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Author Topic:   Swell size
roofer posted 07-10-2002 12:44 PM ET (US)   Profile for roofer   Send Email to roofer  
I have often heard people describe the swells on lake michigan or even on this site. I have an 18ft outrage. how is swell size figured, I do it from the lowest point in between swells to the top of a swell.

Note i am new to boating so maybe I am just a whimp, but I hear people talk about goung 20-30 knots in 4-5 foot swells, and I can't understand. i would be flying with the whole boat in the air if I tried that. Am I missunderstanding the swell concept or is boating in swells like fishing where a little creative extra size is considered ok when telling a story.

Or third choice are there advanced boating techniques that I need to learn to drive fast in rough water?

Tom W Clark posted 07-10-2002 01:01 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Wave height is always correctly described as the vertical distance from the trough to the crest of the wave or swell.

Wave size or swell size of often grossly ever estimated or exaggerated. It is difficult to gauge by eye.

The length of a wave face is not the measurement to use.

Period, the time interval between waves, as well as wave length all help to describe waves.

Wave steepness is the ratio of wave height to wave length and has much more to do with how easily you can run in a given sea.

It is possible to run an Outrage 18 in 4’ swells @ 20 knots (23 mph) especially if you are going across them or with them instead of into them. But 30 knots (34.5 mph) is very difficult to do in anything but smooth water. A true 4’ chop is hard to plane in at all.

Bigshot posted 07-10-2002 02:32 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Swells or waves? I have been in the Grenadines in 10-12' swells and you could easily go 25+. They were about 10 seconds apart. Was more like driving on a roller coaster than waves. Now get in 3-4' chop and you'll have to see a dentist after all your fillings fall out.
kingfish posted 07-10-2002 02:56 PM ET (US)     Profile for kingfish  Send Email to kingfish     
For us inland and Great Lakes boaters, a "swell" (which usually implies a greater length or period than a "chop") is a little hard to appreciate until you've experienced the animal.

This Spring, on the last day of my 2-week vacation that started in Williamsburg VA and got as far South as Beaufort SC, the weather finally moderated off of Morehead City NC to the extent that I could reasonably go "out" in my Outrage 22' that had been following me around for the entire trip.

The VHF weather channels consistently described a 6-foot on-shore swell (that worked against an off-shore breeze creating dangerous riptides at the beaches) and I guess it must have been around that size. Running in it in almost any direction was just no problem, although I couldn't comfortably do much more than 20 mph straight into the face of them.

I anchored over a wreck 3 or 4 miles out (55 feet of water) and spent the entire afternoon in those swells fishing over the side and having a great time; the motion was such that I'd have the complete horizon visible from the top of the swell, and nothing but water visible from the bottom, but they were far enough apart that it wasn't in the least unpleasant.

Boats a lot bigger than mine wouldn't even consider 6-footers in Lakes Michigan or Huron (the two Great Lakes with which I'm familiar), no matter what you called them because at their greatest length and period, the waves are still just too close together and too ugly!

kingfish

Wreckdiver posted 07-10-2002 09:05 PM ET (US)     Profile for Wreckdiver  Send Email to Wreckdiver     
A couple of years ago, we were diving at Whitefish Point in Lake Superior. The wind started blowing about 10Am one day forcing us to get off the lake by noon. It increased and continued all night so that they were running about 7 feet steep and breaking the next morning. All along the coast of Whitefish Bay the lake freighters coming through the Sault Locks during the night had run to the shelter of the coast and dropped anchor.
Swellmonster posted 07-11-2002 11:04 AM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
My girlfriend says size doesnt matter!

Actually the distance between them is what kills ya when running through them. In my 20 O/R I can run 40 in a 3-5 chop staying on top of the waves.

kingfish posted 07-11-2002 11:35 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Not in a Great Lakes 3-5 foot chop you can't...(maybe you could, painfully, for a short while, around 3 foot max).
VMG posted 07-11-2002 01:08 PM ET (US)     Profile for VMG  Send Email to VMG     
Having grown up in the Great Lakes, and with a decade or so of experience in the salty stuff, I don't ever recall seeing anything that I would refer to as swell in the Great Lakes. Lotsa some of the nastiest chop in the world -- but no swell.
jimh posted 07-11-2002 06:51 PM ET (US)     Profile for jimh  Send Email to jimh     
Swell is the remnant wave action of long distant wind-driven waves, typically long wavelenght waves.

The Canadian VHF Marine Radio Service Continuous Broadcast always includes the following:

"Wave heights are forecast for offshore and are measured from Trough to Crest. Winds and waves along the shore can vary considerably due to shoreline effects."

OutrageMan posted 07-12-2002 07:31 AM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
I can tell you for certain that the water I was in off Fish Creek (Green Bay water body)last week had swells. We were rescuing a dismounted jet skiier who had quite a load on.

Swells were 8 seconds apart. No white stuff. In the trough couldn't see land.

Brian

roofer posted 07-12-2002 10:17 AM ET (US)     Profile for roofer  Send Email to roofer     
thanks to everyone that posted this has been helpful. the best I can tell it is not only the size that matters but also the distance between swells and the steapness. ocean swells can produce a less violent ride than an equvilant sized great lakes swell due to the closeness of the swells on the great lakes.
Bigshot posted 07-12-2002 11:53 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
In a nutshell....yup!
TheWiskey posted 08-06-2002 01:37 AM ET (US)     Profile for TheWiskey  Send Email to TheWiskey     
Turn right when you are coming down from the crest. It makes the ride smoother. Why ? I do not have a clue
triblet posted 08-07-2002 11:13 PM ET (US)     Profile for triblet  Send Email to triblet     
Swell heights are measured from the trough
to the crest, but not all swells are the same
height, so what to do:

One option is average. This is not common.

Another is something like 90% percentile
(90 per cent are lower). This is, I think,
common.

And yet another is the max during an hour
(something like the 99.5% percentile).

As long as you know which is which, you can
compensate. Best way is to monitor one or
more forecasts, and compare that to what you
will see.

But then, sometimes the forecasts are flat
wrong, and you are real glad you have a
whaler.


Chuck

David Pendleton posted 08-08-2002 12:14 AM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Lake Superior does indeed demonstrate swells.

As for running on plane in a 3-5' chop...I dare you.

Dave

jimh posted 08-08-2002 12:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Swell differs from other wind driven waves. Swell is the reminant of remote storm waves, and usually consists of long wavelength and non-breaking waves. Swell size and direction may not correspond at all with current wind conditions.

In order for waves to develop into a "fully developed sea state" the wind must blow at a steady velocity and direction for quite a long time, several days perhaps in the case of high winds and large wave development. These conditions will create a fully developed sea state with large, long wavelength waves. They also require deep water, typically at least ten or twenty times deeper than the wave height.

More typical, especially on the Great Lakes, are short, steep wind driven waves with very short wavelengths.

Waves are irregular by nature and can be described only by statistics. One theory is that in a fully developed sea a wave of twice the average height will occur once every one-thousand waves. This is a bit less frequent than the "third wave" phenomenon often cited. To get to three times the average requires quite a few more waves, something like 100,000 waves before a big monster comes along.

William Van Doren's fine work OCEANOGRAPHY AND SEAMANSHIP is a source of endless information on topics like this and a little more reliable than dockside chit-chat. His appproach is quite mathematical--no cute color graphics with snazzy drawings--but the content is very well presented and understandable to readers with a scientific background.

DaveH posted 08-08-2002 02:14 PM ET (US)     Profile for DaveH  Send Email to DaveH     
jimh and triblet;
The actual method of reporting sea characteristics engineering-wise is the significant wave method. Waves can amplify and cancel out each other as we all know, the highest one-third of all wave heights is used to determine reported design sea height:

* Most frequent wave=0.5 wave height
* Average waves = 0.61 wave height
* Significant waves = 1.0 wave height
* Highest 10% = 1.29 wave height
per US Naval Oceanographic Office,1958

There are many indicators and statistical charts at my disposal which I won't bore the Forum with, but ideal wave heigh:

*Is ALWAYS measured crest to trough.
* Is affected by fetch, wind speed, wind duration, and depth of water.
* Will crest when the height divided by the wavelength (H/L) is 1/7 or about 120 degrees.
*Is affected by the bottom when the bottom is less than the wavelength divided by 2 (L/2). Anything greater than L/2 is "deep water".

There's more if you want but I think I put everyone to sleep at their desk.

tomol posted 08-13-2002 04:47 PM ET (US)     Profile for tomol  Send Email to tomol     
Am I missing something? Two posters, one saying he goes 20 mph into 6 ft. seas and another going 40 into 3 to 5 ft. seas?

Can you say, LIFTOFF!? Do either of you have any fillings left? How are those bulging disks?

You Great Lakes guys are tough.

Nate
A sissy from California

jimh posted 08-14-2002 08:00 PM ET (US)     Profile for jimh  Send Email to jimh     
It must be those Accutrack hulls.

In my old classic hull I have to slow down to a crawl in 6-footers.

DIVE 1 posted 08-14-2002 09:09 PM ET (US)     Profile for DIVE 1    
Tomol,
You get used to the water in the Great Lakes after a few seasons of abuse. If you don't like the ride - go faster - then you only hit the high spots and the ride is smooth :):);)
Jim
Wreckdiver posted 08-14-2002 09:46 PM ET (US)     Profile for Wreckdiver  Send Email to Wreckdiver     
I was diving in the Straights last Saturday and it was blowing pretty badly. We wound up on the backside of Mackinac Island later in the afternoon. It was really sloppy by the time we did the four miles run back to the main land. I tucked into the wake behind one of the ferries and ran about 25 MPH. The boat stayed in the water most of the time. Sunday blew harder so we left the Straights and ran down to Lake Charlevoix. I dropped the Montauk in at the Ferry Street launch, and parked next to a gray Cadillac with a galvanized “Whaler trailer” on the back. The lake was like running across a wash board. I had to retighten the console grab rail before tailoring the boat home. Modifying the front rail as recommended by JB has kept me from having to deal with it coming apart so far this summer. I may have to modify the console rail as well. If you are actually out boating and diving in the Great Lakes, you wind up running pretty hard in the sloppy stuff. Not many days are flat calm.
Bob
lhg posted 08-14-2002 11:43 PM ET (US)     Profile for lhg    
That Whaler trailer is shown on Cetacea Page 4, 3rd photo! Sorry I missed you, the boat was docked in the Irish Boat shop marina, just north of the boat launch/beach park. We were out tooling around the Lake in a friend's 1992 19' Outrage II, and the ride was quite bumpy. The 25 went right over that stuff.
Wreckdiver posted 08-15-2002 07:33 AM ET (US)     Profile for Wreckdiver  Send Email to Wreckdiver     
I recognized the car from Jims North Channel post on another part of the web site.

I had a sail boat at Irish for fifteen years, but didn’t go over to the marina that day except to window shop the new Whalers in the show room. We don’t have to discuss how the Montauk would have handled the waves out in the big lake. Short boats just don’t do well in that kind of chop.
Bob

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