To A New Paradigm With FPB

FPB 64 Avatar – Final Test Part Two Of Three

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While the first set of Final Trial photos represented the worst of the conditions, in the real world, even in gale force winds, you don’t encounter an unending succession of such seas. This next set of photos, taken during the same shoot, represent more of a norm. We’ll start with downwind, since that is clearly the most fun.

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The first two photos are for context. The waves do not look that big, cameras tend to do that, but this is the same sea state which generated the dramatic images from the previous article. The FPB 64 has her nose high, bow barely immersed, which makes it easy for the autopilot to do its job. She is cruising at a nominal 9.4 to 9.7 knots, with surfs to 15.

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Now a long series, which takes place over about three seconds. Note that while some of the photos look like duplicates there are subtle differences.

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Avatar is running easily with the seas. You can judge the tendency to yaw or bow steer by the wake and position of the bow in the waves. She has not perceptibly varied her course. We would expect that with pilot controls set to minimum she would stay within five degrees of her course setting.

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Now a bow on series. the fineness of the bow, which allows upwind penetration, is on display. How you get such a lovely uphill shape to support itself downwind, and avoid bow steering (and the resulting broach) is a long and detailed subject, which has taken us a lifetime to master.

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There are subtle attitude differences, but the basic trim throughout this and the previous series is bow up, as you would want.

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The rest of these downwind photos are shot with the camera position moving aft. They take place over about ten seconds.

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Now let’s turn our attention upwind. The next series is what we would expect 90% of the time on a day like this.

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The first group provides an overhead view, and a good angle to evaluate how the bow penetrates. Watch the stern to see how it reacts as well.

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Although attitude is difficult to judge from this angle the flow coming off the stern remains relatively undisturbed.

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This next (and last) series is a long one, covering a number of wave encounters.

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Over the  preceding three waves there has been little change in fore and aft trim, what you want for comfort.

The next few slides are the most interesting design wise. There is enough buoyancy in the oncoming wave to start the bow to lift. If the bow doesn’t lift, then the foredeck is going to get ugly with solid water (as opposed to the spray you have seen before). In order for the bow to lift the stern needs to give. That is what the image above and the following series show.

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Although the stern is now substantially immersed, there is not a great deal of turbulence associated with the change in attitude.

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At this point  the wave pressure is off the bow and the stern is back to an almost normal floatation plane.

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For a higher res slide show of these photos, which you can watch full screen, click here.


Posted by Steve Dashew  (July 18, 2010)




4 Responses to “FPB 64 Avatar – Final Test Part Two Of Three”

  1. Scott Evangelista Says:
    Steve, (sorry if duplicated, i had a connection issue) A long while ago when meeting you in Ventura Ca, you mentioned the ability or desire to remove and stow the anchor during long upwind/head-sea conditions. Looking through these pictures I have to ask if you still would do this or do you find that the anchor diverts meaningful water from otherwise coming on deck. All of these heavy sea condition pictures have been fabulous. I would have loved to been along for the ride. I am most curious about the vertical and horizontal acceleration during wave penetration and when coming down off that beautiful “hang time” thank you for all the updates Best wishes Scott

    [Reply]

    Steve Dashew Reply:

    Hi Scott: Re removing the anchor, it is a net negative where it is. It creates more fuss than it stops. There is a tang on the port side of the FPB 64 forward mast to use with a tackle for lifting the anchor on deck. The decelerations are comparativly soft.

    [Reply]


  2. Bo Leonard Says:
    Steve Looks like the anchor locker got a good drink of water. Any thoughts of evacuating it any quicker, reducing the ability in taking in water or is this just par for the course. Fantactic photos! Bo

    [Reply]

    Steve Dashew Reply:

    Hi Bo: The anchor locker has aft facing scoops on the drains so generally creates a back pressure. On Wind Horse and Avatar there has not been a drainage problem.

    [Reply]



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