SO 479 Onan 7.5 GENSET Raw Water Problem

[Evening Star]

I have a factory installed Onan 7.5KW GENSET in my 2019 SO 479.  The through hull is just aft of the sail drive on the Port side. Periodically, the water drains from the strainer and the GENSET shuts down on a loss of raw water flow on start.  The first time this happened was after I short hauled the boat. I took the lesson on closing the tru hull when hauling he boat.  It happened again in healthy quartering seas while sailing on a Port tack.  It happened today after a 45 NM sail all on the Port tack in 15KT winds, beam reach.  To correct, I have to close the through hull, fill and close the strainer and open the through hull.  It seems to me that the water drains if the thru hull is exposed above the water.  The GENSET will not self prime.  This is problematic as it makes the GENSET unusable while underway and I don't think the design would require always closing the through hull after use to maintain the raw water prime.  

Is this normal?  Are there any solutions?  Would this indicate an issue with the installation.  I am interested in and 469/479 owners thoughts on how their GENSETs operate and anyone who has any advice.  

Thanks in advance.  

[moonshadow]

I have same genset factory installed on a SO469. I have not had these problems. Sounds like some investigation is in order for leaks etc.

[Evening Star]

Ive done full end to end checks on the inlet tubing from the thru hull to the strainer.  No leaks.  The water in the line is draining out of the inlet tubing when the thru hull comes above the water line.  The strainer top is on tight and is making a seal.  I'm not sure why the water would drain so easily.    

[sailbleu]

I sometimes have the same problem with my A/C water , and although the through hull is midship slightly out of center to starboard side in a heeling towards port side the water drains away . Or maybe it is just sucked away due to venturi effect .
Therefor I try not to forget to close the valve so the pump’s suction remains full . Occasionally I do forget of course
As you know the danger of no cooling water for A/C is an overheat of the compressor . I do monitor all the temperaturen of all the heat ( and cold) producing appliances on board with an array of displays and selector switches ( I apply 6 selectable sensors for each display) , but sometimes neglect to follow up after starting the A/C .
I also use a flexible hose in the through hull of the water discharge directly into the sea or dock water to prevent that annoying sound of the output . Not that it bothers us , we have the benefit of the A/C , but our neighbours do not . So i have no indication of coolingwater unless I monitor the temps. for awhile after startup . Or lift the flexible hose out the water.

In your case you can’t start the generator , but that could also have different reasons no doubt . And the safety switch can fail . Murphy’s law !
My A/C doesn’t have a cooling water pressure switch . And sice Murphy’s law has that reputation , 5 years ago we were in the marina on Gozo ( next to Malta) . We were out to a restaurant and the A/C was running . When we returned a few hours later it was hot as hell inside the boat . The A/C breaker had gone , and the unit was hot as a stove . Apparently the waterpump had failed and the unit kept running . It’s only because the compressor had stalled , and I mean blocked , the fuse blew . Lucky us , there could of been a fire . The unit took a hit but is still functioning up to this day .
A wakeup call however , one I took serious . Since that day I never run the A/C when absent.
Confidence / trust in machinery and electronics is ok ,.......monitoring and controlling them is better .

Therefor I’ve decided to look into the cooling water issue in an effective way , either I add audio alarms to the monitoring system and use the alarm signal to also stop the A/C unit . Two shut down systems , one on the output cooling water and one on the compressor housing . Redundancy is a boater’s middle name Is it not .

Or , .....and this might also be an idea for you , I install an electromagnetic valve after the seacock . This extra valve should be controlled by the ignition switch of your generator .
Stop the generator and the valve closes , switch on and it will open . Really easy peasy job .

I think I’ll for both , that way the A/C is also protected for water pump breakdown when we are not present .

Regards

[djpowers]

I have the same setup on my 479.  Similar issue as well.  It appears the water pump cannot self prime, so there is a one-way valve installed between the seacock and the strainer (just below the strainer).  It is a simple ball valve and it can get stuck with debris.  I have to clean it every couple of months.  Otherwise, it appears to solve the priming problem.  The seacock is in an terrible position under the hot water heater with a problematic 90 degree fitting--another topic...