why use nurbs surface modeling
TRANSCRIPT
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Why Use NURBS Surface Modeling...?
Our rationale for using NURBS surface modeling for boat design.
Copyright 2012 - 2014 Michael Kasten
As an extension of our article describing our CAD Design Strea! this page outlines our
use of "#$%S surface odeling to create our boat and yacht designs& 'he ai here is to
counicate the basic rationale for using "#$%S surface odeling as opposed to other (D odeling ethods! such as solids odeling for de)eloping any type of (D free for
design& "#$%S stands for a *"on-#nifor $ational %-Spline* type of surface& 'he
technicalities of +hat that eans! you can research on ,iipedia& 'he reasons for usingthis approach for yacht design are the purpose of this article&&&
'he de)elopent of a ne+ boat shape can be thought of as being a series of steps! each of +hich taes ad)antage of a different aspect of the original (D "#$%S surface odel in a
different +ay! ore or less as follo+s.
1& Creating the Design &&&&&&&&&&&&&&&&&&&&&& /in Maxsurf - no+ called Maxsurf Modeler - in (D
2& Analying the Design &&&&&&&&&&&&&&&&&&&& /in Hydromax - no+ called Maxsurf Stability - in
(D
(& Detailing the Design &&&&&&&&&&&&&&&&&&&&& /in Microstation in 2D4& enerating the Structure &&&&&&&&&&&&&& /in Worsho! - no+ called Maxsurf Structure - in
(D
3& Detailing the arts &&&&&&&&&&&&&&&&&&&&&&&& /in Microstation in (D using 2D entities
5& "esting the arts &&&&&&&&&&&&&&&&&&&&&&&&&&& /in Rhino in 2D6& Cutting the arts &&&&&&&&&&&&&&&&&&&&&&&&&&&& /done by the etal cutter in 2D
7& %uilding the %oat &&&&&&&&&&&&&&&&&&&&&&&&&& /done by the boat builder in (D
'hese 8design steps8 are outlined belo+ along +ith the specific reasons for choosing toinitiate the odel design in a "ree "orm (D "#$%S Surface odeling en)ironent&
#N #$$RO$R%#&' (')'( O" *OM$('+%&,
9t is instructi)e to consider the :uestion of "What is an appropriate level of complexity
for the CAD model...?" 'his :uestion has been elegantly addressed by hilipChristiansen and Andre+ Mason of ;oration Design Systes in a paper that copares
large ship building CAD systes to +orboat and yacht design CAD systes& hilip andAndre+ +rote as follo+s.
When using a CAD system for vessel design and construction, it is important to choose
an appropriate level of complexity for the CAD model. The idea that it will always be
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beneficial to create an entire "product model" of the vessel, complete down to the
smallest detail, is not especially applicable to the construction of worboats.
The cost of any vessel incorporates a percentage allocated to the design. The larger thevessel, the more money is available to be spent in the design process, even though this
may be a lower percentage of its total construction cost than for the design phase of a smaller worboat. After the bare minimum of design data have been generated, further
time can be !ustified in increasing the level of design detail only if it results in aneuivalent saving during the construction phase, or lower repair and maintenance costs
during the life of the vessel.
As more detail is modeled in the CAD system, a point will be reached where the
downstream savings are outweighed by the additional design costs. This point variesbased on the cost, si#e and complexity of the vessel, the cost of available labor, the level
of automation in the shipyard and the number of vessels being produced. $or example, if
a vessel is a one off design, the amount of detail modeled may necessarily be less than for
a production run of many vessels.
9t is +ith this "appropriate level of complexity" in ind that +e approach the design of
yachts and +orboats here at Kasten Marine Design! 9nc& 9n other +ords! +e do not need
to odel e)ery last nut and bolt as ight be desirable for "ASA or to design a ilitarysubarine&&& ;or e)eryday boat and yacht design! that +ould be extreely unproducti)e!
+asteful! and costly& 9nstead! +e ust engage in a strealined CAD process that is
efficient! accurate! and cost effecti)e&
'o+ard that end! +e ha)e found -irect "#$%S Surface odeling to be the s+eet spot
for boat design& 'he follo+ing notes outline our rationale for ha)ing ade this choice&
MO-'(%N / #N#(,S%S O$&%ONS
,hen coparing the coonly a)ailable soft0are tools as they are used for boat and
yacht design! it is useful to differentiate bet+een t+o basic approaches to (D odeling.
• $arametric or *history based* odeling en)ironents +hich re:uire ad)ance
planning of features! constraints! relations and dependencies +ithin the odel& Ahistory of the logical genesis of the odel is aintained so that changing a pre-
defined paraeter changes the odel& Soe en)ironents allo+ directly
changing the odel! +hich updates the underlying relationship constraints&• -irect or *free form* odeling en)ironents +hich allo+ a ore intuiti)e and
flexible *hands-on* anipulation of the odel regardless of ho+ or in +hat
se:uense the odel +as created& 9n any cases relationships can be defined! such
as for triing or to bond surfaces along an edge or to enforce tangency bet+eensurfaces! but they are not needed in order to create the odel! and they do not
affect one8s ability to grab parts of the odel and push! pull! o)e! etc&
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Along +ith those t+o basic types of odeling en)ironent! +e ust also consider t+o
essentially different types of (D odel&
• Solid odels in +hich all parts are ha)e thicness and are assigned ass
properties&
•
Surface odels +hich ae use of ero thicness surfaces +hich ha)e no ass properties&
'here are any excellent Solid odelers such as SolidWors! as +ell as any
outstanding (D "#$%S surface odeling en)ironents! such as Rhino or Maya& Mostof these tools! including $hino! are *generic* tools - rca(D& Although these do not bring$hino any+here near the le)el of functionality in Maxsurf and =ydroax! they are )ery
good tools&
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'he ost fundaental dra+bac to using $hino to originate a design is that surface
triing becoes an unforeseen ipedient& 'he reason is that $hino uses *static*
triing! +hich eans if you tri t+o surfaces! then o)e one of the! you ha)e to*un-tri* the prior tri region and recreate it ane+& 9f you ha)e a odel +ith a hundred
surfaces or so! you are left to figure out for yourself +hich ones ight ha)e been affected
by the surface that +as o)ed! and then edit the one by one& 'his alone is pretty ucha deal-iller in ters of y o+n use of $hino for creating ne+ designs&
A further incon)enience in $hino is that both hal)es of the odel ust be anaged
separately& 9n other +ords! the design is not autoatically *irrored* across the
centerline! so if you ae a change in one half! you ha)e to edit the other half in exactlythe sae +ay& Certainly one can rdinarily this eans the user ust construct the )arious
logical relationships in ad)ance! and then anage the +hile building or changing a
odel&
'he priary utility of soft+are lie Solid,ors resides in this )ery ability to anagecoplex changes gracefully& Solid,ors is the perfect tool for creating achines! +here
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if a piston diaeter is logically related to the cylinder diaeter and cooling galleries! if
you change the piston! the rest is autoatically updated per those relationships&
Solid,ors is a po+erful tool for detailing a boat8s structure! thereby instantly no+ingthe global +eight and center of gra)ity& 9n Solid,ors! e)en if you ha)e accurate ass
inforation! an accurate C! and an editable odel )ia its paraeters! it ay not be fairand you +ill not ha)e any hydrostatic properties for the shape itself&
;or the purpose of originating boat shapes! the resulting odel can :uicly becoeinordinately coplex& 'he abo)e described "appropriate level of complexity" ust be
ept in ind&
,hen attepting to odel free for shapes such as a boat! this approach puts the cart
before the horse& ,hen originating a design! it is preferable to reain unfettered by onesurface ha)ing to be related to another! i&e& not to +orry about +hat effect changing one
surface ight ha)e on another surface! say if they are tied together and re:uired to o)e
together as is generally the case in Solid+ors&
9n addition to its )ery robust solid odeling abilities! Solid,ors also has surface odeling tools& 9 do not no+ +hether triing in S, is *static* lie $hino or
*dynaic* lie Maxsurf& 9n all probability! it is paraetrically defined! therefore
dynaic& More on this belo+&&&
M#+SUR" MO-'('R..3
>ur preference for using Maxsurf Modeler to generate ne+ boat designs is not only
because Maxsurf is a unified suite of progras specifically de)eloped for that purpose! but also because the approach taen +ithin the Maxsurf odeling en)ironent aesultiate sense&
Maxsurf is a -irect /free for NURBS Surface odeling en)ironent +herein
surfaces are used to define an en)elope for fairing and analysis& #nlie +ith Solidodeling! thicness is not a property of "#$%S surfaces or splines. they ha)e ero
thicness& #nlie Solid,ors! Maxsurf does not re:uire that relationships be established
bet+een surfaces! nor does Maxsurf preser)e a odel construction history& Maxsurf does
ho+e)er allo+ certain relationships to be created bet+een surfaces! such as triing!edge bonding! tangency bet+een surfaces! etc&
,oring +ith a (D "#$%S surface in Maxsurf is no different than +oring +ith a 2D
or (D spline& 9n Maxsurf +e are using a *control point net* as opposed to a series of
*through points&* 9n Maxsurf ! a surface is defined by a net+or of control pointsebedded in a control net that is used to define the surface& 'he iage belo+ is an
exaple of a fairly coplex odel generated +ithin Maxsurf ! +ith all surfaces tried
to their final shape and *unloced* so that the control net is )isible& 'hough the odel iscoplex! the underlying control net is :uite sim!le&
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40 Meter inisi Charter ?acht as ie+ed *#nloced* in Maxsurf - Clic for Barger
9age
=a)ing ruled out Solid odeling as a tool for originating boat designs! +e are left +ith
Surface odelers to consider as being the best CAD tool for designing boats& Although
Maxsurf can do any of the sae odeling trics that $hino can do! Maxsurf pro)ides
se)eral ey ad)antages&&&
Modeling. 9n the abo)e iage! you can see that Maxsurf only needs to odel one half of
the )essel since the other half is autoatically and dynaically irrored across thecenterline& 9f you specifically +ant asyetry! that can be set as a property of any
surface! so that a differently shaped surface can be odeled on the other side - say for
designing a proa& 9n the iage abo)e you can also obser)e that +hen odeling "#$%Ssurfaces! there is a great benefit +hen the control net is ept as siple as possible!
+hereby fairness is easily achie)ed&
&rimming. Maxsurf uses *dynamic* triing& 'his eans that if you tri a fe+
surfaces using a spline or another surface! and you then o)e one or ore of those
surfaces or the spline! all of the affected surfaces are all dynaically re-tried on thefly& "aturally! this is coputationally intensi)e! and thats +hy Maxsurf allo+s you to
turn triing on or off globally /as in the abo)e iage& ,ith triing off! you cano)e surfaces and splines around :uicly& ,ith triing on! and precision set to high! it
can tae a fe+ oents for Maxsurf to figure out all the correct tri regions after each
change& 9f the odel is coplex! this can tae se)eral oents e)en on a fast achine! but rarely ore than a fe+ seconds& As a iddle ground! precision can be set to a lo+er
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)alue so that triing can be displayed correctly +ith updates calculated :uicly! then
subse:uently set to high precision for final output&
&ools. Although "#$%S surfaces ha)e ero thicness! it is possible to set surfacethicness properties in Maxsurf& 'his does not add another surface! nor does it create a
solid! but is useful in order to accoodate planing thicness so that the lines andoffsets output +ill correctly account for the planing deduction addition! taen noral
to the surface that has been odeled& Setting thicness and aterials properties inMaxsurf also allo+s those properties to be recognied by Maxsurf Structure /,orshop!
the construction odule in the Maxsurf Suite&
Maxsurf allo+s the surface stiffness to be )aried in either direction! and allo+s thecontrol point +eights to be )aried as needed in order to exert ore or less local control
o)er the surface locally& Maxsurf has excellent tools for creating and editing splines!
+hich can be used for triing surfaces& Maxsurf can create extrusions along an edge or
spline or create lathe turnings around an axis using any spline shape&
Maxsurf can create surfaces fro cloud data by first autoatically creating a series of
editable splines and edges! then autoatically lofting a surface to those cur)es&
Alternately! Maxsurf can fit a collection of fair surfaces to a set of pro)en offsets! say to
accurately reproduce the shape of an existing )essel&
"airing. Maxsurf has excellent fairing tools! such as cur)ature porcupines! aussian
cur)ature analysis! rendering! longitudinal copression! etc& as +ell as tools for
autoating the anipulation of control points! e&g& align controls to planeE align to)ectorE sooth control pointsE sooth patchE rotate sie o)e duplicate irror
surfaces or splines or controls&
)isuali4ation. 9n addition to the standard profile! plan and body )ie+s! Maxsurf sho+s a
perspecti)e )ie+ +hich can be rendered nicely& Colors! transparency and lighting can all be )aried as needed& 9n each )ie+ the grid and the resulting lines on the )essel8s surface
can each be turned on or off& 9f the surface is o)ed! the sections! buttoc lines and
+aterlines are all dynaically updated in all )ie+s&
$arametric )ariation. Maxsurf is able to autoatically iterate a odel according to paraeters that you set! such as to achie)e a specific prisatic or bloc coefficient! or a
gi)en displaceent! +ater plane area or +etted surface! etc& $estraints can be defined!
such as to disallo+ changes to the sheer line! bea! draft! displaceent! and any of the
other paraeters! as long as sufficient degrees of freedo reain to achie)e there:uested )ariations& 'his !arametric 5ariation capability allo+s one to create a faily
of 8candidate8 hull shapes each ha)ing slightly different characteristics! +hich can then be
analyed as to their perforance relati)e to each other! or to specifically stated designre:uireents&
&ri6mesh Surfaces. Maxsurf can create eshed surfaces! +hich can be useful for :uic
odeling and data transfer into =ydroax or other CAD systes& As an exaple!
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Maxsurf can autoatically fit a eshed surface o)er a cloud of data& ,hile a eshed
surface is not sufficiently accurate for a lines dra+ing or to ae parts fro the eshed
surfaces! it is ade:uate for hydrostatics analysis in =ydroax& A eshed Maxsurf odelcan be created :uicly! and can then be opened directly in =ydroax for a coplete
stability and tri analysis&
#nalysis. Maxsurf pro)ides upright hydrostatics analysis! instantly a)ailable +ithin the
progra& A built-in fully prograable calculation sheet is also a)ailable! allo+ingnearly any paraeter to be re-prograed and autoatically calculated fro the basic
upright hydrostatic inforation! e&g& target sail area C Dellenbaugh Angle!
optiu )elocity fuel capacity endurance! etc& 'he odel can be set to a )ariety ofetric or iperial units +ithout iposing any changes on the underlying geoetry& 'his
allo+s rapid s+itching bet+een easureent systes during design de)elopent&
Model -ata7 All of the tried surface areas and centroids are calculated +ithin
Maxsurf! and are a)ailable in a data +indo+ to copy and paste into @xcel& Maxsurf also
calculates the x-y- 8extents8 of each tried surface& 9f it is desired to do so! there is aMaxsurf Autoation interface by +hich this can be done autoatically +ith each
iteration of the design& Since surface properties such as thicness! aterials! and area+eights can be assigned +ithin Maxsurf! +hen calculating the areas and centroids of
surfaces! the Mass Moent of 9nertia /unitsF4 is also calculated for each surface! as +ell
as the suary Moent of 9nertia for the +hole design! +hich data is useful for analysisin Seaeeper /Maxsurf Motions and for other analyses of )essel otions and cofort&
-ata 'xchange. All Maxsurf odules share a coon file forat& As a result there are
ero file translation issues +hen opening the Maxsurf odel in any of the progras in the
Maxsurf Suite& 'he Maxsurf odel is opened directly by each of the soft+are odules&
-ata %m!ort7 Maxsurf can iport bacground iages for each )ie+ in the gif! pen "#$%S H(d forat! or 9@S "#$%Ssurfaces&
-ata 'x!ort7 Maxsurf and =ydrolin support (D "#$%S data export )ia 9@S! 9MSA
"#$%S! ;astship! and the $hino >pen "#$%S H(d forat& A host of C;D and
hydrostatic analysis export forats are also supported! including =S! Autohydro "#S=ABB>! etc& Maxsurf can export to 2D or (D DG; polyline! face or esh geoetry
/AutoCAD to a high le)el of precision& 'abular data such as hydrostatics and surface
areas can be directly copied fro Maxsurf and pasted into @xcel for further analysis&
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708 *;A"'A9B S'@AM@$ * Style ?acht as ie+ed in Maxsurf - Clic for Barger 9age
M#+SUR" SB%(%&, 8Hydromax9
,ithin Maxsurf Stability /=ydroax one can define tans! +hich ordinarily use the hullen)elope as the outer perieter! though internal surfaces can also be used& ,ithin
=ydroax the ass of the tan contents is defined! and for each load case +hat percent
of li:uid is in the tan&
=ydroax then heels the odel! o)es the tan contents to the tri of the )essel at each
heel angle! recalculates the C based on the ne+ position of the tan contents! and erects
a righting ar for that heel angle& >)er the range of heel angles! the righting cur)e is
created& %uilt into =ydroax are all +orld+ide stability criteria! fro +hich =ydroax
+ill create a detailed pass-fail report based on the criteria that you select&
During the genesis of the design! since Maxsurf does not ha)e any *structure*
inforation aside fro surface aterials /say! plating the surface areas and centers are
exported to @xcel! +here a +eight per s:uare area for each surface can be assigned inorder to get the C of the structure& 9n cobination +ith a thorough list of e:uipent
+eights and their centers! tan contents! etc& an accurate C is obtained&
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,ith the +eight and C inforation being generated in @xcel concurrently +ith the
actual Maxsurf odel! +e can iterate the odel shape in order to achie)e the re:uisite
tri and stability! or +e can edit the location of e:uipent! tans and ballast as needed&
,ith an o+ner in)ol)ed in the decision strea during the genesis of the design!
nuerous changes are ine)itable and are to be expected& 'hus the design ordinarily goes bac and forth bet+een @xcel and the )arious Maxsurf progras a fe+ ties before the
best solution is found&
'he 518 %rigantine M@$MA9D as ie+ed in Hydromax - Clic for Barger 9age
M#+SUR" S&RU*&UR' 8Worsho!9
Maxsurf Structure /,orshop is not a Solid odeler& 9nstead! ,orshop is a
$arametric odeler +hich enables one to create fraes and stringers that are
paraetrically related to the underlying "#$%S Surface odel& @)en though the
structures that one defines in ,orshop are *tied to* the surfaces! ,orshop is not ahistory-based odeler! i&e& there is no logic tree or odel genesis history aintained&
?et if the surfaces get changed in Maxsurf for any reason! +hen the design is re-opened
in ,orshop! all parts of the structure can be instantly re-calculated so that theyautoatically flo+ to the ne+ shape +ithout ha)ing to be re-defined&
Worsho! includes a coprehensi)e sections library as +ell as a standard aterials
library& 'herefore once the structure has been defined! one ends up +ith accurate ass
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properties based on the aterials and sections that +e ha)e assigned to the parts! as +ell
as an accurate +eight and C for the odel& 'he ,orshop +eight table can be exported
directly to Hydromax for use as a loadcase! or can be exported to @xcel for a uch oreaccurate +eight and C for )erification of our preliinary +eight calculation&
'he 358 Ketch S=9$AI as ie+ed in Worsho! - Clic for Barger 9age
MU(&%"R#M'
Deterination of the adeuacy of the structure is usually done in @xcel by prograing
the appropriate Classification Society $ule or other structural criteria into a spreadsheet&
;or ore inforation about ho+ +e use the A%S $ule to ad)antage! please see ourarticle on Designing %oat Structure&
;or a preliinary calculation of the o)erall +eigts! once +e no+ the re:uired plate
thicness and the associated fraes and stringers! a *generic* +eight per s:uare area is
found for each region /botto! sides! dec! house! bulheads! tans! etc&& ,ith theaccurate s:uare area and centroid deri)ed in Maxsurf for each surface! and the +eight per
s:uare area calculated in @xcel! the resulting C is fed bac into the loop! +ith re)isionsof the hull odel as needed&
As an alternati)e eans of calculating the adeuacy of structure! the ,orshop structureodel can be exported )ia DG; to the Multifrae odule for a first principles analysis
of the plating panels! the fraes! stringers! or any other details of the strucure&
Multiframe can also be used to analye indi)idual coponent properties independently!for exaple to analye the loads and the resulting strain +ithin the rig /shrouds! asts!
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etc&&
M#+SUR" MO&%ONS 8Seaee!er9
9f it is desired to analye a )essel8s dynaic beha)ior! Maxsurf Motions /Seaeeper isused& ;or this! the surface oents of inertia fro Maxsurf are entered! plus other
loadcase +eights as needed! and SK +ill calculate the accelerations in a )ariety of
standard sea states& Although 9 use the Seaeeper progra! it is rarely +ithin a yachto+ners design budget to indulge in this le)el of analysis& ;or +orboats and high speed
craft ho+e)er! it is highly useful&
As an alternati)e! roll period! pitch! hea)e! etc& are readily calculated in @xcel using basic
forulae published +ithin the )olues of %rinciples of &aval Architecture. Although theresults are not nearly as thorough or accurate as +ould be calculated by Seaeeper! they
are :uite useful for coparing one design to another&
OUR $R'"'RR'- $RO*'SS...
,e can see fro the abo)e that once the odel has been created! Maxsurf is used first to
chec that the Surface odel is fair and that the tri regions are beha)ing correctly& 'hen
still +ithin Maxsurf! the upright hydrostatics can be :uicly checed in order to pro)idefeedbac for editing of the shape! and aterials properties can be assigned for use do+n-
strea in Seaee!er and Worsho!&
>nce the preliinary odel is nearly finalied! Maxsurf can calculate the surface areas
and centroids for export to @xcel! +here +eights per unit of area can be introduced andthe C deterined&
'hroughout the odeling and stability analysis! none of the internal structure is present in
the odel! ho+e)er bulheads! soles! tan faces! girders! etc& can be introduced in order
to ha)e their surface areas calculated by Maxsurf ! and for use as boundary surfaces fortans in Hydromax& All other structure such as fraing! stringers! insert plates and other
structural coponents can separately be accounted for in the @xcel ,eight Analysis!
+hich +ill pro)ide the o)erall C for use in the hydrostatic and large angle stabilityanalyses&
After the design has been finalied! if the )essel +ill ha)e its parts pre-cut the originalMaxsurf odel can be directly opened in ,orshop in order to begin creating fraes!
stringers and plates based on the surfaces present in the odel&
'his arranges the design process in a logical orderJ i&e& first the desired faired surfaceshapes are created and basic hydrostatics are perfored in Maxsurf! then the C is
calculated in @xcel! then the large angle stability analysis is perfored in =ydroax! then
the Maxsurf odel can be edited as needed according to those results&
http://www.kastenyachtdesign.com/maxsurf/motions.htmhttp://www.kastenyachtdesign.com/maxsurf/motions.htmhttp://www.kastenyachtdesign.com/maxsurf/motions.htm
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>nce the design is *fixed* or nearly so! the Maxsurf odel can be brought directly into
the ,orshop $arametric odeling en)ironent in order to create the internal structure
and expand the shell plating& 'his is all done 0ithout file translation by direct use of thefaired Maxsurf Surface odel&
'o re)ie+ this design process in greater detail! please see our Design Strea article& 'osee our design process in flo+-chart forat! please see our Design ;lo+ Diagra&
"%(' *ON)'RS%ON H'#-#*H'S...
Maxsurf is able to directly export the Maxsurf odel to the $hino H&(d file forat&
Since both progras are free for "#$%S Surface odelers! a Maxsurf odel exportedto $hino +ill open fla+lessly in $hino& Maxsurf pro)ides a Maxsurf $lug6%n for Rhino!
+hich allo+s the Maxsurf Assebly 'ree to be preser)ed for use in $hino! as +ell as
+hen subse:uently opening the H&(d $hino file +ithin Maxsurf& 9f the odel is not
ebellished too uch in $hino! bringing it bac into Maxsurf ordinarily +ors )ery +ell&
=o+e)er if the odel has been substantially enhanced or detailed in $hino! there can be
entities that Maxsurf +ill not recognie +hich +ill be deleted fro the odel on iport
to Maxsurf& @xaples are any text or diensions added in $hinoE coplex entities such
as portsE echanical ites! etc& ;or the ost part though! since both $hino and Maxsurfare inherently surface odelers! the round trip bet+een progras +ors +ell for the basic
surface odel&
$hino is hands do+n the best CAD progra a)ailable for translating one CAD foratinto another& ;or the ost part this +ors +ell +hen bringing )arious CAD file forats
into $hino& =o+e)er it can be probleatic +hen trying to use $hino as a possibleinterediary in order to translate one ind of CAD odel into another forat -- for
exaple to get a Solid odel into Maxsurf& 'his is not a failing of $hino! it is
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the Solid,ors generated odel is rarely fair and the surfaces often do not e)en atch at
their edges&
At this point! in order to be of any use in Maxsurf! or if a hydrostatics analysis +ill bedone in =ydroax! there +ill be considerable +or to be done in Maxsurf to delete all of
the non-essential surfaces! possibly in)ol)ing re-odeling the )essel fro scratch in a "#$%S odeling en)ironent such as $hino or Maxsurf /+here it should ha)e been
done in the first place& 'he net result is a lot of +asted tie and effort&
9t is possible that +ithin Solid,ors a ero thicness "#$%S Surface odel can be
created +ithout ha)ing to first create a araetric 8logic tree8 or a Solid odel& 9f so! it
ight then be possible transfer the "#$%S Surface odel to Maxsurf )ia 9@S or )ia$hino using the &(d file forat /both of +hich Maxsurf can read for analysis&
@)en if that +ere a possibililty! Solid,ors appears to ha)e se)eral shortcoings +ith
regard to Surface Modeling& ;or exaple! according to inforation fro S, users it is
not possible to expose nor to directly anipulate the surface control net in Solid,ors!since that +ould )iolate the history based paraetric relationships aong parts& ;urther!
Solid,ors is not able to +rite to a &(d $hino file! so that basically lea)es 9@S as the
only )iable a)enue fro S, into Maxsurf unless $hino is used as an interediary&
@ither +ay! the result +ill liely re:uire :uite a lot of tie consuing re-+or in order tore-tri the surfaces +ithin Maxsurf prior to being able to o)e the odel into
=ydroax&
'he upshot is that Solid,ors or any other Solid odeling en)ironent is inordinately
com!lex for the basic tas of creating a fair "#$%S Surface en)elope&
'his is the essential rationale for the $referred $rocess outlined abo)e! i&e& starting +itha relati)ely siple tried "#$%S Surface odel generated +ithin Maxsurf +hich
can then be properly analyed in Hydromax! e)entually progressing to a $arametric structure odel created +ithin Worsho!! and then do+n-strea to a (D layout or parts
editing en)ironent +here the odel +ill be easily recei)ed! say +ithin $hino! AutoCad!
Microstation or Solid,ors&
#nfortunately this process -O'S NO& +or at all +ell in re)erse&&& for exaple to get acoplex paraetrically generated *solid* odel into =ydroax for analysis&&&
#(&'RN#&%)' ,#*H& -'S%N SO"&W#R'
Are there shortcoings to odeling free for shapes using NURBS&&&L
Since any "#$%S surface ust al+ays be a four sided patch! it turns out that yes there
are&& Soe shapes are
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MU(&%6SUR"
>ne non-"#$%S Surface odeling progra of possible interest is MultiSurf by
Aero=ydro& MultiSurf is a $arametric Surface odeler that uses Relational eometry /$! eploying )arious types of points! cur)es and surfaces to define ey shapes such
as the sheer! centerline profile! ste! transo! idsection! etc& Aong those entities! paraetric relationships are established to assure that they +ill o)e together and reain
*related&* %y this eans! MultiSurf allo+s one to build a non-"#$%S Surface odelusing ultiple types of interrelated eleents& 9t is a po+erful approach&
araetric *logical relationships* ust first be established in MultiSurf! siilar to the
*assebly tree* used in Solid,ors& 'he siilarity bet+een MultiSurf and Solid,ors isso close that a specialied )ersion of MultiSurf has been de)eloped for the Solid,ors
en)ironent! called SurfaceWors&&& essentially a ore CAD oriented clone of
MultiSurf +ithout its hydrostatics analysis capability&
'hough odeling +ith MultiSurf is a relati)ely ore coplex process! $elationaleoetry is capable of extree accuracy& ohn Betcher! creator of MultiSurf! presents a
fa)orable case for using $ odeling especially +here a C;D analysis +ill be re:uired
do+n-strea&
9t should be ephasied that the surface odel created by MultiSurf /and Surface,orsis not a "#$%S surface odel! rather it is a relational araetric odel coposed of a
)ariety of interrelated points! cur)es and surface types& #nfortunately the relational
odel that is created is not recognied +ithin ost coon CAD systes! nearly all of+hich ha)e standardied on "#$%S surfaces& 'hus! in order to be used in other CAD
systes the relational odel ust first be transfored into a "#$%S surface odel&
;ortunately though! MultiSurf includes )ery good tools +hich autoate the "#$%Screation process&
'he "#$%S odel that results is not precisely the sae as the original MultiSurf
relational odel -- rather it is a 5ery close approxiation& #nfortunately though! the bi-
directional file transferability bet+een MultiSurf and other CAD systes is lost -- in
other +ords it is a one +ay street fro MultiSurf to "#$%S to CAD& resuably if oneis +oring entirely +ithin a Surface,ors Solid,ors en)ironent this ay not be an
issue& 'hus if Solid,ors is one8s preferred CAD en)ironent! MultiSurf ay +ell be
the Surface odeler of choice&
Certainly if it +ere necessary to analye the hydrostatics and stability of a MultiSurfodel in =ydroax or another "#$%S based en)ironent! it +ill be easily
accoplished! since the degree of precision in the "#$%S approxiation created by
MultiSurf +ill not ae any difference to the analysis&
>ne ca)eat though is that in creating a "#$%S approxiation of the underlying
relational odel! in y experience +ith any MultiSurf generated "#$%S odels! the
resulting "#$%S control net is inordinately coplex! aing any do+n-strea editing
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nearly ipossible if any seblance of fairness is to be preser)ed& 9n other +ords! another
one-+ay street&
9f the destination forat +ill be NURBS based for the sae of copatibility +ith generalCAD systes! the :uestion arises. "'ave we exceeded the appropriate level of
complexity reuired to create the model, analy#e it, and build from it...(" 9 don8t no+the ans+er! although 9 recognie that the MultiSurf syste is +ell lied by any&
&6S$(%N'S
Another progra cobination that o)ercoes any of the shape liitations of "#$%S
is the AutoDes &6S!lines plug-in for $hino! +hich allo+s three! four! or ultiple-sided
patches to be odeled& ,hile there are other odelers that can do this! one eydifference is that '-Splines can accurately con)ert the '-Splines odel into "#$%S
surfaces for use in other CAD progras&
er y o+n obser)ations! the resulting "#$%S Surfaces are actually :uite usable& @)en
so! the sae ca)eats apply! e&g& since other CAD systes do not recognie '-Splines!exporting a odel to "#$%S is a one-+ay street! although certainly the "#$%S Surface
odel can be brought bac into the $hino '-Splines en)ironent for further editing or
detailing&
And of course $hino ust be paired +ith other third party soft+are such as >rca (D forany seblance of functionality as a tool for boat design and analysis&
2''$%N %& S%M$('...
9n the $referred $rocess outlined abo)e! +e are +oring entirely +ithin the Maxsurf
Suite of progras in order to create and analye the design! and to detail the basic
structure& 'hus! there is no file translation re:uired! and +e therefore experience ero file
forat translation issues fro one Maxsurf progra to the next&
%ut there ay be occasions +here a odel +ill ha)e originated else+here& A odeloriginally created in another "#$%S surface odeling en)ironent such as #utoshi! or
"astshi! can be iported directly into Maxsurf! or alternately iported )ia 9@S! say for
analysis in =ydroax& Soe entities in those progras /nots for exaple are not
supported in Maxsurf! and +ill therefore be dropped on iport! possibly re:uiring soere-odeling in Maxsurf to return the odel to its intended shape&
A Rhino originated odel +ill open reliably in Maxsurf pro)ided that the $hino odel is
ept siple& 'his does not ean the nuber of surfaces need to be restricted in $hino!only that entities +hich do not exist in Maxsurf should be a)oided /text! diensions!
solids! etc&&
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The inevitable conclusion is that if a NURBS )urface environment will be the eventualdestination for the design, the most efficient path will be to oriinate the design using
&*+) )urface modeling.
-'%(%N &H' MO-'(
9 use Microstation as a tool for detailing and illustrating a )essel8s layout and structure&
#uto*#- is ore or less e:ui)alent! and is by far the ost coon CAD progra inuse& And at long last AutoCAD 2012 is finally able to recognie "#$%S&&& a feat that
Microstation has been capable of doing since day one&&&
-R#W%N &H' (#,OU&
resently 9 find it faster to +or in 2D to create the %uilding lan Dra+ings! especially
since they +ill ultiately be output to 2D plots on paper or as 2D D; files& 'o achie)ethis! first a *fixed* set of 2D lines are exported fro Maxsurf as 2D DG; files! then thelines are brought into Microstation for further detailing& Adittedly! in light of the abo)e
discussion of (D odeling! +oring in 2D ight see priiti)e! but it is relati)ely :uic
to achie)e! and since the output ust be in 2D any+ay! there is not uch to recoend
against it&
An exception +ould be if it is desired to create a (D odel for a photo-realistic
presentation or as a (D *+althrough* or in order to pro)e that the spaces in the layout
are as intended& 'his can be helpful! but the tie re:uired in order to create a detailed (Dlayout odel -- and the resulting cost in)ol)ed -- are ordinarily difficult to
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'he ABD@MA$ 3( Structure as ie+ed in Microstation! $eady for "esting - Clic for
Barger 9age
A cool (D Structure Dra+ing in D; forat sho+s the sae design! output directly fro
Microstation to a (D D;& ?ou can rotate! pan and oo the (D odel in the D;! and
you can also turn on and off the )arious layers in the odel& 'his is an excellent
illustration )isualiation tool for counicating the structural arrangeent to the builder&
Although 9 ha)e no doubt that Rhino could be used e:ually +ell for the (D parts
detailing do+nstrea fro ,orshop! 9 a uch ore failiar +ith Microstation& As a
result 9 do not use $hino except as an occasional tool for creating an interestingillustration of the odel! as CAD translating tool +hen needed! and as a nesting tool
after the parts ha)e been fully detailed +ithin Microstation& 'his latter tric is ade
possible by $hinos open architecture and the )arious readily a)ailable plug-ins such as
Rhino Nest&
*U&&%N &H' $#R&S
http://www.kastenmarine.com/valdemar52.htmhttp://www.kastenmarine.com/_pdf/valdemar_3D_parts.pdfhttp://www.kastenmarine.com/_pdf/valdemar_3D_parts.pdfhttp://www.kastenmarine.com/_screenshots/valdemar_frames_aft.GIFhttp://www.kastenmarine.com/valdemar52.htmhttp://www.kastenmarine.com/_pdf/valdemar_3D_parts.pdf
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"ote that NON' of the abo)e described (D odeling and detailing regie in)ol)es a
*Solid* odel& 'he third diension is not needed for actually cutting the parts& 9t is only
necessary to define the 2D *outline* of each part so that it can be used in a 2Den)ironent for cutting& 'his +ors :uite +ell using NURBS surface odeling&
9n other +ords! +e ha)e eployed an "appropriate level of complexity" and no ore&
"C Cut arts for the 238 %>>#M 'abbed to Sheet for @asy Shipping
BU%(-%N &H' BO#&...3
After all the parts ha)e been cut and shipped to the builder! naturally it is all o)ed bacinto a 100N (D en)ironent&&&
http://www.kastenmarine.com/boojum25.htmhttp://www.kastenmarine.com/boojum25.htmhttp://www.kastenmarine.com/_photos/10m_cut_plate.jpghttp://www.kastenmarine.com/boojum25.htm
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>ur O58 Schooner I@%#B#" design! in ;rae
-'S%N %N"ORM#&%ON
lease see our CAD Design Strea article for a coplete description of ho+ +e
ipleent the abo)e soft+are solutions to create our boat designs and to generate "Ccutting files in order to pre-cut a boat8s structure&
Although +e regularly de)elop "C cutting files as described abo)e and in the CAD
Design Strea article! we do not sell "parts its" per se& 9n other +ords! +e do not sell
any pre-cut aterials& 9nstead! +e offer Building $lans and N* *utting "iles for any ofour pre-existing designs! or for ne+ designs +e offer our ser5ices for design! analysis!
and parts de)elopent&
>nce +e ha)e copleted a ne+ custo design! or if +e ha)e pro)ided a client +ith one
of our pre-existing stoc designs! +e +ill then ae recoendations and introductions
http://www.kastenmarine.com/zebulun.htmhttp://www.kastenmarine.com/zebulun.htmhttp://www.kastenmarine.com/design_stream.htmhttp://www.kastenmarine.com/design_stream.htmhttp://www.kastenmarine.com/design_stream.htmhttp://www.kastenmarine.com/design_stream.htmhttp://www.kastenmarine.com/_photos/zeb_mid_frames.jpghttp://www.kastenmarine.com/zebulun.htmhttp://www.kastenmarine.com/design_stream.htmhttp://www.kastenmarine.com/design_stream.htmhttp://www.kastenmarine.com/design_stream.htm
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to :ualified builders +ho +e consider to be suited to the tas at hand& ;or exaple! soe
builders +ill prefer to pro)ide a bare hull! others a po+er-a+ay pacage! and yet others
+ill only tae on the construction of a turn-ey yacht&
Although our %uilding lans pacages are )ery coplete! +e )ery uch prefer to stay
in)ol)ed during the boat8s construction in case there ight be clarifications desired on the part of the builder! or if there are possible changes introduced by the o+ner! or if
additional shop dra+ings ight be re:uested! etc&
WH'R' &O "ROM H'R'...?
;or pricing and ordering inforation on any of our pre-existing boat designs and "Ccutting files! please see our lans Bist +eb page& ,hether +e create the "C files fro
scratch! or offer the as part of a stoc design pacage! +e still include our follo+-
through during the etal cutting&
9n ad)ance of de)eloping any ne+ boat design or other odeling pro