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Thread: Ben Hur cab over (old skool)

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    Default Ben Hur cab over (old skool)

    Here's a couple of shots of my Ben Hur hydro. It's a Hal Kelly design from way back.
    This is the hull I plan on putting a motorcycle engine in the back and run a surface drive system of my own. The "drive" in the pic is a mock up of wood. The tach will come from the bike. The steering is fabbed up in the shop with a steering wheel from a go kart.
    Why I'm so cheap, that I even made my own cowl pulleys.DSCF0006.JPG

    DSCF0007.JPG

    DSCF0001.JPG

    DSCF0004.JPG

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    This looks pretty dangerous to me.

    The thing that bothers me is that you have a pretty severe shaft angle, and the prop is set way back from where it was with the outboard. This is going to create a lot of lift way back behind the boat.

    Add to that the fact that your motor weight is a lot further forward that it was in the original design and you have a situation where the back end of this boat is going to lift like crazy. WHEN that happens (notice I didn't say IF) the back end is going to try to pass the front end in a hurry.

    I understand you want to do this on the cheap, but when you look at it, you can buy a decent outboard (like a Merc 500) for about $300 (I know because I just did). You could have a lot of safe fun with a rig like that. This is simply a recipe for getting hurt. Your weight distribution is way different than what the hull was originally designed for and this alone could be dangerous.

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    The shaft angle on this experiment is 10 degrees. It looks more like 45, but that's the angle of the picture. The engine maybe forward of the motorboard, but that should move the CG towards the sponsons. The areodynamics of the hull wanting to lift at the bow should be balanced by the extended shaft length and the far forward seating position of the driver.

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    Team Member zul8tr's Avatar
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    Default Ben hur

    the operative word here is "should" ?

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    Make it like an Arneson drive....utilizing a gimble joint at transom...a really simple design. Get you a small Chrysler trim cylinder and a Chrysler pump and you can have a trim system. Keep us informed of your progress...good luck, gg
    Attached Images Attached Images

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    Default Listen To These Guys...

    I realize you have bought two props from, not totally knowing what I was selling you. But, Hal Kelly originally built this boat was a ton of "AIR" lift in it (For the ear it was a ton)...and as I recall it has like a 1/2 to 3/4 inch tunnel. Hal Kelly's pictures show the Ben-Hur with a 55-H on it and kicked under, maybe 5 degrees.

    Really, I looked at you plan, yesterday, and came back on today to tell you you need to get the propshaft closer to parallel......Everyone here on BRF have given you good advice...

    Nice job so far on the boat.....Tell us about your Studebaker!!!!

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    This boat has a step in the tunnel where 18 inches down the middle is 3/4 deeper than the rest. The sponsons are 4 inches and tapers to 3/4 inch at the transom. aluminum air traps would hold more air underneath.
    Since this is going to grab a lot of air,,,,,,,,would it be better to have a 8 - 10 degree shaft angle in order to keep the bow from a blow-over?
    As for a trimable-steerable system, it was concidered, but then,,,,,,,,the weight and degree of "backyard engineering" would slow down my "launch" date.
    If this works out even with resonable results, I just might work on that type of drive. I have a SM chevy engine and a 16 foot Sidewinder boat laying around.
    I could fill a thread will Studebaker info and stories, but it's a car. Where would it be posted? Dave

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    Team Member zul8tr's Avatar
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    Default Ben Hur bottom

    There is a tunnel that almost runs full length
    As Ron notes there is a lot of lift in this hull
    In the link Pic # 38 is a shot of the bottom to clarify what Stupidbaker57 describes

    http://www.boatsport.org/PDF/BenHur5.TextMark.pdf

    Here is a profile of the hull that shows the S curve

    http://www.boatsport.org/PDF/BenHur1.TextMark.pdf

    You might find a shaft angle of about 8 to 10 degrees down will cause to much lift at the rear and plow the sponsons with this cabover design..So you need design flexibility for the shaft angle to change to something less than 8 to 10.

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    Team Member JohnsonM50's Avatar
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    Quote Originally Posted by zul8tr View Post
    There is a tunnel that almost runs full length
    As Ron notes there is a lot of lift in this hull
    In the link Pic # 38 is a shot of the bottom to clarify what Stupidbaker57 describes

    http://www.boatsport.org/PDF/BenHur5.TextMark.pdf

    Here is a profile of the hull that shows the S curve

    http://www.boatsport.org/PDF/BenHur1.TextMark.pdf

    You might find a shaft angle of about 8 to 10 degrees down will cause to much lift at the rear and plow the sponsons with this cabover design..So you need design flexibility for the shaft angle to change to something less than 8 to 10.
    1st of all I admire your can do spirit with this but am in agreement with the need to somehow be able to adjust the angle of the drive even if you intend to run it 'fixed' the odds of it being sweet 1st try aren't great. I also agree that it shouldn't be too far back. Since you would want to only drill the transom once & since you might not have a gimbal to work with perhaps the motor mount platform can be made so that higher or lower setting can be reasonably done.
    Considering the possibility that the motors drive output is a couple inches up from the bottom you could connect it to the prop shaft with a belt or chain allowing you to lesson the trim angle too.
    The next concern is the boat. Hydro's are pretty specific, even old ones. For the weight distribution to be changed is always questionable but that can depend as much on how much power you will have at hand. If your putting some wild hi-power thing together well... run it thru its paces in steps & be careful If its too dangerous to drive it wont be fun anymore not to mention finding that out the hard way. Most outboards are designed more for torque requirement than the blaring power some bike motors have. They depend on gears to get over the hump as it were, outboards have to do that on 1 speed. You could find a bike motor thwarted before it reaches its power band. A Ben Hur with a good 55H is going to be a fast & powerful ride, if what you use is significantly more motor ...again go with caution.
    Curiosity, some bike motors have integrated transmissions, will you be shifting gears?

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    I've been down that road with respect to the motorcycle having a transmission that would require shifting. The Honda engine I have is from a cb400a. It has an automatic trans, low and high. I have the drive designed as low as possible in the boat but I am not using a belt. Since the engine will be sideways, the sprocket is off centered to starboard. (31 years in the navy and I think it's still the right side) Power comes thu a 5 inch jack shaft and transmits the power to the sprocket (see pic) via chain. This is where I can change ratios to speed up or slow down the prop shaft to better match HP to speed. Rough figures put this at 50 mph with a 27 hp engine, a 16/21 ratio running 7000revs with a 7X10 prop.
    If this doesn't figure right to you, it might be that my figures on the cocktail napkin got blury when I spilled some beer.

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