Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-28-2018, 06:02 AM   #21
Guru
 
City: Sydney
Join Date: Jul 2015
Posts: 1,646
14.816 kph here
__________________
Advertisement

gaston is offline   Reply With Quote
Old 03-28-2018, 06:33 AM   #22
Guru
 
ranger42c's Avatar
 
City: Maryland
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 5,316
We cruise often at 8 MPH.



Knot really; usually somewhere between 7-8.5 kts. Waterline length is 43' so our economical speeds would theoretically be between about 6.5 kts and 8.8 kts... and at the lower end of that range would use less fuel...

But at the same time, we're usually balancing speed versus sea states versus backwash/froth rocking our aft-mounted dinghy too much if we go too fast but not on plane versus engine temps.

For the latter, we usually need around 1200 RPMs to get temps over the thermostat opening and steady within the (lower end of the) recommended operating range. After we reach that point, we can eventually move to lower RPMs without losing temps...

But it usually happens that about 1200 RPMs (plus/minus 25 wherever I can get the engines synced on a given trip) usually gives us about 8 or 8+ kts with no current to speak of, or about 7 kts into a stiffer current.

But then sometimes we run at 20 knots.

All good.

-Chris
__________________

__________________
South River, Chesapeake Bay
ranger42c is offline   Reply With Quote
Old 03-28-2018, 06:37 AM   #23
Senior Member
 
City: Lutz
Join Date: Jan 2016
Posts: 460
Quote:
Originally Posted by dhmeissner View Post
aren't you dudes something real Admirals of the ocean sea!
geoleo is offline   Reply With Quote
Old 03-28-2018, 07:09 AM   #24
Senior Member
 
City: Lutz
Join Date: Jan 2016
Posts: 460
That's funny, The ICW and the Okeechobee waterways have mile markers. Guess all those people in boats on them are not "real boaters" (maybe robots?) lol And the amateur Previous owner I bought my trawler from had all his instruments set to miles ---- he had only traveled 3600 miles every year for the past 15 years round trip from Maine to Stuart Florida using miles-he evidently was not a "real boater" I wish I was a real boater . I have only traveled in my own sailboat s over 26000 nautical miles offshore in the past 47 years.
geoleo is offline   Reply With Quote
Old 03-28-2018, 07:13 AM   #25
Guru
 
jleonard's Avatar
 
Join Date: Jun 2008
Posts: 4,002
When I am in an area that uses regular miles I set my GPS that way. When I am in an area that uses nautical miles I change again.
No big deal.
__________________
Jay Leonard

New Port Richey,Fl
jleonard is offline   Reply With Quote
Old 03-28-2018, 07:54 AM   #26
Guru
 
Donna's Avatar
 
City: Palm Coast
Vessel Name: Southerly
Vessel Model: 1986 Marine Trader 36' Sundeck
Join Date: Aug 2016
Posts: 1,181
Quote:
Originally Posted by Simi 60 View Post
What indicates it as the sweet spot?
She is quiet, nice smooth ride, gauges look perfect, handles well.
Donna is offline   Reply With Quote
Old 03-28-2018, 08:28 AM   #27
Guru
 
Maerin's Avatar
 
City: East Coast
Vessel Name: M/V Maerin
Vessel Model: Solo 4303
Join Date: Jun 2013
Posts: 833
Speed consideration in a trawler is a bit of an oxymoron, kind of like "sailboat. racing". If the excitement of slicing through the waves with your combover flailing in the wind is your idea of proper boating, perhaps a trawler isn't the best choice.
__________________
Steve Sipe
Selene 4303 Maerin
https://maerin.net
Maerin is offline   Reply With Quote
Old 03-28-2018, 08:30 AM   #28
Guru
 
alormaria's Avatar
 
City: Trenton
Join Date: Apr 2012
Posts: 1,244
I do 1750 RPM. It seems way faster to say.
__________________
Al Johnson
34' Marine Trader
"Angelina"
alormaria is offline   Reply With Quote
Old 03-28-2018, 08:38 AM   #29
Guru
 
City: Northport
Join Date: Aug 2015
Posts: 1,656
Whenever we were happy to go slow we did 6-6.5 knots (45-47' boats) because that was a very quiet and efficient speed. There would appear no reason to exceed that unless we were wanting to go fast which would be sacrifice the efficiency.
We often went fast but it was not a matter of stepping up 25% in speed for a 75% increase of fuel use per mile. ( 8 vs 6 knots)
smitty477 is offline   Reply With Quote
Old 03-28-2018, 08:45 AM   #30
Senior Member
 
schrater's Avatar
 
City: Tacoma, WA
Vessel Name: Matilda
Vessel Model: Ponderosa (CHB) 35' Sundeck
Join Date: Sep 2016
Posts: 121
To the original question, itís not just length, but also beam. Most trawlers increase the beam along with the length, keeping the same basic ratio intact, meaning the same basic max speed, give or take a knot.
schrater is offline   Reply With Quote
Old 03-28-2018, 09:07 AM   #31
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 9,456
Quote:
Originally Posted by geoleo View Post
That's funny, The ICW and the Okeechobee waterways have mile markers. Guess all those people in boats on them are not "real boaters" (maybe robots?) lol And the amateur Previous owner I bought my trawler from had all his instruments set to miles ---- he had only traveled 3600 miles every year for the past 15 years round trip from Maine to Stuart Florida using miles-he evidently was not a "real boater" I wish I was a real boater . I have only traveled in my own sailboat s over 26000 nautical miles offshore in the past 47 years.
Do you call the pointy end the front, the other end the rear, one side the left, and the other side the right? I have no issue with dirt dwellers not learning the nomenclature of boating. It just seems to me that if you have enough of an interest to buy a boat and cruise, you should strive to use the nautical terms.

Btw, in case you weren't aware, the ICW was laid out and marked by government employees (not mariners) for Inland (inside the line of demarcation ) navigation. That's why I differentiated myself from a land locked boater in my previous post.

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
O C Diver is offline   Reply With Quote
Old 03-28-2018, 09:46 AM   #32
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 17,192
6.15 knots for Willy.

Sweet spot is a willy nilly expression that can mean numerous things.

1. Least vibration or noise is probably the most common.
2. Least fuel consumption. But that’s actually a speed almost
knows and it may be only about 4 knots.
3. Hull speed. Many think most things magical happen at hull speed.

And there are others like what the wife likes or what da book says. I think lots of us may just notice that even a bit above a certain rpm the noise seems to suddenly get a bit objectionable. Mark has said for years one knot below hull speed but that’s basically for his WLL and a full disp hull. Few fit into that slot on this fourm. 1 1/2 knot would be closer to cover all. And w many or even most SD hulls here hull speed would be hard to beat. After all SD hulls are designed to go faster.
But re fuel burn one knot below hull speed is a very good target to shoot for. Bigger boats burn more fuel and saving more would make even more sense. I thought the first time Mark said that, it was a good rule of thumb.

But sweet spot may just mean what speed we like the most. My point is that the “sweet spot” is not well defined at all but being inspecific on this forum has it’s advantages. How I got to 6.15 knots? Over time I noticed I very often picked 2300rpm and one day I did some back and forth runs and for all practical purposes the GPS said the average was 6.15.
__________________
Eric

North Western Washington State USA
Nomad Willy is online now   Reply With Quote
Old 03-28-2018, 10:19 AM   #33
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 20,988
'Most trawlers increase the beam along with the length, keeping the same basic ratio intact, meaning the same basic max speed, give or take a knot.'

Changes in the L/B ratio do not matter at displacement speeds till about 6-1 is reached.

More wetted surface at 6-1 means slower speed for same fuel burn, but less wave making at a higher speed is why skinny boats are built.

For most displacement boats waterline length is key to speed , weight is key to power required to get to that speed.
FF is offline   Reply With Quote
Old 03-28-2018, 11:47 AM   #34
Guru
 
ancora's Avatar
 
Join Date: Dec 2007
Posts: 3,775
We run our 36' (40' OA) semi-displacement trawler at 8.5 knots, with the speed accurately ascertained by runnin' the measured mile monthly, before every Predicted Log contest.
ancora is offline   Reply With Quote
Old 03-28-2018, 11:50 AM   #35
Guru
 
Alaskan Sea-Duction's Avatar
 
City: Inside Passage Summer/Columbia River Winter
Vessel Name: Alaskan Sea-Duction
Vessel Model: 1988 M/Y Camargue YachtFisher
Join Date: Jul 2012
Posts: 6,073
Quote:
Originally Posted by ghost View Post
We were dirt hotelers recently in Astoria. I pulled up ship finder and saw some boat named Alaskan Sea Duction on AIS just up river. You should reach out to them having a similar boat name and all.
That is us at our winter dock! We are upriver about 40 miles or so...
Alaskan Sea-Duction is offline   Reply With Quote
Old 03-28-2018, 12:44 PM   #36
Guru
 
Codger2's Avatar
 
City: San Diego
Join Date: Oct 2007
Posts: 6,529
Quote:
Originally Posted by ranger42c View Post
But then sometimes we run at 20 knots.
When I first bought Sandpiper, we topped off the fuel & water tanks, had 5 adults on board & went for a sea trial. The photo below shows the speed results. It does not, however, show the mpg! Suffice is to say I've never seen this speed again but I do run at 15-17 knots frequently. At 8 knots, she's about 1 mpg.
Attached Thumbnails
Click image for larger version

Name:	Panel.jpg
Views:	92
Size:	113.3 KB
ID:	74590  
__________________
Done with diesel power boats! Investigating all electric!
Codger2 is offline   Reply With Quote
Old 03-28-2018, 01:40 PM   #37
Guru
 
AKDoug's Avatar
 
City: Kenai, Alaska
Vessel Name: Melanie Rose
Vessel Model: 1999 Willard PH
Join Date: Feb 2013
Posts: 914
The waterline length to speed ratio only works for pure displacement vessels, many on this forum aren't displacement hulls. They just operate them as displacement vessels at displacement speeds.

My 30' hull has a less than 30' waterline length, since it is a double ender. I can run 7 knots (1 gph) or 5.5 (.42 gph) but the true "happy speed" is somewhere in between where the harmonics of the engine are disagreeable. At 7 knots it's a wet ride in any kind of chop, at 5.5 I am floating in a happy little bubble on the surface.
AKDoug is offline   Reply With Quote
Old 03-28-2018, 02:03 PM   #38
Veteran Member
 
1Sailor's Avatar
 
City: Peconic
Vessel Name: Moondance
Vessel Model: Atlantic Prarie 30 LRC
Join Date: Sep 2012
Posts: 76
Nobody has mentioned the formula for hull speed for displacement boats = 1.34X the square root of your waterline.
1Sailor is offline   Reply With Quote
Old 03-28-2018, 02:10 PM   #39
Guru
 
City: Fairport, NY and Palm Coast, FL
Join Date: Jan 2017
Posts: 1,879
Quote:
Originally Posted by AKDoug View Post
I can run 7 knots (1 gph).
That is awesome!

This is almost double nmpg my 17 foot key west, all of maybe 1200 lbs.
diver dave is offline   Reply With Quote
Old 03-28-2018, 02:59 PM   #40
Senior Member
 
tallswede's Avatar
 
City: Baytown, Texas
Vessel Name: Islander
Vessel Model: Prairie 36
Join Date: May 2013
Posts: 284
Islander's hull speed calcs. to 7.76 kts. I find I like 1400 - 1600 rpm cruise which is usually between 6-7 knots. My boat is semi displacement and I have seen 12 kts @ 2200 rpm but the engines are working hard. Over time, running my usual cruise speeds I find I'm burning between .8 - 1.4 gpm fuel per engine which seems right in line with most Perkins 4-236s I've heard of in similar boats.

Kevin
__________________

tallswede 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





All times are GMT -5. The time now is 11:12 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×