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  1. #51

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    Quote Originally Posted by Dockside View Post
    Yes I've been welding for 20+ year and do heavy collision work for a living. Due to the high water levels I couldn't use this syle lift, it keeps coming up to top of the Seawall.

    Here's what I ended up doing.
    What were the calculations on those "pool noodles"? I fear they may not be up to the task.

  2. #52

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    Wow I just stumbled upon this thread. I bet many people giving advise here have never been behind a welding helmet in their life and never seen a puddle either, be it TIG MIG or stick (keeping the process basic here). You should be over at a plow forum I hang out on. The so called "engineers" have no clue in real life situations. I have fixed countless factory engineer fopars on quite a few snow plows from different companies. Just my .02. Take it for what it is worth. I have some examples of my work here in other posts.
    T.J.

  3. #53
    Bob 1tommygunner1927's Avatar
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    Quote Originally Posted by TJS0712F View Post
    Wow I just stumbled upon this thread. I bet many people giving advise here have never been behind a welding helmet in their life and never seen a puddle either, be it TIG MIG or stick (keeping the process basic here). You should be over at a plow forum I hang out on. The so called "engineers" have no clue in real life situations. I have fixed countless factory engineer fopars on quite a few snow plows from different companies. Just my .02. Take it for what it is worth. I have some examples of my work here in other posts.
    T.J.
    LOL....its "FUBAR" F'd Up Beyond All Recognition.

  4. #54
    guys,

    this has been a great read - As a pwc mechanic for the past 10 years, and a mechanical engineering student.
    1) Engineers make mistakes : oh god yes. The amount of students, and professionals alike that don't use or practice common sense is down right scary.
    2) Given the proper dimensions of the materials used in this lift, 2-3 sketches could be used to conduct a static analysis that would be entirely realistic ( as someone else mentioned, distance to center of mass, length of arms, height of the lift, fixture options, etc
    3) This would be interesting to actually test in solid works. I would be happy to do so, given some simple drawings to work from - besides, i need the practice!

    Lets give this guy a break. Calling the manufacturer was a great way to get an idea of where he stands. Your methodology mentioned earlier about mounting a tv, is sound and applies in many acts of fabrication. Personally, Whenever a design is tested, ( in school or in the real world) you try to consider a factor of safety:

    For those that aren't familiar with the concept, you basically try to make your design's materials only encounter half of the stress that would be required to encounter a yield in material.
    There are many charts available online, that can show you quite easily what typical square tubes can handle.

    The other reason for a factor of safety consideration is simple: fatigue and creep. The material over time will sag, just like wood. Someone here mentioned a jarring motion, causing a metal failure. The extra size up, will often take care of this . In this case since you are making it, 1/4" square tubing wouldn't cost much more, and wouldn't weight a whole lot more, either. But you wouldn't have to worry about fatigue, provided your fixture is sound, and corrosion control is taken into consideration. Even with welds, and galvanization, I would strongly consider Stainless hard ware as well.

    Modern Engineering often goes for optimized designs, that only handle the load in a designated orientation.
    Take a look at how jet pumps from the mid 2000's compare to the newer FEA optimized designs. They are thinner, and "stronger" - but only in the orientation of how it is installed. Mishandle a newer jet pump housing, and it will break.

    Sorry for the lengthy response, but this post really resonates with me and what I have encountered in our industry, as well as with engineers from other backgrounds!

    For anyone else thinking to dive into fabrication, go onto engineering toolbox to use their online calculators, and available data sheets. Save time and money, and maybe even a ski!

    I wish you good luck on your project!

  5. #55
    steve45's Avatar
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    I'm a degreed mechanical engineer. I am NOT a registered professional engineer, which means that I can't tell you how to build something like this for liability reasons.

    Anytime you are building a device to lift objects or people, you MUST have a professional engineer evaluate it and sign-off on it (the exception possibly being that you build it for your own use). If you drop the 'Ski in the water, I can guarantee that your insurance company won't pay for any damage unless your lift design was certified by an engineer and the welds were done by a certified welder.

    That said, Dockside, I'm curious why you're planning to use round pipe for your vertical column. You surely must know that a square column of the same dimension would have a higher polar moment of inertia, and hence would be less prone to buckle.

    As Peter mentioned, it's not unusual for a lift to move in a jerky fashion, which could greatly increase the load on your components.

    Have you got adequate means for water to drain from this device to prevent corrosion? Will it be galvanized? How about stainless (which doesn't have the same properties as steel)?

    I've got a sling that I've used to lift my 'Skis for the last 5 years or so. In spite of only occasional use, it broke last summer. I had to buy a new one and it won't fit my newer 'Skis. Now I'm building a custom sling. It will have the capability of lifting more than a ton. It will NOT have nylon straps, but rather stainless steel cables.

    I wish you luck with your project, but I have to say that I agree with RGUN 100%.

    Side note: today's newspaper had a story about a 4-year-old boy that is on life support because a tree house at a relative's home fell on him. Just sayin'...

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  7. #56
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    That treehouse story was a heartbreaker

    Itís unfortunate that good plans promptly stamped and approved results in fatalities when poor execution is put in the mix

    Typically balconies designed for load x fail when load y is applied during a party if built properly load y should not cause a fail but they did not let the concrete cure long enough. That seldom shows on an inspection unless the take core samples and that is typically done on multi story buildings

    Static vs dynamic loading (dreaded bounce) also is an issue. Perhaps the cause of some of the accidents that made the news last year

    A hard landing on a commercial airline can cost 6 figures for repairs before it can fly again

    I got asked for details on the welder who put the hitch on my work truck

    They would not insure any towed trailer for 30k (two full sized late model pwc) until I provided details on his certifications

    Bottom line

    You can have a fatality even with a commercial lift if improperly installed or maintained

    Iíd say get one installed by a pro as youíll lose the property the moment somebody gets hurt badly on a diy construction job

    And they will

    I paid a licensed contractor to install a new roll up at my shop. Why?

    In a word

    Liability

    I could have done it but I sleep better at night knowing the installer has a multimillion dollar liability policy


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