Holding Tanks and Refrigerators

What do these two systems have in common you ask? I suppose you could say one holds your food while the other holds the waste products of your food. Both are systems on a boat that get a lot of discussion and attention from most boat owners. Both are systems that can cause lots of headaches and demand lots of our attention.

The holding tank on Beach House was the original from the factory and in a very strange place. Both heads are in cabins down from the main salon. The holding tank was a fiberglass tank installed under the seat at the dinette. Other than the fact that this might not be the most desirable location if odors develop, it means that the sewage must be pumped up hill from the heads to the tank, another less than ideal situation. 

This diagram, taken from Don Casey's article on installing a head, is a good approximation of the installation we are currently working on. The old tank has been removed and the process of installing the new tank and replacing all of the connections, hoses and valves is nearing completion. We decided to install the tank in a space next to the head, under the starboard bunk in the aft cabin. This makes for very short hose runs from the head to the tank, the thru-hulls and pump-out fittings and gives us easy access to all of the parts. We decide to use the Trident Sanitation Hose based on a lot of research on the most odor resistant hose for this purpose. The Y-valve is a Whale valve based on years of experience with this valve on our previous boat, Sea Trek. We had the tank custom made by Triple M Plastics in Maine to our specifications as to size and placement of fittings. They did an excellent job, and the tank is well-built and sturdy. Time will tell as to how well-built it is, and of course, we will report back. The current plumbing does not have a anti-siphon valve in the discharge. and we will add this and a larger vent on the tank than is normally found on most holding tanks. We would have preferred a 1 inch vent. but space constrictions kept this down to 3/4 inch. The tail piece on the head was cracked on our repair during the trip north, and although it has not leaked, it will get replaced. Since our forward head is now used exclusively as a shower, the head is disabled, but we can easily recommission it and add a small holding tank under the v-berth if we find we can't live without it.

We also decided to replace the fridge while we are able, even though this breaks our number one rule, "if it ain't broke don't fix it." The old fridge was a 3-way, using 110 volt, 12 volt and propane. We have never used the propane feature although the previous own did and liked it. The 110 volt worked well, but meant we needed to be connected to shore power or run the portable generator while at anchor. In our almost 20 years of living aboard, we have used a strictly 12 volt refrigeration system and found this to be the system we prefer. The advantage is that the system works off of one power source no matter what we are doing. If at the dock, the battery charger keeps the batteries up and the fridge happy. If at anchor, it is still running off the 12 volt system and the batteries can be recharged from the engine at the very least. Our decision to go with the Vitrifrigo C115 12 volt model was based on a lot of research and owner feedback. The unit actually has the same cubic feet interior as the original fridge, but the overall size of the box is much smaller. That means the cabinet has to be modified, but it is a simple modification. One big improvement will be the additional insulation added to the inside of the cabinet in which the fridge is mounted. Another bonus is additional storage space we have gained that we added under the new unit. The unit has the newer Danfoss compressor, and it does not add all of the heat that the old unit generated in the main salon. The Danfoss compressor is quiet, efficient and can be serviced just about anywhere without specialized parts. The power consumption is considerably less than the old unit, and this was a major factor in our decision.

Those are two big projects that should be completed within the next week or so. It is slow going when we have to work full-time. It always amazes me how work can really interfere with our boat time, but what can you do? Once these two projects are completed, we might just take some time and get the boat out on the bay. A new dinghy is to be delivered soon, and we will post on that after it arrives. A big rainstorm last night reminded us that the opening ports need to be replaced, so it looks like we need to start preparations and get the materials ordered. It just seems to never end, but it is, after all, a boat.


  1. Thanks for the great post! I wanted to ask about your portable generator choice. We are trying to decide if it is worth it to get a larger generator (and probably one that is noisier) but that can run the 17k BTU A/C. Are you happy with the Honda 2000?
    We are new owners of a 76 MT 34 DC and avid readers of your blog.

  2. Sarah, Our Honda 2,000 will not power our 16,000 BTU air conditioner, the problem is mostly but not all, the start up of the compressor. We are very satisfied with the Honda realizing the limitations. The size generator you will need depends on the type of AC unit and its age and what the start up requirements will be. I would suggest you have a conversations with the air conditioning manufacturer and the generator manufacturer to determine what you will need and keep in mind that if you want to power more than just the AC you will have to factor all of that into your decision. Good Luck. Chuck

  3. Sarah, After I posted my reply to your comment, I thought I would add this. The Honda was a temporary add on that we will replace with a permanent installation in the near future. At this point in time we are leaning towards a Next-Gen Diesel Generator for a permanent installation. The manufacturer has assured us that it will run our AC with no problem. Chuck

  4. Thanks for the further clarification, Chuck. My lingering question is whether we really need to power the AC when on the hook or if a smaller, less expensive gen would cover all the other power needs (except for AC) and use the money saved to do upgrades elsewhere.
    We plan to start work on our leaky aft windows very soon, following your excellent tutorial! :)

  5. The Honda 2000 will power one of our 45 amp battery chargers, the TV, Satellite receiver and either the coffee pot or the toaster, not at the same time, so we turn the pot off while the toast is getting done. We run lights and fans also. If you go with the Honda, be sure and get the model with the 30 amp twist outlet built in. You will need to do a spread sheet on what you will need to power and determine if the Honda 2000 or something else is suitable. Hope this helps, Chuck

  6. We bought an 86 MT Sundeck 36 this Spring. Your blog has been a phenomenal inspiration. We don't live aboard so our remodeling, replumbing, rewiring, re-hosing efforts are at a much slower pace. But one of my heart-aches is I stand over the holding tank floor hatch when I open the fridge. Keeping the holding tank sweet and not sour has been a learning experience...

    We're on the Neuse River, NC. I think your post somewhere said you're in VA. Would love to see your work some time. Keep writing!

    Ben and Deb

  7. Hi,
    I read your great blog regularly because I have a similar boat that needs lot of work.
    In your fridge project there are two fans in the back. What is the direction of air flow? I have installed new 12V fridge too (the best option for me, too), but now I there is a smell from the engine compartment coming slightly into the cabin. The fridge has a Danfoss compressor and its own fan mounted on it. There are two vent holes on a back wall but with no fans, just natural circlation. Should I install sucking fans there, and how to connect them to work together with the fridge?


  8. Darko, The fans pull the warm air generated by the compressor out of the compartment and have made a big improvement in the box cooling as well as keeping heat out of the cabin. We installed them for the previous fridge since it generated a lot of heat. They are 12 volt muffin fans and can be wired to run continuously or wired to run when the compressor comes on. They also pull fresh air into the compartment from the vent holes that you can not see. I do recommend these for any fridge installation.

  9. Ben and Deb, Thanks for the compliments. We are actually in Pasadena, Maryland right now and will be here or in the Annapolis area for some time until the boat is ready for our next cruise. For all things plumbing and especially holding tanks I recommend you get Peggy Hall's book. She is pretty much the expert on marine heads and is known as the Head Mistress. She discusses in detail how to keep your holding tanks clean and odor free. Here is a link to a source for her book, http://shop.sailboatowners.com/books/detail-books.htm?sku=66438&cat=1304 and it is a good investment. Any time you are in the neighborhood, stop by and good luck with your projects. Chuck

  10. When an engine is set to be "fresh water cooled" does that mean that you can't drive it in salt water?

    That sounds simple, but it is throwing me for a loop as I thought "fresh water" meant creek or lake water.

  11. Being fresh water cooled means only that there is a fresh water cooling system built into your engine very much like your cars cooling system. The difference being that instead of a fan for additional cooling the boat engine uses whatever raw water it is sitting in to assist in cooling. The raw water cools the fresh water in the engine much like the fan would in your car. The engine can be used in both fresh and salt water. Chuck

  12. Could you run the A/C via the inverter and charge the batteries from the Honda 2000? This way the inverter will absorb the startup amps and allow the Honda to properly use the eco throttle when the battery charger is not drawing as many amps.

    You would give up some efficiency due to inverter losses, etc, but it may be worth looking at.

    Brian McCue - Litchfield, NH

  13. Brian, The AC will not run off the inverter without drawing down the batteries very quickly. To try and keep up with the loss, the charger would have to be too large for the Honda. The inefficiency of trying to do this would be too much and there are easier ways, like a bigger generator. But our Honda 2000 may run the AC for us, we haven't tried it yet, but we would not be able to run other things at the same time. Chuck


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