Cooling water inlet. Which way round please?

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hannahman

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Some advice please.

The cooling water inlet grill on the hull of my Hillyard is best described as being shaped like a pear shaped anode, and is fitted to the hull in the same manner, ie 'fat' end forward most.
Now I'm wondering if this is the correct way round, or do you think it should be turned round the other way to act more as a 'scoop', or is it designed so that it should be the original way round as I first described, perhaps where there is less of a chance of trapping weed/muck etc?
The engine in my boat (a raw water cooled Petter 2cylinder diesel) has always run rather hot, sometimes with quite a bit of steam from the exhaust. There has been some scaling up of the water pipes, which I expected, being direct cooled, and at the moment these pipes, together with the water pump and thermostat are off the engine for checking and cleaning/overhauling as neccessary.
I was just wondering whether turning the inlet fitting around would help or hinder.? I assume there is a correct and incorrect way round?
Any advice gratefully received please! /forums/images/graemlins/smile.gif
 
I would say you might have an inlet scoop strainer fitted the wrong way round. The long slope with the grating on it should point forwards. In the case of an inlet scoop the grating would only be in the leading slope and the aft end would be solid to deflect, or scoop, the water into the inlet pipe. These are standard equipment for fast boats, over 12 knots or so, to provide adequate water pressure. On slow boats this isn't necessary.
If the strainer is separate to the skin fitting I would consider dispensing with this outboard strainer altogether (they get clogged with barnacles and/or antifouling), assuming you have a good strainer before the raw water pump inside the boat. If it is integral with the skin fitting then make sure the grating is clean and of adequate open area; 3mm wide slots or round hole perforations. And pointy end forwards!
 
I fitted one on a friend's boat... the old one is long gone, so no reference there.
After walking around the marina hard I was no wiser... they were fitted with the "sharp" end going either way on a variety of boats, including new AWB's.
In the end I fitted it with the fat end aft, theorising that any water pressure would push in, rather than suck out.
Its probably academic, but if the shape is working against the intended flow then the pump will have to work herder, nes pas?
 
The rule is, motor boats have the inlet (scoop) facing forward as they generally go forwards when the engine is running.
Sailboats always have it facing aft, as when sailing the ram effect can on some installations force water in past the pump and fill up the exhaust pipe and pot which can then enter the cylinders, which will cost lot to repair as soon as you turn the key to start.
And the forward motion when motoring with a sailboat with a rear facing inlet is not enough to hinder seawater pump from sucking in sufficient water.
Whereas I once went onboard a V8 engined sports boat and the guy had done the installation himself, and as soon as he hit 25 knts the engine overheated, I sat in the engine room as he drove and saw the rubber inlet hose slowly collapse flat starving the pump as he approached 25 knts, the suction over the intake overcame the suction of the pump at this speed as you guessed it he had mounted the inlet 'Backwards' on a motorboat.
 
Absolutely correct. The theory being that the inlet grill is much less likely to pick up weed and muck that way and the lower hydrostatic pressure at the aft end tends to keep it clean.
 
[ QUOTE ]
The rule is, motor boats have the inlet (scoop) facing forward as they generally go forwards when the engine is running.
Sailboats always have it facing aft, as when sailing the ram effect can on some installations force water in past the pump and fill up the exhaust pipe and pot which can then enter the cylinders, which will cost lot to repair as soon as you turn the key to start.
And the forward motion when motoring with a sailboat with a rear facing inlet is not enough to hinder seawater pump from sucking in sufficient water.


[/ QUOTE ]

Spot on.

Iain
 
Thanks very much for all your good advice, everyone.
It seems then, that it is indeed the right way round.
My friend who took the water pump away to dismantle and check, has confirmed that it is quite worn and in need of replacing or overhauling, so hopefully with this job done, and the descaled pipes and fittings back on, things should be improved. /forums/images/graemlins/smile.gif
 
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