Bobcat Questions

[crsmith]

I finished building my Bobcat Sailboat (aka Tiny Cat) about a month ago. I have about 33 hours sailing the boat and have a couple of questions. When dead running the rudder hums. This does not occur on a beam reach or any other point of sail. What might be causing this? It is not a major problem, but I am curious about what might be causing it? A second question is where can I purchase an “over the side” type of speed indicator. I have seen this speed drag in footage that someone posted on this forum.

[Tom Robb]

Did you make the rudder per the plan? IIRC, the plan shows no sharp trailing edge, rather a sort of blunt notched sort of thing that allegedly stops the periodic wake turbulence that causes the humming.

[crsmith]

Yes, I followed the plans and have the "notch" in the trailing edge of the rudder. The plans state that the notch is to reduce turbulence at the trailing edge of the rudder.

[crsmith]

Not getting much feedback. Does anyone know what the "drag overboard" speed indicator is called?

Thanks

[David Geiss]

Hey CR, notice that the Bobcat has what looks like a daggerboard arrangement.
Maybe a silly question, but are you pulling the daggerboard all the way up when you are running before the wind. Also, looks to be a pretty big barn door type of rudder. Maybe those more knowledgeable than I will chime in, but might consider pruning down INCREMENTALLY until you get the performance you are looking for.

Good sailing takes into account more than just the rudder in maintaining course, ie trim, heel, ballast, sail tuning....

I had a similar situation on an open canoe I rigged. It was a series of reducing the immersed portion of the rudder in profile (bronze plate) until all unwanted hum was eradicated.

Just some thoughts...happy sailing!!!!!

Dave

[James McMullen]

I don't know what you drag overboard to find your speed, but I do use a GPS regularly, which I find very useful indeed. A GPS will tell you your actual speed over the ground as well as helping you figure out how much actual leeway you are making--both far more important measurements for navigation than just how fast the water is moving past your hull.

[I, Rowboat]

Hey, how much firewood can that Bobcat process in an hour?
http://www.youtube.com/watch?v=YeanPDO-D6M

[Lance F. Gunderson]

About the speed-through-the-water device: I once had a tube which loosely resembled a large letter J or an old fashioned skin diving snorkel; it had a ping pong ball inside and calibrated markings on the outside; when placed overboard with the curve of the J facing forward, it indicated speed through the water by the height of the ping pong ball. It worked great and seemed to be accurate. Cheap too. Regrettably I sold it with the boat it was aboard and have never seen another one. Making your own should be easy if you could determine a scheme for marking the outside of the tube. However, I find that now after many years of sailing that I can quite accurately guess the speed through the water by how fast the bubbles are passing the waterline.

[Bobcat]

There was an article in Woodenboat at one point about making such a device. I don't remember when, but I do remember that it was not difficult.

I can't help you with the humming rudder except to say that I have never noticed it on my Bobcat. I have never missed have a way to measure my speed either.

[I, Rowboat]

Hmm. What you describe is a pitot tube. It should be easy to make with rigid clear tubing. It could then be calibrated using a GPS, provided no currents are acting on you.

[paladin]

Look for the Luhr-Jenson Trolling speed indicator......available from Cabellas....
Basically a calibrated ping pong ball that you drag thru the water......or use your second hand on your watch and a chip of wood.....drop chip from bow, check time for the chip to pass the stern....speed will be .6 times the boat length in feet divided by the time in seconds.....

[Lance F. Gunderson]

Hmm. What you describe is a pitot tube. It should be easy to make with rigid clear tubing. It could then be calibrated using a GPS, provided no currents are acting on you.

Say, isn't it a pitot tube that is suspect in the recent French Airbus crash?

[crsmith]

Thank you, for the information.

[Bob Triggs]

Not getting much feedback. Does anyone know what the "drag overboard" speed indicator is called?

Thanks

A "Taffrail Log"

[Tom Robb]

Yes it is, Lance. But if your boat's pitot/knot meter freezes up your boat needs skis.