Conference unifix::sailing

re .0:

No stove? As in none? Gee, I'd want a stove before a hot water system, 
especially since a stove, among its other features, converts cold water 
to hot water. 

An electric hot water heater is out of the question unless you have 
shore power or an onboard 110vac generator (small electric hot water 
heaters need 1200 watts or about 100 amps at 12 v). Shore power doesn't 
get you hot water while cruising (unless you have a very long extension 
cord). 

Given the vintage of your boat and its engine, I would guess that your 
Atomic 4 is sea water cooled. With rather cold sea water not much water
is needed to cool the engine, and, anyway, the engine thermostat will
keep the cooling water below maybe 165 deg F. This means that heating
drinking water using engine cooling water isn't going to be very
effective. Our small fresh water cooled diesel (coolant temperature
over 180 deg F) needs maybe a couple of hours to heat 6 gallons of
drinking water to the engine water temperature. Since the hot water
tanks are small, you want the water as hot as possible to minimize use. 
I'd guess that you'd need several hours of engine running to get 
moderately hot drinking water since the engine cooling water is fairly 
cold and the volume is low.

Gas heaters require propane. Propane tanks must be kept on deck (not 
very seamanlike) or in a locker vented overboard (difficult to build, 
expensive to buy, and hard to find room for). 

No very good solutions, I'm afraid. Using engine cooling water is 
probably the least expensive -- maybe $300. 

    A couple of hours to heat the water tank? Sounds like the way ours used
    to work. I checked the service manual and discovered that the take off
    hose was connected to the wrong port. After some effort (I think I know
    why the factory did it the way they did) the tank will now get the
    water quite hot within an hour of running the engine.
    
    For the record, we have a 13hp diesel in our sailboat, fresh water
    cooled. There is an electrical element for when you are dockside, but I
    don't use it much since we've been on a mooring. Since I fixed the hose 
    take off point, I am very happy with the system.

    I had Moody's (English boat) several times as charter boats in the last
    few years. They use gas (propan) for hot water heating. If your boat has 
    already a gas cooker I would recommend to use a gas heater. All the boats 
    we had it worked very efficient and the consumption of gas was not high.
                                                     

    I don't know why but Moody's have now gone back to heating water
    off the engine ,I guess it could be something to do with safety
    ie gas and boats are a necessary evil but should be kept to a minimum?
    
    Pete

    If you are looking for a diagram for how to install a pressure water
    system complete with hot water tank, shore water inlet, etc. you
    can find one in the Boat/US catalog.
    
    Here is a summary:
    
    Use half inch fittings which means 5/8 hose.
    
    From cold water tank, in order:
    
    Pressure pump to T-connector, one side to hot water tank,one side
    to cold water line,
    
    Check Valve on hot water tank inlet (so hot water doesn't flow out)
    
    An optional accumulator tank can be installed before the T-connector.
    
    An optional shore water inlet can also be installed anywhere on
    the cold water line after the accumulator tank.
    
    Faucets, etc are then run in series off hot and cold water lines.
    
    Heat exchanger comes built into most hot water tanks. Run the inlet
    from the place on your engines where the cooling water exits the
    block (it is hottest here). 
    
    It is really very simple. Make sure you put hot water tank heat
    exchanger below the level of a fresh water cooled fill cap. On raw
    water cooled I suppose it wouldn't matter as long as the water pump
    can handle the flow.

re .2:

The time required to heat the drinking water depends on the temperature
of the sea water used to cool the engine (either fresh or salt water
cooled), how big the heat exchanger is (fresh water cooling), how much
water is circulated through the engine, hose sizes, how hard the engine
is run, etc. Based on fuel consumption data, my guess is that at normal
cruising speed, our engine is making about 8 hp. To be sure, if we ran
the engine faster, it would make a lot more heat and would therefore
heat the drinking water considerably faster. 

Note that adding a hot water heater will probably reduce the water flow
through the engine (due to increased flow resistance) and may result in
engine overheating under heavy load with high ambient air and water
temperatures. The cooling of some engines is marginal to begin with (our
oil consumption increased alarmingly in very hot weather with very warm
sea water due to higher internal engine temperatures when going to
Bermuda). This is not a reason not to add a hot water heater, but it
needs to be considered. 

    
    
    How fast you heat the hot water depend on 
    1. the water flow of engine cooling water
    2. the temp of the cooling water.
    
    If you take engine cooling water as it exits the block and before it
    enetrs the exhaust manifold, it won't be very warm. marine engines
    usually run about 140 deg F , and there is usually excess cold water
    that bypasses the block that is mixed with this "warm" water.
    
     The weater then goes into the exhaust manifold- LOTS of heat picked up
    here- and then it goes into the exxaust elbow and is discharged.
    
     Depending on your manifold design, you may be able to externall
    "plumb" the block /exhaust manifold(just like is done with FWC),
    and the reaw water discharge goes into the exhaust elbow.
    
    The solution is to take the hot raw water as it leaves the exhaust
    manifold, run it through the HW heater, and then discharge into the
    exhaust elbow- this will extract almost all of the heat generated by
    the engine/exhaust. The higher temp water will also give fast heating
    and higher water temperatures.
    
    
    

    The most recent issue of Practical Sailor has a detailed review
    of the two most popular flash type LNG hot water heaters.

    For the past two years, we have had a demand type CNG flash water
    heater installed aboard CAPRICE.  We installed this unit after going
    through yet another heat exchanger type water heater.  The heater we
    got is a marinized CNG unit which we bought at Beckman's in New
    Bedford.  As we already had CNG (lighter than air gas) on board for
    heating, the only cost was a little plumbing, a charlie noble for the
    stack and the heater itself.  The heater is made by Rianna and cost
    about $210.00  It uses a hooded pilot light when in use but has a pizo
    electric ignition system so the pilot is only on when the heater is in
    use.  The unit is water pressue activated so it produces hot water on
    demand.  The temperature is adjustable.
    
    I is really a delight to be able to take a nice hot shower after cool
    fall sail!