This is the original tank.With 345 gallons of fresh water Britannia has a larger than average tankage for a sailboat. The boat has two heads, each with a washbasin and shower and pressure as powerful as a house supply. Unfortunately, with only an eleven gallon hot water tank water can run out quite quickly, especially if both showers are used at the same time, and if the hot runs out, you're on your own so to speak…

Britannia’s hot water tank was the popular square Kuuma make, sold by just about everyone in the marine supply business including Amazon and E-bay, where I bought mine at Eleven gallons might sound a lot to boats that have the smaller six gallon Kuuma tank, but neither of them delivers its full capacity of hot water to a shower or sink. This is because as the hot is drawn off it is replaced with cold at ambient temperature from the boats tanks. This dilutes the remaining hot, so by the time about half of the hot is used up the rest is already somewhat lukewarm. Of course it helps to leave the electric element on and even run the engine to compensate for this loss, but that might not be practical every time

This problem was exposed recently when we had four guests staying aboard who were new to boating. I had to explain, tactfully of course as is my wont, that they were in a boat not a house and the hot water won't run endlessly. I suggested that only one-morning shower should be taken at a time, otherwise there would be a good chance of someone finishing with a cold rinse. It was embarrassing for me to have to admit that, even though my 50’ foot schooner has just about everything that a house has, like a washer/dryer, freezer, fridge, air conditioning, bathtub, 120v in all rooms etcetera, it is woefully lacking in hot water. I therefore decided to look into how I could increase the capacity. NOTE: All temperatures are in Fahrenheit.

The 120 volt heating element.Water is heated in the tank in two conventional ways; from a 120-volt immersion heater element inside the tank and also from the warm engine pumping its every hot water through coils inside the tank. Both methods can be used at the same time and when away from a dock the boats 6.5 Kw generator can produce 120-volts for the heater elements.

The bathtub that needs so much hot water.Another reason I wanted to increase the capacity was more personal. Not only does Britannia have many mod-cons of a house, it also has a full size bath in the aft cabin bathroom. Many boats of Britannia's size have bathtubs, but mine is not just any old tub, it has ten power jets all round, making it a hot tub. I actually consider this to be more important than the shower issue because how many times do we have guests staying over and wanting lots of morning showers, compared to me enjoying a British pint in a massaging hot tub after a hard day's work on the boat? For this I needed to generate 50 gallons of water at a temperature of 102 degrees, and if that could be achieved the shower problem would solve itself.

Backtracking a little: the bath was a conventional household tub in which the makers fitted ten jets, a pump and a 120-volt heater. I had no experience of these in a boat, (and neither did the bath makers), so I relied on the makers to supply the correct heater. However, it only worked for a few baths before burning out because it was only powerful enough to keep water warm after the bath had been filled from a house hot water tank. What I really needed was a heater with enough power to heat a bath full of water from ambient cold to 102 degrees! I then learned this could only be achieved with a 240 volt heater of considerable wattage.

An example of a tankless gas heater.My present marina berth only has one 120-volt 30-amp outlet, so my first thought was; could that somehow be converted to give 240-volts to just run a bath heater? The answer, from much more knowledgeable electricians than me was NO! Not without the risk of blowing all the electrical breakers in the marina.

I looked at propane gas heaters, also called tankless water heaters. Those that are capable of supplying 50 gallons of water at 102 degrees are quite large and need to vent their hot exhaust to the outside. Also, Britannia only has one propane tank that would quickly be used up, so I discounted gas heaters.

Back to the drawing board…

To at least solve the shower problem I decided to install a second eleven gallon water heater and hope that with two heating elements and double the engine heating capacity it would be enough to fill the bath.

The large bilge, where all the machinery sits.Britannia is a long keel full volume hull with an amazingly deep 5’ foot bilge stretching 27’ feet from the stern gland forward and housing all the other machinery as well. It is more like a long engine room than a bilge and the existing heater tank sat on a raised platform in this cavity.

The twin heaters connected together.I removed the tank and its platform then built a new one lower down in the bilge, thereby lowering the heater. I then positioned a new heater on top of the old one and piped them together in series. It was a welcome change to be able to work on the two tanks while they were sitting on the saloon floor, instead of having to hang upside down like a blind bat in a cave. While doing this I also replaced the immersion heater element in the old tank, that was there when I bought the boat twelve years earlier.

Lowering the heaters into the bilge.The water generated by the engine is about 180 degrees, this being the normal running temperature of the engine. The engine hot water outlet pipe was connected to 'hot water in' on the lower tank then from 'hot water out' to the top heater 'hot water in', then from 'hot water out' to the return on the engine. This ensured a continuous flow of nearly boiling engine water being pumped through both coils inside the tanks. I also installed a valve on the engine pipe to close off the heater circuit to allow the engine to initially come to operating temperature more quickly. Then they were both lowered into position, using my “handy Billy,” a tackle strapped to the ceiling handrail supports.

Note: Twin tanks don't have to be placed on top of each other like I did. They can be located anywhere, but they should be close enough to minimize heat loss through the connecting pipes. I also lagged all the hot water pipes using split foam tubing.

Surprisingly these Kuuma tanks have no hot water gauge to be able to read the temperature, so the only way I could test the rising temperature was by filling a glass from the galley faucet and reading it with a thermometer. Within 20 minutes the water quickly rose to 140F and the tank thermostats cut the electricity. As soon as the engine reached full operating temperature I opened the valve that allowed water at 180F to flow through the heater and raise the temperature further. After one hour the water flowing from the galley faucet was a scalding 175F degrees and much too hot to even touch. Later I removed the top drain tap and screwed a capillary water gauge in its place that gave us a constant water temperature reading

All the hot water pipes have been lagged.Britannia has two 120-volt shore power receptacles supplying two separate distribution panels. These split the electrical load of some of the higher draws, like the twin AC units and the washer/dryer. I reconnected the original wiring then installed new wiring to the top heater through a breaker on the second panel. The reason for wiring the two heater elements separately is that if one fails, as they often can after years of use, I could at least heat water in the other tank from a shore power without running the engine.

In my present berth with only one 120-volt supply I use a splitter to interconnect these two panels, but if we go somewhere where there are two 30-amp outlets I can plug them in separately. I also have a 50 amp plug and splitter for use where the larger amperage is available. Flexibility is the name of the game on a boat with so much electrical demand.

                                                                                     THE DAY OF RECKONING.

After all these shenanigans both units were finally installed and it was time to test my armature hydro-electrical engineering theories. The ambient temperature of the water in the boats tanks was 55 degrees on the day of the test and the outside water was 45 degrees, both of which effects the time for the engine to achieve maximum temperature.

I first switched on both heater elements and the gauge showed a discharge of 23 amps from the single 30 amp shore supply. I closed the engine pipe shut off valve and started the engine to run at 1500 rpm, its normal cruising revs. By the time the engine had reached operating temperature the two immersion heater elements had raised the water to 100 degrees. I then opened the shut off valve to allow hot engine water to be pumped through both tank coils and I had to remind myself the engine was now having to heat 22 gallons. The thermostats on the heater elements is set at 140 degrees and non-adjustable, therefore when the engine raised the temperature above this the electrical side switched itself off. The whole process took two hours by which time I had 22 gallons of water at 178 degrees. This is obviously much too scoldingly hot for a shower or a bath, so a lot of cold would need to be mixed to lower it to about 80/90 degrees for a shower. This definitely solved that issue but would it be enough to fill the bath with piping hot water for a long soak?

I opened the bathtub hot water faucet then watched and waited. Blistering hot water at nearly 180 degrees crept slowly up the sides of the bath, until water slowly began to cool as both tanks depleted their initial hot water. I left the immersion heaters on along with the engine, to pump up the temperature. The engine and electronics must have wondered what was happening to their valiant efforts to keep the water in the tanks at a steady temperature. As the bath became almost full the water was still too hot at 110 degrees, so I switched the hot tap off and cooled it to 102 degrees with cold water - bingo!

I then climbed into 16” inches of luxuriously warm water and switched the jets pump on. On the first speed there is only moderate action but on the second it is very powerful and nicely massages an aching back. The pipes and jets had been insulated with foam, so I was very pleased to find the temperature did not drop much for a half-hour soak. I had even fitted a holder for my beer glass, because it would be a major disaster to have that tip over even when in a marina berth. By the way, I only ever use the bath when in a marina. Using it at anchor could be interesting when a big power boat zooms past, and bucket loads of hot water sloshes all over the floor.

When I installed the bath I obviously needed a method of emptying it. The showers were fitted with automatic self-draining units that incorporate a float switch, a filter and a pump in a plastic box. This pumps shower water overboard as fast as it comes in, so there is never any standing water during a shower. Draining 50 gallons from the bath would have taken ages through the shower drain, so I solved the bath drainage by fitting a two-way change over valve in the bath drain with a pipe leading to a diaphragm pump. With the valve switched to bath discharge, the pump emptied the bath in 10 minutes flat!

When we have been out sailing and motor back to our berth the water is usually piping hot, solely through the engine heat alone and there is loads of hot water for virtually endless showers. If I want to use the hot tub I connect the shore power and start the immersion heaters and I soon found the optimum time to get a nice long soak.

It has been suggested that it would have been a lot easier to just buy a hot tub for our house. The easy bit is definitely true, but that wouldn't have solved the boat shower problem, and how would I then have a nice soak when visiting other places on a cruise?

The cost of this project was: $437 for the extra water heater, $22 for a new element, and $39 for connector fittings, a total of $498. The bath itself was $1155, including the jets pump. A total of $2155 and for me a small price to pay for the luxury of lovely hot showers and a fabulous hot tub.


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This popular boat water heater holds 11 Us gallons.