Not practical. Mount a couple of solar panels
instead. And a wind charger
if you like.
You could possibly mount a pulley on your propshaft, if your gearbox
will take kindly to freewheeling. Many don't and prolonged freewheeling will damage it. But assuming you can, then you want to change to a fixed prop or controllable pitch. In trail shaft mode the prop and shaft turn, and energy is transferred to the motor
mounted piggyback over the shaft via belt or belts. A double or triple pulley and vee belts works okay, a flat belt a bit better but possibly harder to find spares or replacements
and they would cost more. A 5kw BLDC/PMAC motor
for this. Permanent magnet motors can produce sparks and limit your use of gasoline or propane
aboard if the motor is mounted below. The controller in regen mode will output fairly clean DC, but probably not at 12v so you will want a 36v or 48v bank. Power 12VDC loads with a DC/DC converter. As a plus, you can flip a switch for electric propulsion
or other low speed or short duration maneuvering. AND when you run your engine
, you can adjust regen to charge the batteries
at whatever rate you decide is practical. One con is having to break the shaft at a coupling to change belts. If you kept a few spares around the shaft tied back in such a way that they do not touch it, you would have ready spares and could go a lot longer without having to break the shaft. There is chain drive, too, but this has its own set of issues. Anyway what I have described is actually a diesel/electric parallel hybrid propulsion/charging system. It would cost you around $3k or less, assuming use of cheap
but rugged golf cart batteries
. And a lot of work
, connecting, building a battery box
, fabricating motor mount, etc.
Keep in mind that this is not free energy. The more you take from the trailing prop, the more you slow the boat
. And the power produced will be far less than you probably envision. The load on the diesel
when engine charging
though, could actually be a good thing if like most boats you are overpowered and the diesel
is just loafing along. Diesels work best at their optimum speed and load. However, you will see an increase in fuel consumption
with the increased load. The major benefit of tailoring the load is in prolonging engine life between rebuilds. This would be particularly true for turbocharged engines, BTW.
To get an idea of worst case scenario for slowing the boat
speed, think of a fixed prop with the shaft locked. The heavier you load the generator
, the more closely the drag will approximate this. The lighter the load, the easier the prop can turn and the less resistance it will offer to the water
it travels through.
The easy way would be to mount a solar
panel or two. This would make a much smaller hit on the boat's performance. Solar
works really well for charging
, with modern MPPT
charge controllers. All the fine engineering is already done for you. Just hook it up, test it, and you are good to go.
Most any shade tree engineering project
using any of the various motor types mentioned will give you some output, as long as no field current
is required by the device operating as a generator. The issue will be in efficiently rectifying and converting the output to the desired voltage, which will change according to what state of charge the bank is in. You would probably want to manually regulate output, after familiarizing yourself with your bank's preferred charging algorithm. Efficiency will generally be pretty low, a small output in relation to the boat's speed loss. One exception... if you commonly reach and exceed hull speed
, actual and not calculated, where the boat is actually fighting its own bow wave, your sails
are producing more energy than the boat can use effectively, and so the drag would in that situation be much less of an issue. You would in a sense be recovering wasted energy.