Closing seacock of generator while underway or not ?

[aerobat]

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

 

[markc]

BS

 

[rafiki_]

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

My gennie sea cock stays open underway, in case the kettle calls. If the sea cock is operating correctly, how can water flow? If it does, then it will run through the cooling system. Your dock mate is mistaken.

 

[jfm]

100% agree with #2 and #3 above. Total BS. Leave it open. As rafiki says in #3 , it doesn't even matter is water is forced in, because its only going through the raw water side of the heat exchanger which is meant to be full of seawater anyway.

 

[Portofino]

Depends !

The Op hasn’t said which geny .
Some earlier Fisher Panda small ones had raw water cooling via a anodic “ water connection block “ .

Agreeing with the posts #2and 3 in so much as if closed cooled via a heat exchanger , or indeed even air cooled ( smaller Mase ) any back flow can’t reach potentially reach an open exhaust valve .

However its theoretical with a early Fisher panda that uses a raw water . This is more likely in a healing sailboat depending on the inhalation hight difference s of seacock , genys elbow to the exhaust valve(s) and the variable water line due to the heel .
This is where this closing the seacock advise originates ^

So until the exact make / model / yr of the geny is known and exactly which seacock you can’t give a 100 % certainty.

It’s the exhaust seacock anyhow that gives rise to potential back flow via the elbow getting past an open exhaust valve ……as a sail boat heels .

If the OP is referring to the inlet ( I think he is ? ) then sea water has to pass the stationary rubber impeller. Very unlikely.
Aside the strainers on the inlet TTH fittings are generally hydrodynamically designed to resist any pressure differences when a planing boat is planing .

We never closed ours , often running the geny planing .

You shouldn’t have to close either in motor boat .

 

[PaulRainbow]

Depends !

The Op hasn’t said which geny .
Some earlier Fisher Panda small ones had raw water cooling via a anodic “ water connection block “ .

Agreeing with the posts #2and 3 in so much as if closed cooled via a heat exchanger , or indeed even air cooled ( smaller Mase ) any back flow can’t reach potentially reach an open exhaust valve . 97 % guessing of instals ?

However its theoretical with a early Fisher panda that uses a raw water . This is more likely in a healing sailboat depending on the inhalation hight difference s of seacock , genys elbow to the exhaust valve(s) and the variable water line due to the heel . 3 % of instals.
This is where this closing the seacock advise originates ^

So until the exact make / model / yr of the geny is known you can’t give a 100 % certainty.

Where does the water intake connect on an air cooled genny ?

 

[Portofino]

Where does the water intake connect on an air cooled genny ?

They have a sea water / air cooler / heat exchanger.

Instead of transferring cool seawater via a water pump and impellers to the conventional closed cooling circuit , they have a fan that blows the now cool air through the fins on the cylinder(s)


Obviously regarding the OP s Q it’s impossible for seawater to get into a cylinder, if he’s got this type ?

 

[aerobat]

Thanks for your interesting inputs !

Specifically we are talking a 2005 paguro 4000 with a farymann 18w , raw water cooled on a motor boat ( gobbi 375sc ) .

Only intake seacock , the exhaust is well above the waterline via a silencer and an elbow . Water discharge via the exhaust .

 

[Refueler]

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 .....

 

[Portofino]

Thanks for your interesting inputs !

Specifically we are talking a 2005 paguro 4000 with a farymann 18w , raw water cooled on a motor boat ( gobbi 375sc ) .

Only intake seacock , the exhaust is well above the waterline via a silencer and an elbow . Water discharge via the exhaust .

Ah !
This Farryman motor is the type I was referring to with a raw water anodic block . Found in some small genys .
Ok you say your discharge is high up and unlikely to get a wave get through the exhaust, has it got a water / air separator - most have - ? Some sort of silencer ? If so a wave can’t really get into the elbow .

Then as refeuler says , if the impeller vanes are such to allow sea water past and the geny hight to TTH fitting is low ….just maybe water could past into the none pressurised ( geny off ) elbow .

This is what your mate probably had in mind in post #1 .
As I said depends on the geny and instal .

 

[PaulRainbow]

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 .....

So you want to boil the kettle, off to the engine room to turn the genny seacock on. Kettle boiled, back to the engine room to turn the seacock off. An hour later, fancy another cuppa ? Rinse and repeat.

What about heads seacocks ? Sink seacocks ? Etc.

 

[PaulRainbow]

Ah !
This Farryman motor is the type I was referring to with a raw water anodic block . Found in some small genys .
Ok you say your discharge is high up and unlikely to get a wave get through the exhaust, has it got a water / air separator - most have - ? Some sort of silencer ? If so a wave can’t really get into the elbow .

Then as refeuler says , if the impeller vanes are such to allow sea water past and the geny hight to TTH fitting is low ….just maybe water could past into the none pressurised ( geny off ) elbow .

This is what your mate probably had in mind in post #1 .
As I said depends on the geny and instal .

What absolute nonsense. What has the exhaust got to do with the intake seacock ?

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

 

[aerobat]

Ah !
This Farryman motor is the type I was referring to with a raw water anodic block . Found in some small genys .
Ok you say your discharge is high up and unlikely to get a wave get through the exhaust, has it got a water / air separator - most have - ? Some sort of silencer ? If so a wave can’t really get into the elbow .

Then as refeuler says , if the impeller vanes are such to allow sea water past and the geny hight to TTH fitting is low ….just maybe water could past into the none pressurised ( geny off ) elbow .

This is what your mate probably had in mind in post #1 .
As I said depends on the geny and instal .

Thanks a lot !

sorry for asking , english is not my mother tongue - what do you mean with "anodic block" ? I thought the farymann is a straight forward single circuit raw water cooled block , similar to most outboards or some smaller marine petrol inboards . I,m not aware i have a heat exchanger , i think not .

I,m brand new to this boat and in the process of learning - the genny itself is installed at least partly below the waterline with a cooling water thru hull pickup and seacock . The exhaust goes horizontally to the first silencer mounted on the bottom of the engine bay ( maybe its the water separator ? ) and then up to nearly the ceiling of the engine bay , via a second silencer / elbow and down again to thru hull exhaust around 15-20 cm above the waterline . Its a wet exhaust with cooling water discharge .

No separate cooling water discharge via a second seacock .

i do not think a wave can crash thru this elbow that high but if yes - what should closing the water intake seacock change in this scenario ? I have no seacock on the exhaust side .

My common sense says me the only way for getting water into the cylinder is via the engine exhaust , not via the engine ( combustion air ) intake . The water intake due to my understanding will in worst case create some cooling water circulation but nothing more .

Further : when we are talking a scenario the genny takes water into the cylinder via the exhaust elbow / high waves etc. Is this not theoretically possible with every genny , regardless if its raw water , fresh water / heat exchanger or even air cooled ?

Best

 

[Meps1983]

I've been wondering this about my generator. Surely of the unit is running any water that did go in the exhaust outlet would be pumped back out like the raw water does? My seacock is situated at the bottom of a confined engine bay which is why mine only goes off when I leave the boat.

 

[Refueler]

So you want to boil the kettle, off to the engine room to turn the genny seacock on. Kettle boiled, back to the engine room to turn the seacock off. An hour later, fancy another cuppa ? Rinse and repeat.

What about heads seacocks ? Sink seacocks ? Etc.

Just a post .. calm down Paul ...

As to other seacocks - yes I do actually ... my sink backfills if I heel to stbd ...... my heads have double valves ... on both in and out. They are at your feet when in the heads in my 25ft MS

The Conq38 has a weird snake pit of pipes and if you don't close of the heads - it backfills. Yes it needs sorting out.

 

[Portofino]

What absolute nonsense. What has the exhaust got to do with the intake seacock ?

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

Didn’t say it had ?
Was referring to the exhaust side with the Farryman 18 .

There were two seacocks on both mt previous mobos .
So both hands up .
One for the fisher panda on the Sunseeker which did indeed have a seacock on the exhaust ( as well as the strainer entry )
Second hand up for the Itama …..it had an exhaust seacock for the air cooled Mase ( which you seem to know nothing about ? ) ….this cock was under a bunk on the transom as it exited there .

Water egress into Farryman 18 s back flowing from the elbow is a well documented issue along with rusty e valve if not regular used .

No need to be rude btw .

 

[Portofino]

Thanks a lot !

sorry for asking , english is not my mother tongue - what do you mean with "anodic block" ? I thought the farymann is a straight forward single circuit raw water cooled block , similar to most outboards or some smaller marine petrol inboards . I,m not aware i have a heat exchanger , i think not .

I,m brand new to this boat and in the process of learning - the genny itself is installed at least partly below the waterline with a cooling water thru hull pickup and seacock . The exhaust goes horizontally to the first silencer mounted on the bottom of the engine bay ( maybe its the water separator ? ) and then up to nearly the ceiling of the engine bay , via a second silencer / elbow and down again to thru hull exhaust around 15-20 cm above the waterline . Its a wet exhaust with cooling water discharge .

No separate cooling water discharge via a second seacock .

i do not think a wave can crash thru this elbow that high but if yes - what should closing the water intake seacock change in this scenario ? I have no seacock on the exhaust side .

My common sense says me the only way for getting water into the cylinder is via the engine exhaust , not via the engine ( combustion air ) intake . The water intake due to my understanding will in worst case create some cooling water circulation but nothing more .

Further : when we are talking a scenario the genny takes water into the cylinder via the exhaust elbow / high waves etc. Is this not theoretically possible with every genny , regardless if its raw water , fresh water / heat exchanger or even air cooled ?

Best

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 .

 

[BB1]

My gennie sea cock stays open underway, in case the kettle calls. If the sea cock is operating correctly, how can water flow? If it does, then it will run through the cooling system. Your dock mate is mistaken.

It won't run through the system if you have an exhaust waterlock!

 

[BB1]

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

To be honest it depends on the type of skin fitting you have, if the scoop faced forward then you could have a problem, this is why sailing boat skin fittings face aft to stop water pushing up while sailing at high speed.

 

[Bouba]

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