BOAT REVIEW Herley 3400 Electric Power Catamaran

November 2020 Launch Reviews
Words by Norman Holtzhausen. Photography by Norman Holtzhausen and Supplied.
Build Quality
MODEL Herley 3400 Electric Power Catamaran
BUILDER Herley Boats
CONSTRUCTION 5083 marine grade aluminium
LOA 10.4M
ENGINE 2 x 100kW peak electric motors, 120kW diesel generator
Maximum Speed 21 knots
Cruise Speed 14 knots
ACCOMMODATION two double cabins
  • Silent running
  • High quality fit-out
  • Latest electric tech
  • 2400nm range at 8 knots
  • Operation leaves minimal carbon footprint

The hottest topic in boating today is electric propulsion, and right now the Herley 3400 is perhaps the most luxurious yet practical electric boat in New Zealand. We had to travel to Tauranga to take her for a spin – it was definitely worth the journey.

This boat has been a long time coming – the culmination of almost four years incubation by Tauranga-based Herley Boats. Herley’s built a solid reputation with its premium range of custom aluminium boats, all featuring the trademark plumb bow and massive internal volume.
It also has a couple of powercats under its belt, with a smaller model launched last year to trial some of the electric technology, and a much larger 5900 model on the drawing board. But it’s their Roger Hill-designed 3400 model (34 foot or 10.4m) that’s hit the sweet spot of luxury, comfort and practicality.


The key feature of this boat is the fully electric drive. Twin 100kW motors (peak output 60kW continuous rating) push this super-efficient hull to a top speed of a shade over 20 knots. The onboard battery bank allows her to run for a couple of hours at a more modest cruising speed.
Top speed is not everything, and the ability to slip out of a marina berth completely silently is almost unreal. Since the motors can run literally from 1rpm (!) she is far, far, easier to manoeuvre at slow speed around a marina than most fossil-fuel boats which typically idle at just under 1,000rpm.

And she has another trick up her sleeve. Because boating should not have limits, the range extender system includes a 120kW diesel permanent-magnet generator, which gives her an estimated cruising range up to an astonishing 2,500 nautical miles at 8 knots.
That from a relatively modest diesel fuel tank (640 litres). Performance figures so far indicate she can run continuously at 14 knots using just 0.73 litres of diesel per nautical mile, or at 9 knots using 0.5 litres.
As this boat was a spec build she has the smallest possible battery bank size – this could easily be doubled or even tripled. Nevertheless, she can tick along for up to 36 nautical miles on battery alone, or somewhat less at faster speeds.
‘Sport Mode’ lets her run on batteries and generator and gives her maximum speed. So this boat offers just about the best of everything – a good top speed for her size, a fantastic total range when required, and silent running when you prefer to be emission-free.

Naturally the cabin roof is covered with 14 high-efficiency solar panels, providing self-charging capacity to power the extensive list of on-board accessories. These include fridge, freezer, hot and cold fresh water, large-screen TV, stereo, navigation electronics and, of course, inset LED lights everywhere including below the waterline.
But more on the motors and performance a bit later. First and foremost, this is a stunningly elegant boat. According to Nick Herd, Herley’s project manager, “we wanted to create a boat that would turn heads, not just attract attention because of the technology.”

The 10.4m vessel (4.7m beam) stands out, with its grey sedan-style hull, smoky grey glass windows and contrasting tan-coloured decking and upholstery in the cockpit. The catamaran configuration provides space for two double cabins in the forward area, each with a generous size double bed.
A toilet on the port side and separate shower to starboard provide facilities for extended cruising. The saloon area is beautifully finished in matching tan leather-look vinyl trim, and the walnut cabinetry and pure-white headliner is very stylish.

The galley is compact and efficient, with a sink, fridge and cooker unit with a double hob and oven. Hob and oven are a Wallas diesel combo unit, so neither petrol nor LPG are carried on the boat – it runs on the same diesel that provides for the extended range. The windows on either side of the saloon feature a unique (and very elegant) cut-out sliding section. “Why go for boring rectangular?” asks Herd, and it’s hard to disagree.
Opposite the galley is a triangular dining table and L-shaped couch that faces the wide-opening rear saloon doors. And it is out through those doors that most time will be spent. An island console in the large cockpit provides a bait-board, live-bait well with tuna tubes, sink, rubbish bin, storage lockers and saltwater washdown hose.

The floor’s covered in SeaDek for a comfortable barefoot experience and easy cleaning. The boarding platform is the full width of the boat, with the running gear tucked well out of the way of both swimmers and fishing gear.
Up alongside the beautifully faired and gunmetal-grey cabin sides is a wide walkway, also finished with SeaDek. Generous grab-rails make it easy to walk up outside the cabin to the wide foredeck, where a large drum winch and stainless anchor take care of keeping her at station. The standard of finish, from the elegant paintwork on the outside to the fine stitching on the interior squabs, shows the fine attention to detail that’s been the ethos of this boat.
Which brings us back to the helm station, just slightly to starboard of the centre line in the main cabin. The plush, two-person helm seat would be comfortable for even extended steering sessions and, when not it use it folds down to provide easy walkthrough access to the starboard cabin and shower.

Given the technology ‘under the hood’, the helm display looks surprisingly simple. The helm’s connected hydraulically to conventional rudders in each hull. And there’s a unified twin-throttle control that wouldn’t look out of place in an episode of Star Trek.
The only other controls are a switch for the anchor winch and controls for the stereo. Everything else is elegant electronics, either controlled by the three black-glass touch screens or an array of backlit C-Zone electronic touch buttons.

The propulsion system’s supplied by Electric Boats ( This includes the motors,controllers, helm display and controls, batteries and battery management system. The control and management system is available to other boatbuilders and is scalable – so it can be put into larger boats and configured to operate in other modes such as electric only, as well as connect to other systems.
Helm controls are also simple to use. The left and right screens are conventional Garmin MFDs, user-configurable to show the skipper’s sonar and chart preferences. The middle screen houses the ‘smarts’ of the management systems, and the controls for the two electric motors.

Lots of effort has gone into developing the software and system to control this technology, and the result is an elegant, simple interface that even the most ‘analogue’ boatie should be able to understand.
In essence, everything is fly-by-wire. The high-tech throttle controls merely control the computer that manages the propulsion system. There’s a good safety reason for this: providing over 300nm of torque each, a foolish skipper slamming the engines from fast forward straight into reverse would literally snap the drive shafts and likely tear the motors from their bearers.

With great power comes great responsibility, and so the team at Electric Boats has developed a foolproof control system. One steering wheel and one twin-throttle control is all you need.
So, to test the system we attempted the above-mentioned foolish action, going from three-quarter forward throttle straight back into reverse. The computer throttled down the motors safely, switching them seamlessly into reverse as soon as it was safe to do so. Which was quick – make no mistake – but without causing any excess strain or damage.
Which also brings me back to the low-speed manoeuvring of this boat. Most conventional engines have a minimum speed of 2 to 3 knots, thanks to the engines turning over at around 800 or 900rpm at idle.
When the prop isn’t spinning a boat has little steerage, and yet when it is spinning the vessel is often moving too fast for safety in a marina. This means hard work when bringing a boat into the wharf, cycling the engines in and out of gear, trying to hold steerage without hitting the wharf. Add a strong tide or lots of windage and you could end up with colourful language and scratched paintwork.

So it was a thing of beauty to feel the big cat being turned into the very tight marina berth at just over a knot of speed, with full steerage and control despite a fair current flowing through the marina. We came straight in first time, under full control and completely silently. The wide beam helps of course – with the props so far apart the boat easily spins on her axis. But having full steerage at minimal speed is an unfamiliar sensation – what a pleasure!
Back at the marina I dug ‘under the hood’ to check out the propulsion system. It’s amazing how tiny (and clean!) the motors actually are. Driving through a planetary 2.84:1 gearbox, they turn shafts and conventional bronze propellers through fairly standard drive hardware.
The motors themselves are cooled by a closed-circuit, glycol-based coolant that is itself kept cool through a salt-water heat exchanger. The noisiest thing on our trial run was a slight squeak from a carbon-brush earthing wiper on the steel shaft, which in time will silence itself as the surfaces conform.

Even the rush of water past the hull was no more than a gurgle, thanks to the super-slippery hull design. These motors are essentially maintenance-free, and apart from checking seals and descaling the heat exchanger annually, there is little to worry about.
Hidden in the starboard hull is the 600kg of batteries, and as mentioned additional capacity is possible. In the same space on the port side is the diesel generator. The 640-litre fuel capacity is split evenly in tanks port and starboard. We didn’t need to start up the generator, but as it doesn’t need to transfer any thrust to the hull itself, it can be completely isolated from sound and vibration.
This is a simply stunning boat, probably the first of many from Herley Boats. Despite the leading-edge propulsion this boat gives away nothing in size or luxury. The builder has also gone to considerable effort to get this boat into MSA survey, not a trivial task given the new technology involved. A purchaser could put the boat into charter work almost immediately.

Would I buy one of these? In a heartbeat, although this boat is spec’d up for the luxury end of the market and so the $1.25m price tag is just a tad out of my reach. But this is a big boat built to a very high standard, and even with conventional power options its price wouldn’t be too dissimilar.
But for the environmentally conscious who like to have a day out of the water without generating a significant carbon footprint, this is the boat for you. Unlike the other low-emission option (a sailboat), you are not limited by the vagaries of wind and weather, and you can have a luxurious day out without leaving an oil slick behind you. This is undoubtedly the way of the future.


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