running speed 4207

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.

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

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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Note: For Engineering Department Use Only -- Not For Publication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
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