ShaftPTO generator is a shaft power take off system. Therefore 2 conditions need to be met:
Propeller shaft that rotates when yacht is under sail, and
Appr. 10cm of shaft length available to install the unit
It can not be installed on boats equipped with SailDrives and/or Feathering props.
ShaftPTO installation typically takes about an hour: secure split pulley on the shaft using 2x screws. Position generator over the pulley and secure with 2x screws on each side. Install locking arm with 2x screws. Install current limiter and DC-DC charger on the bulkhead and connect pos+ and neg- to your system.
Installation is detailed in the manual and instruction videos (link to videos)
Typically, ShaftPTO generator "kicks in" at 4 kts and provides full rated output at 6 kts.
ShaftPTO-200 is rated at 18 amps at 12 volts
ShaftPTO-800 is rated at 40 amps at 24 volts
Once rated output is reached it remains steady regardless of shaft RPM.
In relation to the shaft RPM the generator will "kick in" at 180RPM, full rated output starting from 220RPM
ShaftPTO was designed to generate rated output at shaft speeds from 220 - 1500 RPM. It does not matter how fast the shaft rotates because the generator is set for constant amount of power take off. The radial loads and output in watts is the same at 220 and 1500 shaft RPM.
ShaftPTO can run in both forward and reverse, when boat is under engine or under sail.
ShaftPTO-200 dynotest shows that at full rated output radial load is approxamately 2 lb-ft. This load is neglegent compared to what gearbox and cutlass bearings are designed for. Nigel Calder further clarifies on p.435 of Boatowner's Mecnahnical and Electrical Manual: "When a boat is being towed or is under sail with the motor shut down, the flow of water over a fixed-blade propeller will spin the propeller unless the propeller shaft is locked in some way. This is of little concern with manual and two-shaft transmissions, except that it creates unnecessary wear on bearings, oil seals, and the shaft seal".
With only 2lb-ft radial load ShaftPTO generator is just not strong enough to cause any noticable wear to a shaft that's in good working condition.
Please be aware that some older Detroit Diesel gearboxes can be damaged by towing because they rely on engine pumping oil for lubrication as opposite to splash lubricated gearboxes typically found on sailing yachts.
ShaftPTO generator, like any other rotary generator is effectively an electrical break therefore there will be some penalty.
Expect to loose 0.1-0.3 kts of boat speed. ShaftPTO generator can be completely depowered to stop any load on the shaft
ShaftPTO generators are made to last in the harsh marine environment with Zero maintenance.
It will generate energy for thousands of hours until a belt or bearings wear out. We designed the unit to be serviced and rebuilt "in the field" without special tools. Rebuild kits are available on request
This article describes how to add a shaft driven alternator or generator to a sailboat. When the sailboat is sailing, the shaft continues to turn, which in turn rotates the generator shaft. The end result is an efficient, very green method of keeping the batteries charged while sailing
When Joshua Slocum sailed around the world in 1897 he had an oil lamp for light and navigation lights, a wood stove for heat and cooking, and a sextant and wind-up tin clock for navigation. That was it. No GPS. No chartplotter. No autopilot. No fridge. No laptops. No CD player. No LED lights. No Watermaker. So he had no need for electricity.
But we do
Alternator on the prop shtt?
Years ago I saw ads for towable turbines or props that turned an alternator while under sail. I don't see those kinds of ads any more.
But the other day I saw where someone said they had an alternator attached to the prop shaft (didn't say HOW)... so that under sail, the spinning prop generated electricity.
Does anyone here have such an arrangement? Happy with it? Would appreciate all comments!
The other day, sailing nicely at 5kts to Pwllheli, SWMBO remarked that she could hear a whining noise. I said its the prop shaft spinning. Anyway I went below, I was bored! I had a look and although Ive seen threads about this before, I put my hand on the shaft and tried to stop it. I couldnt, I was quite surprised. There is a bit of power being generated there. My prop is a 3 blade 16" by 11" I believe. Question, anybody know how to work out the power being developed by the prop and anybody succeeded in making a prop powered alternator work properly? Stu
We have the option of putting a prop shaft alternator on the new boat. This is totally new idea for us but sounds interesting as it has the potential to let us charge while under sail and power. No running a genset every other day while on passage. Of course we will have solar and wind for other sources. Boreal has not tried one of these prop shaft alternators yet but believe they work very well and they are used in Europe a lot more than the USA. Does anyone here use one and if so do you like it?
Correct. Less drag. It turns an alternator - the pulley ratio is 8-1. At 5 knots under sail it makes 20 amps, at 7 knots it makes 35 amps.
The gearbox is a PRM and the cutlass bearing is still the original fitted over 40 years ago - a great bit of engineering.
Up until 5 knots of boat speed we lose around 1/4knot when charging. Once we are over 5 knots there is no detectable drag from charging
If you’re planning to go long-distance cruising you’ll most likely be looking to fit one or more forms of power generation to avoid running your propulsion engine
2 euro5 15.3/14.4 volt alternators driven by 44.5mm prop shafts. Pulleys mounted to the propeller brake drums.. The alternators need 'feed back' to terminal 2 to give 14.4 V 7k ohms seems to hold it steady.. 'VicProp' tells me I need 24 hp total for 4.8 knots, at 80000 lb, 12 hp each prop. All I want is 15% of one of these HPs returned as battery charge per prop
By adding an alternator to each of the propeller shafts, when sailing, the power generated by the propeller results in roughly 40 Amps of power being generated per side