my buddies hobie 18 screams when we go about 15 knots. why does this happen. kinda sounds like the rudders...
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FYC, Nacra 5.2 "Chris's Flyer" & Nacra Playcat
Previously owned: Trac 14, H14, H16, H18, N5.0, G-cat 5.0
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Boat screams when underway
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Posted: Apr 14, 2010 - 06:52 PM
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Posted: Apr 14, 2010 - 07:16 PM
I scream when I'am on my 18 to~~~YYYYYYYEEEEEEEEHHHHHHHHHAAAAAAAAAA... It's just the rudders/ dagger boards, just enjoy the ride & hold on..
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Posted: Apr 14, 2010 - 07:53 PM
its more of a hummmm, right?
above 20 my rigging sings
you can gently sand the rudders with fine grit to smooth them up
and you can shim them up to reduce wobble
not sure if this will work but on sunday i gorilla taped up my tiller and crossbars to reduce play -
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Posted: Apr 14, 2010 - 07:58 PM
it is definitly the rudders. we tried changing the toe but it did not really help. instead we just pick up the windward rudder and sail on. my 14ft cat did the same thing. i kinda like it becasue it scares the monohullers when they come for a ride. it is erie
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FYC, Nacra 5.2 "Chris's Flyer" & Nacra Playcat
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Posted: Apr 14, 2010 - 09:35 PM
try the ankles too! -
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Posted: Apr 14, 2010 - 10:41 PM
In Learjets we can pull the circuit breakers on the overspeed warning and see how fast we can go before we get aileron buzz. Usually around Mach .86 or . 87. However in a Hobie 18 I would think its the rudders. They need to be shimmed to take out any play or any wobble in the rudder system. I use to get it in my H16 when I first put the black fiberglass rudders on it( circa 1980). It lets you know when you are going fast.
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Flightlead Bimare F18 HT SpaceCoast
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Posted: Apr 15, 2010 - 09:04 AM
so far my cat only will do mach .04... i will try pulling the fuses this weekend and see what she will do...
Scotty: she's starting to shake!
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Posted: Apr 15, 2010 - 01:06 PM
My wife did a medical transport on a Learjet recently. Boy can those planes move! The got from Winnipeg to Toronto in something like just under 2 hours! And they were so high, they had to put extra screens over the windows for the glare!
My rigging only hums a little, but then I haven't had it out on a big lake yet.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: Apr 15, 2010 - 02:20 PM
I use to fly Air Ambulance in a Learjet. I've made many night landings during snow and blizzard conditions into
Toronto and Kitchner....I never was able to get rid of the buzz/scream in the black rudders on my H16, even with shims.
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Flightlead Bimare F18 HT SpaceCoast
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Posted: Apr 15, 2010 - 04:35 PM
Search hobie rudder cavitation on google or similar.
http://www.hobiecat.com/support/tech/hum.html
Try that and see if it helps. On the hobie forums there's tons of info on the subject. -
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Posted: Apr 15, 2010 - 06:55 PM
Ours does the same thing. The kids love it though as it only happens when we are really moving so I haven't looked for a cure. -
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Posted: Apr 15, 2010 - 07:59 PM
it is a vibration and probably disrupting the water-flow over the rudder and creating drag. it is probably such a small factor that i personally would leave it for the reason Steve mentions above.. it only happens when your really haulin' and at that speed.. your powered up... who cares ..
unless you are a racer.. then its bad -
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Posted: Apr 16, 2010 - 01:20 AM
I wouldn't look for a cure for it.... I think it sounds kinda neat!!!!
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~ Vietnam Vet 69-71~ 17 Hobie w/big jib, ~18 Hobie mag,~DN Ice sailor,
and other toys.......
~~ I live in NY state on the north shore of Oneida lake in
Bernhards Bay. ~~~~~~
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Posted: Apr 17, 2010 - 06:29 PM
The humming is from the rudders. Take a sharp pair of scissors and go over the trailing edge on both sides of the rudders. Open the scissors and scrape/file down the edge on both sides. When they were manufactured there was a bit of a rise formed from the molding process at the trailing edges. This rise or bump needs to be removed making a smooth flat tapered edge. -
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Posted: Apr 18, 2010 - 05:03 PM
Vibration/buzz = fatigue, & eventual failure. I would try to get rid of it. Do a search on the Hobie forum. I had nothing to do in Hong Kong one layover & spent several hours reading that forum. One of the Hobie reps posted a detailed precise on the problem, along with an easy fix.
http://www.hobiecat.com/community/viewtopic.php?f=34&t=2031
Look on this forum, MAtt Miller posted quite a bit of good Cat knowledge. I don't know how much it would slow you down, but from aeronautical engineering knowledge, the drag goes up on a J curve when you start to vibrate. Cavitation on o prop also drops a very large amount of useful power.
I can't imagine pulling overspeed breakers & trying to get ailerons to buzz. We were taught that you would live quite a bit longer on the early Lears by slowing down a bit. The Boss would never notice, & you stayed out of the zone where they tended to go into a Mach tuck, or shed parts, numerous Lears were lost to that problem.
They used to have a reputation for being fast, but everything else caught up, I think the Citation X is the fastest Biz Jet, nearly Mach .92. We only did .82 in the Airbus 340, & the 777 cruises nicely at .84. They can go faster but fuel costs keep your fingers off the cost index button. We used to run the Lockheed L1011 Tri Star at nearly .88. Of course that is only true airspeed, ground speed is what gets you to the cold beer before last call. My personal best is 710 kts in the 777. We were trueing at 480, & riding a 230 jet right up the pipe crossing Japan, en route Hong Kong Toronto.
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Posted: Apr 18, 2010 - 05:39 PM
i liked taking people out for the first time and watching there eyes when the boat started "singing", it added to the thrill. if i could have just got it to shoot sparks and flames too! when i bought my prindle, i was dissapointed that it didn't do it. its kind of like the sirens on the old german stuka dive bombers, striking fear in the poor people who hear it.
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