5.7 mercruiser correct prop

[FishnFreak75]

I have a 21 foot seebold eagle with 5.7 mercruiser 350. Can anyone tell me what the factory prop specs should be? It has a ss 14.5x22 on it now. Boat has no bottom end power and takes forever to plane off. Once it planes I cant trim it up much before it porpoises like crazy. I can also tell that it is running under rpm. Any input is great. Thank you

 

[Bob_VT]

Re: 5.7 mercruiser correct prop

You need a lower pitch prop to run at the correct rpms. The porpoise effect can be any number of things...... loading, trim, got water in your hull?

 

[FishnFreak75]

Re: 5.7 mercruiser correct prop

You need a lower pitch prop to run at the correct rpms. The porpoise effect can be any number of things...... loading, trim, got water in your hull?

Ok, Marina says the prop on it is way to big. They say go to a 14.5x19. Sound correct?

 

[Slip Away]

Re: 5.7 mercruiser correct prop

Or 14 x 20p 4 blade for better holeshot.

 

[jestor68]

Re: 5.7 mercruiser correct prop

It would be helpful to know what your present WOT rpm is.

Slow acceleration doesn't necessarily mean wrong prop size. It could be the nature of the beast(boat). Seabolds don't exactly jump on plane when propped correctly for top speed.

 

[FishnFreak75]

Re: 5.7 mercruiser correct prop

Wot is 4000 rpms

 

[tpenfield]

Re: 5.7 mercruiser correct prop

The 19P sounds about right.

 

[mercruiseralpahmaniac]

i have a 26 ft Thompson with a small block chevy with an alpha one. fully loaded the boat weighs about 7000lbs i had a 15.25 x 15 three blade prop and at 5k rpm it will go a whopping 20mph. I had a 15 x 17 on it and i could get 30mph at 4500 rpm. so i had a couple of questions. 1) how much prop is to much for my boat and 2) what will be the result if i go to a 19 pitch? what i mean by this is will it be impossible to get out of the hole or will it be a good middle of the road prop

 

[blamtro]

This may help you:

Boat is 20ft Sea Ray bowrider with Merc 350 260 hp V8
1st choice:
Michigan Wheel Appollo 4 blade stainless 14 3/8 x 18. #993204

Backup:
Michigan Wheel Vortex 3 blade 14.5 x 19 Aluminum. #992004

More info, had some more time to go test and swap props while on the water so all these numbers were taken within 20 mins of each other. 85 and sunny out, little to no wind, no chop, only ripples, all MPH # are gps. Drive was trimmed to the same setting according gauge, probably 75% of all the way in. Used that position for both prop tests. Although it was just me and 1/2 tank of fuel, I would expect these numbers to have a greater difference in favor of the 4 blade when 4-6 adults + cooler is on board.


WOT: 45mph @ 4350rpm with 4 blade. Plane in 5 seconds @23 mph. Michigan Wheel Appollo 4 blade stainless 14 3/8 x 18. #993204
44mph @ 4500rpm with 3 blade. Plane in 7 seconds @ 25 mph. Michigan Wheel Vortex 3 blade 14.5 x 19 Aluminum. #992004

Both props are in perfect condition with no dents, dings, ect. Both using the XHS hub system.

Plaining numbers were taken with average of 3 passes each time idling in forward gear to slam forward throttle.

I was shocked that the 4 blade was faster out of the hole and on the top end.