markpierce
Master and Commander
- Joined
- Sep 25, 2010
- Messages
- 12,557
- Location
- USA
- Vessel Name
- Carquinez Coot
- Vessel Make
- penultimate Seahorse Marine Coot hull #6
Al, it is a bottomless pit.
I actually figured it out 3 or 4 boats ago....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.
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.
(1) manuveurability < trumped by singles with thrusters>
(1) greatly improved fuel efficiency
(3) less weight allowing for greater cargo
(8) initial cost much less than the same boat with twins
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.
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.
you got a point there, so how to we answer the original question?
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
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.
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.
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[FONT=Arial, Helvetica, sans-serif]. One can always use extra space[/FONT]
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[FONT=Arial, Helvetica, sans-serif]. Thanks[/FONT]
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
Greetings,
Hmmmm...two engines in a car eh?.......Prius, Lexus CT200h, Ford Fusion, Honda Civic, Hyundai Sonata, Ford C-max, Chevy Malibu....Nope, it'll NEVER work!!!!!
markpierce said:Was counting engines, not motors.
Greetings,
Mr. Mark. So what do you put into your JD 4045 for lubrication?
are there any single engined duo proped trawlers?