I guess it partly depends on when (it isn't light very long, if at all, in the winter!). You said near Alaska and boat, so I'll have to say from my 5 years living there that where there's water (meaning around the middle to southern shores) there are more clouds than sun. So, in the summer you'll have clouds which cut down the solar gain considerably, and in the winter you still have clouds, coupled with darkness. Do the boats have motors to use for charging, or are they motorless? Interior Alaska has a lot more sunshine in the summer.