Over proped symptoms?

[bigmac91]

How can I tell if my boat is over proped ? My engine 1gm10 revs freely and pumps out plenty of clean water but under load it won't rev as high and tends to pump out dirty water through the exhaust . Are these symptoms of an over proped engine ?

Using clean diesel, filters the prop and hull are clean .

Thanks

 

[Tranona]

Probably. The 1GM needs to be able to reach at least 3400 rpm, ideally the full 3600. The dirty water is probably unburnt fuel because it is overloaded and cannot reach the required revs for the amount of fuel being pumped in. The engine producers so little power low down and relatively small differences in prop size make a big difference.

Ideally you need to do a series of runs with an accurate rev counter and GPS, preferably in calm tideless conditions and take readings of speed against revs in 200 intervals from 2000 upwards. Expect to get around 3 knots at the lower end and you should get around 5.5-6 at 3400. These are estimates of the typical sort of boat fitted with a 1GM.

You could do a calculation for the prop size using a programme such as Propcalc on www.castlemarine.co.uk. Be aware that there a 3 possible reduction ratios for the gearbox and it is critical that you know which one your engine has.

Hope this helps.

 

[aquaplane]

More info required for a proper answer possibly.

Does it do OK at low revs then get to a speed and won't go any faster?

Does the black (over fueling) smoke start when it gets to that speed and opening the throttle doesn't do any more?

That is what I understand to be over proped.

What's the waterline length and hull speed, does it achieve that?

 

[Bobc]

A typical sign of over-propping is that the engine won't reach it rev limiter and smokes like a destroyer if you put the throttle right down.

 

[lw395]

Props don't grow in pitch or diameter as they get older.
But engines tend to lose power.
The exhaust elbow is a likely culprit.
If it's done a lot of hours smoking, then maybe a de-coke is needed.

Having the injector serviced made a big difference to my 1GM.

A useful test is to see what it will rev to tied to the pontoon. Save a lot of waiting for slack tide on windless days, and you can see if you've improved anything.

 

[ianj99]

For now, just back off the throttle until the current maximum revs drop by 50-100prm. This will reduce the overload condition which you are subjecting the engine too if its left on wide open throttle but can't reach max design rpm.
If nothing has changed then I'd suspect fouled prop, hull not as clean as it can be, or very adverse conditions. (I.e. the engine will likely have been propped to reach max design rpm under ideal conditions and may not reach the same rpm in strong headwind and/or tide)

 

[bigmac91]

Thanks Ian, I'll give that a go

Les

 

[bigmac91]

Thanks, I will try the revs check and the propcalc site

Regards
Les

 

[bigmac91]

More info required for a proper answer possibly.
Thanks Bob

Answer to your questions are

Yes
Yes
21.5feet and no

On that basis the over proped theory is worth checking

Regards

Les


Does it do OK at low revs then get to a speed and won't go any faster?

Does the black (over fueling) smoke start when it gets to that speed and opening the throttle doesn't do any more?

That is what I understand to be over proped.

What's the waterline length and hull speed, does it achieve that?

 

[bigmac91]

A decode is on the cards this winter as I have already renewed the exhaust elbow.
Thanks

Les

UOTE=lw395;6149760]Props don't grow in pitch or diameter as they get older.
But engines tend to lose power.
The exhaust elbow is a likely culprit.
If it's done a lot of hours smoking, then maybe a de-coke is needed.

Having the injector serviced made a big difference to my 1GM.

A useful test is to see what it will rev to tied to the pontoon. Save a lot of waiting for slack tide on windless days, and you can see if you've improved anything.[/QUOTE]

 

[smeaks]

Props don't grow in pitch or diameter as they get older.
But engines tend to lose power.
The exhaust elbow is a likely culprit.
If it's done a lot of hours smoking, then maybe a de-coke is needed.

Having the injector serviced made a big difference to my 1GM.

A useful test is to see what it will rev to tied to the pontoon. Save a lot of waiting for slack tide on windless days, and you can see if you've improved anything. My experience is that tied to the pontoon greatly overloads the engine my engine in the harbour pool with no tide revs to 3300 at WOT but tied up the revs top out at 2600 only is achieved.