Impossible trim tab leak

[peterkvs]

I have a 99 400 DA. After a few months of operation the trim tab reservoir leaks down to where the tabs won't deploy enough to keep the bow down at cruise. So obviously it is leaking. I've inspected everything and can never find a drip. When the boat was hauled I inspected the actuators and they were not leaking. Here's the impossible part. The pump is mounted on the transom in the center of the boat. The tabs are about 5' either side of the pump. The fluid lost from the pump gathers half way between the pump and port tab, right behind the rudder post. If I put an absorbent pad there it wicks up all the fluid. But that area is a high spot along the transom and there are stringers either side of that spot that show no sign of fluid. So how the heck is the fluid getting to the absorbent pad, the only thing that traverses the area is the tubing that runs between the pump and tab, and I've replaced that. Also it doesn't leak unless the boat is driven. The pump pressure isn't enough to make it leak, so I am assuming the pressures are higher underway on occasion.

Anyone have any similar experiences and possible solution?

Thanks,

Pete

 

[Little Ducky]

I don't have a fix for your problem but someone just posted a video made by one of those go-pro's when they were trying to find a leak in their engine compartment. Might want to see if you can borrow or rent a camera...... set it up focused on the area and then take the boat for a spin and see if any thing shows up.

Good luck.

 

[fwebster]

Pete,

I think there is a nylon fitting where the tube runs thru the transom. A brass pipe nipple screws into the nylon fitting on one end and into the actuator on the other. The brass tube has been the source of more than one mystery leak. If you have a haul out scheduled this winter, it is an easy fix to pull the actuator mount off and check the fittings for leaks and re-seal the threads.

 

[Lazy Daze]

The brass nipple (thread sealing) is, indeed, the most common cause of a leak as Frank pointed out. To an extent, running the boat should not make a difference as the pump is completely independent of anything to do with the engine. Meaning, nothing changes (pressure, or other wise) on the pump end of things when the engine is running as compared to when it the engine is not running. BUT, it could be the consistent pressure of water on the tab that is pushing the fluid out. Eventually, it could start to leak when operating the tab at the dock, too.

I suspect the explanation to this: "So how the heck is the fluid getting to the absorbent pad", is that you just aren't noticing the fluid trail as it's small and relatively clear. Tape a paper towel below the port tab - whether on the transom wall or the floor directly beneath it. I would venture a guess that you will find tell-tale fluid on the paper towel after some time. For good measure, do the starboard side, too.

 

[peterkvs]

Update... upon further inspection the brass tube through the transom could easily be turned one complete turn tighter with fingers. Someone had put a huge ball of silicone where the tube enters the hull on the inside. The leaking fluid was trapped in the transom and was leaking out a crack two feet toward the center of the boat. Now I am wondering if I have some coring saturated with ATF. I didn't think the transom was cored, but can't explain how the fluid would travel two feet horizontally. There is a step in the transom thickness which I am assuming is coring or maybe just a plywood doubler so you have something to screw things too. Thoughts?

Pete

 

[Lazy Daze]

The silicone ball is normal - it's to help seal out water from that cavity. Want to see a REALLY big ball? Take a look where electrical lines and hoses leave the bilge on smaller Sundancers, going towards living space. The brass tubes seem to loosen up, somehow, over time. Whether they weren't tightened fully to begin with or the metal to plastic connection causes it, I don't know. But it's not that uncommon at all.

Yes, transom is cored for strength and, yes, the transom is thicker in some places (another layer of ply).

I highly doubt any coring that may have gotten ATF in it will pose a problem. For one, it would likely be a small amount and, two, it might actually act as a preservative (google that, though, I'm just spit balling on that last one). If it was me, I might open that crack (drill a hole) up just so any remaining ATF leaks out faster. The only thing that would make me wonder is whether the ATF caused any delamination.

 

[fwebster]

The transom itself is solid on the 400DA but there is a layer of plywood behind the interior layer of fiberglass to mount things to, not for structural reasons. I suspect the trim fluid has just run to a low place and escaped but has not affected the ability of the plywood to hold screws.

 

[Lazy Daze]

I had thought that that model still used a plywood core, but Frank is usually spot on so go with his statement on the coring subject. Of course, that makes everything better for you. It would also better explain why the ATF was getting in between the wood and fiberglass skin and eventually seeping out. The way that those "screw holding plywood pieces" are fiberglassed in place is done in a faster manner than transom coring. Meaning, there ends up being more voids than there would be in a core. All-in-all, other than cleaning up until it all seeps out, you should be just fine and I highly doubt you'll have any adverse problems because of it.

 

[peterkvs]

Update! With the big ball of silicone removed and the brass nipple tightened one more turn I am unhappy to report that the leak is worse than even. Now atf seeps out the hole for the nipple as well as the crack. At least I know where it is leaking. I suspect that the nylon trim tab mount is cracked though I suppose the brass nipple could be cracked. Anyone ever fix this with hauling the boat? I can't even get back there to work on it. What a pain!

 

[fwebster]

If you can muster enough of your nearby friends to stand on the bow, you might raise the tab mount high enough to remove it from the transom………….beer may help entice them. You will have to get wet and if you can get the tab mount high enough, I'd replace the complete actuator and brass nipple.

We've also done this with a Marina Bull forklift. The 400 is too heavy to lift the entire boat, but you can raise the transom several inches.

Good luck with it…….

 

[Lazy Daze]

I would consider doing it, personally. But you obviously want to be careful that you don't get any water into the system - do it on a calm day, move slowly around the tab, etc. A sealant such as BoatLife LifeCalk will cure in the presence of water, so resealing it should be fine. Just don't go tromping around too fast for a few days while it sets up - you can certainly move the boat, you just don't want to physically force the sealant out. But given how tightly the top of the ram mount attaches, it's not too much of an issue.

 

[Tabman]

I too have seen weight put forward. Most ingenious method I heard about was to place a couple of inflatable dinghies on the foredeck and fill them with water.

I agree, time to replace the actuator and pipe nipple.

Tom
Bennett Marine

 

[peterkvs]

I bit the bullet and hauled the boat and had the trim tab upper mount replaced. There was many hairline cracks around the boss that the brass fitting threaded into. Works like new and the mess is gone.

Thanks for the advice,

Pete