Over propping that causes black smoke WILL cause premature engine problems, as well as excessive fuel
As a mechanic
with 50 years experience I have come accross a few examples of this. The black smoke is unburnt fuel
. It can be caused by many engine problems- poor compression
, incorrect injector pump
timing, old fuel not burning correctly, etc. However with regards to props and underwater boat condition, there are a number of issues also that can be a real problem, when we know all's well with the motor
Obviously, as has already been spoken about, it's paramount the hull
and prop itself is clean and free from barnacles
, weed and slime, as all this will affect engine performance, boat speed, manouverability and fuel consumption
dramatically. I had a Cloud 9 Catamaran
in the 90's, lived aboard and cruised for 7 years. During that time I replaced the 2 blade
fixed props with a pair of Australian designed and made "Autostream" 3 blade
feathering and fully adjustable props. The differences were noticed immediately.
Vibrations were reduced significantly, better cruising speed and fuel economy. The great thing about these props was that you could adjust the pitch
individually for forward and reverse! Now I guess not everyone is happy to hop over the side with a 1/2' spanner and stumpy blade screwdriver to play around with prop pitch! But what a chance to get the best from your prop, ehh! I was able to set the props pitches for each motor
in forward, AND set a different pitch
for reverse also. As we all know, it's great to come into a marina and have your boat stop when YOU want it to! I could in fact wind
up the pitch so far in reverse as to actually stall the motors! Having had this experience really gave insight as to the importance, again as has already been mentioned, in getting the correct balance of RPM, boat speed, and economy from your prop/motor combination. It is correct that if you cannot get to rev the motor, under load, to good maximum revs, you will find carbon and any build up of soot/unburnt fuel will cause premature engine repairs
, particularly when the said motor is used less frequently. You know when WE get in a groove with our life that seems all a bit blase?
Each day seems to "glaze" by. Then we get out and have a great day by doing something really out of the box, give the body a real shake up, and we feel refreshed, invigorated, got a life again!
Well- believe it or not, that's what happens to your motor sitting on the same old revs, every time you start, and sit it at?? 2000 or whatever. When you get it warmed up and then give it a big flat chat run..it blows all the cobwebs out and presto! It can breathe better, operates cleaner and has helped unglaze the cylinder bores, get junk from behind the rings, which is the most common cause of loosing compression
, and generally removes a lot of crud built up throughout your whole motor and exhuast system!
Now if your prop is restricting you from giving this treatment to your only source of alternative propulsion
...MMM. This is why commercial
motors in any transport area last a looong time. No chance to glaze up bores, and in many cases even cool down. For me, I would look at repitching your 3 blade
prop down to suit your needs. Why go back to a 2 blade
with less propulsion and more vibes?
Hope this hasn't been too long of a drag /post! Regards, Paul.