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Cavitation question with turbo fins in Classic...
http://www.hobie.com/au/en/forums/viewtopic.php?f=11&t=5602
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Author:  JimL [ Fri Dec 15, 2006 10:18 pm ]
Post subject:  Cavitation question with turbo fins in Classic...

If I short stroke very quickly (in my Classic with Turbo fins installed), at about 5 1/2 mph or so the boat will intermittently make loud banging noises and it feels like the chains are slipping on the sprockets. When I stop and check, there is nothing wrong.

Has anyone else experienced this? I'm starting to suspect the drive is sucking air down the blades and cavitating. I cannot imagine what else it could be, but it's loud enough everybody around thinks you've broken your boat!

Thanks for any ideas you might have.
JimL

Author:  Roadrunner [ Sat Dec 16, 2006 11:40 am ]
Post subject: 

Hi JimL,

If it feels like you're skipping but nothing is amiss, then it is possible you could be sucking air. This happens to me when in moderate chop or trying to ride boat wakes, when the fins can grab a little air; but not on smooth water.

Mine doesn't make any inappropriate noises though either, so I'm wondering if your chain is snapping against the sprocket edge. Do you have the old style drive (stainless sprocket)? Just for drills, it might be a good idea to inspect your chain tension and drive shaft bushings (older style drive only), and lube your moving parts (including the chain) to see if it makes a difference.

The following settings work well for me: the front chain should have no more than 1/4 " give per side (with a good squeeze) -- 3/16 is better; the rear chain is good with about 1/8"; the idler pulley cable should also have about 1/8" squeezable give per side. Less than these and you start picking up added friction; more and it gets a little sloppy and more vulnerable to chain skips. The tightening procedure should be in your Hobie manual (also available on line if you don't have one).

As a final thought, make sure your drive is well secured in its well so it's not moving around. 8)

Author:  joep [ Sat Dec 16, 2006 12:35 pm ]
Post subject: 

In addition to what Roadrunner suggests, check to make sure that the notches in your masts are lined up with the set screws and that the set screws are seated properly.

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