All about Screws (Propellers)
by Roger Harper

Page 4 of 4

Keeping this technical paper correct, I can't overlook counter rotating propellers.  Since we have went through propeller theory - we can say that one reason for this setup of propellers is to counter the effects of torque.  If you use two propellers that counter rotate, as each one will counter the torque of the opposite motor.  Ship builders have worked out the problems with the use of counter rotating propellers, and we can apply this to our models.  As a general rule, the two propellers should rotate "outwards", i.e. the left hand propeller is mounted on the port shaft while the right hand propeller is mounted on the starboard side, as viewed from the stern. 

This setup provides the best control and maneuverability, than using an "inward" rotation.  "Inward" rotation also causes cavitation.  The propellers are mounted to each side of the centerline of the hull.  So by mounting the propellers in this manner, the ship yards found that it helps to cancel out this problem (torque), plus if they loose an engine, the ship can still be easily controlled with one propeller turning. The Ship will still steer straight because since the propellers are mounted off set from the hull center, so its direction of turn effects, are reduced as well. 

Above are two propellers that were tried on my USS Crockett.  The tree-blade is from Dumas.  Most scale props from Dumas use a 3/16" shafts and brass Drive dogs and nuts to secure the prop to it's shaft.  This set up works, but takes away from the appearance of the model.

The four-blade prop is from Working Boat Models.  This selection of propeller greatly improved the overall appearance and performance of my model.  These brass props use a 1/8" shaft that threads into the boss of the propeller.  To attach it to the drive shaft, I used a thread locker and securely tighten it onto the shaft.

PROPELLER SOURCE That I Highly Recommend:

Harbor Models- Harbor Models is directly linked to the needs of the Radio Controlled scale boat/ship model hobby. They provide a wide selection of accessories from Tugboat Hulls, English Scale Propellers, to accessories. When you want that propeller the hobby shop just doesn't have, or doesn't fit the scale of your boat, give them a try. They have a large selection of English Prop Shop propellers on hand.