Comparing Flexofold Folding Propellers to Feathering and Fixed Propellers

TEST RESULTS

Many propeller tests have been conducted over the past 20 years both by manufacturers and independent organizations. While the manufacturer-sponsored tests may have validity, the published results often emphasize those attributes in which that manufacturer excels. The independent tests, on the other hand, may not have this bias, but may have test parameters that do not reflect reality. The two tests having both independence and well-designed test methodology are the one conducted in the U.S. by "Cruising World Magazine" in 1995, printed in their June 1996 issue, and the test conducted in Germany by the Technische Universitat Berlin in 1997 for "Die Yacht Magazine" and printed in their May, 1997 issue. See notes below.

CRUISING WORLD TESTS, 1995

Key:
A = 3-blade, self-pitching, feathering prop
E = 2-blade, non-geared, folding prop
F = Flexofold 2-blade, geared, folding prop
M = 2-blade, no-twist, feathering prop
W = 2-blade fixed prop

TEST METHODOLOGY:

These tests of powering performance and drag were conducted on a Freedom 35 using a Yanmar 3GM30 engine. Participants were asked to supply their best propeller for that application. The results for the major brands are shown below. Other propellers were also tested but are not included in the results below. In our opinion, those props omitted do not change the conclusions.

NOTE: these tests were completed using "old style" Flexofold Propellers. The current Standard Propellers have larger blade areas than the "old style" Flexofolds, resulting in significantly better performance, particularly in reverse.

TECHNISCHE UNIVERSITAT BERLIN TESTS, 1997

Key:
A = Self-pitching, feathering prop
F = Flexofold geared, folding prop
G = Second geared, folding prop
M = No-twist, feathering prop
P = Large-blade fixed prop
V = Third geared, folding prop

*Note to efficiency graph: A achieved this efficiency at approximately 10 knots. Efficiency increased to 65% at significantly higher speeds. Efficiency at lower speeds was consistently below F and P.

**Note to drag graph: Drag of A increased to 670 N (150 lbs) if allowed to rotate. Drag of P increased to 420 N (94.5 lbs) if locked.

TEST METHODOLOGY:

This test was conducted at the Technische Universitat Berlin in their test tank. The primary methodology was to determine the efficiency of each 3-blade propeller submitted at various "rates of advance" or speed. Efficiency is defined as the percentage of horsepower converted into thrust. Also tested was propeller drag, with the props mounted at a zero shaft angle, as would be the case with a sail drive.

NOTE: the test of the Flexofold Propeller was conducted after the original test had been completed, as the Flexofold was not ready for sale at the time of the original test. However, given that the test was under tightly controlled conditions, in an indoor tank, we are confident the results would have been the same had all props been tested at the same time.