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Mysterious Leak


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I have a 1993 Sea Nymph GLS 175 that I use for early spring browns, bass, walleye etc.  Put a new Yamaha 4 stroke on in 2014.  It has developed a significant leak late last season. Takes on about a gal an hour.  I pulled the boat, let it on the trailer for a week to let it dry out inside and out. Put the plug in and disconnected the battery to kill automatic bilge pump.  Filled it with water nearly to floor level which is above water line. Had one small leak at a rivet, about 6 drops a minute.  Replaced it with a closed end rivet and 3m 5200.  I have replaced a few rivets in the past few years.  Filled again a day later, all good.  Put back in water, still leaking at the dock. Plugged the intake for the live well pump in the transom just in case that or the hoses were leaking. Still leaking.  Live well drains are out the sides and about 4 inches above the water line so it wouldn't be there. No apparent leaks visible from inside the boat in the visible bilge area.

Totally stumped at this point.  Any suggestions ??

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Posted (edited)

Since it started after you replaced the motor - look at the sealant around the bolts that penetrate the transom that mount the outboard to the hull.  Maybe even pull one at a time and re-bed with 4200 of those are under the water line. What about transducer screws?   Those are sometimes a good source of leaks as well.  

Edited by AnglingAddict
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Lower bolt holes that mount the Yamaha?    I would also check over the transom area to make sure you haven't missed any other possible causes.  Inlet/outlet for well at the transom should be double checked.  From the picture it appears that the splashwell joint is high enough above the water so that is likely not an issue.  

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48 minutes ago, AnglingAddict said:

Since it started after you replaced the motor - look at the sealant around the bolts that penetrate the transom that mount the outboard to the hull.  Maybe even pull one at a time and re-bed with 4200 of those are under the water line. What about transducer screws?   Those are sometimes a good source of leaks as well.  

Lower motor bolts are below water line and were well below where I filled the boat with water. Had it filled for a few hours and nothing came out there.  You can also see the bolts and nuts when looking in the bilge, nothing apparent coming in there.  When the boat was filled nothing came out sny transducer mounts, fittings , etc.  I guess it may be a good idea to reseal everything anyway.

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Filling up your boat with water is not going to show you where the leak is. The upward pressure of the water and the downward pressure of the weight of the boat is easily stronger than the maybe fifty gallons you poured into the boat. When the boat is in the water ,things get stretched in all directions which may cause a leak on a seam .Besides, the weight of the water you poured in there may have pressed the leak closed. It sounds to me that you should do a gluvit treatment. This is not something that can wait till fall. It should be done when the weather is nice and warm. because warmish gluvit penetrates every seam and crack and after it dries up properly it is also very flexible and can easily stretch right along with the pressure points in the hull

Good luck.

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Discharge from the fish boxes is up front and about 4 inches above waterline so it wouldn't be that. I plugged the intake in the transom but was no help. This is a GLS 175 which is different than the GLS 195 in that area.  Going to look into Rolmops idea.

 

 

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Am I right to think that you went from a 2 stroke to a 4 stroke with the same or maybe even higher horse  power? If so, the much heavier 4 stroke will have done a job on your rig and this leak which is probably on a seam is only the beginning of more trouble to come.

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16 hours ago, rolmops said:

If so, the much heavier 4 stroke will have done a job on your rig

You thinking just the weight or that it vibrates more?

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He went with a smaller four stroke.  That was back in 2014 as he says because I bought his 2 stroke.  So this is a new issue, now 8 years later.

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I have a 2012 Tracker had a leak, Could not figure it out, Did the same thing filled it with water. The very small leak was around a thru hall fitting toward the front of the boat for the live well. Was a **** to get to,  took part of the floor out and replaced the fitting and silicone all around. Problem solved.

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Make sure your speed gauge tube is hooked up and not flopping around.  I had one become disconnected and it pumped water into the boat anytime it was running hard

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Check the seam between the inside of your transom and the transom splashwell. Before i repowered and replaced my transom and resealed that seam on my Sea Nymph it leaked like a sieve anytime i used the boat and waves or rain washed into the splashwell.  Even when your boat is tied up any movement of the transom in wind or waves can cause the transom to dip low enough for the splashwell drain holes to take on water and if the seam between the transom and splashwell is not water tight, water will leak into the boat. Seal it with 3M 5200 and you should be good to go, if thats not the issue, back to square one. The transom rotting and pulling away from the splashwell was the cause of my issues by the way, may want to take a look at yours if thats what it turns out to be. Good luck!

 

Here is a link to a post from my Sea Nymph repower and transom repair which may help explain what i'm talking about. 

 

 

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On 6/6/2022 at 2:54 PM, LongLine said:

You thinking just the weight or that it vibrates more?

It is probably mostly the weight. But if there is extra horse power as well ,then you get a bit of everything. The damage is not always done in the water. Trailering is often the culprit If you work with a 25 year old transom that now carries a heavier engine at sixty mph..., Anyway, I feel like I am becoming an armchair boat mechanic.

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On 6/5/2022 at 10:10 PM, rolmops said:

Am I right to think that you went from a 2 stroke to a 4 stroke with the same or maybe even higher horse  power? If so, the much heavier 4 stroke will have done a job on your rig and this leak which is probably on a seam is only the beginning of more trouble to come.

Went from a 115 Johnson to a 2014 Yamaha F70LA.  It is enough power and gets great milage.  Johnson was about 290 lbs.  F70 is 257 lbs.  Lighter than most 70   2 strokes.

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On 6/6/2022 at 4:46 PM, Ecto2 said:

Make sure your speed gauge tube is hooked up and not flopping around.  I had one become disconnected and it pumped water into the boat anytime it was running hard

That was happening many years ago.  Got rid of the pickup and tube.  Just use gps speed now.

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18 hours ago, Great_Laker said:

Check the seam between the inside of your transom and the transom splashwell. Before i repowered and replaced my transom and resealed that seam on my Sea Nymph it leaked like a sieve anytime i used the boat and waves or rain washed into the splashwell.  Even when your boat is tied up any movement of the transom in wind or waves can cause the transom to dip low enough for the splashwell drain holes to take on water and if the seam between the transom and splashwell is not water tight, water will leak into the boat. Seal it with 3M 5200 and you should be good to go, if thats not the issue, back to square one. The transom rotting and pulling away from the splashwell was the cause of my issues by the way, may want to take a look at yours if thats what it turns out to be. Good luck!

 

Here is a link to a post from my Sea Nymph repower and transom repair which may help explain what i'm talking about. 

 

 

This leaks just sitting at the dock when the water is well below the splashwell.

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The shame of it is that it has an aluminum floor so I had never planned to pull it up.  If necessary to do a proper Gluvit job I will.  Probably will pull the gas tank first to get a view of some of the hull.  The gas tank has it's own removable, screwed in floor and takes up a considerable amount of the cockpit area. Pull the tank and run it from a 5 gal tank, put it in the water and see what developes.

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After rereading and thinking about your issues starting after the new motor was installed, as others have mentioned you may have hit a point where the waterline is now at. Your splash well ie ports that drain out or transom area might be the area to focus. Try corking them if they are at the water line to see if they leak. Ripping up the floor with removing the tank is a royal pain. You might want to focus on the back. Mine has a couple of side pans in the battery compartment that might get you a visual access to see if water is coming in. Just drill out some rivets to remove them if it’s the sam. If not anything putting the boat in the water with someone’s head and a light to watch where she starts coming from might help to. Hope you find it. I know how frustrating it is. 

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If me, I would get the boat on a trailer & jack the front-end way up.  Then I'd put some water in it, but I'd mix some food coloring in it.  My reasoning is that you said you went to a smaller 4 stroke a few years ago and that you've recently replaced some rivets.  I see from your pictures that you troll with the big engine as I don't see a kicker.  Even though they're quieter, 4 strokes have many more moving parts than 2 strokes and as such their harmonics are different than 2 strokes.  i.e.  they vibrate differently, especially at low speeds.  I suspect you may have multiple rivets, or a seam or a joint just starting to loosen up.  Leaks may be so slight that you can't see them drip.  The food coloring will make it much easier to see.   

 

I'd also check to see if there is some sort of dampening plate/spacers between the engine & the transom.  

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If you had it stored outside in the winter and it got or had small amount of water in it, the freezing of the water at or near the transom probably did a job on a seam sealant. Happened to me with a fishing boat.

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