As I am confident is the case for most other engine converts as well, a question I am
relentlessly asked when detailing the wonders of an electric motor is “How far can you
go with it?” While there are many ways of approaching my answer each time, the core
incredulity behind such a question is in fact over how such a battery bank lightweight
enough for practical storage below deck could keep up with the demands of motoring on
a sizable displacement vessel like my 40′ sailboat. So in laying out the following
description of my Electric Yacht conversion journey I hope to also subside any
misgivings on the surface of the reader’s mind about seaworthiness and logistical
concerns of a Quiet Torque engine application.
To begin with, it is vital to point out that the “measure twice, cut once” principle
translates into “measure twice, order once” when it comes to planning what your
conversion will require, and since nearly every boat is used differently, Mike Gunning’s
frequently advised disclaimer of “it is ultimately up to the preferences of the individual
sailor” bear significant weight in this regard. How proximate will you want your direct
drive and propeller shaft couplings to be to your shaft seal? Will you take the
opportunity of this engine change to install a shaft saver between the couplings, or
perhaps alter the zinc configuration on the shaft as it exits the boat? How much free
play can be tolerated in the space where the engine will mount? Where will the batteries
be positioned in the boat so as to best maintain pitch balance, minimize wire runs, and
remain secure but accessible in the event of faults or upgrades? Once a clear picture of
what is needed mentally forms, prudent purchases of periphery items and materials can
be embarked upon. Although it may seem more reasonable to do so after the arrival of
the actual engine and other standard components. The hardest part of the whole
process was dismounting and ridding myself of the bulky diesel engine that was
crammed into the space where the little electric motor a third its size now sits.
With regard to wiring, while the official advisory is to obtain 4/0 gauge for only runs that
will carry full current, I used 4/0 gauge on every connection made between batteries and
‘aught’ else not only because it allowed a bulk purchase of my 50′ all in the same size,
along with the 46 lugs that I used in total, but more importantly because every foot of
wiring distance saved, and using the largest scale practical, added that much more
efficiency to my 48v DC power consumption. Carefully consider how much saving $100
in wiring gauge really means to you on your one-time installation of a $10-20k+
investment. You’ll have the peace of mind that there were definitely no mistakes made
of accidentally using a smaller gauge where 4/0 was supposed to be. And another
benefit I found of using top size in all my runs was how sturdy all the wiring is wherever
it sits, being hardly dependent on zip ties compared to what smaller gauge would be.

A noteworthy aspect of the configuration of 12v batteries for my 48v setup was how I
ended up facing them for minimum wire distance and complexity. In groups of four, I
stood two side by side and had them face another two mirror opposite. In that style I
positioned all three sets of four batteries adjacent to one another. Thus the shortest
distance was achieved between three sets of the negative and positive terminals for
joining each series together, and the parallel wiring for all three of my series ran
smoothly all along one side of the whole bank as I kept the start and finish of each
series all on the same side. It should also be noted that as I contemplated using the
bottom side of my old diesel tank as a template for the battery tray to replace it with
where the batteries would be best situated, that idea led to my resolve soon after to
simply take a grinder to the tank and turn it into my battery tray, so that its attachment to
the hull was already bolted down and tested for over two decades with far heavier
weight than my lithium batteries in the same space bore.

Now for the juicy part! Plenty of juice! Having subsisted on an inferior 24-pound flex
panel solar array atop my bimini, once I came across some 7/8” stainless tubing that
was soon to be scrapped, I was inspired to upgrade to a 128-pound arrangment of rigid
panels amounting to 800w, thoroughly outdistancing the potential of the old array and
doing away with any need for a slowly rotting bimini cover. Using the newfound tubing to
reinforce key parts of the bimini framing to handle the additional 104 pounds atop it, I
also made use of discarded rubber-coated cable messenger wire from work to
simultaneously lash down the panels and also provide a rubber cushion between them
and the framing so as to avoid long term chafing of the lovely black panel frame paint.

It is IMPERATIVE to configure a 12v solar array intended for a 48v battery bank with
series of at least three panels, but better four, and rely on an MPPT buck converterstyle
charge controller for taking your unnecessary volts and converting them down to
amps. I have hardly seen any boost converter-style charge controllers on the market
that could turn a lower voltage from the panels into a level necessary for charging a
higher voltage battery bank. For those who only ever dealt with 12v battery banks
before, it is easy to miss this aspect of the charge controller technology and go by the
conventional wisdom that it is better for shading risk to have all panels in parallel. Let
me assure you that any affect of shade your mast, sails, boom, or anything else
occasionally casts on your array pales in comparison to the totally nonexistent charging
that will happen for your 48v battery bank when your buck charge controller is only
receiving 19-21v from all your panels run in parallel. Also bear in mind that the larger
the panel series, up to a typical 150v generation for typical controller tolerances, the
better the delivery efficiency to your controller from the panels will be over their wires
and the less excess amperage your controller will be pressed to dissipate when the
batteries are full, potentially leading to longer life on your charge controller.
As for calculating how much solar you will benefit from for keeping the batteries
charged, start from a baseline mindset of packing in as much solar as you conveniently
can above deck. Consider that the more constantly your array can keep your batteries
topped off, the longer the life of your batteries will be by avoiding or minimizing
discharge cycles, no matter what battery chemistry is being used. Two more panels for
$180 that will last twenty to thirty years can help add several years of life onto your
multi-thousand dollar batteries even if it makes as little as a 5-10% difference in regular
discharge amounts. Once panel size and number is known, understanding the true
power of their dark side is a simple estimation. Consider what they are rated at in
wattage, and safely assume that a flat orientation will generate at least 65-75% of that
rating most sunny hours of the day, depending on panel quality. (One of the reasons I
switched to rigid from flex panels was a better known output quality shortly into their life
cycle.) Lesser generation will start shortly after it is light out, and extend all the way to
late dusk in fact, but for the weighing of recharge time it is best to be conservative. Don’t
worry about matching up voltages in your mind between the 48v battery bank and the
higher voltage panels, since an MPPT charge controller will drop the panel voltage to
optimal and spit out the change in the form of more amps to the batteries. So for
example, if a 100w panel is actually feeding 70w realistically, and that rate holds strong
an average of seven hours per day, then altogether that panel generates in one day
upwards of 500w. Multiply that by all your panels and you have the daily wattage of your
array. Divide that by your 48v battery series voltage to arrive at an approximate daily
amperage if you like. (The useful figure in our engine usage and battery capacity
considerations, right fellas?)
For my particular setup, with my 8 panels, I estimate a generation of about 4Kw per
sunny day. Or to express it in 48v terms, around 80 amps. So were I to drain my 300
amp, 48v battery bank down to zilcho, it would reliably only take four days to top off
again using my solar only, let alone hydro generation potential while under sail with the
electric motor! And for a point of reference, I typically achieve 4-5 knots using a rate of
only about 50 amps, which gives six hours of run time at that rate.
“So why don’t you tell us something we don’t already know, Joshua?” …I hear you say.
Well you might be as interested as I am in keeping all your batteries in one bank as
opposed to letting the majority of them sit unused, reserved only for your 48v electric
engine, while a couple of outlying champions do all the 12v grunt work of running your
luxurious daily yachting life. I consider spreading out minimal regular drain on all of
them to be a better long term cost benefit than heavily using a small house bank such
that it will need to be replaced a lot sooner. (Not to mention this configuration is a lot
simper for wiring and charging regimens with panels or shore power charger.) The only
complication I ran into when utilizing a 12v step-down converter was that its 720w rating
was insufficient for my windlass under load. Apparently a windlass rated at 700 watts
takes significantly more to engage under load, perhaps partly due to length of wiring run
up the length of my vessel.
But now for the part you never thought of: regardless of what you read online it is fully
workable to place two of the same step-down converters in parallel and double your
amperage output. Tada! System limitations summarily resolved! “Yeah but what if your
step-down converters break??” Ok fair point. Running straight off a 12v house bank
removes that failure point indeed. Even if step-down/up conversion is done with some of
the most simple non-moving parts that are less likely to burn out than your laptop’s
power cord, any electronic device with resistors or circuitry can more easily fail than
simple insulated wiring. But also bear in mind the excess devices I am not utilizing
which I would be had I the need to split charging voltages between multiple solar charge
controllers or shore power chargers. Far more likely to fail than a simple step-down
converter. (And I do have a spare solar charge controller just in case by the way.) So
the way I consider it, since the only implement on board that doesn’t work with only one
converter is the windlass, I consider that a redundant system already so that if one goes
down the other will likely not be and I can obtain another most likely before they are
both down. Or in a pinch I could swiftly rewire one of my 48v series and turn it into four
12v house batteries, intermittently reversing process for recharge if needed. Thank
goodness for inbuilt battery management systems of Battle Born batteries that manage
voltage balancing like a pro!
On that note, I’ll end by advocating strongly for doing this conversion to a Quiet Torque
engine using Lithium Iron Phosphate batteries, at least until the day that solid state
batteries or the like are mainstream and affordable. They are hands down the most
cost-effective type of battery to get in all scenarios except if you sink your boat, and the
same can be said of an electric motor. So do the right thing by converting and give
yourself the inspiration you need to never sink your boat.