This article was posted before on the Rocket Science site, now that site is down the author gave me permission to publish it here. Thanks heaven for that ;)

Building With A Split Centre Line Mould
By Peter Scandling.

I started looking at building my own boat in 1999. The 'Mini' bug had by this time, bitten me.  As I delved further into the subject I read the standard books by the Gougeon Brothers etc. backed up by what ever I could glean from the Internet and Seahorse magazine. I had assumed that when it came to building the boat I would build 'hull and deck', like the majority.  At this stage I hadn't actually selected the design team, and it was this decision that was to lead me down the seldom-travelled road of 'split centre line'!

The Design/Build Team;

Having made enquiries with several designers I chose to go with the Owen Clarke Design Group (OCDG), run by Merf Owen and Allen Clarke. OCDG played a pivotal role in the design of Kingfisher and had project managed the build of Mike Goldings' Team Group4 (now known as Ecover). Choosing the designer is a very personal thing and the eagerness of Merf Owen to meet following an initial e-mail enquiry impressed me, added to the flexibility and profile of the company, I knew I had found someone I could work with.
Choosing the builder was, in contrast, pure luck!  Through a series a twists of fate I found myself in Melbourne, Australia, talking to fellow 'Mini' sailor Mike Smith.  I outlined my plans and he suggested I talk to Australian designer and builder Robert Hick.  Robert has been responsible for some of Australia's most successful boats and the Hick designed and built Midnight Rambler won the 1998 storm swept Sydney to Hobart race. Robert was keen to help and it was agreed that he would build the hull and deck, and I would be allowed to provide a helping hand during the build.   It was this point that OCDG suggested using a split centre line mould.  Following some discussion we all agreed to give this 'new' idea a try.

Split Centre What?

This technique is not new. Multihull builders have been using it for a long time.  So what does it all mean?  A split centre line mould is exactly what it says.  Take a rendering of a boat, split it down the middle and you have the two halves of your mould. The two halves are constructed over two male moulds, port and starboard.   The plug represents half the hull and deck of each side.

But why not stick with the standard 'hull and deck'? I hear you cry. Well, what follows are some of the reasons why you might consider building your boat using a split centre line mould (SCLM).


Design Considerations

From a design point of view there are several bonuses (all though it is fair to say that all bar one of these can be achieved using the standard 'hull and deck' set-up).

1. Weight - The weight of the join between the two halves is kept lower down in the boat. The join when using SCLM runs from for'd of the coachroof down the bow and along the hull. The majority of the join is below the waterline. With 'hull and deck' there is no alternative but to keep the hull/deck join at the shear and therefore above the waterline.
2.   Safety - Form an aesthetic point of view the designer is able to draw a 'rounded' shear. It looks smart and has an added safety implication.  With no sharp edge to 'dig' into the water the boat is more likely to self right, in the event of a capsize. The rounded shear can be achieved when building 'hull and deck' but it results in the destruction of the mould. (This is how the rounded shear on Kingfisher was created).

3. Accuracy - By constructing the hull and deck simultaneously a degree of accuracy is required, but at the same time achieved. To ensure ease of assembly the moulds need to be constructed as accurately as possible, this should always be the case but in doing so we found that this led to a pleasant surprise.  Having joined the halves we turned our attention to the bulkheads.  Once marked and cut out, we found the bulkheads/ringframes all fitted without alteration.  This proved that the hull had been built as per the CAD drawings provided by Owen Clarke, reassuring for the designer, the owner, and the builder.



Build Advantages

From a builders point of view it really is a win win situation.

1. Space - If your looking at self build then the chances are your going to want to utilise the space you have at your disposal, be it the garage, or the corner of a factory. SCLM involves building the boat on her side, which allows a build of hull and deck in the space taken up by a standard hull plug.  There is no need to build and store the deck, before building the hull.  You do need to build a plug for the coachroof, and cockpit, but on a Mini these are small enough to be made in your kitchen! (Although this may be the quickest way to the divorce court;-)  

2. Time - The hull and deck can be completed and joined in a couple of weeks by an experienced team.  Time = money and therefore if you intend to have the
shell completed by a professional you should save money, leaving you to fit out, make the coachroof and cockpit.  All of which require minimal space.
 
3. Fairing - Most fairing can be completed whilst the halves are on the plugs.  Once joined the centre line can be faired, and in my case, a sacrificial bow section created. When the shell is placed right side up the only area that requires a concerted effort is the gunwhale.  The join itself should present no problems providing a suitable rebate in the laminate was created during lay-up. Bearing in mind the deck has been created form CAD drawings it shouldn't require a great deal of work. We faired Rocket Science very quickly, including the rounded gunwhale, and I had never picked up a torture board in my life.

The Downside

1. Fit out - It could be said that is the potential downside of using a SCLM. When it comes to fitting out, the already cramped interior of the boat can create a few potential obstacles. However the adage 'prior planning prevents poor performance' is particularly relevant.  For example with the hull still upside down we fitted the bulkheads and ringframes.  This meant that not only did the interior stay clean but also there was more rigidity to the structure before we attempted to turn it the correct way up.  It wasn't difficult but a supple member of the build team made life easier.   The cockpit and coachroof are left until last, making access easier, but careful thought should still be given to the order of assembly.

Conclusions

I have had a good experience building with a split centre line mould.  There are, no doubt, those reading this article for whom it was an unmitigated disaster. I do not claim it to be revolutionary or new, merely an option. It has advantages in speed, accuracy, and therefore cost, and in my case it has raised awareness of my project.  She was the first hull to be constructed at Hick Marine using the SCLM. It is interesting note that the current Australian AMS Champion, Toe Cutter was, subsequently, design and built at Hick Marine using a split centre line mould.


Acknowledgements

This project would not have been possible without the support, advice and encouragement of the following:

The Owen Clarke Design Group (www.owenclarkedesigngroup.com)
Hick Marine Pty Ltd, Australia (www.hickmarine.com.au)

© 2002 Peter Scandling All Rights Reserved