Tutorial for bow stern / modelling

[Tim Tilford]

Hi All,

I am new to Delftship and have a few questions. I have used CAD a lot but have very little naval architecture / Delftship experience.

I am trying to build a model of a merchantman vessel built in 1781. I have lines plans of the vessel. The bow and stern geometries are very complex.

I have built a first-attempt model. I am happy(ish) with the central sections of the vessel but the bow and stern are a complete mess. Can I ask if there are any tutorials on modelling the bow/stern of historical vessels? A re there a series of tutorials that I have missed? Any advice would be warmly welcomed.

I also have a second query – the lines plans indicate the inside of the hull. For hydrostatic calculations I need the outside dimensions? Is there a way to add the plank thickness to the internal dimensions?

Thanks

Tim.

[Icare]

Hi Tim, and welcome on board!

Bow and stern:
It isn’t easy to explain the way to do. I suggest you look for an already made model that looks like yours, and to get inspired by it.
My way is to “close the box” first just by creating a more or less vertical surface between the bottom and the flank (I’ll add the deck later). Then I divide this surface in polygons and “inflate” it. when I’m satisfied with the curves, I enter in details drawing.
Concerning the stern, sometimes with this kind f old ships, it’s easier to draw it verticaly and then to tilt it slightly.

Hydrostatics:
The hydrostatics calculation must be based on the outside surface of the hull (the inner structures do not must enter in consideration).
If you drew the inner surface of the boarding, there’s a button to order Delftship to draw an OFFSET SURFACE (that is the planks’ other side), but I’m affraid it will draw the inner surface (theoricaly, you’re suposed to draw the outter surface first). I suggest you EXPORT the surface as a ship PART and IMPORT it again (way to make a copy), then MOVE it slightly outwards (except the symmetry edge), just the distance of the boarding planks thickness.

Planks’ thickness:
In the layers’ dialogue box, you can enter the material’s thickness ans density. This is *NOT* drawn on the model, but is used for the total weight and center of gravity calculation. If the model’s layers are heavier than the displacement (such as drawn), there’s something wrong: you must increase the draught.

Does it help?

[Robert Holme]

Hi Tim,

Yes its hard to get your head around the bow and stern of 18th/19th century wooden ships.

Attached is a model of HMS Beagle. Note the use of layers to give control to visibility and hydrostatic calculation.

HTH
Maryak

Attachments:

• Beagle2.fbm

[Tim Tilford]

Thank you very much for your advice. I have taken the model of HMS Beagle to try to understand what I need to do.I am still having issues but will persevere.

Tim.

[Icare]

If you need a model to “play” with, I posted one here a few of months ago. Change the points position and you may get a pretty good base to draw your ship.
Anyway you can have a glance at the way I positioned them to get the shape of these old fashioned ships.

[Tim Tilford]

Thats very helpful – thank you. I had simplified the Beagle model as a start point. I will play and see what I can do 🙂

[Icare]

If you drew the inner surface of the boarding, there’s a button to order Delftship to draw an OFFSET SURFACE (that is the planks’ other side), but I’m affraid it will draw the inner surface (theoricaly, you’re suposed to draw the outter surface first).

ERRATUM!
I checked for the OFFSET SURFACE button’s use, and I found you can enter a NEGATIVE distance, which gives you an INWARD offset, meanwhile a POSITIVE distance will give you an OUTWARD offset.

I’ll have to read the manual again. :whistle:

[Tim Tilford]

Thanks for your help. I now have a model I am happy with. The stern is not perfect but the issues are above the waterline so should not affect hydrostatics too much.

The problem I have with the offset command is that it gives me a large number of leak points which prevents me from doing the hydrostatics. I think I will just spend the time moving every point out the required distance.

Tim.

[Icare]

I guess that the problem is about the new surface closing: it has no deck, so the software warns you that water can enter the hull by the top of the hull.

There’s a button to identify the points concerned by the leakage problem (to be used in framewire view). If all the pointed out corners are along the top of your new surface, it’ll be the problem I’m talking about, and you’ll have to close the volume, either by drawing a deck (even a fake surface just like a tarpaulin), either by drawing a new surface joining both faces of the skin (the edge’s thickness).

An other leakage problem can come often from the point along the plane symmetry. Then select them all one after the other (keeping the CTRL key pressed) and change their Y coordinate (which must be blank if there’s a problem) to 0. Coordinate Y=0 mean the points *must* be right on the plane of symmetry.

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