Marine Classics
Marine Classics
Boat Designers
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Fast Electric Boats

(This is a magazine  article written about a particular boat)

Water skiing behind an electric boat, is it possible?

 Well yes if the boat is designed to do it. Electric motors are far more efficient at converting energy to movement than petrol or diesel engines.  The limiting factor in fast electric boats is storing enough energy in the batteries for the weight. Making an electric boat go quickly is not difficult, it is just a design trade off between speed and duration.

 The main purpose of this boat was to water ski, so an adequate water skiing speed of 16 knots (30km/h) was specified, rather than a faster speed, to keep duration reasonable for it’s intended use. The boat gets up on the plane properly from about 11 knots upwards, to skim across the water very well.

electric boat batteries

 A big factor also in favour of the series DC motor and controller is that they are rugged proven technology. Hundreds of thousands are in use world wide in forklifts and other industrial machinery. They are easier to fix or replace if they do go wrong too.

  Running at high speed the motor takes about 400A at 90V, and at slow speeds around 140A at 30V. In normal ski boat use, the motor only gets warm to the touch. However if the boat is run a high speed constantly it starts to get hot, but the motor has forced cooling and plenty of ventilation.

electric boat planing at speed

  The batteries are deep cycle lead acid, which have worked very well. Again higher technology was investigated, particularly lithium batteries. But this route was not followed for reasons of reliability, cost and complications. Also the weight savings were not as big as expected when taken as a percentage of the boat’s total loaded displacement. It was a pleasant surprise to find that the batteries don’t get at all warm at these high discharge rates. The charger can provide a partial charge in a few hours or complete charge overnight, and will run off a blue 16A socket (or a standard 13A socket if required).
 Whilst fast electric boats are very rare in the UK, they are becoming somewhat more popular in Europe. European lakes are starting to ban or restrict the use of engines on their waters due to environmental concerns. Which is creating a demand for these fast electric boats. This is not noticeable in the UK, which has very few lakes, or any other inland water which fast boats can use. The builders, Marine Classics Ltd designed and built this boat for Lake Constance, where it was granted this huge lake’s first ever electric speedboat licence.
 The boat was designed and built by Yorkshire boat builder Marine Classics Ltd, which also did the electric installation. Marine Classics makes a range of mahogany and fibreglass boats and launches, with the aim of combining classic good looks and modern safety and maintenance requirements. As well as building a range of it’s own boats the company designs and builds one off custom boats, and does restoration work.

 The electric installation is quite conventional and simple, although large. It has 120V of lead acid batteries and a series wound DC motor. The motor is a ‘Warp 11’ specially imported from the U. S. These motors are widely used in electric vehicles in the states. An interesting application of this motor is in electric drag racing cars. These substantial 100Kg motors can pull 2000A at 180V for drag race starts, but the 5-minute  ‘conservative’ rating is 66KW.

electric boat motor
  A valid question is why not use a permanent magnet or AC motor, either of which could be about 10% more efficient. A source couldn’t be found for a permanent magnet 66KW motor, and the complication of joining multiple motors together was not wanted. An AC system was quoted at £20,000 more expensive than the DC system, and for just 50KW rather than 66KW. 

 So what is the boat like in use? Well it’s very easy and enjoyable to use. Push the throttle forward and within a few seconds it rises on to the plane, and then on to it’s design speed of 30km/h.  It runs and behaves just like a petrol or diesel powered speedboat without the noise and smell. Because of the low down weight of the batteries, it is very stable and less affected by waves than other boats of a similar size.

electric boat by marine classics

The boat is used for water skiing, so it makes a ski run of several minutes then a period stopped or at slow speed to recover the skier, which also lets the battery and motor recover. Used this way the boat will run for a few hours including 8-12 ski runs before recharging. Used for cruising at low speeds, it will run all day.

electric ski boat

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