What is drag and can it be measured?

Drag is the resistance of the boat moving through the water.  Maintaining a clean and smooth hull surface minimizes skin friction which will slow hull speed.  A streamlined hub shape, a small hub diameter, surface finish quality, few protrusions from the hub or blades – flush fasteners and pins – helps to minimize drag.  Retracting the propeller out of the water, feathering the propeller blades or folding the propeller blades reduces drag.

The German Naval Architecture Test Center in Potsdam has tested and compared drag by measuring towing resistance @ 6kn for feathering and folding propellers.  The results were published in the German sailing magazine Segeln:   

• 2-blade free rotating – 198.7 Newton (N)
• 2-blade held fixed – 99.9 N
• 2-blade Volvo – 9.7 N
• 2-blade Variprop – 7.0 N
• 2-blade Flexifold – 3.1 N
• 2-blade Varifold – 3.1 N
• 2-blade Std Gori – 2.2 N
• 2-blade Maxprop – 2.0 N
• 3-blade Gori – 1.4 N
• Gori Race – 0 N (less than .001 N)