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Thread: Singles versus twins

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    Singles versus twins

    I've been thinking about this a lot the last year or two. Seen some here and there discussion of the subject on the site recently, so I am trying to pull it together in one spot.

    For context, I'm thinking about the 24-28 foot size range, although maybe that should be moved up to as much as 35 feet?

    A few things are obvious. Redundancy of twins is an advantage in getting home when something goes wrong. Singles should be lighter and have less drag with less running gear. Also, singles have lower centers of gravity, are more efficient I think (thust/gallon), and are physically easier to work on because of the space in the engine compartment.

    By and large, singles are more likely to be higher-performance engines that will be more costly to maintain. (By this I mean more costly to maintain than ONE of the twins. It gets interesting when you try to sort out the maintenance costs of two smaller, lower-performance motors and their drives versus one larger, higher performance engine.)

    I'm particularly interested in specific experiences. If a boat handled badly, what was the ill behavior? Etc, etc.
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

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    I think when you get up to a certain size, in my mind past 30', I'd want twins. With the larger size, a cramped engine compartment would certainly be less of a concern. In a larger boat like that, you'd be more apt to be "offshore" or further away from any assistance and nice to have a get home engine. Maybe the biggest advantage of twins in something larger is simply the handling at the dock. I really wonder, once you are past 28 or 30 feet, if a single is going to be more efficient than twins.

    I think past 28', I'd have to go twins. Unless it's not a performance boat of course, then a nice, single diesel with a bow thruster would be good.




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    Single Vs Twins.

    This conversation has been going on for decades...in the Aviation community.
    Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

    So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? DJ
    Avatar: RELIANCE (1903) The Largest single masted sailing yacht ever built (Until 2004)...with over 16,000 square feet of sail. Successful Americas Cup Defender.
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    Quote Originally Posted by DonziJon View Post
    This conversation has been going on for decades...in the Aviation community.
    Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

    So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? DJ
    I remember reading that the odds of losing an engine on a twin aircraft is much higher than losing an engine on a single.

    On the other hand, way back when my BIL and I owned a twin screw 30+' FBSF, I would get really frustrated when a single screw 35' commercial fishing boat powered by a 600 HP Yanmar would fly by us going nearly 40.
    George Carter
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    Quote Originally Posted by DonziJon View Post
    This conversation has been going on for decades...in the Aviation community.
    Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

    So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? DJ
    1964 Trojan 31 twin inboard 225 Chrysler Crusaders, We hit a unmarked rock coming from hyannis. going to cotuit Mass,cleaned the prop rudder and shaft on the port engine. starboard engine got us home
    machinist ,bore it deeper,ream it bigger, and lap it to a fine finish



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    Quote Originally Posted by gcarter View Post
    I remember reading that the odds of losing an engine on a twin aircraft is much higher than losing an engine on a single.

    On the other hand, way back when my BIL and I owned a twin screw 30+' FBSF, I would get really frustrated when a single screw 35' commercial fishing boat powered by a 600 HP Yanmar would fly by us going nearly 40.
    And to add insult , he'd handle the boat around the dock like he had twins AND a bow thruster on every corner ...
    Just because something's old doesn't mean you throw it away !

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    Seems this is a constant question with 27 magnum guys. I am going twins for rough water safety getting home in the event of a engine failure. Conquistador went big fast single. I think it depends on how you boat
    Parnell
    Time forSweet Cheekz to find a new home

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    Kind of apples vs oranges. To around 70 mph, a single is a cheaper. Above that it is close. Twins in a smaller boat can be a pita to work on, but I don't hear much grumbling from the 28ZX twin guys so it must not be too bad.

    Twins are better if you boat long open stretches of water due to the get home factor. I like them both in their own way. I love the speed my big single has and it is nice to climb into the engine compartment. I boat mostly on lakes.
    2001 35 Fountain Lightning w500 EFI's
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    Quote Originally Posted by gcarter View Post
    I remember reading that the odds of losing an engine on a twin aircraft is much higher than losing an engine on a single.

    On the other hand, way back when my BIL and I owned a twin screw 30+' FBSF, I would get really frustrated when a single screw 35' commercial fishing boat powered by a 600 HP Yanmar would fly by us going nearly 40.
    I have not heard that stat but I can see that as most twins are complex aircraft (ie constant speed prop, landing gears etc). I do know that if you lose an engine at speeds below VMc (Velocity of minimum control) it is very bad. You have one engine running WFO and the other windmilling. This causes a bad inverted spin that makes for a smoldering black spot on the ground. Many failures seem to occur around that speed as you are squeezing the power and it is just leaving the ground. Much of the multi engine rating deals with that subject. I actually lost an engine on my multi check ride. It was a bad fuel pump. The first step is to turn on the boost pumps. Problem solved.
    2001 35 Fountain Lightning w500 EFI's
    1973 X-18 - Merc 383 Magnum
    1974 Chris Craft Roamer with 1271 TI's

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    Quote Originally Posted by DonziJon View Post
    So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? DJ
    I lost one of the 302s in a twin engine 25' Wellcraft Nova once - no problem getting back, in fact it actually got on plane - barely, though. I lifted the drive on the broke engine as much as possible to help reduce drag. Looking back, I could make the case that it might have had less drag by leaving the drive down with the cavitation plate being parallel to the water flow. Does anyone know which way would be less drag? Bill

    1971 Donzi 18' 2+3
    1985 Eliminator 23' Daytona Offshore - Kevlar hull
    1988 23' Donzi CC F-23 with 250HP EFI Mercury OB
    1989 28' Team Warlock Offshore - single 548CID/600HP
    1990 23' Warlock Offshore - single 525HP
    Bill from Denison, TX - Lake Texoma

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    Quote Originally Posted by Sweet Cheekz View Post
    Seems this is a constant question with 27 magnum guys. I am going twins for rough water safety getting home in the event of a engine failure. Conquistador went big fast single. I think it depends on how you boat
    Parnell
    Yep, if I boated the ocean or went on extremely long cruises I would go twins. I personally think somewhere around 28'-30'+ deep v hulls almost necessitates twins. Bill

    1971 Donzi 18' 2+3
    1985 Eliminator 23' Daytona Offshore - Kevlar hull
    1988 23' Donzi CC F-23 with 250HP EFI Mercury OB
    1989 28' Team Warlock Offshore - single 548CID/600HP
    1990 23' Warlock Offshore - single 525HP
    Bill from Denison, TX - Lake Texoma

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    This discussion could get into a Diesel vs. gas too, since Diesels are so dependable.
    It's easy to imagine a 500-700 HP single Diesel in a 30' performance boat.
    Think about having 75%-80% of 700 HP available all the time instead of just once in awhile.
    This would be Carl's dream boat!

    I remember in the early days of deep-vee offshore racing, Diesels were popular. They still are in Europe, I guess.
    I think it could be a financially workable situation too if you considered the cost of a single Diesel vs. the cost of two built gas engines.
    George Carter
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    http://kineticocentralfl.com/


    “If you have to argue your science by using fraud, your science is not valid"
    Professor Ian Plimer, Adilaide and Melbourne Universities

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    Yea, but what about all those extra guages...and the extra exhausts when pulling up to the favorite eatery?

    And don't forget the syncopation of the stainless trumpets for the crowds.
    24' Nova Sprint 1971
    You are what you drive!

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    Quote Originally Posted by gcarter View Post
    This discussion could get into a Diesel vs. gas too, since Diesels are so dependable.
    It's easy to imagine a 500-700 HP single Diesel in a 30' performance boat.
    Think about having 75%-80% of 700 HP available all the time instead of just once in awhile.
    This would be Carl's dream boat!

    I remember in the early days of deep-vee offshore racing, Diesels were popular. They still are in Europe, I guess.
    I think it could be a financially workable situation too if you considered the cost of a single Diesel vs. the cost of two built gas engines.
    I love the idea and actually thought a lot about doing exactly that. Except, even a Konrad isn't rated for that kinda torque. What sort of drive would you use with it? Gearbox to split it and run two drives (like Dorado Marine)?
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

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    Quote Originally Posted by Conquistador_del_mar View Post
    I lost one of the 302s in a twin engine 25' Wellcraft Nova once - no problem getting back, in fact it actually got on plane - barely, though. I lifted the drive on the broke engine as much as possible to help reduce drag. Looking back, I could make the case that it might have had less drag by leaving the drive down with the cavitation plate being parallel to the water flow. Does anyone know which way would be less drag? Bill
    I'm thinking you did it right, unless you were running really slowly and the water was rising very quickly behind the boat. If you did leave it down and in neutral, might not be too bad either.

    Can I ask about your Nova? (HP, performance)? How'd you like it? What would you change?
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

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