Reply
 
Thread Tools Display Modes
 
Old 11-25-2014, 09:12 PM   #1
Veteran Member
 
SteveandZoila's Avatar
 
City: Nashville TN
Country: USA
Vessel Name: Miss Rita
Vessel Model: 1978 Gulfstar 44MC
Join Date: Jan 2014
Posts: 67
Fuel usage 135hp natural Perkins or Lehman vs.

Fuel usage 135hp natural Perkins or Lehman vs.200hp engines possibly turbo.

Newbie, I am going to retire and buy in the next 6 months, want to explore. I am going to Fl. at X-mas to look around. Looking for ~40' sun deck Trawler ~ 20,000# in the 1980's price range. I have read enough that if you cruise at hull speed , about 7kts, you can get best mileage, but twin 200 hp or larger are not are really not efficient at that speed. I am open to all ideals. Also can you remove Turbos and make the engine a lower HP? .Open to any advice.

__________________
Advertisement

SteveandZoila is offline   Reply With Quote
Old 11-25-2014, 11:12 PM   #2
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 3,882
Comparing the Ford, Perkins 120-135 nats with the 210 Cummins turbo- all should give near identical fuel burns if making the same hp typical of trawler service. No benefit in pulling a turbo, if it is not making boost, it just spins at low speed with little drag on the engine.

Some of the older Perkins and Ford higher output engines, around 200-250hp are rather troublesome due to aging on the various coolers.
__________________

Ski in NC is online now   Reply With Quote
Old 11-25-2014, 11:41 PM   #3
Guru
 
tpbrady's Avatar
 
City: Anchorage/Wrangell
Country: USA
Vessel Name: Silver Bay
Vessel Model: Nordic Tug 42-002
Join Date: Sep 2012
Posts: 505
I would be thinking of cruising at 6kts rather than 7kts. The difference on my Perkins 6.354 is 1.4 gph at 1500 rpm or 2.0 gph at 1700 rpm.

Tom
tpbrady is offline   Reply With Quote
Old 11-25-2014, 11:51 PM   #4
Senior Member
 
GoldenDawn's Avatar
 
City: Brentwood Bay, BC
Country: Canada
Vessel Name: Golden Dawn
Vessel Model: Krogen 42
Join Date: May 2011
Posts: 116
We have a Kadey Krogen 42' with Lehman 135. This summer we did 1,039 n mi, 183 hr on the Lehman and averaged 1.55 gal/hr. Between 6 & 7 knots most of the time. The fuel consumption includes the generator use too.
GoldenDawn is offline   Reply With Quote
Old 11-26-2014, 09:40 AM   #5
Veteran Member
 
SteveandZoila's Avatar
 
City: Nashville TN
Country: USA
Vessel Name: Miss Rita
Vessel Model: 1978 Gulfstar 44MC
Join Date: Jan 2014
Posts: 67
That I can live with, 6 kts is fine, I plan to take it easy, but go far. I think the Krogen is a single, don't know about Mia Terra. Most 40' boats are twins.
SteveandZoila is offline   Reply With Quote
Old 11-26-2014, 11:14 AM   #6
Guru
 
tpbrady's Avatar
 
City: Anchorage/Wrangell
Country: USA
Vessel Name: Silver Bay
Vessel Model: Nordic Tug 42-002
Join Date: Sep 2012
Posts: 505
Mia Terra is a single engine. We've logged about 4600 miles over the last two years mainly between 6 and 7 kts. Average fuel economy based on distance and fuel consumed is about 4.8 mpg.

Tom
tpbrady is offline   Reply With Quote
Old 11-26-2014, 11:36 AM   #7
Guru
 
siestakey's Avatar
 
City: Sarasota,FL/Thomasville,GA
Country: USA
Vessel Name: Steppin Stone IV
Vessel Model: Marine Trader Kelly Trawler 46
Join Date: Jul 2013
Posts: 1,271
Send a message via Skype™ to siestakey
Quote:
Originally Posted by tpbrady View Post
Mia Terra is a single engine. We've logged about 4600 miles over the last two years mainly between 6 and 7 kts. Average fuel economy based on distance and fuel consumed is about 4.8 mpg.

Tom
nice Tom
siestakey is offline   Reply With Quote
Old 11-26-2014, 11:39 AM   #8
Guru
 
djmarchand's Avatar
 
City: East Greenwich, RI
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 2,875
To expand a bit on Ski's post above, it isn't surprising that these three engines: Cummins 6BT, Perkins 6.354 and the Lehman 135 all have the same fuel burn at low hp loadings.

They all are approximately the same displacement and all require about the same "parasitic" hp to turn over the machinery. And at low rpms the turbocharged Cummins isn't producing any boost to speak of, so operates similarly to the other two NA engines.

My 370 hp Yanmar 6LY at 5.3 liters will also deliver about the same fuel economy at low hp loadings at 1,500-1,800 rpms.

So, the point is, there is no fuel consumption penalty to having a high hp, turbo charged engine on a boat if you only want to run it at trawler speeds.

David
djmarchand is online now   Reply With Quote
Old 11-26-2014, 11:51 AM   #9
Veteran Member
 
SteveandZoila's Avatar
 
City: Nashville TN
Country: USA
Vessel Name: Miss Rita
Vessel Model: 1978 Gulfstar 44MC
Join Date: Jan 2014
Posts: 67
engine size

I read in other posts a formula for HP for hull speed. It seems to say its less than 100hp to move a 20,000# at hull speed, ~ 6-7kts. Best engine would be smaller, less heat, less fuel, probably mid range. saying that, if you are right, I could expand my search to larger engines, just want the best economy I can get.
SteveandZoila is offline   Reply With Quote
Old 11-26-2014, 12:26 PM   #10
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 3,882
The best engine would be smaller to get the best mpg, but that may be hard to find in a 80's 40' cruiser. Many boats then were powered with larger engines that could put it up to planing speed or close. Lots of those on the market. Even though the engines are much larger than needed for hull speed, they can still get decent mpg, but not as good as one designed for slow speed and powered appropriately.

A 40' planing style cruiser with 320hp engines can get 2-3 mpg at 6-7kts.

A 40' displacement hull trawler with 120hp single can get 4-5 mpg at 6-7kts.

Only 1 or 2 mpg difference, but can be 50-100% more fuel to make the same trip.

Full displacement trawlers command a higher price than planing cruisers, so you have to weigh cost of purchase against cost of cruising fuel. And weigh another gazzilion considerations!!!!

p.s. Florida boats can be sun baked and corroded due to the clime. Consider expanding your search northward, including Great Lakes. Those boats hardly age at all. And you can take it down the river to warmth!!
Ski in NC is online now   Reply With Quote
Old 11-26-2014, 12:52 PM   #11
Veteran Member
 
SteveandZoila's Avatar
 
City: Nashville TN
Country: USA
Vessel Name: Miss Rita
Vessel Model: 1978 Gulfstar 44MC
Join Date: Jan 2014
Posts: 67
single engines

I don't see many single engines. I think you are right many "trawlers" got too big of engines, don't think 700+HP 40' trawlers are selling well. I know you are right about Fl. boats, but we want to look around. Most big boats here are under cover and up north some are put in heated storage!!
SteveandZoila is offline   Reply With Quote
Old 11-26-2014, 01:19 PM   #12
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,673
Quote:
Originally Posted by SteveandZoila View Post
I don't see many single engines. I think you are right many "trawlers" got too big of engines, don't think 700+HP 40' trawlers are selling well. I know you are right about Fl. boats, but we want to look around. Most big boats here are under cover and up north some are put in heated storage!!
Most Great Lakes boats of that size are in heated storage 7 months of the year. The boating season is typically 5 months and that translates to less sun exposure and usually less engine hours. Salt isn't a problem either if they have always been on the Great Lakes. It is amazing how long a boat and its equipment will hold up on Lake Michigan. But then, I am biased.
Donsan is online now   Reply With Quote
Old 11-26-2014, 01:52 PM   #13
Guru
 
djmarchand's Avatar
 
City: East Greenwich, RI
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 2,875
If you want the absolute best low speed fuel economy (and I am not saying that that is a good decision) then look for a full displacement (round bottom for the most part) hull. There aren't many of these on the market: Nordhavns, Kady Krogens, Willards, Diesel Duck to name a few, compared to semi-displacement hulls.

There is probably more fuel efficiency to be gained by the efficient full displacement hull type than to be gained by the smaller engines in them, but taken together they will give you the best fuel economy.

It will be a rare semi-displacement hull that has just enough hp to get to hull speed plus a small margin. As Ski said, they usually have enough hp to partially plane.

And finally fuel usage is not the biggest cost of boat ownership. I spend about $2,000 per year fueling my high hp, semi displacement boat, probably less now thanks to fracking.

David
djmarchand is online now   Reply With Quote
Old 11-26-2014, 04:57 PM   #14
Veteran Member
 
SteveandZoila's Avatar
 
City: Nashville TN
Country: USA
Vessel Name: Miss Rita
Vessel Model: 1978 Gulfstar 44MC
Join Date: Jan 2014
Posts: 67
Thanks

David, I think from what I have seen, a semi-displacement hull is the target. 38-44 sundeck, aft cabin. Yes from what I read fuel is not the only cost, and for many not the biggest. Just I dream of a lot of traveling and just don't want fuel cost to slow me down. ie 20gals/hr!! Steve
SteveandZoila is offline   Reply With Quote
Old 11-26-2014, 06:13 PM   #15
Guru
 
djmarchand's Avatar
 
City: East Greenwich, RI
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 2,875
Steve:

20 gph of diesel makes about 350 hp. You only need 2-3 gph to go 7 kts almost irrespective of which engines it has in it!!!

David
djmarchand is online now   Reply With Quote
Old 11-26-2014, 07:40 PM   #16
Guru
 
Join Date: Apr 2014
Posts: 1,291
Just look at it this way. No matter what Diesel motor 40-500hp turbo or not they all burn about one gallon per hour for an output of 20 hp. Many full displacement boats don't need more than 30-40hp to attain one knot shy of their hull speed. One two or three motors will need only the same amount of hp to push boat as a single and burn about one gallon per 20 hp between them. What is lost with twins is the extra fuel to idle or run alternators and other add ons but when moving along not that big a deal.Weight of the boat and water line length and beam are very important factors. A long light narrow boat will be best for fuel burn but not for accommodation or comfort. Many sailboats under power meet the criteria for very efficient full displacement craft.
eyschulman is offline   Reply With Quote
Old 11-27-2014, 06:12 AM   #17
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,515
>they all burn about one gallon per hour for an output of 20<

The IDEAL is about 20hp from a gal of diesel in a Properly loaded engine.

With modest underloading (like a claimed 120 hp tractor motor at 35HP), you would be lucky to see 15

With a 300HP lucky to see 12gp/gal at idle.

Many sailboats about 40 ft have smaller harder working (more efficient ) engines and operate at or under 1 gph at 6.5K.

Similar weight , to a 40 ft TT
FF is offline   Reply With Quote
Old 11-27-2014, 09:26 AM   #18
Guru
 
City: gulf coast
Country: pinellas
Join Date: Jun 2014
Posts: 2,197
Ski and DJ are right on target. My semi planning 38,000# aft cabin with twin 400 HP Cummins produces about 2-3 Nmpg at , 8kts, trawler speeds. Even better if I go slower .


Fuel difference from boat to boat turns out not to be as big a deal as people make out. The creature comforts of a wide, stable hull and the ability to go fast when I want all make us happy with the semi planning high HP design.


There are Prius and Tesla buyers then there is everyone else who wants a decent compromise. Those larger boats you mention as not selling to well is true. Mostly because people just don't understand fuel used is mostly determined by the operator ( speed), weight, hull form then down the list to installed HP.


If the maker called the boat a trawler back when it was made it has a higher price than if the maker called it an aft cabin motor yacht. So in the upside down world of used boats today with nobody able to really define what a trawler is larger more comfortable boats are cheaper and produce similar results. Go figure???


What everyone is nibbling around is an engine efficiency measurement called Brake Specific Fuel Consumption. (BSFC). That data is hard to find for each engine make and model but a web search will show that within engine classes (2 stroke, 4 stroke, turbo, etc) the fuel consumption of all engines in that class is similar. For 4 stroke diesels that is about 18 or so hP produced for one hour per gallon of fuel. That is HP used not MAX HP of the engine. So the difference between two same model boats with different engine sizes run at 7 KTs will be small but the one with more power will have the option of going faster.


I recommend forgetting what the boat model is called and getting the best value boat for your intended use in terms of creature comforts, stability, condition, equipment, and don't obsess over engine size. The results may surprise you, it did us and I would make the same choice again.
bayview is offline   Reply With Quote
Old 11-27-2014, 01:07 PM   #19
Guru
 
Join Date: Apr 2014
Posts: 1,291
RE; fuel burn. How many hours/year are you going to be underway? A very large % of boats don't get the kind of hours use where 20% or even 50% more fuel makes a significant difference considering other fixed costs. Many "TRAWLER "type boats get sold after 10 years use with less than 1,000 hours on engines some considerably less. I can see where a owner of a 30+ mile/hour boat that sucks over 60gal/hr might get upset with fuel burn if used >100 hrs year but even then the other costs of purchasing and owning that boat may eclipse the fuel. I agree with the good advise of others here look to the boat first and the fuel burn only if it is excessive and off the curve.
eyschulman is offline   Reply With Quote
Old 11-27-2014, 02:19 PM   #20
Veteran Member
 
SteveandZoila's Avatar
 
City: Nashville TN
Country: USA
Vessel Name: Miss Rita
Vessel Model: 1978 Gulfstar 44MC
Join Date: Jan 2014
Posts: 67
Thanks, I am listening.

Bayview, and others, Thanks for all the advice, you have put alot of thought into helping me, I am processing it. A few more questions: I have come across some different boats, wanted your opinion on fuel usage with in the 6-7 kts we have been discussing. Here's some of the boats:1970s 53' Hatteras with GM8v71s,a 1981 43' Viking 34,000# 275hp Cats,1980 43' Viking 310hp DD 671N.I know all these are planing hulls, does that throw out the fuel usage we have discussed? I gotta say the picture of the Hatteras makes me want it, even if is a 70s boat, kind of like women. Did I just type that!Steve
__________________

SteveandZoila is offline   Reply With Quote
Reply

Thread Tools
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 07:35 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012