|Can this prop be repaired?|
First of all, was your prop doing a good job before it was damaged? That means—
1. Was your prop keeping your motor in the proper rpm range? Failure to do this results in poor fuel economy, poor performance, and most expensive of all—potentially catastrophic damage to your motor.
2. Did your boat accelerate and corner well?
3. Did you experience noticeable vibration from the prop? Nothing good comes from vibration!
If there are issues with these items, it might be time to consult with a prop manufacturer or your propeller dealer and replace your prop. After all, a prop that is perfectly repaired, but is not properly suited for your application—is perfectly improper.
|Can this prop be repaired? Should it be?|
|The left image shows the results of collision with a heavy chain. As you can see the bronze blades are badly bent and damaged. The right hand image shows the finished result. (Pictures courtesy of French Marine Motors, UK.)|
|Cavitation has worked its magic on this stainless steel prop.|
Stainless Steel Screws
Stainless props need to be evaluated on similar criteria as bronze ones. First of all, is the remaining thickness okay? Any signs of cracks? How extensive is the damage? How much metal is missing?
Generally speaking, stainless props are made from two general types of metals. High carbon stainless is very strong and damage resistant. It welds well and can generally be repaired unless it is bent excessively. Given its high strength, it does not like being bent into a pretzel and straightened.
High-Strength or Low-Strength?
Another characteristic of high-strength stainless is the fact that it shows more corrosion than low-strength stainless. This is a natural consequence of the higher carbon steel content used in the alloy. Low-strength stainless uses more nickel in the alloying combination. This provides a significant increase in corrosion resistance, but also drops the tensile strength, typically by 50% compared to the high-strength material.
The material used in low-strength stainless props is more similar to that used for deck hardware. Since the strength of the material is more like bronze than a high strength stainless, it will “pretzel” pretty easily. The good news is that it can normally be straightened out again.
In either case, the issue will be to examine for enough blade thickness to allow the repair to be completed and still have sufficient “meat” left for durability.
|Proper repair takes time and the right equipment.|
Repairing Props is an Art
If the decision is to repair the prop, look for a well-recommended repair shop. The proper repair of propellers is an art. It takes a true skilled technician to do the job you want. There are many good repair facilities available. If you have a prop shop that is doing a great job for you, stay with them. However, if you are looking for a shop, you may want to consult the National Marine Propeller Association (http://www.nmpa.net), which provides training and workshops to help members keep their technical skills current. It may be a good resource to assist you in finding a skilled prop shop.