Solar water heating on a sailboat

[la7qz]

Hi

With my wind turbine and 310W worth of PV panels I'm now pretty much self-sufficient with electricity on the boat. I never have to run the engine to generate power. I'm even self-sufficient with water after I made the rain collector. (That may change when my fiancee moves aboard...) However, there is still one application where I have to rely on infernal combustions, and that is water heating.

I have a 4 gallon hot water tank with a heat exchanger coil that is connected to the main engine coolant. Running the engine for about 15 minutes produces enough hot water for two people to shower. The tank is relatively well insulated, so the water stays warm until the next day. However, I would like to get away from having to use the engine partly because of the noise and pollution and partly because running a diesel engine on low load is not very good for it.

I would like to build a solar heat collector to plumb into the system so that I would not need to run the engine to produce hot water. I would also like to retain the ability to use the engine to heat the water for those no-sun days.

The space I have available for the solar collector is on top of the spray hood (dodger) and around 130 x 70 cm. There will be some shading from the mainsail boom, creating a shad around 10 - 15cm wide across the middle of the panel, but I understand water heating panels are not nearly as sensitive to this as PV panels.

Since the panel will be installed almost horizontal (maybe 5 degrees tilt forwards) and well above the coil in the tank, I assume I will have to have a pump. When there is enough sun to heat the water, I will have enough power to run a small pump from my PV panels, so the power consumption of the pump is not a problem.

Since the panel is installed well above the main engine, I also assume I will have to choose either the engine or the panel as a heat source, otherwise the coolant would overflow out of the engine's coolant reservoir. I'd have to use either manual valves or solenoid valves to select which way the water would flow. I could easily control solenoid valves via an oil-pressure sensor or the alternator charging lamp selecting the engine coolant and disabling the pump for the solar collector when the engine is running. (I don't want to waste solar heat by heating the engine anyway and don't want to heat the solar collector when the engine is running.)

My question is mostly how to control the pump which pumps the water from the solar collector through the coil in the hot water tank. It would seem that I need the pump to run only when the water in the panel is warmer than the water in the tank, otherwise the panel would cool down the water in the tank.

So, what I'm looking for is:

1. : A way to sense the temperature difference between the solar collector and the water in the hot water tank and run the pump only when the collector is hotter than the tank water.
   
2. : A source of temperature sensors for the above.
   
3. : A source of a good slow running low power consumption 12V DC pump capable of pumping hot coolant. I can't see any advantage to a fast flow? (Would it be an idea to use a 24V DC pump and run it at 12V?)
   
4. : A source of 12V DC solenoid valves capable of use for hot coolant.
   
5. : Any ideas on the design of the solar collector including dimensions of pipes etc would be welcome. The panel has to be low profile, preferably no more than 5 cm (2 inches) as the boat has quite a low mainsail boom which sweeps over the top of the sprayhood with only inches to spare.)
   
   

Owen

PS. Yes, I know I can buy a solar shower bag. I've lived with those before, but my fiancee does not like to feel like she is camping so I'm looking for something that will emulate the convenience she is used to from a lifetime of living in a house.

[GaryGary]

Hi,

Part of your control problem could be addressed with this differential controller:

http://www.arttecsolar.com/retail.html

It is made for solar water heating systems with PV powered pumps.  You might be able to power the solenoid valve off the same terminals that power the pump?

Guy Marsden (who designed and sells the controllers) would be glad to answer questions on it -- if you look at his website, you will see that he "walks the talk" -- he has solar just about everything for his house -- I'm sure he would be interested in your setup.

I believe the temperature sensors are standard 10K thermistors -- any solar water heating place will carry them -- e.g. www.KingSolar.com

Differential controllers are the normal means for controlling solar water heating systems -- they sense when the collector is hotter than the tank, and turn the pump on until its not.  They usually have a settable turn on differential, and sometimes a setable turn off differential -- this prevents rapid cycling.  Some have a feature that turns the pump off when the storage tank temp gets above a temperature you set -- this may be a good feature to have with your small tank size.

Most of these controllers work on 120VAC, but Guy's controller works on 12VDC.

An alternative for a water heater with a PV powered pump is to just let the PV panel be the controller.  That is, when there is enough sun for the PV to drive the pump there is (roughly) enough sun to be running water through the collector.  This then would just leave you with the problem of connecting the solar circuit to the tank instead of the diesel.

You might have trouble finding a commercial collector that small.  There are some places that will made a collector to your size -- I believe that www.sunraysolar.com will do this (maybe).  They will at least do custom size absorber plates that could be put into a glazed box that you (or somebody) builds.  There are other places out there that will do at least custom size absorber plates.

You could make one -- here is one example:

http://www.builditsolar.com/Experimental/CopperAlumCollector/CopperAlumCol.htm

I was going to say that 10 sqft is a pretty small collector, but then its actually pretty large for 4 gallons of storage

In fact, running some rough numbers makes me think that it may want to overheat the water in the tank on a sunny summer day.  This can be bad on closed loop systems, as they can actually vent antifreeze or water out the pressure relief valve.  Including some way to cover the collector (e.g. shade cloth) would be one simple way to control this.  

You will likely need a pressure relief valve and a small expansion tank.  You are basically building a small closed loop system -- like the ones shown here in the Basics section:

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Basics

The horizontal orientation will work fine for the summer, and maybe OK for spring and fall, but unless you live near the equator, its not going to be so good for the winter.  It would be nice to be able to tilt the collector up during collection periods.  Or, maybe a reflector could be rigged to get some sun on the collector?

This feels like its getting over-complicated -- maybe someone else will have a better idea?  

An interesting problem -- seems like there ought to be a simple way to do it.

Gary

[la7qz]

Thanks Gary.

The controller looks like just what I want, so that solves my first two questions. I'll probably order one in a day or two, just need to wait for payday and top up my debit card.

It still leaves the question on what pump and solenoid valves to use.

I intend to build my own collector, probably with copper pipe. I'm a bit unsure of the exact design. I see there are some designs that use copper pipe and aluminium fins, but that is a big no-no for marine applications where galvanic corrosion between different metals is a big issue. I was thinking of looking for some thin copper plate and soldering the copper pipes to it? Unfortunately, I have no idea where to find the copper plate on this island. (St Maarten) I would probably build the actual box from a plywood base with a pine frame and a acrylic glass top and coat it inside and out with epoxy with black pigment for durability in the marine environment.

Owen

[GaryGary]

Hi Owen,

You might look here for PV driven pumps:

http://www.builditsolar.com/References/Suppliers/SolarHeating.htm#Pumps

The ElSid pumps are used a lot, and the Laing Ecocirc pumps have a very good reputation.  March also makes some 12 VDC pumps that can be driven by PV.

All are fairly pricey.

The copper tube/aluminum fin homemade collector I gave the link to  should (I think) be pretty safe from galvanic corrosion.  The Aluminum has a good coat of factory enamel on it, and the copper and aluminum are separated by a very thin layer of silicone.

But, you could do the same construction with thin copper sheet instead of aluminum -- it would just get more expensive  -- the copper could probably be down toward 0.01 thick.  If you don't mind soldering a lot, you could also solder the copper sheet to the copper pipe -- but after doing about 4 ft for a test collector, I can tell you its kind of a pain.

I think if it were me, I'd hold off a bit on getting the controller, and see if anyone comes up with an all-around better scheme -- its seems like there ought to be a simpler way to heat 4 gallons of water a day.

Gary

[dnix71]

Something simpler, maybe a black 5 gallon bucket? Paint buckets can be had with a reclosable cap for pouring.  

http://www.usplastic.com/catalog/product.asp?catalog_name=USPlastic&category_name=20327&prod
uct_id=9715&cookie%5Ftest=1

Set it on the deck until warm and then take it below, or drop a plastic tube in the pour spout and pump the warm water to your holding tank, or pump the warm water directly to a diverter on your shower head.

[spinningmagnets]

"...I have no idea where to find the copper plate..."

Get copper pipe, possibly even plumbers scraps. Plumbers normally save their scraps for copper salvage weight.

Pound one flat, grind the edges, and you'll have two fin-plates. Just an idea...

[la7qz]

This would NOT please the fiancee at all...

She'd say "forget that, run the damn' engine".

Owen

[FishbonzWV]

Owen,

I use a one of these at our remote camp.

http://www.cabelas.com/link-12/product/0024908516349a.shtml

It can be run totally independent or tied into your existing water pressure.

Runs on 1 lb. propane bottles and an internal 6v battery.

On my set up, it is plumbed into the water line from the storage tank which is pressured by a 12v shurflo pump. The 6v battery used a 12v wallwart to keep it charged so I just cut the transformer off and used the cable to tie it to the 12v batteries.

I paid $168 at wallyworld for the unit.

It will also need the pressure regulator if you tie it into your pressurized system and shower head.

I had looked into building a solar hot water system at the camp but this was just too easy. Like it says...instant hot water.

Fishbonz

[tanner0441]

Hi

For clip on fins look on the C.A.T. Center for Alternative Technology in the UK.  They do clip on fins for building your own collectors from copper pipe.

Brian

[la7qz]

Hi

My agenda here is to build and install a fully automatic system that uses solar energy to heat the water in my hot water tank, not to find all sorts of more or less sustainable alternatives.

Propane is to the best of my knowledge not renewable energy and I don't want it below decks on the boat anyway. Propane is heavier than air and any leaked gas will gather in the lowest parts of a boat and explode if there is a spark (like cranking the engine). When I bought this boat, I very reluctantly had to accept a propane cooker since pressure kerosene cookers (primus principle) like I had on my old boat are very difficult to find, but the bottles are stored outside and the gas is turned off at the bottle whenever it is not in use. Using a propane water heater on a boat would probably void any insurance too. There are very strict rules and regulations for gas installations on boats.

Please read my original post before anyone suggests any more non-RE devices or plastic buckets. I already have a functional way of heating the water in my existing hot water tank by running the engine. My fiancee likes the convenience of hot and cold running water in the galley as well as the shower. I am looking for a solution that is MORE convenient AND more environmentally sustainable than running the engine for a few minutes every day. Since there is plenty of sun here, it seems logical to use the sun. Also, the skills I learn by setting up a well functioning solar water heating system on the boat will add to my marketable skills and future earnings in the marine RE sector. The best way to learn is from experience of setting up your own system.

In other words, I'm asking for help on some of the details of the solar heat collector I'm already planning to build, not advice on alternatives. Bottom line. My fiancee and I both want to have hot on tap no interaction from our side other than simply turning on the tap. Another part of my agenda here is to convince the lady that it is possible to live totally on renewable energy without having to sacrifice the creature comforts she is used to from her land based life.

Owen

[la7qz]

Thanks Brian

Those would be great... if they were made of copper. I know you land-based guys find this hard to believe, but galvanic corrosion between dissimilar metals is a HUGE problem in the marine environment. We're talking about a 36 foot ocean going vessel here. There will be times in rough weather at sea when the whole boat is continuously sprayed down with salty seawater. It's not only the actual liquid water, but all the tiny droplets that permeate the atmosphere. Even just sitting at anchor in the Caribbean where the wind has come all the way across the Atlantic from Africa, picking up salty moisture along the way means that new tools are brown within a week, and I'm not talking about tools left out on deck, but tools stored in my toolbag inside. Combining copper with aluminium in this environment means the aluminium will form a sacrificial anode to the copper and will corrode very quickly.

I installed the first two PV panels on this boat on the guardrails two years ago with chromed bronze hinges bolted to the aluminium frame with stainless steel bolts. There is now deep pitting in the aluminium where the hinges were because I forgot to isolate the three metals with TefGel paste. So, I appreciate all the helpful suggestions but aluminium and copper together on a boat is a big big no-no. I've lived afloat since 1992, and some lessons I have learned the hard way...

This brings us to the design of the collector... I am not sure I see the advantage to the usual design with a manifold each end and several pipes between the manifolds. It has to be difficult to get an even flow, and there is a lot of open space between the pipes. Would the same space not be used more efficiently by building a tight rectangular spiral from 1 inch black painted copper pipe installed in the same footprint box?

Owen

[zeusmorg]

 You may consider aluminum tubing and aluminum flashing for your collector. It would be a cheaper alternative and no galvanic corrosion between the two. I would however watch the pressure in such a system.

 You could buy a coil of tubing then from the aluminum flashing to fit around it. I would imagine a "bender" could easily be made from simple construction lumber as the ease of bending aluminum especially thinner sheets is not too difficult. Also if you had a single run of tubing you wouldn't have to worry about header distribution problems and hotspots.

[huntedheads]

Owen.

You said:

"I would like to build a solar heat collector to plumb into the system so that I would not need to run the engine to produce hot water. I would also like to retain the ability to use the engine to heat the water for those no-sun days."

     1. I have thought about this for roofs with no south side and it should work for you? Me? Two collectors east & west with separate pumps plumbed to the same exchanger just add a one way brass flow valve at the top of the exchanger for each inlet so neither pump flowed into the other collector ( or motor in your case. Motor off and collector motor on )but shared the same water system. I will try this soon!

    2. A cheep control for the collector has been running on my system for about nine months now without failure. A thermostat from a powered attic fan set at 120 degrees and mounted inside the collector itself. About $23 I think? It shouldn't care whether you feed it 120 volt or 12.

    3. Like Gary said about the heat, you are about 18 degrees on the ball we live on and your going to suck up a lot of sun! 130 x 70cm will cook your little four gallon tank! ~9.5 sq' of collector so plumb it to keep that big diesel warm too because you know starting a cold engine is a terrible thing to do!

    $. As for copper if your island is like my area you have churches, Most "old" churches have copper flashing, gutter, and down spout. There are companies that specialize in church restoration and can get you the copper you need just BEWARE I've called and your going to need to hold out the wallet!!

Just my opinion, and not another bucket.

Lester

[FishbonzWV]

Sorry Owen,

Just thought you wanted hot water without a lot of trouble.

An alternate method to the solar box collector would be black water line (or stainless if you can afford it) ran around the top of the rub rail. You could attach it to the life line stanchions.

With your Cheoy Lee that would give you about 80' of heated pipe without using valuable space on top of the cabin.

Surely you have a bulkhead somewhere in the cockpit you could go through with the lines.

Controls would be the same whether a box or tube.

[BigBreaker]

I'd just use copper.  Your collector is small and all copper will be slightly more efficient without any concerns about corrosion.

Boats are different - everything is small and expensive but also robust and efficient and perfect for its use.

Copper has come down in price by 50% in the last few months, so don't pay the old price.  Copper now is about the same price as aluminum was three months ago.  Some hardware stores in the states sell copper flashing for roofing purposes.  Copper is pretty good in marine environments but not common for roofs.

Don't forget to insulate the back of the collector from your boat.

[Ungrounded Lightning Rod]

Agreed:

• Copper flashing.
  
• Solder a "snake" of copper tubing to it - horizontal runs with vertical turns.  (Yes I know your panel is ALMOST horizontal...)
  
• Paint with black stove paint, available at pellet stove vendors and hardware stores.  Absorbs heat nicely and no issues with degradation due to high temperature.
  
• Your mounts will have to let the collector expand and contract a bit.  Mainly to avoid noises and warping.
  
• Pump cold water from bottom of tank into bottom of snake, let warm water from top of snake return to top of tank.  Need a small valve to bleed the bubble at the high point.
  
• Maybe have an "expansion tank" at the top, consisting of a foot or so closed-off hunk of larger diameter copper pipe to hold a bubble.  Will avoid seepage from the pressure relief valve.
  
• Maybe put it in an insulated box to shelter it from wind and convection losses to the air.  (Build box from fiberglass-coated wood.)
  
• SAFETY!glass top will not just stop air but also help with the heating using the greenhouse effect:  Light and near infrared penetrates glass, is absorbed by the black coating.  Black coating re-radiates some heat as far infrared, which is reflected by the glass and reabsorbed by the black coating.
  

[la7qz]

Hi again.

The black water line is something I have considered, but as a coil in a box rather than around the lifelines. It would be interesting to know how much the usual 10-20 knot tradewind breeze would cool down such a collector compared to the same amount of tubing in a box.

Another problem is that there is a woman involved, so we have to regard the "prettiness" factor. If she says it's an eyesore, then it's an eyesore and it doesn't matter much what I think about it, same if she thinks something is cumbersome. I somehow think a solar collector on top of the sprayhood (where she suggested installing PV panels until I explained about the shading from the boom) would be more acceptable to my fiancee than "piping draped around the boat" which is probably how she would see tubing along the lifelines.

I'm now leaning towards a box collector with a zig-zag snake of 1 - 2 inch copper pipe painted black rather than manifolds or a spiral. I think the zig-zag pattern would be easier to make than a coil and I can not see that it would make any difference to efficiency in a pumped system. I see "ungrounded" is suggesting the same. Since my available collector area is larger than needed, I'm thinking of running the pipes close to each other and not bothering with flashing at all.

I must also admit that part of me would love to see Magic restored to the pure sailing machine Bill Luders designed without the PV panels, wind turbine and all the other technology. Unfortunately, the only way I could write this post or sit here in a brightly lit (LED) cabin at nine in the evening drinking a cold Sam Adams without my RE toys would be to sit in a marina or run my engine several hours per day. That is definitely not on...

Owen

[TomW]

Owen;

Just from the outside looking in:

This may be a compatibility issue. I don't mean dissimilar metals, either.

Just an observation.

Tom

[mkseps]

You may want to look at what a previous contributer furnished:

http://www.fieldlines.com/story/2003/9/23/92535/4705

This differential thermostat is what I think you are looking for.

Gene

[GaryGary]

Hi Owen,

The serpentine collectors works fine, and any performance difference between the serpentine and the parallel tube collectors will be small if the flow rate is about the same.  But, getting an even flow through the vertical tube collectors is not normally a problem if you have the feed at one corner and the return at the opposite corner -- that way the pressure drop from supply to return is the same for every riser. Its not necessary that the flow be absolutely even-- it just needs to be enough to remove the heat -- about 0.04 gpm per sqft of collector is fine, so you will only need about 0.5 gpm (more is OK).

It seems to me that 1 to 2 inch diameter copper is way overkill, and would be difficult to get a small bend radius.  I think half inch is plenty and will be easier (but not easy) to work with.  

On a conventional collector, the fins (the flat sheet part) are the absorber, the only reason the tubes are there is to carry the heat away from the fins.  The usual idea is to cover every square inch of the inside of the collector with fins, and then have enough pipe to take the heat away efficiently.  If you forgo the fins, than the pipes become the absorber -- it seems to me that the problem is that you are giving up most of your absorber area.  I think that the empty space between the pipes will do little to collect heat, and this is probably going to be most of the area of your collector.

So, I'd think twice about forgoing the fins.  But, maybe this is why you were thinking about large diameter pipe? I'd add up the area of pipe you can get with the tightest serpentine you can build, and compare it to what the fin area would be -- I think you will find you are losing a lot of effective area by not having fins.  If you can manage a 5 inch minimum bend radius, than with 1 inch pipe, 80% of the collector area will be between the pipes?  I think that a 5 inch bend radius in 1 inch pipe may be very difficult to do?  I guess that you could solder a serpentine together with a bunch of elbows?

If you don't mind paying for it, you may be able to find a commercial supplier that would make a collector the size you want.  This way you would get good efficiency, good looks, and good weather sealing.  You might just check with some of the companies listed here:

http://www.builditsolar.com/References/Suppliers/SolarHeating.htm#FlatPlate

The glazing material is something else to think about.  Tempered glass (the most common collector glazing) is very strong and abrasion resistant, but is subject to breaking into a jillion pieces if hit the wrong way.  Polycarbonate (Lexan) is very tough -- essentially unbreakable, and has a good temperature capability, but is subject to scratching.

Running the black line around the rail is a neat idea, but I think that without glazing there will be a lot weather conditions where it just won't produce much heated water.

Gary

[la7qz]

Hi

Yes the horizontal snake and expansion tank was what I was thinking too. Easier than a spiral or manifolds. I was thinking of forgetting about the flashing altogether and just use more copper pipe closer together. Good point about the mounts allowing it to move. I read somewhere that 1 1/2 to 2" copper pipe works better than thinner pipe. Stove paint might be difficult to find here since people are more interested in cooling their homes rather than heating them, but I suppose barbecue paint would work?

As for the pumping direction, the heat exchanger spiral in the hot water tank is already marked "in" and "out", so I was going to stick with that.  

I was going to use an insulated box coated with black pigmented epoxy. Fibreglass is probably not necessary as the wood should be strong enough structurally, so the epoxy is just for protection. One of the things 16 years of living afloat has taught me is that polyester, fibreglass and wood don't work well together in the marine environment. Polyester does not have good adhesion to wood, and comes loose after a while leaving a void for moisture to collect in, and then the wood rots. Epoxy is much better. I was going to use an acrylic glass top. Maybe plastic greenhouse glass would work? It's probably easier to find at low cost than clear acrylic. However, with the small storage tank, I might try the collector without the box first.

Thanks "BigBreaker" for the hint on copper pricing. Unfortunately, price changes in the rest of the world tend to take a while to reach the island. I can get stuff shipped by ocean quite cheaply from Miami though as my employer uses a shipping company there.

As for insulating the back of the collector, it will be mounted on top of the canvas sprayhood (it has a stainless steel tube frame), so heating the boat is not an issue, but I will of course want to keep the heat in the box, so might make the box with a double bottom with insulation, or just an air gap.

Owen

[la7qz]

Hi again

Yes, the reason for going with larger diameter pipe was to increase the collecting area. And as you are already hinting at, I was thinking of using ready made pipe elbows and soldering rather than trying to bend the pipe through a tight turn. I was hoping this would give me much tighter spacing than the 20% you mention. I think a trip to a plumbing supplier to see what is available and how tight the turns can be is in order as soon as I can manage it. That may not be before Saturday because of work.

As for the glazing material, I was wondering about plastic greenhouse glass which I think should be readily available cheaper than clear Lexan or acrylic. The steering vane for my Norvane wind-vane self-steering is made from plastic greenhouse glass and it's very stiff and doesn't seem to have any issues with long term exposure to the sun.

Owen

[la7qz]

Hi again Gary

On the pump, I did consider just running it off one of the PV panels and connect it direct the panel upstream of the blocking diode, but with such a small hot water storage tank, this would probably cool down the water in the tank in the mornings before the collector is heated, and it's in the mornings we normally want hot showers. The tank is well insulated, so I normally have warm enough water for a shower if I ran the engine the previous day, and hope the same will be true when the water is solar heated. A thermostat in the collector might work better, or maybe just a snap switch?

I actually already have a snap switch built into the rectifier / S4w booster box for the wind turbine to control a fan for cooling the rectifiers. I also connected the snap switch to an LED so I could see when the fan is running, but so far, it seems the box never got hot enough for the fan to run, so maybe the snap switch and fan could move on to other projects...

Owen

[la7qz]

Hi Lester

I'll consider the thermostat in the collector. It seems like a simple solution. The problem with combining the engine coolant and solar collector coolant at the same time is that the solar collector will be 5-6 feet above the engine. I'm not sure how I would prevent coolant running down from the solar collector and leaking out of the engine coolant reservoir? I'd have to make a drawing to see whether it would be possible to prevent that with one way valves.

My idea is to use two solenoid Y valves controlled by the engine oil-pressure switch. When the engine is running, the valves switch the engine coolant to the coil in the hot water tank and disable the solar collector pump, when the oil pressure drops (engine stops), the valves switch the hot water tank coil back to the solar collector. To avoid over heating the solar collector, this could be combined with the pump controls so it would only happen if the collector was below a certain temperature. The power consumption of the solenoid valves would not be an issue since they would only be active while the engine is running (alternator charging). A simpler solution would be manual Y valves, but that would probably mean opening the engine room to switch, which means removing the companionway steps first.

Also, heating the engine block is nice in cold climates, but we don't want to heat the boat, and unlike the hot water tank, the engine block is not insulated. In fact, apart from sustainable living, noise and pollution, one of the reasons I want to avoid running the engine for heating water is that it heats the living space. Granted, that improved a lot when I redesigned the exhaust so that only the first two inches out of the manifold are dry rather than the first two feet. The fresh water pump is in the engine room and the first litre of water out of the cold water tap (the water that had been sitting in the pump) used to be really hot. This is no longer the case after I rebuilt the exhaust to a much better design than the original Yanmar parts.

Owen

[la7qz]

Thanks.

Looks great. I may have to order the parts from abroad though. There is a Radio Shack in the capital, Philipsburg, but it is little more than a joke...

Owen

[FishbonzWV]

I know what you mean.

I had the honor of sailing in Maine on a 1926 Americas Cup boat that had been through a retrofit that had added the 'comforts' of new technology and then been stripped of all that and restored to original by the new owners.

Navigation was by the original compass only.

Coming in to the anchor bouy was by sail and if you missed it with the gaff you had to go around again.

What a joyous ride!

Good luck on your project.

Fishbonz

[GaryGary]

Hi Owen,

I'll just throw this out for what its worth -- may or may not fit your situation.

There is a type of solar water heating system that was (maybe still is) popular in Japan in which a pillow like tank of water sits inside a glazed container on the roof.  At the start of the cycle, cold water is pumped up into the pillow.  During the day the sun heats the water in the dark colored pillow tank -- probably quite efficiently.  Then, as hot water is needed, it flows by gravity to the hot water tap or shower.  

A very simple and reliable system that should be up to heating 4 gallons efficiently?

These systems (and some others that might be of interest) are described in this free download book (thanks to David Bainbridge):

http://www.builditsolar.com/Projects/WaterHeating/ISPWH/ispwh.htm

I'm not sure if the systems are commercially available now or not.

There might be a simple way to work this into your existing water system, especially if its the RV type with an on demand pump?

Anyway, just a thought.

Gary

[la7qz]

Hi again Gary.

Unless the pillow is really slim, it probably wouldn't fit the space because of the main boom clearance. It would still have to somehow be combined with the existing hot water tank for insulated storage since the priority is hot water in the morning.

The fresh water pump is a Shurflo with a pressure switch.

I've got the book, lots of good stuff there.

Owen

[la7qz]

Hi again

This is the glazing I was thinking of using. Much cheaper than Acrylic or Perspex glass.

http://www.greenhousewarehouse.com/More-like-this_B21NQO.aspx

Owen

[la7qz]

Hi

With my old boat (28 foot, heavy displacement) I would often sail in and out of my marina berth back in Norway. When I was cruising, I would usually sail on and off the anchor. With Magic it's not so easy since I can't reach the headsail sheets from the helm, but I did come into Falmouth Harbour, Antigua and anchor under sail when I was having gearbox problems. I intend to remove the wheel and replace with a tiller to make the boat easier to singlehand.

Owen

[Airstream]

http://tinyurl.com/6sxwcf

The 6x12 (72"x144") panels fascinate me - if/when I get to build there will be a few of those involved; they are located in Mid-Iowa so pickup at their warehouse is doable too!

Many flavors of that available too - forget the bubble wrap on the windows, use polycarbonate sheets...

[veewee77]

OK. . . so let me get this straight. . .You have a fiance who wants to come live with you on the boat, with all of the same conveniences of a land-based, domesticated, immobile environment.

In my opinion, she just needs to realize that life on a boat is very different (not in a bad way at all) to life in a land-based, domesticated, immobile environment. People have been living on boats for many years using the provisions that are available for reasonable use on a boat. It just comes with the deal. Perhaps if this fiance can't live with the differences of living on a boat, she may need to re-think her options. If you lived on a boat when she met you, and is coming to live with you then she will know that you, and your place of residence are a package deal. Line up and be happy. I'd venture to bet that after she gets out there with you on the boat for a while, she'll come to realize that the "conveniences" of a land-based, domesticated, immobile environment are kinda stupid and unnecessary. Sure there are many conveniences that you will have to do without, but that is miniscule to the joy and freedom of living in a mobile, less restrictive environment.

JMHO - YMMV

Doug

[esc]

After reading this a couple of things occur to me.

#1  Do you have to use engine coolant?  Can't you just tap in to opposite sides of the water heater (inlet/outlet) and circulate the "drinking" water?  That way you don't have to worry about any of the issues associated with getting coolant to the top of the companionway.

#2  What if you placed an all aluminum radiator, like those used for automotive transmission cooling in the "Box".  They are all one material and super easy to plumb.  But if you run drinking water through it I would not recommend a used one.  You would have to paint it black of course.

One or two of these might do the job:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=FLX%2D3826&N=700+4294924500+4
294839034+4294888847+4294888841+4294792802+115&autoview=sku

This has a picture of something similar:

http://static.summitracing.com/global/images/prod/large/flx-3820_w.jpg