Five blade prop question.

[NOLA-boy]

Hello, I am new to the forum. I have been researching my question on the forums for a couple of weeks but have not found an exact answer.

I have a 19' X 7.5' 1990 Smokercraft Avanti deck boat, 200hp 5.0 Mercruiser, Alpha 1, 1900lbs. I just bought the boat. It came with a 19p five blade prop. I've read on the forums that the five blade seems to be for holeshot and reduction of prop slippage. My mph on GPS @ WOT is 42 @4600rpm. The holeshot is great. Gets right up on plane. The forum suggests my engine year rpm for wot is between 4400 and 4800 so it seems I'm in the appropriate range. I'm not extremely concerned about the top end but the poor fuel economy. I don't have a fuel flow meter but a 1/2hr of "playing" (some WOT, some cruising speed) ate almost 9 gal of fuel. My tach is the original and may be inaccurate. (probably should use a shop tach) The motor runs smoothly, starts immediately, runs quietly and idles smoothly. The idle rpm is around 900 to 1000 (high?) Makes me think tach error again.

Love to hear any insight..........thanks!

Sorry about the lengthy post. I wanted to avoid wasting time with a vague question.

 

[dbkerley]

Re: Five blade prop question.

It all sounds pretty close to me. Are you familiar with the extremely poor fuel efficiencies of boats? 3gpm is not an unheard of number. Yes sir, that is gallons per mile.

Your boat would likely be more efficient with a 3 blade prop and a clean well waxed hull. Getting your weight and rpm down is the best way to lessen fuel consumption.

If you want to watch it close you can add a flow meter and calculate the most efficient rpm under cruise. Probably somewhere around 2800.

 

[NOLA-boy]

Re: Five blade prop question.

Thanks for your response. This is my 5th boat. For its size, I think 18 gph is a little high. I agree that a 3 blade would probably be better. Should I contact Smokercraft to inquire about the "factory prop"? Would they even know? I think I may have an inaccurate tach as well.(probably should resolve that before changing props) Thanks again.........