Finally getting close to the right prop size

[SKYCHENEY]

After running last year with the wrong ratio transmissions and this year with the wrong props, I finally got pulled and tried on another set. All year I've been running 30 x 28 4-blades and I knew I was underpropped as I was hitting 2400 rpms and showing 87% load. Cat rates the C8.7 as a 2300 rpm engine and suggests topping out at 2320-2350 at 100% load.

I threw on a friend's spare 31 x 32.5 4-blades realizing that I would never turn something that big but hoping to at least get some numbers so we could figure out what I really needed. To my surprise, they turned them just fine. In fact I'm still just a little underpropped as they maxed out at 2380.

 

[Eddieclemons]

What was your old speed?

 

[Flying Dutchman]

That is awesome, way to go!

 

[Sadey]

So jealous.

 

[Timeless72]

What were you running before and top speed compared to now? Would be awesome to see a boat that size blasting by!

 

[SKYCHENEY]

With the 6v92's, I was running 28x28.5 4-blades with top speed 17kts.

Now it cruises nicely 19kts at 2050. The biggest difference is really the noise levels. She is just so quiet now at any speed.

 

[edward]

Fuel consumption??

 

[jim rosenthal]

I would guess less, but I'm interested to hear how much less.

 

[SKYCHENEY]

60gph at WOT
42gph at 19kts
8gph at 9.5kts
6.5gph at 8.6kts

 

[Bob Quinn]

That's some good fuel economy, at least on the hull speed end of things.

That's a real hot rod Lincoln!

Maybe if you get the opportunity to get a video of that high speed action, you could post it so we can all drool

 

[worldsaway]

That is impressive performance

 

[SKYCHENEY]

That's some good fuel economy, at least on the hull speed end of things.

That's a real hot rod Lincoln!

Maybe if you get the opportunity to get a video of that high speed action, you could post it so we can all drool

Boat just went into storage so you'll have to wait until spring for a video.

 

[luckydave215]

Guys, remember when thinking about prop pitch the true "gearing" is the pitch times the transmission ratio.
"Boater Bob has 30"x30" so they most be great for me too"........not so fast! What is the reduction ratio of his gears?

 

[edward]

Boat just went into storage so you'll have to wait until spring for a video.

. What model CAT engines did you repower with ? Thanks.

 

[SKYCHENEY]

. What model CAT engines did you repower with ? Thanks.

C8.7 High Performance

 

[edward]

Thanks !

 

[SKYCHENEY]

C8.7 High Performance

Pretty much the same as a Fiat Marine C90 650 E