The 18m proa was antiffouled this week and it provided an opportunity to make before and after speed comparisons.   Also a few weeks ago we did a bollard pull test with one of the electric thrusters.  The linked clip shows the pull test load cell and some of the before and after antifouling motoring data:

The thrusters achieve close to calculated pull at rated current.  Each unit was designed mechanically for 300kgf but that requires pushing the motor into 2X overload and the "500A Kelly Controller" cannot go over 200A unless motor is in locked rotor condition - not a common situation with a prop. The Kelly manual does state the continuous rating is 200A.  300kgf would also require 65V to the motor and that is not possible with the existing 50V battery.  THe motor is rated to 92V.

The initial speed tests with the electric thrusters were done with reasonably clean hull. During those tests the boat achieved 4.5kts with 4kW total power.  Since January the boat has been getting a little slower under power for the same controller speed settings.  It has been as low as 2.5kts with 4kW.  Before lifting this time the boat was roughly cleaned on the mooring then motored at 4kW to the dock.  Speed during that run was 3.8kts at 4kW.

After antifouling the boat was doing 5.4kts with 3.5kW.  It is getting much closer to predicted performance but still not quite there.  Before applying the antifoul (this time sprayed on rather than rolled) the surface was sanded with 80# paper.  It actually feels smoother than it looks in the photo at the end of the clip.

Drag on the harry hulls is dominated by viscous drag so surface smoothness and cleanliness are critical performance factors.  Much more significant than a heavier displacement sailing boat.  We did not have time today to do any sailing but it is something to look forward to as this is the smoothest/cleanest the hull has been.  

There is a table included in the clip that gives an idea of what is considered "smooth".  The sea lice that breed on the hull in St Kilda Marina are roughly equivalent to 24# paper!  They are not difficult to remove by brushing but stay attached at least to 15kts.

Note that relatively light fouling more than doubles the drag.  So spending wads of money getting a fair shape, perfect rig and rudders will be of little value if the surface finish is not smooth and kept clean.  It is a matter of having the priorities in the right order and a clean bum is way up near the top for a harryproa. Hulls that makes wave are more tolerant of fouling and planning hulls go fast enough to self clean unless they get really badly fouled.