How Ya'll Doin'?
The Honey Bun Kid
There are lots of things floating or below the surface that can ruin your day if your propeller comes in contact with. Rope, fishing line, stumps, even soft sand/mud or grass can become entangled in your prop and all of a sudden.... you're going nowhere... fast.
Most outboard and inboard engines use a plastic or rubber insert that will break away or unfasten from the interior hub of the propeller if the prop should hit something hard or become clogged with rope or a lot of weed. This rubber insert protects the rest of the drive train and gears by sacrificing itself and breaking away from the hub. Although this does (usually) keep you from having a totally destroyed lower gear case, it also can leave you essentially motionless in the water. In other words, you put the boat in gear, the motor rev's, but the propeller doesn't spin. The drive shaft is spinning, but the propeller is not. Thus the term "Spun Prop, or Spun Hub". If you're on the water, this is pretty easy to check. Simply put the boat in gear, and if you don't move forward when you give a little throttle, then you're got your answer. Sometimes, you can limp home at idle speed because the rubber insert has enough 'grip' to spin the prop a little, but as soon as you try to increase the rpm's, the hub just can't hang on to the shaft.
You options are to replace the prop or, in some cases, the propeller hub insert, and you're back in business...or call for a tow. If you carry a spare prop on board, then be sure NOT to drop the prop nut and washer as you're changing it out. And check to make sure there's no leftover rope, fishing line, etc. still behind the thrust washer (between the prop and the gear casing).
Sometimes you can 'almost' spin a prop, and this manifests itself like this. You have power and motion at slow speeds, but as soon as you try to get up on plane, the boat noses up, but just won't quite get there. You'll notice your tach is revving up to where it should be, but it's almost like you're dragging something heavy; and you can't get the boat to come on up on plane. You've got a problem and you need to fix this ASAP.
Here's a way to check to see if you've got trouble brewing....on dry land.
Engine OFF. Put your throttle lever in NEUTRAL, and walk around back. Try spinning the propeller. If it spins without a lot of effort, then so far so good. Next (make sure the engine is OFF) and place the throttle lever in the forward position. Walk around back again, and try to spin the prop. It should NOT spin... or at least be very hard. Imagine if you were trying to make your car move by spinning the flywheel by hand. If this is the case, then (theoretically) your prop hub is in good shape. If the prop spins by hand, while in gear, then you need to go ahead and remove it and check your hub insert. Most likely, you've done something to cause it to break loose.
While you're at it, check the splines on your prop shaft, check behind the washer for grit, goo, fishing line, etc. and clean and re-lube. Also check the zinc anodes that are behind the thrust washer and change them out if they look pitted and/or deteriorated.
Props are expensive. Carrying a spare that you hope you'll never need can seem like overkill, but better to have it and not need it... than to risk being offshore with a perfectly good boat that has no propulsion.