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Twins v Single Shoal v Deep Stability v Ballast Fishtail Rudders Space Age Cores Core Materials Unsinkability
Twin Screws vs Single
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What follows is the transcription of a discussion on the merits of single or twin engines, as originally published on a trawler forum. We have reprinted the thread, because we feel the responses effectively debunk the notion that a single engine boat can be as reliable as a twin-engine design. We acknowledge that there are a number of reasons for buying a single-screw trawler, but reliability and safety cannot be one of them. Some respondents said they would consider a single engine for their next boat, not for reasons of reliability but things such as ease of maintenance. Many of their concerns, however, have been addressed in the design of our Great Harbour Trawlers, whose huge engine rooms provide easy access to all mechanical systems
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The Query
I have decided to sell my Morgan OI 41 and switch to power. Friends with a single engine trawler, a Grand Banks, argue that twin engines are a headache and do not really provide the redundancy because most diesels quit due to bad fuel or clogged filters. They say both engines would die at the same time anyway. It would seem to me that once one quit and there might still be a significant time lag until the second one quit. Maybe time enough to get the problem sorted out. I'm wondering if any of you twin-engine trawler people have had any experience with one engine continuing to run after the other had quit? --Bart Hodge
The Responses
>>>For what it's worth I'll cast another vote for twin screws. I have an Albin 43 with twin Ford Lehmans which are absolutely wonderful engines. However, in the two years I've owned the boat, I have had the water pump shaft fail on one engine and the fuel pump (not filters) fail on the other. Both times, the existence of another working engine saved me a tow... and perhaps worse (both events were in open water). While fuel costs and maintenance costs are higher, they turn out to be a small percentage of the overall cost of boat ownership. The extra costs and maintenance are well worth it in my mind. Ironically, when I was first shopping for a boat, my "ideal" was a single with a bow thruster. I bought this one instead because it was in good shape and the price was right. After after two years of living with the boat, I consider my choice fortunate. --Steve Phillips, Canfield, OH
>>>There definitely is value in two engines. We were in rough water on Lake Michigan in our twin diesel trawler, which is equipped with two tanks and separate water separating fuel filter systems. We usually run on one tank at a time to isolate problems, while feeding both filter systems. We got water in one tank, which fouled one of the filters more than the other. As a result one engine shut down. The other eventually would have shut down also, but I had time to switch to the good tank, stay running, and get to the next port. We would have paid for a very expensive tow if we only had one engine. Having also "graduated" to a trawler from a sailboat, I can also assure you that the handling and docking with two screws will be a huge delight. --Bob Kunath, Sans Souci, Pacific Seacraft 38T
>>>My experience with my twin trawler is that usually only one engine quits at a time. However, I would personally prefer a single with a bow thruster. Half the maintenance, one protected prop, better mileage, and there is always that one engine you can't get at to work on easily. --Sterling, MV Sterling Lady, 44 Marine Trader
>>>The way I have done twins is separate tanks, separate lines and separate filters. The valving to use both engines on one tank is after one filter and before the other. This is a little more complicated, but 200 miles offshore, I had a seam fail and the melted ice enter the fuel tank below, contaminating the fuel and shutting down the port engine. Still had the other tank, and managed to purge the down engine and restore it to running on the way in. Have a single now and "hate it" though the initial and operating costs supported its choice. --Len
>>> Having owned both, I can tell you that twins sure make life easy, in terms of maneuverability and redundancy. Only twice in 10 years of owning twins did I ever come in on one. Once, an engine blew after being rebuilt at about 15 hrs. Bad work. The other was my fault. I had "replace raw water impellers" on my to-do list, but hadn't done it yet, and she expressed her displeasure. That all being said, I own a single now (Krogen 42). With one engine instead of two: Maintenance is cut in half. A few points to consider: You maintain that single RELIGIOUSLY; Fuel consumption is cut in half; Space in the engine room is doubled; Maneuverability is OK, once you learn how to handle a single. I am adding a bow thruster next month, and I expect the maneuverability then to be as good or better than with the twins.
Keep in mind that all kinds of seaworthy vessels, including fishing boats and ships, run with one engine. Note that I keep repeating myself about maintenance. I bet that most folks with single engines take much better care of them than folks with twins. Twins leave you with that feeling of "if one goes out, I'll just get home on the other." This is a debate that will go forever, since a lot of it just depends on personal preferences. --Keith
>>>Three times on my old boat, which had twin Hino diesels, we ran on one engine when the other one failed. Once was due to an oil pump leak. The second time was due to the failure of the safety solenoid on one engine. We were at anchor in a crowded harbor, and only one engine started. Later on Hans walked me through a "hot wiring" session over the phone and I got it started. And finally, the third time we had a clogged fuel line on one engine due to rough going in heavy seas. We throttled back on the good engine, and limped into port under the mantle of the blackest storm clouds I ever want to see. Isolating the fuel tanks didn't work that time as the real culprit was the fuel pickup hose, which had too fine a screen at the end of it. I'm sold on two engines. --Peggy Carr Bjarno, Aqua Vitae
>>>I was cruising up the Pacific Coast on my 49 Defever trawler when I lost my port engine due to water getting into the port tank through the breathing tube. I closed the port tank, and continued to run on my starboard engine until I got safely into Coose Bay, Oregon to fix the port engine. I was happy that I had 2 engines. Another solution is to have a single engine, longer range, and a homing device connected to your genset. --Richard
>>>We've operated a twin-screw 44' trawler for the past eight years. I've owned two other trawlers, one single and one twin. In my experience, yes, it is true that by far the most common cause of diesel engine failure is clogged filter(s). But I've had several incidents of engines quitting for this reason on my twin-screw boats, and I've *never* had both engines quit simultaneously. One might reasonably infer that if one filter clogs, the other will clog shortly, but my experience has been that the second engine has always run long enough to get the problem sorted out. --Dave Goodman, M/V Dragonfly
>>>I've personally never had an engine stop due to bad fuel. I have however had them die due to a raw water pump failure, and air in one of the fuel lines, and a transmission failure, and an oil hose rupturing. In none of these cases was the second engine affected. I'd say that two engines truly provide some redundancy -- but not quite 2x perhaps. The real question IMHO is not whether two engines provide additional redundancy (which they unquestionably do), but rather whether the additional reliability is worth the extra cost in fuel, maintenance, and initial cost? I have two engines, and I'm quite happy with them, but I'd also buy a single engine boat with no qualms about reliability if it happened to be a boat I liked. -Bill Martin, MV Telegraph Hill
>>>I recommend only boats that have two viable means of propulsion. Sail boat with an engine, twin screw trawler, boats with one main and one backup system, big boats with two big engines if you have the money. I feel the same about airplanes after having glided into a cornfield a few years back. Nobody can convince me they can make a 100% reliable engine. The FAA requires flights over water to have multi engine aircraft that can remain flying with one engine gone. -- David Stahl
>>>Contrary to popular opinion among single engine owners, bad fuel is not the only problem you can run in to. I was gunkholing up the Coos river when I hit a log or rock I don't know which, and broke a prop. I came in on the other engine and put the boat in the slip without anyone knowing I had a problem until I told them. There is more to the propulsion system than fuel. --Michael Gibbons, 40' Marine Trader Sea Dreamer
>>>I have twin Cummins 210s on Spirit of Adventure and had the fuel tanks cleaned last year. The first time out after that while going from Ft. Lauderdale to Key Biscayne, the port engine died within an hour or so due to dirty fuel. I decided to continue the trip which took another 3 hours or so and had to have the injectors rebuilt in Miami. To this day, I have not had any problems with the other engine. Some how, particles got through the filters on one engine but not the other. --Mark
>>>I currently have a twin screw and am glad to have it. I have had to come in twice on one engine, one failure was the fresh water pump, the other was a heat exchanger problem. Never had any fuel problems so that issue I cannot answer. I maintenance both engines very well, as well as I would if it were a single. What I find best about the twin is being able to handle the boat in very tight quarters with a good wind and/or current present. Bow thrusters I find are great in most situations, however in strong wind and/or current there is nothing like having twins. --Roy Holleman, M/V Knot At Work
>>>Welcome to the world of power boating. I switched this summer also. Got rid of a 36' sailboat I owned for nearly 20 years. I did not look at any boats that did not have twin screws. Like you, I ran into all the people who said I only needed one. Odd, this advice only comes from people who only have one. I found nobody who owned twins who recommended one! Bad fuel will most likely kill both engines about the same time. It would depend on the condition of each of the engine's filters, but fuel failure is only one thing that can happen. What about overheating? If one engines starts to overheat shut it down and continue on until you find a marina (no tow bill). I bought my trawler and had it trucked to Florida, straight into the yard where it sat for 5 weeks while I put a new bottom (and other things) on her. When I launched, one engine would not start (loose battery wire) but I backed out under one and made it to my yacht club T-dock a short distance away. On my second voyage, my hydraulic steering let go (they pulled the flybridge to ship it and folded the hydraulic hoses into a neat bundle. This loosened one of the fittings). I was over a mile from my slip. I wedged a board into the rudder linkage holding them straight and powered back to my slip using only gearshifts for steering (again no tow bill). Yes, two engines, twice as many gauges etc. are potential failures, but I love redundant systems. --Dave
I have decided to sell my Morgan OI 41 and switch to power. Friends with a single engine trawler, a Grand Banks, argue that twin engines are a headache and do not really provide the redundancy because most diesels quit due to bad fuel or clogged filters. They say both engines would die at the same time anyway. It would seem to me that once one quit and there might still be a significant time lag until the second one quit. Maybe time enough to get the problem sorted out. I'm wondering if any of you twin-engine trawler people have had any experience with one engine continuing to run after the other had quit? --Bart Hodge
The Responses
>>>For what it's worth I'll cast another vote for twin screws. I have an Albin 43 with twin Ford Lehmans which are absolutely wonderful engines. However, in the two years I've owned the boat, I have had the water pump shaft fail on one engine and the fuel pump (not filters) fail on the other. Both times, the existence of another working engine saved me a tow... and perhaps worse (both events were in open water). While fuel costs and maintenance costs are higher, they turn out to be a small percentage of the overall cost of boat ownership. The extra costs and maintenance are well worth it in my mind. Ironically, when I was first shopping for a boat, my "ideal" was a single with a bow thruster. I bought this one instead because it was in good shape and the price was right. After after two years of living with the boat, I consider my choice fortunate. --Steve Phillips, Canfield, OH
>>>There definitely is value in two engines. We were in rough water on Lake Michigan in our twin diesel trawler, which is equipped with two tanks and separate water separating fuel filter systems. We usually run on one tank at a time to isolate problems, while feeding both filter systems. We got water in one tank, which fouled one of the filters more than the other. As a result one engine shut down. The other eventually would have shut down also, but I had time to switch to the good tank, stay running, and get to the next port. We would have paid for a very expensive tow if we only had one engine. Having also "graduated" to a trawler from a sailboat, I can also assure you that the handling and docking with two screws will be a huge delight. --Bob Kunath, Sans Souci, Pacific Seacraft 38T
>>>My experience with my twin trawler is that usually only one engine quits at a time. However, I would personally prefer a single with a bow thruster. Half the maintenance, one protected prop, better mileage, and there is always that one engine you can't get at to work on easily. --Sterling, MV Sterling Lady, 44 Marine Trader
>>>The way I have done twins is separate tanks, separate lines and separate filters. The valving to use both engines on one tank is after one filter and before the other. This is a little more complicated, but 200 miles offshore, I had a seam fail and the melted ice enter the fuel tank below, contaminating the fuel and shutting down the port engine. Still had the other tank, and managed to purge the down engine and restore it to running on the way in. Have a single now and "hate it" though the initial and operating costs supported its choice. --Len
>>> Having owned both, I can tell you that twins sure make life easy, in terms of maneuverability and redundancy. Only twice in 10 years of owning twins did I ever come in on one. Once, an engine blew after being rebuilt at about 15 hrs. Bad work. The other was my fault. I had "replace raw water impellers" on my to-do list, but hadn't done it yet, and she expressed her displeasure. That all being said, I own a single now (Krogen 42). With one engine instead of two: Maintenance is cut in half. A few points to consider: You maintain that single RELIGIOUSLY; Fuel consumption is cut in half; Space in the engine room is doubled; Maneuverability is OK, once you learn how to handle a single. I am adding a bow thruster next month, and I expect the maneuverability then to be as good or better than with the twins.
Keep in mind that all kinds of seaworthy vessels, including fishing boats and ships, run with one engine. Note that I keep repeating myself about maintenance. I bet that most folks with single engines take much better care of them than folks with twins. Twins leave you with that feeling of "if one goes out, I'll just get home on the other." This is a debate that will go forever, since a lot of it just depends on personal preferences. --Keith
>>>Three times on my old boat, which had twin Hino diesels, we ran on one engine when the other one failed. Once was due to an oil pump leak. The second time was due to the failure of the safety solenoid on one engine. We were at anchor in a crowded harbor, and only one engine started. Later on Hans walked me through a "hot wiring" session over the phone and I got it started. And finally, the third time we had a clogged fuel line on one engine due to rough going in heavy seas. We throttled back on the good engine, and limped into port under the mantle of the blackest storm clouds I ever want to see. Isolating the fuel tanks didn't work that time as the real culprit was the fuel pickup hose, which had too fine a screen at the end of it. I'm sold on two engines. --Peggy Carr Bjarno, Aqua Vitae
>>>I was cruising up the Pacific Coast on my 49 Defever trawler when I lost my port engine due to water getting into the port tank through the breathing tube. I closed the port tank, and continued to run on my starboard engine until I got safely into Coose Bay, Oregon to fix the port engine. I was happy that I had 2 engines. Another solution is to have a single engine, longer range, and a homing device connected to your genset. --Richard
>>>We've operated a twin-screw 44' trawler for the past eight years. I've owned two other trawlers, one single and one twin. In my experience, yes, it is true that by far the most common cause of diesel engine failure is clogged filter(s). But I've had several incidents of engines quitting for this reason on my twin-screw boats, and I've *never* had both engines quit simultaneously. One might reasonably infer that if one filter clogs, the other will clog shortly, but my experience has been that the second engine has always run long enough to get the problem sorted out. --Dave Goodman, M/V Dragonfly
>>>I've personally never had an engine stop due to bad fuel. I have however had them die due to a raw water pump failure, and air in one of the fuel lines, and a transmission failure, and an oil hose rupturing. In none of these cases was the second engine affected. I'd say that two engines truly provide some redundancy -- but not quite 2x perhaps. The real question IMHO is not whether two engines provide additional redundancy (which they unquestionably do), but rather whether the additional reliability is worth the extra cost in fuel, maintenance, and initial cost? I have two engines, and I'm quite happy with them, but I'd also buy a single engine boat with no qualms about reliability if it happened to be a boat I liked. -Bill Martin, MV Telegraph Hill
>>>I recommend only boats that have two viable means of propulsion. Sail boat with an engine, twin screw trawler, boats with one main and one backup system, big boats with two big engines if you have the money. I feel the same about airplanes after having glided into a cornfield a few years back. Nobody can convince me they can make a 100% reliable engine. The FAA requires flights over water to have multi engine aircraft that can remain flying with one engine gone. -- David Stahl
>>>Contrary to popular opinion among single engine owners, bad fuel is not the only problem you can run in to. I was gunkholing up the Coos river when I hit a log or rock I don't know which, and broke a prop. I came in on the other engine and put the boat in the slip without anyone knowing I had a problem until I told them. There is more to the propulsion system than fuel. --Michael Gibbons, 40' Marine Trader Sea Dreamer
>>>I have twin Cummins 210s on Spirit of Adventure and had the fuel tanks cleaned last year. The first time out after that while going from Ft. Lauderdale to Key Biscayne, the port engine died within an hour or so due to dirty fuel. I decided to continue the trip which took another 3 hours or so and had to have the injectors rebuilt in Miami. To this day, I have not had any problems with the other engine. Some how, particles got through the filters on one engine but not the other. --Mark
>>>I currently have a twin screw and am glad to have it. I have had to come in twice on one engine, one failure was the fresh water pump, the other was a heat exchanger problem. Never had any fuel problems so that issue I cannot answer. I maintenance both engines very well, as well as I would if it were a single. What I find best about the twin is being able to handle the boat in very tight quarters with a good wind and/or current present. Bow thrusters I find are great in most situations, however in strong wind and/or current there is nothing like having twins. --Roy Holleman, M/V Knot At Work
>>>Welcome to the world of power boating. I switched this summer also. Got rid of a 36' sailboat I owned for nearly 20 years. I did not look at any boats that did not have twin screws. Like you, I ran into all the people who said I only needed one. Odd, this advice only comes from people who only have one. I found nobody who owned twins who recommended one! Bad fuel will most likely kill both engines about the same time. It would depend on the condition of each of the engine's filters, but fuel failure is only one thing that can happen. What about overheating? If one engines starts to overheat shut it down and continue on until you find a marina (no tow bill). I bought my trawler and had it trucked to Florida, straight into the yard where it sat for 5 weeks while I put a new bottom (and other things) on her. When I launched, one engine would not start (loose battery wire) but I backed out under one and made it to my yacht club T-dock a short distance away. On my second voyage, my hydraulic steering let go (they pulled the flybridge to ship it and folded the hydraulic hoses into a neat bundle. This loosened one of the fittings). I was over a mile from my slip. I wedged a board into the rudder linkage holding them straight and powered back to my slip using only gearshifts for steering (again no tow bill). Yes, two engines, twice as many gauges etc. are potential failures, but I love redundant systems. --Dave
