There's nothing wrong with running a diesel at moderate RPM for the
time period you're talking about. Actually, why not run it an hour or
two a day when the wind is light? If you intersperse several hard
runs with the light load runs, there will be no problem at all. Lots
of cruisers use the diesel for charging while hanging out at an
anchorage for a week, then run hard for a few days while traveling.

Also, the power usage of an autopilot and instruments shouldn't be
very high, unless its a large AP for a large boat (in which case, the
alternator should also be large). A Ray 4000, for instance, is less
than an Amp on average. The engine run time should be an hour a day,
maybe less if there's no fridge involved.

Buying the Honda just to sell it in a month is silly. On the other
hand, if you're looking for an excuse to buy one to keep, this would
be a good rationalization. I wanted one for years, and then when I
had a chance to get one at half price, I convinced my wife we needed
it as backup so a vacation wouldn't be ruined by a bad alternator.
Its sitting in the garage now, looking very manly!

Hobbs wrote:
I need to equip a sailing boat for battery charging for a single long haul
trip of about 35 days.
This will be a delivery trip for a boat that will not need any such
capability once it arrives at it's destination. Much of the power
requirement will be to drive an autopilot and attendant instruments and nav
electronics.

I've looked at Solar but I don't think it will be economical to buy the
solar panels that would be required.
I could run the 30 horse diesel for a couple of hours per day but I know
that diesels don't like light loads for extended periods.

I've discounted wind systems because of cost and also some concern about the
ability to reliably generate enough juice as well as noise and safety
issues.

I'm also thinking about using a Honda Portable generator with it's output
connected to the existing shore power system battery charger. Upon arrival
I could easily sell the generator for something like 75% of it's cost or
just keep it. The main disadvantage I can see to this approach is that I'd
need to carry petrol (gasoline) to power it and that consitutes a
significant bit of a safety issue.

Anyone care to comment on the Honda Generator idea?
Any other good ideas that I haven't considered or flaws in my logic?