Correct Prop Size

[24gradyexp]

Boat is a Grady White 24' Explorer weighs about 3800 lb. Motor is Merc 230 EFI fuel is 150 Gallons. Motor is a 30" Shaft mounted all the way up as previous motor was 25. Current prop is a mirage plus 15 1/2 x 17. I can only get about 2300 rpms out of it and the boat does not plane. Motor sounds really bogged down above 2000 rpms. Need to change prop.

 

[andy6374]

Re: Correct Prop Size

First check that anti-cavitation plate, which is the plate on the lower unit just above the prop. That plate should be level or maybe an inch above the very bottom of the hull. If that is fine it is probably the carbs. You need to disassemble the carbs and clean them.<br /><br />Clean the carbs before buying an expensive new prop.<br /><br />-andy

 

[24gradyexp]

Re: Correct Prop Size

Motor is EFI, Cav plate is about 1" below bottom of boat. Should affect Top speed only by a few mph which is good enough for me.

 

[andy6374]

Re: Correct Prop Size

Yes 1" below is fine.

 

[Bigjohn1]

Re: Correct Prop Size

While your current setup will do, you are really handicapping yourself with the cav plate that low in the water. You are dragging around over 2 extra inches of skeg in the water and it is hurting your fuel mileage, time to plane, and both WOT rpm's and WOT top speed. If you can raise that motor up about 2 - 2.5", it will feel like an entirely different boat. The Mirage prop can handle it and should not ventilate. Do you know why a 30" shaft engine was mounted on the boat?

 

[24gradyexp]

Re: Correct Prop Size

Thanks Bigjohn1<br />I bought the engine with full intentions on either converting it to 25" or installing a jack plate as I was not sure of how it would run or sit on the bracket. I will be going with a jack plate as this engine just like the last (Johnson 225 with 25" shaft)hits the rub rail when tilted. But I want to just prove that this rig will work and before I sink any more money into it. This motor should have enough power to plane it for now so I will now be looking at the ignition and fuel systems as that's where we believe the problem lies. Have a Navscan Flowmeter that use to alarm the Johnny for fuel flow but I thought that that was because the motor was beat and just sucking down fuel. Maybe bad transducer. Will remove and test for kinks as well as hook up a timing light to check for fire on all six. Been told that outboards w/o load can run very smooth as long as there is no load on them with low fuel flow or a missing bank. Time to look further.