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What to do if your boat outboard motor propeller stops going round, even if the engine is running:


Here's some helpful advice which might help to get you out of a tricky situation if you get stuck in a boat with a "propeller not going round" problem. If you're chugging along in a boat with an outboard motor it's best if the propeller keeps going round, but it has been known for something to go wrong and the propeller get fouled up on some floating rope, or other common hazards to navigation, such as submerged supermarket trolleys, bicycles, or the surprisingly "not as deep as expected" bottom of the water in the river, canal, or other reasonably presumed navigable waterway.

The symptom I'm on about is where the engine is still running and will rev up aplenty but still the propeller doesn't go round. This mysterious problem is usually curable, and I'll explain how.

First though, if the problem is different, and the propeller has stopped because the engine has stopped, it's a different problem. Advice about general purpose engine mending is available by a search, but I'd try checking the spark plug and electric points first! Unless it's a diesel in which case you check the preheaters first. (Maybe I should write some more pages about this!)

Meanwhile, for those whose engine revs up and runs fast but the propeller is not going round, here is some relief: It's not necessarily knackered nor a major fault with all the fancy gearing inside the outboard motor shaft. Although it may look like a maritime disaster at the time, it's best to avoid the temptation to panic and abandon ship, and instead to carefully repair the problem as follows: (procedure to be performed with the engine not running!)

* Get the outboard motor onboard the boat or onto some dry land if there is any handy.

* If anyone is panicking, give them something "useful" to do.

* Remove any bits of rope or other stuff which might have fouled up the propeller. After doing this, the propeller should be free to turn when giving it a spin.

* Take off the split-pin which holds the propeller onto the shaft. Keep this rather than throwing it overboard, as it will be required for reassembling the machine later.

* Inspect the propeller and the shaft carefully. At this point the secret is revealed: The propeller was fitted to the shaft by a shear pin. A shear pin is like a mechanical engineering equivalent of a fuse in a power plug or electric box. If the propeller drive is overloaded, then the shear pin is sacrificed like a fuse to stop the rest of the expensive machine suffering from damage.

(Sometimes the shear pin is hard to spot as it has been in the shaft for a long time and will need some poking about to reveal it).

* Tap the remains of the old shear pin out.

* Replace it with a new shear pin (available from boating shops and kept in the box marked "useful spares for use in case of emergency" etc), but more realistically, as no such spare shear pin is available under the typical conditions involving being stranded in a boat, a substitute is required. The best substitute for a lost shear pin is a small piece of a welding rod of the right size of the type used on electric stick welding machines. This is strong enough to work, but yet weak enough to protect the machine. Try to avoid using a nail, except as a temporary emergency measure.

* Put the propeller back on the shaft.

* Put the split pin back on the propeller.

* Put the outboard motor back on the boat.

* Make sure everyone and everything is back onboard.

* Start the motor and cruise off at a steady pace.


Experience has shown that an ordinary so-many gauge welding rod can be cut up to make at least eleven perfectly serviceable outboard motor shear pins. The welding rod is obviously much cheaper than boat shop-bought shear pins, but you have to go to the trouble of cutting it up into the right length pieces, and the market for home made outboard motor shear pins isn't so good that it's a perfect business model for success. But at least knowing about the welding rod / shear pin relationship may help you to get out of a tricky situation.

Also see boating, Do It Yourself, and a few other helpful things at this eclectic website (thousands of pages). Worth exploring at leisure, whether on water or on dry land.

If you've arrived here to look for outboard motor propellers, I suggest you have a look at the places mentioned on the helpful page of boat supplies who have all kinds of useful nautical spare parts.


More Nautical stuff here, as well as Boating

I'd be interested to hear if this page has helped people. You can write to me