Storbåt Tacksamheten is a replica of a 19th century cargo vessel powered by an Oceanvolt AX8 electric motor system. It will be used for island excursions and modern-day cargo jobs.
"As the boat takes shape it is time to proceed with the other main components. Zero emission and environmental design aspects are the key elements of this whole project so when it comes to the auxiliary engine we really do not have any other option than electric drive motor.
During my initial research I found several manufacturers and lots of discussion forums and it soon became evident that I would have to choose between AC or DC technology.
AC is a very nice system with a rotor and stator being basically the only parts of the motor and as such the lifetime of the motor is estimated to exceed 50,000 hours.
DC-motor has brushes and the gear ratio is handled through the pulleys connected by a v-belt. The brushes and v-belt have an estimated lifetime of 3,000 hours which sounds very decent when compared against a traditional diesel engine.
The propeller shaft is connected to the motor on both systems so the propeller is always turning no matter if the motor is on or not. In theory you can use this energy to re-charge the system but we decided to choose a self-feathering propeller which will go to a zero angle once the motor is turned off and so the propeller shaft will stop turning.
The cheaper price of the DC-system was the biggest reason for our selection. We decided to go with a domestic, Finnish maker, Oceanvolt.
The "fuel tank" consists of 4 x 12 VDC, 303 Ah AGM-batteries connected in series i.e. the power of the system is 4 x 12 x 303 = 14,5 kWh. With batteries you can only ever use 50% of the capacity. When we took into acocunt the resistance of the boat it indicates that this power-bank will give us 4 hours @ 6 knots of boat speed.
The target is to be able to motor about 20 nautical miles with one charge.
The charging will be handled through solar panels and shore power."
Storbåt Tacksamheten on Helsingin Sanomat, 11.7.2015
Technology used in the Storbåt Tacksamheten:
- Boat waterline length: 12 m
- Boat beam: 4 m
- Draft: 1 m
- Displacement: 7000 kg
- Electric motor system: Oceanvolt AX8 shaft drive electric motor
- Electric motor system nominal power: 8,3kW
- Electric motor system voltage: 48 V
- Electric motor system weight: 28 kg
- Batteries: 4 x 12VDC AGM