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- Propellers-

 

Various aspects of the theory of ship construction are debated and tried under fire over time. There are multiple ways to attempt to maximize the on-the-water performance of a ship. Propellers are perfect example of a performance tweaking while balancing tradeoffs. Rudder size is limited by battle class, and ship top speed is limited by ship classification/length. The other aspects of ship mobility that can be manipulated are acceleration/deceleration and turning radius/speed. A large factor in both of these (though not the only) is propeller design and size. The goal is to try to maximize torque/acceleration especially when the ship itself is moving slowly or stopped while working within the defined speed limit otherwise. The balancing factor is trying to keep the propeller wash as controllable as possible by the rudder area so you don’t lose turning performance. Below are some important propeller characteristics:

 

·       Pitch. The aggressiveness of the angle of the propeller blade will determine the ratio of top speed and torque the propeller puts out. Higher pitch propellers give more top speed and less torque due to cavitation and slippage at slower ship speeds. Lower pitch propellers are the opposite, more torque and lower top speed as the blades are designed to “grab” water more effectively at slower ship speeds. Most higher performance propellers have variable pitch rather than consistent/fixed pitch which also leads to directionality.

 

·       Directional propellers vs flat blades: The nature of variable pitch propellers is such that they are designed to deliver their maximum intended effect (speed or acceleration) in one direction. Lesser pitch variability means that forward and reverse directions will produce similar thrust. It is common in our hobby to try to maximize reverse acceleration by mounting variable pitch propellers backwards. However a too highly variable propeller can lead to poor forward acceleration. Flat blades lead to consistent characteristics in either direction, letting the shape of the hull and other drag characteristics influence speed and acceleration differences in forward vs reverse.

 

·       Blade number and blade size: More blade surface area leads to a higher level of control of the water, leading to better acceleration at slower ship speeds. However too much blade surface area will over draw the motors and can cause the motors to have a hard time getting to a high RPM quickly, resulting in poor accelerations but also leading to current over draw and wearing out the motors and potentially the battery out too quickly.

 

·       Number of propellers: A lot of the generalizations in this article are related to the more advantageous setup (for acceleration) of two drive shafts (and often two other non-powered shafts). Several ships, specifically German ships, have a single drive shaft (and often two non powered shafts). The general theory is that acceleration is better with two propellers and turning is better with one. Often ships with single drive shafts compensate by using a larger size propeller.

 

·       Propeller size: Larger diameter propellers will move the ship better because of more blade surface area. Smaller propellers will cover the limited rudder surface area better, controlling thrust and leading to better turning. The balance becomes finding the ratio of acceleration and turning trade offs that works for the ship and for the play style of said ship.

 

All of these factors are in constant balance with one another. I’ve had fairly good luck with simple, flat blade soldered propellers especially in smaller ships, since lighter ships will require less attention to propeller characteristics to get descent acceleration. I run all but one of my cruisers, all of my convoy ships, and the Derffligner for the first 3 years of her existence with simple fixed pitch soldered propellers. However, to truly maximize performance in any ship but especially noticeable in larger ships, directional propellers do make a difference. Here are some generalizations and specific propellers I’ve had success with.

 

 

Propeller Generalizations:

·       Cruisers: most dual shaft cruisers do great with 1.25 inch propellers, I would recommend 3 blade 25 degrees. Acceleration is already a relative advantage due to small ship weight and sleek hull design

 

·       Mid size and smaller battlecruisers and smaller battle ships: dual shaft ships roughly 22lbs and lower will be good with 1.5 inch props, four blade 25 degrees

 

·       Larger battleships and battlecruisers: 22lbs and higher should have 1.75 inch props, four blade 25 degrees

 

·       Very Large battleships: dual shaft ships larger than 35-38 lbs should probably have 2 inch propellers

 

 

 

Propeller specifics from Tyler’s Fleet:

·       RM Duca D’Aosta: class 2.5 unit light cruiser, roughly 11 lbs – dual 3 blade Octura cast props sanded down to 1.25 diameter

 

·       All heavy cruisers: USS Minneapolis, RM Zara, FN Tourville: class 3, roughly 11 lbs – dual 3 blade 25 degree soldered props

 

·       Derfflinger 1: class 4, roughly 22 lbs – dual 4 blade kort nozzle 1.5 inch props: Prop Shop KNP/1515/4

 

·       Derffligner 2: class 4, roughly 22 lbs – dual 4 blade soldered 1.5 inch props

 

·       HSM Tiger: class 4, - dual 4 blade kort nozzle 1.7 inch props: Prop Shop KNP/1720/4

 

·       IJN Kongo: class 4, roughly 25lbs – dual 4 blade Standard Scale 1.7 inch props: Prop Shop STD/1719/4

 

·       HMS Barham: class 5 – dual 4 blade Standard Scale 2 inch props sanded down to 1.75 inches: Prop Shop STD/2022/4

 

·       IJN Nagato: class 5 – dual 4 blade Standard Scale 2 inch props sanded down to 1.75 inches: Prop Shop STD/2022/4

 

 

Bear in mind that these are rough starting places. To really maximize performance, you have to play with the variables and find what works for your ship. The shape of the bottom of the hull, the shape of the rudder(s), the type of motor (both size and brushed vs brushless), and the play style of various ships all also need to be considered when finding the right propellers and drive train in general. Truly maximizing performance can really only be accomplished by trying different setups on the water.

 

Links/Pictures

Prop Shop out of United Kingdom sells the best propellers I’ve been able to find: https://www.prop-shop.co.uk/

Battlers Connection sells propellers of various sizes, mostly soldered and consistent pitch: http://battlersconnection.com/

 

Soldered Propeller Example:               Kort Nozzle Example:                    Standard Scale Example:

 

                        Kort Nozzle Propellers                               Standard Scale

 

 

 

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