Trying to figure out if a Tankless water heater will supply enough hot/warm water for a short shower?
What units are being used for this?
Don't have space for a tank unit.

We have an entire house operating a Bosch tank-less unit -- YOU CAN'T RUN OUT OF HOT WATER!!! Now this is a gas unit and I have no experience with electric systems but I'm sure they have been offered in other "RV" applications and I personally wouldn't think twice about getting one. The issue that you may experience is within your boat are you running a water softner - if not there is a potential for the heat exchange system to get mineral deposits and clog.

all the best

3pointstar

With the on demand water heaters it is all about temperature rise. They will only raise X amount of gallons per minute X amount of degrees.
Up here in MI people that bought on demand water heaters when we have very cold winter temps have a surprise when they can't get a hot shower.
When you have city water the water lines are buried 6 or more feet down and can freeze if it is cold enough long enough. The on demand water heaters can't heat this very cold water up enough to have a decent hot shower.

We have an electric one on a boat, It works OK..... you have to adjust the flow rate according to the temperature of the incoming water and it requires a dedicated 30A breaker and line.

Used one on a catamaran sailboat I rented for a few weeks.

It was propane. Absolute endless hot water as long as you had plenty of propane.

I have a Rinnai tankless propane water heater in northern New York. I have Endless Hot Water

You're right about temperature rise- A Rinai R75 can churn 7.5gpm of water at a 35* rise. The more rise required, the lower the gpm. So 87* water at 7.5gpm, or 115* water at about 4gpm. Assuming the groundwater temperature is 52*.

But regarding the underground water lines freezing, it was explained to me by a physics teacher long ago; the temperature of a well digger's arse near the surface is close to whatever the ambient temperature is, and the temperature of a well digger's arse at 6ft below the surface will be around 42-50*, and almost always above freezing. Yes, occasionally underground lines freeze and burst, but there's a reason you can get well water in the winter, a reason for the frost line, and a reason geothermal pumps work- geothermal heat. So even at 33*, a decent sized unit will churn it out at 105-110* and 3gpm. Below that, nobody gets a shower- not you, or the neighbors, because the pipes would be frozen.
https://www.libertywholesalesupply.c...ai_flow_chart/
Power outages....The power outage situation can be handled by a backup that sparks the pilot, so as long as you have fuel you have hot water. In the old days that 40 gallons of hot water in a tank meant you could shower before the power company got to work. With electric that's a moot point.

We have a Rinai in our house, never had a cold shower. Flushing the heat exchanger with a bucket, pump, and vinegar is a routine maintenance requirement. I would never recommend tankless to a man with a wife and daughters; your bathroom will be a sauna and you'll never be able to drop a deuce.

A friend had a couple 110v tankless units in his cottage when he first bought it. The sink was always good pressure and temp, but the shower didn't work as well. He switched to a whole house propane unit, they regularly have a half dozen people showering on weekends and no one gets a cold shower. Just prepare to have a bath fan the size of helicopter to get rid of all the moisture.

Western NY, on city supplied water, my gas tankless works fine. Been using tankless for at least 20 years.

Padraig

The only way to really solve this is two boats, one with a tank, one tankless. Put good looking women in each, and record the results for scientific purposes. Feel free to post the video footage. Purely for science and advancement, of course.

propane tanks? not really tankless then