Sea Ray 40 Cummins QSB 380 Prop size

Ckroeger

New Member
Sep 7, 2011
4
Charleston, SC
Boat Info
2008 40', twin Raymarine E120's
Engines
Twin Cummins 5.9 QSB
Hi Everyone,
I asked this on a different part of this forum, so sorry for the repeat.
I have a 2007 Sea Ray Sundancer 40...great boat! It has twin Cummins QSB 380's and I have 21" dia x 23 pitch nibral props. I'm pretty sure I'm over propped as I cannot achieve max RPM @3060. In fact, I'm only getting to @ 2700 at WOT.
I know my boat is not unique, so I'm searching for someone who has the same set-up and would love to know what size your props are...
Thanks,
Charlie
 
You are better served by posting this problem on the boatdiesel.com site. When was the last time the engine turned 3060 in gear? Any black smoke? Are both engines the same rpm?
 
Charlie, see my response in your other post on this subject. The 21x23 props are the factory size. Your props likely need to be tuned.

Hi Everyone,
I asked this on a different part of this forum, so sorry for the repeat.
I have a 2007 Sea Ray Sundancer 40...great boat! It has twin Cummins QSB 380's and I have 21" dia x 23 pitch nibral props. I'm pretty sure I'm over propped as I cannot achieve max RPM @3060. In fact, I'm only getting to @ 2700 at WOT.
I know my boat is not unique, so I'm searching for someone who has the same set-up and would love to know what size your props are...
Thanks,
Charlie
 
I think you would be making a mistake; you have the right props for this boat. If you're not getting over 2700 I'd check other things first, such as condition of bottom paint or running gear. Here are the factory specs but Searay warns that not everyone will be able to match the same specifications. I've never made it to 3000 rpm WOT.

PROP SIZE (DIAMETER x PITCH):
21 x 23 4BC (C=CUPPED, S=STRAIGHT)
GEAR REDUCTION RATIO:
1.64:1


{3} RPM @ CRUISE:
2800
{4} SPEED @ CRUISE:
27-31 MPH
{4} SPEED @ CRUISE:
23.7-27.2 KNOTS
{5} FUEL USAGE @ CRUISE:
31 GPH
W.O.T. RPM:
3000
{4} W.O.T. SPEED:
32-36 MPH
{4} W.O.T. SPEED:
28.1-31.6 KNOTS
{5} FUEL USAGE @ W.O.T.:
40 GPH
 
I have seen your post on the other site. Listen to him and answer his questions. I recently went through this with my 420 Sundancer that actually was so over propped it dropped an exhaust valve seat from exhaust over temps. These were factory props. After going down almost 2 inches of pitch I lost 1-2 mph off of top end but gained speed in the mid range and dropped the exhaust temp from 950-1000 deg. to 725. As stated above you need to start with bottom growth ect. All boats are loaded differently so start with clean filters and bottom, load your boat with your gear and fuel and prop them to reach the required RPM AND FUEL BURN at the various rpm on the cummins chart for your engine. Most manufactures over propped their boats for the real world as we use them.
 
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