1996 Cajun (Fishmaster) 2400 Bay Boat

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
The_Bean
Frequent Poster
Frequent Poster
Posts: 24
Joined: Wed Sep 21, 2016 9:00 pm
Location: Louisiana

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by The_Bean »

Should I plan for patching from both sides?

e.g.

1/8" feathered out 12" and patch and when I flip the hull do the other side?

Or grind through all the way with the feather as you describe and patch from one side?

Apologies to second guess, just wondering if a two sided patch is better? Watched way to many youtube videos on patch work....

Bean

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

I almost always agree with Fuzz. But. You only weaken the hull going out 12".

The rule is 8-12 times the hull thickness. So, for 1/4" hull, grind back 3" away from the edge and feather to zero. Grind one side at a time and repair one side at 12:1 ratio and the other side at 4:1 ratio or less for a through cut. The repair, if it can be bigger on the inside is best. This will make it stronger.

So, for this error and 1/4" hull, I'd grind to the cut hole and feather back 3" all around it to zero. Make the repair inside only and use smaller pieces of 1708 and progressively fill 6 pieces on the inside. Then after this has cured, go to the outside and feather grind the surface for gelcoat. If you decide to paint, feather grind and add a layer os light cloth like 6 oz woven or two to fill, same strategy only you only need to feather a tiny bit to get a finished surface. Other fabrics will print through, but it may not matter on bottom.
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

The only reason to do much work on the facing or outside is to get it smooth. If it cures rough, or with any voids, those must be addressed. For a through cut, you really need to put some tape over the area. I like to use shipping tape on the outside. Yes, it sticks, and if that bothers you, just double side it so the outside of the tape faces the cut and then tape over it. Or, jist tape it and remove the tape after the epoxy cures an extra day and use a sander and a bit of acetone to clean it.

Also, if you decide to glass the outside with light woven, a piece of peelply is nice taped on with masking to keep epoxy from running over good boat.. or you can babysit the work for an hour with a bottle of beer..
My boat build is here -------->

viewtopic.php?f=12&t=62495

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8920
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by Fuzz »

I am not sure how adding extra glass over a larger area on the inside will weaken the hull but I am would be happy to learn. Doing as Fallguy says will make a repair that you should never have to worry about. Lots of glass hulls have been holed, repaired, and never been a problem.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

Fuzz wrote: Fri Apr 16, 2021 12:44 am I am not sure how adding extra glass over a larger area on the inside will weaken the hull but I am would be happy to learn. Doing as Fallguy says will make a repair that you should never have to worry about. Lots of glass hulls have been holed, repaired, and never been a problem.
I never said extra glass will weaken the hull. Overgrinding can if you make it hard to do well.

Just no reason to grind it back 12" and pretty hard to feather it well and not get too thin in the first coulle inches. Each inch would be ground 0.020" and that is just super thin for the first inch and then 0.040 for the second, etc.

Trust me. The ratio/rule is 8-12 times hull thickness.

For an inch thick hull, 12" is okay because it allows for some errors in grinding. An inch thick hull would be feather ground 1/12" or about 0.083" per inch.

Maybe you are thinking back to the old cflex hull of yours? Like I said, I agree with you 98% of the time. But that 12" is too much and not needed.

The initial bond to substrate is far more important than distances from the hole. Clean the area with acetone after sanding and don't sand with any finer grit than 60.
My boat build is here -------->

viewtopic.php?f=12&t=62495

The_Bean
Frequent Poster
Frequent Poster
Posts: 24
Joined: Wed Sep 21, 2016 9:00 pm
Location: Louisiana

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by The_Bean »

Ok thank you both for the instruction. I am sure the repair will fall withing the guidelines of both reccomendations.

Now to throw a curve ball. If you look closely at the damaged spot, the cut is one the top of a strake elbow. So the cut has about a 1.5 inch drop immediately to it's right (looking at the pic). Any reccomendation for that bend? Additional build up to support?

I believe I will have to modify the underside of the stringer for that area from my view of the repair now. As a stringer runs in that slot.

Bean

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

I am not able to comprehend the 1.5" drop from the pictures.

All I can tell you is to grind three inches minimum in each direction. In general terms, think like a doctor.

Firstly, do no further harm. Do not attempt to grind in a valley and drop to 8:1 or even 4:1 to avoid the valley if that is what you mean. A valley can also be filled from the inside with thickened resins. You cannot bond well to flaky chop and it must be scraped off it it flakes.
51487D25-D3F9-499E-9F5D-108460F62292.jpeg
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by fallguy1000 »

Also, into the yellow area, some of that looks a little questionable. Make sure it is not loose or take it back more.

And. This is important as well. Do not bond glass to the hull if the grinding or surface is uneven. If you look at my lines, beyond them is really rough. The lrger pieces of glass need to extend onto existing hull about 2" and this must be bedded in thickened resin that fills in the gaps. In hull repairs or any build work, we also never leave hard edges, so none of your pieces of glass can end in the same place. So if the bigger piece overlaps the hull 2", the next size down would be one inch, for example. This is to avoid making a really hefty repair and ending up with a stress crack at the original poly hull. Think gradual strength change...

If you use 6 pieces of glass, going across the cut is a 6" laminate, add 2" to each side and that piece would be 10" wide, then each of the other pieces would be on the order of 8,6,4,2" wide..and this is one short, but you'll get a better feel for it on the job. Another example would be 10,9,7,5,3,1 or some such.... ths same is true the other way, but I am not sure the cut length, so you can do that, but say the cut is 8" long, the last piece would be 10" wide by 12" long.

Normally, I like to glass largest piece first, but that is not good here. Smallest first here. During a repair like this one, I also like to bed the glass a bit. That means, I like to put down a thin layer of thickened resin over the entire repair before I start. It can be a bit gooey, but what happens is you entrain almost zero air this way. Use cabosil or wood flour only and not too thick. Like about 2:1 by volume.
My boat build is here -------->

viewtopic.php?f=12&t=62495

The_Bean
Frequent Poster
Frequent Poster
Posts: 24
Joined: Wed Sep 21, 2016 9:00 pm
Location: Louisiana

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by The_Bean »

Fallguy,

Thanks for the additional input. You are correct the area has yet to be ground and cleaned. I have a couple of these areas where I got a little too a head of myself while cutting stringers. There were so many pockets that were just resin filled, it was very hard to tell between cutting hull and those filled areas.

I will be duplicating this repair a couple times. Thanks and plan on getting all my major grinding done before I begin these repairs, after that it is on to the building the transom and stringers.

Bean

The_Bean
Frequent Poster
Frequent Poster
Posts: 24
Joined: Wed Sep 21, 2016 9:00 pm
Location: Louisiana

Re: 1996 Cajun (Fishmaster) 2400 Bay Boat

Post by The_Bean »

Received a pack of the 16 grit zec grinding disks that Fuzz reccomended today and put one to quick use. Man those things grind through quick. Can't even allow for the weight of my hand and grinder to push, just feathering those things and they chew everything up quick.

Great use on all the areas with old built up thickened poly. Pretty much everywhere the deck was attached too and the knees/stiffeners along the walls.

Hopefully only about 8 more sessions and I'll be getting to the interior patch work and then off to the transom build.

More supplies received and building a game plan. Hoping to keep a good idea of two steps forward to minimize future issues throughout the re build.

Post Reply

Who is online

Users browsing this forum: No registered users and 13 guests