Trawling sinking

[spannerman]

Just saw on Sky News the dramatic video from the SAR chopper as they rescue the crew from a sinking trawler in the North sea, what was surprising is that the propellor is stationary then as the boat goes down it starts spinning, I would have thought that the engine being well under water and inverted would have stopped already due to flooding, so what would cause a big heavy prop to start rotating other than the engine? Just struck me as odd, fortunately all the crew were rescued so well done SAR crew.

 

[SEARANGER ANCASTER]

Just saw on Sky News the dramatic video from the SAR chopper as they rescue the crew from a sinking trawler in the North sea, what was surprising is that the propellor is stationary then as the boat goes down it starts spinning, I would have thought that the engine being well under water and inverted would have stopped already due to flooding, so what would cause a big heavy prop to start rotating other than the engine? Just struck me as odd, fortunately all the crew were rescued so well done SAR crew.

If gearbox is in neutral , force of water over the prop would spin it ? or is this too simple an answer ?

 

[oGaryo]

http://www.lbc.co.uk/video-crew-winched-from-sinking-boat-103687

 

[SEARANGER ANCASTER]

oh yes , strange indeed ? Maybe the water is being forced into the exhaust and turning over the engine with the pressure ? Or maybe the air pressure in the engine room is being increased due to the boat being submerged in water and it is pressurising the engine and turning it over ?

 

[prv]

oh yes , strange indeed ? Maybe the water is being forced into the exhaust and turning over the engine with the pressure ? Or maybe the air pressure in the engine room is being increased due to the boat being submerged in water and it is pressurising the engine and turning it over ?

Or something shorting out and spinning up the starter motor?

Pete

 

[burgundyben]

Strobescopic effect of the camera?

 

[Mistroma]

Here is a link to an earlier similar thread I started on Scuttlebutt.
http://www.ybw.com/forums/showthread.php?419865-Iuda-Naofa-rescue-near-Lewis

A few similar suggestions to those above. At the end I was leaning towards something falling on a control lever as it made a lot of sense to keep the engine running to power pumps.

 

[sailorman]

oh yes , strange indeed ? Maybe the water is being forced into the exhaust and turning over the engine with the pressure ? Or maybe the air pressure in the engine room is being increased due to the boat being submerged in water and it is pressurising the engine and turning it over ?

not possible, it would hydrolock on compression

 

[SEARANGER ANCASTER]

not possible, it would hydrolock on compression

but if the reason it got into trouble in the first place was that the engine had gone , timing chain broke , valves bent etc etc ??????

 

[Mistroma]

not possible, it would hydrolock on compression

I ignored that option due to lack of volume in exhaust to turn the engine as much as shown on video before it locked. I had thought that air in engine room being compressed as the bow went straight down was more likely. Volume available to be pushed down the air intake could be quite large.

However, that would also require the engine to be left in gear after it had stopped. I also had doubts about the amount of pressure needed to turn over the engine in gear.

That's why I favoured the engine running and something hitting a control lever. But all guesswork and likely to remain a mystery, unless of course someone turns up saying it is a well known phenomenon and provides the generally accepted reason (unlikely).

 

[Niander]

Your assuming the engine room was totally flooded ...not necessarily with watertight doors.

 

[Mistroma]

Your assuming the engine room was totally flooded ...not necessarily with watertight doors.

Don't quite see where you think I'm assuming anything. If I'd said it must have happened in a particular way because the engine room was sealed, then I'd be assuming quite a lot. I just started from the point that the energy must come from somewhere (gravity, pressure, diesel) and wondered which was the most likely source.

It is feasible that air in the engine room would be compressed as the engine intake needs access to air and air from bows could also be forced back through open internal doors. No idea what actually happened, though. I do have a view on the most likely energy source, no proof of course.

 

[Mariner69]

It is possible that the engine and propeller system on this vessel is a CP one. The engine continues running until actually stopped, ahead and astern are provided by changing the levers on the bridge which moves the blade angle on the hub.

Not very assuring when you are getting down into a small boat alongside when the ship is moving up and down and the propeller appears out of the sea alongside you before disappearing again as the bow rises to the next swell.

 

[Mistroma]

It is possible that the engine and propeller system on this vessel is a CP one. The engine continues running until actually stopped, ahead and astern are provided by changing the levers on the bridge which moves the blade angle on the hub.

Not very assuring when you are getting down into a small boat alongside when the ship is moving up and down and the propeller appears out of the sea alongside you before disappearing again as the bow rises to the next swell.

The propeller wasn't rotating at all, some waves even went over it and it still didn't move. It suddenly starts rotating around 30 seconds after the video clip starts, just as the bow drops steeply downwards. That's the odd behaviour I spotted and spannerman started this thread after noticing the same thing.

 

[Oscar24]

Down wash from the helicopter?

 

[cryan]

As the prop isn't initially turning then the clutches are out so that rules out anything to do with the engine.
My guesses are perhaps water entering the gearbox via a broken inspection cover, filler cap or vent. From experience the final drive gear on these type of boxes is usually quite large in diameter and attached to the shaft. Due to the high amount of pressure the the inrush of seawater imparts on the large gear wheel it may in some way act like a turbine. As the hull moves to the vertical the weight of the prop shaft onto its bearing shells is reduced just enough that the water pressure acting on the large gear wheel allows the shaft to spin? Remember on a trawler of that size the gearbox will be not much smaller than a 1960's Mini Cooper so the final drive wheel is quite large so a pressure entering the gearbox from an offset entry point would cause a reasonable leverage force on the shaft to get it spinning.
Just my guess though?

 

[Chris_d]

Perhaps one of those shaft mounted bilge pumps working in reverse as water forced into the outlet.