20hp spun prop or one way clutch

[tink65]

I have a 79-80 mercury tiller I just bought. When I changed the lower unit lube I noticed the prop will spin when its in forward gear (only in one direction) and makes a clicking sound Prop does not spin in reverse. Do these lower units have a oneway clutch? It does release in the right direction to let the motor over rev if the prop suddenly stops...
I only ask because, come to find out, its a 17inch shaft on a 20inch transom, and last night (first time with new boat on water) I had issues with over revving, but I could clearly see the prop was aerating. Someone else had suggested a spun prop, and I want a second opinion

 

[GA_Boater]

Yes, the forward gear has a dog clutch and works exactly as you described.

Spun prop? Possible, but your motor is too short for the transom. The prop is too high in the water by about 5 inches. I'll guess you have a short shaft or 15" motor.

 

[tink65]

Thanks for confirming that. With my 280lb fishing buddy sitting beside me in the back, we could open up the throttle but the bow was so high i couldnt see where i was going i know the motor is too short, i didnt think the 3inches would make such an impact. just one more way i got rolled on this boat project