Robert Holme

[Robert Holme]

Hi Sean,

I exported the fbm file to a 2D DXF and yes the size of the import is 1/12 of the full size in my CAD program, (TurboCAD).

I then re scaled the file by a factor of 12.

In my CAD program I set up paper space called Bodyplan Aft & Bodyplan Frd at ANSI size E. Mainly because at 1:1 scale the whole bodyplan is too wide to fit the paper.

I moved and the rescaled sections to form a “Normal” Bodyplan and created views Bodyplan Aft & Bodyplan Frd. These views were placed in paperspaces at a fixed scale of 1:1

Attached is a zip file of the dxf.

Hope this helps

Best Regards
Bob

Edit also pdf file on ANSI E paper

Attachments:

• SweetPea8.zip
• SweetPea8.pdf

[Robert Holme]

Maybe you need to change the fbm resolution

Best Regards
Bob

Attachments:

• AirFaith.bmp
• AirFaith2.bmp

[Robert Holme]

Hi,

Care to post the file, fbm,dxf,dwg………whatever and maybe we can spot the problem.

Best Regards
Bob

[Robert Holme]

Yes thank you Martjen for a great revision and for bringing the forum back online.

Best Regards
Bob

[Robert Holme]

Seems to me that you are not specifying the paper size in the pdf program.

The other thing is, I normally work in imperial and when I export to DXF/STL, the exported file when loaded into my CAD program is at 1:12. i.e. what is ft in the real world is inches in the DXF file and this requires the CAD file to be re-scaled to match world dimensions.

HTH

Best Regards
Bob

[Robert Holme]

Hi Wakefield,

Quick and dirty but should get you started.

Will need some work to fine it up and some adjustment for development seeing as how plywood only bends one way.

Hope it gets you going.

Best Regards
Bob

Attachments:

• 18Carolina.fbm

[Robert Holme]

It’s me again,

Seeing as how you guys did all the hard work modeling the hull, the least I could do was try and stabilise it!

Now the only complete model I have access too is Tubarao’s so that was the basis of my stabilisation.

I believe that if we add 23.5 tonnes of ballast to the keel with an LCG of 30.6m and a VCG of 2.8m we should be somewhere around the mark of a GM of 0.6m, which is pretty good for an old imperialist who thinks a GM of 2 ft is at the low end of typical for passenger vessels.

Best Regards
Bob

[Robert Holme]

Hi,

Very Happy to help a fellow learner. I find some of the things in yours and Jurgens models beyond me. e.g. I don’t understand how you get things like bilge keels rails and other odds and ends into your models without any control edges or faces, just a series of points connected by “ordinary” edges.

Here is a site which provides what you need, in DS they are input as Tonnes per cubic metre.

http://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html

Best Regards
Bob

[Robert Holme]

Hi Tubarao,

Let me try and explain

1. We are in this instance referring to the transverse settings, (port to stbd).

2. There are basically 3 states of equilibium for a ship.

Stable………. this is when viewed fore to aft from the keel up lowest is centre of buoyancy, next is centre of gravity and last is the metacentre.

Neutral………. this is when the metacentre and the centre of gravity are at the same height above the keel. The centre of buoyancy is still below both the others.

Unstable………. this is when the centre of gravity is above the metacentre.

OK, now when the vessel moves from upright to some angle of heel a moment of force is created between the metacentre and the centre of gravity.

When the metacentre is above the centre of gravity this moment of force acts to try and push the vessel back upright.

When the metacentre is below the centre of gravity this moment of force acts in the opposite direction and causes the vessel to either loll, (take on a permanent list) or if it is big enough the vessel will capsize attempting to put the metacentre above the centre of gravity. This is the case with our designs and is what my diagram is showing.

All of the above also applies longtitudinally in the hull but it is more relevant to damage control and such things as floodable lengths so in this embryonic stage of development the transverse ones are the ones that say if we are viable or not

Attached are a couple of jpgs which show stable and unstable equilibrium.

Hope this helps

Best Regards
Bob

Attachments:

• fig3-11.jpg
• stabil7.jpg

[Robert Holme]

Hi Peter,

I opened both your files and the hydrostatics appear OK i.e.

T28 G=3.681 M=6.444
T28M1 G=3.183 M=5.338

I also added the rudder and keel to hydrostatics in layers dialog.

Best Regards
Bob

[Robert Holme]

Hi Guys,

Well I had a bit more of a play with Tubarao’s design in as much as I added materials to the layers just to keep it simple and to prove my idea I only allocated the same material to everything, (5mm Aluminium).

Woo Hoo………… now we have a proper output in design hydrostatics for VCG :laugh:

Attached is a jpg of the result

Best Regards
Bob

Attachments:

• TbootMCH.jpg

[Robert Holme]

Hi again Jurgen,

Before I discovered Delftship I had occasion to lift an historic iron auxiliary schooner from the water as she was in danger of sinking due to the poor condition of the hull. There were no drawings or lines plans or any relevant information.

It all had to be developed from measurements and photographs.

Attached is a PDF of the way I did it using Simpsons rule and 1st and 2nd moments of inertia. COG was of particular importance in as much as it had to be BELOW the line of lift otherwise the vessel became unstable when it exited the water. Next came displacement because this determined the size of the cranes required for the lift. The lifting lugs and the bulkheads to which they were welded also had to be measured and tested to ensure they could handle the loads.

A very interesting exercise……………. my calculations were within 2 tons of the actual lift weights recorded by the cranes.

Also a couple of jpgs of the vessel up and away.

Best Regards
Bob

Attachments:

• Nellydisp2.pdf
• NelAftLiftingBrackets02.jpg
• NelComingAshore01.jpg
• NelConnectforeward01.jpg

[Robert Holme]

Hi Jurgen,

I like your concept.

I don’t estimate VCG but Delftship does a wonderful job of calculating it in the layers dialog. For reasons I don’t understand it fails to provide a calculated result in the design hydrostatics page.

Attached is a jpg to show what I mean. As you add or remove layers from the hydrostatics in the layers dialog, the VCG is updated in real time.

Best Regards
Bob

Attachments:

• VCG.jpg

[Robert Holme]

Hi Jurgen,

Sorry but I think we must agree to disagree.

My understanding is that this is a real world project so I believe it must fit real world parameters.
I don’t believe that Delftship’s calculation algorithms are suspect therefore I accept what it is telling me.

In my own fbm the VCG is above the transverse metacentre which is unacceptable.

In Tubarao’s design the VCG is raised to some 16 m with the addition of the superstructure and his transverse metacentre is some 7.6 m……………..highly unstable. The centre of buoyancy in both cases is around 3.2 m although Tubarao’s displacement is less than yours and mine by an average 200 tonnes.

Displacement is only relevant in as much as it affects the size of the couple either righting or causing the vessel to loll/capsize.

Attached is my fbm which consists of hull and deck, I saw little point in going further with an inherently unstable design. This was re-enforced by Tubarao’s result.

I also attach a PDF which shows a negative righting moment of 27.475 tonne metres at 5 degrees of heel from my fbm.

Best Regards
Bob

Attachments:

• Boot.fbm
• BootMCH.pdf

[Robert Holme]

Hi Jurgen,

If KG>KM I don’t see displacement having relevance but then again I’m no naval architect. My understanding is a vessel is unstable in the aforementioned condition and once it starts to roll it keeps on going until G is lower than M i.e. it has capsized.

Best Regards
Bob

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