Can you damage your gearbox/propshaft when making a crash stop?

[Canopy Locked]

Following a slight mis-judgement of the big breaking swells running across the harbour entrance today, I had to make a crash stop from 3/4 ahead to full astern, as a swell swung the stern around leaving me heading towards unyielding granite.. We stopped with the fender just nudging the wall.

All seems okay with the engine/gearbox/shaft but being a natural worrier, should I be checking for any damage?

The incident was made slightly embarrassing as one of my passengers was an RNLI skipper... however as his wife said sweetly, "we all make mistakes. Do you remember the time you stepped off the wrong side of the boat?"

 

[PCUK]

I made a crash stop once and took two inches off the pitch of the prop', no other damage although the lack of thrust made me think the worst for a few hours!

 

[[2068]]

On an outdrive boat, you can end up stuck in reverse.
Please don't ask me how I know this.

 

[MapisM]

All seems okay with the engine/gearbox/shaft but being a natural worrier, should I be checking for any damage?

I don't think the crash stop per se could damage the transmission, unless you didn't wait for the engine rpm to slow down before engaging in reverse. That's what could hurt - in fact, modern electronically controlled engines/throttles do not even allow that.

 

[scottie]

Many years ago when the fishing industry changed from slow revving kelvins to the higher revving cat they had very large reduction ratios to such an extent that when then as part of engine acceptance trial did crash stop from full ahead to full astern there was so much kinetic energy that the prop took over and started the engines in reverse and in some cases had to be stopped by closing the air intakes to stop the engines blowing up

I also heard of one of the first frigates fitted with gas turbine Concorde type engines when they crash stopped the turbine the ship dropped back into the water from 30 ish knots to almost stop with such damage that it was not repeated several badly hurt seamen and the a lot of damage to the ship

 

[PCUK]

On an outdrive boat, you can end up stuck in reverse.
Please don't ask me how I know this.

How do you know this?
Ooops, sorry!!!

 

[omega2]

The first thing to "go" is the woodruff key on the shaft that holds the prop, they are designed as such. The next bit to check will be the r&d coupling for deformaty, following that the drive plate will take a bash, after that the flywheel set screws, then the crankshaft, then the engine beds as the lump leaps off them and flys over the side.

 

[DAKA]

Get plenty of light on your flexible coupling , rotate it and use a black washable felt pen all around it, use a damp cloth to remove the felt pen and look for any cracks which will now be seen as fine black lines.


If it is a reinforced one with metal safety figure of 8 linking bolts in pairs look out for a bulge in the outer rim.

With sincere apologies to Wiggo for previously missing the latter bit out

Photo reproduced with kind permission of Wiggo.

 

[Wiggo]

Worth pointing out that coupling had the figure of 8 tie bars (that stop the tailshaft falling off completely) and had also sheared two of the bolts off...

 

[Canopy Locked]

Thank you Gents, I'll have a careful look over her at the weekend

 

[nimbusgb]

I agree with the flexible coupling inspection. Was once on a yacht that regularly did a crash stop into a finger pontoon. One day the coupling let go and 20 odd tonnes of steel boat climbed the concrete caison and left me, standing on the foredeck, looking down into the club house bar, before the whole lot slid backwards off the concrete. ouch