Help. Bought a 15.5 ft. caone from my neighbor, our first canoe. Bought foam block kit, strapped canoe down and upgraded with ratcheting straps from Harbor Freight. At 40 mph the straps(?) set up a wind howl that is very loud, getting louder with higher speed. Any suggestions how to cut the noise?
Howl
put a twist in your straps and this will help.
2nd the twist.
3rd the twist.
Add at least two on each side. It’s the flat straps. Absolutely FREAKED us out the first time we strapped one on. The kids were crying, my wife was irritated and the dog was howling. I pulled over 5 times in 40 miles trying to stuff towels underneath the straps to deaden them. The whole cabin of my Ridgeline was basically the inside of a subwoofer. I couldn’t believe the fix was as simple as a twist or two in the flat straps.
BTW, round rope won’t do that. Something to consider . . . .
You have a howling canoe?! How Lucky!
– Last Updated: Jul-31-07 8:07 AM EST –
It is so nice when they howl ;^)
>:^)
Mick
BTW: Sometimes even twisted they will howl. Sometimes they will start howling part way through a trip. Especially if there are longer distances between where the strap contacts the canoe and where it hooks onto the rack/vehicle, etc. I have found a simple, easy, and quick fix without having to restrap or more. First check that the straps are snug and secure. Next take a double hooked bungie and hook one end near the center of the "bridge" of the strap and the other end to the vehicle, the rack, or even the canoe. Do not over due the tension, a little is enough to stop the vibration that creates the howl. This saves a lot of time and frustration during your trip. And of course we always carry extra bungies!!!
howling and physics
The reason that straps howl is that the length of the strap corresponds to one of the natural vibration frequencies at certain wind speeds. This sets up a condition called resonance. Putting a twist in the strap changes the effective length of the strap (for vibation , the strap is now effectively two shorter straps seperated by a node at the twist), so it no longer vibrates at a resonant frequncy. If you still have howling, or you now have holwing at a different speed, just put in a second twist.
This is probably more info than you wanted, but it is cool to know why something so simple works.
it might be the gray thing howling
Be careful with those bungies!
A fellow paddler almost had his lip ripped off when one end snapped him in the mouth., Like he said" Try to find an emergency room at night in the middle of nowhere."
Something else to be careful of…
– Last Updated: Jul-31-07 1:51 PM EST –
...are those ratcheting straps. Depending on your canoe (and the roof of your car/truck) they can be WAY too powerful. Regular (quality) camlock straps with a stopper knot will do you just fine. Meanwhile, be really careful cranking down too hard on those ratchets. And have way big fun paddling. (The other posts do a fine job of explaining your howl; the first time our canoe dog heard it she joined right in. We found it easier to stop and twist the straps than to accomplish the same w/the dog!)
i have the same issue
when using ratchet straps… try varying your speed, mine usually only do it for about 5-10 mph gap… guessing thats the frequency it needs. speed up or slow down its better or gone completely.
things that work for me… tighten the straps is usually the first and best bet, usually just a fraaction tighter will cure it.
Ive tried twisting it, but it seems like that worsens it sometimes.
Know what you mean about the buzzing though, its loud and gets annoying quickly. If im on a short trip ill ignore it, roll down the window and crank up the tunes, but that brrrrrrrr noise gets old in a hurry lol
Vortex shedding
– Last Updated: Jul-31-07 11:40 AM EST –
You are correct that the strap is resonating at its own natural frequency. That frequency depends on the length of the straps.
When driving, vortices are shed by the strap at all speeds - when the frequency of the vortex shedding matches the natural frequency of the strap, then you get resonance. The shedding frequency depends directly on your speed, which is why speeding up or slowing down can stop the resonance, by changing the vortex shedding frequency (as mentioned by others here).
Putting a twist in the strap doesn't change its effective length, or not by much. If it did, you'd just get the howl at a different speed, which generally doesn't occur.
What the twist does is interfere with the vortex shedding. The twist takes a nice field of parallel vortices that are being shed from the strap and are able to excite the resonant frequency, and turn it into a mess of short, twisted, incoherent vortices that don't excite anything.
This is why car antennas generally have what looks like a twisted cord wrapped around them - it disrupts the organized vortices that cause these antenna to hum and vibrate.
OK, probably way too much detail, but hey, what can I say, it's my bailiwick. Here's a nice picture of the phenomenon:
http://www.efluids.com/efluids/gallery/gallery_pages/wave_resonance_page.jsp
Cheers, Carl
1/2 twist
Works for me at all speeds.
Andy
Ratchet straps???
Or CAM straps?
True ratchet straps are never necessary for hauling canoes, and may do more damage to hulls that cam straps. Yakima, Thule, NRS and many off-brand straps are CAM straps.
As to the howl, twists solve many noises. But another important item is to run the straps under the crossbars as close to the gunwales as possible. If you run your straps at 45deg or so from the bilge to the crossbar you will expose many inches of strap to teh slipstream. A shorter run straight down to the bar may increase the harmonic frequency to above human hearing.
Adult that is. It may still drive teens crazy (hehehehe).
Jim
Just let your dog ride inside.
little piece of
– Last Updated: Aug-01-07 6:45 AM EST –
(thin) sleeping pad material (EVA) between the strap and the canoe hull
http://www.xs4all.nl/~dbarends/images/eva.jpg
works for me.
Twist - You don’t need rachet straps
Twisting the straps works great. Forget the ratchet straps though; they’re overkill and can damage the boat.
Phreon
sigh
i get into this debate every thread about tie downs, but it seems like th pnet bible is dead sent agianst ratchet straps :rolleyes
I have sucessfully used ratchet straps for 5 years of paddling, 5+ times per month year round, and never ONCE had any problems with them. No deformation of any of the dozen different canoes/kayaks that are on my roof on a reg basis have ever gotten any deformation or damage. Plus they are quicker, easier, and stronger than most alternatives ive ever seen
The occasional buzzing from a vibrating strap is the worst problem with them, and I get that maybe 1/10 trips and its a 30 sec fix. I will continue to use this method as it has NEVER failed me and I have yet to find a superior alternative
Really?
Every RATCHET strap I have seen is a pain to thread and tension.
Conversely, every CAM strap I have ever used works well.
Are we arguing over a definition here? Ratchet straps have a take-up spool that is rotated by a ratcheting lever. Cam straps simply have a spring-loaded toothed cam to capture the strap.
Jim
Overtightening issue asside
– Last Updated: Aug-01-07 4:12 PM EST –
There's no way that a rachet strap is quicker than cam strap. One takes a simple tug to tighten, while the other requires cranking the handle back-and-forth, back-and-forth.
I don't think anyone is saying that a ratcheting strap is guaranteed to damage a boat. The simple fact is, there's a much greater change of overtightening the strap (and therefore causing damage to the boat) with a racheting strap than there is with a cam strap. A ratcheting strap is overkill, as you can easiy pull a cam strap plenty tight enough to secure the boat.
Let us know what you find out…
Twist your straps and then report back. I’ll bet two front-row seats at Raystown that twisting your straps makes a huge difference.
-Rob