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Prop difference?
Posted: Sat Aug 04, 2012 4:12 am
by GrandpaGreg
I have a 2012 40hp BigFoot Mercury EFI (four stroke) and the Mercury webpage has several prop options and the topic is discussed a lot here. Does the prop make a noticeable difference on a 19 foot Berkshire pontoon boat?
I can get about 16-17 mph in good conditions with 2 adults and 2 small kids on board.
There are NO ENGINE TESTS on the Mercury Marine website for this motor on this boat.
Re: Prop difference?
Posted: Sat Aug 04, 2012 5:25 am
by Ron Burgundy
Your speed seems about right, but you want to make sure you are in the upper half of your max RPM band at WOT. If you aren't propped correctly you can lug your motor. I'm guessing your ok based on you speed.
Re: Prop difference?
Posted: Sat Aug 04, 2012 6:19 am
by killerkernrich
what is your RPMs, I have the 60 hp merc my owners manual states 6000rpm as wot but I only get 5000 I think I have a 11 pitch prop.
Re: Prop difference?
Posted: Sat Aug 04, 2012 6:52 pm
by GrandpaGreg
Ron Burgundy wrote:Your speed seems about right, but you want to make sure you are in the upper half of your max RPM band at WOT. If you aren't propped correctly you can lug your motor. I'm guessing your ok based on you speed.
OK, Ya got me! 
I'm new to all this! What is WOT?
My Max RPM seem to be about 4500-4700 depending on the load on the boat.
Re: Prop difference?
Posted: Sat Aug 04, 2012 6:55 pm
by GrandpaGreg
GrandpaGreg wrote:Ron Burgundy wrote:Your speed seems about right, but you want to make sure you are in the upper half of your max RPM band at WOT. If you aren't propped correctly you can lug your motor. I'm guessing your ok based on you speed.
OK, Ya got me! I'm new to all this! What is WOT?
My Max RPM seem to be about 4500-4700 depending on the load on the boat.[/quote
I'm guessing that WOT means Wide Open Throttle!!!!????!!!!
Re: Prop difference?
Posted: Sat Aug 04, 2012 7:10 pm
by rbiederwolf
You go it. Important to make sure that at WOT (wide open throttle or full throttle) you max rpm is in the manf. specified range. Spin to fast or too slow and you may damage your engine over time.
For instance my engine - 115 Merc 4 stroke EFI- is specified by Mercury to run at 5800 to 6200 when at WOT. When I first got my boat it only ran 5200 rpm at WOT - spinning too slow. To correct this I had to drop the pitch of the propellor so the engine could spin faster. With a drop in pitch I was able to get to 6000 rpm at WOT.
Re: Prop difference?
Posted: Tue Aug 07, 2012 1:19 pm
by GrandpaGreg
GrandpaGreg wrote:GrandpaGreg wrote:Ron Burgundy wrote:Your speed seems about right, but you want to make sure you are in the upper half of your max RPM band at WOT. If you aren't propped correctly you can lug your motor. I'm guessing your ok based on you speed.
OK, Ya got me! I'm new to all this! What is WOT?
My Max RPM seem to be about 4500-4700 depending on the load on the boat.[/quote
I'm guessing that WOT means Wide Open Throttle!!!!????!!!!
I was just out for a SOLO run...........at WOT was about 16-17 mph (about what I was told to expect with a light passenger load) and 4650-4750 RPM. Does that sound right? If not, is there a website where I can find out what to do about it? As I said before, I have a 2012 40 hp Mercury 4-stroke EFI 'Bigfoot" on a 19 ft Berkshire LTD CL 190 Pontoon boat.
Re: Prop difference?
Posted: Tue Aug 07, 2012 2:01 pm
by Ron Burgundy
rbiederwolf wrote:at WOT was about 16-17 mph (about what I was told to expect with a light passenger load) and 4650-4750 RPM. Does that sound right?
Sounds too low. According to the Merc website your Full Throttle (WOT) RPM's should be between 5500-6000. You seem to be underpropped.
http://www.mercurymarine.com/engines/ou ... 0/?model=6