6/7/13 Boat Gantry Built
In order to get the CC Dory off its trailer and onto boat jacks so I can work on the bottom I need a boat gantry. A built-in boat gantry has been part my plan for the shop all-along, but I elected to wait until I needed it before actually installing it. So my project this week was building a boat gantry.
The big challenge for me was to determine what size beams to put up. I was surprised to learn how hard it was to determine the proper size. I simply wanted to be able to lift a boat weighing up to 5,000 lbs. But to find out how much weight a beam of a particular span, width, and height could support at a single point was just simply not easy to learn. Suppliers would not divulge the information for fear of being sued if the beam failed. They all said to "hire an engineer". So I enlisted the help of my soon to be son-in-law, Justin, a civil engineer.
I explained to Justin that I had a span of 14' and wanted to use Laminated Veneer Lumber (LVL) as a support beam as LVL is stronger than construction lumber. After some figuring using the LVL tables publicized by Georgia Pacific and his engineering know-how, he figured out that three 14' LVL beams 1¾" wide and 10" deep, bolted together side by side, ought to handle a 5,000 pound load at a single point. He suggested I go one size higher (12") to add a "safety factor", as it wouldn't be a great expense. That made sense to me so that became the plan.
I also put a 2 x 10 on the top and bottom of the LVL to form a wood I-beam in order to resist twisting and also to help better secure it the the ceiling of my shop. Justin explained to me that a beam doesn't fail when overloaded simply by breaking apart. Instead it twist's onto it's side and then breaks. So the wood I-beam made the most sense to me. I've probably over-built it, but this is a case where "better safe than sorry" applies for me as it is a one-man shop.
To support the I-Beams when under a load, I added removable lally columns. They can be removed, and stored out-of-the-way when the gantry is not in use so they are not an obstruction in the shop. The way I hung the wood I-beams they will be able to support their own suspended weight when not in use supporting a load. They are bolted from the bottom up into two roof trusses, and from the side into 3 studs.
With my wife's help I hung the I-Beam piece by piece from the ceiling and bolted it together as the pieces were put in place.
To actually do the lifting I'm using two Roughneck 3-ton Levered Chain Hoists that I bought at Northern Tools here in Duluth which I hung from nylon 3-ton Lifting Slings that I bought at US Cargo Control which were slung over the wood I-beams.