You want hot water in less than the 4 SF a hot water heater takes? Plus of course a few hoses to get it there. A little spoliled are we in using ALL that space? Use the instant stuff and die or use 4 SF? Big question, easy answer!
Oi, get your effing facts straight before you start dumping on me OK ?
To begin with , I am NOT talking about instant, so you are arse about face on that to begin with.
The mob I linked to have storage type systems that are 5 or 10 litre, instead of the the four sq ft jobs you are on about that are from 24 litre and up. Electric 12v or 240v NOT gas. Read my post.
First up our current boat is a 34'er and an older style 34'er at that, meaning far less interior space than more modern designs.
We shower now using the stove to heat the water and shower quite happily in approx 6 litres of water per person.
To install a more typical storage tank (4 sq ft minimum) means taking up valuable storage space and as you say running water pipes through the boat. All that in order to provide more hot water than we actually need.
The system I looked at we can install in the head far more easily that having to install something larger in cockpit locker for example. Indeed there is an unused space in the head that would be damn near perfect.
If we had a larger boat, different story, but right now we don't. Space matters and with limited water tankage so does water usage. OK , so if we had twice the tankage and an extra ten feet of boat, different story.
Big Question ? Maybe.
Easy Answer ? Maybe that as well.
So how come you missed by so far ?