Marine Propellers- Manufacturing Tolerances

In the area of the propulsion many applications exist, that they go from crafts of fishing, of pleasure, of load and of speed between many other's.

It's for that reason that a classification of propeller's exists that determine the tolerances that it should have a propeller, according to the necessities of a craft.

The ISO 484/ 2-1981 Norm establishes the tolerances for the production of propeller's in all their geometric dimension. And divide them in the following classes

This norm contemplates all the dimensions of the propeller's like they are: Pitch, Diameter, Chord Length, Rake, Thickness and separation between blades

The norm requests that they are revised the dimensions of certain radios, this according to the type of propeller that is manufactured.

Class	Ratio
S & I	Close to the hub 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95
II	Close to the hub 0.5, 0.7, 0.9
III	Close to the hub 0.5, 0.7, 0.9

The tolerances in pitch vary between the several classes how it show the following chart.

PITCH	S	I	II	III
Local pitch	± 1.5%	± 2%	± 3%	---
Prom. pitch for ratio	± 1%	± 1.5%	± 2%	± 5%
Prom. pitch for blade	± 0.75%	± 1%	± 1.5%	± 4%
Prom. pitch for propeller	± 0.5%	± 0.75%	± 1%	± 3%

The tolerances for the angular deviation between two serial blades are given according to the following chart.

Class	Angular Tol.
S y I	± 1º
II y III	± 2º

TOLERANCES ON TICKNESS

Clase	S	I	II	III
Max. Tol. with a minimum of	+2% 2mm	+ 2.5% 2.5mm	+4% 4mm	+6% 6mm
Min. Tol. with a minimum of	-1% -1mm	-1.5% -1.5mm	-2% -2mm	-4% -4mm

TOLERANCES ON RAKE

Class	S	I	II	III
Tolerance	± 0.5%	± 1%	± 1.5%	± 3%

NOTE: Rake is expressed like a percentage of the diameter of the propeller.

TOLERANCES ON THE LENGTH OF THE BLADE SECTIONS

Class	S	I	II	III
Tolerance with a minimum of	± 1.5% 7mm	± 2% 10mm	± 3% 13mm	± 5% 15mm

TOLERANCES IN DIAMETER

Class	S	I	II	III
Tolerance	± 0.2%	± 0.3%	± 0.4%	±0.5%

All the previous tolerances define the geometry of a propeller in accordance with the ISO 484/ 2-1981 Norm.

The same as this norm for the geometry of the propeller exists, the norm is also used SAE-J755 like reference in order to scheme the hub of a propeller.

This contains specified the dimensions of the most common standard bores, the same as the dimensions of the keyway.

These tolerances are those that they are considered in the production of any RICE propeller.