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Old 13-07-2018, 09:05   #31
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Re: Has anyone solved the Fischer Panda riddle?

A lot of water vapor is generated by combustion,on a Spencer 35 with a gas Grey Marine and a long water jacketed exhaust pipe, it would load the number four cylinder with water if you did not run it long enough to reach operating temperature. Tough old industrial motor would,with NGK tractor plugs, just blow out the water and start. Don't know if that would be a factor or if wave action on the exhaust would create enough back pressure to force to the engine.
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Old 13-07-2018, 09:14   #32
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Re: Has anyone solved the Fischer Panda riddle?

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Originally Posted by stargate View Post
A problem I have had on a vessel, was the intake thru hull fitting. It actually caused water to be forced up the intake line when the boat was moving ahead. Thus slowly filling the exhaust system and eventually into the generator engine causing it to hydraulic.
The solution was putting a valve just before the water pump to prevent this, and a sign to remember the valve. You had to open this valve to run the generator and close it when you shut it off.
It was a strange phenomena and only happen the one time before putting the valve there. The boat had run fine without one for a few years ?? It was strange, but it did happen.
Just food for thought
Dear Stargate,


You raise an interesting and important point. My guess is that the raw water intake scoop was facing forward, so that there was a ram effect whenever the boat was moving. It's well-established good practice to set the scoop for the propulsion engine facing aft on all sailboats, as they are occasionally moving without the engine running and pumping the exhaust system clear, but even on a power boat, I recommend setting the generator scoop facing aft, as the boat's forward motion may be ramming water into a forward facing scoop when the genset engine is not running.


Many Thanks
John Mardall
Vetus Maxwell Boat Equipment
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Old 13-07-2018, 10:46   #33
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Re: Has anyone solved the Fischer Panda riddle?

What I didn't see (missed it maybe) is mention of the raw water injection into the exhaust. Usually there is a pipe from the cooling water to the exhaust elbow. When the engine is off, depending on the height of the cooling elbow and the outside water level, raw water in the heat exchanger can flow through the cooling system and into the exhaust pipe (it siphons actually) and if it fills the exhaust pipe, and then fills the exhaust manifold then it can flow back into the area of the head where the exhaust valves are. If one valve is open water will fill that cylinder.

To check this you only need to un-do the raw water injection hose from the elbow and move the end up or down to see whether and at what point cooling water runs out the disconnected hose. Keep in mind that the exhaust elbow may have an extension to the cooling water tube inside of it, effectively making the end of the hose a couple inches lower than where it connects.

Even if the engine is above the exterior water level the raw water in the heat exchanger and other parts of the system can siphon to a lower level through the raw water injection hose into the exhaust and if that level is above the exhaust valves...trouble.

The solution is to put a siphon break in the raw water outlet before it enters the exhaust elbow. I run the water hose up to a cockpit drain and put a small ball valve there which, when open, allows a small amount of cooling water to go into the cockpit drain, (which I can monitor by looking down into the drain) and then the hose goes back down to the exhaust elbow. Some people put that opening into a galley or head sink. When the engine is off air flows back into the hose breaking the siphon.

This solved the problem I had with water getting into the cylinders.
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Old 13-07-2018, 14:18   #34
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Re: Has anyone solved the Fischer Panda riddle?

This is probably why almost all commercial fishing vessels use a dry exhaust system for their auxiliary as well as their main propulsion engines.

If you must add sea water to cool the exhaust gasses and rubber silencers and plastic bits---make sure that the outlet to the sea is just above waterline and that the water is admitted well below the level of the exhaust manifold--regardless of whatever else you have in the exhaust line. You will have a little more heat in the engine room--but a lot less trouble.

Personally, I would rather vent the auxiliary via a covered stainless outlet alongside the dinghy davits and run a dry system, with the stainless pipes EXTERNALLY water jacketed to cool the gasses a little in the engine room..
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Old 13-07-2018, 16:52   #35
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Re: Has anyone solved the Fischer Panda riddle?

Issue with dry stacking is your exhaust has to be able to withstand 1200F at least, whether itís water jacketed or not, the interior is still hot, so out goes the rubber hoses and fiberglass mufflers.
Itís also usually louder, but you donít have to have water injection to be quiet, listen to a motor home generator.
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Old 13-07-2018, 16:55   #36
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Has anyone solved the Fischer Panda riddle?

Quote:
Originally Posted by JOHNMARDALL View Post
Dear Pilot,


A rubber flapper helps, which is why we install them on most of our transom exhaust fittings, but they are no substitute for a gooseneck in a properly designed exhaust system. By the way, I should have said in my first post on this subject that the determining factors for the size of the waterlock are the exhaust hose diameter and the run from the top of the gooseneck down to the waterlock.
Please let me know if you'd like a PowerPoint on wet exhaust systems.


Best Regards
John Mardall
Vetus Maxwell Boat Equipment


Understood, my generator is above waterline, but I still have a couple of feet of gooseneck, and a vacuum breaker.
However I have heard of a few sailboats that were properly designed, still get salt water enemas if you will from following seas, quite probably a flapper valve may have prevented that.
On another note, anybody know were I can get a 2.5Ē flapper valve? I canít find one less than 3Ē.
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Old 13-07-2018, 20:07   #37
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Re: Has anyone solved the Fischer Panda riddle?

Have also heard that difficulty in starting and prolonged cranking of the engine will cause water lock to fill and possibly flood into chambers before being expelled.
Was just purusing and added my two cents
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Old 14-07-2018, 18:19   #38
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Re: Has anyone solved the Fischer Panda riddle?

Hi, I had exactly the same on a genset powered by a Kubota 3cyl diesel. It was caused by a fault in the exhaust elbow. Better known as a mixing elbow. Where the cooling water entered the elbow upon exiting the heat exchanger and is mixed with the exhaust gasses there was an internal extension to that tube that carried the water away from the manifold. This had corroded off inside and allowed salt water to back flow into the manifold when the engine stopped. I had a new elbow made slightly longer and with the internal tube carrying the water well clear of the manifold. Problem solved. It took a while to find as the elbow looked perfect from outside. Because the cooling water entered a bit further out I lagged the elbow.
Regards
Danny
Amel Super Maramu 299 Ocean Pearl
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