inboard geometry

Discussion in 'Inboards' started by epoxicologist, Apr 17, 2019.

  1. Ike
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    Ike Senior Member

    Interesting discussion. It caught my eye because about 6 months ago I bought an engine from a gentleman in McMinnville, Or, who was converting his 1978 Fiberform 22ft from an I/O to outboard power. And these are not the only ones. I have seen a handful of others in the last few years doing the same to their Fiberforms. What is it about Fiberform that makes owners want to change them so drastically?

    Oh by the way, the engine was a Merc 165 and it is now sitting happily in my 1972 18 foot Sea Ray. I have yet to launch it but I'll let you know how it is doing.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Conversion from sterndrive to outboard is fairly common, now that big four-stroke outboards are available. People like the extra room inside the boat, and generally it is not entering unknown territory, like what is described in this proposal.
     
  3. Ike
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    Ike Senior Member

    Thanks. Fiberform was a Pacific Northwest manufacturer located in Spokane Wa, and they were hugely popular, so popular that Bayliner bought them out. But there are literally hundreds of them still in service here in the PACNW. I see them all over the place. They were and still are considered a very good boat. Anyway, just curious. Don't mean to hijack the thread
     
  4. Yellowjacket
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    Yellowjacket Senior Member

    The reality is that automotive transmissions aren't designed for the duty cycle that you find in the marine environment. You're going to be running at a much higher continuous load factor and you'll burn up the tranny in short order. If you look at what happens when you pull a heavy trailer and what that does to transmissions, you're going to see that effect when you're running a boat on a plane.

    There are two applications where high continuous power is required. Those are airplanes and boats. All other vehicles typically run at 15 to 20% of their maximum power capability for most of the time or even lower if the car is light and has big power. When you add a big trailer you run at maybe 50% most of the time. In a boat or an aircraft you run at 75% at cruise or greater. The heat generated by automatic transmissions at higher load factors like that is huge. In an automatic transmission that work is going through a torque converter and at low power levels it's an efficient machine. But at high loads the converter slip factor goes up and the heat generated becomes much greater. If you use a lock up clutch on the converter you'll destroy it. Lock up clutches aren't designed for high torque they only lock up at light throttle openings. When you push down on the accelerator the clutch unlocks because it cannot handle that much torque. If you had a light boat like a ski boat you might get away with it, but for your application you're going to cook the transmission in short order. In this case you need a marine transmission. There are no two ways about it. I don't mean to say cobbled up to mean poor workmanship, it is simply that the use of inadequate hardware that isn't designed for the application is going to result in endless headaches.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    If its a better than average hull, maybe worth restoration, but I think that is the key, it just has to be a good hull, performance wise, otherwise you are pouring money into something people are not very enthusiastic about, anyway. A bit like restoring old cars, they need to be above average for their times, and have a significant positive point of difference.
     
  6. DCockey
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    DCockey Senior Member

    Some folks like to work on projects which they can afford without concern about "being able to recover their money".
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    No doubt, but it isn't just money I was thinking of, I could not justify putting a lot of work into a boat that you know is an ordinary conveyance, at best, I'd rather put the work into something you know is a superior hull. But, this one may actually fit that description, all I know is a few pictures on the net. But really, it is the gamble of this "novel" drive system, that further complicates things, in a very speculative way.
     
  8. Ike
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    Ike Senior Member

    Tell me about it. If my Sea Ray wasn't such a good hull I wouldn't have paid $4300 to have an engine installed. Fiberforms are good hulls and from what I've seen nearly indestructible. They were built back in the day when fiberglass boats were really overbuilt. Like my Sea Ray they are a lot heavier than boats built today, bu they last.
     
  9. 7228sedan
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    7228sedan Senior Member

    Just thinking, if the Alpha keeps blowing up, why not leave it a stern drive and upgrade to a Bravo? It'll still be a fair bit of work but nowhere near as involved as installing a straight inboard.
     
  10. kapnD
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    kapnD Senior Member

    I’m familiar with Fiberforms, there are still a lot of them around here, and most have been modified and rebuilt to better handle ocean conditions, which usually includes a raised bow area spray deflector.
    They’re known to be “wet” boats, narrow in the bow and significantly slanted entry, which amounts to less than ideal flotation for forward loads.
    I would not be tempted to move the motor forward, it will make the boat plow.
    I believe the stern lines are parallel, constant deadrise, so it might be possible to stretch the length to accommodate your proposed load changes, but that brings back the question of whether it’s worth it.
     
  11. Barry
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    Barry Senior Member

    Why do you think that you need an automatic transmission?

    If you put any automotive transmission into the mix, you will have to design a component to deal with the thrust in the prop shaft.
     

  12. kapnD
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    kapnD Senior Member

    I fully agree, and don’t understand why the op would not just upgrade the sterndrive, if that is the crux of the boats problems.
     
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