It is now more than a year after my first post and I have not had time to get back to you as promised so here is a quick note to say what I have done and make some comments on your answers.
Consumption estimate may be over-generous but seems better to err that way than the other. Production of solar panels can be very low in the tropics, especially if you are up a creek hiding from a cyclone for a few weeks. My capacity is designed to be marina proof. And bear in mind that fuel
capacity on a boat as small as mine is often very limited. Anyway, marinas
are few and far between in many of the most interesting parts
and ditto for SE Asia
People tend to use their own experience when comparing an alternative system, rather than look at the particular circumstances pertaining to the alternative.
The result of my research
has been two high output 70amp alternators running off the PTO for charging the 450 Ahr house bank. One replaces the Volvo
alternator and the other is driven by a larger pulley in front of the one on the crankshaft. Their pulley ratios are matched so that both alternators run at the same speed.
warned me about the vibration problem but seemed reassured when I sent them a photo
of the mod. I also mimicked the volvo attachment arrangement which clamps alternator to the front end of the bracket. This requires very little torque to hold the alternator solidly after adjusting the belt.
There is a DC-DC charger
that tops up the start bank whenever the house bank reaches 13.8v - whatever the source of energy. The start battery is one of two 55Amp Lifeline Start Batteries. They can be paralleled together and/or connected to the house bank in emergencies.
The Balmar controller can be used to reduce the output of the alternators by up to 50% when the engine is being used for propulsion
. When being used just for charging, the engine should be producing 4 or 5 HP depending on the state of charge of the batteries and the amount being used by peripherals such as the fridge/freezer (up to 6 amps) and the 8gph water maker (27 amps)
There is also a delay and ramp
up facility available when starting the engine so that the demand from cold output does not stall then engine at tick-over speeds.
My consumption figures allow for a wider range of conditions than I expect to experience most of the time. Looking at your responses in that light, I reckon I'll be less likely to be caught out than some when faced by the sort of conditions I've allowed for.
Thank you for your interest and advice.