Commander 147

[Commander 147]

Well...after feeling unsure of the actual design specs needed to support my mast and knowing I did not want a problem down the road I decided to enlist the help of a professional.

I started off by sending an e-mail to Jim Taylor who designed the entire Precision line including boats up to 28 feet that used strong back designs. He has also been involved with the design of the Sabre Spirit a 36'-8" daysailer along with 5 other Sabre boats. And that just touches the tip of the iceburg for what Jim has worked on. When I contacted him he put me in touch with Steve Koopman who is the marine structural engineer that Jim partners with on his designs. Steve's business is SDK Structures and he has been involved in projects like Alinghi, and Speed Dream - the quest for the fastest monohull on the planet. So I feel very comfortable with his ability to produce sound structural design work.

The cost to have Steve provide me with an engineered design that would allow me to safely support my mast turned out to be in my opinion quite reasonable. So a deal was struck and Steve has designed my strong back for me. Unlike most Ariels and Commanders my strong back has a pretty wide unsupported area that is designed to be as wide as 39". I wanted the more open feel that this would give me in the small commander cabin.

Steve tells me the loading on this beam came in higher than either he or I had first suspected. He told me the compression loads are maxing out in the 7000 lb range. So to manage the load with my 39" wide unsupported span I will be using carbon fiber caps top and bottom on the laminated mahogany beam. Here is the design I will be using see the first picture below.

As of this last weekend the old bulkheads are out and the old tabbing ground down a lot to allow for the installation of the new bulkheads and beam.