Reply
 
Thread Tools Search this Thread Display Modes
 
Old 07-31-2015, 07:13 AM   #21
Guru
 
kthoennes's Avatar
 
City: Sioux Falls, South Dakota
Vessel Name: Xanadu
Vessel Model: Mainship 37 Motor Yacht
Join Date: Oct 2013
Posts: 2,472
Quote:
Originally Posted by FF View Post
All the replys show almost the same answer, it depends on how quickly you wish to empty your wallet...
I like that answer. For us our most comfortable cruising speed is 2200 rpm, which gives us around 10 or 11 knots give or take with wind and chop and current, bit it's also a very fuel efficient speed, around 2 mpg which is pretty good for twin 454's on a 26,000 lb boat I think. "Cruising speed" has never made much sense to me, it's like asking what the cruising speed is on your car.
kthoennes is offline   Reply With Quote
Old 07-31-2015, 07:17 AM   #22
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,143
Quote:
Originally Posted by kthoennes View Post
I like that answer. For us our most comfortable cruising speed is 2200 rpm, which gives us around 10 or 11 knots give or take with wind and chop and current, bit it's also a very fuel efficient speed, around 2 mpg which is pretty good for twin 454's on a 26,000 lb boat I think. "Cruising speed" has never made much sense to me, it's like asking what the cruising speed is on your car.
That has to be the most efficient gas boat I have ever heard of!

Has to be fuel injected....yes?
psneeld is online now   Reply With Quote
Old 07-31-2015, 07:32 AM   #23
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Comfort or fuel consumption has nothing to do w what speed the hull was designed for. Cruising speed is established by the NA that designed her.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 07-31-2015, 07:48 AM   #24
Guru
 
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
Quote:
Originally Posted by psneeld View Post
that has to be the most efficient gas boat i have ever heard of!

+100
bayview is offline   Reply With Quote
Old 07-31-2015, 07:50 AM   #25
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,143
Cruising speed is whatever you want....

Engine manufacturers recommend an operating range, and a NA can design an efficient speed for the hull...but that is a fleeting number based on load and conditions....

So.....cruising speed is whatever you want...

Now if you want to talk about efficiency for a particular boat...then a few specifics might come into play....
psneeld is online now   Reply With Quote
Old 07-31-2015, 07:59 AM   #26
Guru
 
cappy208's Avatar
 
City: Cape Cod
Vessel Name: Slip Aweigh
Vessel Model: Prairie 29
Join Date: Oct 2013
Posts: 1,219
What is 'cruising speed'

In the original question, it appears the answer is more related to the window stickers on vehicles stating 'estimated MPG highway/city'. What is theoretical under optimum circumstances is rarely (if ever) seen in use, Just as there are no real ways to unequivocally state cruise and max speed for any particular vessel. Cruise and Max differ wildly from stated numbers to what is seen in real life.
cappy208 is offline   Reply With Quote
Old 07-31-2015, 08:04 AM   #27
Guru
 
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
Quote:
Originally Posted by motion30 View Post
[Q catUOTE=bayview;353543]11-13 on a 42' is not cruising speed it is a lie. That is too slow to be on plane and too fast for any reasonable fuel use.


Typically cruising speed on planning hulls is about 15% lower RPM than WOT and well on plane.
On my 44. cruising speed At cats. recommended 2200 rpm. Is 13[/QUOTE]


Astounding that a 44 is well on plane at 13 Kts.
bayview is offline   Reply With Quote
Old 07-31-2015, 08:56 AM   #28
Guru
 
Heron's Avatar
 
City: Cypress Landing Marina (NC)
Vessel Name: Heron (2)
Vessel Model: '88 Cape Dory 28 Flybridge #115
Join Date: Nov 2014
Posts: 1,305
Quote:
Originally Posted by Trundlebug View Post
My FD boat has a plate near the helm, placed by the engine manufacturer (Volvo Penta). It says:-

"Cruising speed 200rpm below obtained top speed"

obtained top speed will be at max revs - 3600rpm officially,
I generally cruise at around 2000rpm, or 7.1 kn which seems the best speed for noise / vibration / speed / fuel consumption compromise.

.
My Volvo is the same...and I also cruise at 2K at 7.5 knots or so. Seems the most comfortable for the engine and SD hull form and averages 2 GPH at that number. WOT at 3600 is around 17 knots
__________________
Steve
Heron is offline   Reply With Quote
Old 07-31-2015, 09:15 AM   #29
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Join Date: Aug 2011
Posts: 6,348
Folks, for virtually any planing boat the manufacturer will have a chart and graphs like this.

http://www.bostonwhaler.com/boat_gra...14101501AM.pdf

See what happens at 4000-4500 rpm?
__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 07-31-2015, 11:33 AM   #30
Moderator Emeritus
 
Pineapple Girl's Avatar
 
City: San Jose, CA
Vessel Name: Pineapple Girl 3
Vessel Model: Silverton 38c
Join Date: Jun 2010
Posts: 2,171
this is a very interesting thread.

I would say to take anything in an ad for a used boat with a big grain of salt. Our current boat was advertised with a max speed of 16 knots. On the test ride, the owner, salesperson and I were below and my husband was on the flybridge driving with the surveyor. The owner pointed to the VHF and said to the broker "see, I told you it would do 16."

__________________
-Jennifer
2003 Silverton 38c (not a trawler)
Marina Village, Alameda
San Francisco Bay Area
Pineapple Girl is offline   Reply With Quote
Old 07-31-2015, 06:39 PM   #31
Guru
 
High Wire's Avatar
 
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,964
When I was gathering data to purchase our Monk, I ran across a old magazine article for a 42 Grand Banks with 375 hp Cat 3208TA's. It stated "She will cruise at 18 knots at 10 GPH". NOT!!!
Be very skeptical of any such claims, even by "experts".
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
High Wire is offline   Reply With Quote
Old 07-31-2015, 06:59 PM   #32
Senior Member
 
Bilgewater's Avatar
 
City: Circleville, Ohio
Vessel Name: Sunset Lady
Vessel Model: 1975 Chris Craft 35 Aft Cabin
Join Date: Jun 2011
Posts: 276
For a displacement boat, hull speed (most efficient) is computed at 1.34 x square root of the water line length. On my Gulfstar, a water line length of 33 feet gives me a theoretical hull speed of 7.69 knots. When I first got the boat, someone on this forum suggested to increase rpm 100 at a time and watch the bow. When it starts to rise, back off because you're wasting money trying to climb over your bow wave. I found a sweet spot at 1750 rpm on my two 85 horse Perkins, which will give me 7 to 7.5 depending on wind and waves. I plan on 3 gallons per hour usage, and usually do better. Canal cruising at 6 knots or less does even better, hovering above 1 gph. Slow and steady wins the day (and the wallet).
__________________
Bilgewater

"Keep putting off till tomorrow, and you'll end up with a lot of empty yesterdays" Prof. Harold Hill
Bilgewater is offline   Reply With Quote
Old 07-31-2015, 07:27 PM   #33
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Join Date: Aug 2011
Posts: 6,348
Quote:
For a displacement boat, hull speed (most efficient) is computed at 1.34 x square root of the water line length.
Nope. That is the speed beyond which inefficiency goes up exponentially, which is what you describe later in your post.
__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 07-31-2015, 08:27 PM   #34
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Cruising speed for most FD boats will be well below hull speed. Cruising speed for a FD boat is only a very narrow range usually 1/2 to one knot below hull speed.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 07-31-2015, 08:39 PM   #35
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Vessel Name: Carquinez Coot
Vessel Model: penultimate Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 12,559
On this boat, a knot below hull-speed is at least twice as efficient as far as gallons per hour goes (less than two compared to nearly four gallons an hour at 6.3 versus 7.3 knots).
__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 07-31-2015, 08:46 PM   #36
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,143
Quote:
Originally Posted by markpierce View Post
On this boat, a knot below hull-speed is at least twice as efficient as far as gallons per hour goes (less than two compared to nearly four gallons an hour at 6.3 versus 7.3 knots).
Fuel burn and speeds almost exactly like mine and mine is supposedly semi-displacement...but it leans heavily towards the line between the two.
psneeld is online now   Reply With Quote
Old 07-31-2015, 08:47 PM   #37
Guru
 
Dougcole's Avatar
 
City: Carrabelle, FL
Vessel Name: Morgan
Vessel Model: '05 Mainship 40T
Join Date: Jan 2008
Posts: 2,162
With our mainship 400 (twin 240 hp yanmars) which I think of as sort of a hybrid trawler/cruiser I often get this same question. "What's your cruising speed?"

I always say that we have two: Slow cruise, which is most efficient, is at 1850 rpm, about 8.5 kts. Fast cruise, which we use when we want to get somewhere or when it is rough is at 2850 rpm, about 15 kts.

So for me there are two cruising speeds. Depends on the day.
Dougcole is offline   Reply With Quote
Old 07-31-2015, 10:11 PM   #38
Al
Guru
 
Al's Avatar
 
City: ketchikan, Alaska
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler(extended to 30 feet) Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 2,206
Anything over 7 knots is unsafe, sucks the wind out of one's lungs. When we do see 7 knots we consider breaking out the skis!

Al
Al is offline   Reply With Quote
Old 07-31-2015, 10:16 PM   #39
Guru
 
cappy208's Avatar
 
City: Cape Cod
Vessel Name: Slip Aweigh
Vessel Model: Prairie 29
Join Date: Oct 2013
Posts: 1,219
I looked on the can of ablative bottom paint I used this spring. It said NOT to exceed 7 knots or the bottom paint would slough off too fast. Who am I to argue? Or was it 7 coats? Maybe 7 beers between coats. I forget.
cappy208 is offline   Reply With Quote
Old 07-31-2015, 10:16 PM   #40
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
The NA of your boat knows what the cruising speed or speeds is.

But conversationally cruising speed is just the speed you run at most of the time.

Mine is 6.15 knots.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 05:18 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012