Fiberglass rot near thru hull

[wileecoyote]

Today while sanding down bottom paint I found an unusual open area around the A/C thru hull fitting. After prodding with a flat tip screwdriver I was able to remove the bottom paint, a small amount of gel coat (which was cracked up) and what appears to me to be about 1 layer for fiberglass, there is one area that is a little deeper. This is my plan, see what you guys think.
Remove the thru hull fitting and get a better look at the damage. If it's not any worse than it looks now flare back the area with a grinder wheel to get a good area to repair glass. I have MAS epoxy resin from other repairs, I plan on using it to lay up a new area around the fitting hole. I may have to repair the entire area and then redrill thru hull hole.
I have interlux Watertite I had planned to cover another spot where the gelcoat had chipped under the bottom paint (about a 3/4" circle). I would use this to seal the fiberglass and sand smooth with the gelcoat. I don't care how it looks because it will be under bottom paint.
Next year I had plans to remove bottom paint and barrier coat the bottom anyhow.
I have searched all over this site and the internet in general and found nothing similar, just transom rot and gelcoat cracks.
Another question, has anyone removed this style thru hull? I don't see screws(unless they are under paint) on the outer portion. Do I remove the 2 screws from the inside and turn the inner portion and then pull the lower straight down?

 

[sbw1]

If it were my boat, I'd cut a square margin around the fitting (assuming you are not cutting a stringer) and remove the entire fitting with the glass attached to it. I'd then re-layup the hull bottom in that hole with a generous amount of glass matting. Once that cures, I would drill a new opening and install a brand new through hull.

 

[SCORPIO]

West Systems fiberglass repair booklet says a bevel of 12 to 1 is required to properly prepare a hole for relamination. Does that mean grind out 12" for every 1" of hull thickness? If so, that would be a very large area to patch. I'd be afraid to remount the thru hull in the middle of a repaired area.
Any Idea what caused the damage? I've never seen glass erode like that before. Almost looks like zinc that has corroded.

You may want to have a glass man look at that and at least get his recommendation, evenif you do the repair yourself.

 

[wileecoyote]

If it were my boat, I'd cut a square margin around the fitting (assuming you are not cutting a stringer) and remove the entire fitting with the glass attached to it. I'd then re-layup the hull bottom in that hole with a generous amount of glass matting. Once that cures, I would drill a new opening and install a brand new through hull.

Thats kind of what I was talking about when I was talking about filling the whole area. The problem is that there is a fiberglassed blacking block there. I was planning on seeing how far back the damage went so I can tell how much I need to remove. If it is just in the lower layers I'm hoping once I grind down some there will be good, clean fiberglass to bond to. Once I get the thru hull out I will be able to take better pics and get an idea of how bad it is.
I work with a guy who does alot of fiberglass, but mainly automotive applications. I'll see what he might say.
Worse comes to worse I may hbe to remove the backing block and redo it as well. Just need to make sure I don't get any air bubbles in there!:smt009

 

[fwebster]

It would be a mistake to cut away everything and try to fix a square hole. THe best approach would be to use the inner gelcoat and backing block as a sort of depth gauge for grinding then grind away the bad glass substrait and relay it to the correct depth using West Systems or a good vinylesther resin.

In a repair done this way, the repair is usually stronger that the non-repaired hull.\ so forget trying to relocate the intake.

If you are lucky, that is a leak around the intake but just between the fiberglass and gelcoat...it look like you've been picking at it. If you find wet or damaged fiberglass when you start grinding, remember that the 12:1 ratio for the bevel is from the outer edge of the glass being repaired, not from the middle of the hole.

Finally, there is way, way too much bottom paint built up on your hull....probably 12-3 kts worth. While you are doing this repair you may want to consider sanding or blasting the whole thing and repainting.

 

[wileecoyote]

It would be a mistake to cut away everything and try to fix a square hole. THe best approach would be to use the inner gelcoat and backing block as a sort of depth gauge for grinding then grind away the bad glass substrait and relay it to the correct depth using West Systems or a good vinylesther resin.

In a repair done this way, the repair is usually stronger that the non-repaired hull.\ so forget trying to relocate the intake.

If you are lucky, that is a leak around the intake but just between the fiberglass and gelcoat...it look like you've been picking at it. If you find wet or damaged fiberglass when you start grinding, remember that the 12:1 ratio for the bevel is from the outer edge of the glass being repaired, not from the middle of the hole.

Finally, there is way, way too much bottom paint built up on your hull....probably 12-3 kts worth. While you are doing this repair you may want to consider sanding or blasting the whole thing and repainting.

I know the bottom paint is really thick, but too late for this year. It's only around 3 -4 coats at the very thickest spots. Most of the rest is 2-3. Thats next years project. 12:1 is going to be a large hole! Hopefully it's not that thick there. If it's 1/4" thats a 3" bevel, 1/2" a 6" area!

 

[SCORPIO]

If thats near the keel it will be thick. My old '82 260 had a speed/distance transducer located about a foot up from the keel and when I removed it, I measured the hull thickness at over 1/2"! They put the glass in these old boats.

 

[Alibuma]

Finally, there is way, way too much bottom paint built up on your hull....probably 12-3 kts worth. While you are doing this repair you may want to consider sanding or blasting the whole thing and repainting.

Why are multiple coats bad? Weight build up? I need to paint mine next year and had not considered taking the old paint off. Now you have me thinking.

 

[wileecoyote]

OK, I went down today to try and remove the thru hull and examine the damage. I can't get the two halves separated. I left the screws in the seacock side and turn the scoop side to no avail. I reinstalled the screws in the scoop and unscrew the seacock, no luck. As you can see from the pic, I removed the top of the seacock and tried spraying with penetrant and tried both ways again, No luck. My next step is to cut the bottom of the scoop off and try to grind it down enough to pull the whole thing out through the top. Needless to say I'll be getting new seacock and thru hull to match my new hose!

Anyone have any better ideas, Or maybe something I'm doing wrong?:smt100

 

[tobnpr]

Not that difficult a repair.
I'm trying to figure out that fitting...the screws going up into the hull from the scoop side- are they just self tapping into the hull bottom? It doesn't look like they could be tapped into the seacock base...

In any case I'd drill out the heads on the screws into the scoop, then it should be easy enough to "unscrew" it from the seacock.

Then just grind away as Frank said. You want to grind until you hit undamaged glass- meaning no "whitish" coloration, feather it back as discussed above and glass it back. Depending on how deep you need to go, you may get by with a layer or two of cloth; if it's deep use some roving to build it up and add strength. Then re-drill the hole through the new layers of glass and put in a new seacock and scoop.

The repair is straightforward because there's no cosmetics involved, no gelcoat...

Alibuma:

Multiple coats- to a point, aren't bad.
Yes, there's the weight of many years of paint if epoxy has been used rather than ablatives, but there are larger issues.

To make a long story short, the bottom paint on my boat failed shortly after the first bottom job I did after purchase. We had hauled the boat because the paint had washed off the running gear prematurely, and Sea Hawk was covering the cost of the re-do.
While the boat was on the hard overnight huge sheets of paint many layers thick literally fell off the boat and were lying on the asphalt. Sea Hawk sent their rep up from the factory in Clearwater, and I called my surveyor who lived nearby to meet me at the yard.
Turns out that at some point many years ago the bottom wasn't properly sanded-, hell, it wasn't even pressure washed- there was still green algae visible on the old underlying paint layer (!) and there were no sanding "swirl" marks or abrasions. Eventually it was the weight of all the paint layers that and improper application that caused it to fail.
I had the bottom sandblasted (and some minor blister repair) barrier-coated and started over like new.

The other problem is the very uneven running surface caused by all the old underlying paint that has flaked and chipped off. Not very hydrodyamic, to say the least. That's what Frank was referring to when he said it was costing 2-3 knots. It's also evident of some very poorly done bottom jobs (sorry- no offense if you DIY'ed, but it is, what it is)...paint shouldn't be flaking/peeling off the bottom that badly. One or two spots isn't unusual, but that looks like a bad skin disease. If you're planning on keeping the boat, you should consider having the bottom blasted.

 

[quality time]

I removed and rebedded my A/C thru hull this winter. I have the same outer scoop but different style seacock. Remove the 4 screws from the scoop/ screws from the seacock and the two pieces should unscrew. The scoop has a long threaded stem protruding through the hull into the bottom of the fitting. The 4 scoop screws are just into the glass.

 

[wileecoyote]

The screws from the scoop have been removed already twice. The two towards the stern are wood screws into the backer block. The two toward the bow go through and if you look close at the seacock picture you can see that they come out on the left side of the pic. I have removed these and tried to unscrew from the seacock(if you look in the pic of the seacock you can see how the screws are now tweaked from me trying to turn) I then placed the screws back in the scoop and tried with a wrench on the seacock side hoping it would unscrew from the scoop. No luck. It is now soaking with penetrant and hopefully that will help, if no the cutting and grinding will begin!

TOBNPR, The PO had most service done at the marina, but there mush have been a bunch of donks working there, because I have found some shady looking repairs. Anyhow it looks to me as if they have simply painted coat after coat of hard bottom paint for years. As I had said earlier, this winter I plan a sand down, barrier coat (when the temps get back to where I can do it) and new bottom paint.

quality time: 2001 vs 1989 may have alot to do with why mine is so hard to remove, and yours was not.

 

[SCORPIO]

If it won't budge, get an air die grinder and some cut off wheels and cut it close to the backer board and then tap out the scoop part. Sounds messy, hope it unscrews for you.

 

[wileecoyote]

I didn't get a chance to go down and try again tonight as I was helping the neighbor install her new appliances. I'm sure it's not coming loose because I really torqued it pretty hard and wouldn't move. You can see in the pic of the seacock how the screws got tweaked over from me trying to unscrew it.
I have plans to use a cutoff wheel to cut the scoop off and try to grind the fitting down to were I can push it back up through the top side.

 

[techmitch]

I didn't get a chance to go down and try again tonight as I was helping the neighbor install her new appliances. I'm sure it's not coming loose because I really torqued it pretty hard and wouldn't move. You can see in the pic of the seacock how the screws got tweaked over from me trying to unscrew it.
I have plans to use a cutoff wheel to cut the scoop off and try to grind the fitting down to were I can push it back up through the top side.

That's the ticket. Grind away, since you are going to replace those parts anyway.

 

[1956olds]

you may want to check the block on the inside of the hull for saturation,I had my through hulls resealed this winter and they checked for rot on those blocks ,if they are rotted this would be an excellent time to replace them as removing the through hulls is no fun anyway.

 

[wileecoyote]

After getting the scoop ground off and the thru hull and seacock pulled out I started to grind back and look at the damage. It appears that more than likely one of the screws in the scoop that were threaded into the fiberglass, but not all the way through, was leaking. After grinding back I have someseperation between layers about halfway through.
IThe backer inside was indead wet and I cut the fiberglass off the inside and used a chisel to get it out. It appears to be 3/4 plywood 5"X6 1/2".
I am going to let the fiberglass sit to make sure there isn't any water inbetween layers before I continue. I was thinking of using my heat gun to put some heat on the hull and see if there is any water that comes out.
One of the dockmates told me there is a fiberglass guy that hangs around the marina and does some yard repairs. I'm going to try and find him and see if he will take a look. Maybe he can give suggestions or even quote for repairs.
This is one I may not want to mess with, last thing I want is trapped water anywhere, or the possibility of future issues.

 

[tobnpr]

Post some pics, maybe we can help.
Rather than a heat gun, to aid in the drying out process, it helps to place a heat source on the area if you want to give mother nature some help. An ordinary halogen work light placed a foot or two away is a good idea, leave it for a day or two...

 

[wileecoyote]

Post some pics, maybe we can help.
Rather than a heat gun, to aid in the drying out process, it helps to place a heat source on the area if you want to give mother nature some help. An ordinary halogen work light placed a foot or two away is a good idea, leave it for a day or two...

I would, but it's sitting out in the yard and not close to an electric plug. I haul my generator down to have electric power. I have pics of the removal of the scoop, but none of the actual problem area once the fiberglass was ground back. I will try to get some tomorrow. I was wondering if a shopvac would do any good??
I'll wait until tomorrow and reassess the situation. Hopefully it's all dry!

 

[wileecoyote]

OK, here is the latest. I have ground back 6" and have a crack that I can't seem to get rid of! It appears that the water has migrated UP toward where the bottom meets the side. If you look in the picture the water is leaking out of both corners and down. Yesterday I used a heat gun and got a small stream (maybe 1oz at most) which then stopped and dried up. After leaving the boat sit all day in the sun, even though the bottom doesn't get any, I had trails from both sides down to where my outer grind edge is. I wiped and will check later. I have no electric there, only portable genny. Any ideas to assure drying except time?? Also I would grind out further, but then I get into the area where I can't keep my 12:1 without removing the ground plate and going up to the chine.