My Cervia was ready built. I have replaced the Electric motor with a large servo motor (Brushed) .Direct drive and being heavy helps with ballasting. lead acid gel cells are power source. Motor rated voltage24 v but run it on 12v . low rev high torque no load current 1 amp. Shaft diameter 0.5 in. Gives some idea of power out. Being servo motor (ex computer drive 30 years old) well balanced no vibration. Photo near shore shows power of motor.
[Score: 5/10] 72" Experimemtal Capable of 11mph and a runtime of 120mins Powered by Lead Acid (12v) 7Amp/h Batteries - Comments: Ebay Purchase. Originally a test tank model. Pumped water ballast no rudder or keel. Now fitted with lead fin ballast plus 2 7ah gel cells. and auxiliary motor. Sailing rig "A" class . 72in long 32 in beam .Hull strip wood deck fibre board. Sail winch and heavy duty rudder servo fitted. Design guess work !! Note picture of setting up rudder. 3 years work.
Long planks best . Put a king plank down on fore deck first . This helps to keep things the same on both sides. You can start from the toe rail (on both sides) inwards with long planks cutting an angle when it meets the king plank. You will end up with few odd gaps .Planks used on the edge and sand down level is a useful tip. Glue used medium thickness superglue. Have just planked a 5 foot yacht - learnt a lot! -John