Introduction

The Transpac 52 rule is based on a simple box rule limiting the primary speed influencing factors such as Overall Length and Displacement. The intention of the class is to provide a class of fast, stable mono-hull race yachts which will race against each other on even terms. The rule is relatively type forming but there are several areas in which we at Tony Castro ltd believe we can develop to produce a very quick design. The major design factor is to determine what the primary function of the yacht is likely to be i.e. whether it is primarily for inshore or offshore racing or a combination of both.

Hull design

Due to the box rule format of the TP52 class rule, a very fair hull has been designed with no “design humps or hollows� allowed. The overall length of the hull is set by the rule at 52 feet [15.75m]. Through the combination of a plumb bow and careful stern overhang design, the optimal waterline length has been investigated to maximize both upwind and downwind performance throughout the wind range. Beam at deck has been pushed out to near the maximum allowed by the rule in order to maximize the righting moment provided by the crew. Waterline beam is a major area where we at Castro can further optimize the design for certain conditions not to mention Immersed volume distribution and Prismatic Coefficient. Minimum waterline beam has the effect of reducing wetted surface and corresponding frictional resistance resulting in a design primarily dominant in light downwind conditions [Possibly for a Mediterranean based client]. However we feel a larger waterline beam would give better performance characteristics throughout the wind range and in particular when sailing upwind as we all know the importance of reaching the first mark first when sailing inshore. All these features are the subject of a VPP optimization with the help of Computational Fluid Analysis.

Rig Design

The rig produces some interesting design considerations. The Tony Castro design office plan to work closely with a leading performance manufacturer on this. A combination of fractional rig and masthead A-sail’s and Code 0’s poses the question whether the top section needs external support [ie. A cathedral rig]. It is our general preference to choose a simple 2 spreader aft swept carbon rig. Thus allowing less drag and a lower centre of gravity. By terminating the cap shrouds above the hounds greater support can be produced whilst still maintaining control of the headstay. Careful FEA design into the carbon laminate plan is needed in this section to ensure the rig will be able to take the loads presented on it. The backstay cannot be removable and so limits the size of the main sail roach. Thus the mast height and mast head crane are pushed out to the maximum allowed. The down wind sail plan is limited to asymmetrical spinnakers only and the masthead code 0’s are limited to off shore racing only. Advanced CFD analysis is useful for comparing the rig options and providing the correct Sail Coefficients for the VPP analysis.

Appendage design

There are few limiting factors in the rule when it comes to appendage design. Materials are limited and trim tabs are outlawed. A single rudder is allowed with a single fin keel supporting a bulb. However, appendage design has always been a specialty of the Tony Castro office and now we have very sophisticated CFD tools at our disposal. Design of specific Low Reynolds’s number Laminar flow sections has been practiced by the office for years but better and faster computers allow more complex calculations and better optimization routines.

This combination of experience and minimal design constraints will allow the optimal design of a high lift-low drag section for both foils to produce blistering performance both upwind and downwind. The bulb width is restricted to a maximum of 0.05LOA [2.3 ft in this case]. The choice of a chinned bulb for example has the effect of both lowering the centre of gravity and reducing speed sapping tip vorticity and can be “sailed� and therefore optimized with the CFD tools for a specific speed range.

Structural Design

This work has been usually the domain of Specialized sub-contractors since about 1990. The TP 52 will likely be built in a Nomex core, Carbon Fibre and epoxy resins to ABS minimum Scantlings. Curiously we were the first designers to build an all-Nomex race boat as well as an All-Carbon one in Britain, for the 1987 and 1989 winning Admiral’s Cup teams.

A detailed Engineering FE Analyses will be made to achieve the lowest possible VCG and yet maintain adequate longitudinal stiffness. Every kilo on the bulb will make the boat faster so the work of saving weight elsewhere is extremely important.

Interior Design

The Interior Layout is dictated by the IMS minimum racing division Accommodation regulations with 6 berths, navigation station, galley facilities and enclosed toilet compartment.

Deck Layout

The deck has been laid out in order to make it as functional as possible for the crew. The deck camber and sheer have been designed to keep as low as possible. A minimal blister coach roof allows for a longer cockpit which again saves weight and creates space for the crew.

The primary winches are used for sheet loads and are driven by a single pedestal in the centre of the cockpit. The single mainsheet winch is combined with a “half-German" mainsheet system led along the starboard side to allow for sheet “bouncing" at starts and mark roundings. The backstay winches can be used for the after guys when sailing downwind as quick trimming will be required when gibing without the forestay. The transom is kept vertical to minimize the backstay-mainsail overlap. The side decks are continued all the way aft to allow for sail stacking when sailing offshore