Single Inboard To Twin Outboards

Discussion in 'Boat Design' started by RYANPO, Jun 24, 2006.

  1. RYANPO
    Joined: Feb 2006
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    Location: SOUTH JERSEY

    RYANPO Junior Member

    I have a 27 foot lang with a 10' 6" beam. It has a deep V keel with a flat bottom stern. It also has a single 440 chrysler which is giving us problems and I just dont want a single engine even if i was givin the Crusader 8.1 for free and forget converting it to twin inboards. We want to keep the boat and i was considering putting a bracket on the stern for twin outboards. The boat is built like a tank and I would just need to know exactly the best place to mount the outboards. To transfer weight the 440, which is located in the dead center of the boat would be replaced with at least a 200 gallon fuel tank. The offshore bracket would hopefully stabilize the boat as well. I was looking into twin 225 Optimax or Verado's. I know people with heaver and longer center consoles that get great fuel efficiency with those engines. How hard would it be to do this and where could I find a place to do this conversion?
     
  2. RYANPO
    Joined: Feb 2006
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    RYANPO Junior Member

    here is what the boat looks like.
     

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  3. mark424x
    Joined: Feb 2006
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    Location: Seattle, WA

    mark424x Junior Member

    Just ran across your post - all I can say is Don't Do It!

    I just got rid of a boat with twin optimax power. Don't know about your neck of the woods, but around here first thing anyone says when you ask for service on your outboard motor is to "bring it by the shop". It looks like you are in worse shape than I was - doubt you have a trailer for that thing or want to pay the bill to haul it in and out of the water everytime you need a little service. If you pay them enough extra for the service call they just might show up at the slip if they are in the mood - if not, the boat will sit for weeks. Don't forget, that 2 engines - means twice the service bill and those electronicly controlled outboards are not so easy to work on yourself. Even if you did have the special mercury diagnostic dongle - you'd be hanging out over the water while you worked on it.

    I had myself all jazzed about the recent advances in outboard power, etc. (I won't go into all the problems I had with the Optis) Might be fine if you have a trailer, but otherwise I wouldn't touch it. Even then, the gas bill will kill you, dragging two legs through the water takes a lot more power than one, or a stern drive. If it makes you feel better to have a get home motor - hang one on a bracket and get one good motor and keep it running - or even a used diesel.

    ok, my rant is over.
     
  4. jgdyer
    Joined: Aug 2005
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    Location: Evansville, IN

    jgdyer Junior Member

    This might help ...

    You will probably be interested in my post on essentially the same topic .. See http://boatdesign.net/forums/showthread.php?t=12782 or click on the topic in this forum a few lines below yours ... entitled Hull extension planning ..

    I have yet to get any replies, so I may yet waver, but today I'm leaning towards the D & D bracket ... Although I was concerned that the bouyancy chamber won't get wet enough to lift the stern, I think a following sea will wet it plenty and lift the stern as needed ...

    All due respect to Mark242X, I agree completely with the direction you're going, although I'd take a hard look at 2 stroke outboards .. except perhaps Optimax due to more than a few bitter testimonials appearing here and there ...

    I've heard nothing but good reports on Evinude E-Tec and the Yamaha HPDI motors ... Fuel efficiency, performance, service ... all good ... I've personally had excellent service over 26 years with 2-stroke engines ... Less moving parts, less complexity than 4-stroke engines ...
     
  5. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    The lines of that hull are just begging for a large-diameter single prop. Yes, it's possible to do a twin-outboard conversion. But when you consider refit cost, reliability, range, fuel efficiency- I think you'd be better off looking for a single good diesel to replace your crapsler (i mean, chrysler....). Not only will you have to fabricate a bracket for the OBs, they are pricey little motors and drink a lot of gasoline. And they fall apart a lot sooner than a good diesel inboard will. Given the choice of $25k for twin outboards, bracket and new rigging, or $25k for inboard diesel with maybe a new prop and some fuel system tweaks, I vote diesel. Need a get-home engine, hang a kicker on a bracket. The most common causes of outboards dying are a) crappy fuel, or b) electrical; either of these problems will usually kill both motors within a few minutes of each other. And a boat like that could only do about four, maybe five knots with one of two outboards dead.
     
  6. jgdyer
    Joined: Aug 2005
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    Location: Evansville, IN

    jgdyer Junior Member

    Matt makes some good points

    Here are some more ...

    Galatea had worn out twin gas inboards .. I went with the Sea Drive outboard for more space in the cockpit, better shallow draft operation, and easier access to the mechanicals .. Changing a bent prop on an inboard while away from port can be a real pain, if not life-threatening ...

    One of the reasons I'm going to twins is that my 25Hp auxiliary engine is almost useless ... I get maybe 3 knots out of it, and rotten handling ... If I ever have to fight weather going home with this thing, I'm in trouble ..

    Another reason is that I have to run my single engine at full throttle to go anywhere ... Fuel efficiency at 5,000 RPM is terrible ... Twins will allow me to run the engines in their sweet spot for better mileage ... Or at least, that's the plan ...

    As to cost, check eBay for the going prices of 10 year old outboards ... I've seen some pretty good looking counter rotating pairs selling in the $6,000 range ... You can buy a lot of gas for the $20,000 difference that a new pair costs ...
     
  7. mark424x
    Joined: Feb 2006
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    Location: Seattle, WA

    mark424x Junior Member

    It all depends on your boat and prop, it's not a matter of HP. I had twin Opti 225, 50 knots WOT, running on one motor I was lucky to do 6-7 knots. They were propped for go fast so with one engine, the prop just couldn't get a grip. I don't know a lot about big foot outboards, but you can't just buy an off the shelf 25hp dingy motor and expect it to push your boat, you need a large prop and the right gearing designed for the job.
    Again, I dont' know your boat, but my guess would be that the drap of the second leg would be worse than the inefficiency of running near WOT. That being said, unless you are up against the limit, you should get a bigger engine. Years ago there was a test - by yamaha I think - that compared running twins on a lightweight 25' boat compared to a single larger engine. The single used 25% less fuel at the same speed - that's not to mentioned purchase and maintenance cost. Of course you have to factor in the get home motor or sea tow membership.
    To be fair, you can't compare 10 year old outboards to a new diesel. If anything a 10 year old diesel would be comparable in reliability to a new outboards - but seriously - compare to a 10 year old diesel - they are out there floating around as well.
     

  8. jgdyer
    Joined: Aug 2005
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    Location: Evansville, IN

    jgdyer Junior Member

    Here's my numbers, for what it's worth

    Aluminum cruiser 28.5' length 102" max beam (less at the waterline)
    6000 lbs more or less
    1985 OMC crossflow outboard rated 205 hp
    27 mph according to GPS at WOT 5000 RPM giving 1.5 statute mpg
    14 1/4 x 13 pitch ss prop

    About 800 hours on the engine

    total maintenance since 1990

    water pump
    flywheel magnets
    stator
    voltage regulator (twice)
    ignition wires
    trim motor

    both tilt/trim cylinders need rebuilding, but I'm repowering, so I'm skipping that job

    I'm betting Ryan's boat is heavier and would need more power than works for mine.
     
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