Speed of swells

[chbpresent]

Marine weather forecast give estimates of wave heights an frequency. When in a following or quartering sea, I find it much more comfortable to travel at the same speed as the waves to minimize yawing or plowing. I do it by just looking, but is there a way to estimate the forward speed of a wave based on the estimated wave heights and frequency?

[GordMay]

Greetings and welcome aboard the CF, chbpresent.
Wave Speed = Wavelength x Wave Frequency

[Shrew]

Originally Posted by chbpresent

Marine weather forecast give estimates of wave heights an frequency. When in a following or quartering sea, I find it much more comfortable to travel at the same speed as the waves to minimize yawing or plowing. I do it by just looking, but is there a way to estimate the forward speed of a wave based on the estimated wave heights and frequency?

When the waves are passing under you, you're still too slow. If you start overtaking waves, you're going too fast. It will be almost impossible to to travel at exactly the same speed. A calculator will not help with this beyond academic curiosity.

Your better off travelling just slightly faster, rather than just slightly slower.

[tkeithlu]

Amen. Your hull and rudder is designed to have water flow fore to aft only. If you go slower than the waves, you are trying to steer in reverse during one part of the wave.

As long as you are engaged in an academic pursuit, realize that the water actually doesn't move with the waves. The water is tracking an oblong-on-end circuit, up at the front and down at the back. The wave in the next second is filled with different water. A wave travelling the length of a slinky spring is a good analogy. Another, if you lay a rope down on the ground in a straight line and then whip a wave into it, the wave travels down the rope, but does not move the rope more than up and down.

[Dsanduril]

I suspect you are looking for the wave/swell "celerity", which is the apparent speed of the peaks or troughs over the ground.

Wave celerity - The speed at which an individual wave advances or “propagates” is known as the wave celerity. For a deepwater wave the celerity is directly proportional to the wave period, T. The formula for deepwater celerity, Co, is Co =1.56T m/sec = 5.12T ft/sec. Note that the deepwater wave celerity does not depend on water depth. Source

For a calculator that includes the effects of depth (which strongly affects celerity in water that is shallow enough for the wave to "feel" the bottom) look at this linear wave calculator.

[rslifkin]

I've never personally experienced the reverse steering thing. Typically, at least on most powerboats that I've seen, there's enough prop wash at lower speeds that the rudder still operates normally. But at lower speeds, the waves push the hull more than they would if speeds were closer or the boat were faster than the waves. And the lower forward speed and reduced prop wash gives reduced rudder authority, both of which contribute to more trouble keeping the boat on course.

[Bruce K]

From experience; I find that wave "speed" in the conditions I travel in, is between 11 and 15 knots. If I find the right speed I can sit on the face of a wave for 5 to sometimes 10 mins, its a good feeling to feel the engines "lighten up" and see the fuel consumption drop, often to 1/2 of normal.