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Old 12-09-2012, 08:08 PM   #21
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Got it, Marin. Didn't I say that many posts ago?
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Old 12-09-2012, 10:14 PM   #22
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While I have no statistical evidence to back it up, from decades around sport fishing charter and private boats, it seams that those in general with twins seem to be less diligent about engine maintenance because they know that there is always a second engine to get them home. Those of us with singles tend to be more preventative maintenance oriented for the obvious reason. Put another way, the guy with twins can wait till he looses an engine before rebuilding; the guy with a single plans a rebuild in the off season. While this doesn't address whether to have a single or twins, I believe a boat with twins on average will have far more than twice as many failures as one with a single engine.

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Old 12-09-2012, 10:48 PM   #23
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Agreed. Borne out with experience as well.
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Old 12-10-2012, 01:45 AM   #24
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OCD says;
" I believe a boat with twins on average will have far more than twice as many failures as one with a single engine."

Probably not "far less" but agreed ... less.

But in order to be unable to make significant headway he'll need to have a 2nd engine failure on the same day ....... highly unlikely.

Why are we talking about this? It's because single engined skippers are afraid of having their engine quit and being dead in the water. No other explanation for it.
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Old 12-10-2012, 02:06 AM   #25
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While I have no statistical evidence to back it up, from decades around sport fishing charter and private boats, it seams that those in general with twins seem to be less diligent about engine maintenance because they know that there is always a second engine to get them home.

I don't agree with this at all. Everyone I know personally with a twin engine boat is just as diligent--- and sometimes even more so--- about engine maintenance as the people we know with singles. A person who's sloppy about engine maintenance is going to be that way no matter how many engines his boat has.
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Old 12-10-2012, 02:07 AM   #26
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Got it, Marin. Didn't I say that many posts ago?
Um.... no.
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Old 12-10-2012, 04:03 AM   #27
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Mark, you starting this post was just plain obtuse. You just did it to yank chains, and because you got bored - maybe because we don't have a good anchor stousch going on at present. You got exactly the replies you expected to get, didn't you...?
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Old 12-10-2012, 10:12 AM   #28
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Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure.
Actually... they happen at exactly the same rate statistically. After all... it's just two singles right?

BUT... the odds of having the same failure, with the same disabling effect as by orders of magnitude less likely on twins.

Same goes for airplanes. Lose one on a twin... execute emergency procedure and head for an alternate destination. Lose one on a single engined plane... execute ditching / emergency landing.

Plus... on a boat, there's the idea that you have spares for every part of the critical engine (from the disabled engine).
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Old 12-10-2012, 11:23 AM   #29
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I love this debate, but the answer is simple.

Anybody thats ever experienced an engine failure was either glad they had twins, or wished they had twins.

As to twins being twice as likely to experience failure, well thats true I suppose.

As to twins ever experiencing a total loss of propulsion power, well thats extremely unlikely and we all know it.
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Old 12-10-2012, 01:43 PM   #30
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Yep. Operating with 5 9's of reliability is pretty common these days.

The key is thinking of twins more as a pair of singles. Either motor will experience 99% of it's failures independent of the other... same goes for boats.

Unless you're talking fuel for the most part... there is very little that'll take both plants offline simultaneously. Even those things that will, they affect a single engine configuration with just as dire consequences.
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Old 12-10-2012, 01:44 PM   #31
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As Marin noted, engine failure in the majority of circumstances happens because of things attached to the basic engine. Many, if not most, of those kinds of things are fixable with a basic spare parts inventory on board, i.e. belts, filters, hoses, impellers, and a bit of knowledge to clear filters, air locks and the like. In today's diesels, catastrophic engine failure is an incredibly rare event. Thus, in my mind, the single v twin arguments has devolved to being mostly a personal preference issue rather than a truly pragmatic one. That said, I have always preferred twins on the quaint notion of having a built-in "get home" system that requires no action from me whatsoever. I have yet to find any other "get home" that convinces me that it is functional and effective for any significant distance in any significant sea conditions, whether it be the Nordhavn folding sail prop driven by a 62HP diesel in a 120,000 lb boat or a hydraulic system driven off a 20KW generator. My personal comfort level is twins with shafts and props fully protected despite the addditional up front and operating costs.

But, hey, that is just me.
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Old 12-10-2012, 02:12 PM   #32
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Thus, in my mind, the single v twin arguments has devolved to being mostly a personal preference issue rather than a truly pragmatic one. That said, I have always preferred twins on the quaint notion of having a built-in "get home" system that requires no action from me whatsoever.
I totally agree on the personal preference influence on single vs twin opinions. As I have related in the past, we have benefited from the get-home aspect of having two engines four times since buying the boat in 1998. None of these incidents were due to the engines themselves, and one of them was entirely my fault.

But just as great a reason for my preference with twins is I just like running multiple engines. I like being able to manipulate the powerplants to do different things. I like the challenge of learning to master a particular combination of rudder and thrust to achieve a new maneuver. As I've said in other threads, I've only recently "discovered" the wonderful flexibility that power can provide during slow-speed maneuvering in addition to rudder and differential thrust. So I'm having a good time exploring the options that power can bring to the formula.

(I say I "discovered" this.... What I really did was watch enough tugs and fishboats around here and lobsterboats on Prince Edward Island that finally the benefit of using bursts of power finally sunk in.)

So we would never go back to a single engine boat (the GB we chartered was a single). For my wife, she is more confident and relaxed with two engines under the floor, and if one's boating partner enjoys the experience more with two engines than one, than it's well worth the extra fuel and oil and filters.

For me, I would not find operating one engine nearly as interesting as operating two. I'd have three if they would fit.
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Old 12-10-2012, 02:48 PM   #33
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Another benefit is the ability to secure one if indications are looking odd. My slip neighbor with a 45 PT just replaced his single main because he drove it home on a mildly overheating impeller. Had he had twins, he would have likely secured the motor and came home on the remaining plant.

Also... twins have the benefit of working half as hard and this would add to their longevity and increase the time between load related failures. I've never come home on a single motor, but would if anything looked even slightly odd.
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Old 12-10-2012, 03:14 PM   #34
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Yes, all our "engine failures" as Mark would term them were actually precautionary engine shutdowns.

Three of them were due to cooling issues and the engine was shut down as soon as the temperature (coolant) indicator began to edge up past normal on the gauge. A previous owner marked all the engine gauges with thin strips of black tape at the normal needle readings so it's easy to tell at a glance if something is beginning to go amiss. So in our case the engine was always shut down long before it reached the overheat stage and we finished the run on one.

That's a nice thing about having two engines----- taking one off-line brings no real penalty so one is inclined to do it-- or at least we are inclined to do it-- the moment something starts looking fishy. Which means the likelihood of causing actual damage to the engine is almost nil.

As opposed to the fellow with just the one engine who begins to experience a problem but might be inclined to run the engine as long as he thinks he can get away with it in an understandable effort to reach a safe haven. The chances of causing damage go up considerably in this situation.

Our fourth engine shutdown to date was caused by my misunderstanding the boat's fuel system and letting an engine get a slug of air during a fuel transfer. So we don't count that one as it was totally my fault. But even in this case having two engines was a benefit because we were in lumpy water at the time with guests who needed to be home by a certain time. So I simply tied off the shaft and we came home on one. We went up the following weekend and bled the fuel system for the other engine in the peace and quiet of our slip as opposed to bouncing around at the south end of the Strait of Georgia with guests hoving around looking at their watches.
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Old 12-30-2012, 08:15 PM   #35
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More on Twin Manuevering Options?

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I like being able to manipulate the powerplants to do different things.
So this is the dual engine functionality discussion I hoped I would find in this thread. I've got 33 years of single engine experience and will likely charter a twin just for the experience. A better conceptual understanding of twin manuever options would be helpful. Is there more of this in another thread in this forum?

Some claims in this thread's R/M/A discussion seem to depart from guidance in MIL-HDBK-217 which is my limited background for the topic.
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Old 12-30-2012, 08:53 PM   #36
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From stories heard around the dock:
A 60 ft charter boat was towed back to its slip in my marina with both engines disabled. The boat had run over a log in the Puget Sound and bent both shafts, props, and rudders. There is a chance that a single could run over a log and survive as the prop/rudder is behind/above the keel.

I watched a two prop replacement on a 100+ft yacht at Shearwater after they bent both props running over a log.

I have heard twin engine boaters talking about not replacing a raw water impeller when due on one engine of twins because 'they can not reach the raw water pump' on the engine with the pump on the outboard side, and "anyway they have two engines". A GB 36 twin has limited access to the outboard sides of the engines. I skipped buying a GB 36 twin because I personally could not access the outboard sides of the engines. When traveling in remote areas I want to be able to reach/repair as much of the systems as possible.

Perhaps because twins cost twice as much for routine maintenance, there seems to be a tendency for maintenance to be skipped when it is too difficult.

I have taken my single engine trawler from the Puget Sound to SE Alaska three times, with no system failures, except having a failing starter battery which I replaced in Ketchikan.

I do carry lots of spares, including a spare starter motor. My Lehman 120 single hasn't quit yet. (said with fingers crossed)

All that said, I still have Boat US towing insurance, and would like to have a tender large enough to side tow my trawler.

All this is my opinion from talk around the docks and from personal observation.
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Old 12-30-2012, 11:13 PM   #37
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So I simply tied off the shaft and we came home on one.
Marin, just how do you do that, so that the undriven gearbox is not being turned by the prop?
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Old 12-30-2012, 11:56 PM   #38
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There are engine failures and then there are propulsion system failures. I don't believe that twins are twice as likely to experience engine failure, but I believe that the design compromises incorporated into most twin engine boats places them at higher risk for certain types of failures, specifically prop/strut/shaft/rudder damage which would not as likely occur with boats with keel protected running gear.

If twin manufacturers simply incorporated twin keels to protect the running gear, I think the advantages of a twin would far more greatly outweigh the advantages of a single-engine boat. But that fact that most builders that I'm familiar with do not protect the twin running gear with twin 'bilge keels' renders twins at greater risk of damage due to debris and groundings, in my opinion.

In addition to protecting the running gear, protective bilge keels would also provide passive roll stability which would be a huge improvement to many of our boats' designs.

I'd love to hear Tad Roberts' perspective on the advantages, disadvantages, practicality and costs of protective bilge keels on twin recreational trawlers in the 30-45 foot range. I've often thought that they would provide the needed protection and roll stability on twin boats (like mine!!) that lack both.
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Old 12-31-2012, 12:51 AM   #39
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I'm 6' 3" and I can get around the outsides of our engines. I won't pretend it's a walk in the park but it's very doable and we have never deferred service or maintenance because it was too difficult to get to the necessary components.

As I've mentioned before, we know or have heard of many, many more instances of single engine boats, including sailboats, experience an engine shutdown or running gear damage and had to come home on the end of a rope-- or in some cases been carried aground--- than twin engine boats that have suffered damage to both sets of running gear or had to shut down both engines. In fact, we have never heard personally at all of a twin engine boat not being able to come home on the other engine when one had to be shut down or after experiencing damage to one set of running gear. And we have never heard personally of a twin engine boat having to shut down or losing power on both engines.

So in our opinion risk of the loss of both propulsion systems on a twin is so remote as to be a non-issue.
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Old 12-31-2012, 01:04 AM   #40
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Marin, just how do you do that, so that the undriven gearbox is not being turned by the prop?
Our boat has convenient tie-off holes in the heavy aluminum extrusions on the inboard engine stringers that hold the primary fuel filters. When we had the boat's original Fram dual-cannister filter system changed to Racor 500s these holes, which are beside the shaft couplers-- were obstructed by the Racors.

So I made a set of strong brackets with shackles that are screwed and glued (5200) to the underside of the heavy cabin floor beams. The shackles are positioned directly above the shaft couplers.

We have a stout line that if we have to shut an engine down I wind around the shaft coupler and secure. The other end of the line is secured to the shackle above the coupler. The line is wound around the coupler in a direction that will oppose the direction the shaft wants to freewheel when the boat is moving forward.
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