Twin Diesels versus single

[rslifkin]

Rock aren't the only danger, swift currents near bridges sweeping you into them or marinas with the same currents.

Many inlets along the East Coast have rock jetties, often quite long and close aboard.

Depending on ones route from New England to Southern Florida if snowbirding or looping, you certainly encounter all these even sometimes daily.

That's why i posted inshore may be as important as offshore when it comes to keeping a power source.

Usually not a problem till it happens to you which can be rare...but not a great moment if it does (try 2 careers seeing just how many it DOES happen to).....

That's exactly it. Coastal close quarters settings are a bit different. Losing power may be a problem in seconds rather than having plenty of sea room and time to work on the issue.

 

[Hippocampus]

Have had Lehmans, Yanmars, westerbeke and Betas. For a sailboat my first choice is a yanmar. Easy to work on and parts easily available and fairly priced. Won’t buy a sailboat with a Volvo in it. But these are not continuous duty engines. Not even M2. So I think engine choice is very complicated and should reflect use pattern and cruising grounds.but importantly engine room parameters as well. In subset of SD boats you’re stuck with being concerned about weight and size so you’re stuck trading off M rating for HP. Things are different for FD boats doing long continuous transits. Here think you need to pay more attention to M (or equivalent) rating. So given available room in the ER in a boat under around 55’ a single (with some form of backup) may make much better sense. I know N has shifted their offerings going with twins in their smaller sizes. Perhaps L is right this is a reflection of only having common rail available. But also they’re being aware most Ns in those smaller sizes are really only used coastal as Peter has pointed out in the past. . When service and repair is done while stationary and in flat sea conditions crawling into tight spots with a cold engine is easier. I can get to all service points on my single engine NT even being a fat old man. And more importantly can get out. But on some typical coastal boats the ER is under the salon and I’d really struggle if twins were put in there. Then there’s monitoring. It our habit at the change of watch to go into the ER. Check for leaks and shoot temperatures. It’s nice to be able to really see stuff without being concerned about getting burnt or needing my phone for snaps. Not a big issue if your runs are short and usually under 4h or so. Keeping an active eye on the engine parameters from the helm is more likely to be the habit without very frequent ER visits. So think space requirements and service access cannot be stressed enough. Most of us don’t have boats with standup headroom and a watertight door at each end. Even with a single the ER is a very crowded hot space. Have to imagine it would be worse with a twin.
PS makes an excellent point. In many respects coastal is more challenging than voyaging. A reason to have strong reliable thrusters at both ends. Recently went through the defunct RR bridge in Cape May at night in dense fog. The thrusters were quite helpful. Probably be helpful in a twin as well. In the past have gone around if not calm and daylight . Probably would go around if presented with those circumstances in the future. Was a boneheaded decision although uneventful. But we live and learn. I learned thrusters are a good way to steer at low speeds in tight quarters and although the bow one is more effective than the stern the stern one really helps some times. Don’t have enough twin experience to say but wouldn’t be surprised both would help those with twins as well.

 

[rslifkin]

But on some typical coastal boats the ER is under the salon and I’d really struggle if twins were put in there.

Even then it depends on the boat, what equipment is onboard and where that stuff is mounted. I've got no problem crawling all the way around my twins, for example. A few spots are a little awkward to get to, but nothing is hidden or overly hard to access. I've got about 2.5 feet between the engines and about the same outboard of them. Available height is about 3.5 feet in the center, about 3 feet outboard.

On the other hand, I've seen twins in some boats without enough space between the engines for good access or with fuel tanks mounted outboard of the engines leaving very little space to reach anything (or forcing you to lay on the floor working from the top down through a hatch). My fuel tanks are aft of the engine room rather than in it, so there's nothing except some plumbing and the mufflers outboard of the engines, leaving more open space to work.

 

[Hippocampus]

Yup agree R it’s boat dependent. Had a pacific Seacraft where the engine was accessed by lifting a hatch in the cockpit floor. All work was done by reaching down. Lived in fear of dropping anything. Even while in my 30s was very sore after working on it. Have also been on cats , some quite big, where all engine access was from the outside. Not a great thing with green water or a seaway.

 

[psneeld]

Both of my liveaboards had hatches in the salon giving standing headroom and plenty of access to the engines. The Albin trawler had access from spaces adjacent to the engine room, but I never used them underway as you had to squirm through. Even with standing headroom, you still had to squat, sit or lie down to work on the engine as it was mounted centerline, very low in the bilge....twins with a center walkway might have been even a little easier.

My twin sportfish (an many other boats I have operated) had installed engines with all regular service items accessible from the cental walkway.

The few items that needed no more than annual maintenance or longer that were difficult to service...I just figured out a way to get to those parts easier than working on "just that item". some required moving other equipment or like the one water pump, just unbolt the housing and disconnect the output hose from the easy to get to aft end of that engine and take the whole assembly out. Now a 15 minute impeller change instead of a knuckle-busting hour plus working in the blind.

The 37' sportfish was usually a gasser with little crusaders but mine had 2X 3208T hp Cat V-8 monsters. Still could work on them pretty easily. The 40 Albin was a simgle Lehman but had no room to stand below around it. So I got busy rearranging all the equipment mounted around it to more sensible locations. In a year or two.... you could lay down on both sides of the engine to work on it and front/rear were both easily accessed (well as easy as most any install considering bolt ons and cables/wires).

 

[MVPacific]

How many out here in Trawler Land ,have used single engines ? I know everyone is going to say two for redundancy in the middle of the ocean. However I would like to know if there are any brave and adventurous souls that have done it. I will be going from South Carolina to Bahamas and further parts south. Please feel free to unload on me .

I flew my family around Alaska for years in a single, piston-engine Cessna. I always thought about it, and I spared no expense on maintenance and upgrades. It never skipped a beat. We now own a 65 foot steel trawler type yacht with a single JD6125. I apply the same approach. Never forget that an engine loss severely increases your risk of harm, and do everything possible to ensure your engine is in perfect condition. And then always factor a failure into how you plan your trips.

 

[Hippocampus]

Would note think sailboat engines are taking an unnecessary hit. Had a yanmar 90 turbo backed up by four 50 g tanks. Run through a maxprop. Each tank had a separate fill but shared the same multi step filtration before getting to the engine. Picked up bad fuel at Hampton VA before leaving for Antigua. Our rule has been to try to only fill one tank from one vendor even if it meant pumping old fuel to other tanks. That way if we got bad fuel only one tank would be contaminated. Anyway on that passage there was no decent wind east of the Gulf Stream until we got to significantly east of Bermuda. Went through 4 racors then gave up on the bad tank wanting to keep at least 6 spares and safety margin of clean fuel. Still the yanmar was on continuously as we motorsailed nearly half the trip. Wanted 30g clean left for approach and landfall so other burnt 130g in a continuous run a 6kts. Look at duty ratings as scored for use in one year and for degree of load during one day. Purposely went slower given it was a small yanmar to control loading and maximize range. Had multiple 200nm with that boat. Easily driven. Think that’s the main difference between small recreational power and sail. Could do hull speed with that boat under power but when range and rating are a concern but you don’t have to. See small sailboat engines as a very viable option for small power given average use pattern. But once again even the small 110hp yanmar is computer common rail.

 

[Irish Rambler]

Twins or Single, it depends,,, on the skippers abilities !
Many people buy a boat with no mechanical experience and the first thing they need to do is go on an engine maintainence course and learn. Folk go on about maneouvering, have they been on a boat handling course ? There are some macho men who think just because they can drive a car or truck they can drive a boat, and thats simply not true.
Our boat has a single Perkins 80 hp diesel, I 'fenced' our rudder and with the bow thruster I can make the boat go virtually sideways, its all about practice and experience.
I've been boating for over 40 years with single engine boats and yes, we've had minor breakdowns but nothing that couldn't be repaired either permanently, or 'get you home' repairs. We carry fairly extensive spares for just such eventualities.
Sorry if I've been abrupt with straight talking.

 

[Hippocampus]

Twins or Single, it depends,,, on the skippers abilities !
Many people buy a boat with no mechanical experience and the first thing they need to do is go on an engine maintainence course and learn. Folk go on about maneouvering, have they been on a boat handling course ? There are some macho men who think just because they can drive a car or truck they can drive a boat, and thats simply not true.
Our boat has a single Perkins 80 hp diesel, I 'fenced' our rudder and with the bow thruster I can make the boat go virtually sideways, its all about practice and experience.
I've been boating for over 40 years with single engine boats and yes, we've had minor breakdowns but nothing that couldn't be repaired either permanently, or 'get you home' repairs. We carry fairly extensive spares for just such eventualities.
Sorry if I've been abrupt with straight talking.

Never had that engine but believe it’s a mechanical, non turbo naturally aspirated engine. Would return to Lepke’s excellent post stating in recent times given that we are restricted by pollution regs options are limited so the commercial fishing folks are putting in twins . Like you my prior boats were mechanical not common rail and I was quite content to be dependent upon a single. I’m still content to have a single as my horizons have shrunk and I’m always in proximity of help.
I also have decades of boating experience but know what I don’t know and can’t fix myself. In the past I could fix just about anything in my engines. Now I can’t. There’s a lot in current available engines of modest HP and above I can’t fix and even if I can diagnose i cannot address without outside help. You’re lucky. Hold on to that old school Perkins. It’s gold.
So if you’re going off the beaten track or voyaging choices are-
Make do with a single and do everything you can to make it bulletproof. Carry appropriate spares and tools. As said by many for many of us it,doesn't present a large risk.
Or have some form of backup. This maybe wise if you’re doing voyaging or off the beaten track. Just trying to point out this doesn’t necessarily mean a twin. Choices are a sailplan or electric or a get home or a twin. For some of us a twin with the extra space, weight and necessary servicing may not be the best choice. Would note for well over a hundred years people (commercial and recreational) did just fine with a single. Mishaps with unremenial loss of propulsion were sufficiently rare that marine activities continued unabated. View this problem as one of the many aspects of life where things I could maintain and fix are now black boxes. See it in my home HVAC system (all computer controlled geothermal), my electronics, my EV vehicle, and other common things in my life. If it isn’t plug and play it’s a phone call or go on the internet to get the latest new and improved (what a joke).

 

[Irish Rambler]

I agree with you on keeping an all mechanical engine. If I were to re-engine our boat I would fit a Mitsubishi S6DT cylinder 130 hp. It's relatively low revving at 2,800 to give you 2100 cruising, all mechanical with a a very useful torque curve and very smooth and quiet. I think its the best engine in that HP bracket.
I'm known by the others in the port as a FOC. In polite terms I'm a fussy perfectionist. I make no apologies but its strange how folk come for a chat which after the small talk, you get the questions, why, what and how do I fix it. Some agree, others don't and you hear of their mishaps later.
Different strokes for different folks.
I admit to keepng IT and electronics to the bare minimum for a peaceful life.
If you're thinking of, or owning an electric car, I would think twice, this one was parked up while the family went shopping, thankfully no one was hurt.

 

[TBill36]

Mechanicals have less failure modes to leave you stranded, but with the right knowledge and spares, electronically controlled engines are very reliable. Most will go into a limp mode if something really bad goes out and they have indicators on what's bad. Carry a few sensors and maybe even an ECU and you're real close to mechanical reliability with added smarts to help you stay healthy. You'll get things like fuel burn rate and load which are great indicators cause if they change you know somethings starting to go wrong. A tech can plug in a computer and do things like injector drop tests that show if there are any injector issues along with other health monitoring parameters.

Interesting note: About 15 years ago, heard that a captain on a large sportfish got a call from Caterpillar while running offshore. Told him his #4 cylinder on port engine wasn't firing as it should and told him to run up to max for a while to try and clear it while they monitored it.

 

[Ithaka7]

Twin engines is always more reliable than a single engine. It is pure statistics. I get the point that if you have a single and you maintain it well to a high standard, it could be quite reliable but no where close to having two engines. If you look at the propulsion system as a whole, you have many failure modes, electrics, the engine itself, hoses, transmission, shafts, propellers. Each of these can fail in the most inoportune time. Some of my experience:

- Anchored close to shore, a mini storm comes in quickly turns the boat around pressing us against the rocks. Tried to start the starboard engine - nothing. It turns out one of the battery terminals had corroded and lost contact. The port engine started OK and I got out.

- Another night, while cruising at speed (22 knots) run over some heavy duty fishing nets. One propeller fouled, one of the rudders bent, blocking steering completely. I managed to get out using the other engine and the bow truster for steering.

- Cruising, again at night in the Bosphorus, at speed, close to shore, one of the engines overheats. You do not have time to figure it out. Just shut it down and continue. It turned out to be a faulty temp sensor.

Therefore, my view is that twin engines are more reliable and allow you to continue the journey if one fails (instead of cancelling the trip). Not to mention that stern docking the the med in heavy wind, could be virtually impossible with a single engine, no matter the capability or experience. What you save on the second engine you spend on the higher standard of maintenance on the single engine. So, it is a wash costwise.

MV Ithaka
48 Superamerica

 

[La Sirena]

Confucious say, "man with two watches never knows what time it is."

I can't tell you how many times I've heard people say, "my starboard engine makes this sound (or vibration) but my port engine doesn't. With a single, you don't have these discrepancies.

Also, twins are usually not as well protected as a single. And they are double the target for logs and underwater debris.

 

[tiltrider1]

Confucious say, "man with two watches never knows what time it is."

I can't tell you how many times I've heard people say, "my starboard engine makes this sound (or vibration) but my port engine doesn't. With a single, you don't have these discrepancies.

Also, twins are usually not as well protected as a single. And they are double the target for logs and underwater debris.

You were trolled and you fell for the bait.

 

[Hippocampus]

Actually car and light truck fires are extremely more common just way more likely with gasoline ICE (internal combustion engine ) vehicles than EVs. What you posted is not true and statistics comes from over 10 years of EVs being on the road. Most recent numbers in link

Gas vs. Electric Car Fires [2024 Findings] | AutoinsuranceEZ.com

Auto fires result in hundreds of fatalities every year and millions of car recalls. Click here to see hybrid, gas, and electric car fire statistics.

www.autoinsuranceez.com

Even if you look at percentage for each type of vehicle EVs have the lowest risk.
Also inspite of much greater torque and acceleration due to body resting on sled of batteries turn over risk is lower as is fatality. You don’t end up with an engine in your lap. There’s a trunk (frunk) in the front which is a crush zone. Your comment is misinformation. EVs are actually safer than ICE. Issue is if a battery fire does occur poring water on it isn’t likely going to work. Given low density of EVs in certain areas local fire departments may not have the experience and equipment to provide best practices for Li Ion battery fires either in houses or vehicles . Fortunately my town does.
BTW when was the last time you saw pictures of ICE vehicles on fire in socal media or news outlets. Unusual either because so common as to not be newsworthy or cherry picking due to an agenda.

 

[mvweebles]

There are several good reasons to select either twin or single configuration. No question that twins, when maintained to same level as a single, obviously benefits from redundancy. There is no question that a well maintained diesel is reliable. In the vast majority of hull configurations, single prop is more protected than two props. Finally, there is no question that a single engine is easier and less expensive to maintain than two engines, and a single engine is more accessible in most engine bays.

I do not think the answer is as cut and dried as most twin owners believe it is. It can be, but in reality, is not. Everyone starts the season with the best of intention to keep everything in tip-top condition. But many hundreds of hours later, stuff drifts from perfect 'tip-top' condition. Ability to deal with a sub-optimal propulsion system varies - liklihood of a twin going south due to complexity is greater than a single, especially given access issues. Either due to access issues, complacency, or over-confidence in redundant engines, I wonder if twin engine owners have more voyages terminated due to mechancial failure than singles.

I understand the paper-argument for twins. But in reality, there is an argument for either.

Peter

 

[rslifkin]

I would not be surprised if twin engine owners have more voyages terminated due to mechancial failure than singles

It wouldn't surprise me either. I've always been shocked by how many people seem to consider coming back in on one engine because of completely preventable issues to be an acceptable situation.

 

[Caballero II]

My sig line has the answer

Yeah, I never liked that sig line. Many, many of us operate singles with a modicum of skill and aplomb.. Sorry, just plain disagree. There are a lot of us out there with well maintained single screws that would dispute that philosophy.

 

[Jklotz]

There are several good reasons to select either twin or single configuration. No question that twins, when maintained to same level as a single, obviously benefits from redundancy. There is no question that a well maintained diesel is reliable. In the vast majority of hull configurations, single prop is more protected than two props. Finally, there is no question that a single engine is easier and less expensive to maintain than two engines, and a single engine is more accessible in most engine bays.

I do not think the answer is as cut and dried as most twin owners believe it is. It can be, but in reality, is not. Everyone starts the season with the best of intention to keep everything in tip-top condition. But many hundreds of hours later, stuff drifts from perfect 'tip-top' condition. Ability to deal with a sub-optimal propulsion system varies - liklihood of a twin going south due to complexity is greater than a single, especially given access issues. Either due to access issues, complacency, or over-confidence in redundant engines, I wonder if twin engine owners have more voyages terminated due to mechancial failure than singles.

I understand the paper-argument for twins. But in reality, there is an argument for either.

Peter

As a guy in the market for a boat, this makes sense to me. I'd prefer to only have to maintain and cary spares for one engine. I'm a newbie, but in watching a lot of videos from folks out on the loop, it seems like most, 80-90%, of the "show stopper" problems stem from hitting something submerged or running aground. Just playing the odds, seems to me that a better protected running gear would be far more important for coastal cruising than a backup engine. Course' the closest I plan to get to an open ocean would be crossing the GS to the bahamas. I suppose it comes down to the intended purpose.

 

[SteveK]

Yeah, I never liked that sig line. Many, many of us operate singles with a modicum of skill and aplomb.. Sorry, just plain disagree. There are a lot of us out there with well maintained single screws that would dispute that philosophy.

 

[Captain DJ]

I agree with Scot on "SlowGoesIt". My 34 ft pilothouse carries 650 gallons and 2,000 mile range is only achievable with:

1) Zero reserves
2) running at 5 knots
3) having a spotless bottom & running gear
4) experiencing extremely favorable water (flat, no counter currents, no adverse winds, etc.)

I did talk with an old guy that took a GB 42 Classic from Mazatlan to Hawaii and those typically carry 600-ish gallons (mine carried 840) and that trip is in the 2,000 mile range, so maybe...but not safely.

 

[captmikem]

I used to drive a single engine tug between Canada and Mexico. Only problem I ever had was once off Nova Scotia we had a fuel problem and the engine died, other than nearly being run down by my tow it was not a problem. Got it squared away and did many trips after that without incident.

I took a twin screw trawler yacht around the world and never lost an engine.

My Monk Trawler is single screw. Heading down to west coast of Washington State the weather got a bit rough which caused a fuel problem and lost my engine. (clogged fuel line when the fuel tank stirred up by the weather), There is no tow company within a hundred miles and it had me a bit anxious for a bit until I got it squared away. Cleaned the tanks and have not had a problem since.

Peace of mind is probably the only problem you may have with single screw.

M

 

[Cold Duck]

Favor singles but have cruised twins to Mexico. Would not travel much in teh third world without some kind of emergency power even if it's an outboard affixed to the swimstep. The Willard cud use sails on it's stubby mast, actually saided pretty good. Things go wrong you can't plan for, a damperplate kills all power to the tranny for example. Singles in civilized areas no problems, long ocean transits and third world, I would absolutely have some emergency power.

 

[Seevee]

Could argue either side of this. I've has both single and twin engine boats, both diesel and gas, and single and twin engine aircraft.

Have had 5 diesel engine failures, one in a single. One "operator induced". In the twin, was a belt shreading, which, to this day, not positive it has been solved (but no failures in the past 7 months).

Of the aircraft, 5 engine failures, all in singles, only one off airport crash. All different causes.

I still have a twin aircraft and a twin diesel trawler, but could easily have another single.

With a trawler, there is no difference in fuel economy (same boat, single/twin), but there's a big difference in aircraft.

 

[Mako]

There was a similar thread here and it was interesting to learn from a Bering yachts broker that many of them are built single with no wing, and several owners have removed the wings altogether.

 

[tiltrider1]

In my fleet Boat A has two engines, Boat B has one engine.

Boat A has 35 year old engines. Boat B gets a new engine every 10 years.

Boat A had an engine shut down due to a failed internal coolant pump at Year 30. Boat B has never experienced any engine related issues.

I feel comfortable with both boats in remote locations. I would feel very uncomfortable with Boat B if I could not maintain her to such high standards.

Boat A could not achieve its mission if it was built as a single. Boat B could not achieve its mission if built as a twin.

Yes, I changed the coolant pump on the second engine at the same time I replaced the failed pump.

 

[Seanair]

Age old arguments; single or twins, Ginger or Marianne, Scotch or whiskey. Its all personal preference, and there is no logic that holds water that one approach is superior to the other so you really cant make the wrong choice. Its whatever works best for you.

For me, if I was doing a long distance cruise, I wouldn't want to take along 2 wives and I wouldn't want to take 2 engines.

 

[psneeld]

Age old arguments; single or twins, Ginger or Marianne, Scotch or whiskey. Its all personal preference, and there is no logic that holds water that one approach is superior to the other so you really cant make the wrong choice. Its whatever works best for you.

For me, if I was doing a long distance cruise, I wouldn't want to take along 2 wives and I wouldn't want to take 2 engines.

Wouldn't want to or wouldn't feel the need to?

Based on a lifetime of coastal cruising or 100,000 miles of ocean crossing, blue water, or remote cruising?

 

[BruceK]

Age old arguments; single or twins, Ginger or Marianne, Scotch or whiskey. Its all personal preference, and there is no logic that holds water that one approach is superior to the other so you really cant make the wrong choice. Its whatever works best for you.

For me, if I was doing a long distance cruise, I wouldn't want to take along 2 wives and I wouldn't want to take 2 engines.

Equating wives and engines is surely novel to the eternal "single vs twins" debate.

 

[Sababa]

My former ~20,000 pound Nordic Tug 37 with a single 330 hp Cummins 6BTA sipped 2 gph at 7.5 knots, 3 at 8.5, 6 at 10, and topped out around 16 gph at 17 knots.

My current Maritimo 52 at ~60,000 pounds with twin 715 hp QSM 11s drinks 4 gph at 7.5 knots, 7 at 8.5, 12 at 10, 30 at 17, and will hit 25 knots at around 60. So roughly twice the fuel to move three times the boat plus a higher top speed. Not a bad deal, especially while I’m still working with the occasional need and ability to trade money for time.

Now of course, there are single engine displacement boats that will move as much mass up to their hull speed for maybe 2/3 or 3/4 of my current fuel consumption. I may well buy one of them when I retire, provided it has a big second generator or a wing engine for a get home capability. Though that may wipe out much of the difference in acquisition and maintenance cost.

But assuming we are talking about modern electronically controlled engines that can be run indefinitely at a fraction of their rated capacity, and you aren’t planning to cross oceans on a regular basis, trawler speed efficiency just doesn’t seem to be a big reason to choose a single over twins. Better to assess your needs and lifestyle, and work back from there.