I still do not understand why it is so important to keep horizontal. The extra nose down from the sail drive for the 12m 1 tonne model is less than 50mm. Does that extra nose down really cause that much more drag, especially considering the slightly greater stability of a rockerless hull in a chop and the accompanying stability of air flow over the rig. Minimal drag within constraints of load, length, dealing with waves and chopis the criteria I am interested in. If I wanted some extra hydrodynamic lift , there are always angled foils and spray rail.
I reallly appreciate the effort and input, especially for the 15m 4 tonne hull maving minimum drag with no rocker and apologise for being a bit of a curmudgeon in hammering my points,
Robert
--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> The length constraint or non-constraint is a function of design speed
> and weight.
>
> As an example a 1 tonne hull with a flat bottom designed for minimum
> drag at 25 knots results in a length of 12m. However this hull will
> not generate enough bow up moment through wave making to counter the
> moment from the rig to drive it at that speed. Extending the length
> to 15m will get close.
>
> I agree on the reserve buoyancy. The more volume you have above the
> waterline the more drag you get. I have a 90 degree V on the deck at
> the bow of my latest hull as a trial to see if it will lift while
> driving into the back of a wave. The rocker in the ends also helps
> with the lift at the bow if buried. The freeboard at the stem is
> 50mm when on the design waterline. It will easily plough through waves.
>
> The low buoyancy and slight rocker in the ends also reduces the
> tendency to surf down waves. The stern tends to squat and is not
> have much buoyancy to lift it. You see surf skis and outrigger
> canoes do not have large buoyant sterns or aft planing surface. This
> helps them to sit on a wave rather than lift by the stern and surf to
> the bottom.
>
> Rick
> On 15/07/2010, at 5:19 PM, robert wrote:
>
> > Allowing the bows to wave pierce reduces drag compared with bows
> > that have more reserve buoyancy. Just make sure the tops of the
> > bows are round enough to allow them to rise again.
> >
> > In general, we are all length constrained. To go over 15m in length
> > starts to bring all sorts of legal changes in Oz
> >
> > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > wrote:
> > >
> > > You need to be logged into HarryProa to see the video.
> > >
> > > Try it with a little rocker on the same length - I expect you
> > will be
> > > surprised. The aim is to keep the trim so balance is maintained
> > > rather than requiring control input.
> > >
> > > Rick
> > > On 15/07/2010, at 8:11 AM, tsstproa wrote:
> > >
> > > > Says file not found.
> > > >
> > > > The model with the orange sail in the previous clip show the
> > > > obvious as you point out longer hull but only to a point 4''
> > inches
> > > > longer with a more vertical buoyancy taller sheer. If I were to
> > add
> > > > rocker or nose flip to the larger hull it would actually change
> > bow
> > > > trim down even more so unless I were to go to an even longer hull
> > > > say 28 inches to achieve same waterline length on nonrockered
> > hull.
> > > > As is with no rocker piercing hull high Cp it simple submerges and
> > > > keeps on going slowing very little as it sinks to depth being
> > > > sailed hard.
> > > >
> > > > Have a look at this clip Its another progression on how I achieved
> > > > what is now.
> > > >
> > > > http://www.youtube.com/watch?v=jgCSYi5pwS8
> > > >
> > > > Todd
> > > >
> > > >
> > > > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > > > wrote:
> > > > Your
> > > > > model with the orange sail shows the bow down attitude and
> > potential
> > > > > for pitchpoling when the sail moment overpowers the wave making
> > > > > moment. The other model with the lower rig and longer hull
> > maintains
> > > > > better balance between the moments.
> > > > >
> > > > > What Flotilla shows is that a flat bottom hull can generate more
> > > > wave
> > > > > making moment for a given length than a round section hull. Also
> > > > > rocker in the ends increases the moment. As well there is
> > little or
> > > > > no drag penalty in going to a flat bottom with a slender
> > hull. In
> > > > > fact at higher froude number it will likely be an advantage.
> > > > >
> > > > > The flat bottom slender hull will never squat like a typical
> > planing
> > > > > hull but it does have potential to keep level trim under sail
> > loads.
> > > > > The canoe stern (bow) means it will leave a clean wake even
> > if there
> > > > > is a slight squat. However at higher froude number the
> > tendency is
> > > > > to get net lift rather than net sinkage.
> > > > >
> > > > > The rocker is not extreme when you observe the hull. There is
> > a bit
> > > > > of turn in the ends. That will be the lowest drag hull shape
> > for any
> > > > > displacement that is not length constrained. It is only when
> > length
> > > > > is constrained that the rocker flattens out.
> > > > >
> > > > > You can see how the drag rises rapidly on your boat with the
> > tall
> > > > rig
> > > > > when the bow is pressed below the surface. This causes the
> > boat to
> > > > > trip up and it gets close to pitchpoling.
> > > > >
> > > > > You could make a flat bottom hull for the tall rig that does
> > not dig
> > > > > in. It would power up until the ww hull lifts. I expect it
> > will be
> > > > > longer than the hull you have now.
> > > > >
> > > > > Rick
> > > > >
> > > > > On 14/07/2010, at 2:35 PM, tsstproa wrote:
> > > > >
> > > > > > So basically once hull over powers bow wave all bets are
> > off. Your
> > > > > > analysis is more in favor of trim at displacement speeds!?
> > > > > >
> > > > > > What is it exactly that beach cats are doing its not exactly
> > > > > > plaining like a 49'er dinghy and not exactly sailing like a
> > lido
> > > > > > 14? Or is it?
> > > > > >
> > > > > > I wouldn't stand on the beach and say wow look at the hobie 16
> > > > > > planning. Like I would say watching a 18" foot skiff race.
> > > > > >
> > > > > > On the cat hulls narrowness and slippery shape would seem to
> > > > easily
> > > > > > over come any displacement waves being made. Hulls finesse
> > ratio's
> > > > > > and coefficients making it so.
> > > > > >
> > > > > > Having rocker on the extreme end of those figures for max
> > > > > > displacement would almost seem to trip it up causing to
> > much push
> > > > > > foward or unnecessary turbulence from the rockered keel bow
> > > > > > section? Holding speed back until lifting clear. Having the
> > bows
> > > > > > (vertical buoyancy) on a nonrockered hull and being double
> > ended
> > > > > > pointy at both ends, placing buoyancy in a more vertical
> > column on
> > > > > > a hull with a hi Cp allows for the expected pitch movement
> > foward
> > > > > > vs rearward and improves drag coefficient vs tail dragging and
> > > > > > kicking up a rooster tail which a no rocker hull will do
> > > > trimmed to
> > > > > > squat rearward.
> > > > > >
> > > > > > Here's a clip showing my conclusion for vertical bouyancy
> > in bows
> > > > > > on hi Cp hull and its effects.
> > > > > > http://www.youtube.com/user/tsstproa#p/u/50/426M9YYxfsQ
> > > > > >
> > > > > > Here's a clip showing a slightly reshaped hull. Granted the
> > > > boat is
> > > > > > larger and 4'' longer The shape was achieved from the model
> > in the
> > > > > > first clip and its out come.
> > > > > > http://www.youtube.com/watch?v=OzqXqDlDwTI&feature=channel
> > > > > >
> > > > > > If either hull were to squat rearward could you imagine the
> > drag
> > > > > > from the flat rocker aft and square chine.
> > > > > >
> > > > > > Just my thought anyways.
> > > > > >
> > > > > > I thought maybe you had bridge the gap between flat rocker
> > wave
> > > > > > piecering and planing speed hull trim. What would the
> > effect be
> > > > > > with a High Cp hull at planning speeds with a drawn out flat
> > > > rocker
> > > > > > middle section with a nice nose flip be? The tip of the
> > nose flip
> > > > > > being level with displacement draft the rest of the curve
> > being
> > > > > > under water?
> > > > > >
> > > > > > Thanks for putting up with me and my armchair designing
> > back yard
> > > > > > tinkering.
> > > > > >
> > > > > > Todd
> > > > > >
> > > > > >
> > > > > > --- In harryproa@yahoogroups.com.au, Rick Willoughby
> > <rickwill@>
> > > > > > wrote:
> > > > > > >
> > > > > > > Todd
> > > > > > > The analysis is based solely on the wave formation around
> > the
> > > > hull.
> > > > > > > The planing forces are not included. These will increase the
> > > > bow up
> > > > > > > moment if the bow trims up due to wave formation at the
> > speed of
> > > > > > > interest. However for slender hulls in the size being
> > > > considered the
> > > > > > > dynamic lift is not particularly significant for speeds
> > under
> > > > 20kts.
> > > > > > >
> > > > > > > The analysis takes a bit of time. I have looked at various
> > > > hulls in
> > > > > > > two ranges. These include the 90kg range for up to 10kts and
> > > > the 1
> > > > > > > tonne range for up to 25kts. Given the time it takes it
> > needs
> > > > to be
> > > > > > > for something definite that might be of real interest for
> > > > building
> > > > > > > rather than just for the exercise.
> > > > > > >
> > > > > > > A limited version of the Flotilla software is available for
> > > > free and
> > > > > > > can be found here:
> > > > > > > http://www.boatdesign.net/forums/design-software/flotilla-
> > > > demo-2-07-
> > > > > > > a-32276.html
> > > > > > > You will get some idea of the difficulty in using it if
> > you have
> > > > > > a go
> > > > > > > at it.
> > > > > > >
> > > > > > > Leo is working on a further development to take in planing
> > > > forces. I
> > > > > > > do not know if this is for the AIS work on rowing hulls or
> > > > something
> > > > > > > for the navy. I doubt that it will have much application for
> > > > a round
> > > > > > > section hull though.
> > > > > > >
> > > > > > > Rick
> > > > > > >
> > > > > > > On 12/07/2010, at 11:56 PM, tsstproa wrote:
> > > > > > >
> > > > > > > > Your analysis for bow up trim is more in favor of a
> > > > planning hull
> > > > > > > > or displacement hull and at what speeds?
> > > > > > > >
> > > > > > > > Yes I know sail forces along with having a flat run to
> > stern
> > > > > > causes
> > > > > > > > bow down trim. So what are the effects by adding slight
> > > > rocker to
> > > > > > > > the deeper narrower hull form? Say on a 12'' vs 6'' draft
> > > > for same
> > > > > > > > displacement?
> > > > > > > >
> > > > > > > > I have a great 10 minute clip unedited I need to post of
> > > > Square
> > > > > > > > harry thats the flat bottom hull I designed with the old
> > > > blue dyna
> > > > > > > > rig in a fair amount of wind and chop. The chop is almost
> > > > perfect
> > > > > > > > scale to the craft looks like 1-2 foot chop with a rolling
> > > > larger
> > > > > > > > swell. Showing a great visual analysis of hulls flat
> > bottom no
> > > > > > > > rocker characteristics.
> > > > > > > >
> > > > > > > > I just have to reformat it and post it.
> > > > > > > >
> > > > > > > > By adding rocker you say the trim could be better , sail
> > > > faster ?
> > > > > > > >
> > > > > > > > Todd
> > > > > > > >
> > > > > > > > --- In harryproa@yahoogroups.com.au, Rick Willoughby
> > > > <rickwill@>
> > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > Todd
> > > > > > > > > A hull with no rocker still has a pitching moment
> > trying to
> > > > > > force
> > > > > > > > the
> > > > > > > > > bow up. Whether it will trim bow up under sail forces
> > can be
> > > > > > > > > determined. From the analysis I have done, adding a
> > little
> > > > > > rocker in
> > > > > > > > > the ends increases the bow-up moment. It also means
> > there
> > > > > > will be
> > > > > > > > > some lift from planing forces.
> > > > > > > > >
> > > > > > > > > If a hull with no rocker trims bow down under sail
> > loads it
> > > > > > gets no
> > > > > > > > > benefit from planing force. It relies solely on the
> > > > buoyancy.
> > > > > > > > >
> > > > > > > > > Also the trim/squat is not my theory it is something
> > that be
> > > > > > > > > determined using the Flotilla software and something
> > I have
> > > > > > measured
> > > > > > > > > on my own hulls to verify the Flotilla output.
> > > > > > > > >
> > > > > > > > > Rick
> > > > > > > > > On 11/07/2010, at 10:11 AM, tsstproa wrote:
> > > > > > > > >
> > > > > > > > > > So are you basing your theory on drawing out
> > > > (lengthening) the
> > > > > > > > flat
> > > > > > > > > > center section of keel towards bows and adding flip
> > in the
> > > > > > nose
> > > > > > > > > > anticipating the trim for the flat section by
> > > > displacement?
> > > > > > This
> > > > > > > > > > would make sense on long hulls as you say due to
> > pitching
> > > > > > is less
> > > > > > > > > > likely due to length and over all weight of hull from
> > > > wave.
> > > > > > The
> > > > > > > > > > actual working area of the hull with its lengthened
> > flat
> > > > > > center
> > > > > > > > > > section (sweet spot) achieving more buoyancy towards
> > > > each bow
> > > > > > > > > > through primary (static) and secondary (planning)
> > > > adding lift
> > > > > > > > > > forward, for a given displacement.
> > > > > > > > > >
> > > > > > > > > > How does this compare in a no rocker hull with the
> > > > buoyancy
> > > > > > > > carried
> > > > > > > > > > out to bows this way. More as a (vertical narrow
> > column)
> > > > > > stretched
> > > > > > > > > > forward in a wave piercing form. Where primary
> > > > flotation and
> > > > > > > > > > secondary flotation seem to have no difference.
> > > > > > > > > >
> > > > > > > > > > Todd
> > > > > > > > > >
> > > > > > > > > > --- In harryproa@yahoogroups.com.au, Rick Willoughby
> > > > > > <rickwill@>
> > > > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > > A flat bottom hull has some advantage over a
> > > > semicircular
> > > > > > > > section to
> > > > > > > > > > > limit trim changes for a proa hull without moving
> > > > weight.
> > > > > > The
> > > > > > > > > > > objective would be to keep the boat close to
> > level trim
> > > > > > > > throughout
> > > > > > > > > > > its speed range and reduce the need for heavy handed
> > > > control
> > > > > > > > > > > surfaces. With a high length to displacement ratio I
> > > > believe
> > > > > > > > this is
> > > > > > > > > > > achievable and have reasonable tools to predict how
> > > > the boat
> > > > > > > > will
> > > > > > > > > > > trim through its speed range.
> > > > > > > > > > >
> > > > > > > > > > > Once the length to displacement is reduced it leads
> > > > into a
> > > > > > > > slippery
> > > > > > > > > > > slope and there will be trim changes that cannot be
> > > > managed
> > > > > > > > without
> > > > > > > > > > > shifting weight and/or relying more on control
> > surfaces.
> > > > > > > > > > >
> > > > > > > > > > > I previously analysed a 1t hull designed for
> > 25kts. The
> > > > > > > > lowest drag
> > > > > > > > > > > hull is 12m long but it cannot produce enough
> > moment to
> > > > > > > > counter the
> > > > > > > > > > > pitching from the sail needed to drive it.
> > Getting up to
> > > > > > 15m it
> > > > > > > > > > > becomes possible to produce a flat bottom hull
> > that will
> > > > > > stay in
> > > > > > > > > > trim
> > > > > > > > > > > up to 25kts.
> > > > > > > > > > >
> > > > > > > > > > > In the case of a length constrained hull the
> > extra drag
> > > > > > of the
> > > > > > > > > > > shorter hull requires more sail. It therefore
> > will be a
> > > > > > > > taller rig
> > > > > > > > > > > for the same efficiency so CoE is higher.
> > Lowering the
> > > > > > aspect
> > > > > > > > of the
> > > > > > > > > > > rig by increasing span reduces efficiency so this
> > would
> > > > > > push up
> > > > > > > > > > > lateral loads. No matter how it is done, the rudders
> > > > need
> > > > > > to be
> > > > > > > > > > > bigger to counter the higher sail moment so this
> > > > shifts the
> > > > > > > > > > resultant
> > > > > > > > > > > drag deeper. The pitching moment from sail to
> > drag is
> > > > > > therefore
> > > > > > > > > > > increased so the bow gets further pressed.
> > > > > > > > > > >
> > > > > > > > > > > You are correct about the higher water level at the
> > > > bow than
> > > > > > > > > > stern as
> > > > > > > > > > > it is the wave formation that is causing the
> > changes in
> > > > > > trim.
> > > > > > > > > > > However it is preferable to generate all the lateral
> > > > > > > > resistance from
> > > > > > > > > > > the rudders rather than relying on the hull in
> > any way.
> > > > > > The L/
> > > > > > > > D for
> > > > > > > > > > > rudders having aspect ratio of 4 could be 20 or more
> > > > whereas
> > > > > > > > the L/D
> > > > > > > > > > > for the hull will be very low. So trim the
> > rudders to
> > > > avoid
> > > > > > > > leeway.
> > > > > > > > > > > (An advantage of bow and stern rudders on a proa
> > is that
> > > > > > they
> > > > > > > > can be
> > > > > > > > > > > trimmed to avoid leeway.)
> > > > > > > > > > >
> > > > > > > > > > > Keeping the sail upright by avoiding it pitching
> > forward
> > > > > > > > should keep
> > > > > > > > > > > it in balance longitudinally. Canting the mast
> > and/or
> > > > > > setting
> > > > > > > > it to
> > > > > > > > > > > windward of the centeline of the lw hull so the CoE
> > > > stays
> > > > > > > > close to
> > > > > > > > > > > inline with resistance as the ww hull unloads should
> > > > also
> > > > > > > > reduce the
> > > > > > > > > > > input required from the control surfaces. With the
> > > > > > proposed flat
> > > > > > > > > > > bottom hulls I would set a static list so both
> > hulls run
> > > > > > > > level at
> > > > > > > > > > the
> > > > > > > > > > > design speed. You will see they do this on the
> > amas of
> > > > > > the big
> > > > > > > > > > > tris. The lw ama sits on its lines when the central
> > > > hull is
> > > > > > > > about to
> > > > > > > > > > > fly. For a cruising boat you would want some safety
> > > > margin
> > > > > > > > but same
> > > > > > > > > > > principle for nice balance apply.
> > > > > > > > > > >
> > > > > > > > > > > Rick
> > > > > > > > > > > On 09/07/2010, at 12:29 PM, robert wrote:
> > > > > > > > > > >
> > > > > > > > > > > > Thanks for this. It gives me some numbers to work
> > > > with.
> > > > > > > > > > Interesting
> > > > > > > > > > > > that the depth to width ratio went up so much
> > for the
> > > > > > shorter
> > > > > > > > > > hull.
> > > > > > > > > > > > Assuming the wave dynamics reducing the bow down
> > > > effect
> > > > > > > > implies
> > > > > > > > > > > > that the bow is deeper in the water than the
> > stern,
> > > > but
> > > > > > the
> > > > > > > > wave
> > > > > > > > > > > > dynamics means the water level is higher at the
> > bow
> > > > > > than the
> > > > > > > > > > stern.
> > > > > > > > > > > > There is still the same movement of CO lateral
> > > > resistance
> > > > > > > > > > forwards.
> > > > > > > > > > > > About 8% extra resistance for 15m against 23m is
> > > > something
> > > > > > > > I can
> > > > > > > > > > > > live with.
> > > > > > > > > > > > 2.9kN generated from 7m from the waterline on a
> > hull
> > > > > > with .8
> > > > > > > > > > > > prismatic is not that different from a couple of
> > > > people
> > > > > > > > > > standing on
> > > > > > > > > > > > a bow. A back of the envelope calculation gives
> > in the
> > > > > > > > order of
> > > > > > > > > > > > 100mm bow depression. On top of this is the
> > induced
> > > > drag
> > > > > > > > from the
> > > > > > > > > > > > foils which clearly are considerable and the
> > > > induced drag
> > > > > > > > from the
> > > > > > > > > > > > leeway resistance of the hulls and the air drag
> > of the
> > > > > > > > stuff above
> > > > > > > > > > > > the water.
> > > > > > > > > > > > It would be interesting to see the the drag
> > from a 10m
> > > > > > long
> > > > > > > > hull
> > > > > > > > > > > > with a bow down attitude of 1:20 at 1 tonne and 2
> > > > tonne
> > > > > > > > > > > > displacements and how much the rocker affects the
> > > > drag in
> > > > > > > > these
> > > > > > > > > > > > circumstances. I am going with 600mm hull
> > waterline
> > > > beam
> > > > > > > > but was
> > > > > > > > > > > > wondering how much an extra 50mm would make
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > --- In harryproa@yahoogroups.com.au, Rick
> > Willoughby
> > > > > > > > <rickwill@>
> > > > > > > > > > > > wrote:
> > > > > > > > > > > > >
> > > > > > > > > > > > > You need to determine how various constraints
> > are
> > > > > > going to
> > > > > > > > > > impact
> > > > > > > > > > > > the
> > > > > > > > > > > > > drag and shape before you overconstrain.
> > > > > > > > > > > > >
> > > > > > > > > > > > > The lowest drag 4t hull for 20kts will have a
> > LWL of
> > > > > > 23.1m,
> > > > > > > > > > BWL of
> > > > > > > > > > > > > 840mm and draft of 363mm. The drag will be
> > 2.67kN.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Applying a constraint to get a hard chine
> > results in
> > > > > > a hull
> > > > > > > > > > with LWL
> > > > > > > > > > > > > of 22.8m, BWL of 813mm and draft of 342mm.
> > The drag
> > > > > > > > increases
> > > > > > > > > > very
> > > > > > > > > > > > > slightly to 2.69kN.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Applying an additional constraint to limit
> > LWL to
> > > > 15m
> > > > > > > > results
> > > > > > > > > > in BWL
> > > > > > > > > > > > > of 783mm and draft of 463mm for lowest drag.
> > This
> > > > hull
> > > > > > > > has zero
> > > > > > > > > > > > > rocker. The drag is now 2.91kN.
> > > > > > > > > > > > >
> > > > > > > > > > > > > The problem with the 15m long hull is that it
> > > > will not
> > > > > > > > generate
> > > > > > > > > > > > > enough pitching moment to counter the moment
> > from
> > > > the
> > > > > > sail
> > > > > > > > > > required
> > > > > > > > > > > > > to propel it to 20kts. So it will sail with a
> > bow
> > > > > > down trim.
> > > > > > > > > > I have
> > > > > > > > > > > > > not checked the trim with the 23m hull but it is
> > > > likely
> > > > > > > > it could
> > > > > > > > > > > > > generate enough bow up moment to counter the
> > > > sail. The
> > > > > > > > lowest
> > > > > > > > > > drag
> > > > > > > > > > > > > hull has nice rocker in the ends that helps
> > with the
> > > > > > bow up
> > > > > > > > > > trim.
> > > > > > > > > > > > >
> > > > > > > > > > > > > There would be now point in analysis the trim
> > for
> > > > the
> > > > > > 15m
> > > > > > > > hull
> > > > > > > > > > > > but it
> > > > > > > > > > > > > would be worth seeing what could be done with a
> > > > 23m long
> > > > > > > > hull
> > > > > > > > > > > > >
> > > > > > > > > > > > > Rick
> > > > > > > > > > > > > On 08/07/2010, at 8:33 PM, robert wrote:
> > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > 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
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > Rick Willoughby
> > > > > > > > > > > > > rickwill@
> > > > > > > > > > > > > 03 9796 2415
> > > > > > > > > > > > > 0419 104 821
> > > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > Rick Willoughby
> > > > > > > > > > > rickwill@
> > > > > > > > > > > 03 9796 2415
> > > > > > > > > > > 0419 104 821
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > Rick Willoughby
> > > > > > > > > rickwill@
> > > > > > > > > 03 9796 2415
> > > > > > > > > 0419 104 821
> > > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > > > Rick Willoughby
> > > > > > > rickwill@
> > > > > > > 03 9796 2415
> > > > > > > 0419 104 821
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > > Rick Willoughby
> > > > > rickwill@
> > > > > 03 9796 2415
> > > > > 0419 104 821
> > > > >
> > > >
> > > >
> > >
> > > Rick Willoughby
> > > rickwill@
> > > 03 9796 2415
> > > 0419 104 821
> > >
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>