G'day,

 

Agree that half a degree of pitch is extraordinary at 15 knots for a double ended boat with central rig.

 

I'm not sure of the relationship between speed and drag (suspect it is at least a square, possibly a cube), but a large portion of it is the rudders, so can be reduced when reefed or off the wind by lifting the front one.

 

I guess the question of what lifts first can be calculated, but no idea how.  Has a lot to do with point of sail (offwind the stern will lift first, beating, the ww hull will) and wave direction.   

 

regards,

 

Rob
 

On 8/9/07, Robert <cateran1949@yahoo.co.uk > wrote:

a rough calculation gives less than half a degree pitch. (working on
2 inches up at the stern and 2 inches down at the bow gives 10cm
over 15m or 1 in 150) At 15 knots is extraordinary. Depending on the
relationship between resistance and speed gives in the order of only
a couple of degrees pitch at 25 knots.
How many deegrees before the stern leaves the water?
Is it possible to do the calculations of which goes first with full
sail up, the stern leaves the water or the ww hull leaves the
water . I realise that you would have to have a much stiffer mast
for this to happen on Vis.
On the trans pac clearly you would be flying a hull first
Robert
--- In harryproa@yahoogroups.com.au, "Rob Denney" <harryproa@...>
wrote:
>
> G'day,
>
> Don't be fooled by the reverse sheer and the spray washing over
the bows.
> It is nowhere near it's limits, in fact, it has barely immersed
the bow past
> the waterline. Harrys have huge amounts of buoyancy in the
bows due to
> their prismatic coefficient (a measure of buoyancy distribution)
of 0.8.
> Most cats are in the 0.6-0.65 range. With the rounded decks and
nothing to
> slow the boat (fore beam, trampoline, forestays, etc) it goes
through waves
> very easily.
>
> Not sure if you mean heel or pitch. Some of both are inevitable.
As the
> lee hull waterline at the bow is just out of sight and at the
stern a couple
> of inches are showing, I would estimate a couple of degrees of
heel, and
> less of pitch. The absence of heel is confirmed by the angle of
the
> stainless lifeline against the horizon. Mark reckons it pitches
and heels
> less than any boat he has ever been on.
>
> The video is indeed sedate seas. Not much we could do about
that. In
> bigger seas, my experience with my boats is that they go through
waves with
> no noticable effect (ie, you do not feel the boat slowing). This
boat is
> bigger and heavier, may have even less effect. What is noticable
on my
> boats, and to a lesser extent on Rare Bird, is that waves hitting
the rudder
> cases do noticably slow the boat. Only happens at high speeds,
with large
> waves and is caused by the cases, rather than the brackets, and it
has been
> addressed in later designs. It is evidenced by the creww feeling
a small
> jerk each time it hits a large wave. As you can see by looking at
the
> passengers, there is none of this.
>
> The rudder brackets have so far proven to be plenty strong enough
to take
> the loads, including running aground at speed with the wooden
sheer pin
> replaced with a large steel bolt, causing case damage.
>
> In 25 knots with big seas? Time will tell, but on all my
prototypes, it has
> not been a problem. There are not many cruisers that sail
consistently and
> comfortably at 15 knots, much less higher speeds. Rare Bird has
punched
> through a wave that washed items off the boom (>10' off the water)
while
> crossing the bar, with no ill effects.
>
> Great that you have advanced from "no good at all speeds" to "good
at 15
> knots wind, 15 knots boat speed", and I appreciate your ability to
accept
> evidence. I look forward to convincing you about the next step.
>
> regards,
>
> Rob
>
>
> On 8/9/07, Todd <bitme1234@...> wrote:
> >
> > No I don't think a flared bow would be any better.It would be
worse.
> > The boat doesn't look to be sailing flat. It looks to me to be
> > heeled 5 to 7 degrees maybe more in the video. To me the leeward
> > hull just seems to shallow at the ends. In the 1 metre swell the
bow
> > is punch through on a few all most buried. The video shows pretty
> > sedate sea state and the boat looks all ready to be pushing its
> > limits with the leeward hull low in the water. Along with the
> > appendage attachments. Load of rudders horizontally and vertical
in
> > proper trim but what about at speed, 20knots being pounded
> > vertically hour after hour. In and out wave after wave?
> >
> > Good at 15 knot winds 15 knot boat speed but what at 20 to 25
knots
> > in lumper seas?
> >
> > Todd
> >
> > --- In harryproa@yahoogroups.com.au <harryproa%
40yahoogroups.com.au>,
> > "Robert" <cateran1949@>
> > wrote:
> > >
> > > The boat looks as though it is riding pretty flat to me . With
3m
> > > swell I am assuming the bow will simply punch into it and
gently
> > rise
> > > without any violent hobby horsing. The flat ride should keep
the
> > sails
> > > working better than with violent motion of a flared bow
bouncing
> > off
> > > waves I can't think of any small boat that would not be pretty
wet
> > in
> > > the same circumstances. The braces are designed to take the
loads
> > of
> > > the rudders. Shock loads from the braces hitting the top of the
> > wave
> > > is nothing compared to loads from the rudders,
> > > Robert
> > > --- In harryproa@yahoogroups.com.au <harryproa%
40yahoogroups.com.au >,
> > "Todd" <bitme1234@> wrote:
> > > >
> > > > --- In harryproa@yahoogroups.com.au <harryproa%
40yahoogroups.com.au>,
> > "Todd" <bitme1234@> wrote:
> > > > >
> > > > > Hello Rob and folks, (sorry about that)
> > > > >
> > > > > Nice video, impressive. But;) Looks like 1 metre swell
> > possible in
> > > > > 15 knot winds for a boat speed of 15knots . Marshall Island
> > Walap
> > > > > will do that. What about 25 knot winds in 3 metre swell?
Looks
> > as
> > > > > throught the bow is pretty close to the edge in 15 knots.
As
> > far
> > > > as
> > > > > all out performance pushing the boat to the limits what is
> > known?
> > > > >
> > > > > What about the braces for the weather boards, how much
abuse
> > will
> > > > > they handle being punched from underneath or swist from
> > changing
> > > > > angle of attacks in certain situations. The bottom brace
seems
> > > > > really close to the water surface.
> > > > >
> > > > > Todd
> > > > >
> > > > > --- In harryproa@yahoogroups.com.au <harryproa%
40yahoogroups.com.au>,
> > "Rob Denney" <harryproa@>
> > > > > wrote:
> > > > > >
> > > > > > G'day,
> > > > > >
> > > > > > My Harry did 15 in 15 with lousy sails, but not much
> > interior,
> > > > so
> > > > > probably
> > > > > > pretty similar. Blind Date will be faster than Rare Bird
as
> > it
> > > > is
> > > > > lighter,
> > > > > > has less windage and a stiffer mast. Rare Bird's sails
also
> > > > need
> > > > > some work,
> > > > > > it has not realised it's full potential yet.
> > > > > >
> > > > > > The only real difference in a Harry is whether you have
the
> > > > > cockpit cover or
> > > > > > not. Bain has it and it works well. I prefer to feel the
> > > > breeze,
> > > > > so the
> > > > > > solo boat will have a pram type fold up cloth cover over
> > part of
> > > > > the cockpit
> > > > > > for keeping out of the rain and wind.
> > > > > >
> > > > > > regards,
> > > > > > Rob
> > > > > >
> > > > > >
> > > > > > On 8/8/07, George Kuck <chesapeake410@> wrote:
> > > > > > >
> > > > > > > How will the 12m (40') Harry (built with the KSS
> > method)
> > > > > performance
> > > > > > > compare to Rare Earth or Blind Date ? Will it have
> > > > a "cruiser"
> > > > > or "sport"
> > > > > > > version option or be a compromise between the two ?
> > > > > > >
> > > > > > > George Kuck
> > > > > > > Chestertown, MD
> > > > > > >
> > > > > > > *Robert <cateran1949@>* wrote:
> > > > > > >
> > > > > > > It is pretty impressive for such a comfortable boat.
Even
> > > > with
> > > > > the
> > > > > > > extra weight it is still pretty light compared to most
> > > > > multihulls of
> > > > > > > similar length,
> > > > > > > \ Robert
> > > > > > >
> > > > > > > --- In harryproa@yahoogroups.com.au<harryproa%
40yahoogroups.com.au><harryproa%
> > > > > 40yahoogroups.com.au >, Mike
> > > > > > > Crawford <jmichael@> wrote:
> > > > > > > >
> > > > > > > >
> > > > > > > > Fifteen knots in fifteen knots of wind? In Rare Bird?
> > Holy
> > > > > moly!
> > > > > > > >
> > > > > > > .
> > > > > > >
> > > > > > >
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