4 Blade Vs 3 blade

[Rixram]

I recently swapped out from a 3-blade 15x17 aluminum to a 4-blade 15x16 aluminum.
New prop is a Mercruiser Alpha-4. Cost $130 dollars.

Old cruise of 3,300 rpm was 18-19 mph. New cruise is about 21 mph at the same rpm.

I didn't time it, but the boat planed perceptably faster, and held speed better.

Boat is a 1987 210 Seville II Mid Cabin.

 

[BritLady]

We have a friend who has a 2002 340 with 6.2 inboards who wants to change to 4 blade props from his stock 3 blade. He tells us he's having trouble finding out the best props with correct pitch for his engines size to buy. He has called SeaRay in TN but tells us he is just being told to check on the web. Anyone have any advice we can pass on to him please? Thanks in advance!

 

[JimFromMD]

We have a friend who has a 2002 340 with 6.2 inboards who wants to change to 4 blade props from his stock 3 blade. He tells us he's having trouble finding out the best props with correct pitch for his engines size to buy. He has called SeaRay in TN but tells us he is just being told to check on the web. Anyone have any advice we can pass on to him please? Thanks in advance!

Is there any discussion about that in the 340 thread?

 

[Rixram]

We have a friend who has a 2002 340 with 6.2 inboards who wants to change to 4 blade props from his stock 3 blade. He tells us he's having trouble finding out the best props with correct pitch for his engines size to buy. He has called SeaRay in TN but tells us he is just being told to check on the web. Anyone have any advice we can pass on to him please? Thanks in advance!

Have them try this: http://www.mercurymarine.com/propellers/prop-selector/#

 

[BritLady]

Have them try this: http://www.mercurymarine.com/propellers/prop-selector/#

Great! Thanks very much will pass link along as it l ooks very useful. I took a brief look at the 340 thread but could not see anything but I may have missed it. Thanks again!

 

[dpvandy01]

Great! Thanks very much will pass link along as it l ooks very useful. I took a brief look at the 340 thread but could not see anything but I may have missed it. Thanks again!

This site didn't give me the option for inboards.... only sterndrives

 

[BritLady]

This site didn't give me the option for inboards.... only sterndrives

Oh no, that's not going to help him much then. I just assumed it would cover all Mercury engines, one would think it would.

 

[Rixram]

Great! Thanks very much will pass link along as it l ooks very useful. I took a brief look at the 340 thread but could not see anything but I may have missed it. Thanks again!

That was the Merc tool I used when I recently went from a 3 to a 4 blade prop as well. I opted to stay with aluminum, though. It only cost a 3rd as much, and the performance difference would never pay off the added cost for stainless

 

[dpvandy01]

That was the Merc tool I used when I recently went from a 3 to a 4 blade prop as well. I opted to stay with aluminum, though. It only cost a 3rd as much, and the performance difference would never pay off the added cost for stainless

You have sterndrives.

 

[Rixram]

Oh no, that's not going to help him much then. I just assumed it would cover all Mercury engines, one would think it would.

Sorry about that. Hadn't realized you were straight inboard.

 

[BritLady]

Sorry about that. Hadn't realized you were straight inboard.

No worries, really appreciate you trying to help

 

[Rixram]

No worries, really appreciate you trying to help

Maybe this one for inboards?
http://www.miwheel.com/propellers/prop-it-right/

 

[BritLady]

Maybe this one for inboards?
http://www.miwheel.com/propellers/prop-it-right/

Thanks, really appreciated it!

 

[Jimmy Buoy]

I don't have a lot of firm numbers but I'm happy with the 4 blade switch....I didn't test the top end because I don't care. My goal was better hole shot and lower cruise rpm. Mission accomplished.

Just a suggestion magstang, but you may actually want to know your WOT RPM. All engines have a listed WOT RPM range. If your RPMs are falling short of the minimum stated in your owner's manual, that could be putting undue stress on the engines even at lower RPMs (i.e. "loading" the engines) from "over-propping". Your setup may be perfect, but without a WOT test and knowing your engine's normal operating range you will not know for sure.

Perhaps another CSR member would know the acceptable RPM range for your engines (wide open throttle)... Anyone??

 

[magstang1]

44-4800 rpm. The starboard side is falling a little short but that's not due to the props. I have carb rebuild kits in the garage waiting. The boat sat all summer last year with almost no use. I didn't want to start messing with carbs until I ran a few tanks of good gas through.