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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Waves on beaches (stupid question?)
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Thread: Waves on beaches (stupid question?) Reply to Thread
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Topic Review (Newest First)
12-22-2011 09:17 PM
casey1999
Quote:
Originally Posted by joelsanda View Post
Huahine and Tahiti. In both cases there were reefs that kept it calm at the beach. But twice I approached a pass on Huahine, once in a kayak and once in a 40' boat. The waves coming in through the pass were like buildings rolling in. Two surboarders looked like action figures they were so dwarfed by the waves. They also sounded like jets taking off when they broke.
http://www.surfline.com/surf-news/th...mea-bay_51419/
Above is a good site that explains wave mechanics. Talks about North Shore of Oahu but pertains to any deep water surf break. In the summer, I anchor at Waimea bay, but winter- no way, check out some of the pics of Waimea when surf is up.
12-22-2011 08:38 PM
joelsanda
Quote:
Originally Posted by casey1999 View Post
Depends where you are in Tahiti, never been there but they have some of the most powerful waves in the world at Tahiti's Teahupo'o. These waves are generated in the Southern Ocean I believe
Huahine and Tahiti. In both cases there were reefs that kept it calm at the beach. But twice I approached a pass on Huahine, once in a kayak and once in a 40' boat. The waves coming in through the pass were like buildings rolling in. Two surboarders looked like action figures they were so dwarfed by the waves. They also sounded like jets taking off when they broke.
12-22-2011 07:57 PM
AdamLein
Quote:
Originally Posted by casey1999 View Post
Depends where you are in Tahiti, never been there but they have some of the most powerful waves in the world at Tahiti's Teahupo'o. These waves are generated in the Southern Ocean I believe.
Nice. Waves like in that photo are easily in the hundreds if not thousands of megawatts per meter (of beach they crash on).

Quote:
Also, the sea breezes near land are actually thermal driven (not low pressure areas over an island).
Technically sea breezes are still due to a low; the low is just thermally generated rather than due to a front perturbation.
12-22-2011 06:28 PM
casey1999
Quote:
Originally Posted by joelsanda View Post
Ah ... thanks. That explains the waves I experienced in Tahiti, when we were surrounded by a barrier reef. The waves were gently and likely caused by the low pressure above land that brought in the breezes. In Mexico, when exposed to the Pacific, they were incredibly powerful.

Haven't seen the Sailing Weather - Marine Weather Forecasts for Sailors and Adventurers - PassageWeather site before. Thanks for that reference!
Depends where you are in Tahiti, never been there but they have some of the most powerful waves in the world at Tahiti's Teahupo'o. These waves are generated in the Southern Ocean I believe.

Also, the sea breezes near land are actually thermal driven (not low pressure areas over an island). The land heats the air which rises and needs to be replaced by the cooler air over the ocean- then the air blows from ocean to the land- usually in late morning or afternoon until sunset.)
12-22-2011 05:54 PM
joelsanda
Quote:
Originally Posted by casey1999 View Post
Noice that if an island is surrounded by real deep water, the wave will not refract so much to the opposite side, if shallow water wave will refract around.

There are 3 basic types of waves, those generated far off shore from large storms that bring in a ground swell and when that hits the beach, very large waves.
Ah ... thanks. That explains the waves I experienced in Tahiti, when we were surrounded by a barrier reef. The waves were gently and likely caused by the low pressure above land that brought in the breezes. In Mexico, when exposed to the Pacific, they were incredibly powerful.

Haven't seen the Sailing Weather - Marine Weather Forecasts for Sailors and Adventurers - PassageWeather site before. Thanks for that reference!
12-22-2011 02:51 PM
casey1999
Quote:
Originally Posted by paulk View Post
I believe there was a calculation made which showed that a wave crashing into a mile of beach represents more energy than man has used since he first learned how to light a campfire. Can't find the right wording to locate it in Google.
Man I wish that were true, we could solve the energy crisis. Here is an equation to calculate wave energy:
http://en.wikipedia.org/wiki/Wave_power
CACR Wave Calculator

Also, this site is great for wind and wave prediction:
Sailing Weather - Marine Weather Forecasts for Sailors and Adventurers - PassageWeather

Use the animate button to make the waves move, you can see how they propagate around islands. Noice that if an island is surrounded by real deep water, the wave will not refract so much to the opposite side, if shallow water wave will refract around.

There are 3 basic types of waves, those generated far off shore from large storms that bring in a ground swell and when that hits the beach, very large waves. This happens in Hawaii when storms around Alaska generate swell. It can be a calm sunny day with no waves at the beach and within 1 hour you could have 20 foot wave faces breaking- a lot of people die this way. Then there is the local sea breeze- air heats up on land, rises, and creates a wind heading to the land which generates a wind chop. Then the tidal wave which is generated by earthquake or underwater land slide. Also you could have a local storm (low pressure area) that would generate waves, but generally it will also be stormy at the beach also (wind and or rain/couds).
Regards
12-21-2011 09:33 PM
paulk
power

Quote:
Would be interesting to know how much energy is in an ocean wave. Judging by how much the sound waves carry in our home from my son's small electric guitar amp sound waves can pack a punch :-)
I believe there was a calculation made which showed that a wave crashing into a mile of beach represents more energy than man has used since he first learned how to light a campfire. Can't find the right wording to locate it in Google.
12-21-2011 06:32 PM
killarney_sailor It is interesting when you are trying to find an anchorage on one of these islands. From the chart and wind direction it looks like there should be no wind waves since they would have to 'bend' (refract) much more than 90° around the point of the island to get you - but they do.

I agree also about the effect of swells. In deep water you have quite long easy swells but when you get close to shore the wave length shortens and the waves get higher.
12-21-2011 05:20 PM
sawingknots oh yeah i forgot reefs
12-21-2011 05:20 PM
sawingknots theres way too many varibles to completely figure,the wind, the natual current,how far distant the disturbance and the proximity to other land,in the philippines i've noted that the small[banka boats] often seek shelter behind islands during squals,about every island that i've noticed anywhere has large sandy beaches on one side and mucky mangroves on the other
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