There are water bags that you can lay in the sun for a warm shower on a boat or while camping. There are also solar collectors to help heat water in houses.

This is similar, but it's a permanent system in a boat. Part of the boat's deck is painted black. A very low power pump driven by a small solar panel, also on the deck, slowly circulates water from a tank through a system of tubes inside the black part of the deck.

If the water becomes excessively hot, a thermostatic valve opens which allows the water to circulate through a copper block heat exchanger mounted on the hull so the hot water can shed heat to the water surrounding the boat.
-- jmvw, Jul 11 2006

The advantage is that the existing products would take up deck space and this allows the deck to remain clear?
-- James Newton, Jul 11 2006


Except I find that in the hot part of the summer I want a cool shower and on the cloudy rainy days I want a warm shower.
-- MoreCowbell, Jul 11 2006


[James Newton]: Yes, and this doesn't require you to plan ahead when you want to have warm water. This system doesn't require any attention or planning and it can be a part of permanent warm water plumbing. If sun is shining with sufficient intensity during the day, warm water will be available inside the boat.
-- jmvw, Jul 11 2006


You can still have a cool shower on a hot day, [MoreCowbell]. Not the entire fresh water supply is heated. The system would work optimally in warm climates.
-- jmvw, Jul 11 2006


I'd ditch the copper block heat exchanger for several reasons - hydrodynamic inefficiency, risk of increasing your hull corrosion by providing a source of Cu++ ions in close proximity to the hull, and increased complexity of the whole system through needing some kind of diversion mechanism to channel the hot water through the block. Better to simply turn off the circulating pump when the tank gets to desired temperature.

Remember that at night, your black 'collector' is going to switch to a very efficient 'radiator' so you'll need some kind of light sensor on/off control for your pump. Also consider the difficulties of manufacturing the tube device and associated connectors and piping for such a harsh environment. Development of UV resistance in polymers has come a long way in recent years, but the materials are not designed to be part of a traffic area.
-- ConsulFlaminicus, Jul 12 2006


[ConsulFlaminicus] Hulls on most recreational boats are fiberglass. As long as the copper heat exchanger is not galvanically connected to other submerged metal parts on the boat, this should not cause corrosion problems, just like brass thruhulls don't. The heat exchanger could have a low profile, so it would cause drag. Some boats use a heat exchanger in the keel to cool the engine.

After the water has warmed up, I want to keep circulating it to prevent it from boiling, but also too keep the deck surface from becoming excessively hot, so you could still walk on it barefoot. The thermostat temp might be around 40-60 degrees C.

The light sensor is the solar panel: at night it does not provide power to the pump

Tubing and connectors really aren't hard to make. It's done all the time: in both fresh water and engine plumbing. Copper pipes can be used in the solar collector in the deck, other parts would probably be vinyl tubing and the reservoir might be poly or frp.

As for the dark deck surface, this could just be normal gelcoat with dark pigment or this part of the deck could be painted. It might need some fresh LP paint after 10 or 15 years. This is the only part exposed to UV.
-- jmvw, Jul 12 2006



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