How do lifeboats launched from a shed have the engines running when they hit the water??

[tudorsailor]

I listened to Radio 4 drama about the Penlee lifeboat disaster. That got me wondering about lifeboats both then and now, that are launched down slipways with their engines running. Are the engines typically marine engines and so water cooled? If so, how can they stay running before hitting the water?
Just curious

Thanks

TudorSailor

 

[CM74]

I've no idea about RNLI type lifeboats, but the ship's lifeboats I've seen had keel coolers - where the engine coolant is circulated through pipes running outside the hull, which works as a heat exchanger, without the need for a seawater pump that has the problem of running dry, or getting blocked.
IIRC they have to be able to be run out of the water for a particular time in order to be approved.

 

[DJE]

A cooling water supply in the boat shed I expect. A small buffer tank on the boat if necessary to cover the few seconds as it travels down the slipway. (If they have wet exhaust systems and indirect engine cooling then the exhaust temperature could become a problem before the engine overheats.)

 

[Alan S]

The Atlantic class have water tanks on the launching trailer connected by flexible hoses to a fitting on the outboard engines which just pulls off when the boat powers away.

 

[mm42]

The engines have coolant, which is then passed through heat exchangers with seawater to cool the coolant. So they can run for a few minutes without overheating.

I work on diesel inboard powered waterjet RHIBs which have the same arrangement, they can be run dry for a few minutes, unlike an outboard which is usually cooled purely by raw water, run them without seawater and the impellers melt very quickly.

 

[michael_w]

Oil based coolant?

 

[duncan99210]

When the Speedseal maker was still up and running, he claimed on his website that the RNLI used his kit, thus allowing dry running of the engines without the risk of damaging the raw water impellers. A few minutes at idle shouldn’t raise the exhaust temps high enough to cause problems.

 

[caiman]

I think that 'Gilks' contactless pumps are fitted to the sea water cooling side of all current RNLI ALB's.They were certainly on the Mersey class.These are 'run dry' bronze impeller centrifugal pumps.Cat 3208T engines with Cats own (indirect conversion).Mostly wet stainless steel exhaust.
Hamilton Jet drive .Sea water for engine etc cooling is 'usualy' provided by a tapping from the jet drive to the engine heat exchangers etc,the jet being in constant drive.The Shannons(indirect) have a F/N/R gearbox(no reduction) fitted which provides a 'backflush' function.They have a Gilks pump in the system which provides cooling water if the jet is in neutral.The Gilks pump being overwhelmed by the flow from the jet when in drive, Scania D13s with own conversion,mostly wet exhaust.
The older boats,Rother etc had a heat exchanger mounted to the hull interior forward,with sea water flowing through the inside,and engine water pumped through the outside of the heat exchanger.Cooling provide by the boat's movement through the water only.A bit like a keel cooler but with the pipework inside.These worked remarkably well on the Ford 4Ds.Mermaid/Thornycroft conversions.I cannot remember for certain how the exhaust was cooled.
As said above,running at tick over with no load there is not a massive amount of heat produced,and the coolant in the block etc can cope for short periods.
Hope this helps.
Cheers

 

[tudorsailor]

Many thanks for the explanation
TS

 

[jwfrary]

The reffited Severn class using mtu engines have bronze impeller type pumps as standard. And can cope with dry running. They are 5000 euro btw ?. Of course theres plenty of other modifications to the breather systems to allow the engine to survive a roll over. Bigger cats and scannias list bronze impeller pumps as an option though its rarely specified on non commercial boats.

Exhausts utillise high temp silicon and stainless risers so can withstand loss of seawater flow.