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Old 23-02-2013, 10:19   #1
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Single vs. Twin

I'm just beginning the process of considering a powered boat over sail and have been reading some old posts to gain some context. I have a couple of questions for which I haven't yet found answers. In fact, I don't understand everything I know.

I'm relatively certain that this has been thrashed out in the past, but my various attempts to find old threads have failed. Perhaps it has to do with the specific terms I'm using, so I would appreciate links, please.

Ideally, I'd like the economy of a single, but would like more of a safety reserve than a radio call for help if the main engine goes south. Are there alternatives, such as a generator motor driving a normally-feathered prop, or something like that?
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Old 23-02-2013, 10:29   #2
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Re: Single vs. Twin

Don't reinvent the wheel. It has been debated exhaustively, maybe nausiatingly on trawlerforum at Single vs Twin: The EPIC Thread - Trawler Forum.

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Old 23-02-2013, 10:31   #3
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Re: Single vs. Twin

Some old fishing boats had a small, secondary engine set off center.

Or you could mount a bracket and outboard on the transom.
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Old 23-02-2013, 10:38   #4
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Re: Single vs. Twin

It boils down to cost per horsepower versus better maneuverability and less of a chance of being dead in the water. For over a certain size I think you are overall better off with a twin. I have had an engine go down a number of times and was fortunate that I did not have to get towed in.

I would not consider a single main engine and some sort of generator powered electrical drive....just get a second propulsion engine. You can also knock out a prop or bend a shaft (both of which I have done) and then what good does an electrical drive do you?

Also, f you don't have a large shipboard electrical load like an air conditioner then you don't need a generator.
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Old 23-02-2013, 18:30   #5
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Re: Single vs. Twin

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Originally Posted by djmarchand View Post
Don't reinvent the wheel. It has been debated exhaustively, maybe nausiatingly on trawlerforum at Single vs Twin: The EPIC Thread - Trawler Forum.

David
I went through post #534 on the linked thread, but it looked to me as if the real answer (for my purposes) was around #309 by "psneeld" --

"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"

There was some discussion that these weren't accurate, but they're close enough for me at my level. There were also such issues regarding wives who is happier with two engines.

There were also discussions related to "get home" engines, such as those optional on the Nordhavn line; apparently, the spare engine cost is around $45k, i.e., nice if you can afford it, but towing insurance is much cheaper.

Finally (though not), there were discussions related to tugs and fishing fleets members who use single engines, apparently as proof that the singles are professionally recognized as adequately reliable. Others countered saying they were singles mostly because they were cheaper, and in any case your buddies' boats are nearby for a tow in many cases.

Reviewing the thread was a good exercise, though I almost abandoned it early with people talking past one another rather to each other. One guy insisted two engines were less reliable because you had twice the chance that one would break, while the others were talking about the system (boat) reliability; they finally noticed that around post #111.

If I do this I expect I'll end up with a single.

David M, thanks for the insight. I suspect, living where I live, the boat will be based on the Texas coast, and I will need A/C. Cost is a factor, so I expect I'll revisit for more advice.
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Old 23-02-2013, 18:57   #6
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Re: Single vs. Twin

Everyone has their own opinion and that's good because it promotes healthy debate. You are very very fortunate in the states with the cost of fuel, here in Europe it is illegal to use rebated diesel and a litre of diesel costs in France(today) 1.40 Euro. I have only ever had single engine boats and cruised thousands of miles and never been towed in, having said that I'm fastidious in servicing. I believe that the key to reliablility is correct servicing because basically the diesel engine is really quite simple.
As for handling, a good man on a single is better than a prat on a twin, I'm sure you've seen the cheque book boaters blaming all and sundry for their cockups and disasters.
Certainly cost both in purchase, running and fuel costs are much lower. There are a lot of twin engine boats for sale here as running costs have become prohibitive. We live onboard and our electricity come's via shorepower in winter, Adverc 4 step alternator, with solar panels via an mcp controller for summer cruising. We don't have aircon, I came for the sun and if I want to be cool I should've stayed in Ireland.
Good luck in your choice, you can see my boat on Apollo duck to give you an idea.
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Old 23-02-2013, 19:09   #7
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Re: Single vs. Twin

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Originally Posted by Jaywalker View Post

Reviewing the thread was a good exercise, though I almost abandoned it early with people talking past one another rather to each other. One guy insisted two engines were less reliable because you had twice the chance that one would break, while the others were talking about the system (boat) reliability; they finally noticed that around post #111.
Actually, that is NOT an unusual approach to defining issues related to choices.

The reason is one that I got into a LOT of trouble years ago with a client (the government!, of course). We were asked to do a study. I asked the client, "How would you like the results to come out?" Boy, was that the wrong thing to say!!! ****

Before one can even begin to make a decision the CRITERIA must be defined. Rather than saying: "One engine or two?" - which is too simplistic a question - the question has to be refined by including issues of cost and reliability and backup and maneuverability, and then providing the "weighted" importance of each to the skipper and crew (which may be two different things, right?). The same "matrix" may be answered completely differently by two different skippers & crews.

Sorry if I'm interjecting "engineer-speak", but that's simply the reality of the decision-making process.

Good luck.

****************


**** The study was for solar power. In 1980, solar wasn't even much of an issue. Almost all studies showed that there wasn't enough sunlight in SF during the summer to "justify" solar, either water or PV. Actually, the reality was, at least for H2O, it really WAS, but the client didn't want to admit that "previous studies" had shown it wasn't!!! Things change, eh?
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Old 23-02-2013, 20:25   #8
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Re: Single vs. Twin

I would point out that Steve Dashew, who has designed probably the best LRC power boat put only one engine in his ocean crossing FPB 64'.
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Old 24-02-2013, 07:09   #9
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Re: Single vs. Twin

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Originally Posted by Irish rambler View Post
As for handling, a good man on a single is better than a prat on a twin, I'm sure you've seen the cheque book boaters blaming all and sundry for their cockups and disasters.



JW, if it helps, I've had both single- and twin-screw boats... and I like both!

Stu's right, lots depends on your own criteria, but in the grand scheme of things (and as you've seen), towing insurance is relatively cheap.

-Chris
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Old 24-02-2013, 10:28   #10
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Re: Single vs. Twin

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Irish Rambler: As for handling, a good man on a single is better than a prat on a twin, I'm sure you've seen the cheque book boaters blaming all and sundry for their cockups and disasters.
Unfortunately, please put me in the "pratt" category at first.
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Old 24-02-2013, 11:55   #11
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Re: Single vs. Twin

I have had a number of boats over many years. All but the one I now own were single engine, single screw( there are other configurations). This is a twin engine motorsailer. I bypassed this one several times when looking for a boat for some of the above mentioned reasons. As it turned out it was the best fit for my requirements at the time so I purchased it. Now I am very happy I did. As a senior person I find the twin the easiest boat to handle in tight situations. I also know that one doesn't have to use both engines while cruising under power. If I can't use sails because of poor wind conditions I usually only run one engine which provides hull speed and economical cruising. I always use both engines in a marina or while making tight space manuvers.
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Old 27-02-2013, 14:20   #12
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I've owned both single and dual. On small boats under 30' in calm waters a single will get you by just fine. When you go above 30' the lack of maneuverability will be a huge pain in the rear. It is more difficult to back up into a slip with a single. As far as your concerns about getting stranded with a single if you make sure it is mechanically sound and do a good job of maintenance and check major components regularly then that really shouldn't be a deciding factor. There is a chance of loosing a prop but if you don't go where you shouldn't and take the time to learn the water you are in then the chances of that happening are small and shouldn't be a deciding factor either. In the last ten years I have damaged one prop and it was my error not bad luck or chance.
If you can afford the added fuel and maintenance then a dual will makes a lot of seamanship issues easier and in my opinion ( every one has one) that should be the only real deciding factor in a decision of which way to go.
Ps, everyone I know that has a single is always the frustrated one when docking, or tying up to other boats especially when the water gets rough. I do miss the economic savings of a single but with a 40' boat I wish I had thrusters to go along with my twins.
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Old 28-02-2013, 05:01   #13
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Re: Single vs. Twin

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Ps, everyone I know that has a single is always the frustrated one when docking, or tying up to other boats especially when the water gets rough. I do miss the economic savings of a single but with a 40' boat I wish I had thrusters to go along with my twins.

Most monohull sailboats have only a single engine, and mostly get docked as necessary.

Capt Bozo might not be able to park a twin-screw with bow and stern thrusters... whereas many owners can dock anything in most conditions.

Something between the ears seems to be more important than the number of engines

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Old 28-02-2013, 06:17   #14
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Capt bozo? Nice, sorry my desire to make boating fun and as easy as possible somehow insults you enough so that you need to resort to insults. Obviously your lack of intelligence and maturity makes you resort to such things. FYI this was about helping with the pros and cons of how many engines on POWER BOAT not a monohull sailboat and your comment does nothing to add to the conversation. Also I do not have thrusters though I would love to have them.
Think its obvious who is lacking between the ears. Grow up or join conversations with other immature people who like to argue and insult each other.
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Old 28-02-2013, 06:27   #15
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Re: Single vs. Twin

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Capt bozo? Nice, sorry my desire to make boating fun and as easy as possible somehow insults you enough so that you need to resort to insults. Obviously your lack of intelligence and maturity makes you resort to such things. FYI this was about helping with the pros and cons of how many engines on POWER BOAT not a monohull sailboat and your comment does nothing to add to the conversation. Also I do not have thrusters though I would love to have them.
Think its obvious who is lacking between the ears. Grow up or join conversations with other immature people who like to argue and insult each other.

I'm very sorry if that offended; I had absolutely no intention to insult anyone, and certainly not you. I only meant to use your comment -- which is perfectly legitimate -- as a spring board to an additional thought about attitude and learning sometimes being more important than hardware.

I only meant that Bozo thing in a generic way: some folks can't park squat, partly because they don't take time to learn and practice (at least in my experience).

Please accept my apologies.

-Chris
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