[C320-list] Engine Seacock position.

[Scott Thompson]

The issue with cranking the engine without starting it is that without 
the pressure from the exhaust gases, the water lift muffler can't expel 
water. So the water level rises in the muffler and exhaust hoses and 
mixing elbow until it floods the pistons. It isn't a question of 
suction, but rather one of rising water levels in the system. When 
cranked but not starting, the pistons will be pushing unburned air/fuel 
out through the exhaust valves, but without combustion there just isn't 
enough pressure there to expel the water from the system, and so the 
water level rises. The only thing limiting this is the top of the "hump" 
in the hose running from the muffler to the exhaust outlet through hull. 
That is supposed to be well above the water line (to prevent backflow 
into the muffler when heeled or in following seas) and thus well above 
the exhaust valves on the engine. So there is no need for water to "run 
up hill" to flood your engine. Rather it is just like filling a pot 
until it overflows. The problem is that the low point for overflow may 
be your pistons.

The engine CAN fill even when not running if the intake through hull is 
left open and if the antisiphon valve in the port cockpit locker fails, 
which is a good reason to do preventive maintenance on that thing 
periodically. It is important that it open properly when the engine is 
not running.


On 9/16/2013 3:15 PM, Graeme Clark wrote:
> Further to previous replies - I think the point you are concerned about is the engine filling with water -  this will not happen whilst the engine is  not running. the danger is when you repeatedly crank the engine and it doesn't start. The recommendation is do not crank for more than 30 secs ( I think) with seacock open as otherwise the water can be sucked into the pistons.
>
> Bear in mind your engine seacock is  for the RAW water system. That water is pumped through the engine by the impeller and into the exhaust elbow.  The exhaust is above the water line so when the engine isn't running I don't think there is much worry about the water 'running uphill'  into the pistons through the exhaust valves.  However once you start cranking the exhaust fills with water under a bit of pressure and will/can work its way back up to the valves and into the pistons.
>
> The danger with leaving it open is if the hose comes off or splits whilst nobody is there in which cad ethe boat will sink!  before that however the bilge pump will be going like mad, continuously so someone might notice!
>
> Bearing the above in mind we never close it when aboard or off for a short visit but do when leaving the boat for any period of time
>
> Hope this helps (and hope I have understood it correctly!)
>
> Graeme
>> On Sep 15, 2013, at 2:55 PM, swampcreek42 <swampcreek42 at yahoo.com> wrote:
>>
>>> I read somewhere that it's recomended to close the engine seacock if your leaving the boat due to the risk of the engine filling with water but we always leave it open when sailing because we might need it at a moments notice, I would think if the engine was to fill with water it would be more likely bouncing and leaning underway. I never closed the seacocks in previous boats. Is there a preferred procedure on this?
>>>
>>> BTW, today was the last day of our week of sailing the Chesapeake, next year I think we'll take 2 weeks...I'm just starting to relax and it time to go back to work!
>>>
>>> Thanks,
>>> Bruce
>>> Nauti Time  #719.
>>>
>>> -------- Original message --------
>>> From: tharrison at innovations-plus.com
>>> Date: 09/15/2013  3:44 PM  (GMT-05:00)
>>> To: C320-List at Catalina320.com
>>> Subject: Re: [C320-list] America's Cup Racing
>>>