Modeling boats in Freeship-The techniques of Using the sofware

[lewisboats]

I am starting this thread purely to discuss the USE of the software Free!Ship/DelftShip to MODEL a design. It will in NO way negate a knowledge of design principals or the theory and physics of the DESIGN process or "spiral" of a boat. Contributions will focus on the use of the software as a TOOL in the furtherance of and facilitation of design rather than as an end in and of itself. To start...Freeship/Delftship (from here on referred to F/D) is a Surface modeling tool...a Tool only. It can and will do any damn thing you want it to do. A Table, a Wall, a House shape, a console, a Hull...anything. It's general structure leans towards boats but it will model anything you really have a mind to do. Thus...it will draw a boat shape but will NOT limit you to things that are impossible or unsafe. To properly use the software you really need to have SOME understanding of the principals needed to design and build a vessel that is usable and safe inside of its unique design envelope.

Please forgive if you are following along in real time...I am typing then adding pics as needed...it takes a little time to get every thing sync'd!

[lewisboats]

Lesson 1:

File: New: OK.

What do you get? A default hull, in Metric, round bilge. If you look at the project settings...12,0 m long, 3,70 m beam and a draft of .50 m

From this shape you CAN form ANYTHING!

I could model the exterior of a 12 bedroom mansion from this simple BOAT hull. Still...we aren't here to do houses but...boats.

Step one: Select your flavor of measurement. If you are like me and use Feet then you will need to select Imperial. Go to Project/project settings/ and select Imperial/OK. Now everything has been changed from metric measurements to Feet and decimals there of. If Metric is your flavor then leave it alone. If you are wanting to do a direct swap...12 m to 12 ft then you have to scale the model. The ratio is 0.3042:1. To do this, the first step is to DE-select all (right click/deselect), then go to Transform/Scale. Scale all layers and select the box at the bottom just to be sure. You will want to scale all axis by .3042. You can use this on any hull that is measured in meters to get the equivalent measurement in feet...ie 12 meters to 12 feet. To eliminate some confusion from the start...go to Calculations/intersections and hit the garbage button for all of the 4 buttons to the left (Stations/buttocks/waterlines/diagonals) then click the checkmark (basically OK). This will eliminate any confusing extra lines (for now). DEselect all!

[lewisboats]

Lesson 2:

I want hard chines in my design!
Easily done! Hold down the CTL key and select the (grey) line you want to be the chine. It should flow from the bow to the stern in one swooping line. Once this is highlighted in yellow...click the button that is displayed as a 90 deg angle under a 90 deg arc >). This is the Crease button and is used to switch between a Hard Crease and a soft or rounded line along a design line. DEselect all! If you only got a partial...Deselect all and highlight the rest then click the same button. Us as necessary for your purposes.

[lewisboats]

Lesson 3: Moving vs Scaling
To get your design to the right shape you will need to move and shape the hull. Moving involves specific points or lines whereas scaling involves the whole hull. If you move a selected point or line a certain amount...only that line or point is involved. If you scale say...the beam...the whole hull is involved proportionally... relative to its original distance to the centerline. Meaning...if the hull is scale 110% then all points along that axis are scaled...even the 0 points. The pointed bow will stay the same, the mid beam will be 110% of the original mid beam...as will any specific point you would care to select...it would be 110% of its original distance from the centerline. the picture below has been scaled 110% along the Tranverse or width wise. If I were to have selected specific points or lines and moved them...only those specific points and lines would have moved...nothing else would have changed. Example 2 has the chine selected and moved 2 ft in the + direction or outwards from the centerline. Not a pretty sight but it does illustrate the point and the difference. DEselect all!

[lewisboats]

Break time to watch tv...be back later. DEselect all!


NOTICE...Feel free to continue where I left off...as I will do the same should anyone else be willing to continue this thread. Please let us try to keep it a logical progression rather than a Mish-mash of initial and advanced. Simple screen shots (suitably scaled to fit most screens) (CTL/PrintScreen) saved as a .jpg will work quite well. DEselect all...notice a theme here?

[M-Sasha]

nice effort, and a carefully done headline!

And why did you not contribute here:
http://www.boatdesign.net/forums/design-software/step-step-design-your-boat-27900-7.html

you have been asked several times!

Did not feed your ego?


Sasha

[lewisboats]

nice effort, and a carefully done headline!

And why did you not contribute here:
Step by step to design your boat!

you have been asked several times!

Did not feed your ego?


Sasha

Nasty!

I simply don't subscribe to the way the thread is running. If you have a useful comment to make please join in ...if not...shoo fly!
I made my points! If you would take the time to re-read the whole thread and see...they were dismissed when it came down to brass tacks. I have since endured a number of distasteful PMs from the author of that thread and I have decided to try and rectify things with a serious thread aimed at what I thought the original one was going to do. So...again...I say...If you wish to contribute with something substantial and related to the thread...by all means have at it...otherwise take the nasty comments back to the other (what has become) mud slinging thread. Deselect all!

[lewisboats]

And why did you not contribute here:
Step by step to design your boat!

Do you really think that I would be allowed THAT much leeway in THAT thread...to post like I am doing now? Me thinks I would be accused of hijacking the thread in a most severe way...don't you?! Deselect all

[lewisboats]

A note on Leak Points...these are the turquoise (default) points along any OPEN edge. You will always have leak points in an open boat. A boat that is decked over 100% would have NO leak points. A leak point is any surface that doesn't meet the centerline and is not connected to another surface. Leak points are not the enemy...in 50% of the cases. If there exists a leak point below the waterline you have a problem...if it exists above the waterline you don't...provided it doesn't go below the waterline at any angle of heel or draft.


There is no Transom!:

Ah...the Extrude command. Highlight the aft curves in the Bodyplan view with a CTL click on as many parts of the line as needed to highlight it all (it should show on the left in the BodyPlan view). Then Edge/Extrude/Transverse direction and go say...-4.00 then OK>. Every Turquoise point that is subsequently generated (beyond the midline to the right) is a leak point...it won't go away until it is reset to 0. Select a point then change the Transverse value to 0. Continue until all the Turquoise points are at 0 and the hull gives you back Design Hydrostatics. The only problem with the extrude command is that you have to extrude ALL edges associated with the one you want in order to eliminate any leak points. For instance...if you extrude the shear but not the connecting transom you will have a leaking seam along the deck/transom line...regardless if you match the points exactly or not. You must also extrude the transom edge along with the shear edge in order to create a solid attached surface after zeroing all the leak points. The same will go for cabin roofs and foredecks. You will need to plan ahead on how you will shape these structures in order to prevent as many leak points as possible...if this is your desire. Your shape may still be developable even if they aren't leak proof...you just need to know the difference and whether it is worth the trouble. Sometimes it isn't and you can still obtain the same results. Deselect all!

[lewisboats]

Note on how I work...:
Please take a gander at the past posts...I often re-read what I have written and will post minor corrections that might be pertinent if I feel the need. Grammar and sometimes syntax will be corrected along with things that I feel might go better in a specific section. It's just the way I tend to work...rather like a perfectionist honing and refining...even if it is somewhat history in the thread. Deselect all! (you gotta get in the habit...it will save you endless self recriminations)

Steve

[Martijn_vE]

Nice thread Steve.
I know there are people out there facing difficulties while modeling.
Maybe one of them can jump in, so we can address those problems directly?
I feel that would be helpful to others too.

[lewisboats]

Nice thread Steve.
I know there are people out there facing difficulties while modeling.
Maybe one of them can jump in, so we can address those problems directly?
I feel that would be helpful to others too.

That is my hope...although I also hope there will be a progression from basics to the more difficult. There are many aspects where I am deficient...I hope you and Bruce will chime in if needed. Perhaps you can start by doing a rough draft of importing and using offsets...tips and tricks and insider knowledge. I have no clue as to that aspect...Same with using a Background image...Bruce! We sure could use your timely and sage wisdom on working with these when the time comes. Once we get to the point of importing other designs as offsets and images this info would be the Bee's knees

Steve

[Martijn_vE]

Perhaps you can start by doing a rough draft of importing and using offsets...tips and tricks and insider knowledge.Steve
I'll try that if I can make the time. That will also make a helpful tutorial on the DELFTship website.
Same with using a Background image...
Steve
There's a tutorial with sample images and model on our DELFTship website.

[frank smith]

Nice thread Steve.
I know there are people out there facing difficulties while modeling.
Maybe one of them can jump in, so we can address those problems directly?
I feel that would be helpful to others too.

It is some of the limitation of the program that force me to go to other sources to find the answers . Not a bad thing.
I find it a great tool to check how the progression of the design is going.
I can also eliminate wrong headed ideas quickly . In that respect it helps in training the minds eye. Not a small thing .

[Martijn_vE]

It is some of the limitation of the program that force me to go to other sources to find the answers
Can you be more specific?

[frank smith]

I tend to use freeships in the same way I use paper and pencil . When I start I of course have a good idea of what I am looking for . My approach is to have a good set of basic dimensions taken from a average of similar types . I have a basic water plane shape in mind , and the rest is also pretty standard.
One of the difficulties I have is maintaining a fair shape to the water plane while work in a multi chine configuration. This could be caused by may my lack of ability to fair properly or a poor understanding of shape itself . I some times use a chine line as the water plane line ,lock the points and work around it ,
that can be fun , and a lot learned from it . It would be nice to have heeled stability with ballast figures. But the program does provide enough info to calculate that . the next time I use freeships I will keep tract of the things that come up , so that I can give you a more concise answer .

Thanks much for your wonderful program ,
Frank

[M-Sasha]

This is a nice thread, and a really nice idea!
born here
http://www.boatdesign.net/forums/design-software/step-step-design-your-boat-27900-4.html
And I hope it provides what you did not provide there.

Do you really think that I would be allowed THAT much leeway in THAT thread...to post like I am doing now? Me thinks I would be accused of hijacking the thread in a most severe way...don't you?! Deselect all


That was rude lewis and not fair.

DEselect All

[M-Sasha]

Nasty!

I simply don't subscribe to the way the thread is running. If you have a useful comment to make please join in ...if not...shoo fly!
I made my points! If you would take the time to re-read the whole thread and see...they were dismissed when it came down to brass tacks. I have since endured a number of distasteful PMs from the author of that thread and I have decided to try and rectify things with a serious thread aimed at what I thought the original one was going to do. So...again...I say...If you wish to contribute with something substantial and related to the thread...by all means have at it...otherwise take the nasty comments back to the other (what has become) mud slinging thread. Deselect all!

Sorry to disturb again, but that statment about PM is a plain lie! I asked Richard and he sent me your "correspondence". And there was only one critical question, but again a request to continue contributing.

I did as you asked me re read the thread and found it was YOU
Merde
Your post was the first negative reply!!!

As I understand it, you do not like your own behaviour....... ah yes, obsessed


Sasha
Deselect all
and continue

[Martijn_vE]

Please, let's not start all over again:(
Instead just focus on what this thread is supposed to do, which is to give tips on how to model certain items using the software mentioned.

[apex1]

Please, let's not start all over again:(
Instead just focus on what this thread is supposed to do, which is to give tips on how to model certain items using the software mentioned.

Right Martijn
though this is a public place, and Sasha was right to correct a lie.


And here are the links:

http://www.boatdesign.net/forums/attachments/design-software/33338d1248034181-step-step-design-your-boat-tutorial01.pdf

http://www.boatdesign.net/forums/attachments/design-software/33339d1248034323-step-step-design-your-boat-tutorial02.pdf

[Rick Willoughby]

These are some hints that might help new users of Freeship/Delftship.

A. It is really important to remember that you are dealing with a 3D surface modelling package. You can extend edges and move points about. The space within the surfaces is hollow.

B. Both the left hand mouse button and right hand mouse button provide useful functionality. You can use these to zoom the image, grab the image and move it over the window as well as view drop down menus. These allow you to get into fine detail on the screen and set different view modes in the view windows.

C. Like most CAD programs it has "layers" that you can place different parts of your design on. It is useful to master the layer controls before getting into any complex design. Have different parts in various layers allows you to assign colours, symmetry or not, when it is viewed, thickness and density, transparency among other options. By turning layers on and off in the view windows it is possible to view each part separately or in combination with any number of other parts.

Rick W.

[lewisboats]

An addendum to the above post...if you have a wheel mouse you can set up the wheel for zooming. I use it mostly when extending a raked transom...It is easy to get the top of the transom to have a really nice curve to it in body view but getting the points straight and lined up enough enough to be in one piece when you view the developed parts...that requires a lot of manipulation and getting in close. Sometimes the mouse is too crude...too twitchy... then I use CTL I and CTL O to zoom in and out.

Another Addendum...the surface has NO thickness. When modeling anything that spans the hull athwartship...you are going from the outside dimension to outside dimension and no consideration is made for the thickness of the hull material. This comes into play later when doing bulkheads and actually laying out materials to build. When assigning a thickness and weight to a layer it doesn't actually add that thickness to the model...it simply calculates the weight of the surface and then provides a CG of the weights.

[frank smith]

I s where a way to eliminate hard spots created when creating say a 2 level deck house . I isolate the deck structure from the hull , but isolating every part is a pain and there is no need to do it

Also is their an easy way to install bulkheads reduced by the hull thickness.

[lewisboats]

Lesson 4:

Your default hull will already have the transom at point 0 but it is vertical and you want a raked transom. So...you go ahead and move the points, get them all lined up properly and have your raked transom. But...the hull no longer starts at point 0...it is now in the negatives. The simple solution is to move the entire hull to the right. Click on the highest and rearmost point of the transom and find the longitudinal number...for example -.321 . DEselect all! Then go to transfom/move and move the in the longitudinal axis .321. Click OK and OK to the markers if it asks...your hull should originate at point 0 now.

Now to put station lines in and get your curve of areas. Go to Calculations/intersections and click on the +N. It will pop up a box with a default of 1 highlighted...this is the station spacing and is in the values you selected in your project settings. You can change the setting to anything you want as far as spacing...same with the other options in the dialog box (Buttocks/Waterlines/Diagonals). Some hulls will give a station 0 some will start at the first value. To get a station 0 for one that isn't there click on the +1 and enter .0001. To get a station line for the bow if it doesn't fall on an even line...highlight the right most point and look at the # for the longitudinal value. Subtract .0001 from that value and create a station using that number...you will get the bow station.

The reason you move the hull to the zero position becomes important when you export the offsets for the hull. If you don't move it to 0 you get a confusing set of numbers to go by... with whole numbers and lots of decimals. Try it and see.

Curve of areas: After you click the checkmark...your model should have its station lines and display a curve of areas to go along with it. The Design Hydrostatics will also have an additional box on the bottom giving the half breadth of each stations area calculation and will correspond to the numbers on the curve displayed. Notice that the curve only pertains to the area of the hull under water

[lewisboats]

I s where a way to eliminate hard spots created when creating say a 2 level deck house . I isolate the deck structure from the hull , but isolating every part is a pain and there is no need to do it

Also is their an easy way to install bulkheads reduced by the hull thickness.

Some pictures would be needed to see what you are talking about.

Sure...you could move all the edges of the surface away from the hull or you could simply reduce the width and bottom height by the appropriate amounts when laying out the panels. In the first method though...you will have leak points if you don't already.

[frank smith]

I kike to set the beginning of the water line at 0 the get stations evenly spaced on the waterline . Then move drawing to include the transom.

[lewisboats]

Lesson 5:

Importing output from another program:

I am going to use Carene as my output program...mainly because I usually use it. Similar techniques are used when importing other program outputs but the specifics are unique to each and will have to be played with. I hope others who use other programs and import into freeship will step up and provide information on any deviations particular to that program. It is mostly a matter of the units that the program outputs in that is the stickler.

Carene software uses metric measurements only and generally I ignore that fact like it doesn't exist. If I want a 12 ft boat I generally model a 12 metre boat like it was in feet. When I import into Freeship though it is still in meters and I have to convert it. First I go to File/import/Carene XYZ file and select the file i wish to import then click ok. Now I have the file...I want to change it to feet like I planned (if you did it up in metres and want it that way...there is no need to do anything). I will go to project/project settings and change the Units to Imperial. I will then Deselect all and go to transform and Scale the model as detailed in the first lesson. Now I continue on as if the design was started in Freeship. One thing to note is...if you did the design already to scale...ie 3.5m and want it to be 12 ft-ish then simply changing the Units will get you where you need to go...you won't have to scale it.

Importing Parts. .Part is an export option that also has important significance. A library of .part s is like having a pro "go to" lineup when you need them. Anything can be made into a .part, exported and then imported into another design. Think ama...design the hull then export it. Import it into your aka design and connect...using connection arms that are also parts. You can model anything and use it as a part or import a part and create anything from it. There is a library of parts at the Yahoo FreeShip group and any additional .parts would be welcome.The best way to creat a part is to assign what you want to export as a part to a separate layer and then export as a whole selected layer as an object. You can then import into another design and scale it as needed to fit the target design. This works for anything you assign to the layer. You can use this to create consoles, seats, bulkheads...virtually anything including entire hulls. Good for building Catamarans...model the hull, Mirror and join points then export and import and mirror again with the connecting hardware. The usages are infinite.

[lewisboats]

I s where a way to eliminate hard spots created when creating say a 2 level deck house . I isolate the deck structure from the hull , but isolating every part is a pain and there is no need to do it

Also is their an easy way to install bulkheads reduced by the hull thickness.


Please post a picture or better yet the .fbm to work with. All copyright rights are still yours and will be respected and not be infringed on. What version of freeship are you working with? I suspect it is the way you extruded the planes... You have to be careful to make sure you extrude ALL the pertaining edges in order to get a decent model.

[lewisboats]

I kike to set the beginning of the water line at 0 the get stations evenly spaced on the waterline . Then move drawing to include the transom.
The only thing that really matters is when you export the lines...THEN the aftmost point is set at 0 when you do the export.

[frank smith]

Please post a picture or better yet the .fbm to work with. All copyright rights are still yours and will be respected and not be infringed on. What version of freeship are you working with? I suspect it is the way you extruded the planes... You have to be careful to make sure you extrude ALL the pertaining edges in order to get a decent model.

Oh, that made me laugh , I dont think any thing I done is so special .
Ill dig out what some thing .

This is good , I t will be a help to quit a few .

ok here it is , the hard point where cabin top raises , this is a fairly common transition

[lewisboats]

I presume you have already tried to take the check mark out of the corner box in the point properties pop up box. I suspect that the way the edges were extruded here is the culprit...not allowing the corner to be deselected. I would save it then save a copy and start by deleting the point and see what happens. Perhaps you can recreate it without having the corner being hard.

[Rick Willoughby]

...
ok here it is , the hard point where cabin top raises , this is a fairly common transition

Frank
The points that define the shape are a control net, not necessarily on the hull. If all faces were flat panels you would have a faceted hull and all control points would actually be on the hull surface. However generally the points of control net are not actually on the surface - the corner point at three or more creases will be on the hull. The actual line of the surface is shown as a thin dark line that is usually a slight distance away from the control points because it is smoothed.

The image below shows a similar situation to what you have. With the point at the stern I split the edge where the edge was close to the actual hull shape and extended in different directions there. The Gaussian curvature shows that this produces a less tortured plate compared to the bow where I have extended from a point on the existing net which is further away from the line of the hull.

In practice you would be making these sections from different pieces of plate or sheet and each would have their own control net. You simply adjust the control net for each piece so the true outline for each are within your cutting tolerance.

There other ways to avoid the severe distortion but the important realisation is that the points and lines of the control net are not necessarily on the hull.

Rick W

[mick_allen]

There other ways to avoid the severe distortion but the important realisation is that the points and lines of the control net are not necessarily on the hull.

But for this case, the important realization is that the hull surface actually jumps out to touch the net at this point to form a singular, peaked location:

The nice original curve of the sheer is destroyed and the actual control curve is now split in two. The problem workaround is to move that point back exactly to where the actual sheer curve was before (if you can remember or had it recorded – say by export and reimport to markers) AND then to add a point on each side and fairly near to this singularity in order to try and get some curvature back close to the peaked location so that it appears as if the sheer is continuous like it was before. It unfortunately doesn’t help that the curvature analysis now does not work thru this point. (Hopefully martijn will improve the tool for delftship so that it doesn’t unfortunately go to 0 at the end of all curves - then it would be useful for these and other situations)

While the abrupt change is especially obvious with crease intersections, whenever a point is added to an edge curve, the original curve is changed – even when it is ‘locked’, its influence location is locked, not the affected real curve. And where the curvature is great, the affect is large. If one is trying to keep the original hull sheer condition, even the right side point addition in Rick’s example causes the sheer to be changed from where it was originallyto be exactly touching that intersection. That it doesn’t add much deformation, may or may not be an issue( but it will be for the in-plane sheer curve!) – but it does make a change that might be an issue – especially if one is trying different cabin tops and expecting the hull to remain the same shape!

When freeship/delftship develops a curvature analysis tool that will work through these typical 3 edged situations, it will change from a schematic tool to a much more useful modeling tool.

Here’s another example of exactly the same thing: I wish to have some way, other than just my eye, to make a fairish curve of the end of the strakes of the Oseberg Ship (highlighted points and 'lines'). Or I wish that I can keep the hull sheer strake in a fairish curve when I add the gunwale strakes. Right now it is just discontinuity after discontinuity - right now, I can only do it by eye:
http://www.westcoastpaddler.com/mick/misc-dwgs/oseberg-bow-1.jpg

[HJS]

It is important that you connect the points in the right way so you not get concave waterlines in front. The bottom is still developable, even more natural.

JS

www.sassdesign.net

[frank smith]

JS , I found that also , I have thought of adding a point as an apex for a guide in development of the bow . This would be out in space , with a line going to 2 chine points .

[lewisboats]

Do NOT forget...adding a "point" will throw off Freeship/delftship more than you really want. The program is Seriously optimized for a 4 point face...anything else tends to give it fits or at least heartburn. If you can...move a point of a 4 point face to get where you need to be rather than add a point and make it an uneven point numbered face. If necessary...add enough points to create another 4 point face...this will help but might not be the optimal.

[lewisboats]

Here’s another example of exactly the same thing: I wish to have some way, other than just my eye, to make a fairish curve of the end of the strakes of the Oseberg Ship (highlighted points and 'lines'). Or I wish that I can keep the hull sheer strake in a fairish curve when I add the gunwale strakes. Right now it is just discontinuity after discontinuity - right now, I can only do it by eye:

And to think...By Eye used to be the ONLY way to build a boat...it is now relegated to an apology for the perceived inadequacies of a program. If it LOOKS right in the software...chances are it will come out within .0025" of what you want...how close do you really really need it to be when a plane stroke is enough to get you off by .005"?

Somehow I think the search for the CAD "perfection" has gone a bit too far. When you start talking about .0001" of an error as something significant in wood...you have lost the spirit of the thing and given over to the mechanics and sterility of the drawing program and not the warmth and tradition of building in wood....after all...even the sheets of peeled and laminated wood veneers called plywood are unstable and subject to the environment. And when talking plywood... .00520833333333' (1/16") is a SMALL measurement in Stitch and glue and the Maximum variance in the old measurement of offsets of a traditional planked hull was (1,1,5+)(inches,1/8's,1/6ths) and was only +/-1/16th of an inch when absolutely necessary. It is very easy to cover an 1/8" variance in ply with the Wonder of wonders...Epoxy...or even more with a sloppy fillet. Do we really NEED to worry about the precise fitting of joints and panels to the hundredths of an inch or is it just stick in the mud tradition applied to an ever diminishing traditional thought line of building which advocates precision in design but "give" in building techniques because someone uses a plane to shape the planks? I use a plane...I use a cordless saw...a drill ...a jig saw, ...a circular Saw.... a sawsall,...a grinder...whatever gets the job done,,,but there are those of us who scorn others if they even THINK of using these techniques.

Sorry...didn't mean to rain on your parade but this got me a-huffin' and a-puffin'!...I'll soon be back to using software to modeling hulls to the .0001 foot.
/100.

[Timm]

What drives me crazy is when I export to my CAD program and it tells me the surfaces don't intersect. Then I check the numbers and it is off by .00001, grrrrrr!

[mick_allen]

. . . . . . . . this got me a-huffin' and a-puffin'
Contrary to your understanding, I am attempting to positively contribute to your thread on freeship techniques. The realization being missed is that inaccuracies are about ½” at the end of some strakes and up to 2” on the gunwale intersection.

The issue I think illuminating, is that the peaked point situation (that Frank raised) happens everywhere that an internal corner point is placed or whenever 3 creases or edges come together. As well, it can happen in the surface and/or an edge at single or multiple locations along a previously ‘faired’ curve edge.

To try and work through this again with a simple situation, here is a 2 panel boat defined by only 3 points along its length – endpoints and some mid point. Although this is a crude example, let’s assume that I designed it and love it as it is – and have resolved lots of measurements both dynamic and static to get to it, or that I already built it this way, or that I just bought it and it is now sitting in the yard. In other words, I spent big bucks, or big time, or big emotion getting to this hull and it is way too late to change it now:

(To re-emphasize – this is a general example; it could be a stem, gunwale, or keel where a strake or panels end, or a multi faceted cabin, or a deck panel intersecting the cabin side or many other situations.):
fig 01
http://www.westcoastpaddler.com/mick/misc-dwgs/01hull.jpg

The first thing to note is that the gunwale is a 'fair' curve. The second feature to note is that point 2 is separated from the gunwale by a significant distance.

So after acquiring this hull (by whatever means: imagination, money or build), I wish to add a most simple cabin top. As this is to demonstrate the general issue that possibly could be an immersed situation below some waterline, I will need to join the cabin to the hull.
I show the cabin just floating above the hull by 1 foot so one can see the intention:
Fig 02
http://www.westcoastpaddler.com/mick/misc-dwgs/02hull-hihut.jpg

And now here it is unjoined, but dropped 1 foot, approximately in place:
Fig 03
http://www.westcoastpaddler.com/mick/misc-dwgs/03hull-lohut.jpg
Note that in a typical case the cabin would be modeled directly and not imported to show two separate pieces. This approach is purely to attempt to clearly demonstrate the issues of what happens next. Note that the hull is unchanged and fair and that the cabin tent is also.

So now there is a weird choice:
1) does one join the two pieces so that the original hull point 2 is retained? That’s the point that truly has defined the hull from now, so shouldn’t that be paramount? But here’s what happens if the cabin joins to the previously good point 2:
Fig 04
http://www.westcoastpaddler.com/mick/misc-dwgs/04 hut2hull.jpg
This contortion is obviously not a straight forward approach.

2) Or alternatively should the cabin corner near to point 2 be retained as that is where the gunwale sort of ends up?
We read that corner points are right on the surface and corner, so it does make some sense. The first problem here is that one can’t ‘snap’ the cabin corner to the gunwale curve like in other programs, so one has to do it by eye and zoom in so that its location is close enough for our desired tolerances. A little slow and cumbersome as one has to do it in 2 views, but no big deal:
Fig 05
http://www.westcoastpaddler.com/mick/misc-dwgs/05hull2hut.jpg

This approach seems works in some fashion, but now the surface is radically dished and unfortunately the rear half of the gunwale curve has been changed into a straight line. And furthermore, the gunwale’s original location is lost.

So to now change the rear gunwale straight line back into a curve, one has to at least add a point. And to take the dish out of the front part of the topside(s) panel, one has to add a point to the front half of the chine curve and join these 2 frontal points up with a ‘normal edge’:
Fig 06
http://www.westcoastpaddler.com/mick/misc-dwgs/06gw-issue.jpg
But now the added rear point dishes the rear of the panel. And the simple point added with no moves at the front chine changes the lower chine curve at the front. The change at the chine of this 12 foot boat is on the order of 2 full inches. And added to this situation, the original chine curve location is lost as well and I think we can foresee that a rear chine point must be added as well.

**

I hope the above demonstrates the cascading series of adjustments that must be made when one adds a single hard point in the edge of a curved surface. Highly curves surfaces or edges are much more affected than those with minimal curvature.

So some considerations come from this:

one cannot retain original hull shape when additions are made.
New points and normal edges must be added to approximate the original shape
Any new points make changes in edges and in surfaces that in turn may require reaction.
Changes can happen in edges that are adjacent to edges that are changed


Some procedures are required to assist getting back to the original shape: First, save the original unadorned hull shape as an inviolate, separate file. Then there are some options:

1) save the linesplan and use it as a background image in the 3 views. After the cabin is added, add and shift points around as necessary to match the background. This approach is exact as the graininess of the lineplan bitmap.
2) Export offsets (only when model is in ‘highest’ resolution) to file, strip off everything except control curves, and read back as markers.
3) Another is to export original as part, read in, change colour, lock all points and remove from hydros. I haven’t tried it, but feels cumbersome and confusing.

Using approach 2, here’s what the markers look like just as the cabin is added and before any steps are taken to try and match things up (2 pics ago-fig 05). The markers coincide with the chine, the surface is dished, but the gunwale is close at the front but the stern gunwale portion is a straight line that misses the original marker curve by probably 4 to 6 inches (I forgot to measure it):
Fig 07
http://www.westcoastpaddler.com/mick/misc-dwgs/07 hull2hutmarkers.jpg

You can see that the markers seem to coincide with the gunwale, but the actual case is that I cannot get better than ¼” error with solely adding (and moving around to 'best' fit) the bow 'quarter' point and the stern 'quarter' point. You can plainly see how out of whack that the chine is before adjustment with the simple addition of the chine bow point. Before adjusting, this is out about 2”.
Fig 08
http://www.westcoastpaddler.com/mick/misc-dwgs/08chinemarkers.jpg


summary

Adding a hard point can have significant effects on areas of high curvature
it is not always a trivial exercise to account for the addition – in some cases many new points will be required
one compensating aid is the use of output/input markering.


-mick

[frank smith]

Mick. , that is what sends me back to pencil and paper . On paper I can put something where I want it and it stays there . But getting quick hydros is good in Freeships . I dont use it as an illustration tool , but for playing with ideas .

[lewisboats]

Why are you using a separate panel to create your top instead of extruding the edge and shaping from there? You would then not have the corner issues because your are adding a surface along the same edge and it would be pulled by the same point along the edge or another point with the same curvature properties would be created if you extruded up then in. You can even combine both at the same time to get the angle of the tent. It might not work for everything but it will definitely work for your example. When adding .parts the expectation is to get it to the same or very close to the modeled surface by adding as many points to the part as needed but not actually joining the hull. Any surface work should be developed by extruding the hull. You point out the exact problem because the part is edged with hard points that often don't want to change...the trick is to add soft points to make the lines conform to faces. Trying to join a hard point to a soft face will only distort the mesh in a very nasty way...as you point out. It is a limitation but it can be worked around for the most part. You try to model the exterior surfaces by using the exterior surfaces and points and extruding. Adding interior stuff can be done using .parts or by separating extrusions and moving into place and shaping. Always extrude up and in if it will affect the hydrodynamics with leak points. A leak point...even inside a hull will throw things off.

[Martijn_vE]

Probably because where the edge of the top meets the sheerline a hard point is created. This happens automatically whenever 3 crease edges meet in a point.

[frank smith]

you have to do the deck and bottom separately. I extrude the thickness of the
hull and then finish the deck , and get rid of the face between . Works out nice for floating the deck structure . Actually breaking the boat down to components works well , but is time consuming. It does not work with areas below the waterline of course .

[lewisboats]

Martijn...are you open to suggestions here or should I email the couple that I have direct?

[Fanie]

When I near 'completion' of the hull shape I rely heavily on the resistance performance curve. This indicates if the shape improves or worsen.

If you select the view mode to developability check you can see if the shape is smooth or out.

[mick_allen]

Why are you using a separate panel to create your top instead of extruding the edge and shaping from there?

To try and clearly show the intention. The issue is that change has an effect.

The statement to be made again is that the same effect happens whether by connection (method shown), by extrusion, or by placing the 2 points on the ridgeline and making the cabin surface between.

As well, so called 'soft points' don't exist. They all (even 'locked points') have an effect like a magnet upon the surface or surface edge. But unlike a magnet, they have greater and greater effects the farther they are from the surface or surface edge.

Just to be clear to Frank and others:
Most of what I have written is NOT a criticism of the program. One has to recognize that a 'corner' is a singularity, but the program behaves essentially as one would hope: but you just have to record where you were, add a few more points and connections and massage the model back to whatever tolerance works for you.

The utility of joined faces outweighs separation by far. It just takes some adjustment.

[frank smith]

Cool , I'll work with that a bit

[lewisboats]

by soft points I meant points that aren't cornered. I'll have to play with it a bit more...maybe I'm missing something.

[mick_allen]

Here’s another look at the same example:

This is the situation that is wished to be retained. Simple hull, lots of curvature, few points. No hull change is desired.
Fig 201
http://www.westcoastpaddler.com/mick/misc-dwgs/201hull.jpg

The display only will now be changed to isolate the steps about to happen. The gunwale and chine only have been exported and reimported as ‘markers’ for reference. Stations on the isolated panel are shown so that surface changes may be seen. But nothing in the model has been changed:
Fig 202
http://www.westcoastpaddler.com/mick/misc-dwgs/202side.jpg
Say for some reason, I place a control point in the chine curve by using ‘create new control points by splitting a control curve in two’, one would not expect much change as the arrow points to where the point will be placed and this point is really quite close to the chine curve. (no movement will be given to the point, the program will just be asked to place it between the two points c1 and c2)


But this is what really happens:
Fig 203
http://www.westcoastpaddler.com/mick/misc-dwgs/203side.jpg
The chine curve has been displaced over a huge portion of the whole curve with the deviation being some inches away from its original position and the maximum deviation is not even where the new point is added! As well, from the station lines, one can see that the panel is dished somewhat towards the middle. One simple, seemingly inconsequential point has consequences.

***
So let’s step back to figure 202 again and instead of placing a new point the chine curve, place it into the existing control edge between point 2 on the gunwale and point c2 on the chine:
Fig 204
http://www.westcoastpaddler.com/mick/misc-dwgs/204side.jpg
This placement (no movement has been done) does not affect the chine or gunwale curves (edges) but does bulge out the middle of the panel.

***

So then let’s go back the original position in fig 2 and add a gunwale point:
Fig205

http://www.westcoastpaddler.com/mick/misc-dwgs/205side.jpg
This simple addition has caused the same sort of situation as that of the chine point addition: The gunwale curve has been significantly altered over more than half its length, the major alteration is away from the point addition and nearer the region of high curvature, and the panel has been dished.

The above has just been with normal 'uncornered' control points.

***

If you add points of any kind near areas of high curvature there will be significant effects. If the original shape is important, take steps to prerecord it so that the base position is not lost.

[Martijn_vE]

While trying to understand this phenomenon one has to be aware of the following:

Points on the interior of the surface behave differently than points
on the boundary or on crease edges. The crease or boundary edges
will be closer to the controlpoints than interior surface points. Or To
use your terms: The magnets of crease points are stronger than interior points.


Further more, the algorithms for the subdivision surface adopted
by the program are optimized for triangular and quadrilateral faces.
By adding a 5th point on your quadrilateral face twist is introduced in
the surface patch. This is clearly visible in the surface of your side panel.
To avoid this you should also insert points on the chine and contour
line, and connect these new points with edges all the way to the
center line

[mick_allen]

Points on the interior of the surface behave differently than points
on the boundary or on crease edges. The crease or boundary edges
will be closer to the controlpoints than interior surface points. Or To
use your terms: The magnets of crease points are stronger than interior points
I regret using the term magnets: I think a better allusion is that of rubber bands from the control point to the surface or edge - the farther away, the more effect and vice versa. The demonstration is to show that even single point additions do influence surface/edge behaviours.


. . . . To avoid this you should also insert points on the chine and contour
line, and connect these new points with edges all the way to the
center line
Note that I have not shown solutions but just demonstrated the initial issue with a corner, or on a crease edge, or on a boundary edge, or on an interior edge.

Solutions involve adding more points in the manner you state, and then adjusting every one of them in order to approximate the previous location of the surface and of its edges.

[gonzo]

Does this program accept a table of offsets?

[yipster]

fef file
surface
carlson
chines
carene
vrml
polycad
offsets

quik download at: http://www.delftship.net/

[frank smith]

I have been adding some bulk heads to a design , and now my nicely fared hull
is all kinked up. I know that makers can be imported , but how do I set markers to a new hull design to keep tract of where I have been .

Frank

[Martijn_vE]

There should be a menu option in the intersection window that will convert any available stations, waterlines or buttocks to markers.

That way you can visualize the difference between any modifications you made to your hull