1. Questions

Physics/Nautical

Further to my post yesterday re wave speed.

If a fast 25Kn 10m power boat had the choice of making a passage against the wind & waves (head sea) or with the wind & waves following (following sea). Assuming 15Kn wind in open sea conditions & no tide the skipper would choose to make the passage with a following sea. This would give a smoother & faster passage.

Once the tide is brought into the equation the picture changes. Wind & tide together creates a smoother sea state than wind opposing the tide. Apparently a point is reached when it would be preferable for the skipper to make the passage into a head sea providing the tide is flowing in the direction of the wind. Rather than in a following sea in wind against tide conditions.

I understand wave speed is a very complex issue but I have noticed waves generated by 15Kn wind overtake my 8Kn fishing vessel. I assume a wave crest speed of 10Kn which I believe is sufficiently accurate to use in the following examples.

1. A vessel doing 25Kn into head sea impacts the waves at 35Kn.

2. Same vessel doing 25Kn following sea impact speed reduced to 15Kn.

Example 1 wind & tide together makes slightly smoother sea state.

Example 2 wind against tide slightly rougher sea state.

Considering the above I fail to understand how a passage into a head sea would be the preferred option.

One thing I have not included is the rate of tide. Obviously the stronger the tidal stream the more noticable the difference in sea state between wind with & wind opposing the tide.

I have personally made a few passages in a 25Kn 10m vessel and have never encountered a situation when we would have preferred to take on a head sea than run with it.

I do hope I have explained my question clearly.

Can someone explain why make passage into head sea and what rate of tide would be applicable to make this preferred option.

Thanks

Mike

  1. 👍 0
  2. 👎 0
  3. 👁 197
Mike

  1. The size of the waves makes a big difference. In a following sea, large waves as they pass the stern lift the stern, then they approach midships, and the stern rises out of the water, rudders and screws. The ship is vernable to the force of the water midships twisting the ship sideways as the rudders are lifted from the water. Once the twisting motion occurs, the ship can roll or be swampled. This of course is dangerous if the wavelength of the waves is nearly equal to ship length (crest midships, trough bow and stern).
    Now heading into seas, or my experience putting the sea two or three points off the bow, allows you to adjust apparent wave wavelength relative to ship to avoid the cork twisting effect, and since the bow of the ship normally has a more vertical line, it can act as a rudder when water lowers. I only have deepwater experience in heavy seas, no tidal effect. But I can imagine a tidal current with the waves would give one more bow steering effect in heavy seas, and allow you to maintain headway. The bows of the ships I had were much more heavily structured in the bow area compared to the stern. In pounding seas, that is a consideration.
    Again, in my own experience, choosing the course depends on how heavy the seas (amplitude), wavelength compared to ship, wind (especially if it is not with the waves, but a cross wind), desired headway direction, and underwater hull shape. Lord help you make the decision in a flat profile bottom vessel, and that may be what you are asking on the 10m.

    1. 👍 0
    2. 👎 0
    👨‍🏫
    bobpursley

Respond to this Question

First Name

Your Response

Similar Questions

  1. Physics

    A boat’s speed in still water is 1.95m/s . The boat is to travel directly across a river whose current has speed 1.20m/s . Determine the speed of the boat with respect to the shore. Despite, I did it like taking the sqrt

  2. physics

    starting from reast a boat increases its speed to 4.12 m/s with constant acceleration. (a) what is the boat's average speed? (b) If it take the boat 4.77s to reach this speed, how for has it traveled?

  3. College Physics

    A fisherman notices that his boat is moving uo and down periodically, owing to waves on the surface of the water. It takes 2.5 s for the boat to travel from its highest point to its lowest, a total distance of 0.62 m. The

  4. physics

    Starting from rest, a boat increases its speed to 4.92 m/s with constant acceleration. (a) What is the boat's average speed? (b) If it takes the boat 5.07 s to reach this speed, how far has it traveled?

  1. waves

    A skipper on a boat notices wave crests passing his anchor chain every 5 s. He estimates the distance between wavecrests to be 15 m. He also correctly estimates the speed of the waves. What is the speed? Speed = (wavelength) x

  2. physics

    A boat’s speed in still water is vBW = 1.85 m/s. If the boat is to travel directly across a river whose current has speed vWS = 1.20 m/s, at what upstream angle must the boat head?

  3. Physics

    Compared to yesterday you did 3 times the work in one third the time. To so so your power output must have been: a) the same as yesterday's power output b)one third of yesterday's power output c)3 times yesterday's power output

  4. Physics

    Ten litre of water per second is lifted from well through 10m and delivered with a velocity of 10m/s if g=10m/s^2. The power of motor is Answer 1.5Kw how ??

  1. Calculus

    A boat is pulled into a dock by a rope attached to the bow of the boat an passing through the pulley on the deck that is 1m high than the bow of the boat ,if the rope is pulled im at the rate of 0.8m/s how fast does the boat

  2. algebra

    The power P needed to propel a boat is directly proportional to the cube of the speed of the boat. A 100 hp engine is needed to propel a boat at 15 knots. Find the power needed to drive the boat at 20 knots.

  3. physics

    A sinusoidal wave on a string is described by the equation y = (0.169 m) sin (0.713 x - 41.9 t), where x and y are in meters and t is in seconds. If the linear mass density of the string is 10.1 g/m ... a) ... the phase of the

  4. physics waves/bugs

    A bug on the surface of a pond is observed to move up and down a total vetical distance of 0.10m, lowest to highest point, as a wave passes. a) what is the amplitude of the wave? [for this, I got 0.05 by dividing 0.10m by 2.] b)

You can view more similar questions or ask a new question.