afinelli wrote:Is it practical to use a Photovoltaic panel to maintain a 12-Volt boat battery?
Yes. This is done everywhere there are boats and sunshine.
afinelli wrote:Any idea what physical size and charging capacity panel we [need]?
The amount of charging current you need is unknown. Apparently you do not need much because your narrative mentions that the boat battery does not become deeply discharge to the point where it won't crank over the engine even after sitting for two weeks. On that basis, ANY charging current is going to be useful, and you really do not need a lot of capacity.
The electrical voltage and current output of a photovoltaic panel depends on the intensity of the sunlight falling on the panel, the orientation of the panel with respect to the sun, and the weather. When the manufacturer specifies a current, that is the MOST current possible. The typical current will not constantly be the MOST possible.
Jefecinco wrote:The charger controller may or may not be weatherproof.
A charge controller is used with large panel arrays that produce perhaps 50-Volts of output. The charge controller converts whatever voltage and current is provided by the photovoltaic array to the appropriate voltage and current to match the attached battery terminal voltage.
Generally with a little panel {like the one Phil linked) that might produce 1-Ampere of current at best there will not be a charge controller. The battery itself will be the charge controller. The panel will just dump all the current it can into the battery.
If you mount the photovoltaic panel on land you can orient the panel to optimize its exposure to the sun. If the boat is on a mooring and swings around into random orientations, the panel can't be optimized in its orientation.
Around me are many docks with boat hoists operated by a 12-Volt battery. Most of these docks have a little photovoltaic panel connected to 12-Volt battery to provide charging current. It takes quite a bit of electrical power to operate the electrical motor in a boat hoist, and these rather small 1-foot x 2-foot panels seem to be sufficient to maintain the battery charge between hoist operation. (Although I do note that most of these boats on hoists seem to get used about once a week or less often.)
Keeping the battery charged by non-120-VAC devices is a good safety measure. Having 120-VAC on a dock is an invitation to problems with leakage current into the sea water.
afinelli wrote:Where would you install one on a open center console boat like [what was later clarified to be an 18-foot] c.1989 Boston Whaler OUTRAGE?
The exact location for a small photovoltaic panel on your particular boat will have to be solved by you. Because the panel output current is going to be low, there will not be a huge concern about voltage drop in the wiring from the panel to the battery, as long as you use a reasonable conductor size. With a small panel, with low voltage and current output, the panel should be close to the battery and connected by suitably chosen conductors so that most of the electrical power winds up in the battery, not in power lost in the cables.
For advice on choosing a conductor size see
https://continuouswave.com/whaler/refer ... tion1.html