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PostPosted: Tue Jun 02, 2009 10:00 am 
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Joined: Fri Mar 23, 2007 8:12 am
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Location: Florida
First let me compliment Hobie on the improvements in the 2009 Island hull.

Wife & I have used & loved the 2007 model since Fall of 2006, but the '09s refinements are impressive. The deeper port side drink holder, better seat scupper plug holes with little wells, click 'n go drive, better pockets, ect. Really impressive stuff!

Now, this is the first time using the up/own rudder lines - which seems to work great and I have had no problems. However, once the boat gets up to a fast speed - about 7 mph there is a definite humming and vibration coming from the rudder I believe. I have handle bungied all the way down. No humming at slower speeds.

I can feel it in the tiller handle and the hull and pretty sure it is in the stern rudder area. The sound it makes is like tie down strap vibrating in the wind while driving.
Never had that on either 2007 boats with older up/down single handle.

The sound is not entirely unpleasant, in fact it adds a sensation of speed. 8)
The Island is literally "humming" along :lol:

Q. Has anybody else experienced this phenomenon?

Is this a result of the bungie cord down line acting like a guitar string when attached to the rudder?

I assume this vibration is also not a problem of something that needs adjusting?


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PostPosted: Tue Jun 02, 2009 12:57 pm 
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Likely similar to our plastic molded rudders on catamarans. They hum at speed due to a foil shape issue related to the molding process.

http://www.hobiecat.com/support/tech/hum.html

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PostPosted: Tue Jun 02, 2009 4:37 pm 
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Location: Maui, Hawaii
All of our AI's (older hulls and new 2009's) hum over about 8-9 mph, mostly when we're sailing downwind, surfing the waves. I thought the hum was the boat just saying "OH, WOW!" :)

Kayaking Bob


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PostPosted: Tue Jun 02, 2009 7:51 pm 
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Location: Florida
reconlon wrote:
All of our AI's (older hulls and new 2009's) hum over about 8-9 mph, mostly when we're sailing downwind, surfing the waves. I thought the hum was the boat just saying "OH, WOW!" :)

Kayaking Bob


Good to know! I kinda like that "feature"

I did not have my GPS on me on that trip with the new boat, but my guess of 7mph might be a little low. Yes this was downwind in about 15+mph wind.

The first time I heard it had me wondering, then I got it to speed a few more times and there it was again.

Well, the humming adds to the feeling of speed - like hearing a well made sports car's engine revup.

Heck, I though Hobie had added the hum to the 2009 boats to make then more exciting. :lol:


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PostPosted: Mon Oct 05, 2009 5:21 pm 
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Joined: Fri Sep 25, 2009 9:11 am
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Location: Keyport, WA, USA
Hull speed on a 16 foot boat is just over 5 knots or about 6mph. So you are pushing over your bow wave and starting onto a plane around that speed.
If you have access to a planing speedboat, try going from no wake speed up to planing as SLOWLY as you can. Speedboats will also shudder, but you usually just jump on the throttle and accelerate through it so fast that you don't really notice. As you go over the hull speed (1.34 times the square root of the waterline in feet gives hull speed in knots) you will notice the stern will squat down as it sinks into the trough of the bow wave. Somewhere in there it will finally crest the bow wave and zip off merrily, free from the bow wave restriction.
Sort of like breaking the sound barrier. Most sailing hulls that can plane will start to shudder, and set up some interesting harmonic vibrations on their way onto a plane.
Note also that your GPS is giving you speed made good, and not actual speed through the water. You could convert if you are tracking your speed and direction with the GPS against the speed of any water currents, but that will involve some trigonometry.
At any rate, it would only indicate that everything is working extremely well, including the operator - it's not easy to get a sailboat up a plane!


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PostPosted: Thu Oct 08, 2009 10:34 am 
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Joined: Tue Jul 28, 2009 12:16 am
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Location: HISC Chichester Harbour UK
I noticed that mine got a definite vibration through the rudder when I sailed at a reasonable speed with the Turbo ST drive fins in the up position. This disappeared when I moved them away from the hull. It didn't do it with the original fins fitted. Wonder if you are experiencing the same thing?
I intend to sail with the fins approx 1/2 way down.

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PostPosted: Fri Oct 09, 2009 4:10 pm 
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Joined: Thu Aug 16, 2007 2:25 pm
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Location: Central Coast NSW Australia
rokraider wrote:
I noticed that mine got a definite vibration through the rudder when I sailed at a reasonable speed with the Turbo ST drive fins in the up position. This disappeared when I moved them away from the hull. It didn't do it with the original fins fitted. Wonder if you are experiencing the same thing?
I intend to sail with the fins approx 1/2 way down.

I've experienced the same Yakaholic and rokraider. I thought it was coming more from the drive than the rudder though. I'll have to pay more attention next time it occurs.
At speed the turbo's do flutter/vibrate as well when up against the hull. That's why I prefer to remove the drive if conditions are right. At about 45 degrees the drive is quieter when under sail only.

Steve0 wrote:
Note also that your GPS is giving you speed made good, and not actual speed through the water. You could convert if you are tracking your speed and direction with the GPS against the speed of any water currents, but that will involve some trigonometry.

SteveO,
I find the Hobie pitot tube helps with estimating current.
Normally the ball is showing about half my GPS km/h speed.
If its not the the difference is due to the current (or some weed is blocking the intake! :wink: )


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