delftship hull thickness???

[Martijn_vE]

That's correct, if you've enabled this setting in the project settings window

[CmbtntDzgnr]

It would be very nice if the added thickness is thrown by direct choice of the user, but even better if that thrown thickness is actuallypart of the file even if as an offset mesh.

I suggest this because after I set the thickness (whether in FS/HS 3.24+, or in DS 4.17 Pro), I assumed the thickness is thrown outward. Then, when I export the model to dxf, and import it into Punch! ViaCAD Pro v&, I convert the mesh to a surface, then thicken the surface to some number of mm. In my case, I don't use a single, half-breadth model. I use creases at station intervals that correspond to main transverse watertight bulkheads so I can get individual compartments with lined up vertically with stations, and I select the correspondnig control points and make them corner points to enforce getting rid of curved meshing that otherwise would make it hard to account for the mass of each compartment.

But, in doing so, my method introduces a vexing problem. Each solid plate that originates form a surface that is itself originated from the exported mesh has a wedge gap between the plate edges. Mostly it's in the horizontal "seams" space due to curvature below the waterline. These wedge gaps or spaces are because I throw the thickness outward, on an outcurving hull. If I throw the thickness inward, i could use the interference tool to remove the redundant material. But, that means increasing my hull beam by the amount of the shell plate thickness, which I presume changes my hydros.

Seams in transverse watertight bulkhead areas are less noticable to me because the curvature is not as pronounced. Where it is, I get to use the interference as I prefer, since the hull is inward curving in the bow area sufficiently enough to need the tool.

Since a model from DS and from FS/HS is so small, I wish that a surface was by default included as outershell to aid in modeling in external tools. if anything I might be another or a redundant safety check.

BTW, so long as the hull model has no tight curvature, it's possible to get some neat, organized grid-lke meshes rather than triangular pieces that if stitched would be LOTs of pieces. Using creases and corner edges helps to generate meshes that can be removed as "windows" or portals into the model for presentation purposes. But, more than that, creasing WTTVBHD stations and corner-pointing the control points allows the color-coding of COMPARTMENTS, and since you can assigne those meshes to conveniently-named layers, you're at a good start in your 3D model.

The major downside to my method is that the hull will effectively have chines in it rather than faired curves, meaning your hydros will account for chines. It seems to be a negligible amount especially depending on the hull size and the power being installed. But, the downside is the model is not as smooth as it otherwise could be.

Why else do I do it this way? Memory consumption. If I want to speed up panning/rotating/zooming the model in 3D (which in VCP 7 moves pretty fast, and I work in shaded mode, not wired -- I want to always see the surfaces), it's fast. When I want to "drill down" into the model, i just select and hide items and the model moves even faster. To bring those things back to visibility, I can select the layer and right-click on "show items in layer", or I can unhide all.

Alternatively, i could remove the corner points and creases (and end up changing the model and the hydros, and undergo tedium), take the half-breadth mesh, convert it to a surface, thickent it, get my decks and hull, and then later "chop" the hull with a cutting plane, but that means having jagged edges of meshes that don't look as good presentationally. I know FS/HS and DS are for hull modeling in their native environ, so I am probably expecting too much. Besides, they are not the $10,000 per seat programs that mostl likely would eradicate my problem.

I'm open to ideas in my process that work withing DS & FS/HS.

[lumberjack_jeff]

Originally Posted by Martijn_vE

Specifying a mean shell thickness on the hydrostatics tab of the project settings however will include the thickness in the hydrostatics.

Free!ship+ 3.24 does not have this field.

The question to me as a S&G builder is "do development drawings take into account the hull thickness, or do they strictly reflect the shapes of the subdivision surfaces?" If the latter, then no (or a small) allowance need be deducted from the bulkheads because the surfaces reflect the inside of the hull... which is fine for me. Simply apply a small chamfer to each hull panel and assemble.
However, this means that the hydrostatic and hydrodynamic calculations are in reality, all wrong.

On a large steel ship on which the hull thickness is a trivial part of the overall displaced volume, this is probably not an issue. On a stitch and glue plywood sailboat, more so.

I suppose a workable approximation of the effect of adding hull thickness could be derived by scaling the various axes of the design up by an amount proportional to the hull thickness. In the case of a 16' x 5' skiff made of 3/8" material: Longitudinal: 1.008, Transverse: 1.0125, Vertical: 1.015.

On the above skiff, this raises the calculated displacement @dwl from 721# to 748#. Good to know it'll carry that additional cooler of beer. :-)

The result is two models. One for cutting parts and one for published dimensions and hydro calcs.

[Martijn_vE]

Typically boats and yachts are designed to the outside of the hull whereas ships are designed to the inside of the hull. So only for ships you'll need to correct the displacement for the added volume of the shell. This means that in your case the hydrostatics should be ok.
The plate developments however are not adjusted for the shell thickness so you'll need to add an allowance in some cases depending on the shape and overlap

[lumberjack_jeff]

Thanks. Knowing what the program does is the important thing.

In my case, I cnc cut the hull panels as designed, (after adding some allowance to account for the transom thickness and the bow chamfer) then chamfer the edges of the panels about half their thickness. This means that I should "trim" each side of the bulkheads and transom shapes defined on screen by half the hull thickness.

My calculated displacement will be slightly (2% or so) conservative and my actual overall dimensions will larger by one hull thickness in the transverse direction and about two hull thicknesses (plus the transom) in the longitudinal direction.

If I made steel or aluminum boats, I wouldn't chamfer the panels, so the bulkheads wouldn't need trimming, but my calcs would be off by the entire displaced volume of the skin materials.

[ancient kayaker]

I usually omit the thickness and design to the outside surface, which gives me correct developments, provided they are chamfered, and then I just have to remember to knock the skin thickness off the stations when cutting station molds or bulkheads. It seems the simplest way, but I don't use S&G.

[metin_mehel]

I have DS free and Rhino evaluation version. First I will model the outside of the hull in DS. And then I ll open it in Rhino. Offsetting outside surface through inside will give me the accurate borders of bulkheads. If I assign a thickness in DS and make some settings like in the attachement will give me higher displacement, Cp, %lcb values. I am not sure DS calculates hyd result accurate enough after assigning thickness. Moreover controlling these parameters(Cp,disp,lcb) are almost imposible after assigning thickness. I also have learnth that delftship does not calculate Cp and Lcb correct for yatch designer. Because it does not uses max cs area for Cp. I am not sure but maybe it uses midship are in order to calculate Cp. The second problem the midship location should be at the middle of the Lwl and when you calculate the %lcb the referance point must be the starting of Lwl (At stern) however it does not use it. So we should recalc. them by hand.

[lumberjack_jeff]

By default, DS and FS calculate hydro by using .5*l as midship. Max cs area is usually not precisely midship. Under project settings/main dimensions uncheck the box "Default at 0.5*L and enter the correct value for the position of max cs.

If you don't, (at least in freeship) you'll get unwanted results such as Cp > 1

[ifix]

Dear friends,
setting the thikness in DS, when i will develope plates, will the timension fit exactly on the stations?????
Does the sw consider automatically the thickness of the stakes in, the cutting plane of the stations, or I have to consider it manually????
I hope I have explained myself.....

[LP]

To the best of my knowledge, thickness is not a consideration when it comes to flat patterns. It is strictly a layer defined by the control curves that is "unrolled" by the software.