Resealing required?

M

mutski

New member
I have been nervous about any holes in the hull since I read about the balsa core rotting out in C-Dory transoms. So now, I'm wondering about the fuel tank cover board the seller removed to siphon fuel before my 2005 C-Dory 22 Cruiser went on the barge to Alaska. Similar to this one:

http://www.c-brats.com/modules.php?set_ ... _photo.php

He left the screws for me to put back in. Is it screwed into a balsa core? How should I seal the screws when I put it back? Seal the holes with a penetrating epoxy before I drive the screws in? 5200? Or is this not an issue?
 
Over drill, (diameter and depth), clean out any balsa--I like to use a 1/4" Dremel bit. Then fill this with thickened epoxy. I prefer to treat the sides of each hole with "neat"(unthickened epoxy). Let this set up. Then drill the pilot hole, and put the screw into the epoxy plug. IF you want to use some sealant, then 4000. The 4200 will yellow and the 5200 is more "Permeant".

The same for any other holes in a cored structure. Your transom may have plywood, or Balsa or foam. I would still treat any cored structure the same way--put in epoxy plug and then put screw into the plug. There should be a couple of tie down screws for the straps holding the tanks in place. those can also be over drilled, Some boats. have wooden or perhaps PVC strips fiberglass/resin into the bottom so that they can be screwed into without damage to the core. (This will vary depending on the year of the boat.)
 
I took it all the way off and cleaned it up with acetone. It was obvious that the original construction was a dab of caulking under each screw; it was never drilled and filled with epoxy. Meanwhile the forward side of the tank is convex, maybe bulged with 16 years of pressure from the fuel. It looked like I'd have to remove the tank to get the drill in position to drill straight holes for the screws, and to do that, I'd have to disconnect the hoses, which might mean removing the fuel fill from the gunnel. At that point, I decided to put it back with 4000 caulking and save pulling the tanks and filling the holes with epoxy for a later date.

Which brings me to the question: If the original construction was to screw the bases of the walls down over a little caulking, are people pulling the walls and the runners that hold the fuel tanks bed the screws in epoxy plugs? Or do most people let the original construction stand?
 
If you can get the screws back in the holes, you can get a drill bit or Dremel tool bit into the hole, and drill it out. (You might have to use a right angle drill, or a long bit.).

No, the factory never did it right. There are very few factors which do it correctly. It is being competitive. The factory would probably charge several hundred dollars more for the boat. (I think it would be worth it.). Some better builders put solid glass or a substance like Coosa board into a place where there will be screws or bolts.

The C Dory is unique, in that it holds its value--or at least for the time I have been involved (about 20 years) they have held their value. (Of course there is this inflation--which is more now than any time in the last 30 years.)

If the boat stays in a dry climate, a non freezing climate, or is kept in a covered climate controlled storage then there will never be an issue with screw into the core.

In your case, you have introduced a different factor. The boat is now in a freezing thaw cycle climate. That is often where problems arise. A little moisture gets into the core, expands and then contracts, more moisture comes in.

Most likely there are other issues with screws into the core--for instance your boat will have the "L" brackets holding the wood furniture in place. In some of my boats of that vintage, I have removed those "L" brackets, and replaced them with taking in 1708 glass, with an epoxy, which seals the hole, and makes a good bond, to be stronger than the screw and "L" bracket. If you ever want to re-do the interiors then you can easily cut the "tab".

The C dory is easy. When I bought My Cal 46, I pulled all thru deck fittings, including a 48' teak toe rail, lifeline stanchions, thru deck fittings and epoxy plugged all of these--hundreds of holes. Why? Because I have done some studies on the cored hulls, and delimitation.


Enjoy the boat.
 
To expand slightly on the comment about using the Dremel tool; the flexible shaft will allow very close use of a bit near the tank or any other obstruction. I hang a Dremel tool up high and then use the flexible shaft for work like this. I dedicate one of the Dremel tools for this type of work and leave the shaft always attached. I find the Dremel tool to be very valuable in working on small boats, and have worn several out during my boating career. I carry one of the battery powered Dremel tools, and a complete set of bits as part of my tool set when I travel in a boat or RV. These are carried in a soft pouch, and take up little room. One can buy a set of different size collets to compliment the drill bit set for the Dremel tool. After you have used the largest bit, then one of the carbide bits will allow widening holes to the size you need in both wood soft metals and fiberglass. Hard steels are more difficult to cut, but it can be done with carbide tipped bits.
 
I have moved on to replacing the Hummingbird fishfinder with a Garmin chartplotter. That means replacing the transducer and a speedometer sensor screwed into the transom. Four screws in a more sensitive spot. Those I will fill with epoxy.

I have a Dremel tool, but 14 hours drive from here. Next time I pass through Fairbanks, I'll grab it. I've used it primarily for model airplane work.
 
For transom transducers, we recommend a Starboard (or any other HDPE block). You can put the screws for it into two of the holes already there which have epoxy plugs set in. I have also had good luck using flex epoxy. Rough up the back of the HDPE block, use the Dremel tool, with a small dovetail bit, and/ or make 45* cuts with a Fein or similar saw. Do a quick pass with a propane torch to flame harden the back surface, which will allow better adhesion with the G flex.

The reason for the HDPE block is that you can put new screws into the block, and move as necessary if it is not in the correct position, or you put a new transducer in place. I have used the big down / side scan, Real Vision, Chirp transducers with no issues.
 
Stern pad is the same thing, just a few more $$. Keep an eye on the adhesion, there are a couple which have been reported to have the glue fail.
 
Now I am hesitating because the one I got goes on with two-part epoxy. I see some go on with double-stick adhesive pads?

I have a 90 HP Suzuki mounted mid-transom plus trim tabs. It's 18" from the centerline to the inside edge of the trim tab. The Hummingbird was mounted with the transducer midway between and the speedometer wheel by the trim tab. I was thinking of moving the transducer closer to the trim tab - I think Garmin says put it 15" from the prop. But would the trim tab make turbulence to interfere with the transducer? Maybe midway between is really the best spot?
 
mutski":kdnqdwho said:
Now I am hesitating because the one I got goes on with two-part epoxy. I see some go on with double-stick adhesive pads?

I have a 90 HP Suzuki mounted mid-transom plus trim tabs. It's 18" from the centerline to the inside edge of the trim tab. The Hummingbird was mounted with the transducer midway between and the speedometer wheel by the trim tab. I was thinking of moving the transducer closer to the trim tab - I think Garmin says put it 15" from the prop. But would the trim tab make turbulence to interfere with the transducer? Maybe midway between is really the best spot?
Click to expand...

Some of the new adhesives are very strong if you apply them correctly. Advantage of adhesives pads is that you don't have to worry about the mixture ratio of the epoxy or that it is mixed well.

I have a Lowrance 3-n-1 transducer on my boat. The gap between the transducer and the trim tab is 1.5 inches. The transducer edge is 17 inches from the engine centerline. Transducer works fine in this position even at high speeds.
 
I just pulled the fuel tanks and over drilled all the screw holes and filled with epoxy. Our boat has a balsa floor. The transom had a lot of water and so took all the balsa out and filled with epoxy and cloth. Solid as a rock now. On the screw holes I found the Loctite brand had a plunger type with a mixing tip and the tip fits in a 3/8" hole and made it pretty simple to fill them. Had about half a dozen holes that had a little bit of moisture. So got those dry and used Git-Rot to fill any voids and then topped off the holes.

Have to keep that water out!

Rob
 
I would use cabosil or cabosil and one of the medium density fillers to thicken epoxy used for filling holes in the deck. "There are several reasons to not use plain unthickened epoxy to fill holes.
 
Holes filled with System 3 epoxy plus silica thickener. New Stern Pad is glued to transom... the epoxy should be cured tomorrow. Then I can mount the transducer and run the cable to the dash and see if the while thing floats.
 
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