Here is a real interesting view as well.

http://www.youtube.com/watch?v=qyzR2ud5RU0&feature=related

All three hulls are similar in form "Square" but all three are different sheer widths, and lengths. This causing volume distribution and rocker dissimilarities due to the differences. First part of clip shows third person view and the second part shows first person view from three different angles.

Todd

--- In harryproa@yahoogroups.com.au, "tsstproa" <bitme1234@...> wrote:
>
> Forgot to add this of course. watch from 2:50 into video its in slow motion x2.
> http://www.youtube.com/watch?v=DCxMexef2_0&feature=related
>
> And this video with a different hull form watch from 2:30 in
> http://www.youtube.com/watch?v=9BpikN9KcvY&feature=related
>
> I know I know scaling up blah blah blah...
>
> There's is a clear difference in motion between the two to be seen and how each one handles the scaled chop.
>
> Todd
>
> --- In harryproa@yahoogroups.com.au, "tsstproa" <bitme1234@> wrote:
> >
> > Both ends on shunting craft hulls are identical. Adding or subtracting buoyancy along with the location where you take it away or add to it becomes complex with many variables to consider. Its best to consider the crafts over all design consideration first. There is no one magical hull that meets all standards.
> >
> > Although my experience is to much buoyancy at the ends on to little rocker adds to bow down at sailing speed and aids in slowing the boat down in chop overall stability is good at the slower speeds in choppy condition. Tring to find the middle ground is the hard part.
> >
> > I compare it to a shock on a MOTOCROSS BIKE spring rate , preload, and rebound adjustments. Looking for the best set up to cross the whoop section. Get it right the rider in the middle seems almost motionless while the shocks due all the work. Pivot point is around midsection from fore to aft. Same with a shunting crafts hull moving through choppy water. One ex. to much buoyancy with to little rocker, stern is sinking causing bow to dive. Another ex. to much rocker to little buoyancy bow diving with stern up in the air. Lots of variables thats just on hull form alone you see.
> >
> > How about weight of craft, weight distribution, crafts center of gravity, sail area, sail area coe ,mast height , where mast is placed, hull draft, dagger board depth, steering board depth, where boards are placed etc.....
> >
> > Todd
> >
> > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@> wrote:
> > >
> > > Ben
> > > You have interpreted correctly. The trim results were based on an
> > > approximated height of CoE for the full wing or sail plan. If the
> > > speed can be achieved with a reefed sail then that reduces the bow
> > > down moment. Benefits can be achieved with end plating the bottom of
> > > wing or sail and/or "twisting" the sail or wing to lower the CoE.
> > > The twisting could be achieved through more subtle means than actual
> > > twist.
> > >
> > > With regard to the pantograph - years ago I took out a provisional
> > > patent on a self-righting catamaran where the hulls folded together.
> > > It did work in small scale. When I thought about a full scale
> > > version I felt there was a lot that could go wrong with nip points
> > > and high stress pivot areas. This adds a level of complexity that
> > > does not appeal to me. In my view it is better to keep simple hulls
> > > without pivoting beams that require adjustment while sailing.
> > >
> > > With a cruising proa you need to be aware of the potential for
> > > pushing the bow under and hence taking time to do the trim analysis
> > > or full scale testing to be confident that it will not be a problem.
> > >
> > > The intuitive solution of adding reserve buoyancy is probably not the
> > > best choice for reducing the tendency to pitchpole. A lot of reserve
> > > volume inevitably results in rapidly increasing drag once the bow is
> > > submerged causing the boat to decelerate. Then the similarly buoyant
> > > trailing end (bow) gets lifted on the following sea while the
> > > momentum of the boat wants to keep going - all combining for a
> > > dramatic swim.
> > >
> > > I am pretty happy with my V15 style hull for wave piercing. There
> > > have been a few developments since I last posted on this.
> > >
> > > A friend in Seattle has now tried the design and makes comment on the
> > > bow in item 4 at the bottom of the linked page:
> > > http://hpb-er.blogspot.com/2011/06/maiden-voyage.html
> > > This comment was only after his first outing while testing in boat
> > > wakes but he is experienced enough to know how more conventional bows
> > > work. This is a video he took some years ago in another pedal boat
> > > that has wider beam, wide transom and more conventional foredeck:
> > > http://www.openwatercycling.com/vidphotos/PICT0722.MOV
> > > I have had both my sister's boat and my new boat in similar
> > > conditions. This is the 5m version in waves:
> > > http://www.youtube.com/watch?v=t4wJ9wFiZpc
> > > Notice how the beamier hull with more reserve buoyancy in the ends in
> > > the first video tends to pitch much more - what goes up has to come
> > > down. The V15 hull just goes through waves. This also verifies the
> > > lower tendency to slam with the V15 hull despite having a flat
> > > bottom. The bang you hear toward the end of the second video is a
> > > wave clipping the stabiliser brace that was a bit too loose and
> > > allowed movement. It all looks a lot worse when the ride is up and
> > > down compared with riding level without constant pitching.
> > >
> > > I have taken the wave piercing concept a bit too for with my latest
> > > variant:
> > > http://www.rickwill.bigpondhosting.com/V15-6m.png
> > > I am finding the side windage over the foredeck makes it more
> > > difficult to turn through the wind. I think the 45 degree inverted
> > > "V" (90 degree peak) as used on the first two is about the best.
> > >
> > > Rick
> > >
> > >
> > > On 17/07/2011, at 10:38 AM, bjarthur123 wrote:
> > >
> > > >
> > > >
> > > > thanks.
> > > >
> > > > so the short answer is yes, the bow down problem is specific to
> > > > proas due to their fore-aft symmetry.
> > > >
> > > > do i recall correctly that your graphs of trim vs. speed were made
> > > > by adjusting only the coefficient of lift of the sail at speed or
> > > > maybe its AOA, and specifically not the height of the lift? in
> > > > other words, maybe the trim wouldn't be so bad if the sail was
> > > > reefed?? not possible with your snazzy wing i know, but applicable
> > > > to most proas.
> > > >
> > > > your four ideas on hull shapes all make sense to me and are very
> > > > good in that they require no moving parts. i still can't help but
> > > > wonder though whether the best solution is a pantographing ww hull.
> > > > it would put the weight right where you want it. such freedom of
> > > > movement could even possibly be useful as a folding mechanism when
> > > > trailering.
> > > >
> > > > ben
> > > >
> > > > (RC'ing for J/24's tomorrow,
> > > > next weekend crewing on a corsair 28cc,
> > > > i miss my weta already!)
> > > >
> > > > > The main difference between say a catamaran and a proa is that the
> > > > > former can be set with an initial trim using weight distribution.
> > > > >
> > > > > Also the transom on a typical cat hull will suck the stern down at
> > > > > speed. This increases bow up trim and the angle of attack for the
> > > > > hull so there is increased dynamic lift compared with a hull that
> > > > > rides flat.
> > > > >
> > > > > With a clean canoe stern there is not as much sinkage in the stern.
> > > > > This means there is greater tendency to ride level under power. If
> > > > > the drive is high up then there is a large bow down moment that will
> > > > > force the bow down unless the hull can counter it.
> > > > >
> > > > > So far I have observed four ways to get the hull to provide bow up
> > > > > moment.
> > > > > A. At displacement speed having full ends (large waterplane at the
> > > > > bows) will increase the static pressure from the bow wave at the
> > > > > leading end and reduce the pressure at the trailing end. This can
> > > > > give bow up moment below planing speed. For high speed displacement
> > > > > hulls the full ends also produce the lowest drag hull.
> > > > > B. Flaring the sides of the hull increases the waterplane area in
> > > > the
> > > > > front end and reduces the waterplane area in accordance with the
> > > > hull
> > > > > waves noted in A to increase the moment created by the hull waves.
> > > > > C. The longer the hull the greater the moment from the lift and
> > > > > sinkage created by the entry and exit.
> > > > > D. Having a flat planing surface in the ends with a slight rocker
> > > > > will provide dynamic lift once the hull approaches planing speed.
> > > > > The rocker on the trailing edge will create suction so it will
> > > > assist
> > > > > with the bow up trim.
> > > > >
> > > > > It is certainly a key issue for consideration with a large proa
> > > > where
> > > > > it is not convenient to move ballast around after each shunt
> > > > > although plenty of racing keel boats use their crew as movable
> > > > > ballast. However I do not believe it results in a limit in speed if
> > > > > the hulls are designed to stay bow up under the drive.
> > > >
> > > >
> > >
> > > Rick Willoughby
> > > rickwill@
> > > 03 9796 2415
> > > 0419 104 821
> > >
> >
>