SWEEEEEEEEEEEAT BOAT LONG AND SLEEK. The lines look almost unreal there so straight/sharp. Very nice work.

But at what displacament, waterline levels, and under water plane area are you working with?

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.
>
> This link shows the hull I have tested:
> http://www.rickwill.bigpondhosting.com/V14.htm
> It had lower drag at higher speed than initially predicted in level
> trim because it lifts due to wave pressure. There is now software
> available that allows the trim and resulting drag to be calculated.
> The highest speed I have pushed it to is 9kts and this is below the
> point where dynamic lift is significant. The trim change is due to
> pressure variation on the hull from wave making and is noticeable
> from about 5kts.
>
> 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
>
>
> On 03/07/2010, at 3:44 AM, tsstproa wrote:
>
> > The trimaran squat, its draggy and inefficient. They used geometry
> > in main hull to anticipate wave action against hull and sails shift
> > of ceo at speed to predetermine at what attitude hull will ride.
> > For years it seemed their theory of weight rearward with high
> > buoyancy forward with main hull highly rockered rearward producing
> > (the squat) was the norm in multihulls. That was their solutions to
> > bow bury. Simple teeter-totter anology. Slowly but surely their
> > getting away from the squat knowing its inefficiencies and its
> > limiting factors. Again weight and displacement balanced fore and
> > aft at a varying point to achieve desired outcome There's only so
> > many combinations. Hows a hull supposed to sit if you take a big
> > chunk out from the bottom half and then add weight sure it will
> > ride bow up even while sailing look at how much sail area is aft on
> > those designs. The old fishing Sharpie hulls had the same rocker
> > contour big swoop under the back half.
> >
> > Most modern high performance tri's have a more evenly centered
> > balance weight/displacement main hull and use fairly flatrockered
> > full amas placed in geometric loction to predicted and counter
> > desired sailing effects now a days.
> >
> > Todd
> >
> > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > wrote:
> > >
> > > I have done experimental testing and detailed hydrodynamic analysis
> > > on long slender flat bottom dory type hulls.
> > >
> > > These hulls have high block coefficients and trim bow up even at
> > > displacement speed. This is due to wave making pressure distribution
> > > not dynamic lift. Setting some rocker in the ends increases the bow-
> > > up trim at displacement speed and increases dynamic lift at higher
> > > froude number.
> > >
> > > With these hulls it is possible to counter the pitching moment from
> > > modestly tall rigs so the boat trims bow up or near level at speed.
> > >
> > > If you take a look at the sections of the amas on BMW Oracle you
> > will
> > > see they are essentially flat bottoms. In the case of a tri the wide
> > > transom will sink the stern a little more than achieved with a flat
> > > canoe stern on a proa hull but it is still possible to generate
> > > significant bow-up trim with the canoe stern.
> > >
> > > Rick
> > > On 30/06/2010, at 1:20 PM, robert wrote:
> > >
> > > > The driving forces of the sails and the resistive forces of the
> > > > foils and hulls creates a torque that forces the bows down. This
> > > > can be compensated in small boats by moving people or even in
> > large
> > > > boats with moveable ballast. There is nothing much one can do
> > about
> > > > this except minimise the resistance by having smooth foils and
> > > > hulls and I think some value can be had from having the drag from
> > > > the foils more to lee of the vector of the centre of drive of the
> > > > rig to reduce the induced drag needed to compensate for an
> > > > imbalance of drag. Theoretically high aspect foils have less
> > > > induced drag for the same lift. These two points suggest having
> > > > fatter bows and the rudders more towards the ends with two
> > leebords
> > > > and then lifting as many foils as possible. Having a high
> > prismatic
> > > > coefficient reduces the depth of the bow depression as there is
> > > > more extra buoyancy on a longer lever arm for the same restoring
> > > > moment. This needs to be balanced against the reduction of drag
> > > > associated with a sharp transom when dealing with double ended
> > > > vessels and wave impacts. Wave impacts include vertical movement
> > > > coming off a wave and horizontal movement due to movement through
> > > > the water. I think the lee bows of the Vis are a very nice
> > balance.
> > > >
> > > >
> > > > --- In harryproa@yahoogroups.com.au, Arto Hakkarainen
> > > > <ahakkara@> wrote:
> > > > >
> > > > > The bows of visionarry are just the way they should be. They
> > have
> > > > enough buoyancy to be safe and fast. However, the force on the rig
> > > > will push the bow down more or less. Having as good balance as
> > > > possible is good for boat performance in all conditions. Having
> > > > bows up in moderate and heavy wind is better than having bows
> > down.
> > > > Having bows up should improve the balance also. That is all I was
> > > > trying to say. Finding a way to both improve balance and lift the
> > > > bows should be good for both perfomance and seaworthiness. What
> > are
> > > > the solutions for achieving those goals and compromises that come
> > > > with the solutions are the questions I was and still am wondering.
> > > > Even with the added complication of four foils (two rudders and
> > two
> > > > boards) I think the improvements would be worth it IMHO. Next
> > > > question is should it be two daggerboards like Ono or some other
> > > > system.
> > > > > Â
> > > > > Arto
> > > > >
> > > > > --- On Thu, 6/24/10, Rudolf vd Brug <rpvdb@> wrote:
> > > > >
> > > > >
> > > > > From: Rudolf vd Brug <rpvdb@>
> > > > > Subject: Re: [harryproa] Re: Rudder lift?
> > > > > To: harryproa@yahoogroups.com.au
> > > > > Date: Thursday, June 24, 2010, 12:35 PM
> > > > >
> > > > >
> > > > > Â
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > The new rudders of BD seem to show that thew minimum distance
> > for
> > > > the large rudders is the old position.
> > > > > Also I would say that lateral balance in a sailing hull is a
> > nice
> > > > thing to have, and that seems to lead to rocker imo.
> > > > > Â
> > > > > rudolf
> > > > >
> > > > > ----- Original Message -----
> > > > > From: Rob Denney
> > > > > To: harryproa@yahoogrou ps.com.au
> > > > > Sent: Thursday, June 24, 2010 8:09 AM
> > > > > Subject: Re: [harryproa] Re: Rudder lift?
> > > > >
> > > > > Â
> > > > >
> > > > > The bows may be narrow, but they have far more buoyancy, much
> > > > further from the mast than any other boat I can find with the same
> > > > sail area.
> > > > >
> > > > > Most boats sail bow down when pressed hard. Â Â They don't have
> > > > control problems.Â
> > > > >
> > > > > I can see how a daggerboard/ leeboard/ fixed keel have lower
> > > > loads than an oversize rudder, but I cannot see how they do
> > > > anything to the centre of lateral resistance that the oversize
> > > > rudders don't, apart from moving a component of it (the rudder
> > > > drag) a metre or so to windward.    Given the extra work, cost
> > > > and danger of the fixed foils, I will stick with oversize rudders,
> > > > built strong. However, keep experimenting, the more data, the
> > > > better.
> > > > >
> > > > > rob
> > > > >
> > > > >
> > > > > On Thu, Jun 24, 2010 at 8:37 AM, Arto Hakkarainen
> > > > <ahakkara@yahoo. com> wrote:
> > > > >
> > > > >
> > > > > Â
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > This reminds me of some of the model testing Todd did a
> > couple of
> > > > years ago. When the boat is pressed hard with high rig the bow
> > > > seems to be pressed under and knocked down and/or luffs to wind.
> > > > Seems quite uncontrollable and violent incident based on the model
> > > > tests. You should find the test videos from youtube. My current
> > > > connection is too slow for youtube search this week...
> > > > > Â
> > > > > It seems that the high rig and narrow wave piercing bows will
> > > > cause the boat to sail bow down at high speed when it is not
> > > > wanted. Bow down may be good for light weather work for boats with
> > > > wide aft sections since it reduces wetted surface. In heavy
> > weather
> > > > and higher speeds bow up would be best choice but how to get thatÂ
> > > > is the problem.
> > > > > Â
> > > > > My favourite boards for proa are the twin bruce foils developed
> > > > by Fulgencio and demonstrated at the proa file. In his system the
> > > > bow foil is canted to give more lift up for the bow and more
> > > > lateral resistance at the aft end. Foils are linked so that
> > canting
> > > > one foil to more horisontal will cant the other foil to more
> > > > vertical position. Canting forward foil to more horisontal will
> > > > lift the bow and move the lateral plane aft which will lead to
> > > > better balance and better hull position.
> > > > > Â
> > > > > Downside of the system is that IMO it needs also rudders for
> > > > added control when sailing and all control when motoring. Also
> > > > making the system strong and simple enough is a challenge and with
> > > > also rudders means four moving foils on the boat which is hardly
> > > > simple anymore.
> > > > > Â
> > > > > Arto
> > > > > Â
> > > > > Â
> > > > >
> > > > > --- On Wed, 6/23/10, Rudolf vd Brug <rpvdb@freeler. nl> wrote:
> > > > >
> > > > >
> > > > > From: Rudolf vd Brug <rpvdb@freeler. nl>
> > > > >
> > > > > Subject: Re: [harryproa] Re: Rudder lift?
> > > > >
> > > > > To: harryproa@yahoogrou ps.com.au
> > > > > Date: Wednesday, June 23, 2010, 10:45 AM
> > > > >
> > > > >
> > > > > Â
> > > > >
> > > > >
> > > > >
> > > > > BD has a rockered ww hull while RB has a straight keel to ww.
> > > > That is a difference that might change something.
> > > > > On BD at the test sail with new rudders sailing with just the
> > the
> > > > main was hard enough. Lots of rudder angle to keep course.
> > > > > Raising the jib (20 m2 on a total of 76m2) gave a lot of extra
> > > > power, we felt the drag, the boat didn't accelerate and
> > rounded up
> > > > uncontrollable.
> > > > > We have always been surprised by the bow down attitude of BD
> > in a
> > > > bit of wind, maybe from 14 knots upwards. Also we haven't seen
> > speeds
> > > > > over 14.5 knots even at winds where you would expect more.
> > > > > With the old rudder set up we tried lifting the front one and
> > > > lots of different positions but it didn't seem to make a lot of
> > > > difference.
> > > > > Â
> > > > > Rudolf
> > > > > Â
> > > > > Â
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: Rob Denney
> > > > >
> > > > > To: harryproa@yahoogrou ps.com.au
> > > > > Sent: Wednesday, June 23, 2010 2:07 AM
> > > > > Subject: Re: [harryproa] Re: Rudder lift?
> > > > >
> > > > > Â
> > > > >
> > > > >
> > > > > Hard to get really high prismatics with rocker, but they may not
> > > > be required. Something else to test.
> > > > >
> > > > > On Rare Bird in the Gladstone race we were hit with a pretty
> > good
> > > > gust and the boat took off on a broad reach. Huge amounts of
> > > > spray from the rudder, but the bow barely went down at all and
> > > > steering remained easy. It was pretty near the comfort limit if
> > > > we had been cruising. Doug put a video of it on You Tube.Â
> > > > >
> > > > > If you are immersing the bows further than this on Blind Date
> > > > (which is lighter, but has the same lee hull), you must be
> > > > putting some serious force into it. How much wind was there?Â
> > > > What sail did you have up and were there any waves? Anything else
> > > > that might be relevant?
> > > > >
> > > > > On Elementarry moving my weight fore and aft does not make much
> > > > difference to the bow trim as I can't move far and it sters pretty
> > > > well bow up opr bow down, except when it is going slowly. Upwind,
> > > > I sit amidships or aft if I need to be near the mainsheet cleat.
> > > > Really pushing it downwind, I sit on the aft beam, but have still
> > > > managed a summersault. . Â
> > > > >
> > > > > What was quite noticable was the difference in bow down trim
> > > > between having the front rudder (reasonably well shaped and
> > faired,
> > > > but nowhere near perfect) up or down. Up and the nose lifted
> > > > noticably and the boat went much quicker. This happened both up
> > > > and down wind, which is one of the reasons I switched to using a
> > > > single rudder. I guess the drag would also add to the tendency to
> > > > luff, but the rudders are still pretty close to the hull, so it
> > was
> > > > not noticable.Â
> > > > >
> > > > > Still plenty to learn!
> > > > >
> > > > > rob
> > > > >
> > > > >
> > > > >
> > > > > On Wed, Jun 23, 2010 at 6:51 AM, Rudolf vd Brug <rpvdb@freeler.
> > > > nl> wrote:
> > > > >
> > > > >
> > > > > Â
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > The buoyancy would be there, but located differently.
> > > > > Changing the lateral profile can change the behaviour of a boat
> > > > dramatically.
> > > > > It could be the boat would seem to have a more bow down
> > attitude,
> > > > but the truth would be the deepest part of the hull moved forward
> > > > just a bit instead of all the way to the bow.
> > > > > High prismatic coefficient is good to prevent nose diving, that
> > > > doesn't change if the hull has rocker.
> > > > > Leeboards have advantages, but I don't know of leeboards at high
> > > > speed( say over 12 knots).
> > > > > Â
> > > > > Â
> > > > >
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: robert
> > > > > To: harryproa@yahoogrou ps.com.au
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > Sent: Tuesday, June 22, 2010 5:28 PM
> > > > > Subject: [harryproa] Re: Rudder lift?
> > > > >
> > > > > Â
> > > > >
> > > > >
> > > > > I don't see that rocker in the lw hull really helps. It will
> > > > still require similar extra buoyancy in the bow to counteract the
> > > > sailing loads. (it would also give more vertical load vectors form
> > > > the sail, but this is pretty marginal) A rockered ww hull would
> > > > make it worse.
> > > > > A higher prismatic coefficient giving greater extra bow buoyancy
> > > > for less side area should make it better.I am working on 8.5-9
> > > > prismatic coefficient, depending on the payload
> > > > >
> > > > > Your work with a single leeboard is dominating my ideas at the
> > > > moment with the rudders at 9m apart just out from the hull, though
> > > > I am wondering about two leeboards. This is starting to look a bit
> > > > excessive.
> > > > >
> > > > >
> > > > > --- In harryproa@yahoogrou ps.com.au, "Rudolf vd Brug" <rpvdb@>
> > > > wrote:
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > The steering problems on BD to me seem related to the bow
> > being
> > > > pushed down so it becomes the deepest part of the boat.
> > > > > > It took me some time to realise that this seems to be
> > happening
> > > > and that it relates to experiences on other boats. For a non-
> > proa a
> > > > solution may be to trim the stern down. For a HP that would mean
> > > > pumping water ballast. Another solution for a proa might be to
> > > > design rocker in the lw hull.
> > > > > > A rockerless lw hull of a HP in my opinion needs its rudder as
> > > > far aft as possible. The small ones like Harriette are easily
> > > > trimmed by shifting weight, which is a instictive reaction when
> > > > sailing a small boat at speed.
> > > > > >
> > > > > > regards,
> > > > > > Rudolf
> > > > > >
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: Gardner Pomper
> > > > >
> > > > > > To: harryproa@yahoogrou ps.com.au
> > > > > > Sent: Tuesday, June 22, 2010 2:58 PM
> > > > > > Subject: Re: [harryproa] Re: Rudder lift?
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > The leeway is not my primary concern. I am worried about
> > > > steering. I have heard several mentions about Blind Date and also
> > > > about Sidecar, that they lose steering control, can't shunt, or
> > > > head uncontrollably up into the wind before their rudders were
> > > > enlarged, moved, etc.
> > > > > >
> > > > > > I don't see the advantage of a shallow draft boat if I need to
> > > > have my rudders down 5' in order to steer. I have been trying to
> > > > find out if this is just a problem when the boats are overpowered,
> > > > or strong winds or something, but no one has admitted to that,
> > so I
> > > > am worried that I won't be able to sail in less than 4-5 feet of
> > > > water. I will be able to drag my boat up near the beach, but the
> > > > last mile will have to be done under power.
> > > > > >
> > > > > > - Gardner
> > > > > >
> > > > > >
> > > > > > On Tue, Jun 22, 2010 at 8:05 AM, robert <cateran1949@ ...>
> > wrote:
> > > > > >
> > > > > >
> > > > > > In shallow water, there is a some leeway resistance due to the
> > > > water having a hard time getting out of the way. The shallower the
> > > > water, the greater the effect for the same depth of boat.
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > > --- In harryproa@yahoogrou ps.com.au, Mike Crawford
> > <jmichael@>
> > > > wrote:
> > > > > > >
> > > > > > > Gardner,
> > > > > > >
> > > > > > > Your Mainecat/5200 idea is safe with me. I'm building a
> > > > plywood dory
> > > > > > > this summer and will be doing the same thing. Even if it
> > > > doesn't work,
> > > > > > > the theory is comforting./ /
> > > > > > >
> > > > > > > So now you're basically tripling your submerged foil area
> > for
> > > > a 1.5'
> > > > > > > depth: two rudders at normal width, and two mini keels that
> > > > I'm assuming
> > > > > > > would each be twice as wide as a rudder. You won't have
> > ideal
> > > > steerage
> > > > > > > and leeway prevention, but my guess is that this is a moot
> > > > point.
> > > > > > > Either you have two rudders, or you have rudders plus dagger
> > > > boards or
> > > > > > > mini keels. Anything you do beyond the rudders will
> > likely help.
> > > > > > >
> > > > > > > I'd try keeping the keels as close to each other, though.
> > This
> > > > > > > wouldn't be idea for beaching, but as Rob pointed out,
> > tires are
> > > > > > > probably better than keels anyway -- that way there's no
> > risk
> > > > of gravel
> > > > > > > sanding off your bottom paint, or of bouncing in the surf
> > > > taking your
> > > > > > > keels off. In keeping the keels close together, almost like
> > > > Rudolph's
> > > > > > > tandem keel, the keels shouldn't impact steering that much,
> > > > and could
> > > > > > > even conceivably help. Two keels far apart, on the other
> > > > hand, might
> > > > > > > make it harder to shunt, particularly when you don't have as
> > > > much rudder
> > > > > > > in the water as you'd like.
> > > > > > >
> > > > > > > At least you'll have the option of two counter-rotating
> > rudders.
> > > > > > > That's definitely going to help steering in minimal depths
> > > > when compared
> > > > > > > to a cat.
> > > > > > >
> > > > > > > - Mike
> > > > > > > / /
> > > > > > >
> > > > > > > On 6/21/2010 1:53 PM, Gardner Pomper wrote:
> > > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > Yes, your description of when to use mini-keels is what I
> > > > had in mind.
> > > > > > > > I would rather not build them, but I am unclear as to what
> > > > the minimum
> > > > > > > > rudder area needed when sailing in light winds. Here is
> > the
> > > > scenario I
> > > > > > > > have in mind:
> > > > > > > >
> > > > > > > > In the chesapeake, or the bahamas, there are many spots
> > > > that are 2-3
> > > > > > > > feet deep that I would like to glide along in relatively
> > > > light winds.
> > > > > > > > The waters are sheltered, and therefore flat, and the wind
> > > > is likely
> > > > > > > > to be less than 10 knots. When doing this, I would like to
> > > > have a
> > > > > > > > draft of 2' or less. I can't have my rudders extended to 4
> > > > or 5' depth
> > > > > > > > to get the requisite 2% of sail area, so I thought that
> > fixed
> > > > > > > > minikeels, maybe 1' deep, would give the boat a 1.5'
> > draft.
> > > > That, plus
> > > > > > > > the rudders raised to 18" draft would give me more foil
> > > > area than the
> > > > > > > > rudders alone. I would not be looking to sail at > 5 knots
> > > > under these
> > > > > > > > conditions, because i really don't want to hit anything.
> > > > > > > >
> > > > > > > > In that scenario, with a boat about the size of a
> > harry, or a
> > > > > > > > harrigami, would I be able to steer with just the rudders
> > > > (total
> > > > > > > > submerged area of 3 sq ft, vs 400 sq ft of sail)? Would I
> > > > be better
> > > > > > > > off with an additional 3 sq ft of mini-keels?
> > > > > > > >
> > > > > > > > My Maine Cat 30 had the mini-keels attached with 5200, for
> > > > precisely
> > > > > > > > the reason you mentioned.. in a severe collision, the
> > keels
> > > > were
> > > > > > > > supposed to break off without ripping open the bottom of
> > > > the hull. I
> > > > > > > > have no idea if that would have worked or not, but it gave
> > > > me peace of
> > > > > > > > mind to believe it, so please don't contradict the idea
> > > > <grin>.
> > > > > > > >
> > > > > > > > - Gardner
> > > > > > > >
> > > > > > > > On Mon,
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > >
> > > Rick Willoughby
> > > rickwill@
> > > 03 9796 2415
> > > 0419 104 821
> > >
> >
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>