Does fetch affect size of chop?

Easterly wind at 9kt, gusts to 12, waves about 1 ft. Would have been fun were it not for heavy chop that was more annoying than circling jetskis. My first encounter of such nasty chop.

The prevailing winds are westerly this time of year.

Does a short fetch result in bigger chop?


Long Fetch = Bigger Waves
Think about why you never see big waves on a little pond no matter how windy it gets. With winds of the speed you mention, there might be a limit to how big the waves will eventually get with longer and longer fetch, but in general, longer fetch means bigger waves.

if there is a 5 mph wind coming straight down a mile long lake there will be some white caps.

If there is a five MPH wind coming straight down a quarter mile lake or pond there will just be ripples.

jack L


More wind

Longer duration of wind

Longer fetch

Chop is in relatively shallow water. Trying (maybe unsuccessfully) to recall college oceanography. I think waves break at 1/7 the depth of water.

Can be estimated

– Last Updated: Sep-25-16 8:22 AM EST –

H(max)=0.332F^0.5 where H is maximum wave height and F is fetch in km. The fetch is ordinarily measured as the maximum distance of the lake along the direction the wind is blowing from. This is from the Jacob Kalff Limnology text.
Of course, not every wind will create maximum wave height and it takes some time to build weaves. Waves build faster in shallow bodies of water than in deeper ones but break before they can achieve maximum theoretical height. There's a formula for that also, but that can wait for another day.

PS: I should add, there are other formulas for this (that I have in my class notes somewhere in a box somewhere) that include wind duration and speed in the calculation. (Mind your units) "Chop" can be affected by many other things as well, reflex waves for example. These estimates are for gravity waves alone.
But it is definitely something to think about on a windy day if you find yourself sitting with your scratch paper on the upwind end of a long lake wondering if you should make a run for the other end... how bad could it get? Puts one's respect for Lake Superior and westerly winds into proper focus.


Did this get backwards?
I am reading the answers like you asked if longer fetch made for bigger shop, but what you asked seems opposite.

As to fetch and chop, you mean multi-directional chop rather than regular waves, yes? Seems like some answers are about the latter.

In my not-expert experience… gusty winds given a chance to play with any existing variations in a regular wave pattern will complicate things with more chop. So give them existing variations, like jet ski wakes or clapitois (sp?) off a nearby seawall, they often can have a pretty noticeable effect.

The effect can be annoying as heck if you just want to get thru it, or can be a hoot and a half if you don’t mind hanging out and bouncing around in every unexpected direction. The latter can feel pretty daunting if you are tired, because keeping the hips loose can start to feel like a lot of work compared to more regular waves.

Shallower water can also make things more so, same as with any regular waves.

Sort of.
I understand that the longer the fetch, the more organized the waves. I was curious about the effect of a short fetch.

What struck me yesterday was that the moored boats were bobbing up and down like popcorn, including the sailboats anchored offshore, not from the organized small waves but from the disorganized demonic blobs of water in between the waves. That’s what I consider “chop,” although I’m probably wrong.

Also wonder if even a slight change of wind direction might have made a difference as the east wind fetch was about three miles.

While not a relaxing paddle to enjoy the scenery, it was a good education.

Wind wraps around objects
as well as land. If it is quite gusty, those moored boats can start creating some interesting wind patterns.

I love the feeling of bouncing around in chop/whatever, multidirectional stuff. But if I am trying to get from point A to B, or I am coming in from a long paddle, it is not so much fun.

Nasty blobs ?
What you were seeing might be caused by shallow water shoaling ( waves become steeper and want to break in shallow water) combined with reflected waves from shore or piers, seawalls etc. The reflected waves combine with incoming chop in an non-regular interference pattern to create nasty blobs, when they start to for a regular pattern of combining and subtracting they form haystacks, which are really nasty blobs, unless you like to play in them, when the waves get really big you can surf in towards shore and then surf back out on the rebounds and jump your kayak when you heat the clapotis line or semi-stationary haystacks.

The demonic blobs sound like they were clapotis from the wind waves bouncing off of any objects in the water, in this case the moored boats.

I encounter it when moderate to strong winds hit the town’s waterfront structures, including piers, breakwalls, moored or anchored boats. I swear the wind waves also clapotize against boat wakes, creating even more unexpected directions of bounce approach.

As Celia said, fun for a small localized patch but a big PITA when wanting to get from Point A to Point B. I find it impossible to get a rhythm going when things are like that. After a while of fighting that slop ‘n’ chop, I wish I was paddling against straight wind and current instead. It’s more predictable.

Not sure about that as
chop extended far from shore, beyond the few moored boats that haven’t been taken out yet. It’s deep water there. What few breakwalls exist are closer to the harbor; area is primarily sandy beaches.

I still wonder if it was that direct easterly wind that set up the chop, as that’s my primary launch site to Lake Michigan and it was my first encounter with those conditions. Not even the Detroit River was that bad the one time I paddled it, and it had big old concrete seawalls the entire length.

I had planned go to from Point A to Point B, changed to Point C, then that got old so I packed up my toys and went to an inland lake connected to Lake Michigan. No chop. Lovely paddle where I discovered earth art - part of the inverted forest shown in the link. The site I came upon had about 30 inverted trees. Looks like a visitor from outer space stopped by and changed things.

Wind on previous days
Had the wind been strong for a day or two before the day you paddled? That can leave some choppy water afterward even when the wind dies down.

Not sure.
What’s fascinating is that I just checked the buoy and right now it’s blowing at 23.3kts with gusts to 29.1, WSW.

There’s a handy-dandy 24/7 live video stream on a building next to where I launch and when I look at that, not a single moored boat or tender is doing the popcorn dance I saw this weekend.

Water’s moving and lots of cats-paws visible so I’m thinking maybe wind direction played a part.

The Tide May Play A Role
Along with the contour, shape and make up of the bottom of the ocean, lake and river? Also the angle of the wind (contacting the water), which differs day to day, despite the same speed and direction, that’s either consistent or intermittent (wax and wane). Is the wind pushing it, dragging it or lifting it up. Basically, just blame it on the moon…

Ah, the moon…
…I was thinking Nessie, or perhaps a mess of feisty piranha…

The Witch of November.

– Last Updated: Sep-26-16 9:04 PM EST –

After all, it is autumn and that's when the Witch comes rolling in.

Gale warnings now. Along the coast. Crazy. Too bad it's night or I'd drive over to watch.

I sure wouldn't want to drive across the Mackinac Bridge right now.

No tide
Rookie is on Lake Michigan - it sounds like often in Grand Traverse Bay.

Thanks - What Me Know?
I paddle mostly S. Kaneohe Bay where it’s protected and many times the chop is smaller when the N.E. Trades blow stronger and the tide is lower. Water is salty too. Sometimes, an agitated hammerhead will kick up the chop with its tail.

Further north

– Last Updated: Sep-27-16 8:48 AM EST –

Lake Michigan from Little Traverse Bay. No tide. Quite noticeable seiches once in a while.