Reply
 
Thread Tools Display Modes
 
Old 01-08-2013, 01:45 AM   #301
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: 2011 Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,254
Al, it is a bottomless pit.
__________________
Advertisement

__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 01-08-2013, 06:20 AM   #302
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,515
Al, it is a bottomless pit.

NO it is a religion , just like anchors, fear of gasoline or propane , or for some leaving the dock
__________________

FF is offline   Reply With Quote
Old 01-08-2013, 04:14 PM   #303
Guru
 
Anode's Avatar


 
City: Missourah
Country: USA
Vessel Name: M/V Scout
Vessel Model: Sundowner Tug 30'
Join Date: Jul 2010
Posts: 645
Quote:
Originally Posted by FlyWright View Post
Wow!! 300 posts and we still haven't settled the question. Let's hope we'll get to the bottom of this in the next 300 posts.
I actually figured it out 3 or 4 boats ago....
__________________
Chip

Deliveries & Yacht Services
www.captainchip.com
Anode is offline   Reply With Quote
Old 01-08-2013, 04:29 PM   #304
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
Quote:
Originally Posted by FlyWright View Post
Wow!! 300 posts and we still haven't settled the question. Let's hope we'll get to the bottom of this in the next 300 posts.
as Eric pointed out in order to answer this question we will have to establish the criteria upon which we will base our answer then graph the results. We would also need a list of the advantages and disadvantages of twins and singles. If we do this it appears that there are only two tentative advantages of twins over singles and those are: 1) manuveurability < trumped by singles with thrusters>
2) less chance of being stranded because of a redundant complete engine system

The advantages of a single according to this thread are:
1) greatly improved fuel efficiency
2) prop and rudder protected by keel
3) less weight allowing for greater cargo
4) half the maintenence costs of a similiar vessel with twins
5) Much quieter operation than twins
6) More room in the engine compartment
7) More storage area for gear
8) initial cost much less than the same boat with twins

have i missed any?
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 04:49 PM   #305
Guru
 
SomeSailor's Avatar
 
City: Everett, WA
Vessel Name: Honey Badger
Vessel Model: 42' CHB Europa
Join Date: Oct 2011
Posts: 784
Quote:
Originally Posted by bfloyd4445 View Post
(1) manuveurability < trumped by singles with thrusters>
Can't get a thruster on a twin?

Quote:
Originally Posted by bfloyd4445 View Post
(1) greatly improved fuel efficiency
Define "greatly"

Quote:
Originally Posted by bfloyd4445 View Post
(3) less weight allowing for greater cargo
Bigger boat... no problem stowing everything the wife has shown up with yet.

Quote:
Originally Posted by bfloyd4445 View Post
(8) initial cost much less than the same boat with twins
Much better resale value, greater perceived market value among those looking for twins over a single for a 40,000# trawler.
SomeSailor is offline   Reply With Quote
Old 01-08-2013, 05:05 PM   #306
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 9,995
Greetings,
Mr. FlyWright. Nope THAT question will NEVER be settled to the satisfaction of some and there's no RIGHT answer. It's like at the strip. Ya run wut ya brung. The vessel I "babysit" was never offered, as far as I know, with a single option. Would i have preferred a single if I had to make the choice? Yes and I concur with some of Mr. 45's points but I got what I got and that's just fine with me. One can ponder and rationalize until they're blue in the face but, in this the 306th post, I just don't care. By the way the answer to the ultimate question is 42.

Just saw Mr. SS's post to which I might add; singles or twins are as quiet as the sound insulation allows. I have to listen quite intently to synchronize the engines at cruise.
__________________
RTF
RT Firefly is online now   Reply With Quote
Old 01-08-2013, 05:38 PM   #307
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
Bigger boat... no problem stowing everything the wife has shown up with yet.



Much better resale value, greater perceived market value among those looking for twins over a single for a 40,000# trawler. [/QUOTE]


Wife good point and so is the resale value. I guess since the inititial cost is more for a twin that the cost savings mentioned in my list as an advantage for the single is canceled out.

new list
advantages of twins over singles and those are:
1) manuveurability
2) less chance of being stranded because of a redundant complete engine system
3) better resale value

The advantages of a single according to this thread are:
1) greatly improved fuel efficiency
2) prop and rudder protected by keel
3) less weight allowing for greater cargo
4) half the maintenence costs of a similiar vessel with twins
5) Much quieter operation than twins
6) More room in the engine compartment
7) More storage area for gear
8) initial cost much less than the same boat with twins
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 05:44 PM   #308
Guru
 
Tad Roberts's Avatar
 
City: Flattop Islands
Country: Canada
Vessel Name: Blackfish
Vessel Model: custom
Join Date: Dec 2012
Posts: 707
I was thinking about this sometime in the night with regards to modern tugs, which almost without exception have multiple engines and drives. While they certainly do this for the aforementioned manoeuvrability and system redundancy, I think there are a couple of other good reasons as well.

Draft......Overall draft (with equal power and thrust) will be less with twin drives than with a single prop. This adds versatility to the job envelope......

Power Density.....In general it's possible to cram more horsepower into a smaller hull using twins. This pays off in smaller build costs and lower operating due to manning requirements based on tonnage. It doesn’t really apply to recreational boats except that (at least in theory) there could be more accommodation space and a smaller engine room.
Tad Roberts is offline   Reply With Quote
Old 01-08-2013, 05:47 PM   #309
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,868
Quote:
Originally Posted by bfloyd4445 View Post
Bigger boat... no problem stowing everything the wife has shown up with yet.



Much better resale value, greater perceived market value among those looking for twins over a single for a 40,000# trawler.

Wife good point and so is the resale value. I guess since the inititial cost is more for a twin that the cost savings mentioned in my list as an advantage for the single is canceled out.

new list
advantages of twins over singles and those are:
1) manuveurability
2) less chance of being stranded because of a redundant complete engine system
3) better resale value

The advantages of a single according to this thread are:
1) greatly improved fuel efficiency
2) prop and rudder protected by keel
3) less weight allowing for greater cargo
4) half the maintenence costs of a similiar vessel with twins
5) Much quieter operation than twins
6) More room in the engine compartment
7) More storage area for gear
8) initial cost much less than the same boat with twins[/QUOTE]

by PSNEELD- Your lists are inaccurate because there are too many examples of one being just the opposite....go back to square one....nevermind, don't start over...it's a waste of bandwidth to come up with absolutes that aren't...compare two boats side by side..but two general categories and all you can produce is generalities.
psneeld is offline   Reply With Quote
Old 01-08-2013, 06:01 PM   #310
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
Quote:
Originally Posted by Tad Roberts View Post
I was thinking about this sometime in the night with regards to modern tugs, which almost without exception have multiple engines and drives. While they certainly do this for the aforementioned manoeuvrability and system redundancy, I think there are a couple of other good reasons as well.

Draft......Overall draft (with equal power and thrust) will be less with twin drives than with a single prop. This adds versatility to the job envelope......

Power Density.....In general it's possible to cram more horsepower into a smaller hull using twins. This pays off in smaller build costs and lower operating due to manning requirements based on tonnage. It doesn’t really apply to recreational boats except that (at least in theory) there could be more accommodation space and a smaller engine room.
Are you saying that the addition of a second drive system's added weight results in less draft?

Power density? Hadn't thought of that. I tend to think of fuel economy and hull speed but then i am thinking of recreational boats
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 06:02 PM   #311
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
you got a point there, so how to we answer the original question?
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 06:28 PM   #312
Guru
 
Sailor of Fortune's Avatar
 
City: Saint Augustine, Fl.
Country: Port of St Augustine ,FL
Join Date: Sep 2009
Posts: 1,946
Tads right in respect to less draft with twins. Think deeper keel with the single engine. To build to a required Bollard pull is easier with twin engine setup. Because of the configuration of the engine room setup, it is usually more tonnage (Think documentation tonnage). Remember, tonnage is a volumetric calculation rather than a weight calculation.
Sailor of Fortune is offline   Reply With Quote
Old 01-08-2013, 06:42 PM   #313
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,868
Quote:
Originally Posted by bfloyd4445 View Post
you got a point there, so how to we answer the original question?

you...nor anyone else can.......
psneeld is offline   Reply With Quote
Old 01-08-2013, 06:52 PM   #314
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
Like TAD said some time ago. Singles are about CHEAP. They cost considerably less. So the greatest advantage of singles is that ther'e cheaper.

And Ilm not convinced singles are more efficient. Twins are more efficient in one significant way. They don't need to deploy their rudders 3 to 6 degrees to keep the boat going straight. Prop walk in forward gear is at least as effectual as it is in reverse but it's effects are felt all day long. And other than the drag of shafts and struts ther'e is no difference except w our typical double power twins except that they are over a ton more in weight to the singles. For slow vessels the amount of power required is most often calculated by the amount of power per ton of displacement so the extra weight is basically directly proportional to the extra fuel burn.

So if you realistically compare twins w the same disp and power (no other way is valid) I think personally that twins will come out ahead. I know most disagree w me but that what I think and why I think it. It all hinges on the question of "is the drag of the prop walk greater than the drag of the struts.

So to compare them honestly you'd need to create a pair of boats both halving their shafts going through a keel and their keel area must be the same and their total power must be the same. Or none of their shafts located inside their keels. I know of no such pair of boats

So if one compares the typical trawler w it's single engine shaft going through the keel w much less weight ... To ... The twin w both shafts dragging through the water and w all that extra weight
SURE the single will be more efficient!

But if tou want to compare singles and twins on equal terms I suspect the twin would come out more efficient.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 01-08-2013, 07:42 PM   #315
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,360
[QUOTE=bfloyd4445;124990]as Eric pointed out in order to answer this question we will have to establish the criteria upon which we will base our answer then graph the results. We would also need a list of the advantages and disadvantages of twins and singles. If we do this it appears that there are only two tentative advantages of twins over singles and those are: 1) manuveurability < trumped by singles with thrusters>
2) less chance of being stranded because of a redundant complete engine system

The advantages of a single according to this thread are:
1) greatly improved fuel efficiency Wrong
2) prop and rudder protected by keel Many twins have deep keels
3) less weight allowing for greater cargo Silly concept on a trawler
4) half the maintenence costs of a similiar vessel with twins Baloney, price out oil changes on a pair of JD 4045s vs a JD 6081.
5) Much quieter operation than twins Two engines at 80 dba or one at 80 dba is same noise
6) More room in the engine compartment If you are comparing a 34' sincle to a 48 foot twin, baloney
7) More storage area for gear Really, gear or junk
8) initial cost much less than the same boat with twins I have recent new boat price lists with a large single vs a set of smaller twins, not much difference overall
have i missed any Yes, there are few single engine choices above 45' unless you go with a very expensive builder such as Nordhavn or Selene. Many twin alternatives are available at much lower costs for a similar sized boat
sunchaser is offline   Reply With Quote
Old 01-08-2013, 07:42 PM   #316
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
Quote:
Originally Posted by Sailor of Fortune View Post
Tads right in respect to less draft with twins. Think deeper keel with the single engine. To build to a required Bollard pull is easier with twin engine setup. Because of the configuration of the engine room setup, it is usually more tonnage (Think documentation tonnage). Remember, tonnage is a volumetric calculation rather than a weight calculation.
I wasn't saying he was wrong i just didnt understand. Thinking about it the light bulb has lit thank you
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 07:53 PM   #317
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
Quote:
Originally Posted by manyboats View Post
Like TAD said some time ago. Singles are about CHEAP. They cost considerably less. So the greatest advantage of singles is that ther'e cheaper.

And Ilm not convinced singles are more efficient. Twins are more efficient in one significant way. They don't need to deploy their rudders 3 to 6 degrees to keep the boat going straight. Prop walk in forward gear is at least as effectual as it is in reverse but it's effects are felt all day long. And other than the drag of shafts and struts ther'e is no difference except w our typical double power twins except that they are over a ton more in weight to the singles. For slow vessels the amount of power required is most often calculated by the amount of power per ton of displacement so the extra weight is basically directly proportional to the extra fuel burn.

So if you realistically compare twins w the same disp and power (no other way is valid) I think personally that twins will come out ahead. I know most disagree w me but that what I think and why I think it. It all hinges on the question of "is the drag of the prop walk greater than the drag of the struts.

So to compare them honestly you'd need to create a pair of boats both halving their shafts going through a keel and their keel area must be the same and their total power must be the same. Or none of their shafts located inside their keels. I know of no such pair of boats

So if one compares the typical trawler w it's single engine shaft going through the keel w much less weight ... To ... The twin w both shafts dragging through the water and w all that extra weight
SURE the single will be more efficient!

But if tou want to compare singles and twins on equal terms I suspect the twin would come out more efficient.
are there any single engined duo proped trawlers? There are boat power system manufacturers that use two counter rotating props on the same shaft with a single engine. Volvo and Merc both make I/O systems like this
Prop walk loss is still there with a twin just that the off tracking is canceled by the other engine. So wouldn't you still have a net loss in efficiency with the twin?
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 08:09 PM   #318
Guru
 
City: coos bay
Country: usa
Join Date: Oct 2012
Posts: 1,203
[QUOTE=sunchaser;125043][QUOTE=bfloyd4445;124990]1) manuveurability < trumped by singles with thrusters>
2) less chance of being stranded because of a redundant complete engine system

The advantages of a single according to this thread are:
1) greatly improved fuel efficiency Wrong Based upon what others have said in this forum there is a fuel savings
2) prop and rudder protected by keel Many twins have deep keels True but all single engine displacement trawlers have protection
3) less weight allowing for greater cargo Silly concept on a trawler No so, i can think of many trips in which every available bit of space was filled with food drink toys for the raft up party on the 4th. One can always use extra space
4) half the maintenence costs of a similiar vessel with twins Baloney, price out oil changes on a pair of JD 4045s vs a JD 6081. Thats like comparing an apple to a pear. I was thinking like one lehman as opposed to two
5) Much quieter operation than twins Two engines at 80 dba or one at 80 dba is same noise I find it hard to believe that a 36gb with twins has the same level of cabin noise as one with a single
6) More room in the engine compartment If you are comparing a 34' sincle to a 48 foot twin, baloney I'm comparing like boat to like boat. Not accurate to compare a porsch to a vw
7) More storage area for gear Really, gear or junk .....your right it will likely end up filled with her junk
8) initial cost much less than the same boat with twins I have recent new boat price lists with a large single vs a set of smaller twins, not much difference overall interesting idea, i will have to check that out. Thanks
have i missed any Yes, there are few single engine choices above 45' unless you go with a very expensive builder such as Nordhavn or Selene. Many twin alternatives are available at much lower costs for a similar sized boat Thats another varible we havent nailed down, vessel size. I'm thinking under 49ft
bfloyd4445 is offline   Reply With Quote
Old 01-08-2013, 08:10 PM   #319
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Eric--- With regards to your above post, it would be interesting to know how the drag of a twin engine boat like our GB36 compares to the drag of the single engine version of the same boat.

The reason I wonder about this is that while our twin engine boat has a pair of shafts, struts, and spade rudders, the deep keel of our boat is cut short and reverse-curves up to blend into the bottom of the boat. As opposed to the deep keel of the single-engine boat which is carried a fair amount farther back to culminate in a vertical trailing ege and a shoe supporting a big rudder.

Don't know how it works with hydrodynamics but the single engine GB36 has, I think, more wetted surface than the twin. Would this result in more drag?
Marin is offline   Reply With Quote
Old 01-08-2013, 09:11 PM   #320
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: 2011 Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,254
Definitely. More wetted surface creates more drag.

A keel-less boat will have less wetted surface.

A keel can provide protection to shaft, propeller, and rudder.

A two engined/propellered boat will need at least two keels to provide protection. Expect two keels to have more wetted surface then one keel.

If two smaller engines were more efficient than one larger engine of the same total horsepower, wouldn't there be more dual-engined automobiles?
__________________

__________________
Kar-KEEN-ez Koot
markpierce 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 11:17 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