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Most economical cruising speed
- MyPleasure
- Deck Hand
- Posts: 68
- Joined: October 18th, 2022, 7:08 pm
- Vessel Info: 1992 Carver 36 aft cabin with Volvo 740b engines. Westerbeke 5kw generator. Bought the boat in Portland Oregon in June, and a friend and I brought it up to Sidney, BC. Great trip!
- Location: Victoria
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Most economical cruising speed
I know that any big block powered boat is not going to get good fuel mileage, but anything better than burning $125 of fuel and hour would be nice. By the way, I’m going by the Navman floscans that are on the boat.
Thanks for any suggestions
1st Carver 1987 32 Aft Cabin
2nd Carver 1989 4207 Aft Cabin
3rd Carver 1995 350 Voyager
4th (current) 1992 36 Carver Aft Cabin
- kgarguilo
- First Mate
- Posts: 107
- Joined: December 5th, 2022, 2:41 pm
- Vessel Info: 1999 Carver 406
- Location: Sugar Hill, GA.
- Has thanked: 112 times
- Been thanked: 38 times
Re: Most economical cruising speed
S0 2X for total gph.
@1050 RPM 1.57 GPH
@2000 RPM 4.54 GPH
@2776 RPM 9.46 GPH
@3550 RPM 14.95 GPH
@3950 RPM 21.14 GPH
Measurements taken from the MEFI 3 ECM via Diaacom software
Lake Lanier GA
1999 Carver 406
- buster53
- Admiral
- Posts: 996
- Joined: May 12th, 2017, 10:41 am
- Vessel Info: 2001, Carver 356
- Location: Lower Potomac, VA
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Re: Most economical cruising speed
kgarguilo wrote:Source of the post Funny you should ask, I just did a test recently on my 1999 Carver Mercruiser 454's below are the readings while under way PER engines.
S0 2X for total gph.
@1050 RPM 1.57 GPH
@2000 RPM 4.54 GPH
@2776 RPM 9.46 GPH
@3550 RPM 14.95 GPH
@3950 RPM 21.14 GPH
Measurements taken from the MEFI 3 ECM via Diaacom software
Those are nice numbers to have, but not knowing what speed goes with them to determine MPG, no way to tell the most economical cruise speed.
To the OP, most economical speed is hull speed or under, 7-7.5 knots or less. If you want a good cruising speed, get up on a decent plane. Anything between hull speed and decent plane, you are wasting fuel.
- pepmyster
- Admiral
- Posts: 978
- Joined: June 5th, 2018, 7:17 am
- Vessel Info: 2004 Carver 360 Sport Sedan
8.1 Volvo Penta
Fresh water boating - Location: Ottawa
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Re: Most economical cruising speed
- Midnightsun
- CYO Supporter
- Posts: 2855
- Joined: March 27th, 2016, 2:27 pm
- Vessel Info: The Midnight Sun
2007 41CMY
Volvo D6-370's - Location: Montreal, Canada
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Re: Most economical cruising speed
In my case (diesels) I burn around 0.75L/km at 1250rpm which is hull speed. Up on plane at best consumption is 2.7L/km. Difference is 3 1/2 times more fuel burned up on plane for the same distance covered compared with hull speed.
- bud37
- Admiral
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Re: Most economical cruising speed
MyPleasure wrote:Source of the post Our 36 Uniflite aft cabin with small blocks got about 6 gph at 9 knots, but this Carver 36 aft cabin with the big blocks burns a whole lot more than the Uniflite with the small blocks, but then the Carver is a lot more boat than the Uniflite was.
It is difficult to compare different hulls even by the same maker.......LWL is will make quite a difference big block or small.....longer hulls will use less fuel to go the same speed for the most part.
9 knots is just pushing water and digging a hole, very inefficient speed for a 36' boat. Like has been pointed out hull speed is with the boat on the water , you can see it as you speed up......most boats around 1500-1650 RPM, depending on propping. This is why some boats become overpropped by owners looking for more hull speed at a lower rpm, therefore using less fuel....the trade off being planing becomes a problem sometimes depending on how far the over propping has been taken.
Nice you have the floscans, they will allow you tune your cruise accordingly.....have fun with your boating.
- bud37
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Re: Most economical cruising speed
- km1125
- Admiral
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Re: Most economical cruising speed
It's not the most economical in terms of nMPG (which is always going to be best at hull speed), but the best compromise of ride quality, fuel economy, passenger comfort and getting somewhere without putting the whole crew to sleep via boredom.
- Midnightsun
- CYO Supporter
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- Joined: March 27th, 2016, 2:27 pm
- Vessel Info: The Midnight Sun
2007 41CMY
Volvo D6-370's - Location: Montreal, Canada
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Re: Most economical cruising speed
This is why some boats become overpropped by owners looking for more hull speed at a lower rpm, therefore using less fuel....the trade off being planing becomes a problem sometimes depending on how far the over propping has been taken.
Over propping does not help fuel consumption at low speeds or any speed for that matter. Putting on a bigger prop while maintaining the same rpm will increase speed but does require more HP to do so which ends up being more throttle (higher fuel consumption) to achieve the same RPM. Bottom line is you have not saved anything by over propping however psychologically since one is travelling faster at the same RPM one tends to wrongfully THINK consumption is better.
- bud37
- Admiral
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Re: Most economical cruising speed
I agree it may not work when the boat is being pushed but...... in effect to make approximately 6 knots ( hull speed approximation ) for a 36' boat ( waterline length maybe 32' or less ) your rpm may be around 1500-1600.....granted it works if you consider going down towards 1200 rpm. Imo it works within reason because the hp output at those rpms is no great difference with the added benefit of big block torque. It does require the boat to be on top of the water and not pushing a large wake though, therefore requiring less force to be applied. One other benefit may be more control at the dock like you diesel guys......
Remember all hull shapes react differently and the longer the water line length the more efficient the hull may be. Also we are of course talking about planing style hulls here and not displacement.
I am not a fan of this but I can see why folks attempt this and lots do.....everything is a trade off compromise of some sort.
I had a boating friend who had a way over propped diesel boat........he made 9 knots with a 30' boat at 1100 rpm......couldn't get it on plane to save his life though......yup there are lots of stories.....I think he may still be on the same tank....
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