by Markus McDowell | Jul 25, 2016 | Custom Engineering
Sometimes the image of a teeter-totter (see-saw) is used to explain how forklifts work. This analogy is okay as a beginning point about the physics of counterweight. Yet it hardly begins to address what is needed for lifting a boat.
The Teeter-totter Analogy
Imagine a teeter-totter that is 20 feet long. We want to place a 35-pound child on one side, 5 feet from the end. If want the see-saw to remain balanced, you would place a 35 lb weight on the other end, 5 feet from the end. It “counters” the child’s weight and placement perfectly. Simple, right? This is the concept of “counterweights,” just as on a forklift.
If you moved the child a foot farther out (four feet from the end), his leverage makes the see-saw unstable, and the child hits the ground, crying, because you are not an engineer. The same would happen if you placed a 45-pound child 5 feet from the right end.) Moving the counterweight back a foot, or adding the properly-calculated weight to it, would achieve balance. This is similar to how forklifts work.
The problem with this analogy is that a teeter-totter does not move, turn, brake, or go downhill like forklifts do.
Moreover, the shape and weights of children on a see-saw are usually not like loads lifted by forklifts—and this is especially true of boats.
Delving into Load Capacity and Load Centers
A better explanation uses the image of a forklift itself. After all, few adults would not be generally aware of what a forklift looks like. So, imagine a forklift.
Suppose that the load we wish to lift (and move!) is a large obelisk—a huge, rectangular weight. This obelisk is 40 feet long, 10 feet wide, and 1 foot thick. (If you have seen Stanley Kubrick’s 2001: A Space Odyssey film, you have the idea.) Our obelisk weighs 5,000 pounds.
Manufacturers let you know the capacity of a lift by telling you what weight (“load”) can be lifted at a certain distance out on the forks (“load center”). Let’s say this forklift has been designed to lift this obelisk, as it sits vertically on the forks, 2 feet out from the carriage:
The manufacturer tells you that this lift can hoist “5,000 pounds at 24-inch load center.” If you put the centerline of the obelisk 2 feet out on the forks, standing vertically, it will lift it. (At the moment, we’ll ignore how high it could lift it—that depends on counterweight, too, because of gravity and other forces). However, if you moved the obelisk one foot farther out on the forks, the lift would become unstable and fall forward.
Forklifts Move (Teeter-totters Do Not)
But there is more to consider. If the lift was designed to lift exactly 5,000 pounds at a 24” load center, and you braked too suddenly while moving it, the lift would also become unstable. Just like when you apply your brakes in your car, the stopping motion produces energy that transfers weight forward, and front of the becomes momentarily "heavier" than the back before it returns to normal. The load did not move forward, but the overall weight distribution did. (This is really an issue of mass, momentum, and the earth's gravity which creates imbalance.) The same would happen if you drove downhill—the vehicle becomes "heavier" in the front.
What we are talking about here is really the “center of gravity.” This is the point or division along a mass ("load") where there is the same weight behind it as in front it. That point is called the center of gravity, and it changed not only from shape to shape, but by increasing or decreasing speed, braking, and traveling up or down slopes.
Therefore, to ensure that our 5,000 pound obelisk can be transported safely while driving, turning, braking, and driving on slopes, it has to be capable of lifting _more_ than 5,000 pounds at 24” inch load center. A salesman might tell you, “Oh, you don’t want to buy that more expensive 5,000-pound @24” lift, when ours will lift 5,000 lbs at 24-inch load center for less money!” It might, but how quickly can you brake in an emergency without creating imbalance? How much of a slope can you traverse without losing the load? Most likely, the cheaper lift has less counterweight and strength in its structure.
If you only plan on lifting a single kind of weight, and never wish to transport it anywhere, then the cheaper lift will probably work fine for you. Otherwise, you may be well on your way to accidents.
Forks, Carriages, and Masts Matter Too!
Furthermore, lift capacity and movement are not the only considerations. A lift might be fully capable of hoisting a load at the capacity you need to the height you want. It might be capable of handling turns, slopes, and braking. But what if the steel of the forks, carriage, or mast is not high grade? What if the axles are at the minimum to handle the stresses put upon it?
The Bottom Line
Wiggins lifts are engineered with these issues in mind, and manufactured using high-quality steel and other components. Some have said that Wiggins forklifts are “overbuilt”—we say they are designed to be tough, dependable, and to get the job done safely. Other manufacturers often scrimp in order to undercut pricing. As the saying goes, “you get what you pay for.” Wiggins lifts are the standard by which all others can be judged.
Lifting boats raises a whole host of other physics and engineering issues—which Wiggins has been addressing for decades. We’ll look at the unique issues of marina lifts in a future post, and discuss how Wiggins solves those engineering challenges, too.
by Markus McDowell | Jun 6, 2016 | Press Release
The American Journal of Transportation has published an article on Wiggins Lift Company, Inc. Highlighting the beginnings in agriculture, the article by Marty Pilsch describes the company’s beginnings in the needs for a custom machine for field workers and the conditions of agriculture.
Now, known internationally as the premiere manufacturer of high quality, custom lifts, Wiggins services the marina, mining, military, construction, and agriculture industries with innovative designs and customers service.
Click to read the article abstract, or, if you are a subscriber, log in to read the entire article.
by Markus McDowell | May 23, 2016 | Custom Engineering, Marina
When a marina owner or operator wants to buy a marina lift, the first question is usually “what capacity?” How big of a boat does it need to lift, and how high?
The answer to that question is not as simple as one might think. In our last post (“A Brief Note on the History of Marina Lifts and Capacity”), we discussed how the terminology for forklift “capacity” was not developed with boats in mind.
The First Problem
In brief, the 36” or 48” “load center” terminology was not coined for lifting boats. Boats are heavy in the stern, light in the bow , and longer and narrower that regular forklift loads. Manufacturers began to specific 96-inch load centers (eight feet), yet even as early as the 1990s, boats had 10’, 12’, and even 15’ load centers. Accidents happened because of the lack of an easy and precise terminology.
The problem was exacerbated when marinas began asking to lift 40- and even 50-foot boats. Some manufacturers began using 144” load centers (12 feet!), but this didn’t solve the problem.
Operators just want to move boats, and do it safely. Using a 96” and 144” load center capacity is not the easiest or most precise terminology.
The Second Problem
Because boats are so long, with unusual weight distributions, they place heavier stresses on the carriage, mast, and forks of a marina lift than regular forklift loads.
For example, 5,000 pounds at 36″ puts 50% more stress on the forks and carriage than 5,000 pounds at 24”. When we lift a 42’ boat heavy at the stern and a bow that extends well beyond the forks, the stresses on forks, carriages, and masts are far more than typical non-marina loads. Accidents happen because some manufacturers do not build beyond the capacity of a typical 96” or 144” load center, necessary for these added stresses. (Wiggins Marina Bull are built 30% to 50% stronger than other forklifts designed for 96” load centers for this very reason.)
So, 96” and 144” load centers:
- do not accurately reflect the load center of any boat
- give no indication of the strength of the carriage, mast, or forks to lift any particular boat
The Wiggins Solutions #1: Build to the Boat
Wiggins spent many decades thinking through all these issues. We constantly research, test, measure, and innovate. We engineer, design, and construct our lifts to the largest boat a customer needs to lift—not to a 96” or 144” load center. Easy for you, standard for us.
The Wiggins Solution #2: MIPs
We use two capacity terminologies: the common “load center” (because it is expected), and a more precise and easy measurement of capacity called MIPs.
In the real world, no one is lifting a boat that weighs 35,000 pounds with a 96” load center (they don’t exist!). A 35,000-pound boat might have a load center closer to 240” (20’). A better measurement of the forces a boat will place on a lift is “millions of inch-pounds” (MIPs). An “inch-pound” describes how much force is exerted by a boat on a forklift per square inch, and takes into account weight and torque when turning or braking. How do you figure MIPs?
Weight of boat (lbs) x load center (inches) = MIPs
A 35,000 pound boat with a 20’ load center is 8.4 MIPs. Since Wiggins’ Marina Bull have MIPs in their model numbers, you know you will need a model W8.4 M2 or higher. (It would be listed as 52,000 lbs at 96” load center for continuity.)
If you have a Marina Bull W8.4 M2, and a boat arrives at your marina that weighs 36,000 lbs with a load center at 216 inches, can you lift it? Multiply 36,000 by 216 to get 7.8 MIPs—then get out there and move that boat with complete confidence!
Lifting Boats in the Real World
Wiggins model numbers are based on boats, not an out-of-date 96” load center. Do you want to know if a competitor model compares to the Wiggins W 8.4 M2? They might tell you that you need their model 600 which has a capacity of 60,000 lbs at a 96” load center. Will it lift your boat? Maybe, but how do you know? First, there is no 60,000 lb boat over 50’ long with a load center at 8’! Second, did they design the carriage, mast, and forks for that much boat? In order to lift the same boat as a Wiggins M8.2, you might need a lift of larger capacity from our competitors, because many manufacturers use the same carriage, mast, and forks across a family of marina lifts.
Wiggins builds our Marina Bulls to lift the largest boat you need to lift, and provides an easy formula for safe lifting capacity. A measurement that ensures the safety of your lift, your facility, your employees, and your customer’s expensive boats.
We will delve into the details of load capacities, strength of components, and MIPs in future posts. Join our mailing list to keep up!
