Disclaimer: If you build something yourself or if you modify a manufacturer’s product in any way the you are assuming all of the consequences for your actions. If it breaks and drops an engine on your pregnant wife it is your fault. If you believe anything else then stop reading and go to some other web site.
Until I had some way of suspending engines, steel or entire boats in the air it is hard to realize how much easier it would make my work. So when we decided to build a large sailboat I was planning on a the crane or gantry long before we knew exactly what we were going to build.
I started with an 8 foot span A-frame from 1/4 inch thick, 2 1/2 inch ID steel pipe and it is great for lifting the sub or the engine but it’s a little over stressed to do both or about 1 ton, and it would never be able to handle the sub with it’s ballast sled in place which would total 2 tons.
The wheels on the A-Frame are good for 300 pounds each and available from Harbor Freight for $9 (2008) each. None of these pivot so turns require dragging a wheel sideways but it is much better that walking the A-Frame around by moving one leg at a time.
The A-Frame is held together at the corners with a bracket made from 3 pieces of 16 inch long 2 1/2 inch OD pipe and a bit of angle for reinforcement. This lets the legs and cross piece just slip onto the bracket and only 1 bolt is used the secure the cross piece so it does not slide out. Each leg weighs about 60 pounds, so standing the thing up is a bit of a task requiring a couple of strong friends or some 2×4 bracing. The steel in 2005 cost $75 from the scrap yard and Harbor Freight had their 3 Ton chain hoist on sell for $65 dollars.
(1) We chose dual gantries because the sailboat will be about 70 feet long and built using the origami method that requires handling a 13 by 75 ft sheet of metal. Having two lifting point will make that a much easier task. Both gantries will be supported by grooved wheels that roll alone a 1 inch steel angle on top of concrete beams in the ground.
There are several online calculators for floor beams but you need to use a calculator is for center loaded beams without an lateral support that would come from having the beam connected to a floor or ceiling.
(2) I found the following resources on www.engineeringtoolbox.com. The “Stresses and Deflections in Beams” page has a calculator specifically for “Beam Supported at Both Ends, Load at Center”. The other page, “American Wide Flange Beams” list all of the standard wide flange beams and their corresponding “Moment of Inertia” number that is entered into the calculator.
Stresses and Deflections in Beams
American Wide Flange Beams
Using the above calculator for my gantry I entered 5 tons for the load and 28 ft for the length and then the Moment of Inertia for various I-beams watching the resulting Maximum Deflection until I settled on a W12x22 beam. The W stands for Wide flange, 12 is the web height in inches, and 22 is the pounds per foot.
Below are the results:
Total Load : 10000 (lb) –5 Tons
Length of Beam – L : 336 (in) — 28 ft open span. The beam is actually 30 feet long.
Moment of Inertia – I : 156 (in4) –This comes from the list of standard wide flange I-beams
Modulus of Elasticity – E : 29000000 (psi)
Perp. distance from neutral axis – y : 6.25 (in)
Support Force – R1 : 5000 (lb)
Support Force – R2 : 5000 (lb)
Maximum Stress – s : 33654 (psi)
Maximum Deflection – d : 1.75 (in)
A 1/400 ratio is normal deflection for living space which would be about 3/4 inch for 28 ft, however that is just because people don’t like floors that bounce. In this case 1 3/4″ is acceptable but there is no room for safety.
I’d complain about the Chinese buying all of the steel, but I just ordered a bunch of chain fall hoist, trolley’s, lever chain hoist, and an electric hoist at prices that are hard to believe considering the number of pounds of steel in the order. I just wish they would bring the quality up a little. I always think about those dirt foundries that Mao had the Chinese farmers setup when I working in the sub and that diesel engine is suspended above me on a Chinese hoist with Chinese chain. Hopefully they are not using the same foundries.
With only a 12 foot high A-frame to work with, the two gantries were assembled on their side.
(1) The V-groove wheels support 3 tons each and came from www.acecasters.com for $40 each, so a total of $340 for all 8 with shipping in 2008. The foundation slopes at 1 inch for every 10 feet and the base of each gantry is 10 feet long, so the wheels on the down hill end are 1 inch further from the base beam.
(1) (2) A jig cut from aluminum guided the plasma torch to cut a slot the bottom end of the vertical beams. With the 20 foot vertical beam laying on its side, the bottom beam was hoisted vertical on the A-frame and set into the slot.
(3) (4) (5) A second hoist then raised the end of the vertical beam 5 feet up so it could be welded to the bottom beam.
WE painted while they were on the ground as a ladder would not be needed. We found paint for only $6 a gallon on www.craigslist.org from a guy who collects incorrectly mixed paint from Sherwin Williams Paint stores.
Erecting the Gantries
Standing the gantries up was a piece of cake. But my neighbor is “Nosack Tree Service”, and Paul Nosack and Calib his 11 son pitched in to lift the gantries. It’s a real hoot having Paul’s business across the street because Paul has his own reality cable TV show. See www.nosackraw.com
Plan “B”, if Paul was too busy or if his crane was out-of-town, was to stand the gantries up without a crane. I had already purchased a 30 foot long 6 inch I-beam that would become the spreader. The plan was to lift that I-beam with the A-frame and stand it almost vertical. Then secure it to the A-frame, secure a steel cable pulley to the top, and another to the bottom. The steel cable would run from the cross member on the gantry thought the top pulley, down to the bottom pulley and then to winch and dead-man a safe distance away. It would have been fun to try, but much more risky than the crane.
(1) This was Calib’s first time to lift a load with the crane and he did a great job, without too much yelling from Paul. I can’t think of a better way to educate a child than to give them real responsibility.
(2) Steel I-beams easily twist, so to keep the vertical beam from twisting while the weight was on the ends of the bottom beams, I ran chains between the wheels on the bottom beams to form a large X.
(3) Then we just stood around and let Calib to maneuver the hook into place.
(4) (5) The gantry whet up without a hitch, but I did not have a 28 foot ladder yet so Paul rode the Bobcat’s bucket up to disconnect the hook. (6) As the sun when down the second gantry went up.
As suspected there was too much side way flex in the vertical beams. Most of this was because they were connected to the bottom beams using only their webbing and not their flanges. The problem was anticipated and easily corrected. Since the A-frame was no longer needed it was disassembled and the legs became braces between the ends of the bottom beam to a point in the vertical flange 12 feet up.
We were surprised at how easily the gantries can be rolled. It is best done with two people, especially in the up hill direction, but it only requires a firm push to get it moving. In fact is was so easy that we wrapped chain around the wheels to chalk them. Even then we had a bit of excitement the first night when a thunder storm blew in. I went out front to see how much the gantries would flex in the wind, and when the wind kicked up to about 20 mph, one started rolling away pushing the chain we used for chalks. Luckily it jumped one wheel off the the track and came to a stop before it reached the end of the rail and the ditch.
With a a little searching on the web about signs, I learned that a 70 mph wind puts a 22 pound per square foot load on a flat surface. The gantries have 30 sq ft in the top beam alone, and that is on the end vertical beams that act like a 20 foot leaver. I figure a 45 mph wind could likely blow the gantries over. To head that problem off we added dead men with chains that can be locked into the bottom beams.
Latter we added lights, and they are wonderful. No more moving a clip on light around or bugs flying up your nose. These are just flood lamps screwed to 2×4’s that are clamped onto the top of the cross beam using lag screws and large washers.
Gantries Finally Get Used as Intended
Flipping over her 5 ton half hull, and a bit of excitement.
…and with Electric Winches!
Flipping again but this time with Budgit electric hoist and not the Harbor Freight manual chain hoist. …what a difference $6,400 makes. Yes. They cost $3,138.76 each.
But buy extra fuses. These use 300v 1/2 amp glass fuses. When a weld broke while lifting a 600 pound plate the winch responded by blowing a fuse.
I purchased 4 very cheap Chinese chain hoist from CVF Supply, http://cvfsupplyco-store.stores.yahoo.net/ for $90 each. They only came with only 10 feet of chain fall so I had already planned switch the chain but that is not easy to do. After talking with a few chain suppliers I learned that there is not a very good standard for chain sizes and the Chinese are bad about following what standards there are. Oddly enough I measured the chain I used for turning my hoist and found it on a few sites but then learned that the numbers listed on the web may not be what they will ship to you since each manufacture’s chain is slightly different and they don’t bother checking it against what they advertise. I didn’t bother asking why they had numbers on their sites that they knew would might be wrong.
Chain is loosely grouped into grades for strength and approximate size. I wanted galvanize chain to replace the short 3/8 inch chain that came on my Chinese chain hoist so I found some grade 43, 3/8 inch hot dipped galvanized chain that was load rated at 5400 pounds. The link size was the close but not close enough.
(1) Unfortunately the 3/8 inch chain I got was just a little too big so I disassembled the hoist and added some weld to the main sprocket to make it big enough for the new chain. I had the same problem with the smaller chain used to raise and lower the main block.
(2) While I had the hoist apart I had a rather hastily thought out idea of replacing the chain pulley with a sprocket and the powering the hoist with a 12 volt windshield wiper motor. I already had the cast aluminum sprockets leftover from a previous experiment so I cut away the rim of the chain pulley and bolted on the aluminum sprocket.
(3) (4) The windshield wiper motor uses a worm gear and with the reduction on the chain sprockets it had no trouble turning the chain hoist. But what I did not calculate ahead of time was the speed. The wiper motor is only 80 rpm, the reduction from the sprockets brings it down to about 16 rpm, and while the chain moves, that is just way too slow. A bigger motor would solve the problem, but I didn’t have any laying around so I welded the original rim back on.