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Old 04-05-2015, 09:16 AM   #81
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Greetings,
Aprox. 2gph/engine (2 Lehman 120HP) @ ~1750RPM. Boat weight-25tons displacement hull. Aprox. speed-8knots.
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Old 04-05-2015, 09:25 AM   #82
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7.5 knots at 1500 RPM around 2 GPH
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Old 04-05-2015, 10:37 AM   #83
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7.5 knts at 1800 rpm. Why would you want to go any faster? I enjoy the trip more than the destination sometimes.
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Old 04-05-2015, 10:52 AM   #84
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6.15 Knots at 2300rpm w a Mitsubishi S4L2. 107 cu in and 37hp.
Willard 30 hull 8 tons disp.
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Old 04-05-2015, 11:03 AM   #85
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When I'm just stooging around with not much distance to cover, 8 KTS at 2.5 GPH. When I'm trying to get somewhere quicker, 18KTS at 14 GPH. Flat out is 27 KTS at 30 GPH
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Old 04-05-2015, 11:07 AM   #86
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Quote:
Originally Posted by Marin View Post
..... well, once you've cruised at 30 knots you realize how little you care about fuel consumption.
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Old 04-05-2015, 11:41 AM   #87
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Quote:
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7.5 knts at 1800 rpm. Why would you want to go any faster? I enjoy the trip more than the destination sometimes.


I go faster across the featureless ocean when it's all about the destination (my work). Prefer a leisurely pace when cruising as the scenery is much more interesting inland and near coastal.

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Old 04-05-2015, 11:44 AM   #88
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25 to 27 knots. .9 to 1.0 mpg. We run 25 knots at 2400 rpm. That's 650 off the top.
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Old 04-05-2015, 11:47 AM   #89
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At 1450 rpm, boat does about 8.5 kts which is fine with us. If on beam seas, I'll bring her up to 10.5 kts which stabilizes the boat (more comfortable).
I twin have DD6V92...
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Old 04-05-2015, 01:58 PM   #90
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6.5 k, .9 gph, 7.25 nmpg
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Old 04-05-2015, 02:54 PM   #91
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7.5 knots at 2400 rpm, depending on the current. About 2.5 GPH.
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Old 04-05-2015, 03:14 PM   #92
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7.5 knots at 2000 RPM's.....Seems to be the happy spot with my 200hp Volvo/boat. Burns about 2.2 GPH at that number..

By "Happy Spot" I mean she's not digging a big hole in the water at the stern, "Feels" pretty efficient at that pace, and the Fuel usage is not killing me.
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Old 04-05-2015, 04:11 PM   #93
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My typical cruise is 1060 rpm, 8.5 knots, 7 gph. 1200 rpm, 10 knots, 10 gph. Going faster is very inefficient: 2100 rpm 17 knot, about 50 gph. Going slower can greatly increase efficiency -- 600 rpm, 4 gph, 6.5 knots.
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Old 04-05-2015, 05:26 PM   #94
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We are typically cruising between 7.0 and 7.5 knots with our AMS 40', running both FL120 between 1400 and 1550/1600 rpm, burning 1.3-1.6 l/nm of fuel.
Never had problems with the FL120s not to reach reasonable temperatures at 1400 rpm as reported by Marin (only at significant lower rpm as it is necessary for some inland channel passages in Europe).
On the high end we go up to 8.2 knots / 1800 rpm / 2.2 l/nm. Since fuel is in Europe still very expensive (up to 1.8 Euros/Liter) we don't like this, so only if it's really a must ...


best regards / med venlig hilsen
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Old 04-05-2015, 06:29 PM   #95
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Just did a 300NM cruise to the Keys. 7.5 Knots @ 1750 RPM while getting down to Biscayne Bay. Then I pulled back to 6.5 Knots @ 1500 RPM and enjoyed the scenery......1.75 Gal. per hour overall total running time. I enjoy going slow. I am not in a hurry to get anywhere while cruising on my boat. It is the journey for me not the destination. If I am in a hurry to get somewhere I'll drive the 911.
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Old 04-05-2015, 08:08 PM   #96
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1800 RPM.....7.0 knots
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Old 04-05-2015, 08:22 PM   #97
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Since I first posted on the thread years ago, much has changed. I stated I cruised at 2300 RPM at 8Kts, which I thought to be the true RPM. Then a little later I decided to use a lower cruise RPM of 2000-2100 to reduce the cabin noise and got about 7 kts, give or take...probably closer to 7.5 kts. In May 2012, I had both props tuned by PropScan which improved my speed very slightly and reduced the vibrations significantly.

My Perkins 4.236 tachs receive alternator inputs and my port tach has always been jumpy, so I always relied on my steady stbd tach to set my power, then sync the port side to match. I replaced my stbd alternator last summer with a Balmar alt and found my tach reading changed substantially. Now I have verified the tach readings with a photo tach and found the stbd tach to be accurate within 40 RPM at all speeds. When the port side settles down (dependent on charging status), it matches the stbd tach very closely.

Baker, Edelweiss and Dougcole were right to question my numbers. As it turn out, they were all wrong! Although I thought I was cruising at 2300 RPM, I was really closer to 2100 RPM. My old 2000-2100 RPM cruise RPM is really 1800 RPM.

Here's what I know now...

WOT RPM on my engines is listed at 2800 RPM in the book, but both high pressure fuel pumps are placarded at 2600 RPM. My WOT tach reading is approx 2500 RPM, so I might be slightly overpropped. My cruise power sweet spot is now 1800 RPM (formerly 20-2100 RPM but the same throttle position and sound level) at about 7.5 kts. My average fuel consumption between top-offs is 3.2 GPH. This gives me 2.3 NMPG.

If I could tolerate a slower cruise speed, I could probably achieve a 3.0 NMPG cruise at 6-ish knots. To me, that's not something I'd be willing to try to save 0.5 gal / $2 per hour.
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Old 04-05-2015, 08:33 PM   #98
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There's always a couple factors...budget for fuel per year and are you a once around the harbor type or the 3000+ NM per year type.

Some are forced into speed ranges based on their finances and cruising miles.

So stating facts are great....comments on what you can and can't tolerate is fluff...unless you ask a speedster to cruise with you...

Sure I'd like to outrun thunderstorms and leap tall buildings in a single bound....big deal if the only working package I cruise in can't do it.
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Old 04-05-2015, 09:18 PM   #99
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Twin Detroit 8.2L's normal cruise @ 2000rpm = 8-9 kts 10gph. Goes up rom there. High cruise is 23-2400 rpm. 19-21kts; not worried about the fuel at that point
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Old 04-05-2015, 09:30 PM   #100
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Quote:
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... My cruise power sweet spot is now 1800 RPM (formerly 20-2100 RPM but the same throttle position and sound level) at about 7.5 kts. ....
My sweet spot too, but with only half as many engines, that gets me 6.3 knots.

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