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Delamination under the coaming

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dhunt
1st Mate

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USA
83 Posts

Initially Posted - 03/07/2004 : 21:46:49

Ooops . . . I opened up the access panels over the quarter berth to remove a couple of cam cleats that the PO installed and got a face full of rotten, water logged plywood. (First year with the boat and will do some serious rebedding of all deck hardware over the next coulpe of weeks.) The backing under the winches and cleats on the cockpit coaming is a mess . . . I'm thinking about just peeling the rest of the laminates of the old plywood away and then installing aluminum or stainless backing plates. Question is . . . Is just backing working devices adequate, or do I need to replace ALL the plywood?

I believe it's just there for distributing load from the working devices. Any words of wisdom will be appreciated.

David and Sharon Hunt on Solitaire, #800 sk-sr, Marietta GA

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 03/07/2004 : 22:49:40

David and Sharon,<blockquote id="quote">quote:<hr height="1" noshade id="quote">...got a face full of rotten, water logged plywood. ... will do some serious rebedding of all deck hardware ... The backing under the winches and cleats on the cockpit coaming is a mess ... I'm thinking about just peeling the rest of the laminates of the old plywood away ... Is just backing working devices adequate, or do I need to replace ALL the plywood? Any words of wisdom will be appreciated.<hr height="1" noshade id="quote"></blockquote id="quote">Based on your description so far, I's suggest removing all the remaining plywood laminations. Then clean up any remaining high spots with a sander or grinder, so that whatever goes back in will fit tightly to the coaming fiberglass.

As for what to put back, I'd say more plywood and lots of epoxy. Plywood would likely produce the best stiffness to weight ratio. By tying the vertical sides of the coaming to the plywood with epoxy putty, and optionally fiberglass tape, the coaming hardware loads would be spread even further, and the potentially destructive hinge effect at the coaming corners would be eliminated. I would start by making a paper tracing of the maximum size piece of plywood that would fit in the top of the coaming. Next, cut out a corrogated cardboard template that shape, maybe double or triple thickness to simulate the thickness and stiffness of plywood. By trimming the cardboard template until it fits through the access opening, see how big a piece of plywood would go in at once. If that's close to the original size and shape, go with it.

If the trimmed cardboard template is no where big enough, you could install the plywood in sections. Let's say you want to end up with 3/4" plywood (about what's there in my 1979 C-25). Cut out either two layers of 3/8" plywood, or three layers of 1/4" plywood. Using a jigsaw, cut those into pieces small enough to fit through the access opening. Be sure to cut each layer in a different pattern, so none of the cut lines fall near each other. coat each piece once or twice with unthickened epoxy. Then reassemble the whole puzzle inside the coaming using slightly thickened epoxy. At that point, it would be easy to include a layer of fiberglass cloth after every layer of plywood (and at least two or three after the last plywood). The cloth would add stiffness, and would retain a reservoir of resin to help eliminate air gaps during clamping. You can use any existing holes in the coaming to insert temporary clamping screws with wing nuts. Dipping the screws in candle wax first would be a good idea.

For any additional clamping needed, cut short scraps of thin wood to wedge vertically inside the coaming. I think that would be my prefered method. Don't forget to over-drill, epoxy fill, and redrill you deck hardware mounting holes, so as to avoid having to do this over again in a few years.

Another possibility would be to build up woven roving and epoxy resin in place. The drawbacks would be added weight for a given stiffness, and the obvious mess of trying to laminate heavy fiberglass upside down in a tight spot.

Separate aluminum backing plates small enough to fit through the access opening for each piece of deck hardware would be a lot of metal working, and still might not spread the load far enough to prevent excessive flex in the coaming.

I would suggest you forget about stainless steel backing plates. The cost and/or labor involved would make any other method look very attractive by the time you were done.

Don't underestimate the loads that winches and cleats are certain to subject the coamings to. And remember that coaming winches and cleats are considered fair game when attaching emergency dock lines or pulling a boat out of trouble. Catalina did a great job of stiffening that area originally -- don't leave it weak now.

-- Leon Sisson

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 03/08/2004 : 13:40:21

I have exactly the same problem on Indiscipline III, the starboard side, aft of the winch (thankfully), where my traveller blocks and the stern light are the plywood looks like soaking wet papermache.

I'll be following your progress because I have to do the same thing someday soon.

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Raskal
Navigator

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USA
162 Posts

Response Posted - 03/08/2004 : 16:09:55

Leon's written a good textbook for doing this. I think replacing the support for the winches and cleats on the upper coaming is essential, and wood is probably the most practical way to go, but when I removed those quarterberth hatches I also noticed that those spaces would lend themselves to being filled with aerosol foam. That would give some overall stiffness and some safety flotation a la the Etap boats from Belgium.

I also noticed that on my boat those areas were still watertight and dry and could be used as a lot of extra storage space if some clever way were found to make the hatches quickly removable...

Rich Kokoska

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dhunt
1st Mate

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USA
83 Posts

Response Posted - 03/08/2004 : 18:48:56

Leon - you da man!

Templating in cardboard is very sensible - the suggestion to clamp the new wood in place using existing holes in the coaming is reallly good. I appreciate the ideas. There is a kicker here . . . that is that I have access to steel or aluminum for true cost and can get the machining and cutting done free. I still have the templet to do but now it has to specify exact hole location and thread - though I could just oversize the holes and nut and bolt it.

How would you prepare the ply? Epoxy saturate? Would you use steel or aluminum if cost and time weren't a factor?

Rich - I've been thinking of compartments . . . can't have enough storage - have you ever computed the volume of foam required to float a flooded c25?

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 03/08/2004 : 20:29:56

David and Sharon,<blockquote id="quote">quote:<hr height="1" noshade id="quote">... it has to specify exact hole location and thread - though I could just oversize the holes and nut and bolt it.<hr height="1" noshade id="quote"></blockquote id="quote">Assuming you were determined to use metal, you could wait to drill and optionally tap the holes until after installing the backing plate(s) with structural adhesive. Then use the actual deck hardware as a drilling template (just long enough to get the "ceterpunch" effect). Then drill using a square beside the bit to maintain perpendicularity. Sometimes I tap metal backing material, but more and more I've come to the conclusion that it's more trouble than it's worth unless there's no nut and wrench access.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">How would you prepare the ply? Epoxy saturate?<hr height="1" noshade id="quote"></blockquote id="quote">Sand and then at least one primer coat of epoxy before installation. If you're good at preplanning, fast with epoxy work, and use a slow hardener, you can do the whole installation as one continuous epoxy project, without letting any one batch cure enough to impede a primary chemical bond with subsequent batches, and without having to worry about removing amine blush.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Would you use steel or aluminum if cost and time weren't a factor?<hr height="1" noshade id="quote"></blockquote id="quote">No. There's still the issue of spreading the peak deck hardware stresses over a large enough area of fiberglass to avoid damaging the deck without over flexing the top edges of the coaming. Not to mention adding more weight high up than needed to get the job done. That location is probably 3'-4' above the CG of the boat, and about the same from the longitudinal centerline of bouyancy (i.e. moment arm).

<blockquote id="quote">quote:<hr height="1" noshade id="quote">... I've been thinking of [coaming] compartments ... can't have enough storage - ...<hr height="1" noshade id="quote"></blockquote id="quote">I plan to use the factory trim rings, but custom build the compartments themselves. In addition to the usual glovebox or center console type storage, these are a great place for a few electrical items. Such as recepticles for GPS, spotlight, autopilot, remote VHF mic, stereo remote, foredeck light switch, small cockpit speakers, etc. I suggest resisting the temptation to create coaming compartments that are not both self draining, and water tight from the interior of the boat.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">.. have you ever computed the volume of foam required to float a flooded c25?<hr height="1" noshade id="quote"></blockquote id="quote">This would be a good exercise for anyone who thinks fixed internal floatation stands a prayer of saving a C-25 from sinking. You can start with the assumption that there isn't much in the original construction that has a specific gravity anywhere near as low as 1. The agregate specific gravity of wet cruising supplies is probably going to be near enough to 1 that they can be discounted as a factor either way. Next, research the specific gravity of your choice of floatation foams (in lbs/cu.ft.). Then calulate the cubic feet of fresh water that would have to be replaced by foam to float the hull high enough to be an even remotely usable rescue platform. Remember that floatation has to be installed very high and wide in the hull, and that the flooded center of bouyancy needs to be directly above the flooded & submerged center of gravity, if the flooded boat is to remain consistantly upright in rough water. But other than that, it's a fine idea.

-- Leon Sisson {a.k.a. Mister Doom & Gloom

}

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Raskal
Navigator

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USA
162 Posts

Response Posted - 03/09/2004 : 15:33:13

<blockquote id="quote">quote:<hr height="1" noshade id="quote">This would be a good exercise for anyone who thinks fixed internal floatation stands a prayer of saving a C-25 from sinking<hr height="1" noshade id="quote"></blockquote id="quote">

Not a lot of optimists out there! You're right that some calculation is called for, but flotation wouldn't be the only reason for foaming that void space--there's also insulation and structural stiffness. To answer David's question, the aerosol foams are very expansive and I estimate 10 cans would do both coamings. Storage, though, is probably the better idea. My coaming void spaces were bone dry the last time I poked around in there so drainage may not be an issue...

Rich K.

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Raskal
Navigator

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USA
162 Posts

Response Posted - 03/09/2004 : 15:49:32

Oops

! I forgot the port side has no void space because it's taken up with the locker--fill that with foam and I guarantee you'll stay afloat...

Rich K.

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 03/09/2004 : 15:51:13

Do I remember reading about a three part whisker pole? I wonder if that would be a good place to store one.

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