Propellers

 

We have come a long way in propeller design and manufacture since the invention in the 1830’s. Depending on the size and type of vessel, the propeller is a part that might not receive much attention until the next haul out. For vessels such as trailable boats fitted with outboard motors the propellers get looked at more frequently and thus receive better care. No matter what type of vessel one may have and how easy it is or not, to inspect the propeller, evaluating the condition of the propeller is important. A propeller endures a variety of stresses in varying magnitude during operation that is difficult to comprehend especially when a propeller is held in hand and appears so stout. Another onslaught to the propeller is the environment it is subjected to. In salt water marine growth is tenacious and grows surprisingly fast. One would never assume that an organism can adhere, grow and stay connected to a fast spinning propeller, but they do and do it well. Most propellers are manufactured of metal. Synthetic propellers are rare and are usually reserved for small horsepower motors although there are propellers that are a combination of synthetic material and metal suitable for a sizable horsepower. Propellers made of metal suffer from electrolysis and cavitation erosion. Frequent inspection of a propeller can identify any of the degrading conditions and allow timely remedy in order to prevent a costly breakdown.

 

Propeller Function

 

A propellers function is basically a screw that when turned will propel the vessel in the opposite direction. All propellers are sized by overall diameter and pitch. Then there is the number of blades and the type of material the propeller is made from. Some propellers are cast as one piece, some are machined from one billet of material and others are a combination of components. The intended function is the same and that is to propel the vessel thorough the water. The larger the propeller, typically the slower it turns and this is supposed to be more efficient. The smaller propeller turns much faster and are technically less efficient. This efficiency is obvious in the handling characteristics, the speed and the fuel consumption of the boat and the effectiveness of a propeller is greatly reduced when the blades are even slightly damaged from a soft grounding, or an unbalanced condition or from fouling by line or debris. Outboard motor propellers usually have a rubber hub that is pressed into the propeller to lessen vibration and this hub has a limited service life. Even with frequent inspection it is difficult to predict when such a hub will fail and, in this case, having a spare propeller is an inexpensive insurance. An alternative is to fit the vessel with propellers that are manufactured with an interchangeable rubber hub such as the RUBEX® from SOALS® propellers. Solas® also manufactures replacement propellers for original manufactures propellers such as for Volvo®, Mercrusier®, Honda®, or OMC®.

 

Growth on Propellers

 

Even the slightest marine growth on the blades of a propeller, be it a Volvo® propeller, Mercrusier® propeller, Honda® propeller or an OMC® propeller they will all suffer the same degradation in performance and increase in fuel consumption. There are many attempts to mitigate this problem and it appears that the best thing to stick to a propeller is still marine growth, until now. There is a product PropSpeed® when applied on a propeller performs exceptionally well in mitigating marine growth.

 

Metal Loss on Propellers

 

Metal propellers suffer from electrolysis in varying degrees either from their metal formulation or from cavitation or both. Attaching significant number of sacrificial anodes manufactured by Canada Metal® on the shaft or propeller can reducing the effects of electrolysis. Cavitation is the result of an incorrect propeller for the application and changing the prop to a different propeller might be a simple remedy.