New Parallel Hybrid System

Readers of this forum might be interested to know of a new retro fittable Hybrid system that has been developed and is just going to market in the UK. Designed to be a cost effective and versatile Hybrid solution the system addresses many of the critisms often levelled at Hybrid systems as applied to boats.

The system itself has been developed and tested over five years by a company called Hybrid Marine www.hybrid-marine.co.uk.

In simple terms Hybrid Marine's parallel Hybrid follows the model of the Toyota Prius car in that as well as providing electric drive for slow to medium speed the combustion engine is retained to drive at higher speeds. This is the same as the Toyota where the car drives around town at slow speeds under electrical power but on the open freeway uses the combustion engine. Key advantages in using this approach in a boat include those of cost and weight. To try and match top end high speed hull loads to an electric system simply does not work, the size of the motor(s) required are cost prohibitive and heavy. It is far better and actually more efficient to allow a combustion engine to meet the high speed requirements. However for the low to medium speed requirements in average conditions relatively small lightweight and cheap electric motors can do the job very nicely. For example in calm waters a 17 ton Malo 46 needs in excess of 50hp to achieve hull speed of 8.5 kts BUT will achieve an acceptable 6kts quite easily with a 12hp electric drive.

Sports Fishing boats suit the parallel hybrid concept whereby they can use the powerful diesels engines to get out to the fishing grounds quickly and can then switch to quiet clean electric drive whilst trolling at slower speeds.

Other key advantages of the parallel approach is that of efficiency, as soon as the diesel engine is switched on the 10kW electric motor becomes a 5kW generator able to recharge the batteries quickly and efficently but also of course able to support on board domestic services including air conditioning through an inverter. The additional generating load on the shaft when the boat is using diesel propulsion assists in "forcing" the engine to operate at a higher point in its efficiency curve - a win win situation.

The parallel system also offers redundancy in that if the combustion engine (or its fuel) fails then the electric drive will get you home and visa versa.

In a sailboat the system can also regenerate up to about 1kW of electricity under sail - very useful in offshore passages - this will introduce some drag (about 1kt at 1kW) but in Hybrid Marine's system you can cleverly tweak how much power you regenerate v how much drag you wish to accept or you can simply turn it off.

At about $8,000 (not dissimilar to the cost of a generator) the system can be retrofitted to any engine on any boat and would seem to be a good solution particularly if you are considering buying a heavy bulky and expensive generator!