Multihull of the year

Electric propulsion when blue-water cruising - for or against?

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I am for…

By Gilles Reigner Managing Director of the builder Catathai

I am a technician, I like technical challenges! Prizewinner in 2003 from the research ministry (creation of innovative technology companies), I created, several years later, a company which manufactured ultra-flat, low consumption sound systems working by propagation of vibrations coming from ceramics; already structural dynamics, electronics and electricity! I appreciate peace and quiet, and the smells of the sea. Which means that the noise and vibrations coming from the diesel engines in our multihulls, as well as their pollution, put me off. It’s with this aim in mind that we validated the electric option for our new comfortable and seaworthy Catathai 50. Above and beyond comfort, the criteria of reliability, safety and easy maintenance are essential for long-term cruising boats. While solutions with higher voltages exist, the choice of 48V dc nowadays seems to me to be the most relevant: this choice of a very low voltage, under 50V, is safer. The assembly and use of classic parts (Victron, Fisher-Panda…), available all over the world, limits the worry of a breakdown, avoiding the doubling of the battery bank. In hot countries, such as Thailand, the life of traditional batteries doesn’t exceed 2 years, and diesel supply is problematic (few marinas, and very poor quality fuel). Electric generation overcomes these difficulties, and the presence of a 13 kW generator reassures and reinforces the charge from the solar panels in the case of prolonged use of the motors over several days. As for the battery life, the choice of so-called lithium accumulators (actually lithium iron magnesium phosphate, LiFeMgPo nowadays) proves to be relevant for several reasons: more than 4,000 charging cycles at 80% discharge (more than 10x the life span of a gel battery), a 50% weight reduction for an equivalent capacity (a 140 Ah weighs less than 20 kg), deep discharge possible, no maintenance, performance more or less equivalent from 10 to 45° Celsius. There remains one unresolved problem: that of recycling lithium! The decrease in the diesel tank capacity is justified by the two other recharging possibilities for the battery bank: solar and hydro-generation by the electric motors when sailing. For the classic propshaft version of this boat, the weight comparison is as follows:

type

engines

batteries

generator

tanks

controllers/inverters

diesel

2 x 33 hp = 332 kg

2 x 140 Ah + 2 x 70 Ah = 108 kg

5 kW 220ac = 165 kg

2 x 300 l = 504 kg

25 kg

electric

2 x 12 kW = 130 kg

10 x 140 Ah Li = 214 kg

13 kW 48 Vdc = 226 kg

2 x 200 l = 336 kg

50 kg

For equivalent functionality and range, a correctly-sized electric system weighs 200kg less than a diesel system; this allows the Li battery bank to be increased, and thus the range, but increases the cost! As for the solar panels, the latest ...

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