• Welcome to this website/forum for people interested in the Morgan 38 Sailboat. Many of our members are 'owners' of Morgan 38s, but you don't need to be an owner to Register/Join.

Holding tank plugging with foam

Terry Davis

New Member
As a lot of 382 owners, i am having waste leaks on top of the holding tank, bottom of the bilge. After reading a lot of posts in this forum, I am going to take out the toilet, plumbing, and thruhulls and replace with a compost toilet.
Does anybody have advice on filling the tank with closed cell foam: how do you empty and clean the tank? pour chlorine? pressure wash thru the pump out pipe at the bottom of the bilge?
Thanks for any advice before I create a big mess.


James M. Cleary
There has been quite a lot of discussion on abandoning the keel holding tank. The reason for the tanks to leak is improper blocking up of the boats when placed on the hard. If a wood block is situated under under the tank at the aft end of the keel, the weight of the boat will flex the tabbing that holds the bilge floor/ tank top. Once the tabbing is broke it is almost impossible to get in the area with tools to fix it. Many, myself included, have abandoned the tank for other means. There are three schools of thought on what to do with the empty, unused tank. First is to pour in foam to fill the void. Second is to cut out the bilge floor to create a deeper bilge. Third is to close off the 1 1/4" PVC pipes that enter the tank and leave the space empty. Filling with foam, in my mind, would be a waste of time and money. Since the cracked tabbing will still be there, water will leak into the tank when the bilge fills to a point above the crack and will fill in the areas around the foam and be subject to freeze/thaw. Cutting out the bilge floor would be the worse option because the aft end of the keel will now be vulnerable to damage if the boat hits a rock. If the back of the keel is exposed to the sea, you will be unable to stem the inflow of water without the bilge floor. The third option, as we have adopted, is to put PVC screw on caps on the existing piping and leave the tank empty. At first the tank was filled with bleach to give it something of a cleaning. Once that was done the only maintainance is to remove the screw cap at the end of the season, Stick a hose down the PVC pipe to pump out any water that accumulates over the season, Add a gallon of cherry antifreeze to the tank, which gets pumped out in the spring. I hope this helps you decide which way to go.


Terry Davis

New Member
Thank you for your input. I thought using closed cell foam would fill every inch of the tank and block any water out as well as reinforcing the structure of the keel. You do have a point though!!!


Terence Thatcher
My holding tank, luckily, only leaks if full and someone tries to pump more in. Then the leak is half way up the side of the bilge wall,,again because the tabbing was not done well enough. If you search the site, I think Mark Pearson posted about his decision to go with a composting toilet,a Nature's Way, I think. Finally, I have thought the best solution for an abandoned holding tank might be an epoxy/glass slurry. That would add solidity to the aft keel. But, not being an expert, I don't know that would work. Without cutting into the side of the tank from outside, it might be impossible to clean the tank sufficiently. Plus, one would have to do it in layers, because if done in one pour, the heat would be so intense it would damage the existing structure. But as Jim notes, if you have any leaks from bilge to tank area, that might be a problem. (All this from a guy who has a 6' draft, so my bilge is deeper than yours.) Finally, be aware that the sides of the keel in way of the bilge and holding tank are not real thick. Pound on it and you will see what I mean. That bothered me, so when all the gelcoat was stripped off the boat for a barrier coat, I had them add 4 layers of cloth to the sides of the fin. In retrospect, maybe not necessary, but I hope it added some strength to the whole keel structure.
I am with Jim on this. Just not convinced I could ever get the old tank cleaned out well enough to fill it with anything that would bond well enough to the sides to prevent water intrusion and problems with freezing/cracking. As the blocking issue illustrates, the design of the keel makes it certain that the walls of the hollow section of the keel will flex when the boat is blocked incorrectly, and I suspect there would also be some slight change in shape from the stress of righting moment when heeling excessively. Of course we are all experts at changing sail area to keep ourselves in balance and would never sail overpowered, but you get the idea :)

It is certainly a little annoying to have to pump it out occasionally, but I just chalk it up to life with an old Morgan. Every boat model has its idiosyncrasies and this is one of ours (the torpedo tube being the other big one).
I agree with Jim as to the cause of the seams giving way on the top of the holding tank (floor of the bilge) around the perimeter of the bilge. I corrected mine by glassing over the points of separation from the holding tank top to the side of the bilge. I sanded down to clean glass and used the West system to seal with epoxy with heavy woven glass material and then repeated the process around the entire perimeter of bilge. It was indeed a project. Access and the depth of the bilge, not to mention the tubing that's in the way, makes this a challenge. I have short arms too. But grinding and sanding down to clean glass was the toughest part which I would not want to do again. Laying the glass weave and then wetting with epoxy was the easiest parts. I have a completely sealed holding tank and I am using it as designed. It is still holding true. I have been on the hard several times since the repair and I am very particular how they block the boat. Only the front of the keel. No blocking under the keel where the tank is or the aft end whatsoever. The yard will not know unless you tell them.
It is because of the knowlege contained in this forum that I became aware of the holding tank issue. Fortunately Sonata's tank was in tact when we purchased her. Shortly after that, I had her pulled for fresh bottom paint. The yard here in Richmond doing the work was great, but I made it a point to follow the crane to her place on the hard. I'm glad I did. If I hadn't, the tank would have been damaged. The crew had no idea of course and began laying blocking under the keel. I haad to convince the guy by banging on the hollow aft end of the keel to persuade him on the blocking locations. I would NEVER let a yard set up a Morgan without being right there to supervise.
Another point to new owners, maybe others; there are diamonds moulded into the topside just below the caprail indicating the lift points/postition fore and aft for slings. I know it's in the manuals, but may not be evident to some.

I hope I don't sound like a know-it-all. I'm not. But I would really hate to hear of someone's beloved boat being damaged needlessly.
And I have said this before, this place was a major factor in my choosing our M 383 over other boats! Thank you all! Ok off the soap box now...


Mark Pearson
Staff member
Yeah Mitchell - I'm always there when Zia is hauled out. And I have a printed version of the haul-out diagram below, which I very carefully show the yard folks with the "no blocking on aft end of keel" instructions.

I can't remember who on this forum did this drawing, but it's been very useful.

That is a great diagram! I would "borrow" this if that is ok? This should be in everyone's chart table or somewhere easily accessible.


Mark Pearson
Staff member
Mitchell - I "borrowed" it from someone else, so have at it! We'll see if anyone asserts their NFT rights to the drawing. It's a Brave New World out there!

Regarding this Thread: We are going to install our composting toilet in the next month. I'm still deciding what to do with the Holding Tank. I'm leaning towards leaving it full of water which is occasionally chlorinated. Reasons: 1) some future buyer might decide they want a Holding Tank again and it's reversible, and 2) it seems like having air (or something light) down there is the exact opposite effect of having a nice heavy lead keel. It's buoyant air that's down there quite far so it has some moment arm. With water, there is at least 135 pounds of weight down there. I guess that's only about 2% of our keel's weight, so maybe not super significant.

I'd appreciate hearing anyone else's opinions.

Filling it with Rum seems appealing from a pirate's perspective, but not from a public health perspective.:oops:

Last edited: