Fuel burn
I also was a bit surprised at the fuel burn figures on the Nordhavn 47. The
average speed reported is 6.6 NM/hour and a burn of 5 gallons an hour, or
1.32 NM/gallon. With 1480 gallons, this gives a range of 1950 miles--almost
1000 miles less than the advertised miles at 8 knots. I would not think
that Bluewater is bucking an adverse current of any significance from the
pilot charts. (also running at a speed = sq rt LWL, or a very effecient
speed).
I have only my motorsailors to compare with:
The Force 50 was fairly close in size to the Nordhavn 47--with LOD of 52
feet and LWL of 45 feet, displacement (weight wet of 60,000#) and beam of
14.2" draft of 6'6" (14,000 lbs ballast). Compared to the Nordhavn 47 LOD
of 47, LWL 43'4", Beam 16'1", Draft of 5' 11" and Displacement of 85,000
lbs. (The Cal 46 was shorter LWL and narrowed, with much less displacement).
The Force 50 had 90 hp, the Nordhavn 47 has 173 hp. At 6.3 knots the Force
50 burned a gallon an hour--or 6.3 nautical miles a gallon. At 7 knots I
burned 2 gallons an hour and 3.5 nautical miles a gallon. The only
conclusions I can come to are that the hull lines, the beam and the
displacement of the Nordhavn 47 make it a much less effecient hull. (Please
understand this is not a criticism of Nordhavn's since they are one of the
few production motor vessels I would consider for ocean voyages).
The interior room of the Force 50 was certainly comperable if not roomier
than the Nordhavn 47 (having 3 staterooms, a pilot house and a lower saloon)
Any other comments why the Nordhavn is not getting better fuel "Mileage"?
Regards,
Bob Austin
At 04:17 PM 11/8/2005 -0600,, Bob Austin wrote:
I also was a bit surprised at the fuel burn figures on the Nordhavn 47. The
average speed reported is 6.6 NM/hour and a burn of 5 gallons an hour, or
1.32 NM/gallon. With 1480 gallons, this gives a range of 1950 miles--almost
This burn rate seems high to me, also. I am willing to factor in 1/2
gallon a hour for a gen set, still this leaves 4 1/2 gallons an hour
to account for. That works out to about 67 hp of power production to
push the boat to 6.6 knots. This seems high. I recall using 1.5
gallons an hour for 3600 miles from Nuka Hiva to the Galapagos at
approx. 5 knots, in a 68' Formosa Ketch(no sails up). The speed would
drop to 4.5 if we were bucking some head wind or if the swell got a
little steep. The boat had one of those 275 hp turbo charged Lehman
engines. I could see 2 1/2 gallons an hour, but 4 1/2 seems quite a
bit out of line. This would get the range back up around 2900 miles
which seems much more realistic with 1480 gallons.
If you consider waterline length versus 1.0 to 1.3 for a better
comparison, here are the figures for the 68' sailboat and the 47 Nordhavn.
Nordhavn 47 = 39' WLL, the square root = about 6.3
Sailboat 68 = 60' WLL, the square root = about 7.7
The 47, at 1.0 = 6.3, 1.1 = 6.9, 1.2 = 7.5, 1.3 = 8.1
The 68, at 1.0 = 7.7, 1.1 = 8.5, 1.2 = 9.2, 1.3 = 9.9.
All approximate. Even if you assume that the water line lengths are
shorter than those I used above, the square roots can't be much less
than 6.0 for the 47 or 7.0 for the 68 footer.
Notice that the 47 is running just above 1.0 times the square root of
it's water line length.
The 68 was running at about 0.6 times the square root of it's water
line length.
I can't imagine the 47 needing over 30 hp or 2 gallons an hour to achieve 1.0.
The 68 was using about 22 hp to achieve 5 knots at about 0.6 times
the square root of it's water line length.
My estimate is that the 68 would have used about 3 gph to achieve 1.0
or 7.7 knots and would have been making about 45 hp. But that is only a guess.
It would be very interesting to test the 47 at ratios of about 0.6
to 0.9 or say, 4.5 knots, 5.0 and 5.5. and see what the fuel burn is then.
Anyone for more figures.
Mike
Capt. Mike Maurice
Tualatin(Portland), Oregon
I delivered 3 N47s last year ~1000 nms north from Dana
Point to either Portland or the Seattle area. From
memory, speed averages were 6.5 knots for one trip,
and just around 7.20 knots for the other trips,
usually running around 1750-1800 RPMs. I do not have
the fuel-burn data at my computer, but I seem to
recall one owner took readings, and it was over 4 gph,
probably around 1800 RPMs. Bluewater's readings,
especially since she probably has a lot of liveaboard
weight, and she had fish in the water, coincide with
my observations on three different N47s.
To contrast, the few N57s I delivered (Mexico,
Florida, Alaska), burned around 6 gph at 9 knots,
1-1/2 miles per gallon.
Peter
www.SeaSkills.com
I can only agree with the surprise that has been expressed at the Nordhavn
47 fuel burn rates.
I think that the things I would check are the angle and gain settings on the
hydraulic stabilizers, and the drag angle (hole selection) on the
paravanes - if they are in the water. (The hole selection effects the fly
angle on the vane - and therefore the drag force on the forward motion of
the boat.)
John Harris
Nordhavn 4657 - World Odd @ Sea (equipped with paravanes)
Could the engine room temp be the cause or part or the cause of the
increased fuel consumption ?
Willy
Invader No 1
39 kishi conversion
----- Original Message -----
From: "Bob Austin" thataway4@cox.net
To: "Passage under power" passagemaking-under-power@lists.samurai.com
Sent: Tuesday, November 08, 2005 2:17 PM
Subject: [PUP] Fuel burn
I also was a bit surprised at the fuel burn figures on the Nordhavn 47.
The
average speed reported is 6.6 NM/hour and a burn of 5 gallons an hour, or
1.32 NM/gallon. With 1480 gallons, this gives a range of 1950
miles--almost
1000 miles less than the advertised miles at 8 knots. I would not think
that Bluewater is bucking an adverse current of any significance from the
pilot charts. (also running at a speed = sq rt LWL, or a very effecient
speed).
I have only my motorsailors to compare with:
The Force 50 was fairly close in size to the Nordhavn 47--with LOD of 52
feet and LWL of 45 feet, displacement (weight wet of 60,000#) and beam of
14.2" draft of 6'6" (14,000 lbs ballast). Compared to the Nordhavn 47 LOD
of 47, LWL 43'4", Beam 16'1", Draft of 5' 11" and Displacement of 85,000
lbs. (The Cal 46 was shorter LWL and narrowed, with much less
displacement).
The Force 50 had 90 hp, the Nordhavn 47 has 173 hp. At 6.3 knots the
Force
50 burned a gallon an hour--or 6.3 nautical miles a gallon. At 7 knots I
burned 2 gallons an hour and 3.5 nautical miles a gallon. The only
conclusions I can come to are that the hull lines, the beam and the
displacement of the Nordhavn 47 make it a much less effecient hull.
(Please
understand this is not a criticism of Nordhavn's since they are one of the
few production motor vessels I would consider for ocean voyages).
The interior room of the Force 50 was certainly comperable if not roomier
than the Nordhavn 47 (having 3 staterooms, a pilot house and a lower
saloon)
Any other comments why the Nordhavn is not getting better fuel "Mileage"?
Regards,
Bob Austin
Passagemaking-Under-Power Mailing List
Today in Nuku'alofa, Tonga, duty-free diesel is TOP$1.43/liter.
At current exchange rate, that's about US$0.725/liter, or only
about US$2.75/USGallon! That's the best price we've seen in a
long time, and more than 20% cheaper than Rarotonga.
Makes a big difference when you're loading 4000+ liters!
Gentle Wind is planning to leave Tonga tomorrow (Friday, local
time) afternoon. Next stop, Suva, Fiji where we hope to get
some help on figuring out the problems with our Naiad active
stabilizers.