Cold Mold & Chine Repair

[cronk]

I am starting the restoration/repair of a 1969 30' cold molded Ridgway Express Sportfisherman and have rot damage to the chines and mahagony laminations in the transom area. I have removed the entire damaged section of the chine and cut out the damage on the hull side including the glass. I will need to replace the (2) layers of 3/8" mahogany and glass from the chine to the shear clamp that is an area of about 40" along the chine and about 36" to the shear. My plan is to use a temporary sheet of plywood as a form on the inside and re-laminate the open section in sperate layers using the temp ply as a form. Then remove temp ply and insatll the replacement mahogany chine (using original profile) by screwing from the outside and countersinking screw heads. My concern is the butt joint between the original plys and the new plys. There are other areas of damage in the hull sides and am wondering if I should add an additional layer of 1/4" to the insides of the hulls ( I have removed all horizontal bracing to accomodate the raised helm deck) I would appreciate any thoughts on this process of cold mold repair.

[Paul Scheuer]

I expected the pros to chime in by now.

If I understand it correctly, your plan is to laminate the 3/4 inch hull with thin layers against a 1/4 inch temporary backer and replace the chine after the hull is formed.

The first question would be, why not put the chine in first ?

What little cold molding repairs I've see involved laying succesively larger lamination layers in correspondingly larger cut out areas so that there is no single butt joint, but a series of steps at the edges of the new wood.

How do you plan to clamp the laminations ?

[imported_Conrad]

The fact that it's only wto layers makes it a bit harder to get a repair of equal strength with the original sections. I'd make a small jig for my router that will allow you to cut a 12:1 scarf where the old and new meet. Make the jig/guide small, say only 10" wide, so you can move it around easily while doing a section at a time. A bit of clean up with a hand plane or scraper, some epoxy, and you're all set.

If you don't feel up to the above, an extra layer on the inside will certainly add the strength you seek, but will look like a second-guessed repair. Maybe that doesn't matter in this situation?

For support on the inside while laminating, I'd probably use a series of battens spanning the opening, say 8" apart. The reason is that then you can see from the inside (as well as outside) how everything is laying down as the fasteners go in, pulling everything together. Fasten from the outside using reference lines to let you know where the battens are. One advantage of cold molded is that like glass, you need only take out the bad sections, not run all the way to the original plank end- but good scarfs are important! Good luck!

[Buddy Sharpton]

Before you remove anything, can you cover the inside of the area to be removed with polyethene, then staple and glue several layers of thin, say 1/8 junk plywood to save your shape. Then remove bad wood. You could consider using your router to make several 1/8 deep shelves instead of a diagonal tapering scarf, but it will need more than just two staggered 3/8 deep butt joints to really trust it. If you go the "stepped shelves" router route ( couldn't help myself), it will go faster and be every bit as strong as you need, invisibly repaired, good as new inside and out without patches of extra inside braces. That chine really should have at least that 12 to one diagonal scarf. I suppose here would be one place to consider adding a "sister" chine for several feet at the break instead off removing several feet of godd chine forward of the cutout, but removal would be invisible.

[cronk]

Thanks for the specific and detailed assistance. The common denominator appears to be a stepped transition between old and new to avoid "in-line butt joints". If the load placed on the joints is from the outside water pressure, then I am assuming that the steps will get larger from inside to outside. How much is enough of a stepped lap? 1"-2". It does make sense to set the chine first prior to adding the lamination repairs (I have cut all of the old ring shank nails flush with the bottom and sides so this should go easy) I will screw into the new chine section from the outside countersinking the heads (brass screws?). I could use a little help clarifying a 12:1 spline. I am getting closer to figuring this thing out. Thanks again.

[Buddy Sharpton]

Twelve to one is ratio. A scarph in say a 2" thick chine would have an overlapping glued area of the two tapered pieces measuring 24" long. Since your hull is 3/4 of an inch the total width of your stepped margins at the join would be 9". If you were using six layers of 1/8 stock for the repair, the step or land for each layer would be 1 1/2" wide. An argument could be made that if the interior and exterior area of the repair was equally accessable, you could make the patches get wider on both sides and lock the repair in physically as well as chemically. But with a 12 to one , stepped or tapered, with epoxy bonds stronger than the wood structure itself, its a moot point. The glue line won't fail before the wood itself snaps.

[Buddy Sharpton]

Oh yeah, about the chine. Are you cutting it to the proper shape first?. Curved in both directions and with properly changing bevels on two sides? This could be tricky. If the short piece of new chine bends in too straight or with a kink at the join, you'll be building in this unfair shape in your planking replacement. Thats why I suggested building in that temporary form of stapled and glued thin plywood on the inside before removing the bad wood to give you exterior applied repair something to mold to,that plastic covered temporay form. You can staple to it.. After the new planking is done, I would pull the temporay mold and bad chine. Then replace the section of interior chine, as the chine could be pulled into shape with screws into the rigid corner formed by the topside and bottom planking.Because of that right angle bend in cross section, while longways the chine will flow in a curve, the panels will be quite unbendable and the chine will have no choice but to take the proper bend and conform to the hull shape.