I've got a new 25cc with a 315 Yanmar inboard. The engine runs out to 3,650rpm at w.o.t., which yields a top speed of about 28-29 knots. The prop is a clean Acme 18x23 4 blade which came standard from the factory, and I get no black smoke. Cruising at 3200rpm, I go approx 22 knots, burning about 10gph by Floscan. The tach is calibrated to "14" from the alternator sending unit, per Mac. Also, these numbers are with a clean painted bottom, half fuel and 2 people. Does this seem normal for a 315 Yanmar/25cc or should I be looking at checking out the tach, prop etc?
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315 Yanmar-Low RPM's
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3,950 w.o.t. gives about 30 knots. Cruise 22-23 knots at 3200, 2.3-2.5 nmpg; 25 knots at 3350 gives about 2.1-2.2 nmpg. All figures are averages, moderately loaded,3/4 to full fuel, using Floscan 9500. One thing that seems clear is that in this setup, the 315 Yanmar uses less g.p.h. than the fact sheet indicates. How does this compare to the Volvo/jackshaft?
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I reach about 35 knots 3500 rpm (wot) and cruise 27 knots at at 2900 rpm. Those numbers are 1/2 fuel, gear and 3-4 people. I reached 36.4 knots once with 1/4 fuel and just me on board. Yesterday we ran 80 nautical miles on 25-30 gallons. About 15 of those miles were trolling.1998 25' Carolina Classic w/ Volvo D6 310
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I had a jackshaft version of the 25 with a Yanmar 6LP. I could also hit almost 37 knots lightly loaded at 3875 rpms. I normally cruised at around 27-28 knots at 3200-3300 rpms. Outdrive boats are definitely more efficient users of power due to straight thrust angle from propeller. But don't have any regrest whatsoever. I would never recommend anyone to get the Yanmar/Bravo III setup. The engine is great and reliable, but the drive simply cannot handle the torque. Mine was a 2000 model and the guy who bought the boat from me is just putting in his second replacement drive. Even the so-called heavy duty "X" version of the BIII disintegrates under the load of the Diesel. By contrast Volvo seems to have gotten this right since from all I hear their Duprop drives do hold up with Diesels.
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Thanks for the encouragement. I'm actually quite happy with the speed and economy of the inboard Yanmar package, even though it clearly gives something up to the duoprop/jackshaft. At the end of the day, there's something to be said for simplicity and reliability, especially offshore.
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25 top speed
Seamoor:
How are you measuring your top speed? GPS or "paddle wheel"? My 25 w/ yamar 315 tops out at 3900 rpm and 27 knts.
Anyone think I should be going 1 -2 knots faster?1965 MFG 16'
1973 Grady White 18'
205' USCG Cutter Tamaroa - Engineer
125' FEADSHIP M/Y "Gillian" - Engineer
50' Gulfstar S/Y - Mate
2005 Wellcraft 23' center console
2007 Carolina Classic 25
2007 Carolina Classic 28
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