Originally Posted by miabellabrian
Ok, lets look at the facts again. Firstly I said I thought the boat was over propped from the beginning, and as I have come to learn this can be proven by the fact that it revs higher in reverse than in forward.(lower gearing in reverse).....?
Whoever gave you the above gem of knowledge has got it completely wrong - sorry to be blunt
You may well be overpropped but this is not the way to confirm it. Many boats rev faster in reverse even if correctly propped.
A quick and dirty test is to motor
in flat calm conditions at WOT with a clean prop, a clean hull
and a good engine
. With the right sized prop, you should get very close to max rpm
as specified by the engine manufacturer. Unfortunately you can't do this right now as you don't have a good engine
The proper way to compare your actual prop to that as specified by the prop manufacturer for your hull
type and engine model.
Please note, this has nothing to do with hull speed
, you will probably reach hull speed
well before max rpm
Here are some numbers that demostrate the above. My boat IS correctly propped and I have a 12 yearvold 2GM20
in as new condition.
With clean clean prop and clean bottom in flat calm conditions, I reach hull speed around 2700.
At WOT, I just make 3600 with no smoke.
With slight (normal) bottom fouling, I get 3400 with light black smoke.
Tied to the jetty and with a clean prop, I get 3200 at WOT and noticeable black smoke and a slight sludge on the water
. With a slightly fouled prop, I just make 3000 with considerable black smoke and carbon/diesel sludge on the water
You should get similar numbers if you have a 2GM20 except you will reach hull speed sooner. At a guess, maybe 2200 to 2400. If you have a 2GM
, I THINK you could reduce all the above rpms by about 300 or so.