Propping a 225

I know there is never a simple answer to this one however I am going to be re-propping the 225 fitted to my 22foot rib.

The Rib weighs about 1500KGs without any passengers so with 3 up about 1800kgs. I am currently getting a miximum speed of circa 50mph which is not too bad although on my last rib which was exactly the same type but 2 feet shorter and maybe 150kgs lighter I used to get the same speed with an E-tec 150 running a 19" Stainless Viper Prop.

Sooo..

I am currently running a 21" Laser II Prop and I believe I am seeing between 5-5,500 RPM fully timmed out at full throttle (need to fit new tacho). The laser has the large hole vent bungs fitted.

My midrange cruising is the bit I am most concerned about as fuel consumption is IMO too high. THe Evinrude used to give me about 1 litre per mile at 30-35 knots. THe Honda gave me about 1.5-1.6 litres at the same speed.

I read this article http://www.boatpoint.com.au/features/2002/honda-bf225-vs-yamaha-f225-8434 which was interesting and seemed to suggest a larger diameter prop is better for the Honda due to its larger and less efficient gearbox design. The laser I think is 14" diameter so I guess perhaps something like a Mirage at 15 1/4" by maybe 19" pitch might be a better bet?

I have just raised the engine a couple of notches too so first things first I am going to fit the new RPM gauge then run some trials with the current prop. I also have a set of vent plugs that block off the holes on the Laser to try as well to see if this makes any difference.

I will post the results when I get a chance to take the boat out however if anyone can share any suggestions I would be grateful !!!

Chris

Chris - you are just going the need to experiment with the props. Keep in mind that the 225 has an rpm limiter at around 6000 to 6200 rpm. You want to be at just 6000 rpm at wide open throttle to get your best efficiency. The largest possible diameter prop for the 225 is 15 3/4 inches - most are in the 14" to 15" diameter range, so your experimentation will mostly be with the pitch. Early on, I charted my efficiency curve by recording gallons-per-hour at different rpm's. You can record that in an Excel spreadsheet, and chart the curve. My particular engine and boat combination (6000 lbs) is most efficient at 4600 rpm with a 14.5" X 15" prop.

Hi there,

The current prop is probably 13.5" diameter and 21" pitch...

I was suggesting that running a bigger diameter prop and reducing th pitch might be a better option. If you read the article is seems to suggest this is a good idea with the Honda due to the dynamics of its gearcase.