Mod 70
Excerpt from interview by Lia Ditton with Vincent Prevost on SA frontpage:
MOD 70
LD: The Multi One Design or MOD 70 is the so-called new one design, which will replace the ORMA 60 fleet. You must be very excited to be the designers for this project. What new ideas about multihulls were you able to exercise with this class?
VLP: The new idea is a very pragmatic one: conceive a multihull, which is the synthesis of 20 years of evolution and development. A new generation of hull shapes, more seaworthy platforms, increased safety factors for structure reliability, all that staying in the same type of power as the last ORMA 60 projects.
LD: “A fast, modern design with foils” says your VPLP website. Am I correct in assuming that if these foils are designed to support the same percentage of displacement as an ORMA tri, a single foil could lift up to 70% of the boats weight in "normal" sailing?
VLP: Correct.
LD: At what point would you say a multihull becomes a ‘foiler’ rather than ‘with foils?’
VLP: Good question! No one has ever asked me that! Maybe a foiler would apply to ‘Geant’ whose main rudder was equipped with a T foil with adjustable angle of attack to get rid of hull buoyancy at the stern.
LD: Standardizing and establishing a one design of this size with such a varied design brief (offshore, inshore, full crew, short handed) must have presented a great deal of technical challenges. What sort of design boundaries has the MOD 70 project pushed for you?
VLP: The MOD 70 design brief is clearly for offshore races with 6 people on board. Inshore races will happen but it is not the primary goal of these boats.
LD: Wave piercing bows seem to be the zeitgeist. Can they be seen as one approach to addressing two different problems: reducing pitch for the purpose of stabilizing airflow over the sail plan and moving reserve buoyancy forward in big seas to reduce the chance of pitch poling? If we assumed a fixed LOA then wouldn't the later of these two benefit by adding reserve volume to the extremes thus allowing a more powerful hull and rig for the length?
VLP: These kinds of bows are possible when, as for the MOD 70, hull length is not limited by any box rule. The volume distribution forward of the front beam to counteract pitch poling is distributed more aft and the extra length allows us to have a finer angle of entry, reducing drag when passing through waves.
LD: Isn't the hull length of the MOD 70 limited by the box rule?
VLP: The idea was to design a boat safer than an ORMA, more in terms of structural reliability than in high speed behavior, notably the longitudinal stability, all of that by keeping the load numbers of an ORMA (same range of rig size, same deck gear, same appendages etc…) Increasing the reliability implies adding structure and weight at the same time. To keep the same load values, we have reduced the beam size to end at the same righting moment.
About longitudinal stability, we replaced the bowsprit with a main hull bow extension to reach the same overall length, which corresponds to adding 10 feet. This extra main hull length at the front, combined with the 5 feet increase in the length of the floats adds some important buoyancy forward to delay the time when the boat could capsize. So you are right! I made a shortcut. It is not a box rule, all boats being identical as monotypes.
