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Propeller |
A standard 3-blade fixed propeller such as supplied by Pearson with a stock 424 is not an expensive piece of equipment, but a folding or feathering propeller is dear. I had already replaced my stock propeller with a 2-blade folding prop several years ago. This made a tremendous improvement in the boat's sailing performance. I'd be reluctant to regress to a fixed propeller again. Unfortunately, my budget was limited, so replacing the propeller yet again was not in my re-power budget. I expected to reuse the propeller, but I found that I really didn't understand the relationship between propeller size, gear reduction, and engine power. Since I chose a larger engine, the old propeller just wasn't large enough to properly load the engine. The propeller just couldn't transfer the engine power to the water because the blades were too small. I changed the V-drive gear ration to adjust for much of the difference in engine speeds (2400 vs 3800), but there wasn't enough bite in the old propeller to transfer that power to the water. There are a number of new folding propellers on the market in the past few years that offer significant performance improvements over older folding propellers such as my old 2-blade Martec. These include both 3-blade and 4-blade propellers. I checked with a couple of manufacturers and found that I could purchase a new 3-blade propeller for about the same price I paid for my old 2-blade unit 10 years ago. The new unit not only offers the smooth performance of a 3-blade propeller, but also has the blades geared together. This eliminates the need to rotate the propeller into a specific position to fold efficiently. While it can be argued that folding propellers suffer in reverse, I've never had difficult stopping or backing. It has been many years since I used my stock fixed blade propeller so I can't offer a direct comparison. My research indicates that performance of a new 3-blade folding propeller is as good or better than a fixed propeller. Performance in reverse is close to a fixed propeller, bearing in mind that you must apply some shaft speed to open the blades. There are many trade-offs when selecting a propeller. The link below will provide a propeller size estimate based on boat size, displacement, engine power and RPM. I eventually selected a Slipstream 3-blade folding propeller. I liked the stainless steel construction and they had a very competitive price. The factory calculated 18.5x12 as the correct size. This computation proved correct, but slightly small. If I had it to do again, I'd probably select a slightly higher pitch, probably 13 since the full throttle propeller speed is at the high end of the recommended engine spec. |