New Moulds produce the most exciting Mackay 470 ever!
In 2012 the International 470 class decided to introduce measurement at every 500mm station on the hull. Previously the class only measured the boats every 1 meter.
Our initial reaction was of little concern because our boats did in fact already measure at all these new stations (except for 3mm on one gunwale measurement).
However, we then thought OK, this is an opportunity to build the perfect 470 moulds so we decided to re-evaluate our current boats and to build the ultimate 470!
We did not want to change the basic characteristics of the MacKay shape that has been dominating 470 sailing for many years now. But we knew there was room for improvement. Added to that were the advances in technology at our disposal here in Auckland.
The first step was to scan our existing 470 hull. We were lucky to have the services of Form Scan at our disposal. In fact they are the building next to us here in Silverdale. They have the most accurate precision scanning equipment available in the world today. Furthermore we already had considerable experience using the equipment for the mould development of both the 49er and the Mackay 420. We had complete faith in the results. The scan is accurate to 1/100th of a millimetre. (much more accurate than we actually need).
The scan data was loaded into an advanced Hull Design program which produces a surface that we can then evaluate and modify as needed. The key to the success of any such software is the guy who is driving it. We were lucky to again receive the services of Kevin Trotter (naval architect and successful dinghy designer) who had modeled the 49er and 420 for us.
The surface is set up in the program with all the electronic 470 measurement stations also loaded. We were then able to superimpose the existing hull into the measurement model and see where we could achieve better results.
Without changing the characteristics of the shape, we were able to move the hull closer to the tolerances in some key areas and generally refine our current boat.
- For example the waterline beam could be reduced in some areas.
- We could make the shape perfectly fair using the software.
- We could further optimize the planning surfaces of the boat.
- And finally we can easily achieve perfect symmetry from one side to the other.
On paper (or rather on screen) the new model was a significant advancement.
New Mould Technology
Next came the question of how to build moulds to accurately achieve the results we had created with the software?
This is where the spinoffs from the Americas cup can be helpful!
Oracle USA have set up an advanced boat building facility in a town called Warkworth which is only 30 minutes north of our factory. One of their investments is a CNC machine that can cut out a boat up to 40ft long.
We built GRP hull and deck master plugs which they could Machine down to the finished shape with extraordinary accuracy. We simply gave them the computer model we had developed and they cut our hull and deck down to that exact shape.
They start by machining an undersize plug, and then apply an epoxy tooling paste. This is then checked carefully for any voids before being machined to the final shape.
Next came the building of the moulds. We brought the master plugs back to our factory and painted them, polished them, waxed them and then began the process of building a GRP mould over the top of them.
The characteristics of GRP can cause a major problem for a boat builder wishing to build high performance dinghies to tight tolerances. GRP has a certain shrinkage factor. What you start with is not what you end with. There are 3 generations of components between the computer and the finished boat. First is the Plug which is CNC cut. Second is the mould which is laminated in GRP. Third is the production boat which is also laminated in GRP.
So our computer model had to be bigger than what the finished boat would need to be. Our experience with shrinkage in our previous mould building exercises told us exactly how much to allow for.
In the last week of February 2013 International 470 class measurer Jurgen Cluytmans travelled from Belgium to NZ to measure our prototype boat. We are absolutely thrilled by the exactness that we have achieved at the end of this long process. The hull measures with just 1mm to spare at all the critical points. It is really beautiful to look over the hull and see the perfect fairness. The deck to hull glue joint is a perfectly even 1mm all the way around the join (evidence of the accuracy of the process).
Apart from the hull shape there are considerable improvements to the internal measurements of the boat. The symmetry that has been obtained means that everything will line up easily. Shrouds, mast partner, centrecase, jib track leads and mast step all line up perfectly.
The MacKay 470 has always been known for its stiffness and longevity. During this process we discovered some areas where we could make the boat stiffer. The accuracy of the above mentioned deck to hull glue joint allows a stronger joint. The inside face of the side tanks meet the hull at a position further inboard then the existing boat. This gives extra stiffness to the flat sections of the bottom of the boat.
We can’t wait to see the first of our new 2013 470s in action in Europe this year. They can only be faster!