Operating Cost of Single versus Twins

[Lepke]

Teach your wife to dock. It will make it more interesting for her. Don't yell at her when you get excited.

You couldn't give me a Volvo engine of any size, warrantied or not. Otherwise most yacht engines are about equal.

Twice in 60 years, I came back on one engine. For that reliability and the ease of docking, I prefer twins. Both times I could have fixed the problem at sea but chose not to.

You have twice the oil changes and twice the equipment to maintain, but you don't use twice the fuel.

 

[psneeld]

I am interested in the "singles are rarely towed" comment.

How the heck does anyone even determine that?....the stats from towing companies may or may not be accurate enough to bet the ranch on that statement in my experience.

While I agree that owning a single should not be a great concern for potential failures....many, many twins power home on one without needing a tow.

Even my single, center console came home on its trolling motor a few times so how anyone can even remotely reference "towing" and engine numbers baffles me. No matter what the corporate stat collectors try and publish.

I owned a single for East Coast snowbirding. Would I be comfortable taking it to the islands or the Inland passage to Alaska? Safety wise yes, convenience wise no. When I don't want to anchor or stay in a bad spot, I REALLY don't want to and would like to go someplace I like, not just where the engine quit.

 

[Art]

It saves fuel with gas engines mostly because they're so horribly inefficient under light loads. But with diesels, the fuel savings from better engine loading is usually lost to the drag from the dead prop plus having the rudders angled the whole time (which also adds drag).

Good points!

 

[Hippocampus]

PS. I clearly offered that comment as the opinion of a experienced professional. His opinion based on his experience. Take it for what it’s worth.
Personally view much of this redundancy discussion as not realistic. In my experience and from tales I’m told and have read the most common disabling failure for blue water cruisers and racers is steering not propulsion (sail or engine). Most oceanic sail races require two totally independent modes of steering. My current boat doesn’t even have a emergency tiller. Prior boats either had wind vanes convertible into rudders or emergency rudders that could be deployed. We looked at steering on multiple boats before purchasing this one. For recreational trawlers steering didn’t have adequate redundancy in many. BTW neither does my fly by wire car. Reality is I’m on a coastal boat. With propulsion or steering failure I’ll get on the horn and ask for help and a tow if necessary. Both are unlikely to happen and in a coastal setting imho unlikely to present a serious risk. Much to do about nothing.

 

[rslifkin]

PS. I clearly offered that comment as the opinion of a experienced professional. His opinion based on his experience. Take it for what it’s worth.
Personally view much of this redundancy discussion as not realistic. In my experience and from tales I’m told and have read the most common disabling failure for blue water cruisers and racers is steering not propulsion (sail or engine). Most oceanic sail races require two totally independent modes of steering. My current boat doesn’t even have a emergency tiller. Prior boats either had wind vanes convertible into rudders or emergency rudders that could be deployed. We looked at steering on multiple boats before purchasing this one. For recreational trawlers steering didn’t have adequate redundancy in many. BTW neither does my fly by wire car. Reality is I’m on a coastal boat. With propulsion or steering failure I’ll get on the horn and ask for help and a tow if necessary. Both are unlikely to happen and in a coastal setting imho unlikely to present a serious risk. Much to do about nothing.

No emergency tiller on my boat either, as it would be pretty impractical to rig and would need either 2 people with headsets or 3 people without to operate one. But at the same time, a steering failure in a reasonably calm sea state wouldn't be world ending with twin engines in a coastal setting. As long as the rudders are close enough to centered (or you can get them there) you'll be going slow, but you'll have the ability to steer with the engines and limp to a safe spot to make repairs. It's when you lose an engine and steering (such as damage from hitting debris that takes out a prop and jams a rudder) that you'll be calling for a tow.

As Lepke pointed out, one of the upsides of a twin when you have a problem isn't necessarily that you have the other engine to get you home, but that you can move the boat to a safer spot to do the work (and probably let it sit for a few hours to cool down) rather than fixing the problem while rolling in beam seas on a scalding hot engine. I consider that ability more important in crowded, confined areas where having to drop an anchor "right now" may leave you in the middle of a narrow, crowded channel, for example.

Then again, a well maintained engine of even semi-modern design should be quite reliable. Even though I have "unreliable" gas engines I can only think of a handful of unplanned engine shutdowns. And I've known my current boat for a lot longer than I've owned it. A couple could have been prevented, but a few were just out of the blue. And most were not the fault of the engines themselves. They were things like a failed oil cooler line (preventable), plastic bag sucked onto cooling water intake, internal transmission failure with no prior indication of a problem, sudden fuel pump failure. The last shutdown was ~250 hours ago when I first got the boat and was the previously mentioned transmission failure. I shut down a perfectly good running engine as the transmission behind it had ceased to transmit power to the shaft, so there was no reason to keep that engine running.

 

[Art]

In a life time of being on boats [70 yrs total]; inland water ways and coastal cruising:

Only been aboard two boats, that each were towed in once over a period of years use. One was single screw, the other was twin screw. Both tow-in were fuel related. The single, a diesel, had malfunction in fuel line. The twin, gassers, ran out of gas.

Showing that when fuel access to engine gets severely enough restricted... matters not the number of engines. Tow-in will be required!

 

[rslifkin]

In a life time of being on boats [70 yrs total]; inland water ways and coastal cruising:

Only been aboard two boats, that each were towed in once over a period of years use. One was single screw, the other was twin screw. Both tow-in were fuel related. The single, a diesel, had malfunction in fuel line. The twin, gassers, ran out of gas.

Showing that when fuel access to engine gets severely enough restricted... matters not the number of engines. Tow-in will be required!

Fuel supply concerns are why I freak out a little every time I see a twin engine boat with a single fuel tank. It's not uncommon on smaller express styles, but in my mind, it's poor design. The more independent your fuel supply is to each engine, the less chance there is of them failing simultaneously (even if you have bad fuel or something that affects both).

 

[Hydrospud]

I wanted to thank everyone for their input. Thanks for your help on the single verses twin's input! Not sure what we're going to end up with but I'm not too worried after reviewing all the different opinions and experiences. It's refreshing to see folks express different ideas and still enjoy the conversations! This world needs more of this.
Blessings
Peter and Deb

 

[Art]

Fuel supply concerns are why I freak out a little every time I see a twin engine boat with a single fuel tank. It's not uncommon on smaller express styles, but in my mind, it's poor design. The more independent your fuel supply is to each engine, the less chance there is of them failing simultaneously (even if you have bad fuel or something that affects both).

So True - "I freak out a little every time I see a twin engine boat with a single fuel tank."

The twin gasser boat was a 1973 31' sedan, flybridge, sport fisher Uniflite. She had one centrally located fuel tank. Gas gauge that had for years been relatively close to reality had gone screwy. Close to 1/2 tank on gauge then = EMPTY! Last time I ever bothered to at all rely on any marine fuel gauge.

Luckily in this instance I was in the 2 mile canal that led to marina in which I docked... with about a mile left to travel. Instructional sail boat filled with ambitious kids took me as side tie and damn near placed me into my slip as well as if I'd motored in. Tried to give some cash as a thank-you! But instruction captain would have none of it, as he tipped the brim of his ornate captain hat... and off they went!

 

[rslifkin]

So True - "I freak out a little every time I see a twin engine boat with a single fuel tank."

The twin gasser boat was a 1973 31' sedan, flybridge, sport fisher Uniflite. She had one centrally located fuel tank. Gas gauge that had for years been relatively close to reality had gone screwy. Close to 1/2 tank then = EMPTY! Last time I ever bothered to at all rely on any marine fuel gauge.

Any time we fill the tanks to full, I confirm what the fuel gauges are saying by using them to estimate how much fuel we'll take and comparing to what it actually takes to fill the boat. I consider that generally good practice, as it'll give you a good idea of fuel on board as long as the gauges are consistent, even if they're not entirely accurate.

 

[Gdavid]

I am interested in the "singles are rarely towed" comment.

How the heck does anyone even determine that?....the stats from towing companies may or may not be accurate enough to bet the ranch on that statement in my experience.

While I agree that owning a single should not be a great concern for potential failures....many, many twins power home on one without needing a tow.

Even my single, center console came home on its trolling motor a few times so how anyone can even remotely reference "towing" and engine numbers baffles me. No matter what the corporate stat collectors try and publish.

I owned a single for East Coast snowbirding. Would I be comfortable taking it to the islands or the Inland passage to Alaska? Safety wise yes, convenience wise no. When I don't want to anchor or stay in a bad spot, I REALLY don't want to and would like to go someplace I like, not just where the engine quit.

I wonder about the data on this one as well, the sample size of boats in the common size range we are looking at and single engine is rather small, most recreational boats of 30' or more are twin engine. Another factor is that many "larger" single engine vessels are in commercial service like commercial fishing or charter fishing and those guys tend to look after their own.

I can understand the idea of put all of your eggs in one basket and watch it closely but many boat owners are lax with their maintenance (single or twin).

 

[Art]

Any time we fill the tanks to full, I confirm what the fuel gauges are saying by using them to estimate how much fuel we'll take and comparing to what it actually takes to fill the boat. I consider that generally good practice, as it'll give you a good idea of fuel on board as long as the gauges are consistent, even if they're not entirely accurate.

I use a torpedo shaped fish weight fastened to a tan cord. Have 1/2 tank and full tank marks on the cord. Feed the weight with line down fill hole and can readily tell when nose of sinker hits tank bottom [can hear it through the fill hole]. Knowing that each inch wet on the line = 4 gallons, can also immediately determine by the 1/2 and full tank marks, I always have accurate measurement. And yes, after that measure is taken... I do still check the fuel gauges to see what they read... just for the heck of it.

Reason I use the flexible line attached to torpedo shaped sinker weight is because straight stick can not pass through twist in the filler line to the tanks. Both identical shape/size aluminum tanks are 100 gal each. As added attraction: Port fill line to tank accepts sinker and line with no holdup. However, Starboard has a slightly sharper twist... thus... I must spray the sinker with WD-40 to enable a smooth drop of sinker to tank bottom.

 

[psneeld]

I wonder about the data on this one as well, the sample size of boats in the common size range we are looking at and single engine is rather small, most recreational boats of 30' or more are twin engine. Another factor is that many "larger" single engine vessels are in commercial service like commercial fishing or charter fishing and those guys tend to look after their own.

I can understand the idea of put all of your eggs in one basket and watch it closely but many boat owners are lax with their maintenance (single or twin).

It's not only that...

In my roles on the water....sometimes that sometimes "simple" single engine repair that many fix and go on their way... winds up with a different story.

The simple replacement part fails, the tool breaks and even the repairer gets injured and needs to be Medevaced.

Having run singles both pro and private for the last 25 years, I have had a lot of failures that would have stopped me for not my jury rigging, outside of the box thinking. Based on internet postings, doubt many would have even tried many. So no, not stranded.... but a few times, didn't mean their wasn't a fair share of that single shutting down unexpectedly. Sometimes in spots many would have found were going to turn out bad if some corrective action wasn't taken.

Do I recommend against singles? Not in general but there is lots of boating where I would prefer or demand twins.

 

[wkearney99]

even twin engines and thrusters can Challenge marital status while docking.

For us, the #1 rule of boating is "You can't un-yell at your spouse."

 

[Nomad Willy]

Cost difference single v/s twin is almost always fly stuff.

A big difference between the two is that most rec trawler twins have engines of twice the power as a single because the manufacturers forced one to have double power w twins. They used the same engine. The question of s/vs/t in essence has (should) have nothing to do how much power is installed in the boat. Most s/vs/t question is about how much power a boat and has nothing to do w the number of engines.

To the OP … I think the biggest element re purchase choices is the get-home question. Most don’t (judging from TF conversation) take this factor as seriously as they should. Safety at sea is a very important consideration. Safety enters into most every question about boating. I had a girlfriend that wouldn’t go out on a boat w/o a dinghy of suitable capacity.

Other old wife tales like singles cost half as much to maintain is very misunderstood. Sure you “need two oil filters instead of one” dosn’t even hold water. The twin will usually need two smaller filters instead of one larger. But then re rec trawlers most have the same engine so filters ARE twice as much as is the cost of lube oil. A twin w the same power as a single (almost dosn’t exist) would have much the same maint. cost so as a principle for discussion … at least very close.
And if one compares singles and twins w the same amount of power the difference in fuel consumption or maintenance is so small as to not be not worth considering.

The widespread overpowered state of twin engined trawlers should be a significant element of consideration re purchase .. IMO. But many think one can’t have too much power. More level headed skippers would tend to look for a boat w the “correct” amount of power or whatever amount of power it takes to get the job done. And there’s considerable misunderstanding about that as well.

But IMO the cost of buying and operating a rec trawler the question of get-home power should be most important … for safety. So twins get my nod. But if I was buying a 36 or 42’ GB I’d buy the single for economy .. and think about a small auxiliary engine for get-home power.

 

[Hippocampus]

Seems interesting that the wings on Nordhavns are commonly never used in anger. Just occasionally exercised. Seems interesting that the guru of lugger/NL Bob Senter apparently lead me wrong. Took care of a lot of lobstermen and small commercial trawler men who all ran singles.
So my inference is recreational boaters are idiots. They don’t care take of their boats. They don’t do routine maintenance. They don’t know how to work around the simplest problem.
Currently in NEB doing restoration work on my interior woodwork. Can see three fingers. Of course all the sailboats are singles. Two to four outboards off the back of the go fasts. Even split single/twin for the rest. Berthing for 40-55 my finger. 36-40 off my stern. 60 and up off my bow.
Seen unsafe sail attempt passage. Seen unseamenlike behavior on all sizes and types of boats. But suspect failures are less likely with appropriate maintenance. Suspect more coastal miles are traveled in single screw vessels than twin. Suspect people on “tugs” and single screw “trawlers” are more likely to do more miles(hours) than twins. Have no reason to discount what Bob told me.

BTW I have a 40hp outboard on the back of my Rigid dinghy. It launches with a push of a button. Doesn’t share fuel nor running gear. It’s my get home. Hope it’s never needed.

 

[Sailor of Fortune]

Any time we fill the tanks to full, I confirm what the fuel gauges are saying by using them to estimate how much fuel we'll take and comparing to what it actually takes to fill the boat. I consider that generally good practice, as it'll give you a good idea of fuel on board as long as the gauges are consistent, even if they're not entirely accurate.

I would never trust a fuel gauge on any boat..They are notorious for being stuck/wrong when you need them. Preference is a stick method or sight gauges. Ullage is important....

 

[rslifkin]

I would never trust a fuel gauge on any boat..They are notorious for being stuck/wrong when you need them. Preference is a stick method or sight gauges. Ullage is important....

I trust mine only because I routinely confirm their readings vs reality, and I've replaced the senders with good quality, known working ones. No sight tubes for me as it's gas, not diesel. And the filler hoses make a compound S curve and come into the top of the tank at an angle, so no good way to stick the tanks (short of maybe Art's method).

 

[Gdavid]

So my inference is recreational boaters are idiots. They don’t care take of their boats. They don’t do routine maintenance. They don’t know how to work around the simplest problem.

I don't think anyone is saying that recreational boaters are idiots and most people buying a serious blue water trawler with a wing engine were successful in life. That said a professional mariner is more likely to have greater levels of experience maintaining and repairing the mechanical issues first hand, most (not all) that can make a go of it financially have learned how to do much of their own maintenance and repairs for decades.

 

[Hippocampus]

Perhaps I stated things too strongly. But still think the folks on this site are intelligent people who are diligent in servicing their boats. Further think those fortunate enough to be able to pay for professional servicing still get good work done. Perhaps in some cases better than that provided by amateurs. With restricted days at sea, lobster moving north, decrease in ground fish stocks family run boats have taken many hits. Economics may force deferred or work arounds. As a younger man I did all my car and motorcycle maintenance. Now I do none. Is that to say my vehicles are less safe now? I continue to do belts, impellers, fluids and filters on boats. But still want a pro for more involved stuff. Does that make me less safe? When I was cruising internationally I carried injectors all pumps , hoses and other replacements for key points. Also did several diesel courses. Felt confident beyond major catastrophes I could keep an engine running either mid ocean or remote places. Now I simply don’t see the need. Follow the service intervals as per manufacturer. Don’t see it matters much who does it (it’s me in most cases). Failure is unlikely and in a coastal setting manageable without too much difficulty. Still feel the extreme belt and suspenders attitude I had in the past isn’t necessary in a coastal setting. Do continue to believe there’s those who respect their boats and are diligent in maintenance and those not so much. That’s true for any size boat and any setting.

 

[ronobrien]

I like twins for handling but they are more difficult to access. Guess I can live the the access issues since that is what I have been buying for the last 5 or 6 boats. The fuel burn difference isn’t twice, more like the 10% mentioned above. But it is nice when one engine quits to be able to get home on the other engine. Also the docking is easier with twins. Yes, the maintenance is double but typically with diesels the maintenance isn’t terrible. Oil changes, impellers, heat exchanger maintenance, etc. in the scheme of life buy the boat that fits your needs and desires and live with the engines that it comes with, except Volvos. I had them once and never again.

Check for insurance before you buy. You are making a big jump in size and you may have hoops to jump through in order to get coverage. Better to find out before you buy what you need to do, if anything.

I have heard very few good things about the Volvo's.

 

[NancyD]

Trawler

There are trawlers that have twin outboards that are easy to maintain and economical on fuel. I have a trawler that has a range of around 1000 miles @ 10mph and 350 miles @ 15-18mph.

 

[Landshark]

Some things to consider when weighing twin engines vs a single:
*Twins offer better maneuver control in tight places, but a single with bow and stern thrusters is just as good,
*With twins two of everything for maintenance is required,
*Twins will constrict engine room access,
*With twins the props are more vulnerable to underwater obstacles,
*The notion that with twins if one engine fails the other will get you home is grossly overrated. Operating a twin engine vessel with one engine is exceedingly difficult.
*While addressing engine failure consider how many private and military airplanes have single engines in a situation where engine failure is much more critical.
*Fuel economy is about par with either configuration.
*A vessel with twins will typically have less draft.

 

[AdamC]

The Mainship 350/390 that I own is one that comes in both flavors. When I started shopping for this model, I was looking at the singles and ended up buying the twin because "the perfect boat" fell into my lap.

I would say that I wish I bought the single, but I'm glad I own the twin . I find the smaller Yanmar 4 cylinders to be manageable for service but there is no question that accessing the outboard sides of the engines is difficult. I relocated and put quick connects on my main engine strainers so they are not so much in the way and can be removed quickly. However, most jobs on the outboard side must be done with one hand unless you start pulling off major components that open up the space. So, for every maintenance job that you want to do on both engines, there is one easy job and one hard one. So far <knock, knock>, the hardest job I've had to do is replace the starboard oil cooler which is naturally on the outboard side.

As to cost breakdown, I can't comment because I've not owned the single-engine version. My twin engines are rated 190 HP continuous while the singles came with 300 HP. This gives a small top-end performance advantage to the twin but neither boat is efficient at top-end speeds. Either version is reasonably fuel-efficient at hull speed.

-Adam

 

[rslifkin]

The notion that with twins if one engine fails the other will get you home is grossly overrated. Operating a twin engine vessel with one engine is exceedingly difficult.

That depends a lot on the boat. A twin with the engines set very far outboard and small rudders can be a handful. But with slightly closer engine placement and/or larger rudders, it's not so bad beyond becoming significantly speed limited on one engine. Maneuvering in close quarters can become a bit interesting though (mostly if you need to back up more than a very short distance).

 

[Mac2]

I have heard very few good things about the Volvo's.

I was wondering about the volvo comment as well. When talking about costs, I would absolutely avoid the Volvo engine. Great engine, but replacement parts are absolutely stupid! I had a 95 hp volvo and a raw water pump was around three times the cost of something like a Johnson pump.
When considering cost between single vs twin, replacement part costs should also be considered.

 

[psneeld]

That depends a lot on the boat. A twin with the engines set very far outboard and small rudders can be a handful. But with slightly closer engine placement and/or larger rudders, it's not so bad beyond becoming significantly speed limited on one engine. Maneuvering in close quarters can become a bit interesting though (mostly if you need to back up more than a very short distance).

Agree, haveing run all kinds of hulls with twins, one out is easy to get home on in almost all cases, but tight quaters maneuvering might be an issue depending on the boat.

 

[JYoung]

If you know what you are doing, single is the advantage every step of the way. Today, so many seem to need thrusters. Do not understand why. If you know how to drive a boat and you know what you are doing, single is a snap. As far as cost, efficiency and overall value, one engine is all you need.

 

[mvweebles]

Today, so many seem to need thrusters. Do not understand why. If you know how to drive a boat and you know what you are doing, single is a snap. As far as cost, efficiency and overall value, one engine is all you need.

Well, I can tell you why for me. After 25-years of owning the same boat - a single Willard 36, a very mannerly boat, I am installing a bow thruster.

Now, I have a decent resume so you might be surprised. I'm a past delivery skipper of primarily single engine trawlers; plus about 4-5 seasons as a presenter at TrawlerFests as both seminar instructor on close-quarter manuevers and hands-on instructor at TF University. I also was a captain of a 84-foot dinner cruise boat in SF Bay (a twin, but sailed in all but the foulest of weather). So why am I going with a thruster now? Because not all slips are a snap. Not every problem is solvable with a single. And I now own a slip in Florida that is challenging and frankly. I don't want to worry about it.

I have thousands of really impressive docking maneuvers, a few earned me a drink at the yacht club bar. And a handful that were pretty embarrassing which blot-out the sun of all the great ones. For those familiar with SF Bay, one crazy attempt at Angel Island still makes me wince.

I worked hard to get comfortable docking a boat. But I still get nervous. I'm all for thrusters if it will help someone get their boat out and use it more often and comfortably.

Peter

 

[psneeld]

If you know what you are doing, single is the advantage every step of the way. Today, so many seem to need thrusters. Do not understand why. If you know how to drive a boat and you know what you are doing, single is a snap. As far as cost, efficiency and overall value, one engine is all you need.

Snap? Some singles, some conditions.

Me, most singles and most conditions but unfair advantage of experience.

But snap for most? Not really as getting the experience and maintaining proficiency is nit a reality for many.