Summary of Working Paper No. 78-1997

I.1.9: Experimental Study to Separate into Components the Interaction Force between Propeller and Ice Piece

By Kenkichi Tamura, Ship Research Institute, Tokyo Japan; and Hajime Yamaguchi, Tokyo University, Tokyo, Japan

When an ice piece collides with a propeller, it leads to an impact load on the propeller blade, causing damage to the propeller blade and/or engine trouble. So far, the impact load has been treated from the aspect of ice breakage only. It is presumed, however, that other factors, such as hydrodynamic force and inertia force of the ice piece, also affect this phenomenon. The importance of these forces has recently been investigated and reported. The shallow water along parts of the Northern Sea Route requires a shallow draft ship, resulting in more frequent interaction between the propeller and ice pieces. Also, the limited propeller diameter due to the shallow draft leads to greater load on the propeller. A nozzle propeller has some advantages over the conventional open propeller in such conditions.

Taking the above issues into consideration, our study deals with ice interaction with a nozzle propeller. Ice impact load is divided into 4 components: force due to ice failure, force due to momentum change of an ice mass, force due to the added mass of ice, and hydrodynamic force due to proximity and flow distortion between the propeller blade and ice. This paper describes the experiments on the division of the force into these four components. An ice collision test in water contains all of the force components. An ice blockage test in water, where an ice block is placed in front of the propeller without touching the propeller blade, yields the hydrodynamic force. An ice collision test in air yields the ice failure force and the inertia force due to the ice mass only. Finally, an ice collision test with ice of various strengths reveals the effects of ice strength.

A nozzle propeller model of a 267mm-diameter propeller was used in these experiments. The thrust, torque and spindle torque of one blade were measured and analyzed for all four experiments described above. The following results were obtained:

1. The ice failure force component seems to be proportional to the ice strength.

2. For the thrust, the inertia force is by far the major component and the ice failure force is minor. The hydrodynamic force increases the thrust, while the other forces decrease it.

3. For the torque, the ice failure force is strongly dependent on the ice strength and is the largest of all the force components, followed by the hydrodynamic force and then the inertia force which is about half the hydrodynamic force.

4. For the spindle torque, the inertia force and the ice failure force are the largest components and are comparable to each other. Hydrodynamic force is approximately half the inertia force.

As mentioned above, inertia and hydrodynamic forces are comparable to or larger than the ice failure force. Rational scaling laws must be considered and applied to the respective force components when ice forces on a full-scale propeller are extrapolated from the results of the model experiments.