Design Transmission System

Well, if you mention that 40 Kw is transmitted to generator, and generator shaft is turning at 1500 rpm, so, you must have a torque of approx. 255 Nm (Power = torque x angular speed, use consistent units).

With this value, please inform what kind of transmission do you need. Do you need to locate the generator aligned with the turbine? Or it's an offset? Or it needs to have an angle? Please specify the location of the generator in respect to the turbine to allow a better choice of materials.

With the type of transmission, check if the generator shaft can be used to support the transmission element, or if you'll need a shaft with a pair of bearings to support a pulley and transmit only the torque to que generator.

Post some more details.

You could use the bottom-end from an outboard motor (many are available in 40 to 100Kw range)... and then put chain drive to the generator on the dry end with sprockets sized appropriately to turn 1000 rpm into 1500 rpm.

Naturally, this supposes that you will provide adequate support for all components.

40 Kw Vertical shaft 4-pole Alternator will not be more than 1 meter high.

Order such that shaft extension is uppermost and the body mounting is at bottom.

If need be, have forced air ventilation from outside blower.

1000 rpm Hydro turbine 's output shaft be extended up to Electric Machine Room with a "Propeller Shaft" (Self Alignning) of a heavy Truck.

Sprocket Teeth Z1:Z2 should be 25:38 Steel.

On the top, connect these 2 shafts with a Duplex 1" ANSI Roller Chain with self-aligning compensator like Renold ROLL-RING.

Above combination will be out of standard productioin line availabilty-hence most inexpensive and long life between replacements.