Reduction gears for yacht Electric Motor

So we have the main components for the reduction gears for our electric motor. Note that in the picture the items are laid out on their side, in reality the electric motor will be above the reduction box shaft.

On the left is a sheet of paper representing the electric motor (An HPEVS AC-34 ) out of the top comes it’s 1.1/8″ drive shaft.

Connected to the motor drive shaft is a 2012-1.1/8 Taper Bush (Dunlop) which is used to attach a 56-8M-30 Taperlock Timing Pulley The Taper bush has key (a length of square section metal that connects slots in the motor drive shaft and in the taper bush to keep them locked together when the motor spins).

This 56 tooth pulley is connected to a 80 tooth pulley by a 30mm wide timing belt with 8mm pitch teeth.

The ratio from the 56 tooth to the 80 tooth pulleys is chosen so that the motor can be set to spin the propeller at it’s designed maximum of 1400 rpm.

The 80-8M-30 Taperlock Timing Pulley is connected to a 1.1/4″ stainless sheet reduction box shaft via a 2517-1.1/4 Taper Bush (Dunlop) which again will be prevented from rotating with a key connected a slot (to be cut) in the shaft to the slot in the Taper Bush.

On the reduction box shaft there are two stainless steel thrust bearings. One of these will be bolted to each end of the motor frame. They will be facing in opposite directions to absorb the thrust from the propeller in both forward and reverse directions.

The ends of the motor frame are each made of 2 sheets of 3mm stainless steel sheet. These sheet frame ends will be bolted directly to the two ends of the motor and to these bearings. We have lengths of stainless steel right angle and flat bar to hold this frame together rigidly and attach it to the engine mounts (one we buy them). The motor will be bolted to slots in the frame so that the belt tension can be adjusted by raising or lowering the motor in the frame.

At the bottom of the picture we will connect the reduction box shaft to the existing 1.1/4″ propeller shaft. A Clamp on Coupling on the reduction box shaft will be bolted to flexible coupling on the propeller shaft. This means we don’t need to achieve perfect alignment of the reduction gear shaft and the propeller shaft. It also helps reduce vibration as the motor can be attached to more flexible mountings.

To keep the electric motor in as dry and salt free environment as possible the original stuffing box (that creates a waterproof seal around the propeller shaft as it exits the boat) will be replaced by a modern dripless model. While very reliable the original stuff box isn’t maintenance free and always drips a little salt water into the boat. We are looking at the Manecraft Deep Sea Seal at the moment (we are trying to avoid products that require a pressured water supply to the seal as we won’t have engine cooling water to connect to it). These dripless seals also cope better with vibration and movement in the shaft without causing wear in the bearings.

As the propeller shaft goes out of the boat in runs in a cutlass bearing. These wear out and ours needs replacing. Until we can get the existing one out I’m not sure of the dimensions we need.

The propeller needs a clean but otherwise is in good condition so we won’t be replacing it. The three bladed design creates more drag when sailing than either two bladed or folding designs. However, it is more efficient when using the motor and should also be better at regen (charging the batteries by turning when sailing and using the electric motor as a generator).

Once the motor arrives with it’s controller we can get the details of the frame sorted and start on all the connections to power and control the motor.

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