Took the HT out for the first time yesterday and had a near catastrophe- the shackle that held the forestays together went BLAM when we sheeted in but amazingly enough it held long enough for us to tie some trap lines to the bow tangs. We didn't have the spin pole on (no snuffer hoop yet... LONG story) which might have prevented the mast from coming down if it wanted to. Before anyone pulls out their guns... this was a stupid hardware failure and has nothing to do with Bimare/HT class/Jav2. I redid the standing rigging and didn't crimp the eyes into the originaly SS ring and used a oval shackle which may have been defective or just not strong enough. Amazing how much faith we put into 4-5dollar shackles. If the mast had come down backwards like that I can imagine the $$$$$

ANYWAY.. the real reason behind this post- there is a buzzing/vibrating sound when you get up to moderate speed. This happened on my 6.0 but I generally didn't give a crap. I know the sound comes from the foils but we didn't have the time to figure out which one given the problem I explained above. What truly causes this and how do you fix it because I know it is slow. Is it too much play in the board wells/bad fairing on the trailing edge?
Thanks

I would challenge that it is slow this way. There are plenty of catamaran sailors in the top of any fleet that have rudders or daggerboards that make some amount of noise. A bit is careful work on trailing edges and making sure that leading edges do not have some kind of snag will eliminate most of it. But consider this, with the noise you have an idea of whether you are going fast or not. If you are sailing along and the boat is making all kinds of racket then all of the sudden it is silent you know immediately that you should make some adjustment, right? For someone who is not on their boat all the time this could be the best way to know if you are keeping the pace you need to the whole time. It may not ne a bad thing. A little noise is not a big drag on performance.

Later,
Dan

I think there is a difference between "humming" and "screaming".

Humming happens at moderate speeds and then disappears when you break a certain threshold.

Screaming happens when you're just going like a raped ape.

The two definitely have different "tones" to them.

At least, this is my uneducated, ancedotal observation. Ya'll are welcome to blow it away with scientific, engineer-talk.

I had a 12kt and a 18kt "hum". I faired out the daggar and rudder trailing edges and removed the 12kt hum, but the 18kt hum remained. Over 18 kts, and the wind, water, and boat was making so much noise I couldn't tell if it faded out again or not....

Someone told me to fair the trailing edges unequally (like an airplane wing trailing edge) so that the edge does not vibrate as much as a symmetrical edge would.

In addition to fairing, having the correct mast and rudder rake should help too.

Hi All

If you go www.ahpc.com.au and look under the technical info, theres a document about noisy foils, I think written by Jim Boyer, might be worth a read, I can't remember all the detail, its been a while since I read it.

Regards

Boyer is on the right track, but I would add a
couple of things.

Generally the trailing edge lower 1/3rd of the foil is the offending part, and deserves attention first. Square
it off and then bevel one side at 45 degrees. His drawings
show about a 30 degree angle and thins the trailing
edge more than is needed. In fact, the thinner the trailing
edge, the more prone it is to flutter.

Take care of this, as vibrating the hell out of the
foil is bad bad bad for laminate structure
of the foil.

And how would mast rake and rudder rake affect it?

Mine hum at about 3/4 speed and then quiet down when I really start hauling [noodle] (either that or I no longer focus on the noise at those speeds). I like it for the reason mentioned... it lets me know when I'm moving along nicely and when I lose speed. It is not a loud hum at all, my son calls it "whales singing".

-Rob V.
Nacra 5.2

tell him that its the fat lady, and she's warming up.

In the Boyer article posted above he mentions how putting on an assymetrical trailing edge creates some pressure on the foils to fix the problem, I think it would be along the same idea. Mast rake and rudder rake will change the pressure on the foils too. It seemed to work for my rudders but maybe it was because I didn't have these things adjusted correctly at first, though the changes I made were not huge. The first thing I did was switch the sides the rudders were on just to see and it helped a little.

Guys:

It has been my experience that mast rake LOADS the rudders up, raking the rudders forward REMOVES the load. Just make sure you have a little weather helm. NEVER want lee helm.

Doug

Rudder rake doesn't really remove the load, it just changes the way it feels to the person steering.

Hokie:

You may be be right. BUT in a long race, holding the ariba with two fingers is MUCH sweeter than having to PULL the %$$&**%^&^% <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" /> out of it. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" /> <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

Doug

I went out today for the first time since doing a bottom job and the humming was a deeper tone and started (and stopped) at a lower speed. I would guess it started around 5 knots and stopped by 8. I didn't get much faster than that since winds were pretty light today, but at least I was able to determine that it did indeed stop and it wasn't because I couldn't hear through the splashing. I haven't done any work to my rudders or daggerboards, but I did change the standing rigging which might have changed the mast rake a little (not much though).

-Rob