Single vs Twin: It's Baaaaack!

As many as you care to feed ,maintain, and fix.
I can only afford one.

Welcome aboard. You're certainly choosing a very controversial topic, but a very interesting one. In times like this where boat prices are highly depressed, I would recommend buying all the boat you can afford to maintain and operate. Twins can be seen as an unnecessary luxury or expense, but that being said, I love mine and what they add to our boat.

bfloyd4445 said:

I cant find the link. but this is similiar except that it uses four pisrones in teo cylinders. The one that impressed me used two pistonsw which fired both up and down making the two cylinders into four. The piston top and bottom were the dame and the wrist pins extended to operate rods to the crank

EcoMotors OPOC Two Stroke Engines – Opposed Piston Opposed Cylinder

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The "Ecomotor" is a flat engine like a Subaru or air cooled VW. Flat fours. An opposed piston engine always has two pistons per cylinder and two crankshafts. And the piston crowns oppose one another. They are all two stroke engines.
As I recall they ingest air from one end of the cylinder and exhaust it from the other. Port timing and the ratio of port area to cylinder volume is probably unique to the opposed piston engine.

If I liked the boat, and thought it was a good deal I wouldn't let single or twin worry me. Either will push the boat.

You will be in a great cruising area.

I'm a single engine fan but the argument about the single being more protected? Maybe yes but you'll still hit stuff. We were doing a sea trail in January when we picked up a serious vibration. The prop had just come back from the shop plus we had done a lot of other things below the water line. Over the side and here's what we found stuck around the prop.

I don't see why anybody would want a single if they could afford a twin but like Don says it's not usually a deal breaker.

Figure I'll have half the engine failures with one engine as compared to two. Hey, let's go for three like the WWII PT boats! Oh, wait a second. Many have a genset in addition to two propulsion engines. Now that's thrice the failure rate.

Greetings,
Ya, don't forget twins sink twice as often as singles as well...

RT Firefly said:

Greetings,
Ya, don't forget twins sink twice as often as singles as well...

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Oh, good! I am going to break down 3 times as often, sink twice as often and the expense of maintaining all of that I don't even want to talk about. I think I'm getting the vapors.

The problem with the "twin twice as likely to suffer an engine shutdown as a single" theory is that this is the wrong formula.

The meaningful formula is that AN engine in a twin is just as likely to suffer an engine shutdown as THE engine in a single. Which is why I know plenty of people who have been boating for decades in twin engine boats and have never had to shut an engine down due to a problem, and at the same time I know people who had been boating for two seasons in a brand new single engine boat (Nordic Tug) and had already experienced two engine shutowns and come home on the end of a rope. Twice.

And of course the whole theory is blown out the window when one starts taking into account the age, condition, operation and service practices attached to each engine. A well-maintained, properly operated engine in a twin engine boat is far less likely to suffer an engine shutdown that a poorly maintained, abused engine in a single-engine boat.

So the actual reality is, the number of engines in one's boat has absolutely no bearing whatsoever on that person's likelihood of experiencing an engine shutdown because there are far too many variables that affect the reliability of every engine in every boat.

I have a 40-plus year old, twin engine boat and in the 14 years we've owned it we have never had a driveline failure. Nothing's broken, we haven't hit anything, nothing.

Mark bought a brand new single engine boat and within what, a year? his driveline fell apart into a zillion pieces.

So much for the "two is twice as likely to experience a failure as one" theory. If everything was identical across the board in every boat--- same engines, same drivelines, same maintenance, same operating procedures--- perhaps the "twice as likely" theory would hold a degree of water. But given the total inequality between boats, engines, and owner practices, there is no way to make a blanket statement like that.

So as psneeld said, every boater should get the number of engines they want or are comfortable having and for whatever reason they want. Redundancy, speed, easier engine access, or like me a person simply likes running as many engines at the same time that they can, all these reasons and more are valid.

The one thing a boater should NOT base a decision on in my opinion is the "two is twice as likely to experience a shutdown as one" theory because in the real world, it's simply not true.

Marin said:

The one thing a boater should NOT base a decision on in my opinion is the "two is twice as likely to experience a shutdown as one" theory because in the real world, it's simply not true.

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Sorry, Marin. That's not logical. If one has twenty (whatever) engines, eventually there will be twenty (whatever) failures. With one engine, only one failure.

Marin said:

Mark bought a brand new single engine boat and within what, a year? his driveline fell apart into a zillion pieces.

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Yeah, but since we blessed the boat, that happened in the berth.

markpierce said:

Sorry, Marin. That's not logical. If one has twenty (whatever) engines, eventually there will be twenty (whatever) failures. With one engine, only one failure.

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I don't argue that but it doesn't reflect reality. Define "eventually" in terms a boat buyer will find meaningful.

Reality is any engine can/could/might/may break down... or not!

Single screw engine breaks down = No Mo Power / Tow In!

Twin screw one engine breaks sdown = Plenty Mo Power / Motor In!

Twin screw both engines break down = New Mechanic From Then On!! LOL

markpierce said:

Sorry, Marin. That's not logical. If one has twenty (whatever) engines, eventually there will be twenty (whatever) failures. With one engine, only one failure.

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Not sure that advances the issue. For present purposes, try this summary:
If you have twins, lose one, you almost certainly still have one; if you have a single, lose one,you unarguably have none. It`s why a member fried his single FL by not closing it down, as he would have if he had two.
How long will it take all 20(or whatever) to fail?
I`m sure if anyone trawls the previous 800+posts, this and probably everything else,is covered, more than once.
Just saw Art`s contemporaneous post. Spot on!

Me thinks you want the ability to exceed hull speed with multiple engines and transform your boat from a trawler to a sedan cruiser.

markpierce said:

Me thinks you want the ability to exceed hull speed with multiple engines and transform your boat from a trawler to a sedan cruiser.

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Not so, we`re strictly a hull speed "plodder" but figure the handling and "get home" capability is worth the cost of twins. I had a single, never had a failure, but concede a single will likely get more carefully (? fanatically) maintained. And I don`t rule out ever owning a single again.

The meaningful formula is that AN engine in a twin is just as likely to suffer an engine shutdown as THE engine in a single.

IF the engines were properly sized , not installed on lowest purchase price by the builder , the single engine boat would have a larger , probably more robust selection.

The larger engines frequently come from more industrial sources,so can run at rated rpm and load.

Most of the smaller lighter auto or yard implement conversions are time limited at high power settings.

EG , run a Detroit at 2100/180HP its rating ,no problem.

IF used as a single the engine would have to use the same light loading , which reduces efficiency.

Run a Ford Econo-Power marinization at 135HP , not for long!

The overrated twins survive because they are usually operated at only a fraction of their advertised rating.

As a single the light duty engine would need to observe the same light load requirements , which harms efficiency.

Now that my heart rate has calmed down, let's talk about realities. I had a single screw trawler for 6 years. It had two failures that required towing. One was a collapsed fuel line that caused the engine to starve for fuel. The other was a broken E clip (a 10 cent part) in the transmission causing it not to shift. In either case if I had twins I would have made it home under power. On my Blackfin with a single engine about 20 miles off shore a hydraulic steering line ruptured beyond repair at sea. The engine was fine but from torque steer the boat would just go in big circles. If I had twins I could have made it home steering with engine power.

I have had twins for many years, and never had to be towed back to the dock. I have lost an engine, but never two at once.

Would I buy another single screw? Depends on the boat, but I definitely would not rule it out. There are advantages to both.

Greetings,
Mr. jorge. "Depends on the boat, but I definitely would not rule it our. There are advantages to both."
And THAT is the ultimate, sole and decisive answer to your question!.....#832

jorge said:

Hi Guys
For the last 30 years I have being sailing on sailboats, and because I`m moving to Fort Myers where I have an apartment with a dock included, that only accept up to 5`0 draftI So I sold my 52 Amel Supermaramu. Now I`m looking to buy a power boat, trawler, or similar. Because I`m ignorant on this matter the first question is: One Engine or two engines.Y will be concentrated in the ICW, or Bahamas.I had in mine Mainship or Grand Banks type.
Any suggestion are really welcome.

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hahahah....a single is better for fuel economy and maintenance costs but twins are very popular with many because of better maneuverability and alleged get home capabilities. Many singles have get home capabilities as well. In today's world of escalating fuel costs I like the single with get home option.

".a single is better for fuel economy"


Floyd you should say "most think" as there are reasons that show that twins could be more efficient. Bigger props for example.

Tired arguement...if properly set up...hard to imagine a twin would ever be as efficient as a single...ALL things being equal.

Every boat test where they tried it (and there's only been a few as it's almost never equal)...the single edged out the twins...find those tests you say?

Sure I can't.... otherwise I would post the link...but the articles by the top writers for all the yachtie mags or manufacturer's seem to think singles are slightly more efficient...AND all the other costs do add up over time owning twins.

Of course this is more of a theoretical discussion than what most people will encounter in reality...because finding 2 identical boats for sale, setup properly with exactly the same hp...etc...etc...good luck.

Slam Dunk!

Single - most economical... more ways than one!

Twin - greater maneuverability/safety ... more ways than one!

Single boats are great!!

Twin boats are great!!

Each Captain to their own...

That's the answer... What's the question??

All I know is my dock neighbor... in his single FL120 45 came in after cracking the block because he "limped it home". I said said I would have shut it down and came in on one screw. He said "I wish I had that option...". I didn't realize he was a single.

I thought of this thread when he made that comment.

SomeSailor said:

All I know is my dock neighbor... in his single FL120 45 came in after cracking the block because he "limped it home". I said said I would have shut it down and came in on one screw. He said "I wish I had that option...". I didn't realize he was a single.

I thought of this thread when he made that comment.

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Overheating crack the block, frozen coolant??

Another reason a twin could be more efficient is that it's not having to counteract the propwalk w a deflected rudder creating more drag.

manyboats said:

Another reason a twin could be more efficient is that it's not having to counteract the propwalk w a deflected rudder creating more drag.

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I move the rudder and so does the autopilot so much more that the teeny tiny bit of rudder necessary to overcome the almost non-existent prop walk AT SPEED , that you can't even realistically measure it...at least not on the dozens (maybe more) of sngle engine boats I have driven.