MS 350/390 Drain hole in Keel

[Cold Duck]

There is a 3/8" hole in a fitting mounted on the back of the keel just below the prop shaft. It is connected to a plastic 3/8" tube that then enters the hull right below the prop shaft just aft of the shaft log. It is flush with the fiber glass. It appears that it was filled with something like Marine Tex. Mine came out and I had a 3/8" gusher of water coming into the boat. Mine is a 350, but I checked my friend's 390 and it was the same, his still has a glob of Marine Tex type filler stuck in the end of this tube. Does anyone know what this tube was/is used for and proper way to seal it? I have never had a boat with a hole like this from outside into the bilge. Only thing I can think of is a drain while boat is on the hard, but then it should have a threaded plug or equivalent. Any help would be appreciated.

Jim

 

[tiz]

Mine has the threaded pipe plug. I took it out in the fall and a little water came out. Installed in the spring, no bilge geyser so far. Not sure I have the tube you mention.

There was a second drain under the swim platform. Same deal - a little came out in the fall. I reinstalled in the spring.

--Kevin

 

[Comodave]

Welcome aboard. Can you get a photo of it and post it here? Doesn’t sound like something that I would want to have on my boat.

 

[Cold Duck]

Can't get a picture as underwater. Forgot, we are in Cailf. and never pull the boat for winters here. Haven't even hauled the boat yet, we are in the freshwater Sacramento Delta. If I knew the thread used I could buy a plug, dive down and try it. It might be 3/8" or 5/16". If water clears up I might be able to take an underwater picture. I might try that.

 

[tiz]

So, get a 3/8" pipe plug and a 1/2" and have diver try each. Gently. One will work and be fairly obvious. Mine are hex drive but a normal square drive would be fine. Bring a wire brush to clean off the receptical where the plug threads into. Worth a try.

--Kevin

 

[Cold Duck]

Thanks. I am a diver so no issues there. I have been reading more posts and it pretty much appears to be a drain. Just coming from Calif, I've never had to winterize so drains are just not common. I would think the plug is brass. I think I will try a couple of taps and see if I can find one that will run thru fairly easy to determine the proper threads. It's obvious that the bottom paint has just been applied over the fitting without a plug installed so it's all over the threads. I just wanted to make sure I wasn't missing something here. It is pretty much at the lowest point in the bilge.

 

[Comodave]

It should be bronze not brass. There are many varieties of bronze out there, buy from a reputable source.

 

[tiz]

Note that the stock plug is a hex drive, not a conventional square top. Dont tap the hex......

First try to clean it out to see what is there.

--Kevin

 

[Cold Duck]

I probably didn't communicate properly. I don't plan to tap it but use the tap just to determine the size bolt (plug). Sorta like just picking a 3/8" course/fine or 5/16" course/fine and trying to screw it in without resistance. Since there is a lot of bottom paint in the hole, a bolt won't start where a tap might just do the trick. I actually think the bolt size is a little smaller than 3/8". I plan to do some measurements before I do anything rash LOL!

 

[Bacchus]

I probably didn't communicate properly. I don't plan to tap it but use the tap just to determine the size bolt (plug). Sorta like just picking a 3/8" course/fine or 5/16" course/fine and trying to screw it in without resistance. Since there is a lot of bottom paint in the hole, a bolt won't start where a tap might just do the trick. I actually think the bolt size is a little smaller than 3/8". I plan to do some measurements before I do anything rash LOL!

I would measure as carefully as possible and try to determine what it is.
Pipe sizes are very different than bolt sizing and the "bolt" is likely actually a pipe plug.
See https://www.engineersedge.com/hardware/taper-pipe-threads.htm

You will note a 1/16" NPT pipe plug is a little under 3/8" dia.
Also be aware there are differences between NPT and NPS threads ( although I suspect a plug would be NPT (tapered) for sealing.

You would likely be able to start an incorrect but close tap and damage some threads trying. It may be hard to tell what is resistance from paint vs a mismatched thread.
A pick might be helpful to scrape out the paint to get a better look at what's there and trying to match it correctly. The tap is a hood idea once you are pretty sure it's the correct one.

 

[Cold Duck]

Agree about NPT threads. Turns out to my surprise the hole is larger than 3/8" and is most likely a 1/4" NPT pipe thread. I have the 1/4" NPT tap but have not been successful yet getting it to take. Just trying to turn by hand so I don't put undo pressure on it. I have a 1/4 NPT Galvanized plug that I am going to try tomorrow. If correct, I will find a bronze plug. I can't image it would be some odd ball size. Doubt it's metric since built in the USA. It is funny that in our club we have my 350 and a 390 and both do not have a plug in that fitting. Makes me wonder how many other boats are missing that plug? It is disconcerting that there's just a dab or Marine Tex or something on the inside of the hole in the bilge sealing that drain hole. That makes me very nervious. Right now a good 'ol cork plug is keeping us afloat

 

[Comodave]

That is pretty small for a drain plug. And it has a hose hooked to it? That is also strange.

 

[Cold Duck]

Not really a hose but a plastic tube that connects to and runs from the outside fitting on the keel, thru the keel and into the bilge just below the prop shaft. Definitely by design. I have only dove on my 350 and friend's 2002 390, but both have the same installation. A 1/4" pipe fitting produces about a 1/2" hole at the fitting and inside the tubing is somewhere between 3/8-1/2" hole. I can just barely reach it on the inside with arm squeezing beside the prop shaft so can only get a finger on the hole on the inside of the boat. My guess is all 350/390s have this installed. If a flush plug is installed in the fitting one might not even notice it is there when boat is hauled unless you are looking for it.

 

[Comodave]

I can’t imagine what it was supposed to be for. If it was a keel drain why the tube???

 

[Bacchus]

I can’t imagine what it was supposed to be for. If it was a keel drain why the tube???

Likely just to get through the V depth of the keel vs a normal garboard drain only needing to get through the hull thickness.
I wonder how the tube is attached to the drain ftg? Hose barb threaded in the opposite side of the ftg? Or built in attachment forbtubing ( never seen that configuration?)

 

[Cold Duck]

Think of it this way. Factory drills a 3/4" hole thru the keel into the bilge, just the thickness of the hull. They have a fitting maybe with a barbed hose fitting (just guessing) where they put a tube on then insert it into the hole and screw the fitting to the outside of the keel ( again, only assuming it's screwed, I cannot see any screws under the bottom paint. Remember I am diving in murky water). The tubing is nothing more than a liner inside the hole they drilled thru the keel into the bilge that leaves a 3/8-1/2" hole passageway. The tube is cut off flush with the fiberglass in the bilge, no fittings, nothing. That's the best way I can explain it. Why they did this? I have no clue. Why did mine have no plug and just a Marine Tex type sealer jammed in the tube end in the bilge as the only protection from sinking, well, I would love to ask someone who built the MS 350/390s. Does this seem slipshod, well it does to me for sure. I would feel much better if I could assure that this is just a 1/4" NPT pipe thread standard plug that I can just install and all is well. Anyone who knows for sure that this was the design and solution would make me feel a lot better about where I am going and that this is the correct method to solve the issue. Luckily the boat is docked in back of the house so I can watch it while a simple cork plug keeps me afloat LOL!

 

[Cold Duck]

Was able to put in a 1/4" NPT pipe plug so problem solved. Need to get a bronze or SS plug for final fix.

 

[Comodave]

Was able to put in a 1/4" NPT pipe plug so problem solved. Need to get a bronze or SS plug for final fix.

I wouldn’t use stainless for underwater if you can find a bronze plug. The fitting that the plug goes into is probably bronze. Dissimilar metals under water isn’t a good thing. But get the bronze from a reliable marine source. Hardware stores sometimes call brass bronze and there is a big difference.

 

[Cold Duck]

SS was a fall back if I couldn't find any bronze. Got 3 bronze plugs ordered from Pipe Fitters Direct. $6 for parts, $25 to ship.

Would be curious if any MS350/390 owners check to see if they have a plug in this drain. Small sample, but no plug in 2 for 2 checked in Calif. This just doesn't seem right.

 

[Comodave]

Gotta love the shipping cost…

 

[johnma]

My 2003 390 has a 1/2" npt plug in the keel a few inches below the prop shaft. Its the drain plug for the bilge that i pull and leave out over the winter. There's also a 1" npt plug in the bottom of the swim platform that i also pull out for the winter. never saw anything like a plastic tube there.

 

[PM]

Walk your marina, I would be willing to bet you will find one or more older boats with drain plugs in the keel. I would also be willing to bet that 99% of them are aftermarket additions.

pete

 

[Keysdisease]

Garboard drain plugs are common on inboard boats that typically stay in the water. Mainship sourced much of their underwater fittings from Marine Hardware Co.

https://www.marinehardware.com/

The "plugs" can be square head, countersink square or T handle. They are typically installed to access from inside the vessel in the bilge, but I have seen an outside access install for keels.

As noted, bronze is the only acceptable material.

 

[Cold Duck]

The tube is put in as the fiberglass is laid up during construction to allow the path from bilge to plug. The problem I had was there was no plug in this drain, just some kind of rtv or something inserted from the bilge side. So, when the water started coming in because that rtv popped out, it was a very startling event. We got it fixed now, but I still have to fix a buddies boat as it has no plug either. Will see him in May and screw in a plug. I had just wondered how many other boats didn't have the plug screwed in? I have only personally checked 2 boats in Ca and both had the plug missing. Small sample but bad results.