I've been the proud owner of a Lagoon 420
Hybrid for the last nine years and have been very happy with the propulsion
system and delighted with the whole boat.
Like all boats its design is a compromise and some elements of the design were very radical. The design delivered class-leading accommodation and liveability, for its size, but sacrificed sailing and motoring performance. The boat is heavy, not just because of the twelve lead acid propulsion
batteries, weighing in at 840 kg (850 lbs), but also because of the wide capacious hulls and the large superstructure.
Even so, the motoring performance at 6.5 knots cruising speed and 7.5 knots maximum in calm seas, is adequate for most occasions, partly because the class-leading accommodation makes it a joy to be aboard.
Originally Posted by SDChristian
It is my understanding that the hybrid system of the Lagoon 420
was essentially a failure due to battery
issues and high gas usage.
I've always been happy with the fuel consumption
, so I'm not sure why you think it is poor. It's possible that some people found it poor because they went at full power all the time, because they were not content with its cruising speed. The genset uses 6.1 l/h at maximum output (17.5 kW) and about 4 l/h at cruising speed. I've always thought that anything less than a liter per nautical mile is OK for such a big boat.
The two electric
motors are nominally rated at 10kW and the Kubota diesel engine
that drives the 17.5 kW generator
is 29HP, but together these push the boat through the water
at a speed that is only about one knot
slower than the 80HP non-hybrid Lagoon
420 hybrids, powered by twin 40HP engines, so it is pretty clear that the hybrid arrangement is more efficient.
It is right that the lead acid batteries are the Achilles heel of the system. This is not just because of the enormous weight, but also because of the complicated control system required to protect the batteries. I'm just waiting for my lead acid batteries to fail, so that I can replace them with LiFePO4
batteries, which will make an enormous difference. It will not only halve the weight of the battery
bank, but it will double the usable capacity and I'll be able to ditch Lagoon's complicated electronic control system. It will also be more efficient, because I will be able to charge them at full power, so I'll no longer have to run a 17.kW generator
at its most inefficient low-loading, just to trickle charge the batteries for the last hour of charging
, to get them fully charged.
I'm not convinced about the viability of solar
power to propel the boat. It's fine for re-charging the batteries and keeping up with normal loads, but not for the heavy propulsion loads, unless you are motoring on very short trips.
Some people have installed folding props to reduce the drag when sailing, but this has three drawbacks that I've been unwilling to accept. First, you would lose the ability to generate serious amounts of power under sail, which is very satisfying to recharge the batteries for free. Second, I use the prop drag under ReGen to slow the boat down, when we are going a little too fast for comfort. Third, you lose some manoeuvrability under power as you can't go straight from forward into reverse and get instant thrust. One of the real joys of the hybrid is it's outstanding manoeuvrability under power, owing to the instant torque. Note: the other great joys of the hybrid are: the silence of the whole propulsion system, the low maintenance
, the side-effect of abundant AC and DC electrical
power for other purposes (cooking, cooling
, water-making etc. etc.).
The sailing performance of the 420 hybrid is relatively poor in light winds, owing to its heavy displacement
and conservative sail plan, which give it a low SA/D ratio. On the other hand, its performance in stiff winds is great. Last year, I sail a thousand miles from Portugal
in constant winds of 20 to 30 knots and there is no boat I would rather have been on in those conditions.