Prop Suggestions? 89 Bayliner 21ft 3400lb 5.8L

[garfieldreturns]

Anyone would like to make any sugestions?

The prop on this boat is mangled (15X17 Michigan aluminumium).

Boat is a 21ft bayliner 2155 ceirra. It sayes 3400-4000 rpm.

Most of the gauges are faulty are it planes at 2500rpm, at 3000rpm syes going 35mph. And I am passing everyone with a newer boat.

Previous owner sayes he pulled 2 water skiers at same time. Probably to big a motor for such at small boat.

I am after fuel efficiency, best prop for that.

Any ideas? The doctor v2 online prop program says to use a 14 1/4X21 for water sports, or a 14 1/4 X23 for extreme speed. (that includes adding another 500 ibs for ods and sodes)

I just want to get best gas efficency, only need to pull one skier, and don't want to scar myself to death by going 65mph+

Motor runs great, so far used about 30 hours since changed pluges(platinium) oil filter, thermostat, water pump in the stern drive, oil still looks like new.
Has a 4 barrel holley carb on it also.

I am going to convert it as soon as I can to electronic ignition as have read that get another 25hp.

Hope this is enough info to help me out here in SC.

Any suggestions/ideass would be appreciated.

The gauges

 

[steelespike]

Re: Prop Suggestions? 89 Bayliner 21ft 3400lb 5.8L

You really need to confirm the tach is accurate.You can use a dwell meter.
Perhaps you can borrow a gps for more accurate speed.Without accurate specs you really can't make prop change and if you do make a change you won't know if you are within rpm specs.Very inportant for motor health to stay within range.You said "it says 3400 -4000rpm"
Did you mean it makes that or that is the recommended rpm range?
(sounds low for both)Selecting the prop that gets your max rpm at wot(wide open throttle)will help mileage. Your motors GPH(gallons per hour) at wot will be approximately 10% of the hp. if 240hp it would be about 24gph.
Best pratical mileage will be somewhere between just on plane and about 2000 rpm higher.careful experiment with speed and fuel observation will determine the best speed.The online prop figures you got sounds like the range to me.The 17 seems really small and if the accurate rpm stays within range with the 17 I would be surprised.