The heart of the DSe is her battery array. Composed of 12-volt Enersys AGM-style batteries, the resulting banks have 200 Amp Hours/48v each (20 kW Hours total). We bench tested this array for months - charging - discharging - charging - discharging - over-charging - running down to zero. Our tests conclude that the batteries will provide up to 1,000 discharges. Each battery array is fed by its own Outback MPPT FX60 controller/charger which in turn is fed by a 3 kW section of the solar array. We use the same “bullet-proof” batteries for the 12 vDC system and for diesel starting batteries. The 12v system is charged by DC/DC chargers from the main battery arrays.

To get the maximum amount of current from a solar array, we use state of the art MPPT (Maximum Power Point Tracking) controller/chargers from Outback. These controllers optimize the match between the PV array and the battery bank, getting every watt of available power. Note: All these installations are temporary for the trials ONLY.

For purposes of this sea trial we used the water-cooled Ossa Powerlite 35 HP motors. These gave us the performance figures through our electric-mode speeds and beyond to 9+ knots. Production DSes will be fitted with the Steyr Hybrids and sail drives which will produce similar electric performance at displacement speeds.

Each production DSe will be fitted with the Steyr Serial Hybrid Propulsion System fitted with a ZF saildrive. The Steyr diesel delivers 75 HP. The green “bell-housing” (pictured right) houses a 5 kW flywheel generator/7 kW motor. In diesel mode, the hybrid portion acts as a generator and passes power through to the saildrive. In electric mode, the hybrid portion disengages from the diesel and powers the saildrive directly.

Each Hybrid drive has its own 10 kW hour/48v battery array. This array is charged from shore power (the grid), 3 kW solar array and the 5 kW generator. Away from the dock, all of the DSe’s electrical needs are in turn fed from these battery arrays. In electric mode, the Hybrid 7 kW motor gets it’s power from the batteries which, in turn, are being constantly charged , during daylight, by the solar array.

How We Tested. We made dozens of runs up river (against tide and wind) and down - with sun and without - with rain - with 4 different sets of propellers and 3 different load conditions. We took readings of current in from the solar array, current out to the motors and current at the batteries. All up river runs were immediately followed by down river ones, in the same section of the river to make averaging accurate. The speed shown to right is from Trane’s cell phone (which tended to agree closely to a Garmin handheld). This speed of 7.39 knots would be from one run and averaged later. The ammeter at the bottom is reading the amps being used by one motor (13.43 A) - this is multiplied by the system volts to get the watts being used at any given time.

George Petie, N.A., takes careful notes of all the data generated by the days of water trials. At the end of each day, the data was tallied, averaged, entered into a spreadsheet for analysis. The first graphic representations confirmed that our key goals had been met - the DSe Hybrid will cruise at speeds up to 6 knots in equilibrium - power in from solar equal to power out to the motors!

The curve to right is based on the sum total of all our test runs in January. It shows a speed of 4.6 knots with only 3 kW of power - 1/2 the capacity of the solar array. We achieved 6 knots using 6 kW - the maximum possible from the solar. And, 7 - 1/4 knots at 10 kW. This is a reasonable solar/battery electric mode using energy from both the sun and the battery arrays for silent cruising for a limited time.

CONCLUSIONS & PREDICTIONS BASED ON THE SEA TRIALS.

Based on the sea-trial data from January, our tank-test data from Shanghai and kW/Fuel curves from Steyr, we feel that our current forecasts for the DSe performance should be quite close to final sea trails to be conducted this June.

The sea-trial data ends at 9 knots, but confirms our tank test data for speeds vs. energy consumed for this range of speeds. The three curves at right reflect the combination of the two sets of data and the Steyr data.

1. The DSe will be able to run at solar/battery speeds in electric mode up to 7 1/4 knots (see red curve).

2. In diesel mode, we are predicting speeds up to 13 knots plus.

3. The most efficient “displacement,” diesel-mode speed is 7 -1/4 knots at about 10 NM/Gallon (see green curve).

4. At 10 knots, the DSe will get about 3 NM/Gallon.

5. At 13 knots, she’ll get over 2 NM/Gallon.

6. The Steyr diesel emits the least emissions of any marine diesel in her class. She can also cleanly burn not only diesel, but kerosene, heating oil and of course, Bio-Diesel.

SUMMARY OF SEA TRIALS. If there were CAFE standards for motor yachts, the DSe Hybrid would be at the top of the list! With a potential of infinite range at just under 6 knots and a no-solar range of 1,000 NM on only 120 gallons total (with 10% in reserve) at 7 knots, and 1,350 NM at 6 knots (2,200 NM with only 3 kW solar boost), the DSe sets a new bar in efficiency. Since the Island Pilot DSe Hybrid’s goal is to be the most efficient, most environmentally-friendly motor yacht, we have chosen to outfit her with just enough power to go efficiently at displacement-plus speeds. A monohull trawler this size would be limited to top speeds of 8-1/4 knots using no less than twice the horsepower and twice the fuel per hour and per mile. The slippery hulls let the DSe get up to a top speed 13 knots or more (depending on load) and have an extremely efficient speed of 7-1/4 knots. One other advantage of the Steyr Serial Hybrid Propulsion System: you have 4 motors! Think about it. 3 motors can fail and you still have a way to get home. No other yacht has this amount of redundant “Get-Home” power options.

The wake of the DSe at speeds past 7-1/4 knots (upper photo) - the G T Men River is a bit disturbed indicating a waste of energy. We are advocating cruising the DSe at speeds under 7-1/4 knots, unless of course, you’re in hurry to catch a bridge, get into a safe harbor before sunset or dinner’s on the table! The wake at her “Sweet Spot” of 7 plus knots is minimal (lower photo) - there is NO wasted energy traveling at these speeds or below - perfect for silent, economical, “Green,” long-range cruising!