Hot water on Boats - best solution ?

michael,

Very good advice.

The welded aluminum tank features are numerous in construction. The tank is removable. Placement of the heaters and sensors in relation to the tank shape and pickups are important. A common theme is an inspection/clean out hatch, and a drain.

All for now,

Mark Cat

 

I don't think the weight of water in a hotwater storage tank should influence the choice of instantaneous hot water heating as opposed to a storage tank system. Basically, the starting point is to decide how much fresh water you need to carry on board. If you want hot showers on board then you have to allow extra for that. Once you have determined the total amount of fresh water that will be carried, it makes no odds whether some of that water is in a hot water tank or whether all of it is in the main cold storage tank(s). It could actually be marginally advantageous to have a bit of fresh water in a hot water tank since this could provide an emergency drinking supply if the main fresh water tank springs a leak - a good stock of beer in cans could be an alternative of course.

 

You beat me to the reply, That's exactly the reasoning in my mind. The point made by a few people about the solar boost is a good one to consider. I would 'assume' that if I had even a lukewarm reservoir to draw from for the gas heater, it would save gas.

Many semi-storage caravan heaters have ceramic lined stainless tanks to get around the metal eating water.

There are some nooks and crannies in the design that could become insulated warm water reservoirs, with the appropriate inspection holes.

 

Ah yes, I understand. In my part of the world it seems 90% of the 'villages' are right on the coast ( due to a mountainous interior ), and the gas bottles can be found very easily, so I am lucky here. Mind you, most of the bottles are the non marinised 'swap and go' variety, and I may need to think about the special stainless variety that needs physical refilling. There arent quite so many of those places around.

 

Why bother, just swap them over before the rust blooms are too obvious.

I'm still looking into a heat exchanger for my boat but I have a decent inboard diesel.

PDW

 

The RV propane HW heaters are quite robust , they are hard mounted and have to absorb decades of potholes .

Most have a large burner so could be operated only a short part of the day for showering.

As the boat will probably have a propane range , as well as a propane reefer , the added use of a HW heater will not add to the fuel bill.

A large sized propane RV reefer will use 20lbs of propane in 30+ days .

Really good compared to making , storing and using electric.Silent too.

 

I thought gas fired fridges were not safe or feasible on monohulls, probably not on trimarans either, just possibly ok on catamarans. But I do like the idea of a gas fridge on a sailing catamaran, it could dramatically reduce the electrical requirement. With gas providing the refrigeration (when not on shore power) and LED lighting, the remaining electrical requirement is only for any electronic toys you fancy, plus maybe an autopilot if you want to make long passages, plus maybe an anchor winch if you are not young and strong. On that basis, the electrical requirement could be met by a unit along the lines of the 'Supercharger' (see post above) running for perhaps one hour a day when away from shore power to whack 30amps into a 12V lithium house battery. That's about half a litre of petrol each day, about 70pence worth in the UK. Auxiliary propulsion would be by one or two small petrol outboards, so there would in any case be petrol stored on board. Now, if I could take the exhaust from the Supercharger and pass it through a heat exchanger that is part of a small hot water storage system, that might quieten down the noisy generator a bit and if I could extract say 200W from the exhaust that would heat about 8.5 litres of water to shower temperature during that hour of battery charging, enough for a few quick showers with a fine spray. Maybe make the gas to water heat exchanger by adapting a stainless steel heat exchanger supplied as a spare part for a domestic condensing boiler? Of course there would be an electric immersion heater to use when on shore power. Voila - now we have the electrical, refrigeration and washing/showering requirements for our hypothetical small catamaran all sorted at pretty minimal weight and without the need to clutter up the boat with solar cells or windmills, neither of which can be relied on to produce anything close to their rated outputs at the times you actually need them to.

As it happens, I done a drawing of a possible galley layout based on a small gas fired fridge - see below. The purpley bits in this drawing are only intended to represent the limits of the galley space, the actual structures around the galley being detailed in other drawings. The fridge is in the far corner, is drawn based on the dimensions of the fridge model RM123E. Its a gas fired absorbtion cycle fridge that can also run on mains electricity when on shore power, or from 12V as a last resort. This is a very small fridge by domestic standards, only 30litres, but better than no fridge at all I think. Perhaps those big drawers under the cooker could be surrounded with 100mm+ of thermal insulation to provide supplementary ice box cool space. According to the manual, this fridge would use 0.2kg bottled gas per 24 hours on the coldest setting, so up to a month away from shore power from a 6kg gas bottle, which is about the max I would care to lug to the gas store, total weight of full bottle being about 16kg I think. Would actually be a bit less than a month allowing for cooking with gas. Would carry two bottles for a reserve of course. The ventilation above the fridge is in accordance with the fridge manual but I have shown it ventilating either into the galley space or through a grille to outside. This is because I have heard people report that gas fridges overheat their galey in hot weather, they do produce more heat from a given amount of cold than an electric compressor cycle fridge. With the arrangement you could blank off either the vent to interior or the vent to exterior. Ventilation below the fridge is straight down to under the catamaran bridgedeck - I think that's important in case of a gas leak.

What do you think of all this, makes a bit of sense, or do I need to rethink?