New to boat design (watermaker for a small 60'-ish ocean cruiser)

I'm new to boat design it will never be more than a hypothetical dream like hobby. However that does not mean I am not serious about learning how its done. I have an idea that a diesel electric boat might be very efficient dependent on many factors like availability of motors etc.
Can anyone tell me for a small (60' ish) ocean cruiser would such a boat have an evaporator to produce fresh water to supliment a small on board tank, or would a large tank have to be fitted.

 

They are called reverse osmosis water makers.... you can make virtually unlimited fresh water from the sea water....

 

Making fresh water is always complex. The preferred solution is a large tank and carry the required capacity. If you cant carry enough , then watermakers can be used. Ive not seen evaporator desalinators on small craft , only reverse osmosis. The typical RO unit would be AC powered , takes up nearly as much space additional tankage and is very expensive.

The secret to great design is simplicity. The more mechanical systems you use...diesel electric for instance, the bigger the challenge to keep them online during use.

 

$5k gets you a high quality 500 gal/day RO watermaker, weighs 80# and it's footprint is about 6 sq/ft. $9k gets you 1000gal/day at 100# and the same footprint.
If weight and space are a consideration RO watermakers make a lot of sense, also frees you up from worrying about questionable water sources.

 

Thank you for your replies gentlemen.
I think $5k dollars is not a lot for 500gall a day. It would be a small percentage of the cost for a small trawler yacht. The money saved on a smaller water tank offsetting the water maker, and weight and space saved would assist in running economy.
Your replies have allowed me to know what to look for. Found a 200gall set up at 121lbs. I recon a Tank of 160usg would do for a crew of 8 to ten. I know I don't go through anything like 30gall a day.
New York to Liverpool 3043 miles @ 11kts =10 days =2400USG for 8 on board.

A 250USG tank would make a tremendous saving in space and weight.

Knowledge leads to more questions. I thought boats ran on 24V DC. So you also need a 115V 13.9amp inverter to convert AC to DC.

 

Not if you want to use the boat in the EU or a lot of other places including Australia. You need 220-240V single phase power @ 50 Hz.

12V DC appliances are so common and cheap that 24V makes no sense unless you're dealing with 24V starter motors etc for a big diesel.

PDW

 

Getting across the Atlantic in a small motorboat is a challenge. Very few boats have that kind of range. It would be a mistake to design to Transatlantic capabilty. Your whole boat would be a fuel tank.

Concerning watermakers. Ive never used one on an oceanic trip. I have an HEM 120 liter per hour unit onboard. In 19 years and covering 300,000 miles I have only put 600 hours on the unit. The watermaker only becomes useful when you are on station for a few weeks having fun and water is difficult to come by. In transatlantic mode you sail with a small crew and only use 25 liters per day. Remember each hour you run the Generator burns fuel and reduces your total fuel range.

 

You can find watermakers that have engine driven high pressure pumps. A 500 gal/day watermaker will use about 8amps at 120V AC so you can run it off your inverter, so just make water when the engine is running and you won't have to factor in additional fuel usage for your passage

 

Transatlantic capability:

Transatlantic capability:

 

Sean,
Fuel consumption does go up for the miles per gallon/litre as the energy must come from somewhere even when the high pressure pump is attached to an electric clutch on the main engine...

To Cross the Atlantic under power you will need quite a big vessel... A sail boat may be worth considering to extend range but KEEP AN EYE OUT FOR OTHER LARGE COMMERCIAL VESSELS, as you may well be almost invisible - even if they are keeping good watch (not likely on most cargo vessels mid passage)

As Jessica Watson found out on the first day of her solo passage around the world just outside Brisbane...

My 40ft cat can carry a tonne of fuel and is VERY fuel efficient at 2 miles per litre at 7 knots - My range is around 2000 N Miles starting with full tanks in fair weather... - - The Atlantic is far too big for me to cross...

I am looking at a 60 litre/hour RO watermaker powered by a 240VAC motor and replacements can be found in Europe, India, SE Asia, Western Pacific, well beyond my usual cruising region... I can carry 13 PV panels to deliver 2275 Watts or more - depending on rating and sun when anchored...

 

Watermakers are durable. Ive never had a component fail in decades of using them.

Consumables are and issue. Fit a sand filter. The sand filters incoming sea water greatly extend the life of the watermakers very fine sea water pre filter.

Waterwakers need a supply of sea water via a supply pump. These pumps seal fail. Use a high quality easy to service pump.

To make a watermaker last a long time you must flush the saltwater out of the system with fresh water each time you use it. Some RO units have an automatic freshwater flush cycle or you can add a manual fw feed to flush.


Dont mount the membrane in a hot area like engine room or the membrane will foul.


Watermakers are noisy buggers. Use attention to detail and best practice sound isolation when mounting.