Shallow River Pushboat Preliminary Design

The preliminary design of a river pushboat is presented. The design method consists of four parts: (1) Estimation of pushboat “push” EP; (2) estimation of barge tow resistance $R_T;$ (3) selection of pushboat horsepower based on equilibrium speed from equating 1 and 2; and (4) for the horsepower obtained from 3, determine the pushboat dimensions and tunnel stern arrangement. Using published data, the writer introduces the following expression for pushboat EP: $\mathrm{EP}=A\mathrm{HP}[1.0+C(h/T-1.78\left)\right][1.0-E\cdot V^2]$ lb. This expression is shown to be in good agreement over the range of $1\text{,}800\leqq \mathrm{HP}\leqq 5\text{,}600;1.78\leqq h/T\leqq 5.0;0\leqq V\leqq 12\mathrm{mph}\text{.}$ For the deep water resistance $(h/T=5.0)\text{,}$ a modified Howe's formula is shown to give a good estimate for the barge tow resistance, $R_T\text{.}$ This formula is shown to be unsatisfactory for estimating the shallow water $(h/T=1.78)$ resistance $R_T\text{.}$ Therefore, the method of P. A. Apukhtin is extended using published barge tow resistance data. The shallow water resistance predicted with Apukhtin's extended graph is shown to be in good agreement with available data. The estimates of the tow speed and propulsive efficiency are then completed. It is shown that for the two pushboats considered, 1,800 and 2,400 horsepower, the shallow water conditions reduce the propulsive efficiency by 16–23%. The paper closes with a review of guidelines for estimating the pushboat length, propeller diameter, and tunnel stern arrangement. Criteria for insuring adequate tunnel inflow and outflow are presented in the form of tunnel inflow angle, ${\theta }_1\text{,}$ and tunnel outflow angle, ${\theta }_2\text{.}$