Fuel tank supports

C

CDory23

New member
So, like many on here I removed the fuel tanks because of bulging and screws directly in the hull not being sealed properly. I have undercut and epoxied all tank supports succesfully and luckily found very minor rot. Then I predrilled the new holes where the supports will be fastened and undercut and epoxied for the new screws to be screwed in with 4200 for a double seal. Now with the issue.

My C dory does has straps which connect from the saddles screwed on the transom to the starboard peice on the other side of the tank. The screws were very loose on the transom that held the saddle in place. I removed them and drilled and epoxied. I did not undercut since there was no water damage. Unfortunately on one of them I must have gotten really close to going completely drilling through the transom because I saw a heat mark the same size as my drill bit on the other side of the transom. Since then I screwed the saddle/screws attachment back in place and found an airpocket in 2 of the holes that I epoxied. (I"m still learning with epoxy especially when filling a hole on a vertical surface. I did do peanut butter consitincy.) On those two holes with airpockets the screws did not get as good of a bite and kept spinning oppsed to the other ones, but they held well. My questions are

Does undercutting help provide strength and support in this application? Even with no rot should undercutting always be method of approach when screwing into epoxy.

How concerned do I need to be with the heat mark I saw on the other side of the transom, especially with an airpocket in the epoxy job I did. It concerns me that without epoxy filling the whole void I potentially have a small layer of gel coat keeping water out.

I'm considering taking the tanks back out of place drilling holes out again, undercutting, epoxying then screwing saddles back in.
 
I would watch the area on the outside of your transom. Gel coat, is not that much more effective in keeping water out, than is just plain laminating resin.

I assume that these holes are well out of the bilge. If there is no way of standing water over these screw holes, I would just sit tight. Are the screws holding the straps adequately?

As for the strength of under cutting vs just filling--there is a small amount of increased strength by under cutting. But filling a 1/4" hole is easier than a 1/8" hole, and 3/8 to 1/2 " is even easier. I use tooth picks, or splinters cut form tongue blades or popsicle sticks to tamp the thickened epoxy into the hole. This is also a good place to point out that un-thickened epoxy into the hole before putting in the thickened epoxy.
 
The holes are below the waterline. I couldn't go with the uneasy feeling of leaving it alone so I took the fuel tanks back out, removed saddles and drilled holes out that were originally 5/16 to 3/8 and then undercut. I still didnt hit them exactly on center and there is some cured epoxy still in the holes. Is this going to cause a bonding issue, maybe because of amine blush?

I hate to have the first pics in my album uninteresting work pics but my album shows the heat mark on the outside of transom, the holes inside and a bad picture of me trying get a close up of a undercut hole with bits of cured epoxy in place.

At this point I"m thinking I should fill with neat epoxy, then thickened making sure to get all air bubbles out and then again finally re drill and screw back on saddles. The hole that I believe caused the heat mark was the only one I didn't drill deep enough to remove all of the original epoxy depth wise.
 
Although these holes are "below the waterline" they don't look as if there will be standing water over them. I would not worry about amine blush, since you cut thru the epoxy plug with a drill. You should get excellent adhesion with what you propose.

The photos are fine. I think you will be fine with that hole where there was "burn" marks. If you really want to be "safe", and since this appears to be in an area which has bottom paint on it, you can scrape off any bottom paint, coat this area with epoxy, and then repaint with bottom paint. Frankly I have never seen any "burn" when drilling fiberglass--and I have drilled a lot of it--but I suppose it is something which could happen.
 
Thank you for the advice. I went ahead and filled all of the holes today. I even took out the bilge because I noticed that had 4 screws into the hull as well. Very minor rot but still drilled, undercut and filled. Its nice to finally get some grip on the epoxy work. I made up the epoxy neat and put enough in to coat holes, then added my silica and filler to a peanut butter consistincy and used weed whacker line to keep pushing in the holes to get all air out as I continuously pushed in the thickened epoxy.

I never felt a need in the past to thicken epoxy when filling holes on a horizontal surface since gravity is your friend and you fill them up. I understand now the neat epoxy will tend to flow into the wood not filling the hole completely up on some after cure. This happened to my holes that I drilled out and filled for the tank starboard cleat supports. I did a quick wash with water and rubbed with scotchbrite to try to get amine blush out and then dried and topped off the hole with neat epoxy.

Is this a big concern to have the two layers of differently cured times epoxy on top of eachther? It was really hard to scrub the top of the cured layer and I don't feel I did that great of a job removing the blush.
 
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