Before someone comes and suggests a Laser II... why would you want to bury the engine so low?
I must say I haven't ever propped a Marshan but assuming it's rather similar to Phantom and Ring I would go with a slightly bow lifting prop capable of running also close or at the surface.
Personally I would invest a few hundred quid on a manual lift to be able to adjust engine height based on conditions. As an overall sporty and speedy pleasure prop I would first test Trophy Plus and Tempest from the Mercury line up, most likely in the 25-27" pitch range, this is with the prop rather close to the surface. From the after market props I would consider Turbo TXP, both 3 and 4 blade, Solas Scopion and Hydromotive 3 and 4 blade props. Some have also had succes with 4-blade Ballistic as well.
These are just the ones that have worked on the Phantoms and Rings I know. Personally I have always ended up with a 4-blade Hydromotive. Not necessarily the ultimately fastest prop but suits very well my driving skills and preferences. The prop question is one of the eternal questions and is a matter of choise. Others might have differing opinions