Thanks for the item. I'm having fun experimenting with electric boating.
The post you referred me to was consistent with what I've learned, and I
think I've made all the right choices so far.
I expected that even the 70 lbf thrust motor would be marginal or
inadequate in any substantial current or wind, so I did as the post
suggested, went all out to minimize any unnecessary resistance in the high
current circuit (45 A max at 24 V). I used AWG4 marine grade (tinned)
cable to connect to the two group-24 size, 95 Ah batteries. I bought a
proper crimping tool and crimped and soldered all the terminals. I
presently have a 60 A fuse in the circuit, but MinnKota has subsequently
suggested a 50 A would be better.
The wet-cell batteries were only about $40-45 a piece at Costco and have a
higher ampere-hour rating than most group 24 deep cycle batteries - 95 Ah
vs the usual 85 Ah. Judging by the weight of the batteries (45 lb each) the
higher rating is probably correct, since more lead should indicate more
capacity. Group 27 batteries would have been preferable but wouldn't fit
crosswise in the cabin footwell as the 24s do. (I wanted to leave some
footroom for stepping in and out of the cabin.) I would have liked to avoid
concerns about battery acid, but the wet cells are smaller and lighter than
gel cells for the same capacity, and are much cheaper. The best wet cells
are reportedly 6 V Trojan batteries, the type used in golf carts and many
electric boats and electric autos, but they were too tall (and expensive)
for my application. As it is I will have to relocate one of my batteries
temporarily if I want to sleep comfortably in the boat.
The RT70/S Riptide motor has "Maximizer" pulse width modulation, which
gives infinite speed control from 0 to 100 percent power, and it has both
forward and reverse. It's wonderful to have all that instant-on-off control
in both directions after years of using the Seagull with no reverse
capability and no neutral. Also the pulse width modulation is more
efficient than the switched resistance used in cheaper trolling motors.
The motor is so clean that I store it in a closet instead of in the garage.
I bought a smart battery charger from Sears for about $90. It has both 12 V
and 24 V outputs, so I leave my batteries connected and charge them in
series at 24 V. The charger also has modes for different types of batteries
- deep cycle, gel cel, and other, and I can charge at 15 A, 10 A, or 2 A.
It has a maintenance setting for long term storage. Since it is usually
days between sails, I generally use the 2 A charging rate to minimize
battery stress and boiling away of electrolyte. The charger is designed to
prevent overcharging for the selected type of battery. I always put the
charger on as soon as I get the boat home, to minimize sulfation of the
batteries.
The MinnKota doesn't have the kick of the 3 hp Seagull, and I didn't expect
it to with little more than a kilowatt input to the motor (<1.5 hp input).
Acceleration is weak at lower settings, so to get steering speed quickly, I
may crank in 100% power, then back off to 50-75% power as needed for the
conditions. It moves well against a 15 knot wind, clocking over 3 kn on the
GPS. So far I haven't been in any conditions where I couldn't make
reasonable headway, but I haven't tested it in any strong currents or
choppy water.
On my second time out, I went way out into the Bay to visit the wreck of
the destroyer Thompson with my son. We were alternately, motoring, sailing,
and motor-sailing, but we logged about 4 hours on the motor. The water was
calm and the winds were light and I used about 60% power when motoring,
then switched to 100% when in sight of the ramp, just to "push the
envelope." Never did notice any diminishing power, but the battery charger
readings indicated the batteries were run down about as far as they should
be (for long life). I need a "fuel gauge," so my next step is to install an
accurate voltmeter so I can monitor the battery state of charge while
underway. Theoretically the no-load voltage on a 12 V battery should be
about 12.8 V when charged and about 12.2 V when about "out of gas." An
ammeter will be another useful addition so I can see the current draw for
different throttle settings.
My wife is not comfortable sailing and avoids it. Last week I invited her
to go on an electric "boat ride" instead of "going sailing." Although I
rigged the boat, I left the sails down, and we had a very pleasant 2-hour
sightseeing tour of the Redwood City harbor in our soundless motorboat. It
was windy, but the sheltered water was smooth, and Sandy was impressed at
what a gentle ride we were having compared to the hiked-out crew on a
heeled-over dinghy that was sailing nearby.
I've only used the Seagull once since getting the MinnKota, and that was
for the all-day trip to the South Bay to see the grounded sailing ship,
Estela. I carried the MinnKota as a backup.
Regards,
Harry Gordon
P14 #234, Manatee
Mountain View, CA
>Harry: I think you might find this item from the Trailer Sailor's BB of
>interest
>
>Best -- dwf
>
>http://www.cruisecortez.com/webbbs/trailersailor/index.cgi?read=24193