Closing seacock of generator while underway or not ?

[Portofino]

In fact all seacocks not in use should be closed....but that does detract from the boat’s useage. Personally I don’t like playing with seacocks () away from my home berth...in case something breaks....where I know I can get help and a lift out....or at the very least it cannot sink very deep

Yep drifting to excising seacocks I tended to only do it at the home port . At every visit .
During lay off ( in between Med visits ) I closed them all , as no one’s aboard . Never got into a insurance wrangle as never had a claim in 19 yrs .but I suspect they would use open seacock s when away for extended periods with a dim view …..putting into weasel words of poor seamanship if a claim resulted - dunno no experience.If closed you are denying them that particular piece of ammo for a refute . Plenty of others I suspect though ?

During usage opened them all and left them all open .
Remember have bilge alarms and pumps , with a 48 ftr you can hear the bilge pumps humming if they come on @ night @ anchor + had illuminated alarms on the helms if they went on running ….drowned out by the main engine s .Also illuminated warning lights on the saloon console .
Carried a bag of soft wood cones as well - never used them .

Never exercised the main engine s while away on a cruise …..incase they jammed shut or handle snapped off .
As you say those scenarios are best handled in your home port .

Last boat had a transparent lid on its geny stainer easily visible at the foot of the ER ladder so I could with the sun shining see the sea under the boat . As said left it open while running as often ran the geny while returning from a day out @ anchor to the home berth to run the Aircon to chill down the below deck spaces .

The scoop faced backwards btw .

However the far larger main engine scoops faced forwards to collect water .

 

[aerobat]

Great informations and a lot learned here !

I will take a closer look at this but tend to leave the seacock open . Its not a big issue to open the engine hatch , enter the engine bay and open the seacock when the genny is needed but not even close to being as sexy as just pushing the knob on the remote .

You are welcome from a fellow ex Farryman geny owner .

The “anodic block “ in your raw water cooled Farryman 18 is the sq zinc looking thing bolted on the side of the engine.
This gradually degrades and saves the actual engine . It has a life of many yrs but really is a serviceable part and will require replacing . For the avoidance of doubt with the “ rainbow “ guy ) this is on the inlet side .

For the benefit of the rainbow guy we now move to the exhaust side …..

Yes by the sound of your instal , the box will be the gas water separator and the loop of hose that goes up as high as it can in the engine room is good and should together as I said prevent seawater backing into the elbow .

The wider issue of backfilling is when it’s not running the impeller stops . If ( most likely) it’s a good seal then un extruded seawater sits in the elbow ….obviously just below its entry port .
If any seawater then tops that off from the exhaust side it might dangerously rise above into an open exhaust valve leading to a hydrolock.

How ever as you describe , the water box muffler and the high loop of pipe this shouldn’t happen .

For the benefit of the rainbow guy we now move back to the inlet side ……I do wish Pauls keeping up ?

So from first principles you want that elbow to drain …..eventually even with a decent rubber impeller it will ….but only with the inlet sea cock OPEN .
Assuming geny is mounted above the WL ?^

So in your case the route to minimise future expense is leave the inlet open when running .

You could before a long lay up ( leaving the boat for extended periods ) run the geny for a few seconds with the inlet shut to pump out the elbow ……to achieve two things .

1- to empty the elbow to mitigate sea water vapour effect on the exhaust valve and cylinder corrosion.If it stops with the exhaust valve open ….that’s the thing you don’t know the valve status at shutdown.

2- the decrease the hight of seawater sitting in the elbow ….if despite the exhaust plumbing some how an unlikely senario occurs whereby seawater enters .eg boat caught in a large wash by another boat ….rocks side to side and that 4 to 6 cm air gap at the top of elbow is reduced and sitting seawater flows into the cylinder head . = Not good !

As far as running with it open ….your original Q ( if I understood your post #1 ? ) ….you should be ok .
If anything seawater will be sucked out not pressurised in when on the plane .Assuming the entry TTH fitting is in the posterior 1/3 rd of the hull .

Let’s park hull pressure here for the benefit of those who don’t under stand the the effect salt air from the water sitting in the elbow - on the valves / cylinder .

Additionally not mentioned thus far most instals have an anti siphon valve / loop fitted on the water inlet side after the strainer pretty high up above the WL . This is designed to prevent at shutdown seawater siphoning into the exhaust elbow . As the engine has stoped there’s zero pressure from exhaust gases to remove this water filling the elbow , blow it out .
So eventually the level rises and if the exhaust valve (s) are open ( very likely in a multi cylinder set up ) sea water flows into the cylinders = hydro lock .

 

[aerobat]

Personally I don’t like playing with seacocks () away from my home berth...in case something breaks....

Wow ... that scenario is not only an eye opener but also a sure starter to give a solid shot of fresh s**t into the pants if it happens without the infrastructure of an immediate liftout .

 

[Bouba]

Wow ... that scenario is not only an eye opener but also a sure starter to give a solid shot of fresh s**t into the pants if it happens without the infrastructure of an immediate liftout .

I’ve never had a seacock snap off and water gets in....but I have had the handle snap off...as said before, I was exercising them in my home port...and the port towed me to the take out and I fixed it in the sling overnight.. A real pain to be sure...but it would be a thousand times worse if I was out to sea...and ten times worse if I was in a strange port

 

[Portofino]

Another safety thing to check / test is the bilge pump switches .

The traditional float switches you simply lift up the float they have a little lever to assist this .
The electronic solid state you take a wet cloth and touch across the two electrodes .Might take a few goes and more water in the cloth to get it work ?

I used to do this every time we attended after a lay off .

Also if I was fiddling around with something nearby and could reach across …more for curiosity in a “ while iam in there “ kinda way .

Always had spares aboard and immediately replaced if none functional.Then bought another .
Every marina shop stocks them . You should do this right away( replace a duff switch ) no need to wait to return to the home port .

 

[PaulRainbow]

Another safety thing to check / test is the bilge pump switches .

The traditional float switches you simply lift up the float they have a little lever to assist this .
The electronic solid state you take a wet cloth and touch across the two electrodes .Might take a few goes and more water in the cloth to get it work ?

No need for wet cloths, just touch them both at the same time.

 

[john_morris_uk]

Sorry guys - but any seacock left open is a potential hazard. If the Genny is not in use - why leave Seacock open ? A simple card hung on the genny start panel to remind opening seacock ?

Second ... where does the seawater exit ? Into the exhaust similar to many marine engines ? If marine engine is not running - there's no exhaust gas pressure to carry the water out ... and you can in theory get water into cylinder .... MAYBE .. I only say maybe - the genny could do same ? Post #8 .....

That’s one point of view. Our seacocks stay open all the time. I know where they are. They get exercise regularly so I know that they work. They’re there to close in case there’s a problem. Some of them are in places you don’t want to start crawling into every time you start the generator or use the heads or empty the galley sink. They’re not inaccessible but it would be a pain in the backside to open and close them all the time.

For example, our generator seawater intake is in the engine compartment and quite near the rotating shaft from the main engine. You’d have to stop the engine (or at least put it into neutral and ideally put some air defenders on) remove a panel and reach inside the engine bay to open or close the generator seacock.

 

[john_morris_uk]

Hands up anyone who has a seacock on the genny exhaust ?

We have a water separator on the generator exhaust so that you don’t get the splash splash of water from the exhaust discharging over the side when the generator is running. It also helps silence the generator which is almost inaudible even when you’re close up to the boat. There’s a seacock on the underwater discharge from the water separator. Does that count?

 

[Mr Googler]

Would water rushing past at say, planing speeds not cause a suction effect as much as a inflow I wonder?

 

[PaulRainbow]

Would water rushing past at say, planing speeds not cause a suction effect as much as a inflow I wonder?

Of course not.

Why do you think the heads overflows and the sinks all fill up and overflow when you go on the plane.

 

[PaulRainbow]

We have a water separator on the generator exhaust so that you don’t get the splash splash of water from the exhaust discharging over the side when the generator is running. It also helps silence the generator which is almost inaudible even when you’re close up to the boat. There’s a seacock on the underwater discharge from the water separator. Does that count?

I suppose it does.

Although the OP relates to water being forced up the inlet when planing. Unless an idiot fitted a forward facing scoop i can' see that happening, more likely the opposite.

 

[ARE]

Hello to all !

Its now my first boat with a genny and a dockmate told me to close the seacock while underway , especially on plane , since dynamic water pressure on the thru hull might force water into the genny .

Imho its bs since even if , it will only make similar flow to the generator running and not flood e.g the cylinder .

Am i missing something ? Do you close your seacock in such a situation ?

Best regards

I have got a lot of experience with installing generators on all kinds of boats and your dockmate is not wrong in some ways. It is possible to flood the generator engine with sea water if while underway if there is positive pressure on the sea water inlet supply. The impeller sea water pump will not hold back the sea water flow and this water will end up filling the exhaust muffler with sea water and then back flow this water into the engine via the exhaust valves.

This is why a generator sea water intake should never be fitted with a scooped inlet, it doesn’t matter if the inlet is Aft facing or forward facing. The generator sea water intake should be a static type with just the open hole. Even then if you get the static intake in the wrong place on the hull you can get positive pressure forcing water into the generator and risk flooding it.

We always sea trail a new boat generator install with the sea water inlet hose removed from the generator to make sure there is no water pressure while operating the vessel. If there is any doubt then we recommend fitting an electric sea water inlet valve to the system which only operates while the generator is running.

Most of the time there is not an issue, however I have seen a number of boat with flooded generators because of positive sea water intake pressure.

 

[Hurricane]

I have got a lot of experience with installing generators on all kinds of boats and your dockmate is not wrong in some ways. It is possible to flood the generator engine with sea water if while underway if there is positive pressure on the sea water inlet supply. The impeller sea water pump will not hold back the sea water flow and this water will end up filling the exhaust muffler with sea water and then back flow this water into the engine via the exhaust valves.

This is why a generator sea water intake should never be fitted with a scooped inlet, it doesn’t matter if the inlet is Aft facing or forward facing. The generator sea water intake should be a static type with just the open hole. Even then if you get the static intake in the wrong place on the hull you can get positive pressure forcing water into the generator and risk flooding it.

We always sea trail a new boat generator install with the sea water inlet hose removed from the generator to make sure there is no water pressure while operating the vessel. If there is any doubt then we recommend fitting an electric sea water inlet valve to the system which only operates while the generator is running.

Most of the time there is not an issue, however I have seen a number of boat with flooded generators because of positive sea water intake pressure.

I believe Magnum (rest his soul) had that problem on his early Princess 67.
I seem to remember a problem with the generator flooding.
You might have been involved in that case at the time.
Our Princess 67 has its input strainer quite high up above the water line.
The strainer is one with a plastic screw top so I can see the water level is below the strainer when the generator isn't running.
I also know that the inlet skin fitting is a simple hole - not a scoop.
I was running it last week and ours is set so that the raw water pump primes the strainer every time.
So I'm pretty sure that water can't be forced up to the generator when it isn't running.
The muffler is also quite high above the water line.
Anyway, I always keep the sea cocks open unless leaving the boat when I'm away - and I have never had any problems.
Maybe in my case, the raw water pump has to prime the pipework each time.

 

[Hurricane]

I guess this issue is (to a certain extent) the same with the main engines.
We have Halyard Exhaust stacks - huge 3 feet diameter cylinders behind the engines. Raw water in injected into the exhausts which pass into the exhaust towers. Some seawater remains in the towers when the engines are stopped. There are drains with cocks that will drain that water. The manual says that you should drain the exhausts when lifting the boat, especially if you are shipping the boat by sea or water can find its way back up the exhaust into the engines.

 

[aerobat]

Great further information ! I must admit i never wasted a thought on this and made several runs with the seacock open without having an issue but also never took a closer look if i,m slowly filling my exhaust via the cooling circuit or not . Since the boat is new to me i lack the experience what will happen during prolonged planing cruise with some waves in open sea .

This theme is interesting !

 

[stelican]

Can't be tossed to read thread but all seacock need exercising so it wouldn't harm to close them whilst not in use.

 

[john_morris_uk]

Can't be tossed to read thread but all seacock need exercising so it wouldn't harm to close them whilst not in use.

I think you might benefit from reading the thread!

 

[ARE]

I believe Magnum (rest his soul) had that problem on his early Princess 67.
I seem to remember a problem with the generator flooding.
You might have been involved in that case at the time.
Our Princess 67 has its input strainer quite high up above the water line.
The strainer is one with a plastic screw top so I can see the water level is below the strainer when the generator isn't running.
I also know that the inlet skin fitting is a simple hole - not a scoop.
I was running it last week and ours is set so that the raw water pump primes the strainer every time.
So I'm pretty sure that water can't be forced up to the generator when it isn't running.
The muffler is also quite high above the water line.
Anyway, I always keep the sea cocks open unless leaving the boat when I'm away - and I have never had any problems.
Maybe in my case, the raw water pump has to prime the pipework each time.

You will be surprised how much pressure will come up through the generator inlet hose if the skin fitting is in the wrong place in the hull at planning speed even with a non scooped fitting. I have seen it clear the flybridge on a 76ft boat during testing. I do remember Magnum’s boat, I think this suffered flooding from the water drain of the exhaust gas water separator by pressurised while underway. You will see all Princess boats now have a one way valve fitted in this drain to prevent this.

Having said all this, if the generator is installed correctly. Then you can operate the boat with the seacock open all the time.

 

[PaulRainbow]

Can't be tossed to read thread but all seacock need exercising so it wouldn't harm to close them whilst not in use.

But you can "be tossed" to comment on something you have not read ?

 

[stelican]

I think you might benefit from reading the thread!

As I said all seacock need exercising.
Don't think I would benefit from trawling through the whole thread.