Fitting a Watt & Sea Hydrogenerator

Auckland’s Andrew Berry has just installed a Watt & Sea POD 600 Hydrogenerator on his 13.5m Elliot pilothouse yacht, Mariana. It’s the first of the units to be fitted in New Zealand.
Supplied by Kiwi Yachting, the POD 600 is a new variant of the Watt & Sea Hydrogenerators – mounted on the hull. More commonly the units are transom-mounted on retractable brackets so that they can be lifted clear of the water when not in use.

The new version is widely-used by race boats – from the Vendee Globe to the Volvo Ocean Race – and the technology has been tested in the most extreme conditions.
I caught up with Andrew to ask what led him to choose the POD 600 for his power generation requirements.
The Yacht
Andrew purchased Mariana in July 2017 with a view to cruising through the Pacific, visiting islands in Tonga, Fiji, Vanuatu and New Caledonia.
Sailing during the 2017-18 summer, he had plenty of time to consider what additional gear he needed for comfortable and safe cruising. The list included a watermaker, bow thruster, new B&G instruments and
an autopilot.
The refrigeration on the yacht is a compressor-driven freezer and fridge, with a 12-volt plate added to the fridge.
Another important consideration was the power generation required to run the yacht’s electrical equipment, and to minimise engine running.
A pair of 100-watt flexible Juice solar panels are fitted to Mariana’s bimini, but these can’t provide for the boat’s requirements.
“This really left us with two options – either wind generator or some form of hydrogenator,” says Andrew. “We discounted the wind generator early on – for two reasons.
“The yacht has a relatively narrow transom as the beam isn’t carried all the way aft, so adding a stainless-steel pole to the stern to carry the wind generator didn’t make sense – and secondly, the noise!
“We shifted our thinking to the hydrogenerator option and pretty quickly came to check out the Watt & Sea technology. There’s a transom-mounted option or the fixed, POD version.
“I didn’t like the transom-mounted version – partly because of the relatively narrow transom, but also the aesthetics – I wanted to keep the exterior of the boat looking clean, as it was designed, rather than start bolting on things willy-nilly.

“We discovered the POD 600 option on the website – I hadn’t seen it in the flesh. I made some enquiries and although the POD’s a relatively new option, the mechanics of it and the way it generates power is exactly the same as in the transom-mounted legs. We cruise comfortably at 6.5 knots plus, and at that speed I could generate 250 watts
or more. Perfect!”
On passage the POD will be running the fridge, electronics and autopilot, and Andrew anticipates that the only time he’ll need the engine is for the freezer.
Installation
The yacht was pulled out of the water at Half Moon Bay to have the new equipment installed. Joe Richardson and his team from The Boatbuilders undertook all exterior work, with electrics done by Simon Jennings from Half Moon Bay Electrical.

The installation instructions recommend mounting the POD 600 slightly off the centreline, away from the keel, to ensure a clean water flow and keep any minor turbulence away from the rudder.
Practical considerations, however, dictated the unit being installed slightly further to port in a space that was clear of the engine, with good access.
Three 10mm diameter holes were drilled for the two mounting bolts and the electrical connection. A backing plate and sealant was all that was required to physically mount the unit.
As the POD 600 is made of aluminium care is required with the type of antifouling used.
“We scraped back the standard antifouling we had put on the boat around the unit and used non-copper antifouling – extending it a reasonable distance around the unit. The unit itself has been covered with Prop Speed,” says Andrew.
The three-core cable from the unit was run to a three-pole relay. The relay goes to the control module, with the other side going to the battery positive and negative. The controller should be mounted vertically so it can be cooled by airflow.
The control unit can also accept solar power – in fact it operates as a full MPPT controller, though the converter prioritises the hydro system ahead of the solar. But on Mariana this option is not used as the solar power goes through a Mastervolt inverter, which is a controller as well.
The battery house bank was increased to 660 amp-hours, using AGM (Absorbent Glass Mat) batteries.
Performance
At the time of writing only one test trip had been undertaken which was mainly to test out all the other new electronic systems on the yacht. As the batteries were full (they’d been connected to shore power) the hydrogenerator was not required.
Performance is detailed in the accompanying speed output graph showing the power in watts produced with different-sized propellers. Mariana is fitted with the 280mm prop, which will produce 200 watts at 6.5 knots.
When the batteries are fully charged the prop freewheels and makes a rumbling sound – and that’s the signal to turn it off, via the isolator switch on the instrument panel.
At 6 knots the estimated drag is 10kg, which for a cruising boat is a small percentage of the total drag.
“If we were a racing yacht we’d have considered a transom-mounted unit. The Vendee Globe boats all had the retractable carbon fibre racing stern option. Which can come up and down like an outboard,” says Andrew.
Maintenance
The manufacturers recommend a maintenance programme for the POD600 at every two years or 10,000 miles. Andrew says this lines up with his expected biannual haul-out for antifouling, so it’s not a significant issue.
In the event of the unit taking a knock, he carries a spare propeller which can be replaced underwater with scuba gear.

The future
Kiwi Yachting marketing manager Tristan Campbell – the supplier of the POD 600 – sees a great future for hydro generators.
“We’ve seen a growth in cruiser numbers in New Zealand, with the bigger boats looking to go offshore for considerable amounts of time. There’s also been an increase in longer-distance, shorthanded races, like the Melbourne Osaka two-handed race and the Round The North Island race.
“Race yachts want to save weight by carrying less diesel. In the last Vendee Globe, almost every Open 60 was equipped with a Watt & Sea because the weight-to-power output equation is so much higher,” says Tristan.
Kiwi Yachting is always on the lookout for clean, green, quality products that use renewable resources and Tristan says the Watt & Sea Hydrogenerators meet this objective.
“We hope to see more boatbuilders recommending it as a low fossil-fuel power generation option.”