Tech Article : Riblets and your PWC

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  1. #1
    Tech Guru Resident Guru
    Join Date
    Feb 2002
    Fort Mohave, AZ

    Tech Article : Riblets and your PWC

    Riblet Technology … and your PWC
    On February 4, 1987, skipper Dennis Connor and his ten-man crew guided the Stars and Stripes racing yacht past the finish line at Fremantle, Australia, to recapture sailing's most coveted prize, the America's Cup. Representing the San Diego Yacht Club, Connor and Stars and Stripes scored a 4-0 sweep in the best-of-seven finals over Australia's Kookaburra III. The win was attributed, in large part, to a NASA developed surface applied to the hull … called “riblets”.
    Learn more at:
    The PWC version of this Story
    When Yamaha released the first 650 SuperJets in 1990, they were kind enough to offer me one for the development of our Group K Sleeper Kit. The peak speeds of the stock 650 SJ were a meger 38-39mph. However, once we finished our Sleeper testing, we had a boat that would run 45-46mph … but unfortunately it was so evil handling (in a straight line) that you could barely control it.
    I did most of my initial SuperJet testing at a small local So Cal lake, and was often joined by my buddy Rick, who had purchased one of the very first SuprJets. Rick was tinkering with his SJ too, and he had a bit of a head start on me because he had been riding/testing for a couple of months. Rick had custom fabbed a ride plate and scoop grate for his ski to help with handling. Needless to say we started drag racing the two boats to compare them. My sleeper boat was clearly more powerful than Ricks, but at top speed he could drive away from me like he was on rails, while I was trying to manhandle my ski into a straight line. Rick rode my Sleeper SJ and agreed that it handled horribly. With that, we started swapping his custom ride plate and scoop grate on to my Sleeper. To my disappointment, my Sleeper still handled horribly in a straight line, while Ricks SJ still handled great (even with my stock plate and grate on it). With that, it was obvious that the difference was the hull.
    My buddy Rick was a good rider, and a nice guy, but he had on riding habit that drove me crazy. Every time we headed for the beach, he would approach at speed, then kill the motor so he could coast 5-10 feet up the beach … and he did that a lot. The underneath of his SJ showed the countless deep scratches from all these “beachings”.
    It was then that it dawned on me. My older brother was a sailing enthusiast, and a big fan of the Americas Cup races. I remembered him telling me about the “riblet” coating technology that allowed the USA to win the cup back in 1987. This coating (developed by NASA for aircraft) was like the grooves of a record surface laid in a straight line from nose to tail. These “riblets acted like thousands of tiny rudders that made a boat (or aircraft) cut through the water (or air) with much better control. I suspected that Ricks countless “beachings” had inadvertently mimicked the effect of these riblets.
    With that, I loaded up and took my SuperJet back to the shop. I flipped the boat upside down on a trailer, and got some 20 grit sandpaper to make full length longitudinal grooves on the bottom of my (still glossy bottomed) SuperJet. When I was done, the entire bottom was covered with full length scratches, and there was no paint shine to it at all. I loaded up & headed back to the lake so I could run the same day on the same water. The difference in straight line handling was unbelievable. I could easily ride the boat at peak speed one-handed (something that was impossible before the hull sanding). Not only did the boat run on rails in a straight line … but it actually held turns much better too.
    A few months later I was at the jetski races chatting with a long time racer about the experience. He commented that in the early 440 days of IJSBA racing, it was routine for guys to tie their new race boats to the back of a jeep, and tow it up and down a sandy beach to accomplish same bottom surface finishing…. A hull that had been “dragged” always handled better.
    As years went on, and 70mph runabouts became common), it was absolutely mandatory to “sand” the bottoms of these 70mph boats … just so you could go in a straight line. We encountered many PWC customers who had gotten beautifull custom paint jobs on the bottoms of their boats …. But every one of those custom painted boats handled like crap until they “got sanded”.
    Unless otherwise stated, responses to all forum posts are based on my personal experiences working within the PWC industry, and developing high performance PWCs since 1987.

  2. #2 Is My Home Away From Home Matt Braley's Avatar
    Join Date
    Dec 2011
    Niceville, FL

    Re: Tech Article : Riblets and your PWC

    Great write up Harry. I enjoyed that.

  3. #3
    Frequent Poster
    Join Date
    Feb 2016
    New Jersey

    Re: Tech Article : Riblets and your PWC

    This post was a good read. Keep them coming!

  4. #4 Is My Home Away From Home Grumpy Old Guy's Avatar
    Join Date
    Dec 2003
    Sunny Fla

    Re: Tech Article : Riblets and your PWC

    Good stuff !!

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