Lost & Found
Jack not only drew the hull for the sailboat, but he also threw in a rough model for the tender, “Lost and Found”. The design has a couple of great ideas in it. It’s basically a RIB or Ridged Inflatable Boat but instead of inflated pontoons which wear out and leak it uses ridged foam that is sandwiched between two sheets of aluminum and which is held in place by a vinyl cloth cover. The foam will extend 6 inch beyond the aluminum sheet to provide a soft bumper that wraps around the boat. And squared off nose gives it a good surface area to push against hulls for moving boats around as well as an elevated work deck.
We made the decision to scale it down from 20.5 ft to 16 ft so it fits onto the sailboats transom easier. To convert the model into plans I dissected it to make it easier to measure and then created a CAD drawing from the the pieces.
After the plan is in CAD it is easy to scale it as needed and then start the cycle of printing it out, cutting it out, hot gluing it together and adjusting the CAD drawing for things that don’t fit nicely together.
I cheated and use our CNC cutting table. By putting an ink pen in the router I simply have the pattern drawn onto poster board. See more about the CNC table here: Ballpoint Pen CNC Tool
Poster board is about the limit for a 16 inch model; the heavier card stock works much better even when I increased the scale to 1.5 in to 1 ft which makes the model 24 inches long.
Gripes? Where do they come up these? A gripe is a line secured under a boat to hold it in place on a davit. And a davit is a marine jib crane.
We asked our viewers to help with the FEA, or Finite Element Analysis which is a computer process that predicts if a structure is adequate for a specific load. My engineering background is “that looks strong enough” and all items are measured by the number of pounds they sustained before doing permanent damage to the structure. Engineers work from the other direction. They start with a design load then build a structure in the computer and plug in a “safety factor” such as 2.5 which means the structure should actually only fail when 2.5 times it’s design load is applied. The FEA simulation identifies the portion of the structure nearest the safety factor. Unfortunately this is a complete waste of time on us farm boys who know they do this and will apply twice the recommended load with little concern. …unless it is Chinese made.
Francys Therrien from Montreal, Quebec stepped forward and modeled our davits in CAD, ran the FEA process and generated a detailed report. It was best to run the FEA without the attachments to the pilothouse roof, but we will attache them to the roof as they will add support to the roof as well as gain some support from the roof. The bottom line is that each davit can be loaded with 3371 pounds and it stay within the 2.5 safety factor. So will I be willing to put 7000 pounds on one davit? Hell Yes!
Thank you Francys!