Sydney Yachts
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Jason Ker

Introduction
After a number of spins of the design loop, we have finally settled on the high-performance road for the new Sydney GTS37. Reducing the overall weight, maximising the waterline length and ballast ratio.  Not only does this fit well with our general design philosophy, but it also came out of our studies as being the most competitive route, something that bodes well for IRC.  The hull shape is also very competitive under ORC.

Hull shape
The origins of the shape can be traced back to research on AC90's (2007-2008), which is perhaps the first time the full weight of AC R&D resources was applied to an unconstrained hull form, leading to some considerable advances over a six month period.  Adapting and applying the lessons we learned then and since to the problem of a fair-form IRC racer, we ended up with a powerful but low drag hull form that picks up additional stability when it heels.  The transom width is moderate on the sailing waterline but on deck the max beam carries aft to allow the crew to sit further outboard and also give the helmsman very good visibility of telltales and waves.

Performance characteristics
A strong characteristic of our designs has been that they are all-rounders, able to pick up top results whatever the conditions. The Sydney GTS37 is no exception, with a generous sailplan ensuring light airs performance, good stability for reaching and upwind, while low drag is always helpful!

Most of her competitors are relatively heavier.  We found through our CFD analyses that with our powerful hull form we were able to reduce displacement while still remaining competitive in windward-leeward racing but gain a lot of performance downwind as the wind increased and in light airs.  Of course a great side benefit of reduced displacement is that the boat will be more responsive and fun to sail, being over 10% faster downwind in a breeze than a 40’ racer-cruiser from one of our competitors.

       

 Keel
We explored both fin only and fin+bulb options for this design and what became apparent was that the problem had to be considered holistically. A fin without bulb was looking good when we were looking at the heavier option, because we had stability to spare.  It also has an effect on rating, so if trying to avoid being in a certain class then it can also be an advantage, especially as a few square meters can come off the sail area which further lowers the rating.

In the end my favoured choice is to go fast, through maximizing stability with a bulb keel and matching it with sail area so that performance is retained in light airs.

Construction
Built from composite materials like all Sydney Yachts before, the GTS37 is engineered to ISO 12215 standard. We have paid particular attention however to engineering the laminates and details to increase strength and reduce weight wherever practicably possible.  Our old 11.3 design is testament that strong does not necessarily mean heavy and even our V5 AC design Shosholoza was able to ground on a rock at 11.5kts while only suffering superficial damage to the structure supporting the keel, while any surveyor will attest that a typical production cruiser will not survive such an accident.

The keel and mast-foot supporting structure is a 316 stainless steel grid, which ensures an extremely stiff and strong connection, free of maintenance.
The Rudder is a high aspect ratio blade with composite stock and quadrant, balanced for good helm feedback.