Octave is our current M Class boat.
It is a ‘clean sheet’ design incorporating a number of new ideas.

Overall beam is moderately narrow at 148mm.
The underwater sections are fundamentally semicircular.

The canoe body is characterised by a high prismatic coefficient achieved through pronounced rocker at the ends.

The result of the high prismatic is a reduced cross-sectional area, a gentler slope of the wave resistance curve and enhanced pitch-damping. Moderate flare amidships maintains trim and dynamic balance throughout the heel angle range. Aft hull chines just above the static waterline are being trialled to aid clean separation of the water flow when appropriate.

The included angle between hull and deck and hence the gunwales becomes sharper aft of amidships, to aid clean separation of water flow when heeled.

Particular attention has been paid to the aerodynamic design of the deck. A piercing bow smoothly transitions to a strongly chambered deck designed to interact with the all swing-rig sailplans.

The deck is clean and uncluttered in order to minimise aerodynamic drag and shed water cleanly when pressed downwind. The aim is to reduce hydrodynamic drag when the bow is immersed, avoiding a reduction in boat speed that would in turn increase apparent wind and hence trimming force.

The prototype was completed in October 2009 and is being readied by Ray Joyce who will campaign it in Tasmania. CNC milled tooling is being prepared to allow a construction method incorporating a number of novel structural solutions in the production boat.

As documented by the construction pictures on this page, the prototype was laminated as a separate hull and deck joined by a moulded strip along each side.

These pictures are representative of the key stages of construction of the prototype.

As illustrated, the hull and deck shell were moulded separately.

The mast tubes and fin were glued into the hull then secured with secondary bonding (strips of carbon cloth laminated over the joint). Separately moulded internal joining strips were glued to the inside of the hull, extending 6mm above the sheer line.

A plate was bonded to the top of the mast tubes and fin where they were to mate with the deck. This plate provides sufficient gluing area to transfer the keel and rig loads to the deck.

Finally the deck was glued on and the finishing work could begin.

This is a rather labour intensive construction method that requires very precise cutting and fitting. It is acceptable for a prototype but needs to be improved upon for production boats.

Our investigation into construction methods has resulted in a few options for quick, light, strong and ‘seamless’ construction.

The hull of a modern Marblehead consists only of a stressed shell with panel stiffness dictated by hydrodynamic loads rather than mechanical ones. Therefore the only areas left where significant weight reductions can occur are the fin and mast interfaces. Stay tuned for the results of our experiments in these areas...

In all other respects Octave is an evolution of our long line of M boats. Beam has remained similar since Nexus. Waterline beam is determined parametrically as the only dimension that will allow a semicircular midsection for a given combination of displacement and prismatic coefficient. For any given displacement and prismatic there will be only one semicircle that gives the correct midsection area.

In the case of Octave the shape above the water is a bit fuller and more flared than Nexus, continuing the direction explored by the Ajax family. The centre of gravity has continued to move forward and the prismatic has increased. Some optimisation work has gone into the hull to fin junction resulting in a local deformation in the hull and a revised LERE.

Onboard systems are much simpler than on Ajax. This is mainly due to the return to an all swing-rig sail wardrobe. The winch system will be a captive loop housed entirely below deck, lowering the winch centre of gravity and maintaining the deck free of clutter.

We are heartened by the resurgence of the M class worldwide after the recent slump and hope to remain at the forefront of development with Octave. Please enjoy the pictures and drop us an email with any comments or queries...

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