ASA and PSIA Instructor
Join Date: Apr 2000
Thanked 27 Times in 27 Posts
Rep Power: 16
You don''t really need to decide - the space between the shaft and the hull determines the needed number of blades. If a two blade of an adequate size fits with space to spare, you''re all set. If it doesn''t, you need a three blade. There''s not inherent advanatage to a three versus a two other than it''ll cost more.
Consult a prop supplier and follow their advice.