When getting over the hump to planing speed smoke question.

[Joe Monaco]

I recently changed props (I posted before after the info on this forum) and I’m wondering about the smoke getting on plan. Old props 4 blade 20×24 The new props are 3 blade 22×23. I think I’m getting more black and some noticeable white smoke coming onto plane (after trolling a few hours @ 850rpm) than I did with the old props. Would this be expected/normal because of the 2 inch increase in prop diameter?

The motors are CATS rated 420 HP at 2800 rpm. Both motors (checked with laser) turn 2850 with both the old and the new props. She now still gets to 2850 but it takes a little longer than with the old props but the boat is also going 3+ knots faster.

Once on plan there is no detectable smoke trail just white smoke in the prop wash that dissipates. Am I over thinking? How much black/white smoke is too much getting on plane?

Thanks!

Topic

[Joe Monaco]

I worked with Jim @ ACME props. I was looking for better performance and range and thought my 2002 boat’s stock props were not performing based on what I was reading about similar boat’s with less HP motors running ACME props. The boat has 420HP 3126 MUI motors. You’re right I need to get fuel flow numbers and see where I am on the HP curve at my cruise power setting.

I picked up about 50 NM range on a 350 gal tank, which is significant and the boat can easily cruise fully loaded loaded at 20.5 – 21 KTS at 2100-2150 RPM (which is normal for me) but I’m wondering about how much loading “smoke” is normal while getting on to plane. I may be obsessing.

I posted the speed RPM numbers again here but need to install a fuel flow device to really understand what’s really happening load wise at cruise. Just been procrastinating.

[Tony Athens]

Transient acceleration smoke is common.. Obviously you are asking more power from the engines at equal RPM’s than you were before. 2″ in diameter is MAJOR——————-Why the change? Who was guiding you in this prop change endeavor?..

As to “HOW MUCH” smoke?–That is way too subjective to answer..

As to WOT–Who cares?–Do you run around at WOT? It’s cruise RPM’s and load that matters.. Compare your GPH to the factory prop demand curve at 2200-2400 RPM.. That’s what matters if you are concerned about engine life..

What exact CAT model?

Tony

Tony

[Author]

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