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    Response Amplitude Operator
    From: Brad Morris
    Date: 2013 Mar 10, 16:30 -0700

    Hi Frank

    You wrote, in regards to dip, the following

    You look over the side and see where the waves are peaking relative to your position on deck. Of course, if you're on a small vessel, you have the added complexity of waiting for the vessel itself to be near the tops of the waves if they're large enough.


    In my view, the misconception that the vessel you are on will rise and fall to the same amplitude, frequency AND that the frequency of the boat and waves are synchronous is what is holding back our understanding of dip.

    While I don't claim to understand the equations, one can see the complex nature of a ships response to waves. Its called the RAO (response amplitude operator). Look at the wiki page for this and you will immediately see my point. While you may sense when your vessel is at the top of its cycle by the acceleration, there is absolutely no guarantee that your vessel is at the "top of the wave". So you are at the high point, is it higher than the apex of the aves or lower.


    As we have seen, there is clearly a correction for wave height in the calculation of dip, and that it may become significant. This wave height correction will be affected by the up and down response of your vessel to the waves.

    It just simply won't be one to one with the waves. Yes, I am aware of all the literature that states "take your sight at the top of the wave". Easier said than done.

    Each vessel will have its own RAO, something I alluded to in an earlier response to Greg. This is particularly why a singular dip table, without a wave height correction or vessel RAO correction, seems so unpredictable and wrong.

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