Raw Water Hose Blown Off

[Petronella]

After 6 weeks quarantine it was time to move again. Engine on, water from exhaust as normal. Motor 1 mile. No problem. Increase revs to 2,000. Many alarms scream, water filling engine bilge. Stop engine, close sea cock. Run bilge pumps. Sail back to starting point.

What had happened? The raw water hose downstream of the water pump and connecting the outlet of the oil cooler to the inlet of the heat exchanger had come off. This is a factory fitted hose on a relatively new Beta 75. It has never been removed.

What have I checked? I assumed the problem was downstream of the water pump as the pump was still pumping water into the bilge! However I checked the skin fitting and the strainer, removed the impeller (looked fine), removed the heat exchanger (some minorly blocked tubes but not enough to cause the hose to blow off I would have thought), checked the anti-syphon and finally the exhaust elbow (completely clear).

What else could have caused this? I expected it to be a blocked heat exchanger or exhaust elbow but it seems not. This engine does throw out a huge amount of cooling water so I suppose the heat exchanger could have been the problem (see picture of worst part). It seems strange that it happened after not moving for 6 weeks.

At the moment all I can do is but it back together again and take it up to 2,500 revs for a good while and hope it doesn't recur!

Thanks for your help.

John (S/Y Mehalah)

 

[Malish]

Hose not correctly tightened in the first place (ever checked it?), A bit of blockage in the heat exchanger or some crud in the elbow then tips the balance and off it comes?

 

[duncan99210]

Or might have been some debris that caused the hose to blow off but the debris was flushed out into the bilge by the water.

 

[neilf39]

Did you take the tube stack out and clean it or just take the end cap off to have a look? How blocked is it at the other end?

 

[oldgit]

On a previous boat it was rust scale that accumulated in the exhaust riser passages that caused a hose to be forced off the exhaust.

 

[Plum]

After 6 weeks quarantine it was time to move again. Engine on, water from exhaust as normal. Motor 1 mile. No problem. Increase revs to 2,000. Many alarms scream, water filling engine bilge. Stop engine, close sea cock. Run bilge pumps. Sail back to starting point.

What had happened? The raw water hose downstream of the water pump and connecting the outlet of the oil cooler to the inlet of the heat exchanger had come off. This is a factory fitted hose on a relatively new Beta 75. It has never been removed.

What have I checked? I assumed the problem was downstream of the water pump as the pump was still pumping water into the bilge! However I checked the skin fitting and the strainer, removed the impeller (looked fine), removed the heat exchanger (some minorly blocked tubes but not enough to cause the hose to blow off I would have thought), checked the anti-syphon and finally the exhaust elbow (completely clear).

What else could have caused this? I expected it to be a blocked heat exchanger or exhaust elbow but it seems not. This engine does throw out a huge amount of cooling water so I suppose the heat exchanger could have been the problem (see picture of worst part). It seems strange that it happened after not moving for 6 weeks.

At the moment all I can do is but it back together again and take it up to 2,500 revs for a good while and hope it doesn't recur!

Thanks for your help.

John (S/Y Mehalah)
View attachment 91299

It is good that you are inspecting your complete cooling circuit but impeller raw water pumps are good at pumping volume but bad at pumping pressure. Even if you had a complete blockage after the pump you should not get enough pressure to force off a hose connection that is correctly fitted. The hoses on the non-seawater coolant circuit are under more pressure when the engine is hot than the jabsco can produce and they do not (hopefully!) pop off under pressure.

Www.solocoastalsailing.co.uk

 

[PCUK]

Deleted after rereading OP post!

 

[Graham376]

Any chance a collapsed exhaust hose could cause this amount of pressure?

 

[Stemar]

Another vote for a clamp that wasn't tightened properly in the first place. When my exhaust elbow was blocked, all that happened was that the rate of flow dropped, eventually to almost nothing. As Plum says, a rubber impeller is never going to give enough pressure to blow a pipe off.

Just a thought, is the pipe run a bit tight? could engine vibration be tugging on it as well?

 

[Petronella]

Did you take the tube stack out and clean it or just take the end cap off to have a look? How blocked is it at the other end?

Yes. Tube stack removed and cleaned with Barnacle Buster. The end shown was the 'worst' end.

 

[Petronella]

Stemar: It's only a short 6" hose wedged between the oil cooler and heat exchanger. Don't think it would 'drop' off.

Graham 376: I suppose it could be back pressure from the exhaust side rather than forward pressure from the water pump side. Will investigate further.

Thanks all.

J