1974 Mariner Possible Leak Points

[MonkeyBird747]

A couple of questions on water in the bilge and how much, if any, is considered acceptable/normal on these riveted boats. I have an automatic bilge pump installed on the hot batt bus. After a full 8-9 hours on the water the other day i was pulling the boat up the ramp on the trailer and the auto bilge kicked in. First, it was good to know it works! But it puked out maybe a gallon or so of brown water (hard to judge, but a 3/4" stream for 20-30 seconds maybe?) out of the upper exit on the side of the hull. I had not drained the bait tank yet, so some of this was likely overflow from the bait tank drain at the top of the tank.

The next trip out the auto bilge never kicked in, and I put the boat away in the garage. When I was hooking up the trailer for the next adventure I had to rock it around to position on the hitch. When I did, the auto bilge kicked on and puked a gallon or two of brown water onto the garage floor.

The trip last night was very short at maybe 3 hours. When loading up to leave and while the boat was still on the ramp I manually turned on the bilge pump. A small amount of water pumped out, but you could hear the pump cavitating the whole time, so it wasn't completely submerged.

After the pump ran a bit I shut it off and pulled the drain plug. I was thinking that the bilge couldn't possible pump ALL the water out as low as the drain plug, but when I pulled it nothing came out. It was damp inside, but not even a trickle. So maybe the bilge pump is doing a great job.

Is some water intrusion to be expected on these older riveted boats, or should I be chasing down possible leak points? I have a few suspects at the transom where previously installed equipment bolt holes have been plugged with some type of rubbery silicone. What would be the proper method to plugging these old through-holes in the transom? I was thinking a bolt with washer and silicone on either side, but I'd have to cut out some of the rear decking to access these, and I don't really want to do that. Is there a good method to plug them from just the outside?

I was also wondering if some water is just filling up the bait tank line and being routed into the bilge later. I usually keep the bait tank plug pulled, so if some water were coming in that way it would just circle around and get routed back to the bilge. The pump should have a check valve that prevents this, but maybe it isn't working properly.

The bottom of the boat looks great to me. No signs of abuse that I can tell, and I don't see any missing or suspect rivets. Check out the pics. I don't know if there is enough there to account for that much water coming in.

 

[SHSU]

From what you are describing, sounds like a slow leak from somewhere or your are taking some waves/splash over the bow while you are running around. If the water was leaking through your transom I would be more concerned about the condition of the transom then the water leak.

As for how much is to much, it depends who you are. Some of us don't like to see any water, others are willing to live with some. I have read where people have to pump out the bilge a couple times in a trip.

As for the drain plug, I hate its location on these boats. It is not at the lowest point so you will always have some residual.

In the end it is up to you.

Just my 2 cents for what little its worth...

SHSU

 

[GA_Boater]

Yeah, the plug is in a bad place for getting all the water out because down low and centered is in the inside of a knee brace.

In the last three photos showing the keel and some separation - That's normal as the keel is not sealed to the hull. There is a drain hole in the keel, don't remember which end, that drip when you pull her out of the water.

Because the transom plug is poorly positioned, when I pull mine out of the water and the stern is clear, I pull the plug on the ramp and while I finish winching and tying the boat to the trailer, it's draining the bilge if there is any water and leave the plug out until the next trip.

I keep my tinnie covered outside and crank the jack to raise the bow as high as it goes in case any rain water gets under the cover during a driving rain storm. It happens occasionally.


You do have a lot of extra holes in the stern. What you can do is take the boat to a ramp with the plug in, keep it tied down and back down the ramp until all the suspect holes are underwater. Climb inside to see if any water is leaking through the holes. Actually, I would remove the silicone and plug the holes with a machine screw and nut. Seal with some 3M 4200 for a permanent repair.

 

[MonkeyBird747]

Good suggestions and info SHSU and GA_Boater. I like the idea of sealing up the holes with some screws and 4200. I just can’t find any obvious intrusion points, so I’ll have to address what I can see. We are on small inland lake with nothing to splash over the bow, so I think your correct about the slow leak.