...And that ain't good.

Anyone know what to do about it? I put the teflon shims in, I scraped the trailing edge with scissors (as per On the Wire).

This hum is loud and I can feel it slowing the boat. Yesterday, my GPS clocked the hum starting above 8-9 mph. And it didn't stop if I went faster (even up to 18.5 mph top speed yesterday. Yahoo!) But you know, as a Hobie sailor, you always want a little bit more...

So, please, advice, comment, tips, fokelore...

Eternal thanks,

Al
Carumba 16 - Seattle

Well, file or scrape your edges a bit more. It has always been the trailing edges of the rudders in my experience. Make sure you get the tips too. I wouldn't go past the centerline of the tip though. You don't want to make them chip easy.

It took me three sessions with a rasp to do my first set because I didn't want to take off too much. After that I usually got it in one session.

cheers
Bill

The rudder problem is due to the shape of the rudder that hobie makes so what type of rudder is it? Sand down the whole rudder a little it will make you go a little bit fast and you would notice the hum will dim abit. The edge of my rudder is thin as and i cant get a hum easyly the only time i could get the hum is when i pushed my boat as hard as i could in 42 knotes of wind with the boat flatish. Well It comes down to experiments. have fun

They are the stock plastic rudders. Nothing fancy.

Just scrape down those trailing edges, eh? What kind of rasp do you use? And how sharp do you make them?

I used a big file that took off shavings but anything coarse enough to take material off should work. You don't really want them sharp or they will chip easy. You do want to smooth the trailing edge. When the rudders are new they have kind of a bulb on the trailing edge so you need to taper the sides of the rudders to the edge leaving just a tiny flat on the trailing edge.
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/ \ crude ascii representation

that tiny flat should be like 1/16" or so.

cheers
Bill

This is exactly what I did when I owned a H16. I went from lots of hum to none at all. Sort of missed it later,
Jack

Thanks guys. I'll give it a try Friday, when I'm taking off work to Go SAILING!

I use a sanding block with 180 grit paper to do mine, and I put a sharp v on the trailing edge. No hum whatsoever!

The scissors thing just doesn't work very well.

David

What you are trying to do is knock off the radius
at the trailing edge, this is where the water tries to follow
the contour/radius of the trailing edge causing humming,
rather than flowing straight aft.

I have been successfull with pulling a sharp knife with
pressure along each side of the trailing edge knocking off
the radius, and chamfer it at 30-45 degrees until the
trailing edge becomes 1/16". Takes about 5-10 min per rudder.

Here is a little tech piece from the Hobie Cat support pages ( Hobie Cat Support Pages)