Run engine whilst on trailer without hose access

[joydivision]

Morning All, this is my first post since moving from the old site, its great to be back.

Don't ask why, but we have a requirement to fire up and run our engine whilst the boat is on the trailer. We would usually run on muffs from a hosepipe, but this currently isn't an option.

Is there an advisable way of running using a water butt as a water source or maybe even dropping the leg into a large bucket barrel type thing.

Has anyone done this? Is it possible?

Thanks,
Richard

[Ianfs]

Hi Richard
Good to see you back.

My first thought is how big is your engine? A small outboard no problem but a stern drive or bigger outboard would need a very big barrel or tub so how would you fill it without a hose? Plus if you bought a dustbin and had to fill first it would be extremely heavy.

[joydivision]

Ah yes, that information would be helpful!

It's a Mercruiser 4.3 Sterndrive, so quite big, but I'm thinking that the barrel/bucket would just need to be big enough to submerge the inlets where the muffs would usually go?

I have access to a tap nearby, but the tap is of the type that you get in toilets where you push down to turn them on and they turn themselves off after a few seconds. The shape of them makes it impossible to connect a hose too.

I have a couple of those gorilla buckets which are about 40Litres, my thinking would be to fill one of these, lower the leg into it, turn the engine over to suck up the water, top up the bucket and then try and run. I'm not sure if they would be big enough though. Wickes also do a 50cm by 50 cm bucket that could well do the job.

[_Ed_]

I use a loft water tank, to test my OB's in. fill it up to the cavitation plate and it also keeps them much quieter Works fine.

[joydivision]

Awesome cheers Ed, I can't see why it wouldn't work as long as I keep an eye on water levels and make sure it doesn't overheat. I'll let you know how I get on!

[_Ed_]

It works fine. Just keep it above the low water intake. One thought I do have however is I dont know where the water pump is on those engines. If its in the leg you should be ok, (like outboards) if its on the engine, it may rely on the fact the boat is sat low in the water to start pumping. That I'm not sure of.

[Cap'n Jack]

OK that would work. Might take a bit of time to fill it though and wouldn't last long running in the Summer, maybe 10-20 mins before it would get hot, but it would clean it through.

The water intake on stern drives is just below the Ventilation Plate, that's the lower one often mistaken as a Cavitation plate!

Just a thought, a square metre of water weighs 1 tonne.

[_Ed_]

Strange I've only ever heard it be called a cavitation plate.

https://www.google.co.uk/search?q=boat+ ... 5&bih=1194

[Ianfs]

Sorry Ed, I don't know why I hadn't spotted your post, but no, I'm certain that the lower plate on either a stern drive or outboard is actually an Anti Ventilation Plate and not a Cavitation Plate as a lot of people like to call it as a colloquial name.

I'm sure it is supposed to reduce ventilation when the prop rises in the water after a boat goes faster and therefore help prevent the prop from ventilating.

My reasoning is this and if I'm wrong then my old adage is, you are never to old to learn.

Cavitation where a propeller is concerned is where there is a pressure reduction on the front face of the blade, which can often cause burning. A good propeller will have reduced pressure but not enough to cause cavitation, on the other hand one which has been damaged or misshapen can produce enough pressure reduction for the water to boil on the leading edge, then on the leading face create water vapour, the bubbles work there way to the centre where they implode. I'm told they are powerful enough the cause chipping and burning. It has always amazed me that if you reduce atmospheric pressure enough water even at 10c will boil.

I would say that the plate above the prop would have no real impact to prevent this and the only reason I can think it is called a Cavitation Plate by some people is the creation of the bubbles.