1993 Stingray 556 Leak in Bilge

Joined
Nov 16, 2020
Messages
11
Hello all,

3.0L Mercruiser with Alpha One Gen 2 Sterndrive.

I recently noticed a leak in the bilge that I cannot figure out.

I've run the ear muff test to make sure it is not a bellows leak. The bellows around the shift cable, one around the U-joints, and one at the exhaust seem to all be in good order.

The leak is very slow and happens when the engine is off or on. It's slow but constant.... my bilge pump runs once every 5-8 minutes.

Here is a video of the leak.... For orientation purposes, I'm on the port side, facing starboard, looking toward the stern (transom). Notice how some of the small particles are moving away from the transom. I put my finger down there and I cannot feel incoming water, but the video appears to indicate otherwise.


The picture below is what I assume is the approximate location of the leak. However, I am unable to see any significant damage. I ran aground approximately four years ago, but haven't noticed any leaks until now.



20240920_141250.jpg



Plan of attack:

I will take the boat out later this weekend to clean the hull and take additional photos. I will circle back when I have more photos.

Other things to note:

When I started this troubleshooting project, I disconnected the battery (so the bilge wouldn't run) and filled the bilge with a few gallons of water. I was hoping that I might run into something like this:
(Note: this is not my boat or the situation, but it what I was hoping for in the test). No water leaked from inside the bilge to the outside. The leak only occurs when the hull is in the water.

Also of note, when the hull is in the water, I see no leaks around the flange of the stern drive. The leak seems to be emanating at the bottom of the bilge at the 90 degree angle where the bottom of the hull meets the transom.

Thanks for any suggestions you can offer. If we are looking at a fiberglass hull repair, how much does that run? Are there tools a shop can use to isolate the leak? The only thing that comes to mind for me is "magnafluxing an engine block." Clearly, there must be different detection tools for this material. Are there similar methods used in the fiberglass industry?
 

flashback

Captain
Joined
Jun 28, 2002
Messages
3,974
I would remove the garboard drain fitting and inspect the wood around it.
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,475
I would remove the garboard drain fitting and inspect the wood around it.
Agreed bar garboard drain is probably loose. Mine was moving in the hull, bent the screws, new screws took it out bedded it in 5200 legit dry over night been good for years
 

Grub54891

Admiral
Joined
Jun 17, 2012
Messages
6,090
Had myself a leak similar. I had already replaced the bellows and gimbal bearing. Still had a leak. What I found was that the block on the gimbal ring, where the trim lines are attached, that gasket there was cracked/leaking. Easy fix once I found it.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
49,758
There are 3 screws on the garboard plug flange. Do you really need a video to show you how to remove screws?
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,304
may also be a exaust pipe leak , the exaust in underwater running or not
 

Grub54891

Admiral
Joined
Jun 17, 2012
Messages
6,090
Check post #4. Also check the exhaust tube inside the boat when in the water, if no leak shows there, start the motor and check. Be very careful when the motor is running.
 

JASinIL2006

Vice Admiral
Joined
Feb 10, 2012
Messages
5,678
Thanks for the clarification.

Wouldn't it be strange for this to be leaking inward and not outward? I originally filled the bilge and no water exited the garboard flange. Have any of you encountered this situation before? The flange leaks but only in one direction?

The pressure from a little bit of water in the bilge is nothing compared to the pressure of the water when the boat is floating. That's one of the reasons filling the boat with water is a bad idea.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
49,758
Not to mention filling the boat with water not only adds a few thousand pounds to the trailer, it pushes water in areas it's not supposed to be
 
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