Boat showers are much less glamorous than those on land. They don't have fancy tiled walls, or pretty shower heads; they typically look like a cheap shower head on a hose stuck in a corner of the boat.
On Wisdom, this is no exception. I changed the disgusting looking plastic stick of a shower head with a more acceptable looking one, but there is no shower curtain or divider. The shower is crammed between the mast and the composting toilet. Maddie was a good sport about this fact when she first moved in, accepting the truth that a large shower is a waste of space in a small boat.
The part of the shower she did not accept was the fluctuating water temperature. The water would fluctuate between scalding hot and freezing cold every few seconds. When she questioned me about this horrid situation, I demonstrated the "shower dance".
The "shower dance" involves listening to the water pump and careful setting of the water temperature. I would set the temperature at a time when I heard the pump running. As soon as the pump would cycle off, I would get out of the water stream because it was going to get really hot. When I heard the pump turn on again, I would hop back into the stream and rinse the soap off. Maddie was not impressed by my dancing skills; she wanted to set the temperature and enjoy steady water temperature.
Why does the temperature fluctuate and how can this be fixed? The temperature fluctuation is due to resistance in the water system. The hot and cold water systems run through separate piping with different resistances. The cold water runs from the pump to the expansion tank to the shower. The hot water runs from the pump to the water heater to the shower. They run different lengths, and have a different number of turns and twists in the hoses. This means that they run at different rates. When the pump is on, the whole system is pressurized, when the pump turns off, it becomes a race for the pressures to run out.
In my case, the cold water stops flowing almost instantly when the pump stops pushing but the hot water keeps flowing a while longer, causing the spike in water temperature. Once the pump cycles back on, the cold water flows again and cools the mixture. This constant back and forth can be easily fixed by keeping the pump on constantly.
The choices available to fix this problem include
Perfectly balancing the water systems
Installing a manually activated water pump
Installing a switch that bypasses the pressure switch
Adjusting the pressure switch on the pump
Installing a system to trick the pump into running constantly
Balancing the water systems is not practical, it would involve equalizing the resistances in the plumbing so that they will both respond the same way.
Installing a manually activated water pump is a very good choice. You simply flip a switch and enjoy a perfect shower with consistent temperature control. This does involve the purchase of a new pump that does not have a pressure switch.
If you already have an automatic water pump, you can adjust the water pressure sensor on it to make it run continuously when the shower is on. There is usually a screw on the sensor switch that allows adjustment. Once the switch is calibrated to keep the pump on instead of cycling on and off, the shower temperature will be perfect!
If your automatic water pump is not adjustable (the way mine is), you can connect a bypass switch on the pump. This switch will bypass the pressure sensor and keep the pump on continuously. The switch can be mounted in the shower, allowing you to easily turn on the pump at the start and off when you are done with your shower.
If you don't want to add more points for corrosion to start on, there is a non electronic method to trick the pump into staying on. A bypass circuit will trick the pump into running continuously. The bypass circuit is a hose teed into the inlet and outlet of the waterpump. A gate valve in the hose will allow for a controlled opening of the circuit. When the bypass is opened, pressurized water from the outlet will be dumped back into the inlet side of the pump; this will make the pump think it needs to keep pumping and that will keep the water temperature consistent in the shower.
To trick the pump, simply open the valve a little at a time. Once the pump runs continuously, you are ready to shower. If you have insufficient pressure, try closing the valve a smidge. The circuit will let the pressurized water escape into the pump inlet which will cause the pump to detect a drop in pressure and stay on as it tries to pressurize the system.
When you are done with your shower, simply close the valve and the pump will work as normal again. It is not as convenient as the switch, but it involved zero wiring and was very easy to install and operate. Maddie was able to get the hang of adjusting the valve and now enjoys her comfortable showers, no dancing involved!