My understanding is that once you get over waterline length speed, the rocker of a displacement type hull is only going to cause drag.
Fast offshore single ended multihulls have a sharply truncated stern to avoid drag and only enough rocker to allow tacking. A double ended vessel can't do this and so a fine exit is needed. This exit someway dictates the entrance as it is a double ender. Looking at the time of impact of a bow and the vertical forces of the impacts reinforces the need for a deep forefoot, no rocker and preferably reverse stem. --- In harryproa@yahoogroups.com.au, "tsstproa" <bitme1234@...> wrote:
>
> How deep of draft on a none rockered hull could you take it. Vs rockered hull. It just seems the nonrockered hull would take more of a beating even though its piercing most of the time except in the big stuff. What kinda of forces on the wave piercing lee hull are at play running a close reach in 25' sea? Do you really want it piercing? Seems like an awful lot of side torsion going on as windward clears and leeward still submerged?
>
> Wouldn't the rocker help to cushion the ride in the big stuff or just make it worse sitting higher on the water? The only thing I see is that on the rockered hull you lose some buoyancy at the front also changing the entry of the bow to water.
>
> Todd
>
> --- In harryproa@yahoogroups.com.au, "tsstproa" <bitme1234@> 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
> > >
> > >
> >
>