Converting outboard to inboard

Discussion in 'Boat Design' started by Twinluis, Jan 10, 2014.

  1. Twinluis
    Joined: Jan 2014
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    Twinluis Junior Member

    Hi guys I just need help to know if is possible to convert a maycraft 27 pilot house in a inboard diesel engine. Due to her similitude to the judge 27 pilot house boat(inboard) And I love that boat ..thanks ,any help will be appreciate
     
  2. gonzo
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    gonzo Senior Member

    It is possible, but very definitely not advisable. The hull structure need to be redesigned. It will be heavier and slower. The inboard engines will take a lot of interior space, with possibly large engineboxes on the cockpit. There will be shafts sticking out the bottom which will increase the draft and make the boat very hard to trailer.
     
  3. TANSL
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    TANSL Senior Member

    Gonzo, I think it ought to be studied in more detail, before totally rejecting any solution.
    The structure does not have to be completely redesigned, simply add the engine mount. It will probably be slightly heavier but you can not say, without more, to make the boat slower. There are many other factors involved in the boat speed.
    The weight of the new axis, depends on its length, could be similar to the weight of the tail of the outboard.
    Clearly inboard engine removes space inside the boat. Apparently this is not debatable.
    Possibly the draft will increase (no, if a waterjet is placed) but boat´s trailerability has nothing to do with these changes, in my opinion.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Looks like a hull that might accomodate a single diesel inboard or better a sterndrive, has moderate vee and enough size, but unless you do a lot of hours, not going to be worth it, especially if slowing down significantly is not acceptable.
     
  5. gonzo
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    gonzo Senior Member

    Trailerability is partly a function of the total height of the boat on the trailer. With inboard and straight shafts, the boat will sit higher which will restrict the access under low overpasses. This may not be a problem. However, any inboard diesel setup with the same HP as the outboards will be considerably heavier, which translates into a slower boat.
     
  6. TANSL
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    TANSL Senior Member

    The issue of weight and speed should be studied in depth as a total load, even bigger, better located, can improve or worsen the condition of a small boat navigation. I only say that we have no evidence to say one thing or the other and that, in giving advice, we have to be cautious.
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    [​IMG]

    The Maycraft 27 Pilothouse.

    As typically setup:

    [​IMG]

    An I/O, outboard or bracketed outboard is the usual propulsion arrangement. An inboard would chew up valuable, usable cockpit volume. Given the choices and the desire for a diesel, I'd opt for a diesel I/O setup, instead of the inboard.

    With an inboard you'll lose a great deal of maneuverability and the engine box will divide the cockpit into a "U" shaped thing, making an odd setup to say the least. The pilothouse door is right in the way and would need to be moved, meaning unless two doors where used, you'd have to walk around the inboard engine box, just to get to the other side of the cockpit. This could be solved with an open pilothouse, like used on the Judge 27, though you'll lose some structural integrity, hacking out this bulkhead. This could be "returned" with some steel or well placed laminate.

    What is the logic behind this change?
     
  8. AndySGray
    Joined: Jun 2014
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    AndySGray Senior Member

    The Journey?

    There is a joke about a man asking the wrong person for directions, who replies;-

    It'd be much easier to get there, if only you weren't starting from here...:rolleyes:


    But, actually for boats it is much better advice.

    would it be better to sell an existing twin O/B boat and buy one with (and optimised for) diesels - a hull with prop tunnels for shallower draft and easier trailering? or as PAR suggested I/O?

    You could probably find a 30 footer which was shorter overall than a 27' with the platform and O/B's behind the transom.

    might actually be a more cost effective to swap a Gas/petrol to diesel if you want to have new motors and want a less daunting project.

    But, I'm sure you'd already considered that - I guess that if you're asking the question, it's not simply because you want a Maycraft 27 Inboard Diesel, but more likely because you fancy the journey that will take you there...

    Do as much research as you can, and make sure you have 20-50% more time and money than you originally budgeted. Carpe Diem.


    Personally I am a fan of diesels, which was reinforced when I found the reason a boat in one of my local marinas was called "La Swan Blue" - had nothing to do with swans but was a reference to the demise of his previous vessel = Last one blew (up) :eek:
     
  9. messabout
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    messabout Senior Member

    If you are planning to go for extended trips under power, the diesel makes good sense. Extended trips taken to mean cruise hours or days on end,

    If you are thinking of messing around in Biscayne bay or maybe taking the ICW down to Marathon, Islamorada, or other short distance, the outboard makes a lot more sense.

    Servicing the outboard is far more convenient and more available than with an inboard. Marina docks almost always have gasoline but not always diesel. Even if they have diesel fuel, there is doubt about its age, bacteria count, and water content. Diesel also costs more in Florida. Lot of practicalities to consider when assessing diesel vs gasoline.
     
  10. Poida
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    Poida Senior Member

    I have an inboard, and the beams bearers or what ever they are called go almost the full length of the boat, which I assume are to distribute the load and vibration over a larger area. I would assume that a boat that wasn't designed for an inboard motor would not have a structure built to accommodate one.

    With outboards you tilt the motors to give clearance when towing on a trailer but you can't tilt the prop of an inboard so the trailer may have to be raised to provide the clearance. Gonzo mentioned this in regards to overpasses, but I would like to add - you have to back the towing vehicle in further to launch and retrieve the boat and may require extending the trailers draw bar.

    Servicing an inboard is difficult, an oil change for example you can't just undo the sump plug and let it out.

    The problem with manoeuvrability has already been mentioned to the point that I consider an inboard belongs on a moored boat and not one that has to use a boat ramp.

    The only advantage I can see to an inboard is the use of the swim platform.

    Poida

    PS. I can think of other problems with an inboard but that was enough.
     
  11. PAR
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    PAR Yacht Designer/Builder

    The engine beds, which also serve as longitudinal stringers have multiple functions and shouldn't be assumed simply engine beds. Engine beds are locally oriented, usually against or part of the longitudinal stringer system. This saves weight and kills two birds with the same stone.
     
  12. Poida
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    Poida Senior Member

    Jeez Par, just when I think I've got something right, you blow me out of the water, (so to speak)

    Poida
     
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  13. PAR
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    PAR Yacht Designer/Builder

    Not trying to blow anyone up Poida, though maybe just some clarification about engine beds and longitudinal stringers.

    It usually depends on the boat, but since most power craft are full plane, the bottom loading can rise significantly, so longitudinal stiffeners are run as far forward as practical, regardless of propulsion type. In fact, a somewhat standardized spacing has been established at ~24" (12" on either side of the centerline) with most boats. This offers enough room for a small block's motor mount brackets (the mounts are on top of the bed) to nest between them and still have room for an oil filter and pan (assuming sufficient depth).
     
  14. ChrisN67
    Joined: Jan 2008
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    ChrisN67 Senior Member

    Convert Outboard to Inboard

    Having done this in a recent exercise, the areas I found to be relevant are CG and thrust angles of the fixed inboard, I/O or Surface Drive; the later giving better adjust-ability of thrust vector.

    I understand the install angles (of prop strut or other drive) should be designed for best trim at neutral drive angle if adjustable.

    Engine beds with foam core and a full length 1"x3" embedded aluminum flatbar with Keenserts (Stainless inserts for the engine mounts)

    Engine Bed lamination:
    -2 layers CSM over initial foam core.
    -then alternating 2 layers +-45 biax and one layer 0/90 for 9 layers.
    -Belt sanded every three layers to maintain shape.
    -Each successive layer overlapping 1 inch across hull bottom (they interlocked after layer 8)
    -Then flatbar set with epoxy/milled fiberglass putty. Then 9 layers as a cap.
    -Engine beds flared into transom and forward bulkhead.

    Extension:
    Transom:
    -8 Layers biax with carbon fiber exterior skin.
    - 1" Coosa bluewater
    -4 layers biax interior skin

    Hull bottom and sides:
    8 layers biax +-45 and 0/90 then airtex damage tolerant foam vacuum bagged with 4 layers on top.

    9" overlapping of glass hull bottom to sides to transom.

    Early apologies if my terminology is not standard. I am not a professional, I am still learning everyday.
     

    Attached Files:


  15. ChrisN67
    Joined: Jan 2008
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    ChrisN67 Senior Member

    We use this boat for running to different locations in the Persian ...I mean Arabian Gulf; we are contractors working for DOD. Every possible consideration for safety and functionality has been incorporated.


    Almost every component on engine, transmission and drive monitored to include non contact infrared pyrometer for Aquadrive CV temp.

    Fuel boost pump for priming/ and recirculation /conditioning

    Remote oil change system for engine and genset (Jabsco)

    Engine room cooling system via Thermatron copper nickel heat exchanger/radiator on circulation pump (this is better than a "blower") << in Arabian Gulf ambient temps in summer can be as high as 140F. The engine rooms heat soak after engine shutdown. We have had an extinguisher discharge from high temps. The copper nickle radiator can keep engine room near water temp (95 F)

    Strainer water sensor with remote fuel strainer purging overboard

    Engine flushing fresh water flush and emergency bilge pumping system

    Borel Exhaust over temp alarms on Engine and Genset

    Cole Hersee MinBus USB programmable power distribution system

    Balmar 220 Amp Alternator

    DC and AC systems have blue sea amp and voltmeter on deck for quick reference on battery and genset voltage/amps/frequency

    Fire Suppression System

    Kiddee engine shutdown on extinguisher activation

    Raymarine Lifetag for auto shutdown from remote pendant if overboard or more than 30' from helm

    (2) KC 50 watt HID carbon fiber light pods looking forward

    Cameras for drives, bow pulpit, anchor locker, and engines.

    Pulnix Ibeam sensors on deck for remote notification (GSM) of movement on vessel, high water alarm, bilge overrun alarm, battery level, temperature as well as GPS location and remote shutdown and fuel cutoff capability.
     

    Attached Files:

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