Ground Swell Questions

[altoning]

Check out swellinfo.com for Gold Beach. Can someone explain to me the pros/cons of NW versus SW ground swell? Graham Ezzy mentioned to us at Pistol River that SW ground swell is preferred but I didn't quite understand why. I also read somewhere that longer periods are accompanied by stronger waves. Is trading off some wave height for longer/stronger waves preferred?

[rkwave]

An physical oceanography text book would help you. This is the way I would sum it up. Ground swell or swell has long period...wait I have to tell you what period is. When you look at a pure wave coming in. It has a wave length. We indirectly measure his with Wave Period. That's the time it takes to go from a specfied point on a wave to the next wave. For example the top or peak of the wave to the peak of another wave. Or trough to trough if you prefer. That's wave period. Wave period and wave length in the deep sea are pretty well defined. Wavelength = about 5 x the period x period (period squared) feet. For waves of the same height there is more water under waves with longer periods than shorter periods. Therefore more potential energy because there is more volume of water. The amount of energy goes up with square of the period. Generally what we call "Swell" has periods greater than 10 seconds. Wind waves are less than 10 seconds. When the depth of water under a wave is less than 1/2 the wave length then the height starts to peak up. The limitation is about when the depth is about 1/2 the wave height. That's about when it becomes a breaking Surf. I'm generalizing quite a bit.
To complicate things the slope (steepness) and topography of the bottom also makes a big different in the quality of a surfing wave. That's why some spots are better than others even though they are actually physically quite close to each other.
Hope this helps and I didn't confuse you more.
RK

[altoning]

@rkwave: many thanks for the explanation. Almost forgot about my high school physics. Wave shoaling seems to summarize your explanation.

Magic Sea Weed is forecasting a SW swell 2 feet 17 seconds in Pistol River/Cape Sebastian this weekend. I'm curious how high it's going to jack up. Got to wait to hear back from the BWD crew down there. This week they've been getting NW swell 4-5 feet 7-9 seconds and knee to chest high waves. Maybe this weekend will really deliver.

[rkwave]

The forecast is 2 feet. That is Significant Wave Height which is the average of the highest 33 percent of the waves. Maximum Wave heights are between 1.5 to 2 times Significant Wave height. Breaking wave Height will be about 2 times wave height. So look for 4 to 6 foot breakers. Most probable are going to be between 3 and 4 feet. Again it will depend on the site environment. 17 seconds is a real nice wave.
RK

[DavidM]

Alton, how you doing Here is an article on wave mechanics complete with diagrams. All beaches have their best swell direction. There may be Islands and reefs the interfere with the swell reaching a beach as well as the type of break.... beach break, reef break or point break and the direction it faces. DavidM
http://www.surfline.com/surf-news/malib ... ics_55498/

[altoning]

Alton, how you doing Here is an article on wave mechanics complete with diagrams. All beaches have their best swell direction. There may be Islands and reefs the interfere with the swell reaching a beach as well as the type of break.... beach break, reef break or point break and the direction it faces. DavidM
http://www.surfline.com/surf-news/malib ... ics_55498/

Hey Dave. It's been a while. I've been racking up the sessions lately (57 year-to-date). The Vancouver crew has about the same wind addiction as when you moved to Nanaimo. There's a handful of young new comers. Haven't lost many to kiting expect Fraser, Jerry and Clay (maybe an age thing where quality of sessions become more important).

I'm curious about swell because my first time in real waves was throwing myself into the Pistol River Wave Bash competition last month. First, a little intimidating in 40 knot winds and huge break on my first day but it just got easier as winds settled to 35, 30 then 25 on the following days. Lucky to have scored 5 out of 5 days on the coast and I want to go back to catch some more DTL rides.

Since it's a 12 hour hike to Pistol River/Cape Sebastian, I'd like to invest some time to understand forecast models for "ideal" conditions before committing. After comparing Magic Sea Weed against the sailing log and Dave's (C36) log along with the explanation from you and rkwave, it appears that SW groundswell over 12 seconds is the preferred swell for Pistol River, Cape Sebastian and Florence - maybe even the entire Oregon coast?

The next challenge is trying to predict the wind. It looks like BWD MM5 model generally works well for Pistol River when it forecasts N to NNW 25-30 (red). However, it did fall short on Mon and Sat. I guess the only way to score is to look for a good forecast of 3 consecutive days, commit then pray for wind (KUS's rule).

[DavidM]

Alton, You may want to diversify your experience to make use of all that driving if conditions are not right. A stand-up paddle will give you lots to do in the waves when there is no wind or sub planing conditions.
I got a Starboard Wide Point 9'5". It is about 155 litres.

I find the most fun with it is putting a 5.8 or 5.2 when the wind 18knts and under and surfing it in the waves without having to paddle. All the fun of surfing and no paddling! If there is no wind, you can stand up paddle it into waves as well but that is more work.

[altoning]

Alton, You may want to diversify your experience to make use of all that driving if conditions are not right. A stand-up paddle will give you lots to do in the waves when there is no wind or sub planing conditions.
I got a Starboard Wide Point 9'5". It is about 155 litres.

I find the most fun with it is putting a 5.8 or 5.2 when the wind 18knts and under and surfing it in the waves without having to paddle. All the fun of surfing and no paddling! If there is no wind, you can stand up paddle it into waves as well but that is more work.

Definitely have to look into it. That's what the BWD crew has been doing on those windless SUP days. Heard it also improves your wave sailing skills.

SUP is making more sense since this week's BWD trip got 4 windy days out of 7.

[nanmoo]

A SUP is a game changer... especially if it has a mast bung, go down to the coast and you score everyday. Just try and get one that is the smallest you can 'comfortably' balance, that way it doesn't surf and sail like a barge.

[firstonlastoff]

Alton, your first question was why was SW swell better than NW swell. My response would be, simply the direction of the resulting peeling wave from a SW swell will be nearly perpendicular to the prevailing N, NW winds at Pistol River, giving side-off conditions. And in fact the SW swell at 2 ft did give 4 - 7 ft breaking waves for the Island crew and Mike C. to have several turns on at Cape Sebastian on July 6.

[altoning]

Alton, your first question was why was SW swell better than NW swell. My response would be, simply the direction of the resulting peeling wave from a SW swell will be nearly perpendicular to the prevailing N, NW winds at Pistol River, giving side-off conditions. And in fact the SW swell at 2 ft did give 4 - 7 ft breaking waves for the Island crew and Mike C. to have several turns on at Cape Sebastian on July 6.

Makes sense. I'm beginning to understand that the preferred SW swell for the Oregon coast appears to be longer (than 12 seconds) periods and NW swell appears to be shorter (about 9 sec). It's almost as if SW is from distance storms and NW is locally wind generated.

Now I'm curious what swell direction, period and height was responsible crazy logo high waves that KUS and Eastside got on Mon June 18 and Tue June 19 (after I left the Pistol River Wave Bash). These are conditions I'd like to avoid.