Engineering question

Steve B · 2011-08-16T04:31:52+00:00

I have a span of 60". I want to put a tube of hitch stock, 2" x 2" x .250"(?) across it, attach an electric hoist and lift maximum 100# several times to bring my welder up on the roof of the containers during construction. Would that be safe? What would be the actual maximum I could lift with this? I don't want to lift maximum, just like to know how close I am to the bending point to allow for safety.Steve

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Carl Ijames 15 years ago

Since no one actually answered Karl's question I'll play what-if. For fun using your 3000 lbs and a beam simply supported at the ends with a span of

10', I used a load of 9000 lbs concentrated at the center (using the x3 factor for a live load to take into account when it bounces up and down as it comes off the mounts :-)). With 4" square tubing 0.5" wall the max deflection is 1" and the peak stress is 48 ksi which is getting right close to (or over) a typical yield strength for structural steel, so if you use square tubing it better be 5" and heavy wall, or bigger. There are two types of I beams, S and W, looking at S beams a 5x10 which is 5" tall and 10 lbs/ft (and the flanges are 3" wide) standing so it is 5" tall and 3" wide is a tad weaker, and the lightest 6" beam, S 6x12 is more than enough (assuming no additional safety factor and a yield strength of over 40 ksi), deflection .51" and max stress 37 ksi. In the W series the 5x16 is about as strong as the S 6x12. So any 6" I beam or a W 5x16 would just do it. Make sure you have the beam tall and narrow and clamp it so it can't twist and all fall down :-). I like the shareware program engineering power tools available at

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for doing this stuff. The free version is fully useable and does basic beam stuff like this along with lots of other useful stuff, and if you pay the $45 and get the full version you get lots more. Well worth it. (I'm not an engineer, this is worth what you paid for it, yadda, yadda :-)).

----- Regards, Carl Ijames

You guys are all forgetting about the tranny that comes out with the engine. Marine engines blocks are far larger allowing for raw water cooling. I think 3,000 is still a good guess.

Karl

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Larry Jaques 15 years ago

Finally, someone with some _sense_...

-- ...in order that a man may be happy, it is necessary that he should not only be capable of his work, but a good judge of his work. -- John Ruskin

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Richard 15 years ago

Thanks for the tool link, Carl.

But I still think 3000 pound guess is a bit high for a 600 pound motor.

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Richard 15 years ago

Plonk

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clare 15 years ago

When he says "big block" I'm ASSuming he's talking a GM V8 Elephant -

396, 427, or 503 - or a Ford 460, or a big Mopar (413 etc) , all of which see a fair amount of Marine use.

Fully loaded for marine use, the ENGINE will be under $1000 in all cases - the gearbox (straight or V Drive) will add a couple hundred. I'd say 1500 would be pretty safe for an "all in" weight

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Steve W. 15 years ago

Karl, The engine block used in marine engines is the exact same one used in other applications. If it's a big V-8 then it's either something like a 460 Ford or a 454 or

502 Chevy. Mercruiser uses mostly GM products, Volvo/Penta uses Ford and GM if the engine is a gasser, The only real difference between the street engines and the marine engines are the camshafts and the exhaust manifolds. The cams are usually ones ground to give a flatter torque curve at a lower rpm than the street versions. The exhaust manifolds are cast so they can be water cooled. The rest of the parts can be interchanged easily. BTDT a lot. Until you get up into the BIG diesels most of the boat engines used are nothing more than heavy equipment engines. Cat/GM/Perkins/Cummins/Waukesha/Mitsubishi all have been used as well as some others. Nothing special about them.

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Jim Wilkins 15 years ago

120lbs (12Lbs x 10') of steel could be difficult to set atop the posts safely without an engine hoist etc. The 8' rail for my temporary gantry crane extension is bad enough to maneuver overhead at 80 Lbs. I balance it on a second taller stepladder to allow one free hand to align it and insert the bolts.

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I have been considering a gantry with the beam hanging from a tripod on each end. It won't be as mobile as one on wheels, but the posts will be in pure compression, without bending loads, so they can be lighter. The beam can be heavier since the tripods can lift the ends. The trolley would likely be moved with block-and-tackle attached to the beam ends, minimizing lateral tipping forces on the tripods. It would disassemble into channel and round posts for compact storage and not have any welds to rust.

Has anyone ever seen or used such a rig?

jsw

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Carl Ijames 15 years ago

Thanks for the tool link, Carl.

But I still think 3000 pound guess is a bit high for a 600 pound motor. [/quote]

I'm not disagreeing at all, but at least now Karl knows that if it really is

3000 lbs then a 6" I beam is the bare minimum, and if it really is 1000 lbs he will have an extra factor of 3 safety margin. The rest is up to him (hey, us Carls have to stick together even if he does spell it funny :-)).

----- Regards, Carl Ijames

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