Are twin diesels worth more than a single?

[JustBob]

When one engine dies, yeah.

 

[SoWhat]

"First issue, had an overheat of the exhaust hose that could have gone undetected. I was planning on replacing the exhaust elbow that fall (preventative) anyway. Cost to troubleshoot and repair at a transient marina over $7,000 and a month's moorage, new exhaust elbow (custom made and shipped to our location), and a complete off boat overhaul of the raw water cooling system."

$7000 for an exhaust elbow installation??????? I understand the part alone can be >$2000 but thta seems excessive.
On my poorly maintained 35 yr old boat, I decided to update both exhaust systems on my Lehman's.
Exhaust Elbows - ~$400
Centek Vernalifts - ~$400
Centek Elbows - $300
Hose - ~$200
Misc - ~$200
Total ------------~$1500

[QUOTE/]"Next year preventive replacement of raw water pump that was just starting to leak ($2,000)" [/QUOTE]
I just rebuilt my raw systems.
Raw water pumps - ~$700
Groco ARG strainers- $300
Hoses - $100
Misc - ~$100
Total--------------~$1200

I have replaced all coolers. I rebuilt the Fuel System Added 2 dual racors and a separate polishing system. This spring I am updating the fresh water system, propane system, and most electronics.

None of these are maintenance items. They are cost of ownership items, same as dockage, fuel, insurance, etc.
Maintenance to me is filters, zincs, impellers, etc.

Exhaust elbows, starters, raw water pumps, alternators, rarely fail and when they do they are relatively easy to replace. (Relatively speaking. My exhaust elbow has 4 bolts, but add in the time to install the helicoil...) If you get stranded in a remote yard then all bets are off but I would not characterize the costs as routine maintenance.

 

[firehoser75]

So What,
I am glad that you find things easy and inexpensive on your boat. If you like to "categorize" your costs differently than I do, (for example: cost of ownership instead of maintenance), then OK. But to me, routine "servicing" (call it maintenance or cost of ownership) is still a cost, and with 2 engines instead of 1, the cost is higher. Two heads cost more to maintain than one. To me, just makes sense.
However, what I was describing (in my new to me boat) was an "effective" breakdown at a "strange" port. I was forced to use a paid mechanic ($120 per) to do the work, as I had no way to be mobile (no car, poor bus service, etc.). It was, at my choice a total redo of the entire cooling system. All raw water items were serviced off engine, pressure tested, cleaned at radiator shop, repainted, and reinstalled. This included fuel cooler, aftercooler, gear oil cooler, heat exchanger and exhaust elbow. The new elbow had to be shipped internationally (from the US, more cost, duties, etc.), coolant flushed and changed. I disagree with you, to me these are all maintenance items that require periodic maintenance and/or replacement. I guess the other modus operandi would be to wait for these parts to fail and then replace them. That would be a "replacement cost" and not maintenance?
And you are correct that work was expensive. In Canadian funds that elbow was just over $2,000 delivered. I had to pay labour for travel time to and from the shop, rad shop, etc. as well as some fabrication for a new support bracket for the new, larger elbow, etc. Including a month's moorage, that I would not have spent but for this issue, it was $7,000.
No wonder you think twins don't cost much, you don't factor in very many of the costs. I will leave it at, we agree to disagree on this.

For me, another factor of why I didn't want twins was all of the boats I looked at in the 35-42 foot range that had twin engines, had very cramped engine rooms with poor access to many regular maintenance items. Not something I wanted. JMHO.

Twins are fine, but not for everyone. All have pros and cons.

 

[Vadim]

Just my 2 cent's, gas engine price is about $ 10000.00 vs. diesel would probably start somewhere in $ 20000.00 range. Add gear boxes, props, other equipment and you will be up there. IMHO with twin you have a better chances get home or to where you may need to be.

 

[koliver]

As demonstrated by Firehoser, Lose a single during a cruise and you lose a month and $$$. Lose one of a twins setup and you get to chose where and when you do the layup and if you are able, DIY instead of $$$.

 

[mvweebles]

Two days running after we bought our boat, a DeFever 44 with twins, we cracked an injector line. We had no choice but to shut down the engine. It was almost dark. The wind was blowing hard. We tried to anchor but the bottom would not hold our boat. We were definitely in peril. As an earlier poster opined, no problem, just call a tow boat. Nope. We would have been blown onto the nearby rocks in no more than 30 minutes. Instead, having luckily found a T-dock in the waning light about two miles off we motored there on one engine and tied off with great difficulty, without permission. So, you one-engine guys, go ahead and rationalize all you want about singles being good enough. Indeed they are until they are not and you become pretty much screwed as we would have been. And tow baots are no so available in Canada as they are here and no Seatow of BoatUS insurance either. By the way, we lost propulsion in the Ottawa locks and had to motor 18 miles down the Rideau Canal to a repair marina. I hate to think how much a tow would have cost. Still, I might consider a single in the future and take my chances knowing and accepting the risks.

I am not oblivious to the redundancy benefits of a twin. I forget if it was this thread or another recent thread where the owner of a diesel duck loses his engine midway to Hawaii. Stuff happens. For all the folks who talk about how commercial fishermen run singles, just binge watch a season or two of Deadliest Catch and notice how many times they are fixing something on their engines.

All things considered, for me, I'm a single engine guy. CatalinaJack happens to own one of the few twins I respect, though the windage is horrible and stabilization is not optional on a defever 44. But she has an amazing engine room and I have wet dreams over the sea chest. She's a total sleeper in the pantheon of trailers.

There is no risk free configuration. Twins carry their own costs and risks. I suppose the risks are manageable with an adequate credit limit. But I agree - headed offshore with a single diesel and no backup increases the risk profile. Anyone who disagrees is simply being argumentative and will likely be unprepared when the time comes.

Peter.

 

[catalinajack]

I respect everyone's opinion here. Yes, stabilization on a DeFever 44 is great to have. With stabilization the DF44 is, well, surprisingly stable. With it's highly flared bow, it takes a lot of head seas before water will begin to wash over the bow. Seven-footers don't do it. We once transited St. Andrews Sound in very bad conditions. We followed a Mainship 40 into Brunswick Harbor. While we were taking occasional splashes of water on the lower helm windshiled, we learned later that the captain of the Mainship was forced to drive the boat from the upper helm because so much water was coming over the bow. Even at that, water was hitting the upper helm eisinglass which was open at the center so the captain could see where he was going. He got drenched.

I am not oblivious to the redundancy benefits of a twin. I forget if it was this thread or another recent thread where the owner of a diesel duck loses his engine midway to Hawaii. Stuff happens. For all the folks who talk about how commercial fishermen run singles, just binge watch a season or two of Deadliest Catch and notice how many times they are fixing something on their engines.

All things considered, for me, I'm a single engine guy. CatalinaJack happens to own one of the few twins I respect, though the windage is horrible and stabilization is not optional on a defever 44. But she has an amazing engine room and I have wet dreams over the sea chest. She's a total sleeper in the pantheon of trailers.

There is no risk free configuration. Twins carry their own costs and risks. I suppose the risks are manageable with an adequate credit limit. But I agree - headed offshore with a single diesel and no backup increases the risk profile. Anyone who disagrees is simply being argumentative and will likely be unprepared when the time comes.

Peter.

 

[FF]

"headed offshore with a single diesel and no backup increases the risk profile"


The risk profile is altered by the engine choice. Industrial rated diesels , think big Cat Detroit , big Cummins rather than repurposed yard implement or light delivery van sourced engines.

 

[rslifkin]

"headed offshore with a single diesel and no backup increases the risk profile"


The risk profile is altered by the engine choice. Industrial rated diesels , think big Cat Detroit , big Cummins rather than repurposed yard implement or light delivery van sourced engines.

I'm not sure that really makes a huge difference in risk of an engine shutdown. It'll make a big difference in engine lifespan and how hard you can safely run it, but in my experience, engine failures and shutdowns are usually a cooling system issue, fuel issue, or an ancillary component beyond the base engine. Outright engine failures are rare.

 

[slowgoesit]

Two days running after we bought our boat, a DeFever 44 with twins, we cracked an injector line. We had no choice but to shut down the engine. It was almost dark. The wind was blowing hard. We tried to anchor but the bottom would not hold our boat. We were definitely in peril. As an earlier poster opined, no problem, just call a tow boat. Nope. We would have been blown onto the nearby rocks in no more than 30 minutes. Instead, having luckily found a T-dock in the waning light about two miles off we motored there on one engine and tied off with great difficulty, without permission. So, you one-engine guys, go ahead and rationalize all you want about singles being good enough. Indeed they are until they are not and you become pretty much screwed as we would have been. And tow baots are no so available in Canada as they are here and no Seatow of BoatUS insurance either. By the way, we lost propulsion in the Ottawa locks and had to motor 18 miles down the Rideau Canal to a repair marina. I hate to think how much a tow would have cost. Still, I might consider a single in the future and take my chances knowing and accepting the risks.

Not to nitpick, but how do you motor 18 miles when you've lost propulsion?

 

[rslifkin]

Not to nitpick, but how do you motor 18 miles when you've lost propulsion?

I'm assuming he means lost propulsion on one engine.

 

[stubones99]

Occasionally, PAE has built a Nordhavn with twin engines. A few N57s come to mind. Pretty sure these twins are less desirable and less valuable than a single with get home. I believe there was a recent thread on an early KK42 with twin engines.thaf would be a very tough sell.

Almost all Nordhavns are twin engine vessels. Just that the second engine is a smaller get home engine, so you have to stock spares for multiple brands, sizes of engine. If you had two of the same make and model engine, you only have to have spares of one type. It is about like discussing anchors, politics or religion. It is a no win thing. Either you're a for 1 engine, or for two engines, it's a personal decision based on where you want to go, and what you value in life.

I would far prefer having two diesels over one for maneuverability, even with thrusters. Having been a diesel mechanic for years, the first problem you're likely to have is fuel, then cooling. On a boat, that's probably reversed or at least tied, unless you use keel coolers and closed loop cooling system.

 

[Dougcole]

Since this thread has evolved (devolved?) beyond the OP's question and into another twins vs singles thread, I'll throw in my twin cents (see what I did there?).


Here are the underway breakdowns I can recall, all in twin engine boats.


1. About 8 miles out of Port St. Joe, Florida. Ran out of fuel on stb tank which shut down the stb motor. The boat was pretty new to us and the fuel gauge wasn't functioning, still a dumb thing to do. Motored in on one engine. I could have gotten both running on one tank, but it was easier just to run on one. Rolly, uncomfortable conditions.


2. Carrabelle, FL. Steering failure, hydraulic line ruptured as we were leaving the dock in very tight quarters. Backed into the slip using both engines. Would have been a very difficult spot with no power, likely would have damaged other boats, would have been embarrassing at best.


3. Little Bahama Bank, about 35 miles North of Green Turtle Cay. Impeller failure, then very quickly a resulting exhaust hose failure. Had to shut down and run the rest of the way on one engine. This one would have been a sticky situation with a single as we were pretty far off of the beaten path. No commercial towing services available.


4. Sea of Abaco. Tried to set an anchor on a sand bank in windy conditions. Anchor drug and dinghy painter fouled a prop shutting down the engine. Poor seamanship, for sure. We were being blown toward a very close by rocky, lee shore. Used the second engine to help us retrieve the dragging anchor, then gain a little sea room. We got the anchor to set the second time around, then cleared the line from the prop. Maybe I could have gotten the second anchor set before we hit the rocks, maybe not, the holding was very poor there. I was glad to still have the ability to maneuver.


5. Stuart, Fl pulling into a slip in Sunset Bay Marina. Starboard electronic throttle controls failed. Stb motor went from idling in reverse to 1200 rpm in forward in the blink of an eye with no warning whatsoever. Port motor allowed some maneuverability while I got the Stb shut down. Managed to avoid the multi million dollar boats surrounding us. Came into the slip on one motor. Cleaned out my pants.



Could I have survived these situations with one motor? Probably yes. Could they have been avoided with perfect seamanship and maintenance? Some yes, some no. But no matter how you look at them, I was in a much, much better spot because I had a second motor.


I think about things like that when I'm changing two impellers or two fuel filters. Makes it a bit more palatable.

 

[Pete Meisinger]

Man, we always go down this road in the single vs twin discussion. Even if the O.P. puts a new twist on the question.

Are twin diesels worth more than a single?

Not to me they are not!

pete

 

[firehoser75]

Pete,
I agree. And that has been the entire "thrust' of the points I was trying to make, not saying one is "better" than the other. Giving some negatives when it comes to twins, others were already listing the positives. Some like twins, some don't. On the used market, twins does not ALWAYS mean your boat is worth more than the same model with a single, and for some models (one's where most buyers want and expect a single) having twins may make it harder to sell and could result in a lower price. I also think some here are trying to "muddy" the waters with the "get home" option is actually really twins. Don't think so, not the same at all in function.

New boat, obviously a different kettle of fish.

 

[Nomad Willy]

If the boats being compared are both with the same total amount of power I’d be preferring the twin if it was the power that is more appropriate for the boat in question.

Re the above boats are only ideally suited to a narrow range of speeds. Planing hulls having the widest range of preferable speeds. SD boats have a narrower range and FD boats have almost no options but one speed. Assuming the FD boat is properly powered. So basically there’s only one amount of hp a FD boat can use.

But about half of the SD boats can run well at a higher and lower speed. A good example is the Nordic Tug line. There is some rocker in the hull (at least the 32 (and I’m assuming the other sizes do to)) so a wider range of speeds can be utilized.
With a planing hull one can go from just barely above hump speed to as fast as the boat can go at the recommended continuous power setting. The widest range.

Since most all trawlers are SD one has a rather wide range of good speeds to cruise at. But a boat w twice as much power would have a much narrower speed range. And very unlikely to be well power loaded in each boat size. This is my msg for the post. One would think (and assume for conversation) that the single would be underpowered and the twin overpowered. Neither one would be ideal.
But if a manufacturer was building a boat w/o power options (single) it would likely be the ideal power for the hull. It should be.
Of course some model trawlers with two power options one would be ideally powered whereas the other would be underpowered or overpowered. And if one is shopping for this hull model proper power loading would make one boat worth more than the other. The 42’ GB is probably underpowered as a single and about perfect w twins. So the value nod would appear to go to the twin. In another boat it may be otherwise.

But the above indicates proper power loading can easily put either a single or a twin engine configuration into the preferable power zone making one or the other more valuable. Value could be attributable to other variables too like bow thrusters. Fly bridge or no.

The above is assuming that one runs their boat at 40 to 45% loading to about 65% loading.

 

[catalinajack]

Not to nitpick, but how do you motor 18 miles when you've lost propulsion?

You missed where I said our boat has two engines.

 

[BruceK]

31-second video of a tour boat on an Amsterdam canal making a very tight turn. Single engine, no thruster. Looks like rudder swings through at least 120-degrees....Peter

I was so impressed I spoke to the skipper of the boat we took. No articulated rudder either.
However, I`ll stay with the twins...

 

[stroutmail]

Thanks for all the replies. It seems like the higher price for twins in a new boat is based upon the additional cost of the second power train.

However, as the boat gets older, that additional price will decrease based upon the likes/dislikes of particular buyers?

Does this seem right?

As someone who just went thru the buying process for Grand Banks 36 Classics I can share my personal thought process..

Two engines give me a "spare" if one fails enroute.

Two engines are a little easier to maneuver in high wind than a single with bow thruster.

Two engines give me a bit more speed..a little in a trawler..a lot in a cored hull boat that will get up on plane..like a 4588 Bayliner or an Sea Ray Express Cruiser.

Two engines cost a lot more to run in terms of fuel and routine maintenance. And it is ALOT harder to work on them. Lots or space around a single.

Twice the risk of major engine repair.

Since a did not desire a speed much above 7 knots hull speed...the deciding factor was the lower risk of major engine repair. $20,000 to $30,000 engine overhaul replacement is a big enough risk...doubling that was just too much for me. Even though diesels can last 15000+ hours, there is a significantly increased risk of failures as you approach 4000-5000 hours..depending on how previous owners operated...something that is often opaque..unknown.

So I give up a wee bit of speed, but at 3-4 gallons per hour, fuel cost is no big deal for my single. (My trawler is a real speed demon compared to my sailboat!)

Only issue is I would be dead on the water if engine failed....so a good radio and towing boat membership works for me since I am almost always in sight of land.

If I was going 20+ miles from shore..I would need a "get home" mini-engine with my single engine. Not an option on the GB 36, so i would have gone with twins if i was going far out to sea.

I could not see much difference in price for 30 year old boats..singles and twins were about same. Price more influenced by condition and features like late model working auto pilot and chartplotters.

 

[ddw36]

Could someone, who knows him better, ask Wxx3? I've been reading his blogs & he's sailed his F/L single engine KK42 across the Atlantic at least twice & sailed the North & Baltic Seas. So far (I've started from the beginning), I see no serious issues w/ his engine. It could be all he does is make sure his engine is well-prepared, as he's meticulous about the condition of his boat.

 

[mvweebles]

Almost all Nordhavns are twin engine vessels. Just that the second engine is a smaller get home engine, so you have to stock spares for multiple brands, sizes of engine. If you had two of the same make and model engine, you only have to have spares of one type. It is about like discussing anchors, politics or religion. It is a no win thing. Either you're a for 1 engine, or for two engines, it's a personal decision based on where you want to go, and what you value in life.

I would far prefer having two diesels over one for maneuverability, even with thrusters. Having been a diesel mechanic for years, the first problem you're likely to have is fuel, then cooling. On a boat, that's probably reversed or at least tied, unless you use keel coolers and closed loop cooling system.

Under this logic, it's a 3 engine boat due to generator.

Im not sure you're familiar with how these boats are equipped. The wing engine often runs hydraulics so it gets exercised regularly. Regardless, the engines are carefully sized for their usage.

Also, there are very credible arguments against dry stack and keel cooling. Different thread, but suffice to say there are many more details than described.

 

[Nomad Willy]

stroughtmail wrote;
“there is a significantly increased risk of failures as you approach 4000-5000 hours..“

If an engine is in good condition why is that so?
Sounds snarky but no I would like to know. My engine is just barely over 1000hrs so I’m not personally concerned but can’t see why an engine should be less dependable. Not durable but dependable. I would think if an engine is 100% maintained it should be dependable.

 

[SoWhat]

I just did a highly scientific survey of GB 36 Classics for sale on YW. US boats only.
Equal number of singles and twins for sale. Did not track condition or features.
GB 36 single: mid 80's, mostly lehman 120's, avg ask price - $85,000
GB 36 twins: some late 80's, lehman 120/135's, avg ask price - $120,000
GB32 single: variety; mostly lehman 135's, avg ask price - $74,000

Sparse listing of cruise speeds but 7/8 knots common with max of 9/10.
One report of 12 knot max with a Cat 325Hp.

Conclusion: Equal number of each sold for GB36 in the 80's.
There's probably a 10-20% premium for twins
I can't find any empirical data indicating there is any significant performance advantage so I am guessing the decicions are based upon emotions.

 

[stroutmail]

stroughtmail wrote;
“there is a significantly increased risk of failures as you approach 4000-5000 hours..“

If an engine is in good condition why is that so?
Sounds snarky but no I would like to know. My engine is just barely over 1000hrs so I’m not personally concerned but can’t see why an engine should be less dependable. Not durable but dependable. I would think if an engine is 100% maintained it should be dependable.

Lots of things can go wrong, even when perfectly maintained. No analogy is perfect, but consider human life expectancy...85 may be life expectancy, but some die at 50..some make it to 100. Poor maintenance will shorten life. Good maintenance, may not extend it. Effects of overheating, and overloading and other things in diesels seem to start showing up significant % in the 4000 to 6000 hour range...even though a good one may make it to 20000 hours, few do that without significant cylinder head and injection pump work.

A well maintained low hour engine is "dependable" but still has some small probability of failure. Even new engines fail..that is why there is warranty coverage.

On the other hand, Lindbergh flew over the Atlantic with one engine.

 

[rslifkin]

On a well maintained engine of a known-reliable design, the base engine will typically wear out gradually, rather than let go with a bang. So high hours wouldn't indicate reduced reliability as long as everything checks out healthy.

 

[stroutmail]

On a well maintained engine of a known-reliable design, the base engine will typically wear out gradually, rather than let go with a bang. So high hours wouldn't indicate reduced reliability as long as everything checks out healthy.

Certainly this above is correct. Keep in mind that in 4000 hours, each exhaust valve has slammed into its seat more than 200.000,000 times..that's 200 million. Like hitting a piece of steel with a steel hammer 200 million times. Then consider the turbo that is very hot and spinning a very high rpm. Perhaps in excess of 20,000 rpm. These experience a very different environment than a main bearing and crankshaft protected by a very slippery hydrodynamic oil film at a relatively low temperature.

 

[stroutmail]

I think it is wise to think of a turbo diesel as a "collection" of components and systems rather than one homogeneous unit. Cylinder Block Assy, Cylinder Head/s, Fuel and Cooling Pumps and exchangers, and Turbo. Each have different life expectancies.

 

[Nomad Willy]

OK gents,
Take an exhaust valve.
In 10k hrs one can compute how many times it’s gone up against 1700 degrees and slammed down against the seat and slid up and down in it’s guide.
But what’s actually different in the molecular structure after 10k hrs? And what else may be different?
I’ve heard of metal fatigue and does that mean the molecular structure Changes such that strength is affected? I know a Willard owner that had an old Perkins 4-107 and was on his way up Chatham Strait near Angoon when his crankshaft broke. Does that mean his crankshaft wasn’t as strong as when new? What made it weak? Was it a fault in the shaft when cast? Then why didn’t it break soon?

 

[Nomad Willy]

Re your post 87 wouldn’t one replace these individual components as part of regular maintenance?
But once these components had been replaced dependability is again bumped up into the future.

But re a cylinder .. after the bore is worn to the point that along w the rings where there is too much blow-by to have enough bmep to perform to new specs?
If an engine is good for one re-bore then the re-bore is considered part of maintenance?

It would appear then that cylinder/piston wear will determine the life expectancy of an engine. Or does it determine when maintenance is due?
But one always would need to ask if repairing is more economical than replacement? Could one “repair” an engine forever? No. Parts availability would decide that. So perhaps the availability of parts control the life expectancy of an engine?

 

[stroutmail]

Re your post 87 wouldn’t one replace these individual components as part of regular maintenance?
But once these components had been replaced dependability is again bumped up into the future.

Yes. I had dental implants...teeth again almost like "new". My father had heart bypass...almost like new..but he passed from cancer a few years later at 72. Grandmother made it to 104 without any surgeries or replacements. Different..but sort of similar....life of machines and people is a bit uncertain...very complex and many "unknowables".

And, yes..metal does have a finite fatigue life..no two forging or castings are exactly the same..so hard if not impossible to predict accurately.