1996 Cajun (Fishmaster) 2400 Bay Boat

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
fallguy1000
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Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

By the way, I want to make a small correction to my earlier comments.

For a small hole in the boat 12:1 is the standard grind, but for a significantly larger repair; you can go quite a bit fiirther to ratios much higher, like 20:1. A 20:1 ratio for 1/4" hull is 5" grind away.

If you have a large hole, say 6" around, a 3" grind is not very much original surface. Or say a 12" hole, etc.

So, there is a time when a wider grind would be needed.
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OneWayTraffic
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Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by OneWayTraffic »

Since it's just that crack, any reason why he can't just fill with epoxy and put a couple of layers over on the inside? I'm not recommending this but curious.

As to the smooth surface if I know that I will be secondary bonding later I try to fill the weave with something. What doesn't matter so much. I've used microballoons in places where maximum strength isn't required. A microballoon putty will have a shear strength proportional to the amount of epoxy in it, or as much as wood if it's not too thick. Since my boat is a wood core, that's often enough. If you need higher strength then use a higher density filler, but do that just before glassing or you will never get it fair. Since this is a complete rebuild I don't know if you are considering putting a thin core on the inside for strength but it might be worth a thought.

fallguy1000
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Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

OneWayTraffic wrote: Thu Apr 22, 2021 1:19 am Since it's just that crack, any reason why he can't just fill with epoxy and put a couple of layers over on the inside? I'm not recommending this but curious.
It would crack open most likely. Not absolutely, but probably and then it is under the sole.
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The_Bean
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Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by The_Bean »

Additional pic of the repair area. Click on the pic for it to show right side up. Not sure how it flip flopped on the forum???
strake repair.jpg
Grinding progress
22Apr grinding.jpg
In the new photo you can see the elbow/bend I was previously referring too. You can also see that there is almost a small "pizza slice" style cut that is the issue. I understand all the commentary so far, but am still having some issues figuring out a good way to start this patch. I have been thinking as OneWayTraffic has suggested and fill the cut area with Gel Magic. My reasoning for this is to brace the current "injury" and allow for some meat to grind on while creating my taper.

The other issue I am having is that the bend creates a difficult area to patch. I am concerned as Fallguy stated that I will get a crack under the sole a year or two from now if this patch isn't rock solid. Any ideas for best material to bend that patch starting off? I have 12oz biax 6" tape, 17oz biax and 1708 all available.

I have been thinking build "injured" area with Gel Magic, grind taper on top and bottom of patch area, start with a 12oz patch for a couple layers (to make the bend) and then progress to 17oz and or 1708. I think this patch will require some creativity. But I really want it to be solid.

Bean

fallguy1000
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Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

So, I think I understand. Your cut is imperfect and if you grind it out too far; the pizza slice will get super thin; perhaps even break.

It all depends on the depth of the cuts. If they are thru, then just suck it up and grind and see if it all has to come out.

If it is just superficial, then fill it with thickened epoxy and grind next day. You don't need anything super fancy. A 2:1 mix by volume of cabosil and epoxy will work.

The main thing is no loose materials or paints can be left before the repair, or bond strength is compromised. That includes dirt or oils, etc.
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OneWayTraffic
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Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by OneWayTraffic »

I think I understand about the grinding. If it were mine and I didn't need it to be flush with the inner surface, I'd probably put a 6mm marine ply patch on top then glass that in with overlapping layers like a stringer. (Edit: with grinding and glass on the outside as well so the ply's a core.) But a flush repair will maintain the hull stiffness as designed. WEST's book on fibreglass boat repair also state 12:1, but that's for bonding area.

If you are concerned about the strake elbow getting in the way, fill it with putty. Woodflour mixed with epoxy until it's as thick as peanut butter would be the best. I can't get woodflour that I trust in NZ easily, so I use the WEST fillers and chopped glass. That works as well. Then you can glass over it.

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