Ben Hur cab over (old skool)

[stupidbaker57]

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.45175

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[Yellowjacket]

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.

[stupidbaker57]

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.

[zul8tr]

the operative word here is "should" ?:eek::eek:

[marchettih2o]

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

[Ron Hill]

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!!!!

[stupidbaker57]

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

[zul8tr]

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.

[JohnsonM50]

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 :eek: ...again go with caution.
Curiosity, some bike motors have integrated transmissions, will you be shifting gears?

[stupidbaker57]

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:D) 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.

[JohnsonM50]

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:D) 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.
:cool: In terms of what your working with seem to be within reason & workable. It will be an interesting moment when it up-shifts. I was thinking 2 stroke at 1st but guess this is a 4?

[stupidbaker57]

I've been thinking, and that alone could be dangerous, about the shaft angle. Even tho I measured and checked as many points as possible, there could be a chance that the shaft angle may need (may?) some change after a test flight. So be it.
This is where it gets scarey. I have designed (cocktail napkin again) a trimable drive without U joints. Seems there isn't much room in the back for them.
My method is the pivot the entire drive, engine and shaft to get the right angle while underway.
The hole in the transom would only need to be 2 inches in diameter and slightly elongated up & down.
The pictures may help. I first built a mock up from wood, then went the steel route. The shaft will be stabalized by a 4 bar system with heim joints.45291

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[JohnsonM50]

The Ben Hur as a racer would have the prop a certain depth, angle & distance back. Not sure exactly what those #'s would be but guess you would want to be close. Considering the Honda & drive to be possibly lighter & its core weight farther forward Id guess you would want less aft lift. This can of course be compensated for by driver position & prop choice [bow lift prop]. Im pretty sure you'll need the thru transom point to be right on he bottom to get 'ballpark' on drive or maybe since it has to enter the water as a shaft before prop anyway even a little lower might help. That way when you adjust the angle lowering the motor to 1-3 degrees of prop shaft/bottom you wont be raising the prop too high to work. Im not trying to be a nay-sayer, just sayin that even tho its different being near what the established setup would be is probably going to be close. Then your move the whole thing plan might be able to bring it right where it should be considering the pivot being at the transom, the hole shouldnt have t be too large either. Good Luck with further planning.

[stupidbaker57]

The centerline of the shaft can't be any lower than 2 1/4 inches from the bottom. Reason being is the sprocket and chain are there.
I'm now working on a way to raise and lower the engine cradle (max 5 inches total) electricly. I don't want hydrolics because of weight. I opened the hood on my Stude with a jack screw and a power window motor. Maybe I'll have to go that way.
Shifting will be electric. I'll use a door lock solinoid. (push pull type)

[stupidbaker57]

Here's a couple of pictures of the final drive less the rudder. The trim action works smoothly with no binding.
Next is the mounting of the engine to the cradle and installing the jack shaft. I have everything for this so I should be able to get it done in about a week or so. Dave45348

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[Ron Hill]

Make sure those transom pieces are strong, might brace them with some aluminum angles, inside.... You will be pulling hard on those two transom piece make sure they are braced. I've seen rubbers pull out of the transom and the results ain't pretty...

What horsepower and gear ratio are you using?????

Do you have a pilot's license?

[JohnsonM50]

It looks cool, I agree, these mount area's need to be hard points. One advantage it might have if you can get it to easily adjust on the fly for routine driving is lowering the prop to get going & raising it to cruise.:cool:

[stupidbaker57]

This drive will be trimmable on the fly. The entire engine and drive pivot at the transom. There is a total of 4 1/2 inches of travel for the prop. The inside has been braced for the extra torque that will be present. The engine is only a 27 HP 2 cylinder 4 stroke and the ratio is 16/21 like an outboard.
Ron, How's that experimental outboard doing? I was thinking of laying:rolleyes: a six cylinder merc on its' side and useing it as an inboard. Dave

[Yellowjacket]

That's a really odd linkage. I guess it will work, so long as the motor and torque tube aren't rigidly attached to the cradle (pivot point) inside the boat. If they were, the whole thing would bind up and the forces in the outboard links will get huge. Just seems that you've got to have some flexibility right where you may not want it. You have to support the motor but let that support be flexible or it's going to bind up. I'm curious to see how you are going to work out the rest of it.

[stupidbaker57]

Imagine this,,,,,, A fat kid on a seesaw, (engine) and a little girl (prop). My engine will be mounted on the cradle. The prop tube is also mounted on the cradle inside the boat. To submerge the prop deeper in the water, the fat kid goes up. I'll be raising it up and down via a motorized jack screw. So far this project has cost less than $500. (not counting the 2 Ron Hill props and beers) Dave

[Yellowjacket]

Imagine this,,,,,, A fat kid on a seesaw, (engine) and a little girl (prop). My engine will be mounted on the cradle. The prop tube is also mounted on the cradle inside the boat. To submerge the prop deeper in the water, the fat kid goes up. I'll be raising it up and down via a motorized jack screw. So far this project has cost less than $500. (not counting the 2 Ron Hill props and beers) Dave

You are missing what I am trying to say.

I already understood that you were going to attach the torque tube to the cradle, but when you attach your torque tube to to the cradle the linkage will bind up because you have two extra links that make the linkage rigid.

Correct me if I am wrong, but I beleive you are planning to put the pivot point of your cradle near the bottom of what was the motor board inside the hull.

If the torque tube is attached to the cradle with a rigid mount, then the shaft must pivot about the inner pivot point, near the bottom of what was the motor board. If the two links that go forward to the transom aren't in line with that inner pivot point the linkage becomes rigid. It can't move without putting high forces in the links. In a car suspension there are ball joints that allow angular movement of the upright, but your upright is rigid, it is welded to the torque tube, so no angular motion is present in that section.

Right now your linkage will move, only because the torque tube isn't firmly attached to the engine cradle. If you attach the engine to the cradle and leave the torque tube free, you will need a coupling that will allow the shaft to move relative to the engine. You will need both axial, radial and angular misalignment capability in the coupling to make it work. If the engine is rigidly mounted to the shaft, then you will need to have some type of mount that will allow it to move relative to the cradle. Neither is a good solution.

You should probably go through the range of motion with a scale drawing to see what is moving where, but right now the kinematics are such that it will bind up unless there is a lot of slop in the joints. You have Heim joints in the links now and that doesn't allow for any slop.

In order to make it work the transom mount links need to have their pivot axis on the same line as the cradle pivot. If they don't you have a static system and it won't move unless something bends or breaks.

I would simply get rid of the transom links and design a structure that holds the torque tube without them. Keep your pivot to one axis and it will work. Otherwise you are just going to have problems.

[stupidbaker57]

Everything in the picture is tight, shaft tube and all. The cradle assembly moves freely from the lower starting off angle all the way thru to the full speed trimmed out position with no binding any where. I understand triangleation where as pivot points must line up or binding will occur.
I might be building this in a garage and using a drill press as a bridgeport, and a radial arm saw as a surface planer, with a cocktail napkin for a drafting table, but I think I have done what I planned to do without any trouble.

[Yellowjacket]

Everything in the picture is tight, shaft tube and all. The cradle assembly moves freely from the lower starting off angle all the way thru to the full speed trimmed out position with no binding any where. I understand triangleation where as pivot points must line up or binding will occur.
I might be building this in a garage and using a drill press as a bridgeport, and a radial arm saw as a surface planer, with a cocktail napkin for a drafting table, but I think I have done what I planned to do without any trouble.

If your holes are loose enough and the range of motion is small, and the mounts aren't too rigid, you can get away with it. More power to ya!

[stupidbaker57]

I finally got the jack shaft parts from the machine shop . They've been there for over 2 months. In that time I've built 2 rowboats and sold them, one "cocktail racer" (for sale) and got a 10" Atlas lathe from a friend for free and rehabed it to working condition. Now I can do my own lathe work.
My steering is going to be "push pull" useing PTO cables conected to the steering wheel.
Now that I'm getting near the end of this monster, I have another plan in my head for the jet ski engine I have, but first I must draft it out on a cocktail napkin.