Underway off the coast of Okinawa, Japan
There are many electric powered boats afloat today. Among them is the sailing vessel, Intrepid. S/V Intrepid is a unique boat. This Bristol 32 sloop, built in 1967 was the third of about 300 Bristol 32s that were designed by Ted Hood and Dieter Empacher for Bristol Yachts in Rhode Island from the mid 1960s to the early 1980s. The Bristol 32 was designed as a modest production coastal cruiser, based on the old CCA racing rules design which featured exceptionally long overhangs, giving the boat a classic look. Bristol 32 number 3 was also the only Bristol 32 that was built with a fin keel, instead of a full keel or full keel and centerboard design, like the others.

The only Bristol 32 with a fin keel and skeg rudder
S/V Intrepid was already unique but in 2009 Greg Martin decided to modernize this classic with a new auxiliary propulsion system. After removing the Yanmar 3GM30 diesel engine, the old engine was replaced with an Asmo Marine Thoosa 9000 electric propulsion system, powered by a 48 volt battery bank. The conversion project was done by the owner (an inexperienced amateur) in about 9 months, working part time and for the total expense of just over the resale value of the diesel engine.

Auxiliary electric propulsion system
The new electric auxiliary propulsion system uses a 9 kilowatt Lynch motor on a stainless steel mounting frame, which sits on the same motor mounts as the previous diesel engine. The propeller and shaft are also the same as with the previous diesel engine. The system consists of the motor, a motor controller box, a throttle control unit, a Xantrex Link 10 battery monitor and of course the batteries. The batteries that were chosen for this system were the best and cheapest that could be found in Japan at the time. They are lead-acid/ wet cell deep cycle forklift batteries. In Japan, the ratings for batteries are different than in the U.S. and elsewhere, but these Panasonic EB-160 batteries are the equivalent of 200 Amp-hr (C/20 rate) batteries that would be used for this application elsewhere.

Improved cabin and navigation desk
Converting Intrepid to run on electric involved a major change in many aspects of the sailing experience. First, the removal of the diesel engine made the boat smell better. The USCG mandated oil placards were removed, since fuel and oil is no longer kept on board and the crew was now able to notice other smells, like mildew... which is easier to clean! The other big change was the change in the use of space on the boat. With the engine removed, the electric motor takes up much less space. The batteries now sit on the engine mount, which keeps the trim of the boat about the same but the battery box also makes a nice support for a teak ladder that was made in place of the engine compartment steps. In order to make room for the battery box, the old 1960s- style ice box had to be removed, which allowed for a small navigation station to be built in the corner. Also, in place of the fuel tank, an equal sized fresh water tank was installed, which doubled the fresh water capacity.

Under sail
The removal of the engine and all of the associated systems actually made the boat a lot more simple. Now instead of an engine, with associated fuel, oil, coolant and 12 volt electrical systems, Intrepid just has one big 48 volt electrical system, with a simple 48 volt DC- 12 volt DC converter to power house loads. The 12 volt distribution is handled with a simple panel and master breaker switch that isolates the house loads from the DC-DC converter. This takes the place of the battery selector and isolation switches in the conventional combustion engine system arrangement. Gone are the days of having to remember to isolate the starter battery or switch between different house batteries. When designing this system, it seemed that there was very little information and authoritative guidance available on how to reconfigure the overall electrical system when installing the electrical propulsion system. However, this amateur, jury- rigged design seems to be working perfectly so far. When the batteries aren't being used to run the motor, this giant house battery bank can also power any appliance you would ever want on a 32 ft boat. Once a new 48 volt inverter is added to the system, it will be interesting to see what other amazing improvements this new electrical system allows.

Raising the mainsail in the Kerama islands
Since the electric conversion project was completed, s/v Intrepid has been back in service as an American Sailing Association (ASA) sail training vessel, taking sailing students on regular trips to the islands around Okinawa. Within limitations, the electric propulsion system has performed very well. The crew that embarks on these trips in open ocean conditions are always aware that s/v Intrepid is primarily a sailing vessel.

Intrepid crew
The electric propulsion system has been totally reliable and works wonderfully for getting the boat in and out of the marina and maneuvering around the dock. The system can even drive the boat through occasional lulls in the wind on the open sea and can help generate apparent wind when there is no wind at all. With the system always on while sailing, if the crew accidentally tacks the electric motor is immediately available to help save the boat's momentum. One thing the electric motor system can not do however, is propel the boat great distances when the crew is too lazy to raise the sails. The crew of s/v Intrepid therefore, never fails to learn the importance of optimal sailing performance and always gains a full appreciation of the sailing abilities of a well designed sailing vessel.