A powered craft is very different from a sailing craft due to the sailing loads. I would be interested in a 20 knot 15m double ended minimum drag hull with a 900mm stem and a .85 prismatic coefficient with 4 tonne displacement with the bow just submerging and the stern just on the edge of lifting.
At the ww side it needs a 10m length hull varying between 3 tonne at slow speeds and .8 tonne at 20 knots and bow down attitude of 1:18
I am not sure why you have flare in the bow. I feel a better method is to have more buoyancy down low and a reversed stem
--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Todd
> If you give an idea of the speed you would like to achieve with that
> displacement then I can give you an idea of what the lowest drag hull
> would look like and then what lift can be achieved with various flat
> sections.
>
> The wave piercing is no problem going upwind if you keep the draggy
> bits above the wave crest. With the slight flare in my hulls I get a
> bit of extra lift in waves because the volume immersed for average
> draft increases on an irregular waterline. The increase in drag is
> of the order of 5 to 10% with waves unless you are dragging unfaired
> parts through the water.
>
> It can get very wet on my boats though because the seating position
> is not quite high enough to get me above the waves that I plough
> through. In larger waves the boat tends to rise and fall with the
> waves. On a proa it comes down to how high the bridge beam is set,
> how much of the windward hull is going to be forced through water and
> the fairing of all the bits that could be submerged.
>
> Going down wind I have not yet managed to eliminate diving if I press
> hard down a wave. I can drive my hulls into the back of a wave to
> the point where I am pedalling in water with the bow fully immersed.
> In my latest hull I am playing around with the deck shape with the
> aim of making it easier to lift when submerged. At present I get
> more down force with the deck submerged than lift from the flat
> entry. The faster I go the deeper it gets.
>
> Some recent power boat designs are fully wave piercing - eg Earthrace:
> http://www.youtube.com/watch?v=dxJOJDGchTs
> There are others with same concept.
>
> Even with wave piercing to the degree shown in the Earthrace
> modelling the water drag does not go up much if all the bits are
> faired. When dolphins want to travel fast they fly and dive
> repeatedly. They get deep enough to avoid wave drag and then get
> airborne to avoid water drag. This results in lowest overall drag at
> their high speed. It also gives them the opportunity to breathe of
> course.
>
> There are some interesting videos on Youtube of amas on big tris
> driving through waves.
>
> Rick
> On 07/07/2010, at 7:24 AM, tsstproa wrote:
>
> > Hi, Rick nice work.
> >
> > What about narrow flat sections with a deep draft 14-18'' with very
> > pointy bows with large displacement 2,500-3,500lbs.
> >
> > Doesn't this negate the whole wave making drag and lift theory even
> > when rockered 12'' lift from center keel to bottom bows?
> >
> > I Know that if you have a high displacement shallow draft hull
> > without rocker or very little the stern can cause problems for the
> > bow, especially for high prismatic coefficient hull, unless its
> > extremely slim usually meaning deeper draft Piercing hull vs riding
> > over(heavily rockered low draft under 12''). Where's the cut off
> > for Rockered depth of draft and non rockered piercing hull depth of
> > draft?
> >
> > It almost seems you can't have you cake and it too. Commit to wave
> > piercing for coastal waters and rockered for off shore sailing. For
> > large hull proas 40-60 feet. Difference in wave heights to be
> > encountered while sailing.
> >
> > Anyone seen the deadliest catch can't imagine a 50 foot wave
> > piercing sailing hull smoothly cutting through those kinds of seas?
> > There are two distinct boats types I can pick out on the show .
> > Ones a barge style and the other Norwegian boat sharp bow with
> > flare sits deeper in the water. Not sure on the entire bottom
> > shapes but seeing them both punch through 30foot seas one can see
> > the difference in how the ride through the waves.
> >
> > Todd
> >
> >
> > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > wrote:
> > >
> > > Problem with a large proa is you are not going to shift a large
> > > amount of weight each time you shunt.
> > >
> >
> > > The simple wetted surface argument for a round section hull is not
> > > valid once wave drag comes into the equation. There is very little
> > > difference in drag between round sections and flat sections but the
> > > flat sections will lift more and trim more bow up. This should be an
> > > advantage on a large proa where the weight distribution cannot be
> > > easily adjusted.
> > >
> > > Rick
> > >
> > >
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>