Peter Edmonds

[Peter Edmonds]

Hi, Hans

G’Day from Western Australia.

I am currently in a DELFTship revival, after some earlier work, insufficient to really consolidate  the skills. For much of my working life (Naval Architect) I have been involved in small commercial vessels, fairly well addressed within Australia. I am used to dealing with dispersed projects. I will be very interested to hear what design issues you are addressing, including not specifically related to DELFTship modelling.

I have just re-established contact with forum contributor Sean Russel of Canada. We could correspond directly by e-mail, where the content is not relevant to the Forum. I am now on peter.edmonds39@gmail.com.

Probably outside your scope at present is that I have been using DELFTship to generate hull shape, then transfer by IGES surface to Solidworks, then build vessel model and drawings within SW for the vessel build. Only 2 projects so far.

Regards

Peter Edmonds

Naval Architect

Perth, Western Australia

[Peter Edmonds]

Bottom emersion angle did appear in Australian commercial vessel simplified stability criteria (essentially where KN information is not available), but does not appear in  current criteria.

Currently downflooding angles are required. These angles can be evaluated using the same procedures.

Simple procedure:

• Draw upright waterline on relevant transverse section of the vessel.
• Draw line from intersection of waterline and  vessel centreline and bilge emersion point (or downflooding point, or other).
• Record the angle.

More precise ;procedure:

I have used this with Hullform software, but  haven’t had occasion to try it in DELFTship.

• Set up model to required displacement and LG.
• Using free trimming hull  balance, heel vessel progressively until required ;point is at the waterline, in an end  view.
• Print this view for  inclusion in the relevant document.

Peter Edmonds

Naval Architect

Perth   WA

[Peter Edmonds]

I can’t offer anything about importing an autocad mesh.

If you can get orthogonal views of the autocad shape you could use it as a background for the DELFTship model. You probably need not  be too fussy on fairing for a stability analysis.

The DELFTship model will allow you to  explore metacentric height readily over a range of displacements.

An alternative approach is based on very basic stability naval architecture:

• Strike a waterline on the autocad views.
• Measure cross sectional areas to this waterline.
• Integrate these longitudinally (Simpson’s rule or otherwise) to get volume of displacement.
• Obtain waterplane inertia I from either an equivalent rectangle (L B^3 /12) or by offsets and factors.
• Eyeball vertical centre of buoyancy B (not the breadth B)  from the cross sections.
• BM = I/V  ( V = volume of displacement ft^3, m^3)
• Determine vertical centre of gravity  G, and thus GM.

Only do this if you have some understanding in this area of naval architecture.

However I caution you against expecting to get anything meaningful from GM analysis for a boat. You may get something of value by comparison of a proposed design against a similar existing vessel of known but marginal stability.

For small commercial vessels GM on its own has long been abandoned as a  criterion for adequate stability. For current multi-factor stability criteria GM is  very rarely a make or break criterion. This comes from my preparation of stability particulars for many small commercial vessels over the years in the course of my professional practice in Australia, where we do small commercial vessel stability quite well.  (Reference – The National Standard for Commercial Vessels – Australian Maritime Safety Authority)

I expect a lot of this posting more properly belongs under Hydrostatics and Stability (?)

Peter Edmonds

Naval Architect

Perth  WA

 

[Peter Edmonds]

Sean

Was I corresponding with you around 2012? Skiffle 10 and related. I have lost all my e-mails of the period, but lots of DELFTship models remain in the computer.

Is your issue with a dory type bottom? If so, has it rocker in profile? I attach jpg of 2012 lines, with rocker as above.

This hull shape has little change of topsides flare and of chine panel deadrise, so the shapes should come out quite well for fully developable, with only minor cross curvature.  This is showing in the chine strake in the forward 2 transverse sections. It would be a great candidate for ply stitch and glue.

I have just looked at my most recent Skiffle 10 model. It shows modest non-developable areas forward on  both  topside and chine strake (I expect from stem curvature), and a small area right aft on the chine strake; probably an abberation.

If you are interested please drop me a line on my new e-mail peter.edmonds39@gmail.com.

Shortly I will be moving into flat pack boats, for which DELFTship developable will be significant.

I could write heaps on developable surfaces, both within and outside DELFTship.

It is some  time since I looked at developable surfaces in DELFTship. I recollect you should be able to get rollout flattened shapes.

I have just posted on Solidworks and DELFTship in this forum.

Peter Edmonds

Naval Architect

Perth  WA

Attachments:

You must be logged in to access attached files.

[Peter Edmonds]

Riccardo

I would be very interested to hear how you are going with your canal boat design. I would have no hesitation in embarking on such a project with DS/SW if it were to come my way.

One issue you will be addressing will be parts etc for the steel structure. Have you done anything like a canal boat  in Solidworks?

For my mooring buoys I used 1 part = 1 welded panel of plating, and 1 part = group of stiffeners to go with the plating. These made up the fabrication  SW subassemblies.

I will welcome your correspondence outside the Forum if you want to pursue this topic.

Peter Edmonds

Naval Architect

Perth   WA

[Peter Edmonds]

riccardosercia

I have  been moving down the DELFTship to Solidworks path for  some years. I am a Naval Architect, and started Solidworks to design a batch of 20 t embedment anchors. I then went on to design single point mooring buoys, in 2 sizes.

I moved over to DELFTship because it offered the IGES output, acceptable to Solidworks. I wasn’t prepared to generate hull shapes within Solidworks – far too cumbersome. Much better to use a dedicated hull package.

So far I have done the transition for 2 designs a 14 ft round bilge rowing/sailing boat (private), and a 15 m fast fishing chine form catamaran (commercial). Both are GRP vessels. I was able to lift hull shapes from pre-existing moulds in both cases. As it turns out, I did not have to generate the hull shape for construction in either case from the DELFTship/Solidworks combination. However, I did need to generate arrangement, structural and other drawings in Solidworks, to the levels required by the projects.

The procedure:

• Generate hull shape in DELFTship.
• Save as IGES file.
• Import IGES file into Solidworks.
• Scale by factor  1000; numbers are m in DELFTship, mm in Solidworks.
•  Rotate the IGES surface to get correct orientation –  bow to Solidworks right etc.
• Copy elements of the IGES surface into Solidworks surfaces, and onwards to parts, bodies etc, for the hull shell. The IGES surface does not appear as such in the Solidworks model.
• Populate the Solidworks model with decks, framing, and all the other stuff as required.
• Set up drawing sheets and views as required for the  project.  Suppress/unsuppress parts and bodies as required  by the drawing and view. For instance, doors and stairways will appear in the arrangement drawings, but not in the structural drawings. From this stage it is just another Solidworks design project, with the DELFTship contribution just a memory.

Essentially this worked in  context.  I was a single person designer, so I did not have to deal with shared access to a Solidworks model

For years I had been using Autocad look-alike 2D  software, and 3 orthogonal 2d  views of the vessel, with selective layer switching for level and function.

Peter  Edmonds

Naval Architect

Perth  WA

[Peter Edmonds]

Anders

An interesting concept. I am looking  at using  DELFTship as a way of getting quickly from a lines plan or similar source to a 3d printed model for the modelmakers.

It wouldn’t be hard to create a hull shape in DELFTship for a person familiar with hull shapes and general ship construction. It is just a small subset of the total ship design process.

Anders – how did you  go with solving the issue? Your link didn’t work.

Petrer Edmonds

Naval Architect

Perth   WA.

[Peter Edmonds]

We appear to have 2 topics running, starting from basically the same initial post. The other is #5423, to which I posted a response.

Look for this parallel, but further developed topic.

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

Keep up the manual to deal with features appearing in new releases.

Also, explore the YouTube DS tutorials. I have had a lot of value from these.

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

Automatic fairing is fairly new into DS. I don’t put new hull shapes through DS very often, and I just haven’t tried the auto fairing to see how its function matches my specific intents at the time.

I’d welcome comments from any readers who have become familiar with this automatic fairing, and how to use its strengths.

2 recent DS hull shapes I have done were of existing GRP power catamarans. One was from offsets lifted from an existing hull; the other from the offsets lifted from a 12 m mould, then extended to 15 m. In neither case did we need to actually generate hull structure at shape from the DS model

The smaller vessel lines essentially generated KNs and hydros; the larger n IGES hull shape, moved into Solidworks, th. My concern was to reproduce the existing shape as well as possible, including its fairness, in generating arrangement and structural drawings.

It has taken me a long time to get to the position of being able to generate a hull shape in DS, transfer to Solidworks by an IGES file, and then build the SW model, for drawings etc. I have yet to tackle using SW parts of individual hull shell plate/sheet entities, flattening with SW sheet metal, and generating cutting templates.

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

Andy, Robert

I’ve had a quick look at Andy’s reference. It spells out the second step I outlined (adding with parallel sinkage), and addresses the third step, in reverse. The example derives draft change for defined shift; you need allowable shift for defined (derived by you) aft draft change.

You are on your own for the first element – the change of water density. This should be quite straight forward for you if you are tackling this kind of problem.

Please let me know if you can’t get to the nominated answer.

I used to teach (briefly) this kind of NA problem many years ago at Sydney Technical College.

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

Short answer, without trying it out.

There are 3 stages here. Do them one at a time.

Move the ship from seawater to fresh water, Treat this as a straight sinkage. Count this increase in draft at LCF as being increase in draft aft.

Add the 300 t of cargo at LCF position 55 m from stern. Again, count this as an increase in draft aft.

Calculate how much draft increase is left for the trim. This is 0.3 m – both these previous values.

Calculate trimming moment to generate this trim, using the displacement (now 10 300 t) and the longitudinal metacentric height. From this calculate the shift from LCF of 300 t to generate this moment.

Convert this position to distance from stern (= LCF position 55 m – the shift)

.I’ve just had a look at your spreadsheet. It looks messy relative to my 3 steps as above. DS software is irrelevant to the solution – I can’t see how I could use it.

Regards

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

To hold 1 or 2 of x y z while editing see the manual > The DELFTship Interface >Manually Modify Points, Control Point window
To hold X use Y Z Plane,
To hold Y Z use x-Axis.

Sometimes (eg working from pre-existing offsets) it is useful to enter numeric values for the point, rather than a drag. This is also useful at fine fairing, where you may want to increase or decrease an ordinate b a fixed amount, say 0.005, 0.001.

Once you are getting near the desired shape you can switch on the curvature combs (which are 3D) for longitudinal lines, and adjust ordinates to smooth down the curvature comb, and get the curvatures concentrated and oriented where you want them. This is very useful where a line, or its projection, is straight. Example – a sheer line straight in elevation.

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

This is an ambitious project.

I believe you need to generate an indicative budget, of both your construction time and effort, plus the purchases, for the project. A building site is also important. The rule of thirds (structure, outfit, propulsion) should be reasonably applicable for such a boat.

After this you should assess your intended use of the vessel, and where it will be kept. These are both significant commitments of resources.

You may well get some frights here.

I have recently generated DELFTship models for 2 GRP Leisurecat power catamarans – see website

http://www.leisurecat.com.au

The first was for a 9 m existing boat, to support generating stability particulars for commercial operation. Shape was lifted off the existing hull.

The second vessel was a newbuild high speed 15 m commercial fishing boat. The shape was lifted off the existing 12 m mould, and extended to suit. This shape was then used to support some design investigations, and to generate arrangement and structural drawings. This boat is shown (4 outboards) on

http://www.leisurecat.com.au/product-category/some-extended-models

For this vessel I generated an IGES surface in DS, put it into Solidworks, and built the hull, etc from the surface. (It has taken me years to get to this capability.)

Neither project involved building the hull shape defined by the DS model.

I can make these hull shapes available. (File for 9 m boat attached.)

Now to consider construction methods. This comes in part from some investigations in support of a website design.

Traditional ply S&G is limited to fairly light and small boats – cartop and light trailable. A major limitation is that the ply has to be fairly thin – say 6 mm or so – to allow it to be bent up into hull shape. A second limitation is that framing up (transverse frames and/or stringers) isn’t very easy inside a S&G shell.

Another issue is that chine strakes, longitudinal steps and knuckles, spray strips etc can soak up a lot of effort.

One common solution is to build the hull in ali plate, which can be rolled or pressed close to shape.

There are a number of solutions to building a one off boat in GRP without the traditional mould (great for multi-boat programs). However, many of these bring in the labour intensive requirement to finish the “as laid” exterior surface to fair and smooth.

DS is well suited to designing hulls for cutting panels from the flat, and bending and joining to hull shape. Whilst it does analyse and display “developable” surfaces, I have yet to find an easy way of generating the hull panels as fully developable.

A suggestion here is that you consider designing and building a small trailable catamaran, using the construction technique you intend for your dream boat. Look to existing designs to give you some starting points for your designs. The sooner you start on your design spirals (function, size, layout, shape, weights, costs etc) the better. Your dreams have opened up a very interesting topic

Peter Edmonds
Naval Architect
Perth, Western Australia

[Peter Edmonds]

I am working on what is quite a pricey solution.

I am now doing my main design work in SolidWorks, and have moved into DELFTship to generate hull shape, and transfer by IGES file.

This is replacing the environment where I generated hull shapes in Hullform (Blue Peter Marine), transferred lines in dxf, and then generated the working drawings in AutoCAD lookalike.

There may be an affordable solution going from DS to a low-cost AutoCAD lookalike.

Peter Edmonds
Naval Architect
Perth, Western Australia

[Author]

Posts