Operating Cost of Single versus Twins

[Hippocampus]

If trading stories.
Friend runs and occasionally charters a Henriques 38 with twins. Had a charter and was running to the canyons on plane. Went over nylon netting with steel cables along edges. Nylon melted. Cables ruined props to point of needing replacement. Cutlasses as well and one transmission. Expensive day.
Crossing gulf of Maine in a GB twin. Well offshore. Calm night with sea like glass. Owner running the boat. Loud bump. One engine gone. Would run in neutral but not if in gear. Got towed. Maine water is cold. Made no attempt to dive. At haul out a thick wood pole (?telephone? fence?other) was wedged so neither prop could turn nor rudder the owner told me.
The northeast is littered with traps of all sorts. People use black used oil containers, floats so dirty you can’t pick a color to describe them. They’re in marked channels and way offshore. Add in fish weirs, nets and traps there’s a lot of stuff to miss. Turn one way there’s another in front of you. Even on single screw have gotten snagged once or twice. Often no good way to turn as even with two watching out as you get into the field or chain too close at hand. Also there’s occasions you have no choice but to dodge through the field. Single screw go to neutral and slide over. No hurt no foul. Sometimes more problematic with twins.

 

[rslifkin]

On the debris issue, I've never hit anything on plane, but I've had a few low speed debris hits with my twins and exposed running gear. So far, I've yet to have any damage. One un-seen bit of debris did bounce off the props last year (but with no visible marks at winter haulout). I heard it hit the hull and got the engines out of gear before it made it to the props / rudders. Every other bit of submerged wood I've hit has either hit the hull and been kicked out to the side, or it's hit the keel and gotten thrown down and under the props/rudders (or rolled along the keel where it cuts away aft and went between the props and rudders).

I've had a few hits where the debris was sunken enough that I never saw it before or after the hit. The last hit I had was debris that was invisible before the hit, made 2 good thuds along the keel, then popped up behind us (and then sank back out of sight). A twin with a deeper keel like a Grand Banks, Defever, etc. will have less of a risk of a prop strike than I do, as those keels are deeper than the props (while mine is not, it ends about 5" above the props).


Because of the net and line concerns, I do periodically debate what I should add for line cutters. Twins are definitely at a bit more risk of a tangle there, but a single is still at risk if you don't get the engine out of gear in time (as it'll suck stuff into the prop even if it would otherwise just slide past).

 

[Art]

Just an interesting side note... not usually mentioned:

With twins I simply LOVE the hum of two engines turning at exact same RPMs... gets my jolly! Besides an old-world light-glow synchronizer and two tachometers at both pilot stations... I always sync my engines' RPMs by sound [the old light-glows are pretty much correct, not so much the tachs]. Back and forth hum of the engines "singing" to each other also works well to provide instant "sound" notice if one or the other for some reason has slight or a bit deeper stumble. I like the tone of sounds emanating from twins when in sync!

 

[BandB]

Wifey B: Ok, no one jumped on the six engines. I'll try again. What about three with no props? Shallow draft.



Or how about jets in general? Maybe a Hinckley Talaria 43 with a draft of 2'4"?

Many great tinnie's (used the term for our Aussie friends, translate to aluminum boats or aluminium). Quite a few in the PNW that are jet powered.

 

[rslifkin]

Jets are cool and the shallow draft is a bonus, but I worry about maintainability (compared to shafts) and low speed handling. So while they're really useful for some stuff, I don't know that I'd want them on a general purpose cruising boat.

 

[BandB]

Jets are cool and the shallow draft is a bonus, but I worry about maintainability (compared to shafts) and low speed handling. So while they're really useful for some stuff, I don't know that I'd want them on a general purpose cruising boat.

Wifey B: Maintainability? Less to maintain. Fewer parts.

Low speed handling? An adjustment for those not experienced, but ultimately equal handling and with enough experience, superior. That comes from learning to use power to docking. Other low speed isn't an issue.

Now you do still have units you could run aground and knock off if you chose. Not impervious to logs or other things.

Love to watch the wardens on Louisiana Law barreling through the swamp waters. :lol:

 

[Nomad Willy]

Hippocampus makes good point.

His post 121 is a clear case for single prop on CL.

But one needs to evaluate the good and bad of everything and make decisions. What’s worse? Hitting a submerged object w a prop or loosing power w an on-shore wind?

I’ve only hit a submerged object once. A log. About 1’ dia. and 10’ long. I know that because it came up astern and I got a good look.
I instantly thought we were going to sink .. mostly because of the sound of the hit .. boom. Scared the stuff out me. But never found the point of contact. And it missed the prop.

So IMO the single gets the nod re crashing into submerged things.

 

[Nomad Willy]

Wify B,
Aren’t “jet” drives quite inefficient? At one speed? Or anytime. I see few jet boats so they’re must be a big drawback. Expense probably.

 

[rslifkin]

Wifey B: Maintainability? Less to maintain. Fewer parts.

Low speed handling? An adjustment for those not experienced, but ultimately equal handling and with enough experience, superior. That comes from learning to use power to docking. Other low speed isn't an issue.

Now you do still have units you could run aground and knock off if you chose. Not impervious to logs or other things.

Love to watch the wardens on Louisiana Law barreling through the swamp waters. :lol:

Maintainability isn't so much about how many parts, but also how easily I can get parts for it anywhere and everywhere. And how reliant it is on outside techs vs DIY (I hate relying on other people to work on my boat).

 

[BandB]

Wify B,
Aren’t “jet” drives quite inefficient? At one speed? Or anytime. I see few jet boats so they’re must be a big drawback. Expense probably.

Wifey B: Not designed for a full displacement boat. However, inefficiency is overstated and often associated with prior technology. Great improvement over the years. Now, all forms of propulsion seem to have their most efficient areas on their performance curves and least efficient when comparisons are done.

 

[BandB]

Maintainability isn't so much about how many parts, but also how easily I can get parts for it anywhere and everywhere. And how reliant it is on outside techs vs DIY (I hate relying on other people to work on my boat).

Wifey B: Carry the main parts with you and others quickly shipped in. Not available at West Marine.

Learning curve for DIY'er really short and simple. Just not a lot to learn.

As to number of jets out on the water, I'm afraid some overlook the obvious, fastest growing propulsion for years in small boats with Yamaha and then with all the PWC's. Doesn't translate directly to larger boats, but the principles are all the same and they have similar parts, just much larger ones.

Just look at the photo on the linked page. That's all there is to it.

https://www.marinejetpower.com/waterjets/csu/

Here is all there is to a Hamilton Jet:



I'm not trying to convert the world, but just clearing up some misconceptions. Our group maintains 15 RIBs with jet drives plus our AB with triple jet drives.

All I'm pointing out is if running aground and logs into props were the only concern, then singles and doubles lose to jets. Reality is we all find the setups we like and select them. May be single or six engines, straight drives, v drives, pod drives or jet drives. All have pluses and minuses.

 

[HTurner]

Who would want jets, when you can really have fun with:


https://www.marineturbine.com/turbine-powered-workboats/

 

[Marco Flamingo]

For a very entertaining comparison of boat styles, check out The Grand Tour episode called Seamen (starring Jeremy Clarkson, Richard Hammond, and James May). They take three very different boats down the Mekong River (a Vietnam war era jet boat, an over the top twin engine cigarette boat, and a classic single engine English putt putt). The various shortcomings of the vessels are presented with classic English wit. Highly recommended, as is the original series Top Gear, although that is about cars.

Listening to the engines synchronize reminded me of good advice given at a boat show diesel seminar. When you hear something change, don't say "well that's different." Find out why the noise/vibration/rpm changed. That can save anything from an inconvenience to a rebuild.

 

[socalrider]

What about wing engines?

A lot of the bluewater "singles" have wings. This always struck me as a pretty poor solution as you end up with a 99.999% useless engine, usually from a different maker with its own set of spares, maintenance, etc. and a feathering prop, cutlass bearing, etc.

The new Nordhavns mentioned earlier with twin small mechanical Beta engines seem like a superior solution in a lot of ways. If redundancy is important, I'd rather rely on a system that's in regular use! Those engines are so small that access is probably not a big issue either. I know that if I had twin ~75hp Betas instead of twin 120hp Lehmans my engine room would be a heck of a lot nicer. Top speed would drop from 11kts to 9kts. Who cares? Wish it had come that way from the factory.

 

[BandB]

What about wing engines?

A lot of the bluewater "singles" have wings. This always struck me as a pretty poor solution as you end up with a 99.999% useless engine, usually from a different maker with its own set of spares, maintenance, etc. and a feathering prop, cutlass bearing, etc.

The new Nordhavns mentioned earlier with twin small mechanical Beta engines seem like a superior solution in a lot of ways. If redundancy is important, I'd rather rely on a system that's in regular use! Those engines are so small that access is probably not a big issue either. I know that if I had twin ~75hp Betas instead of twin 120hp Lehmans my engine room would be a heck of a lot nicer. Top speed would drop from 11kts to 9kts. Who cares? Wish it had come that way from the factory.

You highlight a point on wing engines, that I also apply to second generators. I want the second engine and the second generator capable of doing everything I need to continue safely and comfortably. If 75 hp will do it, then fine. Otherwise I want more. I think many wing engines would be hard pressed to get you home if you were crossing an ocean. I see boaters with small second generators stranded, waiting on a repair of their main generator because the second won't power the boat as they need. It's not redundancy, if it won't do the job.

 

[rslifkin]

With either twins or single+wing you're likely to be speed restricted after an engine failure due to less available power. The only way you're not is if you have twins in a boat that's significantly overpowered to start with.

 

[BandB]

With either twins or single+wing you're likely to be speed restricted after an engine failure due to less available power. The only way you're not is if you have twins in a boat that's significantly overpowered to start with.

Doesn't mean it's significantly overpowered. Just means it will go faster than displacement speed. However, speed restricted is fine. What I don't consider acceptable is having inadequate power to assure the ability to still make headway. For instance, if the wing engine isn't enough to offset sea conditions such as waves or current. If you're stranded 800 nm off shore and can proceed at 5 knots, just will take you 7 days, no problem. However, if you can't proceed at all or net 1 or 2 knots or waves push you backward, then a problem. I do encourage all to put their wing systems to a test. I have no idea what a 40 hp Lugger will do for a 90,000 lb, 52' boat in ocean conditions, one that normally is driven by 160 hp. However, if I owned such a boat, I'd find out. I think the builder has probably tested and found it adequate.

 

[Gdavid]

Doesn't mean it's significantly overpowered. Just means it will go faster than displacement speed. However, speed restricted is fine. What I don't consider acceptable is having inadequate power to assure the ability to still make headway. For instance, if the wing engine isn't enough to offset sea conditions such as waves or current. If you're stranded 800 nm off shore and can proceed at 5 knots, just will take you 7 days, no problem. However, if you can't proceed at all or net 1 or 2 knots or waves push you backward, then a problem. I do encourage all to put their wing systems to a test. I have no idea what a 40 hp Lugger will do for a 90,000 lb, 52' boat in ocean conditions, one that normally is driven by 160 hp. However, if I owned such a boat, I'd find out. I think the builder has probably tested and found it adequate.

A twin engine boat running on a single engine brings all of the discussion and concerns of over propping/pitching. This shouldn't be any trouble if you are willing to run at displacement displacement speed but if you are going to try and run as fast a possible on fewer engines, it is critical to watch your exhaust gas temps. While a wing engine may be painfully slow for you, it should be set up with the correct transmission ratio and prop pitch to prevent damage to the wing engine on the long, slow trip home.

 

[Art]

Some of this engine/propulsion-delivery what ifs and could be, should be, would be is beginning to employ the full definition of semantics!

se·man·tics
/səˈman(t)iks/
noun
the branch of linguistics and logic concerned with meaning. There are a number of branches and subbranches of semantics, including formal semantics, which studies the logical aspects of meaning, such as sense, reference, implication, and logical form, lexical semantics, which studies word meanings and word relations, and conceptual semantics, which studies the cognitive structure of meaning.

 

[psneeld]

In my experoences and/or opinion...

1. I specifically chose a single for fuel consumption. All the arguements here rarely discuss why I believe the way I do....and its a waste of my time to argue about it. People can accept or reject my experience on the matter.

2. Some twins truly are hard to dock on one...but they made it to the or a marina most of the time on their own. While partly a safety issue, to discount that advantage is beyond me. Yet for me, it is more convenience over safety, but they are both legit issues in some situations.

3. The "outboard maintenance" discussion is a joke. If well maintained the outboard side gets the required maintenance it needs. The point was already posted that many boaters dont maintain well is all too true. I have a friend that had a twin 32/33 Egg Harbor sportfish that hardly maintained it at all and ran on one engine for nearly 3 seasons. What does that prove? I have no clue, your guess ia as good as mine.

4. A twin aground hardly automatically ruins one prop or shaft. Possibe? Probable? Maybe either, but not always.

While its a good debate, I really dont agree with many of the "theories" presented.

 

[mvweebles]

3. The "outboard maintenance" discussion is a joke. If well maintained the outboard side gets the required maintenance it needs.

Clearly you've never tried to use the lift pump to prime a starboard-side Perkins 6.354.....

Lot to be said for the old Detroits that came in mirror-image engines so they could be close-coupled into a single transmission. Could barely fit a dozen sheets of paper between them.

Peter

 

[Simi 60]

Just about all the working trawlers over here run singles and do big miles in often adverse conditions and remote locations.

If twins were a better thing from a financial and safety aspect I imagine they would have them.

 

[Nomad Willy]

Simi 60,
You don’t speak so much about engine reliability as you do about history. Having many hundreds to thousands of hours time running a specific boat, engine, control systems and electrical systems builds history …. the kind of history that breeds confidence. Quite a few times I had the chance to fly ultralights built by little or not known people w strange control systems … death craft or wonderful flying machines. History tells the tale and it’s the same w trawlers. Over time near perfection is achieved.

And boats w a great history are very much more safe than others. This difference is IMO far greater than the number of engines. Many times TF skippers have pointed out that many different kinds of commercial craft like fish boats to freighters that go great distances over long periods of time w single engine power. They usta require four engines on trans ocean airliners that carry people for money. Now they only require two engines. The engines are considerably different being gasoline reciprocating early on and jet engines later. And there was a considerable length of time .. thousands and thousands of ocean crossing hours w the new engines before the FAA ok’d twin engined aircraft crossing oceans carrying paying passengers. History is what allowed the change in policy. History showed us it was safe .. or safe enough.

Twin engines in rec trawlers almost certainly are much less likely to have power failures leaving the craft adrift at the mercy of wind and sea. But I would much rather travel on a trawler that had a good and documented history of safe travel. I guess what I’m saying is that positive mechanical history is more important than number of engines. But all else equal .. singles are much the same but less safe than twins.

 

[Circumnavigator]

I.....

If your plans include traveling to extreme remote locations or crossing seas and oceans, buy twins for the above reason.

....

I disagree. Singles -- with a skeg -- are much better protected than twins (Skeg - extension of the keel that goes under the prop and supports the bottom end of the rudder). An interaction with a log or container is likely to wipe out both sides of a twin, while the single may be untouched or at least still usable. When off the beaten path, I'll go for the extra protection every time. We crossed the Atlantic in Fintry 17 years ago.



As for handling, I can put Fintry (for sale, see photo) or Morning Light (our new to us 42' trawler) anywhere that they fit, with or without using the bow thruster. Both are singles with large props (60" and 30") and rudders to match.


And, in many twin screw boats, the ability to get home on one engine may be more illusion than real -- the off center thrust can be close to unmanageable.


Jim

 

[rslifkin]

I disagree. Singles -- with a skeg -- are much better protected than twins (Skeg - extension of the keel that goes under the prop and supports the bottom end of the rudder). An interaction with a log or container is likely to wipe out both sides of a twin, while the single may be untouched or at least still usable. When off the beaten path, I'll go for the extra protection every time. We crossed the Atlantic in Fintry 17 years ago.



As for handling, I can put Fintry (for sale, see photo) or Morning Light (our new to us 42' trawler) anywhere that they fit, with or without using the bow thruster. Both are singles with large props (60" and 30") and rudders to match.


And, in many twin screw boats, the ability to get home on one engine may be more illusion than real -- the off center thrust can be close to unmanageable.


Jim

Some twins are a handful on one, but many have big enough rudders, etc. that it's not bad except for being awkward in close quarters.

As far as protection, some twins (like the Great Harbour builds) do have twin skegs to protect the props better. If doing lots of travel in debris-strewn areas, any design (single or twin) merits a careful assessment of whether the props are protected enough or not. Even with a single some are not nearly as well protected as others.

 

[Circumnavigator]

Some twins are a handful on one, but many have big enough rudders, etc. that it's not bad except for being awkward in close quarters.

As far as protection, some twins (like the Great Harbour builds) do have twin skegs to protect the props better. If doing lots of travel in debris-strewn areas, any design (single or twin) merits a careful assessment of whether the props are protected enough or not. Even with a single some are not nearly as well protected as others.

All true -- all generalizations about boats are false. However, protecting twins with skegs adds significant drag -- the better the protection, the more you pay in speed or fuel consumption.


Jim

 

[rslifkin]

All true -- all generalizations about boats are false. However, protecting twins with skegs adds significant drag -- the better the protection, the more you pay in speed or fuel consumption.


Jim

Skegs do add drag, but because the skegs will aid tracking, it can often be at least mostly made up by reducing or eliminating the centerline keel. I don't think the penalty is so large that other design adjustments can't keep the total drag down to reasonable levels.

 

[O C Diver]

I disagree. Singles -- with a skeg -- are much better protected than twins (Skeg - extension of the keel that goes under the prop and supports the bottom end of the rudder). An interaction with a log or container is likely to wipe out both sides of a twin, while the single may be untouched or at least still usable. When off the beaten path, I'll go for the extra protection every time. We crossed the Atlantic in Fintry 17 years ago.



As for handling, I can put Fintry (for sale, see photo) or Morning Light (our new to us 42' trawler) anywhere that they fit, with or without using the bow thruster. Both are singles with large props (60" and 30") and rudders to match.


And, in many twin screw boats, the ability to get home on one engine may be more illusion than real -- the off center thrust can be close to unmanageable.


Jim

Jim,

You missed the point. My post was about being able to return from remote locations unassisted. Nothing (except possibly money) prevents you from having a twin engine, twin keeled boat with the skegs under the propellers and supporting the rudders.

Ted

 

[Mako]

Singles -- with a skeg -- are much better protected than twins (Skeg - extension of the keel that goes under the prop and supports the bottom end of the rudder). An interaction with a log or container is likely to wipe out both sides of a twin, while the single may be untouched or at least still usable. When off the beaten path, I'll go for the extra protection every time.

And I suppose if, even with a protected single, that you were purposely spending time in debris strewn waters, including heavy ice, then adding a couple of ice horns in front of your prop would be easy enough for a metal boat.

 

[Mac2]

Protection would be my number one concern. I'm saying this based on boating in the PNW. I've owned both single and twins. Both have protected running gear. My current boat is triple keeled at the stern-designed to sit on it's own bottom.
Five years ago I hauled out at Delta in Seattle to fix a shaft seal. It was prime boating season July/August. I was the only one in the yard. During the next 10 days, boat after boat came in. 5-6 total. All in the 60-90 foot range. All high end yachts.
All of them had run aground. I was shocked. I have never run aground, but there have been several close calls and I expect to run aground at some point. All of the boats that came in were of the fast/SD types. It really got me thinking. Higher speeds give you less reaction time, add to that exposed running gear and the odds start to stack against you. I would say the argument over twins and singles should be based on safety first, which in turn relates to where you boat. The PNW has has many logs along with "islands" that disappear at high tide. I can see the argument in other areas of the country where safe means going fast to avoid weather, waves etc.