I am still waiting to see a flat bottom HP in operation - where is Bucket List?. I am an advocate of a narrow flat bottom with some rocker in the ends to provide dynamic lift. It has potential to reduce hull drag by around 20% on a lightweight boat compared with the round section and dead straight keel line.
The bow on the 18m proa will likely get some more treatment to make it finer but spray rails are not likely. The volume of spray has been at least halved with the last modification. It should be reduced even more with the proposed modification. A rough estimation of the current power loss is less than 2kW at 15kts. It would be better to deflect this flow down and gain maybe 300N uplift from doing that but it is relatively minor in the overall mass of the boat.
Once there are some flat bottom versions in operation there is the opportunity to make comparisons. It would be nice to see the stem above the water level and a hard chine parting lateral flow rather than the attached flow observed with the round section.
On 06/09/2015, at 8:38 PM, "robriley@rocketmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
its a common fix for aircraft wings,to run fences so slow the transverse flow, reduce vortice energy lost in the wake. What they are after is adjusting the power required to the lift gained.
So Im thinking, in similar ways there is that possibility to lift the hull no matter how much, but drastically reduce the spray which is pretty amazing in the video. What I think Im looking at there is a lot of otherwise lost energy.
I know that a sort of chine lump is common on power boats, but I dont think that would be that effective here, and doubtless it would weigh more. I tend to think there are better fixes such as a fence, or an inverse notch or sawtooth. What happens is they generate a high energy vortex which will suppress that transverse flow and suck up that virtual waterspout.
Inevitably it would generate lift as a consequence, but Im also thinking is the flat bottom (looking longitudinally) might not be the most ideal form.
https://www.dropbox.com/s/sox099g9dn6mbfo/100_2166.JPG?dl=0
Perhaps a profile that concedes an amount of chamfer. Thats something way outside my area so its open to critique.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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