E-tec 75 on 16ft RIB, prop question

[Daba]

Hi all from Croatia!

I have an 75 e-tec for two years now and I am very pleased with it. People ask me just to fire the engine an let them hear how quiet it is! They just cant't belive it is a two stroke.
It is mounted on 4.85 m (16ft) RIB . Initialy with the original prop (13 3/4 x 15) it hit the 5500 rpm so I bought 14x17 (no try befor you buy here ) and rpm's dropped to 5200 with speed of 32.5 knots.
I have just read another post here (75 e-tec 4 months report) with the sugestion for an 19 inch prop and the optimal revs 4500-5000.
Could someone suggest an 19 inch prop for me please.
Btw. I am very sad to inform the BRP guys that here in Croatia we have to pay around 65$ for a galon of XD50 oil (through regular BRP service network) so I don't even consider switching to XD100.

Best regards and thanks in advance!

Mladen

[ChampioNman]

We are truly international on this board, I need to put a sticky pin on the country of Croatia! Welcome to the BBC!! The Aussies, the Irish, the Swedes and now the Croats! My how this little link has grown I sometimes feel like I work for BRP customer service ! DABA to answer your question what is the motor height on the transom, Not sure what a rib boat is if you could post a link so we could check out the hull I'm sure we could give you a better definition. Sorry that the exports are so high for your OIL but with the 75 after break-in that should last you almost 2 seasons depending on usuage. CM

[RUSTY63]

Welcome to the BBC.

From you post I don't think you will be able to turn a 19 pitch prop, it will pull the RPM's to low on your motor.

The operating RPM range on your motor is 4500 to 5500, you want to prop it to run towards the top of the RPM range, with the 19 your RPM's will be around 5000.

[Daba]

Thank you all.
I can't tell you exactly the height because I am on the continent at the moment but the anticavitational plate is in plane with the keel. RIB is an rigid inflatable boat. Hull is a deep-V. Here is the link: http://www.adboats.hr/eng/infl...0.htm

RUSTY, I am aware of the operational range but the guy in that post mentioned a "sweet spot" between 4500-5000 rpm. It sounded a bit strange but I had to ask.

The gas mileage is 0,75 NM/l (5,8 MPG) with 4000-4100 rpm and I don't think that's optimal. I was wandering about a prop with a smaller diameter (the hole shot is exceptional now and I don't need it that much) and more pitch.

Thanks!