Wave forecasts: Twice what you expect

[REBrueckner]

In another thread (Following Seas) I posted the following website for reference on waves,

http://boatsafe.com/nauticalknowhow/waves.htm

I found one section particularly interesting:


".. Therefore, in order to classify wave height we determine the significant wave height, which is the average of the highest 1/3 of the waves in a system. This is how weather reports will specify wave height.

Average height: 0.64:1
Significant height: 1:1 (weather forecast height)
Highest 10% 1.29: 1
Highest 1.87:1

So when a forecast is for "seas 3 to 4 ft" you should expect seas 1.87 times as high, close to 6 to 8 ft!!!

I, for one, did not realize that was the basis for waves forecasts... I always attributed higher seas to the action of tidal currents with waves, now I'm not so sure.

 

[Genesis]

Yep!

Came across from Clearwater to Appalach on a day with forecast for 6-8s (not much choice - the other days on both sides were 10-12s - for two weeks straight!) and GOT the 6-8s, with frequent 10s and more than a few 12s.

Short-period 12s are NASTY. Every square inch of the boat was SOAKED.

 

[Akyla]

If you look at any of the data buoys info and look at the wave trend charts you can see the prediction uses the highest 1/3. But don't be scared off the ocean by predictions alone as they are still just best guesses. Often fairly good ones, but still have a margin of error due to the large variables that go into the equation. Once you run a patch of ocean long enough you known when to believe the weather prediction.

However, the action of wind against tide or current and shoaling effect has a great deal to do with waveform as well as the height. In my area, the wave form changes greatly anywhere near the Diamond Shoals as the current changes from either tide or Gulf Stream position and of course the direction of the wind driven waves opposing those forces...

 

[Trojan]

We have the same problem here on Lake Erie. You can just about add on 2 ft. to any of the forecasts. They said 4 to 5 and we left port. They were 6 to 10 head on. What a ride. It was all I could do to stay in the seat. On Lake Erie its a 6 t0 10 chop. Water over the bow. Shame on me we were totally unprepared. After 50 years of boating I should have known better. I guess every now and then you need a wake up call.



BILL

 

[Nonchalant1]

Bill,

Lake Eerie in 6 tp 10 ft. is a real challenge! Been there, done that in 6 to 8 and don't want to do it in 6 to 10. 6 to 8 with a 70 ft wavelength just buries the bow, throws green water on deck, and scares the Admiral.

Doug

 

[Genesis]

I grew up on Lake Erie. In a "small craft" it can be absolutely terrifying. The closest I've come to meeting Davey Jones was on that lake.....

 

[Angela]

I've had a special dose of Lake Erie myself which I'll NEVER forget! Ahh, the many memories of Lake Erie where my love of boats really started ("big boats" came later). Way back when I thought my friends' 23' Wellcraft cuddy cabin model was a "big boat", we were out near "C" can (or was it "D" can? - Canadian border, anyway) where we often wandered, a storm came up as they suddenly did on Lake Erie (well, by the time we saw it off in the distance, we started heading full throttle for port, but could not out run it). I remember plowing through what seemed to me to be huge seas at the time - one moment we were on top of the world seeing everything, and the next we were in a valley with nothing but a wall of water around us, and couldn't get any faster than a fast idle. I think that was the first time I was really scared on a boat. It really was a struggle and I was white-knuckled. It took us 3 hours to get back to where we put in (Port Clinton or maybe it was the yacht club at Catawba Island - can't remember) in those beating waters.

I remember eventually going into the cuddy cabin with the black labrador retriever, Tyson, until I got tired of taking the head beating from being thrown against the roof of the cuddy area. Tyson and I decided we were better coming out to take the beating of the waves over the windshield. It was only June, and the water was freezing...and every inch of the boat, including us, was soaked - it was like standing in front of a fire hose at times. I think that day on Lake Erie was the worst boat ride I had ever had. That was before we had GPS...just the compass to get home on (and someone to remember where we had been in order to be able to use the compass!) ...but, once home and at the fish cleaning station (we were walleye fishing that day), I had the biggest fish! The day before, the talk amongst the guys around the cleaning station had been that if you take women on your boat you can't catch fish. All the guys were looking at my big walleye as I dragged it to the table and began gutting and filleting it. I said to them, knowing what they had said the day before, "See what happens when you take a blonde fishing..." They were silent. It was the best horrible day I had on Lake Erie! I don't live in Ohio anymore, but I sure do miss my walleye (and a little bit of Lake Erie too).

Ang

 

[ADaily3224]

I live right at the end of Lake Erie, the Buffalo Harbor, Break walls, Erie Basin Marina. There is housing all around the Marina, it's a fun place to live. Many special events are staged out of Erie Basin, it's kind of the focal point of the City of Buffalo. We have had those huge Bass fishing tournaments, hundreds of those shinny metal flake low slung boats with monster outboards. The inexperienced guys go flying out the basin channel, into the harbor, so far so good. They head for the lake, there is a series of break walls shielding the harbor sometimes staggered 3 thick. As soon as they pass the last break wall and hit their first Lake Erie wave throttles come way back. It's almost always choppy. They usually swamp three or four of those guys the fist day, after that they learn. A bass boat is not the proper craft for these waters.
A few years ago the big off shore racers were here, helicopters, trailers, all the big sponsored boats. It was exciting. I went out in my 21 Outrage to watch the practice runs. They had to stay behind the brake walls, a few decided to give the lake a try, one sunk, one broke up. The newspaper had, accounts of damage and injury, the statement was made, they won't be back. Too bad there was such a good crowd, lots of support from the city, but it was too rough, they called the race. That's the way it is on Lake Erie, 60 feet is the average depth, 225 westerly fetch, more ship wrecks than all the Great Lakes put together. It's calm now because it's frozen for the winter, it'll be kicking butt by April 15th or so.
You need a good boat and good skills to travel on Erie.
Tony D

 

[GeorgeJW]

Thanks for the post on wave height....as a "boat rookie", I learn two or three new things every time I log onto this site. I flew planes for a living for 20 years as did a surprising (perhaps shouldn't be) number of other Hat owners. Lots of formal training during that time on WX phenomenon, but related to aircraft etc. I still have a lot to learn on this new boat passion/obsession.

Anyway, my learning experience (never liked those in the air!!!) related to this particular tread was last fall turning up the Potomac river from a pretty rolly ride down the Chesapeake. Wind was WNW@15G25, inbound tide (I pay attention to this now). Waves in the bay were 3 to 4...not too bad. As we turned NW with about 10-15 mile fetch (I pay attention to this now as well), the waves grew and shortened in frequency and generally made the ride pretty interesting. Constant spray over the entire boat with the deck bell ringing every 10 seconds or so. Slowed to 7 knots...lasted about 2 hours. My wife has a new rule...if the bell tolls more than 3 times in a minute, we head to shelter.

 

[Trojan]

Many a foreign ships captain that has entered our Port Of Toledo and been in a storm on the lake say it is worse than the ocean. I have been in may storms on the lake, seen many water spouts. Its not fun. The admiral says ( she is new to boats )we only boat now in calm seas. I can live with that idea. We spend many a week at PUT-IN-BAY and Kelley's island.





BILL

 

[spartonboat1]

To quote the "mouth of the South", Ted Turner, the Great Lakes are ponds compared to the Ocean. Then he sailed in a Chicago to Mackinaw race (caught some very strong south winds, the maxi-cruisers were surfing at 35 knots!!), after which he declared he would not be back, as it was the roughest sail he had ever had.

 

[Genesis]

Hehehehe... yeah, right - ponds....

I used to have an office in Two Prudential in Chicago. Overlooked Lake Shore Drive. We got one of the famous winter storms one year and I was working late - I saw breakers throwing car-sized pieces of pavement that were being torn up from the roadway and rip-rap fronting it.

Now this would be pretty amazing all on its own - but what made it truly amazing is that to get to the road those waves first had to crest the breakwall at the outer harbor about 1000 feet out from shore!

I estimate the waves were running 20+ that night. Easily the equal of a full-on hurricane around these parts...

The only thing the Great Lakes have going for them in terms of being shipwrecks on them is that you can drink the water. Other than that I'll take the sea, thanks much.