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Ben752

H.M.S. Atalanta - Drafting my own plans

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Good day everyone,

I've recently moved to Edinburgh for work. My personal effects are somewhere in the middle of the atlantic (above water hopefully).  This has given me time to focus on planning my first scratch build, the H.M.S. Atalanta.

 

I've selected this ship due to the wealth knowledge in the TFFM series, availability of contemporary plans from Admiralty models, historical plans and many build logs.  The hope is that with all of this information, it will give me enough information to stumble through the creation of plans using CAD and construction of the ship to a high level of quality.

I'm using Fusion 360 as my CAD program due to it's excellent price (free for hobbyist), professional quality and integrated t-spline, anlysis tools, parametric modeling features and CAM support.

 

I have made several false starts on the plans as Fusion is stew relatively new to me. One of the trickiest things is getting a good scan of the draughts into fusion and scaled.  When you can zoom in to miniscule details of the draughts it becomes apparent how warped and skewed they are.

One technique that I've found useful in fusion, is that when using the "attach canvas" that if you first create a component,  you can then duplicate the component and translate it.  This is quite welcomed after you go through the laborious process of aligning and rescaling the draught.

 

To start off, I've made a considerable effort to follow the practices outlined in Steele.  The dimensions have been sourced through a contract I found for the HMS Hornet at the RMG and the TFFM books.  When there is a discrepancy I've sided with the TFFM as the books are my guide.  My effort is to not trace but rather draft using a combination of traditional methods and 3d approaches.

 

Given this, the sheer plan is first up.  In Fusion, I've created "primary" sketches for each major major plan with the exception of more detailed aspects (following the order of Steel lends itself well to this approach).  For more detailed areas, I then create a separate sketch and project or intersect the references needed.  Fusion prefers this approach as it runs faster and easier to apply constraints and such.  For starters, here are my sheer sketches.

 

sheer_no_dimensions.thumb.png.4d76cebc5a02838c1e077582386f952f.png

Below is the sketch in edit mode so the dimensions are visible (when zoomed it the dimensions are more manageable).

sheer_dimensions.thumb.png.9357fa6367cdb15262b4d9039163b318.png

 

I've found using custom parameters exceptionally useful for cataloging scantlings and the source reference material I used.

 

5b0bdf0a25677_parametersmenu.thumb.png.2e8f01c5289b3538f4b5d85f3dc60daf.png

5b0bdf111657a_parametersdetail.thumb.png.55da8a56ef3a5fe38b7a662a0efa040a.png

 

 

 

Mike Y, paulsutcliffe, cog and 4 others like this

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Interesting, I'll be looking over your shouolder to see how you use the CAD software

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For obvious reasons I will be following this with a lot if interest.  I am particularly interested in aberrations in the draughts.

mtaylor likes this

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On 5/30/2018 at 6:47 PM, tlevine said:

For obvious reasons I will be following this with a lot if interest.  I am particularly interested in aberrations in the draughts.

These have really thrown me off.  I started tinkering with this Fusion model about 5 months ago and while I was able to make some progress in the drafting, I would hit a spot where dimensions would be way off and I"d start second guessing everything.

 

My natural inclination is to stop and review my work, and years of technology work has taught me to exhaust all explanations of issues using my own work before second guessing the work of others.  However, I have found that the body plan on the TFFM plans appears to be inconsistent in some areas.  Last week the use of the diagonals clicked and made a strong case the plan does seem to be off (incidentally the station on the designed and built draughts are very close to where i've drawn the curve).

 

I will say that the HMS Hornet contract I found in the RMG library (outside of the plans collection) has been very useful in providing a 3rd party dimension reference. It contradicts some of the dimensions in TFFM in ways that appear to be consistent with the draughts.   For those that are interested, http://collections.rmg.co.uk/archive/objects/512680.html#uaX1DK6V18Qgr5bl.99 the hornet contract is in SPB/27

 

This is not a criticism of TFFM at all!

mtaylor likes this

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When I initially started this project, I started down the path creating a 3d model in Fusion following the order of the book.  It quickly became apparent that this strategy is not an optimal way of working.  However, the work below on the keel is fairly simple and was able to be salvaged before I shited to following a construction order closer to what is described in Steel.


The process used is as follows:

 

1.  Under a new component create separate sketches for the fore, aft and a middle timber of the keel.

 

5b128b89accd6_ScreenShot2018-06-02at1_08_20PM.thumb.png.2d8ca2dfa22710df4d19fb569d3a7f5e.png

 

2.  The top plane worked well to construct the aft and middle sketches as  it lends itself well to a extrude along the Y axis.

 

5b128bc4e00ea_ScreenShot2018-06-02at12_33_14PM.thumb.png.e1c9ecedc01f756fcc56db7f0dd29a17.png5b128bd273f5e_ScreenShot2018-06-02at12_33_44PM.thumb.png.fc563730c979413bff4508e61bbe217b.png

Because the mid keel components are repeated, I repeated the component using the rectangular pattern feature.  This gives me a reference edge to project in the fore timber sketch with the added bonus of propagating tweaks forward.

 

5b128c3d292b1_ScreenShot2018-06-02at1_11_09PM.thumb.png.1bc182566a4dcee67b8d9391588c4a27.png

 

3.  On the fore timber, I constructed the sketch using the left side plane as it allows for projecting the arcs of the stem to model the the boxing.  Whenever possible, I"ve used projections off of one of my "master" sketches to allow for propagation of changes to the bodies that model the timbers.

 

5b128bf55863a_ScreenShot2018-06-02at1_13_34PM.thumb.png.d17c73e6ca5eafa8bb8a2222e3c8adb9.png

 

4.  To create the simplified boxing joint I created the sketch for the lower stem on the left plane, extruded on one face left face to 1/2 the thickness and used the combine/cut option on the fore keel.   Then did the same on the other side but make the fore keel the cutting tool.

tlevine, wrkempson, dvm27 and 5 others like this

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Hi Ben;

 

I am not sure if you are doing this for ease of draughting,  to be altered later,  but the joints in your keel are what is called a 'half-lap' joint.  This is much weaker than the joint which was actually used in a keel,  the 'scarph' joint,  where the cut was only one third into the timber at the shoulder. 

 

I suspect that as you have obviously read the TFFM volumes,  you are aware of this,  but I thought it best to be sure. 

 

All the best,

 

Mark P

Bob Legge, mtaylor and druxey like this

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Thank you for pointing this out.  I plan to go back and alter them but wanted to keep it simple as I work through the various components. 

mtaylor likes this

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