Building the Pentwater Yacht Club Boat Weighing System
David Roseman
May 5 - July 22, 2006
The Ensign is a one-design class of sailboat, meaning that, in theory, all boats are equal. To help ensure this, the Ensign Class Association has recently added a rule calling for each boat to weigh no less than 2,800 pounds. With the fact that the PYC is hosting the Region V championships this summer, combined with our very active fleet, we needed a way to easily and accurately weigh the boats.
I have been working with electronics most of my life. I have often said that I know just enough to be dangerous, and that has not been challenged. I felt that the best way to weigh the boats was to use load cells to suspend them, and electronic readouts to give the results. Using Google, I found an inexpensive source for the load cells, and drew up schematics for the electronics.
Frode Maaseidvaag volunteered to take on the job of building the electronics. Frode was Director of Research for Ford in Europe, and has a PhD in Biomedical Engineering, so it seemed reasonable to trust him with the job. As usual, he had a better idea. He found some surplus, very high quality, amplifiers.[1] These far exceed our needs, but were very reasonable (cheap). He emailed the manufacturer, and they supplied all of the old manuals. He then enlisted the help of Ray VanderBok, a highly-qualified engineer with years of experience with this specific amplifier. They wired things together in a few hours.
Frode's next door neighbor is Greg Harrison, whose background is in art and philosophy, and who is a very skilled professional woodworker. Greg built a box to house the electronics [2], which we covered with epoxy for weather protection. Then the problem was getting the box and electronics from Ann Arbor to Pentwater, since Frode was on his way to Washington. Mike LaHaye volunteered that he had business in Flint, so he and Greg agreed to meet at Brighton. Tony Sisson happened to be in Grand Rapids, so Mike gave him the device. It was in the next day-faster than Fedex, and a good deal cheaper.
We needed a way to calibrate the load cells, and decided to buy a calibrated unit from the internet source, and use it to calibrate the other load cells. We needed some steel for this, so we contacted Jay Petter, longtime owner and president of Pentwater Wire. Jay, Joe Nameth and I spent an enjoyable hour or so at Pentwater Wire. With the help of Paul O'Grady and colleagues. we left the factory with 4 nice pieces of ½ inch thick steel. Ted Cuchna agreed to help design and fabricate the test stand. Ted has spearheaded very large construction projects (for example, HVAC for the Sears Tower ), and is an expert metal worker. Jack Patterson, who has a huge inventory of marine parts, and many years experience as a sailboat rigger (among many other talents), provided steel for the backbone of the test stand. Ted, with a little help (hindrance?) from me, welded up the jig and provided some key parts. The fabrication was done at the Pentwater Artisan Center, which was built by Gene Davidson. This is a fantastic community resource, with a very wide variety of tools.
Jack Patterson then provided some heavy-duty rigging parts to complete the stand. I painted the steel, and it all looks pretty sharp.[3] This work was done at Patterson Marine. A couple of linking straps needed to be shortened. This was done at the Artisan Center, again with Ted's help. Excellent suggestions were received along the way from Arnie Samuel, Tom Sturr, Gordon Veldman, and Tony Sisson.
The first boat weighed was the Sisson's. Tom Sturr and I set things up, and Tom, Jack and I did the weighing. All went smoothly, and Tony's boat met the weight requirements, so everyone was happy. This was before we realized that the geometry of the lifting system overstated the boat weight.[4]
As far as I know, everyone had a good time putting this system together. At usual consulting rates, the project would have cost about a jillion dollars. Furthermore, it would have been very difficult to buy the talent that contributed to the project. Maybe this all could have been accomplished anywhere, but I doubt it.
The weighing at the Regionals went smoothly, except that the stringers that we made to prevent the geometry problem were a couple of inches too wide. They caught on the uprights, and we managed to fray a lifting cable. Gary Nicholson drove to Ludington for replacement cable, and a couple of our visitors jumped in to help. One of the guys (I think it ws Dave Sligh-correct me if my memory is bad) worked with me to pass a guide rope, and Bob Conkey and his son climbed the lift to string the new cable.
Was this all worth the time and effort? I'm not sure. So far, there doesn't seem to be much correlation between boat weight and race outcome, although I suspect it will take a few seasons to know. In our Regionals, the lightest boat did win the event, but the boat was sailed superbly. The project has been fun, and has helped focus attention on the importance of the class rules.
If the Class continues to keep the minimum weight in the rules, we will probably rebuild the electronic. Version 2 will use instrumentation op amps to condition the load cell signals, and analog-digital converters and an imbedded microprocessor. Thsi shoul dbe substantially more accurate, and less fussy, than the present system. We'll see.