Repair of sideck carlin/stringers

[Guest]

Fellow DSers,

My DS1 (1971-ish, Oday, #3501) since purchase about a year ago has had more side deck deflection when captain and crew were hiked-out than is good for comfort. As a winter project I had planned to stiffen this area by fabricating and installing additional knees (there already is one at the aft end of the cuddy) between the deck and hull. However, after removing the combings, the source of the deflection is apparent.

The wooden carlins (fore/aft structural beam) have begun to rot and the two fiberglass panels that boxed in the beam have started to separate.

Rather than just adding the knees I am considering the following: cutting out the bottom of the fiberglass box that contains the wooden beam, removing the beam entirely, develop a pattern from 1/4 inch marine plywood, using the pattern, laminate in enough layers of epoxied together plywood to make a beam of the same thickness (height), replace the bottom of the box with fibreglass.

Each layer of plywood would be epoxy sealed before installation.

Also, I expect that much of the water that contributed to the rot came through the holes for the wood screws that secured the combings. Therefore, I intend to use through bolts to secure the combings. This will allow me to epoxy seal the holes.

Can anyone provide comment and guidance to keep Sparkle Grrl sailing for another 30?

Thanks in advance!

Gary Tabor (ratracer-at-rust.net)

[Guest]

Matt Hammatt wrote:

>Gary,
>
>Why not use a closed cell foam instead of plywood? Plywood and resin will rot
>and if you use a foam similar to divinycell or corecell, you would not have
>any loss of strength and it would be lighter.
>
>Matt Hammatt


Matt,

Thanks for the input.

I too had visions of foam when the problem became apparent. At the time I thought of using expanding polyurethane foam

The procedure would be something like: remove bottom of boxed section, remove rotted wood, replace bottom of boxed section with fiberglass and resin, pour in expanding foam, remove excess foam and seal up hole(s) used to pour in foam.

This will work, but will not provide the side deck stiffness I desire. Also, the fasteners for the coamings must either be "wood screws" which would bite into the foam or through bolts backed up with washers and nuts which would crush the foam. The foam can not support these fastener loads.

Let me know if I've missed something.

Gary Tabor

Gary Tabor (ratracer-at-rust.net)

[Guest]

I had/have the same probelem on my DS #4000 which sat out side incovered for twenty years before i got her. As a temporary repair i sistered the side rails by removing the rotten coaming and screw 2x2's in their place. Still not too stiff but better.

Bob Torson (safehbr-at-pioneer.net)

[Guest]

>Gary,
>If you were making them over using 80kg/m^3 foam you could insert a solid
>glass plate 3mm think in way of the fasteners and it would work fine. I also
>believe that if you laminated the part with epoxy and e-glass uni's then
>cover it with a ply of400gsm double bias it would be stiffer and lighter.+
>Matt


Matt,

Hmmm ... I'm warming to your suggestion.

I've checked out several sites for the materials and the engineering's certainly sound. The foam will also be easier to work with (cut and bend) than the plywood.

Perhaps I'd fine tune your repair scheme by adding one or two layers of the uni-directional glass tape to the top of the fabricated carlin (bonded to the underside of the side deck) to improve compression strength under bending. I'm also considering holding the uni tape in place by applying tension to the ends as the resin cures. This should simplify retention during cure as well as assuring that fibers are aligned in the direction of primary (bending) stress.

Regarding your idea of inserting a glass plate for the fasteners to bite into. I'll either fabricate my own fiberglass plates or through-bolt and use a fender washer or better to spread the load.

Gary

Gary Tabor (ratracer-at-rust.net)

[SaltLakeSailer]

After removing the coamings to repair or replace due to cracks, I noticed the same excessive flex in the side-decks. This possibly led to the cracks in the coamings in the first place. Any updates or further suggestions on what worked best to stiffen the side decks?

[jackal]

When fiberglassing the carlins back in, could I use a strip of fiberglass cloth/tape of the appropriate width? I've seen some in the 2, 3, 4, and 6 inch denominations. As long as 50 yards.

Have we already had the epoxy resin vs. polyester resin debate and I just can't find it? My local repair shop said they only do polyester repairs. I've been reading Don Casey's writings that indicate the strength of a polyester bond will be around 20 percent weaker than the same bond made with epoxy.

Thanks!

The attached picture is how mine look right now. I haven't started the project.

[GreenLake]

Yes, you can use strips. If using epoxy, you want cloth, not the mat that they used in the factory. If you can source / make corresponding strips of plastic sheeting / foil then you can lay your cloth strip on the plastic (which should be a bit wider) wet it out, squeeze out the excess resin and then use plastic and cloth like "tape", essentially you get a backing tape to your wet laminate. Makes handling a lot easier. You can also use a 6" strip and a 4" strip - that gets you two layers, and if you align them right, you get a gradual transition in laminate. You assemble that on the same plastic "backing tape". (Or, you can go whole hog and use vacuum bagging - that's a different discussion and you'd need to learn about it first).

I'm partial to working with epoxy (always mindful to not touch the hardener or uncured mix because it can sensitize) and I don't like the styrene smell of polyester. It bonds better to cured polyester than polyester resin, but for some applications that may not be the crucial factor. It also shrinks on curing, setting up tension in the repair. Again, some repairs are forgiving. Polyester promises not to give you grief if you want to cover it with gelcoat, although well mixed/cured/prepared epoxy surfaces apparently work with gelcoat despite the reputation to the contrary (it's not a black and white).

If you haven't worked with either material, then do a small sample piece with your chosen resin. Get the feel for it.

[jackal]

Any suggestions on the core material? I'm a little hesitant about the foam... Marine Plywood? Balsa Core?

Do I want more than one strip of wood for each side for easier bending and shaping?

[K.C. Walker]

If you are replacing the wood, save yourself aggravation and use epoxy. Epoxy sticks much better to wood than polyester does. It sticks better to old polyester than polyester does but it's not as much of an issue as with the wood. Though the original was fiberglassed in, if you use epoxy this is not necessary. In this situation the fiberglass mat added no additional strength. It was just to attempt to encapsulate the wood. Fiberglass cloth would add more strength but with this dimension of wood, it would be insignificant. If you make sure and have a good coating of epoxy on all sides of your wood so that it is encapsulated you will have all the protection for it that you need. When you screw your comings back in, be sure to seal the holes with a bit of epoxy, as well. wax your screws and they will back out just fine when you need it.

[GreenLake]

As K.C. wrote, with this small clarification:

With the wax, you can screw before the epoxy has set, thus forming a perfectly threaded hole around the screw, even if you had overdrilled before.

If it weren't for the need to screw the coamings into something, one could replace the carlins with a hollow fiberglass tube (any non-waterlogging material would do to hold the shape while you laminate). But, K.C. is right, the wood works there as designed and just glue it place instead of trying to hold it in place with glass. So much easier. Epoxy sealing works fine, and was something that they may not have had in their repertoire then when they built the original.

Hold on to your thoughts on cloth tape though, for when you might want to add stringers under the cuddy deck. Those could be wood, but you can also make them hollow - nothing screws into them, except for the foredeck cleat - that needs to have a backing plate whether it's part of the stringer or a separate piece. The foredeck can be soft / get soft, so there may be a reason to add some addtl stringers there.

[jackal]

Thanks very much for the helpful advice!

I'm seeing 2'x4' sheets of end grain Balsa 3/4" thick on the Jamestown website. I could run them through my table saw and cut 1.5" wide strips. (1.5"x3/4"x4')

So the carlins are 1.5"x1.5" and about 7 feet long (if memory serves). I would need 2 pieces (each one being 1.5" x 3/4" x 4') to make a 1.5"x1.5"x4'. I would still need 3 more feet.

If anyone reading this is still awake...we're looking at four strips for each side of the boat. I'm thinking I would stagger the combination of 4 foot and 3 foot pieces. Would I epoxy them together and then install, or install each piece by itself so they can adjust to the curvature of the sides. How flexible is Balsa?

Will this work?

Honestly, I was hoping to get one continuous piece of core material for each side.

[GreenLake]

My immediate reaction is: you don't want to use balsa.

The wood that's there originally is strong enough to hold the wood screws that attach the coamings. Balsa wouldn't qualify for that (and forget the weight savings-the DS isn't light enough for that to matter).

If you were to use balsa, it would solely be the core on which to laminate, and you would need to a) make your laminate strong enough to hold the loads (read, beefier than what was there before) and b) you would need to through-bolt the coamings instead of being able to use wood screws. There appears to be no benefit to using balsa over structural wood, which you can then install without having to use glass at all.

You can scarf-join the wood into a single piece. It should bend enough to accommodate the gentle curve. Because of the scarf join you would need four 4' pieces, the overlap should be a bit less than a foot. I think a 1 in 8 scarf would be fine. That gives you 4" at the end for final trim. Get some hardwood, and given the location in the boat (where it is out of the water) and sealing all 6 sides of it (and any holes) with epoxy, I don't think you'll have issues with rot, even if the wood you select isn't a traditional boat-building material.

As K.C. wrote, you can just glue that in place using epoxy. There should be enough contact area for the glue joint, so there's no need to add glass.

Epoxy doesn't like UV. With the coamings installed and the wood being underneath the decks, UV exposure is already reduced. However, I would still give it a bit of paint, to be on the safe side, because over the lifetime of the boat, even reflected UV could add up. It doesn't matter what paint, because it's not visible, so you can use a coat or two of some automotive spray paint, or whatever paint you use for the inside of the hull.

[K.C. Walker]

I'm with Green Lake regarding balsa. It's not the appropriate wood for this particular application. You don't really need to do a core, what you need is a stringer that can hold screws. The side deck becomes quite stiff once it is supported by decent wood, especially after you screw the coaming back on. I don't think you need to change the dimensions from the original. I'd be inclined to use southern yellow pine, but even a soft pine would not be much of a problem, especially if you do the epoxy in the screw holes thing. I think if you poke around in the piles at a half decent lumberyard you should be able to find full-length pieces that you can rip what you need out of.

[jackal]

Ok, thanks for the heads up on the balsa. Bad case of tunnel vision. It's core material and belongs between two layers of laminate. This isn't that application.

I'll go pick up some 2"x2"x8' southern yellow pine. Is cedar an option, or should I stick with pine?

What's the best method for neatly cutting out the bottom of the fiberglass box to get the wood out? Dremel tool?

[GreenLake]

Cedar is pretty soft. If anything I would go with harder wood. In a wooden boat, for similar purposes it might call for white oak for example, red oak being less rot-resistant - however, with epoxy encapsulation I wouldn't hesitate to use the latter in your case, and it's easier to get. In other words, I would read K.C.'s recommendation of pine as the minimum in terms of strength and ability to hold screws.

If it's not too substantial, you may be able to just snap it off and then sand flush. When I last looked at my boat, it seemed pretty flimsy, but it might be more tenacious than I imagine. For a tool, I think nothing beats a Fein multimaster (or knockoff). You can get the blade flush with the underside of the deck, I think it fits, and as it vibrates, it cuts on only one side. (If you haven't seen any of these, the fact that there is a bit "missing" from the cutting disk is not a mistake in the photo, the disk doesn't rotate, just vibrates. Which means you can't cut yourself on it - they use that kind of tool to cut casts off people).