94 2300SC 5.7 Prop

[colin311]

I have a descent size chip on one of my blades on my 3 blade prop. I just bought a 4 blade 14/19 Turning Point Aluminum propeller.
I'm thinking I should get better performance with this one. Do u guys think this would be true? I'd like to get onto plane quicker than I do now. I assume the chip doesn't help as I feel I'm guzzling gas and can't get much speed. Any thoughts?

[mmwjr]

Well you haven't provided any real data to respond to.

What was the WOT with the old prop?
What do you mean by guzzling? mpg or gph at a given rpm.

Going to four blades will improve low end performance but decrease top end. Really depends on what you want but the best efficiency is to keep the WOT in the rated range of 4400-4800 rpm.

[colin311]

WOT was 4800 on the old prop. Getting less than 1 mpg at 4000 cruising. I'm hoping this new 4 blade helps. My question is will a bigger 14/19 be better than my 14/17 3 blade. I've read a lot of different theories on 3 vs 4 blade. I'd assume w a 5.7 the 4 blade would be better..

[bman440440]

was the 4800 with the chip in it? if it was pre chip IMO I would go with a 14x17 4 blade.. you might loose a few hundred RPM top end but you will get better performance out of the hole and that will save you some fuel

[mmwjr]

Originally Posted by colin311

WOT was 4800 on the old prop. Getting less than 1 mpg at 4000 cruising. I'm hoping this new 4 blade helps. My question is will a bigger 14/19 be better than my 14/17 3 blade. I've read a lot of different theories on 3 vs 4 blade. I'd assume w a 5.7 the 4 blade would be better..

Adding a blade plus increasing pitch will result in about 400 rpm loss at WOT but will increase holeshot and time to plane. Not sure it will have much impact on fuel economy.

[Luvdamaxums]

Originally Posted by colin311

I have a descent size chip on one of my blades on my 3 blade prop. I just bought a 4 blade 14/19 Turning Point Aluminum propeller.
I'm thinking I should get better performance with this one. Do u guys think this would be true? I'd like to get onto plane quicker than I do now. I assume the chip doesn't help as I feel I'm guzzling gas and can't get much speed. Any thoughts?

I am running a 18.25x21P SS currently. Had a 17.75x17P alum. Both are 3 blade. Night and day diffence on hole shot. Alum struggled to plane. SS you need to Hold on. Lol.

[mmwjr]

Originally Posted by Luvdamaxums

I am running a 18.25x21P SS currently. Had a 17.75x17P alum. Both are 3 blade. Night and day diffence on hole shot. Alum struggled to plane. SS you need to Hold on. Lol.

Welcome aboard.


What boat model and engine do you have? Similar to the OPs?

[Luvdamaxums]

2700 scr single 7.4L 1996

[mmwjr]

Originally Posted by Luvdamaxums

2700 scr single 7.4L 1996

Nice but a completely different boat and engine than the OP.

While your BB can handle that much pitch in a SS prop the OPs SB would be loaded too much. He can go SS but with less pitch.

[mmwjr]

Also I think you have a BII drive vs his Alpha which cannot use that large of a diameter.

[shrew]

Do I understand the details correctly?

Old Prop: 14" x 17P (3blade) = 4800 rpm
New Prop: 14" x 19P (4blade)

At 4800 you were already at the absolute height of the max rpm range for the engine. As MMWJ was saying, increasing pitch will lower max rpm. Increasing blades will lower max rpm.

The net effect will be:

1) Slower hole shot time
2) Lower RPM's at the same cruising speed.
3) Faster top speeds
4) Lower Max RPM's
5) Increased load on the engine.

I also agree with a net decrease in around 400 rpm off of the max at WOT. This will theoretically bring you down to around the lower limit of the max rpm (4400-4800)