Mystery Leak In My Monark

[AC2717]

I just purchased a 85 Monark modified v hull Jon boat (fishing set up) it has a 20 hp evinrude and. 40lb thrust foot controlled thruster

So here is my problem- keeping in mind that I replaced the drain plug already with a T type expandable rubber (and will be putting in a float switch for the bilge this weekend)

The boat is sitting on a mooring on the lake and after sitting during the night when I go out to it in the morning about 8am and switch the bilge it runs for about 4-5 seconds. When I then go out there about 7-8pm I switch the bilge on and it is running for about 30 seconds?

I am obviously leaking, previous owner never moored it as he day fished multiple lakes, not being swamped and have a new Basspro cover on it
I am off the belief that the rocking of the wakes during the day and causing pressure somewhere while attached to the mooring? While trolling or just drifting no water at all. I am thinking the rocking and back and forth tug on the mooring is creating sucking around the drain plug?
(my larger pleasure boat gets water in the same way but not to this extent or does it and it just does not seem it because of the size?

There are no dents in the hull, no cracks that I can see as I also filled it up with water and did not see anything before launching it. I have read about the drain plug tube being misshaped over time? Also there is marine epoxy on the stern from where something used to sit and that did not see to be leaking when filling the boat before launch. The forward live we'll is also dry so I do not believe it is coming there as I also have the drain tube straight up to prevent backwash from the drain
noticed also that my rear live well wont drain also not filling up unless pump turned on, and I think that is supposed to go into the bilge so I don't think its coming in through the live wells

I am thinking of putting some gasoline grade rubber line and clamping it around the drain tube and putting a ball value on it, and if it will fit, the drain plug on the outside to see if this is the problem, other than that there would have to be a crack somewhere, or are the few rivets on the boat (hull is welded except for stern and some floor supports, boat was sent from factory as a fishing boat) leaking
Help me out please

[slonezp]

Frustrating. Sounds like you've covered your bases pretty well. Do you notice anything while you're running the boat? 

[AC2717]

nothing coming in while underway, trolling, or drifting, only while sitting on the mooring

thinking might be some rivets on the stern, only place there are rivets, also will check the live well pump connections at the stern. I don't know 

[slonezp]

Just because it has rivets, doesn't mean it's going to leak. Lund, arguably the number 1 aluminum boat manufacturer rivets their hulls. Personally I don't like the T expandable plugs. I like the lever type. http://www.overtons.com/modperl/product/details.cgi?pdesc=Drain-Plugs-1-Stainless-Steel-Snap-Handle&i=71744

[AC2717]

I have a new one of those type of plugs as well, I can put that one in, agree on the rivets, just thinking I got nothing left to check, I am putting a float switch in it tomorrow but don't want to kill the battery pumping for like a minute everyday or will it not matter and get me to the end of the season as long as I try to run the motor to charge the batter

 

another day yesterday and this morning:

 

nothing yesterday am (less than 3 second pump when last pumped about 8pm prior) then yesterday at about 6pm pumped about 25 seconds, this morning less than a 5 second pump

[F14A-B]

Rivets can and Do leak, not saying that's you're issue, but it has to be considered. Hairline cracks are also probable in aluminum. Sometimes bigger than hairline...

[AC2717]

Rivets can and Do leak, not saying that's you're issue, but it has to be considered. Hairline cracks are also probable in aluminum. Sometimes bigger than hairline...

I agree, but I would think if there was a hair line crack then no matter the time of day, water would be a constant issue

[F14A-B]

Yea, it's often real difficult to find, I've been there, there is at least a trifle bit of expansion and contraction... I believe you will locate it though, thru sheer determination.

Good luck on it!

[AC2717]

just went to west marine on my break and picked up Capt. Tolleys. Spoke to an old salt in there as well, He was saying the same thing, the heat in the day could be causing the aluminum to expand and contract and allowing water to seep in. Said this should fix the problem. Also I am going to check and more than likely just replace my live well pump line as that could have a small crack in it, but I doubt it, because any crack in a line or hull would show a continuous amount of water in the boat when checking at 12 hour intervals, but you never know if it is rocking back and forth during the day on the water line

 

http://www.westmarine.com/buy/captain-tolleys--crack-cure-sealant-2-oz--243990

[F14A-B]

Yep, you will find it, you're in the zone! Good keep at it, I wondered a bit on the tube, it felt unlikely to me, but I would Persue it. Post back on you're findings...

No Hill to High For A Climber....

[AC2717]

yanked it on Friday evening, let drain, got underneath it, found most of the rivets dripping, also pulled the floor and found that someone used 2inch plant foam (like the stuff that you poke the stems in and retains water) was used as ballast foam. Must have removed water wait of close to 60lbs, and I ended up replacing that with 2 inch closed cell water and mold resistant foam insulation found at any home depot type stores. coated all exposed rivets from the inside and even the ones under the fishing decks, went underneath and did the same thing. Let sit for over 24 hours launch it fished for 4 hours nothing in it, put it on the mooring, waited over 9 hours......still taking in water but only pumped for about 20 seconds.

 

Think I will pull it and have someone weld the rivets, would that be a problem? I would not think so

[AC2717]

has any heard of coating the bottom of the boat with Gulvit?

[F14A-B]

I have replaced rivets many times, but with you're rig? I simply cannot say... But I am not surprised by you're findings. Welding? Maybe... I mean you can do it that way, I never did, but... Make sure you get a first class welder to do it and I would still babysit it.... How many rivets do you suspect?

[AC2717]

i think I would just have them all done that sit at waterline and lower. Maybe close to 50

 

I was looking into the Gulvit stuff, but now someone is telling me that goes in the inside of the boat, seems they way they sell it, it would be a coating material for the whole bottom

[wordfactories]

 

 

Think I will pull it and have someone weld the rivets, would that be a problem? I would not think so

 

 

If it is certainly rivets I'd get a buck, a ball-peen hammer, and a buddy and try to tighten them before I resorted to that. 

[AC2717]

definitely the rivets, a lot of them, even when I tried to seal them I watched the sealer drip down them from the bottom