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Old 17-04-2019, 07:32   #1
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Boat: 1979 Tanzer 7.5
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Fixing holes in the hull

Good morning everyone. I would like to tap into the collective brain of this amazing forum. Longtime lurker. Short time boat owner. Picked up a 1979 Tanzer 7.5 and have the marina slip booked. Doing some repairs on it, have even replaced a section of rotted core around the starboard chainplate. First time epoxying and it turned out beautiful. Now the boat came with an ancient propeller type speedometer starboard side beside the keel. All the blades were broken and it didnít spin. So I removed it. Now I have 4 screw holes and one slightly larger hole in the hull under the waterline. I understand the bevelling of the hole 12:1 and the fibreglass process. However my question is. Do I do each hole separately, do the whole are as one big one, or only bevel and fibreglass the big hole and with a drill bit bevel the screw holes and only fill with thickened epoxy. The hull is 1/2Ē thick approximately solid fibreglass. The entire area of the holes is less than 4Ē.
Thanks for all feedback.

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Old 18-04-2019, 17:37   #2
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Re: Fixing holes in the hull

Hi what I would do, and I have done a reasonable amount of glass repair, is treat the two groups of holes separately. Bevel the right and left group, sort of an oval. 12 to 1 is ideal but since you are dealing with solid glass something close it good.

Grind them out and then build back up with some fairly heavy biaxial cloth. That is fiberglass cloth with matting attached, much easier than doing cloth and matt separately.

The first layer covers the entire taper and then reduces as you add more layers to fill in the hollow. Build it up and then sand it down fair.

Good Luck

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Old 18-04-2019, 18:11   #3
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Re: Fixing holes in the hull

Grind the holes individually: where they intersect don't grind extra. Don't grind very deep, 3/16" to 1/4" so that the grinder taper is about 2.5" diameter.

I would use only cloth (light, woven) and cut the pieces so that the first big ones cover multiple holes and ending with the small ones for each hole separately.

Next grind the inside. After grinding, if the holes are deeper than what you grinded away, fill them with some epoxy with colloidal silica (Cabosil) filler so that there won't be a void. Then repeat like outside.

After sanding smooth and fairing with epoxy filled with cabosil, seal entire area on both sides with a coat of unthickened epoxy. Scrub with water and Scotchpad to remove any amine blush, then sand flush again and finish with anti-fouling on the outside and something like BilgeKote on the inside. If you have an epoxy barrier coat on the rest of the boat, you could add that (InterProtect2000) instead of the sealer epoxy coat. I also like to use Interprotect2000 for the bilge inside
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Old 18-04-2019, 18:13   #4
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Re: Fixing holes in the hull

You do not need to bevel small holes 12 to 1. That is for structural repair. These holes do not effect the strength of the hull.

Start your repair from the inside. Grind off a clean spot around the holes. It does not have to be too big - Just an inch bigger than the area of the holes. Grind out each hole, just enough to get to clean fiberglass, taper the holes slightly larger on the outside of the hull. Epoxy one layer of mat and one layer of cloth on the inside of the hull. You are done on the inside. Let it cure hard.

Sand out the holes again and then build up layers of chopped mat in the holes. Be sure to make each buildup solid - no trapped air. For the large hole you might want to put some cloth in as part of the buildup. You should be able to do small holes completely in one go. Build it up proud of each hole and cover each hole with some masking tape to hold the patch in place while it cures. Once cured sand to match the shape of the hull. You are done.
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Old 19-04-2019, 09:13   #5
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Re: Fixing holes in the hull

Thank you all for the replies. Itching to get started, however here in sw Ontario itís rain for the next week or so and 3 C right now.
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