3208 & prop sizes

Symeon · Post by **Symeon** » Fri Jun 27, 2008 4:44 am

Below are comments taken from the thread "bought one" since the topic was different. _________________________________________ Symeon, You have the 3208's correct? Is so, your boat came from the factory with 20x22 3 blade props with a cup. Regards, Doug L. 1986 33 Bertram FBC Cummins 6BTA's Queen Elizabeth Marblehead, MA ------------------------------------------------------------------- Doug, Thanks for the fact, which is corroborated by another source I have been tracking down. My question then moves to propellers and to what extent we should be changing from what came originally with the boat? I have read a number of sources claim that 4-bladed props are more efficient, but such blanket statements without considering weight distribution and even different laods according to different owners, make me weary. My current props, the 4-bladed, run well and with my CAT3208 @ 275Hp we cruise 18+ (at times touching 19) knots with 3/4 diesel and full water at 2350 RPM. From what I have read on other boats with similar engines, this is typical. What, therefore, is the norm for the right propeller and how is it sourced? The previous owner to my boat informed me that he sent an extended email to Michigan and they were the ones who decided on the 4 bladed props. Any thoughts or studies on determining the right and best prop would be welcome as this is a topic could benefit all. Kind regards, Symeon KISMET B33SF'82 Greece

Post by **dougl33** » Fri Jun 27, 2008 5:07 am

I already posted this on the other thread, but what is your RPM and speed at WOT?

Symeon · Post by **Symeon** » Fri Jun 27, 2008 5:59 am

Yes, you had posted this elsewhere but because it is a different topic to "Just bought one" I opted not to confuse the forum. To answer your question, my RPM at WOT at idle is 3050 for stbd engine and 3000 for port engine - measured with the appropriate hand held instrument and not my dials. My RPM at WOT when travelling - is 2800 for stbd engine and 2740 for port engine. considering that the engines have 1800 hours and with minimal service (only regular change of oil, filters and straps), maybe i need more service as opposed to revert to original props ... ?

Post by **dougl33** » Fri Jun 27, 2008 7:23 am

Well 2800 ia the Cat recommended max rpm under load, though a lot of guys have propped their Cats to run at 2900+rpms at WOT.

lwrenn · Post by **lwrenn** » Mon Aug 11, 2008 4:32 am

Called Bertram and for the 3208's three blades 21" prop by 22" pitch. I tied different combos as my 3208s were turning up also. Best I found after lots of $ was 21"x22" full cup. Captain Larry Wren 305-360-4900 www.apirateschoice.com [img]http://www.bertram33.com/photogallery/p ... Choice.jpg[/img]

Post by **dougl33** » Mon Aug 11, 2008 5:19 am

That's close to what I'm running with my Cummins. 21x22 3 blade with a med/#5 cup.

IRGuy · Post by **IRGuy** » Mon Aug 11, 2008 6:25 am

With 315/330HP Cummins 6Bs I run 1.5:1 transmissions and 21"D x 23"P 3 blades with no cup. Engines are rated for their Max HP at 2,800 RPMs.. and will turn 2,900-2,950 at max throttle. I am told by Tony Athens and two reliable Cummins techs this is exactly where I should be.

Gonzalo · Post by **Gonzalo** » Wed Dec 10, 2008 8:26 am

Hi IRGuy, I was told also that is what we should run in rpms, however was given cruising speeds that seem much faster to what I'm reaching. Do you know at what speed your cruise for a certain rpm? Thanks

Post by **dougl33** » Wed Dec 10, 2008 8:50 am

Gonzalo, I have essentially the same setup as Frank (IRGuy). I cruise at 2400 rpms and get 23-24 knots depending on load and conditions. WOT rpm is 2900+ and top speed is 28-29 knots, again depending on load an conditions.