The hydraulics selected are all from Wesmar www.wesmar.com although it was a close call as there are a few capable companies that can supply the solution. In the end it came down to a decision between two companies that had been used extensively on Selene's; Wesmar and Keypower, with Wesmar being selected.
As I knew very little about hydraulic systems when I started this exercise, the only criteria I had was that I wanted only one supplier for the various hydraulic sub systems and I wanted the system fully factory fitted.
The system will consist of the following Wesmar hydraulic sub systems:
- RS900 stabilzers with the new digial controller
- V2-12 25HP bow and stern thrusters with proportional controls
- Auxilliary Propulsion Unit (APU)
- Separate 220A alternator with regulator and hydraulic motor
- Maxwell HWC3500 windlass with hydraulic drive
These systems operate from a central hydraulic reservoir, which has an integrated hydraulic oil cooler, sized to meet the requirements of the system, together with flow, pressure and temperature meters. On Buena Vista, we selected the 30 gallon reservoir rather than the 18 gallon one as the 30 gallon unit allows increased flows when used with both hydraulic pumps running (engine & generator - more on this later).
There are two hydraulic pumps, one mounted to the PTO (Power Take Off) on the Twin Disc Transmission and the other mounted to the PTO of the 26kW Northern Lights Generator. These pumps are Load Sensing allowing variable speed based on load conditions.
Primarily the transmission mounted pump is used for the stabilzers, thrusters, windlass and alternator, while the generator pump is used for the APU (Auxilliary Propulsion Unit) or "Get Home" drive and the hydraulic alternator when at anchor. However, if presented with particularly difficult conditions like docking in a very strong cross wind, both these pumps can be used together to provide maximum power to both Bow & Stern thrusters at the same time. However, beware of doing this with the 18 gallon reservoir as it will quickly overheat and could cause some catastrophic damage.
To understand this concept a bit better, it is necessary to understand the flow requirements of the systems and also the output of the pumps.
Let us start with the pumps. The transmission PTO generally used on pleasure craft has an SAE C face, which limits you to a SEA C face hydraulic pump. As I am also having the Wesmar APU, I am restricted to a 110cc unit due to space limitations. This pump provides 26hp @ 207 bar and a flow rate of 18gpm. The largest SEA C face pump is only 131cc , so not much larger capacity and only 4hp extra.
Now given that the thrusters I am using are V2-12 units, which are 25hp that require a flow rate of 15gpm each at full power, it can be seen that the hydraulic system can only fully power one of the thrusters at a time, or if used in combination they can share 26hp between them. This is usually not a problem as the 12" dual counter rotating propeller units have plenty of thrust and generally there is rarely any need for full power on the stern thruster.
However, just in case, the second hydraulic pump can also be brought on line by starting the generator, providing sufficient power to use both thrusters at full power at the same time and being hydraulic they can do this virtually indefinitely. It's a 'belts & braces' approach but I can't help thinking about being woken at 2am with a storm front blowing me on to a lee shore with anchor dragging. Under these circumstances you need all the help and power you can get!!
Full power flow requirements of the various sub systems are:
Active Fin Stabilizers 10 gals / min at 900psi (62 bar)
Bow Thruster 14 gals / min at 3000psi (207 bar)
Stern Thruster 14 gals / min at 3000psi (207 bar)
Alternator 15 gals / min at 3000psi (207 bar)
APU Get Home 16 gals / min at 3000psi (207 bar)
APU Cylinders 0.5 gpm/ min at 500 psi (35 bar)
Windlass 10 gals / min at 1900psi (131 bar)