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Old 22-08-2018, 16:24   #16
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J Clark H356's Avatar

Join Date: Jun 2010
Location: Grand Rivers, KY
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How to estimate roughness of sea?

Get Sailflow and it will give you the forecast period and wave height. A good rule of thumb is a wave with a period the same as the height = period 1 will be rough.
A period of 1.5 x wave height will be choppy, and a period of 2 x wave height will be acceptable.

So if you have 2 foot forecast waves, look for a period of 2 x 2 = 4 seconds or greater. A period of 3 would be choppy 2 x 1.5 = 3.

Remember that the forecast is the average of wave heights so even though the average may be a 2 or better, you will have waves larger and smaller with the same period so some will be rough even with a good forecast.

Sailflow will give you 3 hour forecasts for waves and period for 7 days. Best software I have found, but even with 2 feet and 10 knot wind forecasts I usually see a small amount of 3-4 foot waves and 15 to 20 knots. No forecast is constant and during unstable weather conditions can change fast.

See the forecast below from my Sailflow Pro account for Pensacola Buoy. It goes like this for 7 days. Click image for larger version

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Old 27-08-2018, 05:58   #17
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Re: How to estimate roughness of sea?

Shoals and bars can mean all forecasts will be off as well as the aforementioned land effect. If the information is related in a story simply multiply by half.
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Old 27-08-2018, 06:35   #18
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Re: How to estimate roughness of sea?

Originally Posted by jsc7 View Post
The marine weather reports I read don't seem to have enough information to estimate how rough the sea will be. For example, I want to take a 30-mile trip that has the following forecast:

Normally I go out in sub 10-kt winds no problem in my 32-foot boot with a V-hull, but if there are 2 foot waves spaced 5 seconds apart it will be a rough ride. The spacing of the waves is the difference between just rolling swells and slamming.

How can I estimate how rough it will be?
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