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12-14-2018, 02:19 PM
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#1
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Member
City: Tisbury
Vessel Name: ALITA V
Vessel Model: Cape Dory 28
Join Date: Nov 2018
Posts: 15
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Fuel efficiency
Hi everyone... oh, and Happy Holidays!
Just recently purchased a Cape Dory 28 with a 100 hp Westerbeke.
What should I expect for a cruising speed and at what would that most likely be. How much fuel per hour etc.
Newbie here, so all advice appreciated.
Paul
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12-14-2018, 02:28 PM
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#2
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Guru
City: Narragansett Bay
Vessel Model: Grand Banks 36
Join Date: Sep 2016
Posts: 1,115
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I would expect hull speed or maybe 1/2 knot shy.
(HS = 1.34 x √LWL
Not sure but assuming 27 foot waterline maybe 6.5 or 7 knots? Fuel economy should be great. Maybe 2.5 -3 mpg would be my guess. 3-4 gallons per hour?
Enjoy the boat. Are you on the Vinyard?
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12-14-2018, 03:22 PM
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#3
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Guru
City: Cape May, NJ and Englewood, FL
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 3,614
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A good cruise speed would be 1.2 times square root of waterline length.
Guessing 1 gallon per hour.
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Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Englewood Florida.
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12-14-2018, 03:22 PM
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#4
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Valued Technical Contributor
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 5,673
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My CD 28 gasser had a rudimentary Flowscan device installed. It showed 3 gph at 6.5 kts and 4 gph at 7.2 kts. Your diesel should do a third better so maybe 2 gph at 6.5 kts and 2.7 gph at 7.2 kts.
Fuel will be the least of your ownership expenses.
David
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12-14-2018, 03:40 PM
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#5
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Member
City: Tisbury
Vessel Name: ALITA V
Vessel Model: Cape Dory 28
Join Date: Nov 2018
Posts: 15
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Thanks everyone from The Vineyard!
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12-14-2018, 03:48 PM
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#6
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Member
City: Tisbury
Vessel Name: ALITA V
Vessel Model: Cape Dory 28
Join Date: Nov 2018
Posts: 15
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Any of you have a sense of what rpm’s that would be?
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12-14-2018, 05:21 PM
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#7
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Valued Technical Contributor
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 5,673
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It will take about 40 hp to hit 7 kts in that boat. Westerbeke doesn't give a prop hp curve in their spec sheet, but I would guess it should be in the low 2,000s to make that hp.
David
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12-14-2018, 05:26 PM
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#8
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Guru
City: Fort Myers, FL... Summers in Crisfield, MD
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 9,935
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Hi Paul my brothers, sister and I own an inherited house in Chilmark. Good general rule of thumb is 20 HP per gallon. So, a 100 HP engine should burn a maximum of 5 gallons per hour. My guess on fuel burn is:
6 knots 1 GPH
7 knots 2 GPH
8 knots 4 GPH
Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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12-14-2018, 05:34 PM
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#9
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Member
City: Tisbury
Vessel Name: ALITA V
Vessel Model: Cape Dory 28
Join Date: Nov 2018
Posts: 15
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Please get in touch if you’re gonna be here. My wife is artistic director at the MV PLAYHOUSE in VH.
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12-14-2018, 08:03 PM
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#10
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Guru
City: Fort Myers, FL... Summers in Crisfield, MD
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 9,935
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Quote:
Originally Posted by Pauliemv
Please get in touch if you’re gonna be here. My wife is artistic director at the MV PLAYHOUSE in VH.
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Oh to back the clock up one month. It's been a family tradition to do Thanksgiving on the Vineyard since the early '70s. While I will be up next Thanksgiving, not sure what my spring and summer schedule are this coming year. You won't see me there during the winter. 
Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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12-15-2018, 02:50 PM
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#11
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Guru
City: Cypress Landing Marina (NC)
Vessel Name: Heron (2)
Vessel Model: '88 Cape Dory 28 Flybridge #115
Join Date: Nov 2014
Posts: 1,303
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Happy cruising speed on mine is 7-7.5 knots. 2K RPM's on the Volvo, and about a 2 GPH fuel burn. I'd expect you'd have to spin the Westerbeke a bit harder but I'd expect the fuel burn to be very close..
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Steve
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12-15-2018, 03:10 PM
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#12
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,984
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My guess is 7kt at 1.5gph, less at 6.5kt. The Westy 100 I think is a Mitsubishi or Nissan with indirect injection (glow plug diesel) so is a little less efficient than the direct injection. Not much worse, but some.
If you have to preheat to start, it is the indirect injection or pre-chamber type.
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12-15-2018, 05:10 PM
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#13
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Guru
City: gulf coast
Join Date: Jun 2014
Posts: 3,344
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Forget the math. cruise at the max speed where the bow is down. more than that the extra fuel is being used to push the boat up with minimum increase in speed
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