Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-15-2018, 11:51 AM   #1
Member
 
City: Hilton Head Island
Country: United States
Join Date: May 2018
Posts: 18
Diesel Engine choice question

I am looking at getting a trawler with a full displacement hull (40 ft). If I have the choice of getting it with a 250HP, 350HP or a 480HP single diesel engine, will I get much better operating characteristics out of the larger engine? Aside from fuel consumption and cost of the larger engine, any other benefits or issues I may face by going up or down in engine size. Thanks!
__________________
Advertisement

Mark P is offline   Reply With Quote
Old 05-15-2018, 12:20 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: 4,424
Post the engine brands and models of your choices. 250hp is more than necessary for a 40' displacement hull. At cruise you might need about 60-80hp so a 120-200hp rated engine would be plenty. No advantage going with a 350 or 480, but there is some brand specific stuff that might favor one or the other.
__________________

Ski in NC is offline   Reply With Quote
Old 05-15-2018, 01:36 PM   #3
Senior Member
 
Vashon_Trawler's Avatar
 
City: St. Petersburg, Florida
Country: USA
Vessel Name: M/V Sherpa
Vessel Model: 24' Vashon Diesel Cruiser
Join Date: Jun 2013
Posts: 481
Both 350 HP and 480 HP seem like extreme overkill for a 40' FD trawler. I agree with Ski, 120 HP to 200 HP would be far more practical.
__________________
Go small, go simple, go now
― Larry Pardey, Cruising in Seraffyn
Vashon_Trawler is offline   Reply With Quote
Old 05-15-2018, 01:42 PM   #4
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 6,868
Quote:
Originally Posted by Ski in NC View Post
Post the engine brands and models of your choices. 250hp is more than necessary for a 40' displacement hull. At cruise you might need about 60-80hp so a 120-200hp rated engine would be plenty. No advantage going with a 350 or 480, but there is some brand specific stuff that might favor one or the other.
+1

Not only post the engines but I'd be curious to see what the 40' boat is.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 05-15-2018, 02:19 PM   #5
Senior Member
 
Gabe n Em's Avatar
 
City: Savannah, GA
Country: USA
Vessel Name: In Sanity
Vessel Model: 1981 Mainship 40'
Join Date: Jan 2015
Posts: 381
At 480hp, that sure sounds like a planing hull.
Gabe n Em is offline   Reply With Quote
Old 05-15-2018, 02:22 PM   #6
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 6,868
Quote:
Originally Posted by Gabe n Em View Post
At 480hp, that sure sounds like a planing hull.
Yeah, I am a bit surprised that a FD hull would even offer it.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 05-15-2018, 02:37 PM   #7
Guru
 
djmarchand's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Join Date: Aug 2012
Posts: 3,647
What boat are you considering. There are very few full displacement hull trawlers in the 40' range: Krogen, Nordhavn, Willard, Hatteras LRC. That is about it. All of those use much lower powered engines than 480 hp.

I suspect you are talking about a semi-displacement hull.

David
djmarchand is online now   Reply With Quote
Old 05-15-2018, 02:50 PM   #8
Member
 
City: Hilton Head Island
Country: United States
Join Date: May 2018
Posts: 18
Thanks for great info. Looking at those names but also a Helmsman 38E or 43 Pilothouse, and they seem to offer quite a range in terms of engines, so that sparked my question.
Mark P is offline   Reply With Quote
Old 05-15-2018, 03:01 PM   #9
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 5,874
My 45' trawler requires 70 HP to cruise at 8 knots. The semi planning hull could also do 14 knots, but that required a 450 HP engine. Figure out what you want for a cruising speed (displacement or planing) and then pick the appropriate engine.

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 online now   Reply With Quote
Old 05-15-2018, 03:19 PM   #10
Guru
 
AusCan's Avatar
 
City: Adelaide
Country: Australia
Vessel Name: Kokanee
Vessel Model: Cuddles 30 Pilot House Motor Sailer
Join Date: Jul 2012
Posts: 2,489
Helmsman don't offer a displacement hull. It is a semi-displacement hull, although most owners prefer to cruise them at displacement speeds to avoid using 20+ gallons per hour.
AusCan is offline   Reply With Quote
Old 05-15-2018, 03:22 PM   #11
Senior Member
 
Woodland Hills's Avatar
 
City: Jacksonville
Country: USA
Vessel Name: Alzero
Vessel Model: Hatteras 63' CPMY
Join Date: Apr 2017
Posts: 382
If this is a new boat and you can order her with a choice of three different engines, then I would get the one that is the most popular. All three choices will cruise as well with similar economy at hull speed, but the most popular size engine will have the best resale value. If we are talking about used boats more than a decade old then the condition of the individual motor is more important than its horsepower.
Woodland Hills is online now   Reply With Quote
Old 05-15-2018, 03:57 PM   #12
Guru
 
djmarchand's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Join Date: Aug 2012
Posts: 3,647
Quote:
Originally Posted by Markpadilla View Post
Thanks for great info. Looking at those names but also a Helmsman 38E or 43 Pilothouse, and they seem to offer quite a range in terms of engines, so that sparked my question.
Ok. The full displacement hulls won't benefit a bit from the higher hp engines you asked about. So your question only relates to the Helmsman and similar semi-displacement hulls.

First the semi-displacement hull is not as efficient as the full displacement hull at displacement speeds. So just to go as fast as a full displacement hull takes more hp, sometimes 50% more.

The Helmsman 43 is listed at 35,000 lbs dry but could easily weigh 45,000 lbs with full fuel, water, crew and gear. A rule of thumb (confirmed from data in Bebe's book) is that it takes 1.5 hp per thousand pounds of displacement to push a full displacement hull to its displacement speed. Displacement speed is 1.34* sqrt(lwl). So it could take 68 hp to do that and over 100 hp for a semi-displacement hull. That really means a 200 hp engine so you don't have to run it at red line all day and also have some headroom for pushing into head seas.

So, Helmsman offers the Cummins QSB 6.7 250 hp engine for that boat. It would be a good choice but you can't expect to cruise at more than displacement speed with it. But they also offer the 480 hp version of THAT SAME ENGINE.

There is no mechanical difference between a 250 hp QSB 6.7 and a 480 hp one, just computer chip tuning differences. You can buy a 250 hp version and later if you think you want more hp, Cummins for a price will change the chip to let it produce 480 hp. It will probably take a prop change or maybe a prop and transmission change, but the base engine stays the same.

I am guessing 480 hp won't do you much good. It takes about 100 hp to hit displacement speed or about 8.5 kts. With 300 hp which is probably all you should cruise the QSB at, you won't go that much faster, maybe 12-13 kts. A good comparison would be the Mainship 400 with the Yanmar 370 hp engine. Mainship's old website says that boat and engine will do 13 kts at 3,000 rpm which roughly equivalent to the QSB 6.7 at 300 hp.

So does that answer your original question? In summary the higher hp engine isn't any different mechanically from the 250 hp engine, so fuel economy and longevity will be the same at or below displacement speeds. It takes a chip and maybe a transmission and certainly a prop to make and use 480 hp and that will maybe get you another 4 kts.

David
djmarchand is online now   Reply With Quote
Old 05-15-2018, 07:13 PM   #13
Guru
 
ancora's Avatar
 
Join Date: Dec 2007
Posts: 3,548
Any make but VOLVO...run from them as you would the plague.
ancora is offline   Reply With Quote
Old 05-15-2018, 07:32 PM   #14
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 6,868
Quote:
Originally Posted by Mark P View Post
Thanks for great info. Looking at those names but also a Helmsman 38E or 43 Pilothouse, and they seem to offer quite a range in terms of engines, so that sparked my question.
As many of us thought, semi-displacement. Most of the time you will run them at displacement speeds so don't really need a lot of power. I have a North Pacific 43. It has a Cummins 380hp engine. The boats were offered with a 330hp version of the same engine. I don't think I benefit at all by having the extra 50hp, but it doesn't hurt me either. As David mentioned above, the different is just in the ECU programing.

If you are looking at the Helmsman, I would also suggest looking at the North Pacific Yachts in the same size ranges.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 05-15-2018, 07:52 PM   #15
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 2,879
Quote:
Originally Posted by ancora View Post
Any make but VOLVO...run from them as you would the plague.
It is not the first time that I ask that question and never received much answer, why is that?
I do not own a volvo nor have any involvement with this brand just try to educate myself.
Only thing I know about these engine is that I have friend who got a new boat built (not a trawler) and put a Volvo in it (don't know the exact model something around 450ch) and it is nicely running and quite fuel conservative for the speed.

May you elaborate?

L
Lou_tribal is offline   Reply With Quote
Old 05-15-2018, 07:56 PM   #16
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 2,817
For what it is worth, my boat weighs north of 65 tons. She as a CAT 3306 and uses 80 hp to move her at 8 knots with a clean bottom, burning 4 gph. At WOT she burns 15 gph and I move at 9.5 knots. I travel at 7.5 knots and around 3 gph, using 60 hp so I run her up to WOT for 20 minutes every 8 hours of run time or so. If you are going to be traveling at trawler speeds, a 40 foot trawler could get by easily with a 100 hp engine. My boat could do just fine with 150 hp to 175 hp.

Semi-planing is a different story altogether.
__________________
Delfin
"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis." - Jack Handy
Delfin is offline   Reply With Quote
Old 05-15-2018, 08:16 PM   #17
Guru
 
Ken E.'s Avatar
 
City: Bellingham WA
Country: United States
Vessel Name: Hatt Trick
Vessel Model: 45' Hatteras Convertible
Join Date: Nov 2016
Posts: 519
Quote:
Originally Posted by Lou_tribal View Post
It is not the first time that I ask that question and never received much answer, why is that?
I do not own a volvo nor have any involvement with this brand just try to educate myself.
Only thing I know about these engine is that I have friend who got a new boat built (not a trawler) and put a Volvo in it (don't know the exact model something around 450ch) and it is nicely running and quite fuel conservative for the speed.

May you elaborate?

L
I've never owned Volvo but I have friends that do. Most talked about is the high cost of parts. On the plus side, Volvos are used extensively in Alaska's Bristol Bay fishery where they run the hell out of them and they're are loved for their durability. Plenty of power for their size and weight.
Ken E. is offline   Reply With Quote
Old 05-15-2018, 11:51 PM   #18
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 5,506
Quote:
Originally Posted by djmarchand View Post

I suspect you are talking about a semi-displacement hull.

David
+1
__________________
Codger2

My passion for improving my boat(s) exceeds my desire to constantly cruise them.
Codger2 is offline   Reply With Quote
Old 05-16-2018, 01:08 AM   #19
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: 1,800
Send a message via Skype™ to siestakey
Quote:
Originally Posted by Lou_tribal View Post
It is not the first time that I ask that question and never received much answer, why is that?
I do not own a volvo nor have any involvement with this brand just try to educate myself.
Only thing I know about these engine is that I have friend who got a new boat built (not a trawler) and put a Volvo in it (don't know the exact model something around 450ch) and it is nicely running and quite fuel conservative for the speed.

May you elaborate?

L
I hear it a great deal also I am the 3rd owner of my boat with Volvo TAMD great engines but parts can be pricey if your not willing to shop
__________________
Alan
Skype roatan63
siestakey is offline   Reply With Quote
Old 05-16-2018, 03:36 AM   #20
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: penultimate Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,880
With a full displacement hull, the fewer HP is needed. Eighty HP would be sufficient. But is the boat a true FD?
__________________

__________________
Kar-KEEN-ez Koot
markpierce 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 07:28 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012