Twin Diesels versus single

Have learned from this thread and thank contributors. Know for blue water sail unlike coastal you have a different attitude. You stay well within expected service life and replace things then. Although on coastal boats folks will replace sails only when they fail or bag out. On ocean boats usually before 7 years with over weight non film sails and in less time with higher tech performance sails. Same with standing rigging. 7-8 years and a slight bit longer for rod. At least the terminals are replaced.. Doesn’t matter if it looks perfect.
Would thing with voyaging motor it would be the same. Beyond routine preventive maintenance you could make a pretty decent estimate of the service life per fuel burnt of the components . Would think (but don’t know) voyaging under powerfolks would have a similar attitude. Even to the level of their spares and specs. On my sailboats carried water in flats inspite of a watermaker and big water tank. Carried a dozen racors inspite of it being under sail 95% of time. Have work arounds for all the failure points you can think of in place before leaving.
Currently on power my concern is lightening strike. Twins or single no power. Fishing nets or other debris. Twins or single shafts/props entangled no propulsion. Think a single in a Kort behind a keel maybe safer in some settings. I understand why we’ve moved to computer controlled engines but think every time we add complexity we add potential single point failure spots. Don’t see twins totally eliminating that. If I went back to voyaging agree a different drive train and power source does add peace of mind. Easily could be a get home of some sort. But think the primary mode of propulsion needs to be a serviceable and bulletproof as possible. Here protection of the prop/drive shaft has merit. In larger boats possible with twins behind skegs but easier to do and more robust with a single behind a keel in smaller boats . Interested in hearing from power voyagers. Beyond direct engine troubles whats your read on the other reasons to lose propulsion?

Hippocampus said:

Beyond direct engine troubles whats your read on the other reasons to lose propulsion?

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Been watching a ton of videos, great loop, bahamas, etc recently. Beyond the guy with the failed mooring ball in the BVI and the tornado in Italy, it's been running aground, hitting something submerged underway, running over fishing nets or crab pots, failed hydraulic steering pump and one sail boat started taking on water due to a thru hull speed sensor failing. (In that case, I question how well that boat had been maintained in general. Was an old, ratty boat) There was one engine failure on a 40+ year old Tollycraft that had to do with seals/gaskets. The admittedly newbie owners were aware of some coolant/oil leakage but hadn't gotten around to addressing it and continued to run the boat. That engine had to be rebuilt. It was probably due anyway but they helped it along.

slowgoesit said:

We're the single engine Muirgen Peter referenced in the third post on this thread. We left Seattle Area 2 September of last year. We arrived here at our new home in Florida on 26 April.

• 6 months and 24 day later. 6,400 nm
• a little less than 1000 engine hours
• three oil changes
• speed varies between 6.5 and 7.5 kts
• Average fuel burn of 2.4 gph
• in the neighborhood of 2,400 gallons of diesel consumed
• longest non-stop "sprint" was across the Caribbean, 8 days, 1,250 miles
• groundings: two . . . no I don't want to talk about that
• Anchors dragged, 1
• chased by pirates, once
• macerator pumps replaced, 4
• electrical issues, 1 with generator, 1 with a nav light
• refrigeration issues, 2
• fish caught, lots, more than we could eat on the trip
• long lines snagged, 7

Engine failures . . . . nope, none, nada, zero, zilch. Like Peter said, we're aware of the probability of an engine failure, but it wasn't high on our list of concerns.

Add in the 2,200 nm trip to Glacier Bay, AK and back to PNW, and in and around trips in PNW. Over our 40 months and 10,000 nm during our ownership we've had zero engine problems that weren't caused by our selecting a fuel tank totally filled with air, . . . no, I don't want to talk about those either.

We love the access our single engine gives us in our stand up engine room.

Singles aren't for everyone, but we've never regretted having only one engine. YMMV

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Thank you so much for your list - it become so real with it..... specially, pirates chase....

Purchased with 46 hours on the engine, 8298 hours on the Hobbs now. Oil filters, fuel filters, alternator belts, and one front oil seal in all of those hours of operation, including a round trip from Seward Alaska to La Paz Mexico and back. I have never experienced a mechanical breakdown, and maintain to the highest level possible preventively. I average 1 gph at 7 knots, and .62 gph at 5.5 knots, slower cruise .4 gph at 4.5 knots. Size matters...

rslifkin said:

I agree that speed to outrun weather is a dumb idea for the most part. But 2 engines for redundancy depends on where you operate. In plenty of areas there isn't much in the way of towing services, so you may be waiting a while if you need a tow, so it's best avoided whenever possible. And I can think of a few places I've operated through where an engine quitting would likely put you on the rocks before you could get an anchor down (or you could drop one and you'd swing into the rocks). Most of us don't operate through places like that all that frequently, but if you do, that may be a consideration for whether you want twins. In some of those places if I had a single + wing, I'd probably fire up the wing engine just in case.

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Bingo. I experienced exactly this a week ago when I had an engine starting to overheat - caught it quite early- and so I shut it down. It occurred in a place that was very problematic if I didn’t have the other engine to run. (It was a failed impeller that just got replaced a month ago - these things do happen). I’m now a firm twin believer now or at least a get home / boat controllability option.

So despite high maintenance standards and overall high reliability, these things do happen. It sure saved a lot of stress though on myself and crew.

And with one engine and just 4 or 5 degrees of rudder deflection, I was able to continue to my home port to address it.

Lepke said:

Before electronically controlled diesels, most commercial fishing boats were single screw. Now they're mostly twin screw.

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Lepke,

Great observation. Why do you think that is? Curious. All the older fishing boats are singles around here, but the more modern commercial boats are twin "go-fasts".

I am sometimes frustrated by the lack of maneuverability with my single in tight marinas, and wish for two engines. Not for redundancy, but for the ability to maneuver at slow speeds. But I sure like the simplicity and economy of the single tractor engine under the floorboards. Yes, a thruster would alleviate that, but twin engines with room in the ER would be my choice.

#1 reason. Reliability. #2 reason is maneuverability.
I know commercial fishermen with newer electronic controlled injectors that keep hundreds if not more in spare electronic parts. That's why I run older design engines. And doubts, borrow my diesel pickup for a few weeks. And I keep about $2000 in spares counting injectors, controller.
You don't use 2x fuel with twins because you need less hp per engine. You do use 2x filters but probably not 2x oil because smaller engines have smaller pans and hold less oil. I use to have an early v12 Caterpillar that had a 50 gallon pan. I think it was a 398 or 399. I think it was Cats first V12. Getting old and the memory. But every oil change was a 55g drum.
I use a centrifuge now so don't change oil, just clean, test, and add lost oil.
I never had a thruster that I used, but if I had another single screw probably would. I love twins, so easy to dock and maneuver.

• In order for the ship to sail at the required speed, it is necessary to overcome the force of resistance
ship in navigation. This force must be created by the ship's propulsor.
• The power required to propel the ship depends on the resistance provided by the ship's hull
movement and the usability of the propulsor that creates the thrust force.
• The calculation of the resistance force of the ship has a significant place in the design of the ship and affects it
to the selection of the propulsion plant, the selection of the main propulsion engine and
ship screw.
• The ship's resistance is influenced by sailing speed, displacement and shape of the ship's hull.
• Hull shaping aims to reduce drag while increasing efficiency
propulsor is provided by shaping the aft part of the ship and designing
optimal propulsor.
• The movement of the ship through the liquid is opposed by hydrodynamic forces
fluids and aerodynamic forces of air.
• The total resistance force of the ship is the result of the action of three different resistances:
- viscous friction resistance,
- residual resistances that include wave resistance and vortex resistance (behind
prominent parts of the ship and stern), winds
after the designer calculates this have RT= RF+ RW +RE+ RA and have PE= v ·RT

and all energy coming in engine(fuel) only 27% go in ship propeller

and (lot more calculation) designer have some number of watt need on propeller.
he now searching for engine. sometime he easy find 1 engine sometime need over dozen if not hundred in big modern cruise ship

Dnnsmrgn said:

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 .

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IMO, it is a personal choice. If you go ‘single’. If you opt for single, I suggest a strong bow thruster, learn to swing your rudder as necessary, practice. Remember, neutral is a gear, use it. Learn to coast. Don’t be in a hurry

When I bought my single engine trawler, the PO had apparently suffered from PAD (propulsion anxiety disorder) and mounted an outboard bracket on the swimstep where he could use his 15hp dinghy outboard. First, 15hp is an unnecessary amount of power for a dinghy (plus noisy, heavy, smelly) but I guess it might have pushed a 30' trawler at 2 knots (no wind or current). Second, it required having gasoline onboard. Third, the bracket made a dangerous trip hazard on the swimstep. So overall, his PAD and desire for a secondary engine made the boat more dangerous, IMHO.

As to having two inboard diesels, I wouldn't want them where I cruise. I have twice run over gill nets. Once at night inside Deception Pass. I'm not sure what VHF channel the fisherman was on, but he was yelling so loud I could hear him without the radio. I wasn't sure what the problem was until I motored cleanly over a line of floats. So there was no problem. The other time, I didn't see a ghost net until the few floats were right in front of me (probably because the net was full of dead fish and the floats were low). No problem. I've also been aground several time. Again, no problem thanks to a full keel single engine. Well, once I was inconvenienced by having to wait an hour for the tide to rise. For me, that is preferable to a tow and sending two props (and maybe a shaft) off to the shop.

I understand that by having two engines, one engine might still operate if you suffer one of the common problems  caused by having two engines. It makes the risk analysis somewhat convoluted.

Mark

You only need one working engine. That's why I have one.

Just had to post after Marco to show my signature.

SteveK said:

Just had to post after Marco to show my signature.

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He is correct on one point.... there are factors that can sway the argument either way.

But as a risk management guy...giving equal risk factor to skipper induced errors (going aground, running over into things, crappier maintenance because one had two vs one engine and on and on) is not how it all works.

The hardest thing of risk management is determining the most realistic probability for each and every determined risk.... probably why this is a circular argument like "best anchor".

Every skipper is going to weigh different risks differently..... depending on so many factors..... this is a lifelong, happy hour discussion. Trying to do it in paragraph version winds up the same discussion year after year just with a different time stamp.

Same with boat selection (and so many other TF threads)...much easier to do for a specific person with specific goals rather than trying to relate one's own experience which may or may not be similar.

The difference between twin and single is truly a personal choice. Prior to buying a big boat over 40' in length I was obsessed with details like twin vs single and fuel burn rates and maintenance details. Way down the list was winter storage that dwarfs fuel burn.
I ended up with two engines and at first I was cruising a bit under 7 knots @ 3 gph. After 5,000 miles in two years I am cruising a bit over 7.5 knots @ 4 gph. I am happier and my engines are happier.
The major difference here is I now know all the costs and the boat is well within my comfortable budget and I think that is the key.
Let your budget drive the choices and adjust your expectations to be within those parameters. Going to the Bahamas from SC is cheap and easy vs going to the Caribbean from SC. Shop within your capabilities of money, time and mechanical ability. Don't buy twins if you are on a single engine budget. Excellence, is being in a boat that you can handle from the total package perspective. Perfectionist never push off the dock. Perfection is the enemy of excellence.
I regret my younger life perfection where things had to be right before I went. I can afford it now, I have the time, I have the knowledge and I have an excellent boat but have pared back the objectives due to ARC (Age Related Complex). A politically correct way of saying too f-ing old.
I don't know for sure yet whether I have waited too long.

Does it change the equation if the twins have protected props/shafts (full skegs designed to be beached)?
I think a lot of the decision would be based on where you cruise. I wouldn't even consider a boat in the PNW that doesn't have protected props/shafts (based on the logs, fishing nets I have run over), unless you have a big bank account. Every anchorage is a lee shore. Everyone will touch bottom eventually. If you're not sure about protected props/shafts, walk into your nearest boat yard and ask what the most common damage (human error) to a boat is. Several years ago I pulled my boat out at Delta in Seattle. It was the middle of summer and I was the only one in the yard. Over a weeks time, 5-6 boats came in. All of them came in due to damage from striking/grounding. 100%! A true eye opener.

As a guy who towed hundreds of boats off groundings (assistance tower).... I wouldn't assume that a large percentage of boaters who went aground signal that it is an across the board indicator for all boaters. Experience and personality have a lot to do with it.

Will everyone windup going aground in a lifetime? Probably....maybe... some swear they haven't....we will see....

But I am not sure a mistake or two in decades of boating that require a haul and prop/shaft fixing is a reason enough to alter one's risk assessment to the point choosing single over twins or vice versa.

psneeld said:

As a guy who towed hundreds of boats off groundings (assistance tower).... I wouldn't assume that a large percentage of boaters who went aground signal that it is an across the board indicator for all boaters. Experience and personality have a lot to do with it.

Will everyone windup going aground in a lifetime? Probably....maybe... some swear they haven't....we will see....

But I am not sure a mistake or two in decades of boating that require a haul and prop/shaft fixing is a reason enough to alter one's risk assessment to the point choosing single over twins or vice versa.

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Have you boated in the PNW? Groundings are only one part of my equation. You will, 100%, hit a log/stick. Trawler speeds help tremendously in avoiding most and limiting the damage. You will be avoiding sticks/logs every time you go for a cruise. My point is that, depending on where you cruise, threats should be taken into consideration when considering the type of boat you purchase.

If parts of Alaska counts...... and all of the East Coast from Maine (lots of rocks and driftwood) to major Eastern rivers after floods (lots of logs) to the Florida/Keys have hard bottoms that are shallow for hundreds of miles.

But yes, the PNW is a minefield of big logs.... and protected props are nice...but I am not sure that would be the overwhelming reason to swing me from twins to single or vice versa.

As I said, every skipper is going to rate different risks at different levels based on experience and personality.

psneeld said:

As I said, every skipper is going to rate different risks at different levels based on experience and personality.

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True. My comment is for those who don't have experience. I lived here in the PNW all my life, but had no idea, until I started trawlering, how often I would be dodging logs on a single trip to the San Juans from Seattle. Now consider the same cruise in December, which I did for the first time this year, and the amount of trees (not logs anymore) were at least 20 fold. Totally changed my cruising plans as there was no way I was going to cruise after dark-my decision making was made easier after hitting a partially submerged log. My experience in these parts led me to buying a steel boat with twin skegs protecting both props (shafts are not exposed) along with a center keel. Twin vs Single is much more complex then beginners realize and I wanted to throw in the "where do you boat" as part of the equation.

Fair enough....

Mac2 said:

True. My comment is for those who don't have experience. I lived here in the PNW all my life, but had no idea, until I started trawlering, how often I would be dodging logs on a single trip to the San Juans from Seattle. Now consider the same cruise in December, which I did for the first time this year, and the amount of trees (not logs anymore) were at least 20 fold. Totally changed my cruising plans as there was no way I was going to cruise after dark-my decision making was made easier after hitting a partially submerged log. My experience in these parts led me to buying a steel boat with twin skegs protecting both props (shafts are not exposed) along with a center keel. Twin vs Single is much more complex then beginners realize and I wanted to throw in the "where do you boat" as part of the equation.

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Location/cruising grounds matter, I suppose. We were looking at a boat we both really liked, but with a 6.5" draft, had to rule it out because of where we plan to cruise. How isolated/remote you are certainly should factor into the equation between single or twins.

Irish Rambler said:

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.

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Please explain "fenced" our rudder? I have a GB 36 single screw. I would like more maneuverablity at slow speed.

Caballero II said:

Please explain "fenced" our rudder? I have a GB 36 single screw. I would like more maneuverablity at slow speed.

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Compare cost of rudder mod yo adding stern thruster.

Caballero II said:
Please explain "fenced" our rudder? I have a GB 36 single screw. I would like more maneuverablity at slow speed.

I believe that's referring to adding a fishtail to the rudder for increased maneuverability. I've seen the video and it's very impressive.

I don't discuss religion.

rgano said:

I don't discuss religion.

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Bless you my son,

Caballero II said:

Please explain "fenced" our rudder? I have a GB 36 single screw. I would like more maneuverablity at slow speed.

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Good morning Caballero. Great name, we've just come back to France from along the Spanish coast.
Apologies for the late reply. My old Acer laptop battery died and I had to get a new laptop and then search the backup hard drive for the photo.
Explanation. Take a large spoon, place it under a fully open tap and you'll see the way the water spreads as it hits the face of the spoon.
This is the same effect the propeller thrust has on your rudder face.
To 'fence' the rudder we welded a flat plates on the top and bottom of the rudder and two sections in the middle, the leading edges slightly angled back to reduce resistance and ensure that they don't obstruct the propeller when turned fully left or right. There's no resistance travelling forwards.
When you're maneouvering your vessel at slow speeds, turning, approaching your mooring, the thrust from the propeller hits the face of the 'fenced' rudder and directs the thrust more effectively.
Its far cheaper and less complicated than fitting a stern thruster.
In conjuction with this modification we also changed our single lever throttle/gear control for a Morse 1700 which was orginally designed for an outboard with an integral switch for tilt and trim.
We reapplied this switch, via a relay to control our bow thruster, this give us single handed control when coming alongside to berth, with a little practice you can make your boat move virtually sideways.
As Old Dan 1943 correctly stated earlier, neutral is also a gear to be used when maneouvering alongside.
I hope you find this helpful.

mvweebles said:

Transmission failure is what I worry about most.

Peter

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Some gears have a "get home" mode. My Twin Disc MG509 deep case trans can be locked into forward by removing a cover and installing a couple small bolts. You'd still have an issue getting into your slip, but at least you wouldn't be stranded.

I've a 42' Grand Banks with a newer single John Deere 6068 without turbo. My gph meter runs at 1.5 gph at 1600 rpms and 7 knots. This is about 4.5 nm/gal. I love my boat, largely because it's a single. I have a bowthruster which I need in my tight marina which is subject to tidal currents. Sure I'd love to have the manueverability of a twin, but not for the added noise, fuel expenditure, maintenence and space issues that twin's bring to the table. I've taken her from North Puget Sound to just 70 miles south of Alaska without worry.

Skag said:

Some gears have a "get home" mode. My Twin Disc MG509 deep case trans can be locked into forward by removing a cover and installing a couple small bolts. You'd still have an issue getting into your slip, but at least you wouldn't be stranded.

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The PRM Newage gearbox uses the same oil as the engine and has a simple mechanical 'lockup' to get you home. Checkout their details on www mail@prm-newage.com they have some good p.t.o add ons too.

Incidentally we'ree designing our next boat, a 58' GRP motor cruiser for sea and European inland canal use, our engine choice is a 6 cylinder Mitsubishi S6DT Tier 5 all mechanical engine with wet liners and timing chain for any future overhauls. coupled to a PRM 8 deg down angle gearbox with PTO for hydraulic bow thruster, Python drive system. We're not the slightest bit worried about single engine reliability where we are absolutely meticulous is a self cleaning the fuel storage and delivery system.
Different boats for different applications.
p.s Because I'm so meticulous I'm called an F.O.C