just curious what others are doing... I have the 4207 with twin 8.1 mercs. Now that I am comfortable running the boat, what are the best rpms to run... dont have a fuel flow meter.... so far I have run at 1100 rpm marinas and slow... 1800 for a very slow cruise and I hope gas savings... and 2800 rpm which is not a bad speed but slow... havent gone higher so wondering whats next.....
Cruise speed with gas inboards is generally 3200 rpms, but you can safely run 8.1's 3600-3800 rpms......I'd run them at whichever speed keeps the boat on plane, where they sound like they're running the easiest, etc. This all is provided the boat is propped to achieve the proper WOT RPM.
thanks.. will giv it a try... been running at 2800 will go to 3200... trying not to use too much fuel... lol
You burn the same fuel at 3600 rpm as you do at 3000 rpm. Looks like some body change engines. I hope they match the prop with that engine and size of your boat, I would think you have a 4 blade prop.
You will get your best fuel economy just below hull speed or probably around 8 knots. After that your best fuel economy should come just after the boat gets on a full plane. If you plot a rpm/speed graph with readings every 200 rpm or so you should be able to see where the boat is just on plane. After the boat is on plane increases in throttle should result in near linear increases in speed. Or you could run it up and find maximum rpm at WOT and use 80% of that as a daily cruising speed, assuming that rpm is fully on plane.
That has never been my experience. A gas engine is a fuel/air pump. The faster you turn it the more gas it burns.
8.1 engines are made to run at higher rpms they are fuel injectors 3600 rpm is there sweet spot for running with best fuel and speed.
Joined: 18 September 2002 Location: syracuse, ny Posts: 10 Posted: 29 May 2008 at 3:39pm | IP Logged -------------------------------------------------------------------------------- These are numbers directly from Carver. I have a 2003 356, with Volvo 8.1's and have found my real world results to be very close to these stats. By the way, my 356 is for sale. You can e-mail me directly if you have any further questions. Carver Boat Corporation,LLC -- Boat Performance Test Note: For Engineering Department Use Only -- Not For Publication YACHT DATA HULL WEIGHTS & MEASURES PERFORMANCE SUMMARY Boat Model 356 MOTOR YACHT Boat Weight: est. 21000 Lbs RPM @ MPH Date: 5/24/2001 Fuel Weight: 1908 Lbs Planes @: 2500 @ 11.6 Test No.: TYP356-M8.1SMPI-055B101 Water Weight: 511 Lbs Cruises @: 3600 @ 26.4 Hull I.D.#: CDRP0055B101 Pass. Weight: 480 Lbs W.O.T. @: 4495 @ 33.0 Eng. MFG: MERCURY Misc. Weight: 100 Lbs W.O.T. Trim @: 0 Eng. Model: 8.1 S MPI Total Weight: 23999 Lbs Time To Plane: 8-9 Seconds Eng. Hp @ RPM: 370 @ 4600 LOA: 41' 2" Ft-In Gear MFR & Model: ZF-HURTH-630A Beam: 13'3" Ft-In Gear Ratio: 2.45:1 Draft: 39" Ft-In WEATHER STATS HULL WATERLINE MEASUREMENTS Test Location LAKESIDE GREEN BAY WI. Bow: Inches Course FOX RIVER Port-Aft: Inches Elevation 560' Stbd-Aft: Inches TOP OF SWIMPLATFORM TO WATERLINE Wind NE - 9 PROPELLER SIZE WIDE OPEN THROTTLE RPM'S Humidity 99.9% RAINING Manufacture Michgan PORT STBD Temperature 56 Diameter 22 N-RPM NO TRIM: 4490 4515 Barometric Psi. Pitch 24 S-RPM NO TRIM: 4488 4490 Water Temperature No. of Blades 4 - BRONZE N-RPM TRIM: 0 0 Sea Conditions CHOPPY Prop Serial No. S-RPM TRIM: 0 0 RPM TRIM Degree's MPH (N) MPH (S) MPH (average) GPH Both Eng. MPG db(A) Helm db(A) Salon db(A) Aft Deck 1000 0.25 6.70 5.70 6.20 3.40 1.82 1500 0.50 9.00 7.90 8.45 5.60 1.51 2000 2.25 10.80 9.80 10.30 10.60 0.97 2500 5.25 12.60 11.70 12.15 18.60 0.65 3000 6.50 20.00 18.70 19.35 26.40 0.73 3200 7.00 22.10 20.90 21.50 29.40 0.73 3400 7.00 24.40 23.40 23.90 32.30 0.74 3600 6.75 26.90 25.90 26.40 27.00 0.98 4000 6.25 29.90 29.20 29.55 47.00 0.63 W.O.T. 5.25 33.30 32.70 33.00 57.30 0.58 Edited by timeout on 29 May 2008 at 3:55pm Back to Top