Electric Propulsion - Our First 2,500 Miles

Every decision starts somewhere: You hear about a new system idea, read an article,

talk with others about options, do research - but it is often hard to say where the specific

start of the process begins.

For us, the idea for implementing electric propulsion started when we read an article in

Sail Magazine by Nigel Calder. The idea was intriguing but we did not realize how

deep it would take us when we first thought about it. We talked with friends about a

conversion to electric propulsion from diesel on a bluewater cruising sailboat. Many

thought it was crazy. Others, like us, were intrigued and even urged us to proceed.

our boat we found out that we would be having a child. Our new expanded family

changed everything for us but we still wanted to be near the water. It took us three

more years to finally make the plunge into electric propulsion.

In some ways it is easy to put facts on paper and say “this is how much it costs”; “this is

how the motor works”; “this is much quieter than diesel.” To provide the most useful

information we wanted to wait until we had really used the system in a variety of

conditions over a longer period of time. With this in mind, we have been cruising for 9

months - 2,500 nm of off-shore and coastal cruising along the East Coast of the US, the

Bahamas, and in the Gulf of Mexico.

This is an account of how and why we did it, the choices we made, the costs, and our

Table of Contents

................................................Why Electric Propulsion! 10

..........................................................................Savings During Our First Year! 16

............................................................................................................Our Cons! 17

.............................................................................................................Our Pros! 18

Electric Propulsion - The Conversion

1. Remove existing propulsion diesel engine

2. Clean and prepare boat for the new system

3. Install new electric propulsion system

We have included photos to illustrate the steps and narrative to give some detail to the

process.

Remove Existing Propulsion Diesel Engine

Our sailboat had an existing Yanmar 4JHTE diesel engine that is rated for 55 H.P. and it

had approximately 5,500 hours of runtime. This number is approximate because the

hour gauge was replaced by a previous owner of the boat. The engine ran well enough

when supplied with clean fuel. It could push the boat at over 6 knots while burning an

average of 1.25 gallons of diesel an hour (based on personally collected data).

Once the engine was removed, the cleaning process began. The first phase of the

clean-up was the removal of old wiring and hoses (fuel, exhaust, and air venting) but the

real work was getting rid of 20 years of oil, grease, and rust buildup. The sound

proofing material was saturated with diesel and oil odors that could be smelled

throughout the boat but most prominently in the aft cabin.

After removing the bulk of the material and scraping the bilge and bulkheads with paint

scrapers and drill-driven wire brushes, we cleaned the compartment with degreasers

and a high-pressure washdown. There was a considerable amount of over-spray but it

An installation process will vary based on the motor selected but it is a fair assumption

that the motor will weigh less than the diesel that it replaces. However, adding in the

weight of the batteries the overall weight will be similar the diesel but in smaller, more

manageable parts. Our Thoosa motor was light enough to carry it up a ladder onto the

boat while in the boatyard.

We selected the ASMO Marine Thoosa 12000 and six Northstar AGM batteries to

provide the 72v DC needed to drive the motor. The Thoosa motor and the Northstar

batteries have the following characteristics and was close to a 1:1 match of weight

compared to our old diesel.

Thoosa 12000

•

12 kW motor

•

Total system weight (per ASMO) is 44 kg / approx. 96 lbs

Northstar AGM batteries

One of the biggest challenges during the installation was that the new motor dimensions

were so much smaller than the old diesel. The old engine struts were too far apart to

hold the new motor. The struts are u-shaped steel that is through-bolted through

fiberglassed stringers. To adjust for the width, we had additional steel (2 inches per

side, total of 4 inches) welded onto the old struts to narrow the separation between

them.

New Wider Struts with Motor Suspended Above for Initial Measurements

In addition to the narrower motor supports, the vertical length of the new motor was

smaller. To adjust for height and allowing for motor shaft and propeller shaft alignment,

we used motor mounts rated for much more weight than was required but allowed for

greater flexibility in the height adjustment of the motor. The motor mounts we selected

was also laid up with several layers of fiberglass to support the weight of the batteries.

the batteries.

We built a plywood panel on top of the batteries as a mounting surface for the

contactors and wiring used to connect the six batteries into a single 72v DC battery

bank needed for the motor.

New Motor Mounts, Battery Platform, and Unfinished Wire Platform

After mounting the motor and batteries, the next steps were to attach the batteries and

the different motor components: motor controller, key, throttle, and battery monitor.

At the helm, we installed the on/off key, the throttle, and battery monitor. In the electric

propulsion world, the battery monitor is now the “fuel gauge” and the power output

guide. The AMPS OUT view provides an indication of the effort from the motor which is

similar to the RPM gauge for the old diesel. The AMP HOUR view indicates the “fuel”

remaining in the batteries.

At the Helm - Key and Throttle (left) and Battery Monitor and Auto-pilot Controls (right)

In the motor compartment, the remaining components are readily accessible despite the

batteries occupying much of the space. In addition to the motor, motor controller, and

We chose to introduce some additional complexity to the battery configuration. The

motor requires 72v DC. Six batteries in series would have been the easiest

configuration but we have a 4 year-old child onboard and want to reduce the potential

shock voltage when the motor is not in use. Therefore, our design allows for three

banks of 24v DC each. These three banks are then combined or separated as

The Motor Compartment

(clockwise) Batteries & Wire Platform, Battery Chargers, Motor Controller, and Motor

Note on labor costs: we did not include the cost for our labor but we did spend most

weekends and an occasional day during the week working on the conversion over the

course of a year. We hired out a few items to ensure we leveraged experts as

necessary. For example, our battery wiring design, with the contactors, shore power,

We have had a great break-in period, using the boat in almost all conditions:

Our Cons

•

In addition, depending on the speed we are trying to make, we might use the power

when pulling into a marina this is not an issue.

•

Slower motoring in a sea.

frustrating when we remember how the diesel continuously pushed better through a

sea. It is important to note that the electric propulsion pushes well through a sea but

Our Pros

There are many advantages to electric propulsion. For us:

Authors’ Biography

Atlantic East Coast, Bahamas and the Gulf of Mexico.

They are members of the Ocean Cruising Club (OCC) having crossed the North Atlantic

in 2001 aboard their CSY 37. They cruised the Mediterranean as far East as Italy and

Counting their current cruise, they have cruised or lived aboard for over six years on

three different boats.

Test Data 2 - New Electric Motor with Same Propeller

s/v Marama! ! ! October 22, 2011

Test data for new motor

Test Data 3 - New Electric Motor with New Prop and Gearing

s/v Marama! ! ! July 1, 2012

Test data for new prop - Diameter 18” (Fixed 3 Blade) with 13 pitch and cup