about a half pound of wood flour to glue each one in place. The fillets took about 60-70 ounces of epoxy plus a pound of wood flour each.

I'd suggest you just mix up about a 20 oz. or whatever cup size batch and see how far it gets you.. you won't take long to get a rough idea how much resin goes how far. You can't mix a big batch of it anyway without risking overheating.

Roughly the steps (each one evening, 2-3 hours) I took to do my stringers were:

*Cut stringer to size (port), Laminate with peanut butter
*coat with spare epoxy from other tasks over time
*Glue stringer in place with peanut butter (measure 3x-4x)
*Fillet and glass port stringer (4 hours)
*fillet and glass aft stringer (2 hours)
*cut stringer to size(starboard), laminate
*Glue stringer in place
*Fillet and glass starboard stringer
*Fillet and glass aft stringer

I assume by one of your last messages to me, when you said sanding and grinding on the transom, this was so the Resin/cloth has something better to grip to? Do you just Rough Sand it? I seriously scuffed up the inner parts of the Transom with the Grinder, for sandwiching them, but I had not planned on doing that to the exterior of the Ply, or the Stringers for that matter, should I?

It depends on how long it is since you epoxied it. If your wood has a coat of something on it, epoxy or otherwise, you need to rough sand it and preferably wipe with acetone to make sure it's clean. Epoxy will bond anyway, but it'll bond better with clean stuff.

If you've never epoxied a given piece of wood, it's a judgement call. I like to at least acetone the wood in case there's grease or something else on it from the manufacturing process. It only takes a few minutes, and it's good insurance. If the acetone soaks in you may want to let it dry a few minutes before coating or glassing.

One more thing, I am seriously considering using the PL for adhering the Transom wood and the stringer bedding, the 28oz tubes are a bargain, and that stuff really grabs, what do you think?

Sorry for hogging your space, I am charging on here and am finalizing things then doing it, I am fortunate to be semi Retired and have plenty of time and energy.

Sure, go for it with the PL. It's gaining popularity here fast, and some of the more knowledgeable folks (eg. Tashasdaddy) have been using it a while.

More power to ya... I wish I could be semi retired... I'm actually thinking of working building fishing boats when I do that, although it's just a dream at this point, I've got a long time to go.

Erik