Reply
 
Thread Tools Search this Thread Display Modes
 
Old 12-12-2021, 09:52 AM   #1
Senior Member
 
SILENTKNIGHT's Avatar
 
City: Bayport
Vessel Name: STELLA DI MARE
Vessel Model: 2006 MAINSHIP 34T
Join Date: Oct 2018
Posts: 159
Am I at the right cruising speed

its a 2006 mainship 34T WITH A 6LYASTP
Perfect conditions
1. half full fuel tank
2. one person on board
3. not fully loaded
4. Calm breeze 10 knts wind speed

This is what she likes....
Attached Thumbnails
Screenshot_20211212-093644_Gallery.jpg  
SILENTKNIGHT is offline   Reply With Quote
Old 12-12-2021, 10:06 AM   #2
Guru
 
HeadedToTexas's Avatar
 
City: Sandusky Bay
Vessel Name: Escape
Vessel Model: Mariner 37
Join Date: Jul 2016
Posts: 886
Depends how much fuel you want to burn, among other things.
HeadedToTexas is offline   Reply With Quote
Old 12-12-2021, 10:29 AM   #3
Guru
 
High Wire's Avatar
 
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,451
I can’t read the units. Is that 9.2 knots and 8.5 something?
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
High Wire is online now   Reply With Quote
Old 12-12-2021, 10:30 AM   #4
Guru
 
City: Rochester, NY
Vessel Name: Hour Glass
Vessel Model: Chris Craft Catalina 381
Join Date: Aug 2019
Posts: 5,255
Quote:
Originally Posted by High Wire View Post
I can’t read the units. Is that 9.2 knots and 8.5 something?

Looks like 9.2 ft (depth) and 8.5 kts (SOG)
rslifkin is online now   Reply With Quote
Old 12-12-2021, 11:19 AM   #5
Senior Member
 
ofer's Avatar
 
City: calabasas
Vessel Name: Unicorn
Vessel Model: 1970 50' DEFEVER OFFSHORE CRUISER Timber
Join Date: Apr 2020
Posts: 359
2400 RPM is great running speed since its right at the top of the torque curve.

if she feels right i would say it's good speed. At 2200 you could be a little more fuel efficient.
ofer is offline   Reply With Quote
Old 12-12-2021, 11:22 AM   #6
Guru
 
ranger58sb's Avatar
 
City: Annapolis
Vessel Model: 58' Sedan Bridge
Join Date: Aug 2013
Posts: 6,132
Just doing the math, I'd have guessed most economical cruise speeds would be between 5.8 - 7.8 kts based on a guess at waterline length of 34'.

-Chris
__________________
Chesapeake Bay, USA
ranger58sb is offline   Reply With Quote
Old 12-12-2021, 12:02 PM   #7
Guru
 
tiltrider1's Avatar
 
City: Seattle
Vessel Name: AZZURRA
Vessel Model: Ocean Alexander 54
Join Date: Aug 2017
Posts: 3,116
Certainly the boat is happy cruising at 2200 RPMs. Is it fuel efficient? No! What is more important to you, fuel efficiency or time? I am not very sensitive to being fuel efficient so I would be happy with what you are doing. The boat probably rides better at 8.5kts than it would at 7kts.
tiltrider1 is online now   Reply With Quote
Old 12-12-2021, 01:03 PM   #8
TF Site Team
 
Bacchus's Avatar
 
City: Seneca Lake NY
Vessel Name: Bacchus
Vessel Model: MS 34 HT Trawler
Join Date: Nov 2014
Posts: 6,474
Quote:
Originally Posted by ranger42c View Post
Just doing the math, I'd have guessed most economical cruise speeds would be between 5.8 - 7.8 kts based on a guess at waterline length of 34'.

-Chris
I'm the same 6LYA STP and hull but w/o flybridge.
That is close to my optimum slow cruise.
I run about 1700 - 1800 RPM and get 7 - 7.5 kts.
I think I could do a little better efficiency a little slower but I find that a decent compromise.

If I want to go faster I run 2700 - 2800 RPM and get 11 kts +/-
In between those RPMs I'm not very efficient.
I avg 1/2 MPH for every 100 RPM at low and high end but it takes more RPM to get MPH in the middle.

I avg 2.5 MPG and est thats 75% slow, 25% fast cruise
__________________
Don
2008 MS 34 HT Trawler
"Bacchus"
Bacchus is offline   Reply With Quote
Old 12-12-2021, 02:24 PM   #9
Guru
 
OldDan1943's Avatar
 
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116
Join Date: Oct 2017
Posts: 9,546
Speed, gph, NM,.... something has to 'give'
According to the charts.... my Cummins 380 5.9 QSB, at 1000RPM, speed 6+kn, 1gph, 400gal fuel = I can go a long long way. 1200rpm, speed 7+kn, 1.4gph 5.1 NMPG. 1400rpm 8kn....2.1gph 3.76 NMPG. Of course, open the deck fills, wink, WOT, 3000RPM, 17kn, 18gph, .95 NMPG
The boat is loaded light. 100g of fuel, 150g water, 275' chain, 44# anchor and per usual the fridge and freezer running.
That my friends, may not equate to the real world. Add in a couple 100 pounds of tools and spare parts, 50-75 pounds of clothes.... etc.... that fuel charts is but a mere suggestion.
Again, according to the sea trial chart, my sweet spot should be about 1200rpm or 7+knts, 29% engine load, 1.4gph, 5.14 NMPG. Someone can figure out the "other way" and I suspect it will be pretty close to the chart.
__________________
The meek will inherit the earth but, the brave will inherit the seas.
OldDan1943 is online now   Reply With Quote
Old 12-12-2021, 03:52 PM   #10
Guru
 
Giggitoni's Avatar
 
City: Vallejo, California
Vessel Name: Mahalo Moi
Vessel Model: 1986 Grand Banks 42 Classic
Join Date: Jun 2008
Posts: 2,053
Shouldn’t we also be discussing the propellor specs and transmission ratio?
__________________
Ray
"Mahalo Moi"
1986 GB-42 Classic
ΜΟΛΩΝ ΛΑβΕ
Giggitoni is online now   Reply With Quote
Old 12-12-2021, 04:09 PM   #11
Guru
 
OldDan1943's Avatar
 
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116
Join Date: Oct 2017
Posts: 9,546
Quote:
Originally Posted by Giggitoni View Post
Shouldn’t we also be discussing the propellor specs and transmission ratio?
I cannot disagree with you but there is such a thing of information over load.
__________________
The meek will inherit the earth but, the brave will inherit the seas.
OldDan1943 is online now   Reply With Quote
Old 12-12-2021, 04:15 PM   #12
Valued Technical Contributor
 
DavidM's Avatar
 
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,295
I owned a 34T for several years and boated in Southern California. I would cruise slow at about 7 kts and burn 2.5 gph. I could also cruise fast and burn 11 gph.

8.5 kts is fine but you are beginning to push a bow wave so it won't be that efficient, certainly not as efficient as 7 kts. Don't try to cruise at 10-11 kts because there you are pushing a big bow wave and it doesn't smooth out (not that it ever does like a planing hull) until you hit 12 kts.

David
DavidM is offline   Reply With Quote
Old 12-13-2021, 08:49 AM   #13
Senior Member
 
Cartouche's Avatar
 
City: Kingston Ontario
Vessel Name: Cartouche
Vessel Model: Mainship 390
Join Date: Dec 2017
Posts: 383
Quote:
Originally Posted by SILENTKNIGHT View Post
its a 2006 mainship 34T WITH A 6LYASTP
Perfect conditions
1. half full fuel tank
2. one person on board
3. not fully loaded
4. Calm breeze 10 knts wind speed

This is what she likes....
I get 8knts at 2000 in a 390 with the same engine if I run at 2200 i would be doing 9knts and burning fuel
__________________
Joanne & Edward Billing
M/V Cartouche Mainship 390
Home Port Kingston Marina in the 1000 Islands
Cartouche is offline   Reply With Quote
Old 12-13-2021, 08:59 AM   #14
Guru
 
OldDan1943's Avatar
 
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116
Join Date: Oct 2017
Posts: 9,546
Quote:
Originally Posted by Cartouche View Post
I get 8knts at 2000 in a 390 with the same engine if I run at 2200 i would be doing 9knts and burning fuel
Yup, I agree. With the Cummins 380hp (5.9L), the sweet spot will be between the mid 7 knots and the low 8 knots.
This is IMO, based on the sea trials chart.
The burn rate will be between 1.4 to 2.1 gph
Hmmm, 2200rpm would put me at 11 knots, burning 9 gph.
Your boat may vary.
So many things will cause a big difference.
1. sea state
2. wind speed and direction
3. current
4. attitude of owner
__________________
The meek will inherit the earth but, the brave will inherit the seas.
OldDan1943 is online now   Reply With Quote
Old 12-13-2021, 11:02 AM   #15
TF Site Team
 
Shrew's Avatar
 
City: Westerly, RI
Vessel Name: N/A
Vessel Model: 1999 Mainship 350 Trawler
Join Date: Jan 2014
Posts: 3,493
I have a single 6LPA STP2. I run it at 2400 rpms. Redline should be 3800rpms. At 2400 the turbo is whining nicely. Any more and the noise and fuel burn isn't worth the extra knot.
Shrew is offline   Reply With Quote
Old 12-13-2021, 11:12 AM   #16
Guru
 
OldDan1943's Avatar
 
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116
Join Date: Oct 2017
Posts: 9,546
So let's see. If the Gulf Stream is 5mph, I center the boat in the Stream, I should travel at or very close to 5mph without the engine? Now that is fantastic fuel stretching.
Now for all you math wizards, how many RPM must I add to travel at 10 mph?
Oh no, a simulation equation!!!
If I were to try to do figure that, I would do it the easy way..... move to the center of the Gulf Stream, make note of my speed, slowly adding RPMs until I reached 10mph and make a note of the RPMs.
__________________
The meek will inherit the earth but, the brave will inherit the seas.
OldDan1943 is online now   Reply With Quote
Old 12-13-2021, 12:16 PM   #17
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,448
A good cruising speed has more to do w the hull and it’s design .. as to form (shape).

Long slender hulls will (more or less) just go faster. Fat boats will seemingly fun into the brick wall .. attaining a slower speed and being very reluctant to go faster. FD hulls to be sure but SD hulls and very much planing hulls.

For the few FD hulls on TF just about one knot below hull speed is for all practical purposes the “only” cruising speed. Lower is mostly ridiculous and higher is accompanied w much more engine noise and fuel consumption.

Long and narrow SD hulls (nearly non-existent on TF) will have the luxury of running nicely well beyond hull speed. But 99 to 100% here are not narrow so will need to stop pushing on the throttle about hull speed or less.

There is much talk about a “sweet spot” and this expression has come down through the years used by many. IMO it is the rpm, or range of rpms that produces the best speed (or range of speeds) that has noticeably less noise and vibration. Some boats have a wide range of speeds that may be cruising speeds that vibrate and make noise at most any speed. No sweet spot. And other boats that upon reaching a certain speed shake a lot. Frequently and fortunately those boats will be quite smooth above and below that speed.

Under propped boats are probably more likely to have sweet spots and over propped boats less so. This is so because under propped engines (lighter loaded) will be less likely to transmit vibration to the boat mostly through engine mounts and engine stringers.

Large surfaces of cabins and hulls will/may be prone to “oil can” and cause significant vibration. Stiffeners on these surfaces including the hull bottom may have profound effects on vibration. Look first on cabin sides, floors and roofs. Lightly built boats will be more prone to this kind of vibration.

Vibration - noise.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 12-13-2021, 01:11 PM   #18
Veteran Member
 
LovetoBoat's Avatar
 
City: Liberty Corner
Vessel Name: Lady J
Vessel Model: Donelle 35 Sport
Join Date: Nov 2020
Posts: 61
I am not trying to hijack the thread - I have a 500hp Cummins with a turbo charger. Those of you running at lower speeds - if you don't kick on the turbo charger - aren't you simulating a "blown turbo" and isn't that bad for the engine?


I maybe new to diesel and turbo's but I thought you wanted to run at least a speed where the turbo kicked in - if you are cruising more than 5 miles or so...


Am I missing something?
Thanks
__________________
Douglas MacArthur: “Preparedness is the key to success and victory.”
LovetoBoat is offline   Reply With Quote
Old 12-13-2021, 01:29 PM   #19
Guru
 
backinblue's Avatar
 
City: Stratford, CT
Vessel Name: Blue Moon
Vessel Model: Mainship Pilot 355
Join Date: Jan 2019
Posts: 2,864
Like everyone else, I have an opinion, right or wrong because I don't have any experience with that particular boat. Firstly, LWL is likely less than 34' on a 34' boat, but that's a separate issue. If you want best fuel economy, stay a little below hull speed. However if you want to go fast and can get on plane, I think you will get better mpg at higher RPMs. Again I am assuming you can plane. At 8.5 knts you are likely barely planing and not very efficient. If your boat does plane, the engine is more efficient at 3000 rpm than 2400 and you will get better mpg. "Generally" if you look at tables for turbo diesels with a planing hull you will see best mpg around 80% of max RPM (unless you are below hull speed).
__________________
“In my walks, every man I meet is my superior in some way, and in that I learn from him.” ― Ralph Waldo Emerson
backinblue is online now   Reply With Quote
Old 12-13-2021, 01:31 PM   #20
Guru
 
City: Rochester, NY
Vessel Name: Hour Glass
Vessel Model: Chris Craft Catalina 381
Join Date: Aug 2019
Posts: 5,255
Quote:
Originally Posted by LovetoBoat View Post
I am not trying to hijack the thread - I have a 500hp Cummins with a turbo charger. Those of you running at lower speeds - if you don't kick on the turbo charger - aren't you simulating a "blown turbo" and isn't that bad for the engine?


I maybe new to diesel and turbo's but I thought you wanted to run at least a speed where the turbo kicked in - if you are cruising more than 5 miles or so...


Am I missing something?
Thanks

The turbo will still be spinning at low speeds and light loads. As long as the engine burns clean enough under light load to not load up the turbo with soot, it shouldn't be an issue if you're under a light enough load to not build any boost.
rslifkin is online now   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 11:03 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012