Diesel Exhaust Thru Hull Leak

[reckless42586]

Hi everyone,

I recently bought a Catalina 27' last November and have a small leak in the inboard diesel exhaust thru hull. The leak is not in the tube, but rather the hull/fitting so there's a small drip that drains to the bilge. The thru hull is above the waterline with no crew, but when occupied and under sail is partially submerged. It's on land now so that I can fix it. In the photos you can see how the waterline is sometimes at the bottom of the thru hull and the degraded white sealant has gone missing. My thinking is that the right thing to do is unscrew enough so I can install a better sealant (5200 or something similar) or somehow remove completely and reinstall. It doesn't seem to have any internal fins though to be able to unscrew. The thru hull fitting does not seem to be a seacock in that from the outside the tube goes in and bends with no valve. From the interior it's an extremely difficult spot to access and I'm thinking about cutting an access hatch in the stern locker and for future access in case of emergency. Any thoughts?

[Uncle Bob]

Originally Posted by reckless42586

Hi everyone,

I recently bought a Catalina 27' last November and have a small leak in the inboard diesel exhaust thru hull. The leak is not in the tube, but rather the hull/fitting so there's a small drip that drains to the bilge. The thru hull is above the waterline with no crew, but when occupied and under sail is partially submerged. It's on land now so that I can fix it. In the photos you can see how the waterline is sometimes at the bottom of the thru hull and the degraded white sealant has gone missing. My thinking is that the right thing to do is unscrew enough so I can install a better sealant (5200 or something similar) or somehow remove completely and reinstall. It doesn't seem to have any internal fins though to be able to unscrew. The thru hull fitting does not seem to be a seacock in that from the outside the tube goes in and bends with no valve. From the interior it's an extremely difficult spot to access and I'm thinking about cutting an access hatch in the stern locker and for future access in case of emergency. Any thoughts?

Hi, firstly welcome to the forum, secondly, in my opinion there should be a valve screwed to the through hull with an elbow of sorts (possibly 45deg) facing upwards and a barb for the exhaust hose which should lead up well above the waterline then curve down to the muffler. The fitting needs to be removed to be properly resealed.

[C420sailor]

Don’t cut an access panel in anything structural unless you 100% know what you’re doing. If it’s non-structural, have fun.

Don’t use 5200. One day, when that fitting needs to be replaced, you’ll curse it’s impressive adhesive properties. If you want to use a 3M product, 4200 is a little less of an adhesive. Heard good things about Lifecaulk and Sikaflex, too.

[reckless42586]

Thanks for the welcome.

It's been a couple weeks since I've looked on the interior, but there is a valve, I was surprised it wasn't visible from the exterior though. I'd have to completely crawl into the engine compartment to get my hands on it, if even possible, let alone doing any work. I agree, removing and reinstalling is probably best, I'd plan to inspect it and replace if there were any signs of cracks or damage.

As far as structural components go, I was looking at removing a portion of the bottom of the stern locker, is there a way to tell if that's structural? I could contact Catalina Direct, they seem pretty helpful here. However, since the boat was built in 73', I feel like this isn't the first time someone's had to work here unless it's only been done when the engine was lifted out.

[Uncle Bob]

Originally Posted by reckless42586

Thanks for the welcome.

It's been a couple weeks since I've looked on the interior, but there is a valve, I was surprised it wasn't visible from the exterior though. I'd have to completely crawl into the engine compartment to get my hands on it, if even possible, let alone doing any work. I agree, removing and reinstalling is probably best, I'd plan to inspect it and replace if there were any signs of cracks or damage.

As far as structural components go, I was looking at removing a portion of the bottom of the stern locker, is there a way to tell if that's structural? I could contact Catalina Direct, they seem pretty helpful here. However, since the boat was built in 73', I feel like this isn't the first time someone's had to work here unless it's only been done when the engine was lifted out.

Hey, good to hear that there is a valve after all, as far as cutting into the bottom of the stern locker, how would a larger circular access port go, say 8 inch or so? Also given that access is somewhat constrained I reckon that if you can unscrew the retaining ring on the skin fitting enough to allow the fitting to be moved back, say an inch or so to allow the removal of the old sealant and squeeze a good bead of new into the gap then tighten it up it would be acceptable. You would be looking to get the new sealant in to the gap far enough to reach the backing plate when it is tightened.

[Wotname]

FWIW, going by the last picture posted, the inner seems to be screwed or pushed) into the outer and it also seems that a cold chisel or perhaps visegrips have been used in the past to free the inner part of the fitting.

[reckless42586]

Originally Posted by Uncle Bob

Hey, good to hear that there is a valve after all, as far as cutting into the bottom of the stern locker, how would a larger circular access port go, say 8 inch or so? Also given that access is somewhat constrained I reckon that if you can unscrew the retaining ring on the skin fitting enough to allow the fitting to be moved back, say an inch or so to allow the removal of the old sealant and squeeze a good bead of new into the gap then tighten it up it would be acceptable. You would be looking to get the new sealant in to the gap far enough to reach the backing plate when it is tightened.

I like that idea, I can start with the smallest access hole I think will work and go from there. This would be a great simple fix, to back out the fitting just enough to remove the old and apply new sealant (4200, lifecaulk, or Sikaflex). Guess it's just time I get in there and get a closer look with this plan in mind. Thanks!

[reckless42586]

Originally Posted by Wotname

FWIW, going by the last picture posted, the inner seems to be screwed or pushed) into the outer and it also seems that a cold chisel or perhaps visegrips have been used in the past to free the inner part of the fitting.

I noticed that too, doesn't seem ideal. Maybe I could find a strap wrench if I need to wiggle it free.

[joelhemington]

Originally Posted by reckless42586

Thanks for the welcome.

It's been a couple weeks since I've looked on the interior, but there is a valve, I was surprised it wasn't visible from the exterior though. I'd have to completely crawl into the engine compartment to get my hands on it, if even possible, let alone doing any work. I agree, removing and reinstalling is probably best, I'd plan to inspect it and replace if there were any signs of cracks or damage.

As far as structural components go, I was looking at removing a portion of the bottom of the stern locker, is there a way to tell if that's structural? I could contact Catalina Direct, they seem pretty helpful here. However, since the boat was built in 73', I feel like this isn't the first time someone's had to work here unless it's only been done when the engine was lifted out.

I think I'd pursue the access hole - a seacock you can't get to is not worth much

[mitiempo]

Originally Posted by reckless42586

As far as structural components go, I was looking at removing a portion of the bottom of the stern locker, is there a way to tell if that's structural? I could contact Catalina Direct, they seem pretty helpful here. However, since the boat was built in 73', I feel like this isn't the first time someone's had to work here unless it's only been done when the engine was lifted out.

Call Catalina, not Catalina Direct.

Catalina Direct is a separate company selling Catalina parts.

[reckless42586]

I forgot I had another access hole that gives me pretty good access to the inside of this thru hull. I don't plan to cut a new access hole in the stern locker. Another correction, this fitting does not have a valve, assuming since it's an exhaust thru-hull and doesn't seem like it's common to have a valve on it, although when crewed it can touch the water line. I also noticed that it's corroding and is green, which I've read confirms there's probably a leak. My thinking now is to disconnect from the exhaust tube, work it free and remove entirely, and replace with a new stainless steel fitting with a similar bend. I may try cleaning/brushing it, but is probably just worth replacing.

[Wotname]

Originally Posted by reckless42586

I forgot I had another access hole that gives me pretty good access to the inside of this thru hull. I don't plan to cut a new access hole in the stern locker. Another correction, this fitting does not have a valve, assuming since it's an exhaust thru-hull and doesn't seem like it's common to have a valve on it, although when crewed it can touch the water line. I also noticed that it's corroding and is green, which I've read confirms there's probably a leak. My thinking now is to disconnect from the exhaust tube, work it free and remove entirely, and replace with a new stainless steel fitting with a similar bend. I may try cleaning/brushing it, but is probably just worth replacing.

It is green because most likely it is bronze. If it bronze, a wire brush will remove the surface green and let you see the condition of the bronze and again, it most likely to be OK. Bronze will outlast SS in this application by a long shot.

It does look like it has been leaking on the lower section - most likely to be the lack of sealant as described in your OP.

If it was me, I would be checking the complete exhaust hose routing to make sure it goes well above the waterline at some point and has a suitable waterlock between the engine and the high point.

[reckless42586]

Originally Posted by Wotname

It is green because most likely it is bronze. If it bronze, a wire brush will remove the surface green and let you see the condition of the bronze and again, it most likely to be OK. Bronze will outlast SS in this application by a long shot.

It does look like it has been leaking on the lower section - most likely to be the lack of sealant as described in your OP.

If it was me, I would be checking the complete exhaust hose routing to make sure it goes well above the waterline at some point and has a suitable waterlock between the engine and the high point.

I didn't know bronze would outlast stainless in this scenario. I'll give it a good clean and look for any cracks. The exhaust hose routing does go through a waterlock and then is routed as high as possible in the compartment.