Do I need a 'scoop' on the engine water intake ?

whipper_snapper

whipper_snapper

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Do I need a \'scoop\' on the engine water intake ?

I am about to fit a new through hull for the engine raw water intake. All that is immediately available is a 1" bronze with a plain hole as opposed to the traditional scoop with slotted screen. The existing system is half inch with a screen and scoop.

I am not worried about the screen - I will have an inline filter. But I wonder how important the scoop is ? It is perhaps 1 foot below the water line and the boat is reputed to to reach 12 kn on a good day. At those speeds, will the lack of a scoop mean that the engine can't pull enough water in ? The engine is perhaps 3' above water line, so we are already asking a lot of the raw water pump.

Thanks
 
Re: Do I need a \'scoop\' on the engine water intake ?

Scoops are often perceived as bad, raising the possibility of flooding the exhaust and engine with raw water. If you are replacing an intake that has a scoop however it may be worth some professional advice to see why it was fitted in the first place
 
Re: Do I need a \'scoop\' on the engine water intake ?

For my new engine, the manufacturers, Westerbeke, stated that any scoop must be removed. In any event, the grill thing is a waste of time as it gives a lovely safe home to the little wrigglers, whom you can't evict easily.
 
Re: Do I need a \'scoop\' on the engine water intake ?

On my old boat the engine would overheat due to lack of water when pushing a strong current and I thought at first that a scoop might stop the water whizzing past the intake. When I got a new engine with a decent water pump the problem went away. Suck is better than scoop.
 
Re: Do I need a \'scoop\' on the engine water intake ?

scoop indicates wrong thinking - the slatted bit is fitted so that its downstream. its there to prevent things getting up the intake and if its facing up stream you can easily get a piece of plastic, for example, held onto the slats by water pressure and suction.

personally I would always used one of the slatted intakes - much less likely to get blocked IMHO
 
Re: Do I need a \'scoop\' on the engine water intake ?

Agreed in principle but make sure that the slats and hull within are well antifouled. Last year mine was very nearly blocked by growth of of weed with small 'bubbles' in it.
 
Re: Do I need a \'scoop\' on the engine water intake ?

The slotted "scoop strainer" devices are meant to be fitted with the slots facing aft on sailing boats, and with the slots facing forwards on power boats. They're not really intended to force water into the engine.
 
Re: Do I need a \'scoop\' on the engine water intake ?

> .... scoop indicates wrong thinking - the slatted bit is fitted so that its downstream.> >

New one on me. All the Westerlys and many other boats I've seen have the grid facing forward and it's the same on mine. I suspect it has next to nothing to do with providing a 'scoop' effect and more to do with deflecting rubbish.

Turning it the other way though might mean the water forming a low-pressure point aft that the pump then has to overcome. Not a problem, but unnecessary.

From a water input point I doubt if it makes much difference either way, though I would definitely not have a straight hole in preference to the grid. It's all very well to say 'I have an internal filter', but once the rubbish has got into the inlet piping, it may well not even reach the filter!
 
Re: Do I need a \'scoop\' on the engine water intake ?

OK, thanks all. I will not worry.

I could not picture how much cavitation and turbulence at reasonable speeds would impede suck - obviously not much.

As others have said, I am very dubious about the slots. They always seem to fill with dead barnacles and other crud. And anyway, we don't have plastic bags in the water here!!!
 
Re: Do I need a \'scoop\' on the engine water intake ?

[ QUOTE ]
New one on me. All the Westerlys and many other boats I've seen have the grid facing forward and it's the same on mine. I suspect it has next to nothing to do with providing a 'scoop' effect and more to do with deflecting rubbish.

[/ QUOTE ]The logic behind having the slots facing aft on a sailboat is so that water isn't "forced" into the engine whilst sailing. On power boats, the reason for having the slots facing forward is to enhance water flow, but the intake seacock has to be turned off if the boat is moving without the engine running (eg under tow, or if a twin-engined boat is motoring on one engine).
 
Re: Do I need a \'scoop\' on the engine water intake ?

I've had a plain intake block dueto weed or plastic or something, I was grateful that the strainer was straight in line so I could quickly poke the blockage with a long screwdriver.
When the slatted sort do get blocked it can be a nightmare, and its more likely to be a slowly worsening problem that catches you out, as the flow drops below what is needed.
Is your whole engine really 3ft above lwl?
Cheers,
 
Re: Do I need a \'scoop\' on the engine water intake ?

Thanks pvb. You are quite right of course, and on reflection it was daft question!

A scoop shoveling water into a stopped engine as we surf down waves at 12kn+ is obviously a Bad Thing.

(Yes lw395, the engine's water pump is close to 3' above the water.)
 
Re: Do I need a \'scoop\' on the engine water intake ?

Agree. That is the arrangement I have, although it puts the intake in an awkward position. The grids not only make clearing difficult but a few years of AF soon close the slots and the devil to clean.
 
Re: Do I need a \'scoop\' on the engine water intake ?

would water be forced passed he impeller if the valve was open and engine not running> I doubt it, but would like to hear opinions.
 
Re: Do I need a \'scoop\' on the engine water intake ?

[ QUOTE ]
Agree. That is the arrangement I have, although it puts the intake in an awkward position. The grids not only make clearing difficult but a few years of AF soon close the slots and the devil to clean.

[/ QUOTE ]

Yes, it seems the main objections to a 'grid' is that of keeping the 'nasties' out. Others, like me, in the yard, get over this by simply anti-fouling inside the grid each year. We use a small 'artist' type paintbrush that fits into the slots and makes it relatively simple to ensure the vast majority of the metalwork is coated.

I have had the grid intake type for the last 47K+ miles and not once had the grid got anywhere NEAR clogging up, but, just like anything else below the waterline, it will get fouled if not protected. A couple of friends who didn't bother for a couple of seasons, had no difficulty in clearing some small barnacles that had made their home inside the grids. Cleared them in exactly the same way as one would with a straight hole.

Incidentally, I agree with tabernacle_man's thoughts, I cannot see how water could be forced as far as the engine by the scoop 'pressure', which even at ten knots, would be tiny. If one has a Vetus type filter as well, I would suggest it's virtually impossible. Be interested in others views - and reasoning.
 
Re: Do I need a \'scoop\' on the engine water intake ?

[ QUOTE ]
would water be forced passed he impeller if the valve was open and engine not running> I doubt it, but would like to hear opinions.

[/ QUOTE ]The advice I quoted re direction of the slotted intake comes from Volvo Penta, who know a thing or two about engines! /forums/images/graemlins/wink.gif
 
Re: Do I need a \'scoop\' on the engine water intake ?

So why would Volvo Penta bother to give the advice? /forums/images/graemlins/confused.gif
 
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