Mini Transat

Hull

The design and build of the hull mould was carried out by Ian Munslow. This mould has 'thrown' Ishtar and Gelpeixe, and is being used once more. A hire fee has been paid to Ian via OCDG (Owen Clarke Design Group).

Hull Preparation

The hull mould was moved by the Milford Docks Company's forklift truck, assisted by student muscle into the entrance of the MITEC centre. The mould has been stored under the Ice Factory on the east side of Milford Docks since the beginning of the summer.

The deck mould was hoisted up, away from the hull mould, so that the interior of the hull mould could be cleaned. Repairs to the surface of the mould were made by applying 'blu-tac' into the indentations and then trimming off the excess with Stanley blades.

The blanking plate was installed in the bow of the mould and rebates were inserted for the deck joint and chain plates and a plywood black was inserted for the dagger board rebate.

Internal Structure

The design of the internal structure was simple to keep everything to a minimum. Where one part of the structure could be used to do two things it was engineered to do so. The main bulkhead was cracked in order to take the mast loads and the shroud load, which were swept back at 8 degrees.

Cockpit

The rule set down by the Mini Transat Organisation dictated a few of the specifications of the cockpit arrangement. The first of these was the minimum depth of the cockpit floor - which had to be no less than 150mm above design water line.

Another larger consideration in the design of the cockpit was the escape hatch that is required in the transom. The standard solution for the hatch is to put lump in the cockpit that the hatch can be fitted in. We decided to take this one step further by extending the lump into a tunnel that runs the length of the cockpit.

Deck

The deck issue was decided on very early. We decided to keep the deck mould used last year. This meant that we didn't have to spend time on the design and build of a new mould. Another thing we were all keen to do was have a radius on the deck edge. This would give several benefits to the performance of the boat and provide a very aesthetic look. We decided, eventually, after much debate that our time would be spent elsewhere.

Deck Preparation

We then set about making the old deck mould useable. Gelpeixe's mould was partially dismantled to reveal frames and stringers beneath. Repairs were made to the damaged frames, some of which were due to the age of the mould but also due to impromptu bashing on the part of those taking part in the dismantling. Extra longitudinal stringers were added to ensure the mould retained its shape over the coming months. The new deck planks were made from MDF. This made fairing of surface an uncomfortable task. Parcel tape was applied to the surface of the deck mould to form a surface for vacuum moulding. Tape was re-applied to the starboard side of the deck mould as the original tape was peeling off. This started peeling immediately, so we tried a different brand of tape which solved the problem.

Dagger Board

The data for the section of the dagger board has been sourced from NACA (National Advisory Committee for Aeronautics) research. I have chosen a 64-130 section for the board. The 64 means that the widest part of the board will be 40% from the leading edge and the 130 implies that the section is 30% wider than the original section. By increasing the section the board will be stiffer.

Rudder

There are no specific rules relating to the rudders. They must, however, comply with the overall dimension of the vessel and may not exceed the maximum beam of 3 metres (rule J2-b) or exceed the maximum draft of 2 metres (rule J2-c).

Although the rudder provides some lateral side force in conjunction with the dagger board, its main function is to provide enough turning moment to manoeuvre the yacht under all conditions. The rudder section has to be designed for the maximum lift required.

A thick foil section is suitable for rudders because it maintains laminar flow at greater angles of attack, whereas a thin section will stall abruptly at lower angles of attack, with a large loss of lift as a consequence.

The current design utilises foil section NACA 64 A-0012. The 64 series foils have the minimum pressure 40% along the chord from the leading edge, the final two digits of the series (12) denotes the thickness ratio in percent, i.e. the maximum thickness/chord length = 12%. Sections with a thickness ratio in the range 12-15% generate the greatest lift. Surface piercing rudders generate spray at the leading edge, the amount of spray, and its associated drag, is proportional to the thickness of the leading edge squared. Therefore a section thickness of 12% should generate the required lift without excessive spray.

The large lift coefficient will also allow a small area, and therefore a small wetted area, to produce the required lift.

Aspect Ratio

The maximum aspect ratio of the wetted blade is 1000:263, approximately 4:1. A large aspect ratio is beneficial as it reduces the tendency for water to pass over the foil tip in an attempt to get from the high pressure face to the low. The aspect ratio therefore seems a good choice.

Coachroof

The design of the coachroof was confined by a number of restrictions. The rule states that there must be a minimum volume in the coachroof of at least half a metre cubed.

Once we had drawn up a few ideas for the coachroof. We discussed the design as a group and decided on what we did and didn't like. Once we knew what we wanted as a team, the appropriate modifications were made, then agreed.

Keel

The mini keels designs are some of the most complicated and radical in the industry. They are just under two metres long fin and bulb arrangements and most can be moved in some way. As they are relatively small and inexpensive in terms of long distance performance sailing yachts, and they can normally be moved by hand (with some gearing), they are perfect for developing new ideas.

We had the design of the mini keel that was used on the previous boat. The reports on it were that it was strong enough (as it had suffered and survived impact damage), but the build was difficult resulting in distortions in the finished product. It was manufactured out of stainless steel plate welded together.

Recent Projects

Printable Documents

Short Courses PDF (248 Kb)

MITEC Brochure PDF (4.5 Mb) or View Online

Terms & Conditions PDF (52 Kb)