US Sailing Nine Model Series

INTRODUCTION

By Jim Teeters, Director of Research, US Sailing

In 1996, the NRC Institute for Marine Dynamics and US Sailing began a collaborative tank test program. A fleet of nine models was designed with systematic variations in the most fundamental parameters: displacement and beam for fixed length. The models were tested both appended and bare-hull, in calm water and head seas. Analysis of residuary resistance, both upright and heeled, was used to improve the Velocity Prediction Programs (VPPs) employed by both the International Measurement System (IMS) and AMERICAP rules.

BACKGROUND

The IMS rule VPP used a hydrodynamic model based on several tank test series. Specifially, the VPP represented residuary resistance with a regression fit of the tank data. A description of this regression is in Claughton, 1999, available through the SYRF Library. The tank test database consists of several parametric series of models tested at Delft University and at the University of Southhampton. These tests are described in the following literature: Gerritsma 1981 and 1993, and Keuning 1996.

In the early 1990s, several changes were made to the IMS rule's resistance model, resulting in dramatic shifts in boat ratings. The primary source of these changes lay in the formulation for residuary resistance, which could occur either through changes to the regression formula or through the addition or subtraction of model tests in the tank test database. The US Sailing series was designed to more closely represent contemporary hull forms and to better inform the IMS rule to handicap contemporary yachts.

DESCRIPTION

An analysis of the International Technical Committee (ITC) test fleet, circa 1996, was performed to determine the characteristics of the model fleet. The parameters for the nine model fleet (Table 1) are defined as canoe length volume ratio (LVR), length beam ratio (LBR), and beam draft ratio (BDR). A number of design offices, all of whom were active participants in the IMS rule, contributed to the development of the lines of the parent hull (Model 5) and series hulls.

Table 1 - Model Fleet Hull Parameters

Model 5 - Parent Design

The models were tested in calm water with and without appendanges, upright and heeled. A number of tests were run at low speeds to enable Prohaska analysis. The speed range then extends up to a Froude number of 0.6, the highest speed used by the IMS in its handicaps. The models were tested at heel angles of 0, 15, and 25 degrees. At each heel angle, there were leeway sweeps at each of three speeds, corresponding to Froude numbers of 0.25, 0.325, and 0.40. The leeway sweeps were from 0 to 6 degrees in one degree increments. Rudder angles were always set equal to the leeway angle.

ACKNOWLEDGEMENTS

This project was supported in part by: