Bertram33 User Forum

Interesting Gerard, I run with 21X19's with 2:1 gears. 4,400 RPM and about 28 knots with 1 POB, 2/3's fuel. No floscans so I can't quote fuel burn but the on-board computers say 14 GPH (per engine) at 3,000 RPM. Rick Ticket 85 SF Merc 454 MPI's Falmouth, MA

Gerard, I'm running 2.5:1, 8 degree down angle Borg Warner's.

Thanks Joe.

Gentlemen, Thanks for all the info. As far as definitive info MarinePower (MP) in writing advised me to prop out the engines at 5200+/- 100 RPM. MP's spec for the engine (GM's spec doesn't count as it is fully marinized using MP's MEFI 6B program for the ECM). The stbd tach is within 50-100 rpm and we are using both Fluke and ESI inductive pickup tachs for all testing. The engines certainly do not feel overloaded and MP warrants them in this application for 5 years, so I don't think this is to far out of line (small block/big boat). After ~18 hours of break in operation we seem to have picked up ~100-150 rpm at WOT to 4900-5000 but lost some speed (36 mph vs 38) but I have also put all the fishing gear, inboard trim panels, etc back on the boat. Based on all the discussions I am thinking the next step is to take 1" out of the pitch. The two local prop shops won't go more than 2" off pitch (3 after fighting) or diameter (no wiggle room). Making to great an adjustment will also affect blade shape and efficiency they say (true). The 21p x 23d props used in the early testing started out at 23 x 26 so That's what prompted the 21 x 25's that became available. I'll work my way down and add cup as necessary. Having engine data NEMA 2000'd to Garmins in the next few weeks to have as accurate as possible data on rpm, fuel consumption, etc.

First of all I'm no expert. But I remember when Yanmar hit the market and the opinion was those engines won't last. They run too fast. I think they have a pretty good track record now. Cummins had their issues too. Look what they are squeezing out of them now. Technology has come a long way since the old 671 days. Weight down, horsepower up. My main concern with Wet Process line of reasoning is fuel consumption vs. dollars spent. That investment gets you a pair of reman's, (well close anyway)gets rid of fuel tank issues if it hasn't been a issue and most likely gives you the speed you want and the fuel burn/range you need.

gents, Maybe I'm lucky, but my 33sf has an aluminum tank! Fuel burn TBD next two weeks with full instrumentation.

Rick, Nice I'll take that fuel burn any day!

Cruise at 4000RPM, 33 mph, 0.7 mpg WOT 5050RPM, 38 MPH, 0.45 MPG Both number fully loaded...water, fuel, ice (no fish though, 30 gal bait tank, 6 good size POB plus all the crap that accumulates in storage!

Still working on props as there is another 2000-4000 RPM available without stressing the engines per Marine Power!

Al, I think you mean 200-400rpms. Nice numbers!

Would like to see the RPM & Fuel burn numbers at 23/24 knots (26.5/27.5 mph)to make a apples comparison to what the cummins guys claim. That is a better fuel burn than the BB mercs give at 19/20 knots. That said, pretty impressive!

Just as a side note. Something that throws me off when having discussions about speed / efficiency / fuel burn is the flip flopping between mph / kts, mpg / nmpg, and such. So for those of y'all that think in knots and not mph. His cruise of 33 mph is equal to 28.67 kts. His cruise efficiency would be 0.61 nmpg. His WOT would be 33 kts and efficiency would be 0.39 nmpg. Still pretty impressive numbers. I would be interested in the gph burned at the 24kts speed range as well.

DougL33: Correct, the available added RPM's is 200-400! Will do burn tests through the cruise range (~3000-4500 RPM =~18-28 knots) when I have enough time and weather conditions to go thru a range of sea conditions. The numbers reported earlier are indeed in nmpg...the main 12" display is all in nautical, while the smaller chart plotter is set up for statute, since most folks down here in FL don't use nautical believe it or not. I guess I'm to old and still use paper charts for plotting and them enter waypoints!

WetProcess, how far did your engines move back, and did you have to get new shafts? I ask because I just purchased new motors and transmissions, and my trans are the ZF Hurth with the 8* down angle. They are about 7 1/2" shorter than the original velvet drive transmissions. I am doing all the mechanical work myself, I am looking for some info so I have an idea where to start before I am working under an engine dangling from a crane. Thanks Tom

Hi Tom, I'm the one with the down angle trany's. I moved the engines back almost a full foot & yes, I needed new shafts. The plus side of this is you get lots more room in the front of the engines to work & the boat tends to sit better in the water. (SF's are a little bow heavy with an empty fuel tank.)I also had to re-prop. The extra weight aft requires a smaller set of wheels to get you at the correct RPM range. I'd try what you have first & play with cutting them down if needed. I also added 70 gals. of water back where the generator used to be so you may not need as small a wheel as I'm running. You will also need to re-mount the engine brackets on the stringers. The down angle requires the engine to sit more horizontal on the beds.