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Have a stuck engine sea water cock. Any suggestions how to free it while at mooring? It is stuck open and want to close it as have a blockage somewhere as no water is coming out back of exhaust
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Might be best to identify the type of seacock you have. If it is a Blakes you may be able to loosen off the nuts that hold the tension on the cock and then apply pressure to the handle. If its a gate valve you can pull it apart but be aware the water will rush in at some force. If its a ball valve some can be pulled apart but best not on a mooring. What ever you do, avoid using too much force and have your tapered wooden plug handy.
Not sure why you need to shut the valve to sort out no water flow. If the valve is blocked disconnecting the water pipe above the waterline and back flushing may help. No water flow out the exhaust is most likely a worn impeller or a worn impeller face or even a broken shaft. I would suggest checking the water pump first.
Hi Ramano
Not sure what sort of seacock it is. Is made of plastic. Will try & insert a photo.
I wanted to shut the valve as I had cracked an engine water filter lid between it and the impeller pump and water is slowly leaking in. Ended up gluing the crack for the moment and clamping the hose as I sure didn't want to break the seacock!
The previous owner (of about 30 years!) had rebuilt the impeller etc in the pump about 18 months ago. It is an old Yanmar and he suggested to look past the pump where the hose attaches to the engine. It is a funny cylinder that has an anode amongst other things in it. Any way that's the next job after I replace the sea water filter .
Yes....wooden plugs...I suddenly realised their usefulness when I had a leak and couldn't find any!!!
Looks like a plastic ball valve. Not sure why its even on the engine. I presumed we were talking about hull seacock to the engine. What's on the other end of that rubber hose? Should have a valve at the skin fitting to shut off the water flow. If that hose comes from just a skin fitting with no valve then removing that clip and pulling off the hose and quickly replacing with a correctly sized bung and reclamp will enable you to service the valve.
CAUTION; depending how far below the waterline that valve is, water will enter at a startling speed! I used to regularly pull off a 2 inch hose to clear and I can assure you it comes through at some force.
That funny cylinder sounds like a heat exchanger. The anode could have disappeared and salts blocked all the spaces or tubes where the cooling water flows. The end should be able to be removed and the tubes rodded out. It could also be an oil cooler. Try posting a photo showing the whole unit.
Impellers in water pumps will last only a couple of minutes if run dry. I would be checking the state of the impeller first. If the water is going past the water pump then the heat exchanger is probably the culprit for the blockage. Underneath the heat exchanger there will be a cast iron section of pipe where the hot exhaust gases mix with the usually cool seawater, a Y section. This is a sacrificial section that blocks up. Pull off the heavy hose and poke a screw driver up the hole. This regularly blocks up with engines that are not run hard enough, running at idle or fast idle with no load for an hour or so charging batteries for example!
Hi Ramano
Thanks for all the feed back.
I'll make myself a bit clearer.
The photo is of the seacock which is attached to the skin fitting on the hull. If it is a ball type as you suggest
then I'll leave it alone until I slip the yacht in a couple months time (for the !st time since I've owned it) The top photo is another angle of the seacock valve.
The hose runs to the plastic engine sea water filter that I cracked the lid on.
The funny cylinder is not part of the heat exchanger. The bottom photo shows the salt water intake hose attached to the funny cylinder.
That funny cylinder is just an intake with multiple screw fittings for fitting other stuff.
Not good, not good at all.
We had a yacht leave Camden Haven a couple of years ago and he got the bar all wrong on the way out.
Resulted in taking a couple of big greenies 
and attempting to dive to the sea floor on the other side of the breakers!
What he didn't realise was that his batteries had broken loose during this attempt to dive [or fly] as he went over the bar.
The loose batteries did only one bit of damage, they destroyed the inboard engine's raw seawater plastic seacock! 
Now those onboard did not realize that anything was wrong at first, until the yacht became sluggish and SEEMED to be lower in the water.
Quick action got them back inside the bar, without anymore drama, where MR Camden Haven quickly came to their rescue.
Change the seacock to a bronze ball valve ASAP!
Could it be a blockage at the inlet.does water come in if you loosen the cover on the basket filter.abuild up of antifouling and a little growth greatly reduced water flow on my boat
and attempting to dive to the sea floor on the other side of the breakers!
Ramano
Yes it is a steel ketch. You are correct with the gal skin fitting, hose, 90 bend then plastic valve.
Cisco
Yes it is an Yanmar 3qm . Thanks for the flushing and anode advice. Havnt worked out where the thermostat is yet but will.
Doug27
Yes I wanted to check that 1st but that's where all my problems got worse as I cracked the plastic lid on the strainer and had a woorysome leak to say the least as I couldn't turn off the stop cock!
NSWsailor
Scary story!
The lid for the strainer should be above the waterline. The water leaking out is possibly just back drain from the engine.
Good point, from what I can remember the lid is below the water line. Have only owned the yacht a few months and still sorting out a lot of things. Have had had conflicting advice wether it is a problem to have the filter above or below the water line.
