In real racing boat I dont see rudder and why we are using rudder in our rc racing boat?
what if using thrust cone behind propeller? what is the plus and minus?

also why all gas boat rudder position always on right side of propeller? why not put it in the middle and behind propeller?

just wondering from new boaters here

Racers in US turn right - so in right turn rudder is deeper in water if mounted on right side, Center is ok for Sport boats who turn left and right - but makes it harder to change props as rudder is behind prop.

Real boats use a steerable drive most times and you can do that on a Sport boat too



Some do have a Rudder look at Mystics here which needs one due to the high speeds - the boat rides high and most of prop is NOT in water or when jumping - so it needs a long rudder to steer or may not steer at high speeds





Cheers

Randy

"also why all gas boat rudder position always on right side of propeller? why not put it in the middle and behind propeller?"

On high speed model boats the rudder must be kept out of the wash of the propeller. The water coming off the propeller is coming off faster than the speed of the boat & is rotating as it comes off. Placing the rudder directly in the prop wash would create stability problems. Also the shape of the rudder needs to be such that it equalizes the water pressure on each side regardless of the speed of the boat. Only a wedge shape, from leading to trailing edge, will stay in contact with the vortex formed by the water at high speeds. Rudders also have lifting, camber & caster type reactions that must be considered in the tune of any high speed boat.


Jim Allen

ok got it

when turning, rudder also create elevator effect which make bow push deeper into water
this is creating drag and inefficient., anything we can do to reduce drag and inefficiency?

A rudder's leading edge should be perpendicular to the water line at the maximum speed of the hull. The faster the hull travels the more sensitive this becomes. If the leading edge is angled backwards, it will raise the tail when the rudder is turned to the right or left & vice-versa. The effect can be very pronounced as the hull speed & the angle increase. The location of the leading edge in relation to the pivot point should also be considered. If the leading edge is to far in front of the rudder's pivot point, the rudder will be more sensitive & vice- versa. I build assemblies that keep the leading edge centered on the rudder blade's pivot point. Taper on the back edge of the rudder reduces these effects & reduces the rudder's total drag amount.

The total thickness of the wedge & the depth of the wedge will effect the amount of lift generated at any given speed. A thinner wedge on blades that have the same total area in the water will have less lift than the same thicker wedge blade & less drag.

Jim Allen