It is gospel among multihullers
that weight=slowness. Multihulls are more susceptible than
monohulls because they have a lot more wetted surface area than
monohulls of similar dimensions. Wetted surface area translates
into drag, which is what slows your boat. (Wave action also slows
your boat but that's a different topic).
Multis have more wetted surface area mainly because they have two or
three hulls in the water instead of just one. I'm not going to
get into the geometry of it, but think of it this way: if you dumped 50
lbs of sand into an oil drum, sealed the lid, and dropped it in the
water, then dumped 25 lbs of sand into each of 2 oil drums, and dropped
them into the water, the 2 drums together would have more surface area
under water. Trust me. Think of the boat's hull(s) as the
drum(s) lying sideways in the water.
The second reason why multihullers go to extremes to keep their boats
light is because of pride. You've already insulted the
hierarchical, status-conscious conventional sailing community by
choosing a multi over a mono, so the
last thing you want them to be able to say is, "I told you so.
That boat isn't any faster than mine."
Very large multis (over 38 feet LOA or so) aren't as susceptible to
weight, mainly because there's only so much junk that an individual can
bring on board, and the proportion of the boat's weight that is payload
is much less. But the large, overweight charter cats have a
well-deserved reputation for slowness. If you've ever sailed a
Hobie Wave, you know that
adding a second person is the kiss of death. My boat is somewhere
in the middle of the spectrum between the Hobie and the big condomarans
that you charter from Sunsail or the Moorings. This
was one of my deliberate choices: it's possible for two people to
cruise on a boat as small as an F-27 with the same amount of gear that
Tanya and I had, but it's going to be slow going. If I'm not
racing, my boat can hold just about everything I need for a few weeks.
Back to electricity, or more specifically, how to make it, keep it, and
use it. If weight weren't a concern, I would simply have a large
bank of batteries and a generator. If you figure out how much
power each device on the boat uses, add them all up, and double the
sum,
you know exactly how many batteries you need. Each device will be
rated for the number of amps in current it will draw. Multiply
this by the number of hours you will use the device (for instance, you
will almost certainly not be transmitting on your VHF for more than an
hour a day or so, and you will probably want to use your cabin lights
for at least 4 hours) and you have your total expected consumption in
amp
hours. Your battery bank should be double your expected
consumption because it's generally not good to run standard marine
batteries down below 50% charge. As far as I know, more
specialized batteries like lithium ion laptop batteries can be
discharged almost 100% without ill effects, but they're not in
widespread use in boats because they're still expensive.
I have two Group 27 batteries. It was a hard decision to install
that second battery, since each weighs around 60 pounds. On the
other hand, I wasn't ready to shell out for a small generator instead
of a second battery, and I'd rather have a passive battery than a
generator that needs to be turned on and makes noise and smell.
The Honda eu1000i is quiet and doesn't stink (I've seen them running
indoors at boat shows and you can barely tell that they're on) and
weighs only 27 pounds, but it also costs
around $700. You also have to add the weight of the gas you will
use at 6 pounds per gallon, but I think it's almost inconsequential if
you're able to refill every few days.
The main consumers of electriticy on my boat are the instruments and
GPS, which run all the time, the laptop which runs some of the time,
lights, and a stereo. The lights that are likely to be on for
long times are LEDs. I generate power when the outboard is
running, and from two 15-watt solar panels. So far this has been
sufficient to keep the batteries charged even when I'm on the boat for
several days. I also have a 110v battery charger but I've never
plugged it in anywhere except at home when the boat is in storage.
The outboard is a Nissan 9.8 with 25" shaft. Despite the long
shaft, the prop still comes out of the water in steep chop. I
need to rework the fixed carbon bracket on the stern to which the
aluminum motor bracket attaches, as well as replace the aluminum
bracket, because even though it's theoretically rated for 120 pounds of
engine, it's insufficient for my 95-pound Nissan. The Nissan
pushes the boat at hull speed (just over 7 knots) at about 1/2 throttle
with no current or headwind, and doesn't go much faster at full
throttle. It is nice to have the extra power when the wind and
waves are against you, though. Unfortunately my electric
start/charging cable isn't working so at the moment I'm relying on the
pull-start to get the engine going and solar to keep the batteries
charged.
Electrical Notes
The 5-prong deck plug for mast lights is wired as follows:
- masthead read positive (running lights)
- masthead black positive (anchor light)
- deck light
- steaming light
- ground
The masthead light has black (anchor), red (running), and ground wires,
attached to black, green, and white respectively in the cable.
The deck/steaming light has red (deck), black (ground), and blue
(steaming) wires, attached to white, black, and green respectively in
the cable.
The deck light isn't currently working so check prong 3+ against 5- in
the connector.