What's your cruising speed.
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Heron
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- '88 Cape Dory 28 Flybridge #115
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.
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.
MYTraveler
Guru
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.
waddenkruiser
Senior Member
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
wadden
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
wadden
Billyfeet
Senior Member
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.
Old deckhand
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1800 RPM.....7.0 knots
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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.
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.
psneeld
Guru
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.
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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markpierce
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But it sure was fun to get your 34 LRC up to WOT!! Here's a view looking aft at the fastest I've gone on CHC's 34 Cal! I think it was 23 Kts WOT, right Chris?
CPseudonym
Moderator Emeritus
I cruise at 400-500 off the top. *-450 gives me 27 knots on flat, slack water.
It's really tough being in the minority again.
Joining you in the minority here Don with similar speed. I'll worry about fuel consumption if we ever get a larger boat and go serious distance cruising. Until then the option of kicking it in the rear and getting where I want to go is nice.
- 4.5 to 5 knots on one engine = 2.75 to 3 nmpg (occasionally utilized in thin canal areas where docks / anchored / moored / small fishing boats abound)
- 6.5 to 7 knots on twins = 1.75 to 2 nmpg (often used in SF Delta - calced hull speed is 7.58 knots)
- 16 to 17 knots on full plane = 1 nmpg (whenever in relatively open water needing/wanting to get some distance covered)
- 21 to 22 knots at WOT = Way Too Much Fuel (used for short bursts when needed)
- 6.5 to 7 knots on twins = 1.75 to 2 nmpg (often used in SF Delta - calced hull speed is 7.58 knots)
- 16 to 17 knots on full plane = 1 nmpg (whenever in relatively open water needing/wanting to get some distance covered)
- 21 to 22 knots at WOT = Way Too Much Fuel (used for short bursts when needed)
Victoriana
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A single FL120 pushes our Taiwanese Tub at 7.5-8knots @ 1800-1900rpm. We have made it go up to 9- 9.5 knots but that is with a clean bottom and WOT. Also have a 4 blade prop if that makes any difference.
Unlike you other fellows, I have no idea what kind of fuel consumption we get any calculations ever done have been pretty rough.
Unlike you other fellows, I have no idea what kind of fuel consumption we get any calculations ever done have been pretty rough.
LarryM
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I cruise at or just below the 7kt hull speed which is about 2/3 throttle. The boat is overpowered by about 50% so this puts the engine power and speed where Yanmar recommends. Fuel burn is about 1.75gph or 4nmpg. When throttled back to 6.5 kts, the fuel burn is more like 1.25gph or about 5nmpg. My normal cruising grounds are about 25 nm away and I really wish now I had a somewhat faster boat. Having been a sailor most of my life, I thought I would be comfortable at those speeds, but I find that is less and less so.
In contrast, my prior boat was a beautifully restored Donzi 22 Classic which cruised very comfortably at about 45-50 kts, but was much faster. The fuel burn was horrible, but it was stable and fun. It was just a lark though. Maybe that's what wrong with me now, I was seduced by speed. Is there a rehab for this?
In contrast, my prior boat was a beautifully restored Donzi 22 Classic which cruised very comfortably at about 45-50 kts, but was much faster. The fuel burn was horrible, but it was stable and fun. It was just a lark though. Maybe that's what wrong with me now, I was seduced by speed. Is there a rehab for this?
AKDoug
Guru
5.5knots at 1850 rpm's and .4 GPH. I think that figures out to about 14 mpg Little Yanmar 4JH3 in it with 150 gallons of fuel. Got to love that! 7 knots is 2650 rpm's and 1 gph, and that's faster than the hull really likes. Engine vibration sets my cruising speed and it doesn't like anything between 1850 and 2650 very much.
Little Yanmar 4JH3 in it with 150 gallons of fuel. Got to love that! 7 knots is 2650 rpm's and 1 gph, and that's faster than the hull really likes. Engine vibration sets my cruising speed and it doesn't like anything between 1850 and 2650 very much.
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Wifey B: Speed...Maybe a fast boat to play around in or a fast woman to play around....with...I was careful there
markpierce
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High-speed (greater than hull-speed) is the antithesis of a trawler. Here, a knot below hull-speed:
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River Cruiser
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I was once passed by a tow with 15 barges while we were both going upriver.
AKDoug
Guru
I got passed by tugs towing logs on my trip up the Inside Passage
Wifey B: I got passed by a snail and a turtle....and the turtle had a broken leg.
markpierce
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Tugs towing barges seem threatening to me.
(Carquinez Strait)
(northern San Francisco Bay)
Pushed barges seem to be under control.
(Petaluma River/slough)
(Carquinez Strait)
(northern San Francisco Bay)
Pushed barges seem to be under control.
(Petaluma River/slough)
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long-cours.62
Guru
Depending if
we can get diesel at "reasonable" price for refuelling !
If we navigate at economic speed :
1 engine @ 1500 rpm, speed 7 kts, 0,81lt/1 nm
2 engines @ 1780 rpm, speed 8kts, 1,14lt/ 1nm
And little quicker :
2 engines @ 1850 rpm, speed 9,8 kts, 1,78lt/nm (0,8 edited to 9,8 kts)
Maximum we do , just for this photo 11,6 lts @ 2300 rpm just for the photo
we can get diesel at "reasonable" price for refuelling
!If we navigate at economic speed :
1 engine @ 1500 rpm, speed 7 kts, 0,81lt/1 nm
2 engines @ 1780 rpm, speed 8kts, 1,14lt/ 1nm
And little quicker :
2 engines @ 1850 rpm, speed 9,8 kts, 1,78lt/nm (0,8 edited to 9,8 kts)
Maximum we do , just for this photo 11,6 lts @ 2300 rpm just for the photo
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Ziggy8321
Veteran Member
At 1000 RPM, 8.6 knots 4.7gph for 2.1mpg. I usually do 1200 RPM (10 knots) and 10gph for 1 nmpg. Fast cruise is 2200 rpm 21 knots 31.6 gph .77 mpg and WOT is 2625 for 27 knots, 46 gph .68 mpg.
For us, this is the best of both worlds. Most times we are at 10 knots or less.
For us, this is the best of both worlds. Most times we are at 10 knots or less.
Alaskan Sea-Duction
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We have twin Cats 3208 T/As. Well in the Columbia River we cruise at about 8kts turning the props at 1400 RPMs but she really likes 2100 RPMs which pushed the boat up river at 14kts. Over the course of last year we averaged 6gph and 1.75mpg. I am going to interested what changes when we start cruising the inside passage.
