Lost My Edge / Effects of a Damaged Prop and Skeg

 

 

 

Lost My Edge / Effects of a Damaged Prop and Skeg

 

 

 Props and Skeg that are damaged or out of tune.

 Most boaters believe that the reason for bad performance, issues with hole shot or top end flat lining of power must be related to the way the motor(s) is (are) running. There is some truth to this, if you have weak spark, fuel delivery (bad fuel) issue or the engine is failing to advance the timing then yes the boat will run like crap. However if the motors are running well and the boat is still a dog then you need to assess the prop(s) and the skeg.

Props will go out of pitch over time, it is a given the blades are trying to flex under load and they eventually loose their pitch. You should every couple of seasons take the props off and send them to a repair shop were they re-pitch (tune) the props for you. Should you all of a sudden notice a difference in the way the boat performs than you may have hit something or mowed through a chunk of wood (not even knowing it) This is not as uncommon as you may think. The prop is where all the work is done to move your boat through the water. You can have a perfectly tuned motor but if you cannot make the prop bite the water, it is all for not. A badly damaged prop will cause vibration through the boat and will damage bearings and seals at the prop shaft as that vibration is passed down the shaft.

 

 

What is happening to your boat when the blades are out of pitch.

 

When the prop is out of tune, the blades are trying to travel different distances through the water at the same time this will cause cavitation or aeration at the blades, this water can be so hot it will burn the paint off the prop. When this is happening the prop starts to slip, and the push of the prop is lost. An example of this would be at the top end of the throttle you push the throttle down and the engine just revs and there is no more push by the prop to match the increase in the RPM, or as you move up through the RPM range the speed of the boat does not move smoothly up with motor and eventually the speed catches up. This is all prop slip and if you look behind you in the wash you will notice excessive air or bubbles in the wash. The reaction is similar to driving with the drive trim to high.  Should you see that one or all blades of the prop have the paint worn of the faces of the blades (it will look like the prop was sand blasted). This is a sure sign of bad cavitation and the prop or the case has to be fixed or tuned. 

 

 

Cavitation can also be caused by the flow of water that the prop has to work in. The skeg at the bottom of the gear case can disrupt the water flow to the prop. If it is bent or damaged the water getting to the prop already contains air and the effect on the prop is cavitation. A damaged skeg will affect steering, create a pull to the right or the left, lack of low speed control, Bad pull to one side or the other (at low speed), slipping at high speed when cornering, large damage can also effect the flow of water to the water pick up used for engine cooling. As a matter of fact any damage to the lower gear case will be detrimental to the running of the boat and or the performance of the boat.

 

 

Damage to the lower gear case , which includes the cavitation plate above the prop is not the way you want to operate your boat at all. Leaving damage not only effects the way the boat performs, but will lead to corrosion setting into the metal and in some cases were cracks have occurred contaminated gear oil, and additional gear case pieces falling off.


 

Aluminum props are continually flexing as you power up, and are the most susceptible to pitch variations, One blade or all blades maybe out of sinc with each other. If you have a chip or a bend in the blade or blades then you have completely defeated the props expected performance. These props are the easiest and cheapest to have repaired, If you have a damaged aluminum prop take it to your local prop repair facility and have them assess the damage and let you know if it can be fixed. You cannot just keep repairing props over and over there is a limit to how many large repairs can be done. Always keep a spare on board with the tools you need to change the prop. Never try to change the prop in water were you cannot reach the bottom easily, it is common to drop parts or the whole prop.

 

Stainless Props are less likely to flex under load which makes them a popular choice with boaters. do not assume that because the prop is painted black that it is aluminum. There are black painted stainless props. Stainless props have a draw back, if you are a new boater or operate your boat in a body of water that has a hard bottom such as rocks, beware. With an aluminum prop you can hit a hard object and knock a whole blade off and usually not damage the inner workings of the gear case. With stainless steel the blades are so durable that damage to the inner workings of the gear case is inevitable. The way to try and prevent this is with a break away hub inside the prop between the prop and the shaft so at the moment of impact the plastic hub will break into pieces and save the inner workings of the gear case. If  a stainless prop is actually wedged up against something I have seen the coupler on the engine sheer before anything else. This is were the drive shaft from the out drive couples to the engine the repair in this case requires pulling the drive and the motor out of the boat.
 

Stainless Props also need attention it is a good idea to have the stainless props checked and tuned by a prop shop if you require the shop can also custom tune these props giving you a pitch to better suite your needs let the repair shop know what you are trying to achieve in performance and they can adjust the pitch by a half a pitch up or down. This really works and the difference  in performance and fuel burn can be out standing. Stainless props can also be repaired if you do manage to bend or chip a blade, expect to spend more money repairing a stainless prop.

 

 

Gear Case damage can in 90 % of the cases be repaired by the same repair shop that handles your prop repairs. Never assume that the case can be repaired however this is due to the fact that the heat from the repair can change the shape of or do damage to the inner workings of the gear case. Gear Case repairs must be done by someone with gear case experience! If the leading edge of the skeg has small chips you can file the edge to a clean as new finish with out removing the gear case from the boat. If you have a damaged gear case and plan to remove the case yourself and have it repaired there are a few TIPS for you.

• Contact the repair shop and ask if they require the gear oil drained out before they fix the gear case
• Ask for an estimate when they PU or when you drop the damaged gear case off
• If they paint the repaired gear case ask the repair shop if they use zinc chromate primer, if the answer is no tell them you will paint the repair yourself
• Always use the correct zinc primer on gear case repairs before you top coat
• Do not paint with cheap spray paint buy quality paint for repairs.
• Always pressure check the drive before refilling with gear oil to be sure that the heat from the repair has not damaged a seal.
• Always test drive the repaired gear case before you head out on your first big trip.

By keeping the props and gear cases on your boat in good working order you will get the best performance they can give you. You cannot expect the same performance out of a three year old prop as you would a new one with out maintenance. Of all the money we spend on or boats to me the prop is the most overlooked for maintenance and the prop to your annual list of things to do and you will be paid back in fuel burn and in performance when your out on the water. Basic prop maintenance is not expensive and if you are a seasonal boater what better time to send the prop in to be tuned then when the boat is laid up for the winter!








 

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