Why is my boat slower than my buddy's?

Damaged prop at top compared to new prop on bottom

Edge of blade has been ground away by striking a rock

This is a question we sometimes get at camp. There are two likely reasons for this: 1. something to do with the propeller and 2. the weight inside the boat. Most often it is the first.
If there is just one weed caught on the prop (or the leg) of the outboard, the drag it creates will slow down the boat significantly. So, that is one possibility -- something is caught on the motor. The other big likelihood is the prop itself is damaged.
There is nothing as contentious in dealing with anglers as when it comes to damaged props. The problem doesn't come from badly wrecked props -- it's obvious to everyone when the prop blades are folded back or missing entirely -- but rather ones that have minor damage like the one in the photo above. Any alteration to an edge of any of the blades will create a decrease in performance (i.e. speed). This change may not even be noticed by the driver unless he has been tracking his speed with a GPS. It might just be one or two mph difference. No big deal, right?
Maybe not to him, but the next person who drives the boat will complain to us that his boat is slower than his friend's. There is no remedy other than to replace the prop with a new one.
How did the prop get damaged in the first place?  It struck something. In the case above it clipped a rock. You can tell that by the way the aluminum has been ground away. But even if the prop hit something softer, like wood, it will still likely be ruined. In that case the edge will be flattened or bent but all the aluminum will still be there. Either way it won't perform like it did before.
Striking an object can also damage the rubber hub in the center of the prop. This surrounds the brass bushing which fits onto the prop shaft. This damage isn't obvious to anyone other than an expert. But the result is the prop wobbles in its rotation since it no longer is aligned properly on the shaft. This causes the engine to shake when driven at higher speeds and, again, decreases speed.
The rubber hub on modern engines has taken the place of the old shear pin. Younger readers will have no idea what a shear pin is but up until maybe the 1990s propellers on smaller outboards had short brass pins inside that connected them to the prop shaft. If the prop struck anything the soft metal in the pin broke and the prop shaft spun freely. This lessened the chance that the prop shaft and the expensive gears inside would be damaged. Today the rubber hub does exactly the same thing.
There is a sign on all our boats that states: "The Operator is Responsible for any Damage." Everyone who signs our Weekly Boat Rental Agreement, which also doubles as a one-week boat operator's licence required of all persons operating a boat in Canada, agrees to pay for damage to the boat and motor.
Propellers for the 20 hp Hondas cost $100 Cdn. At least they did last year. The 25 Honda props are more expensive.
"But it's just barely damaged! Couldn't you just file it straight again or get someone else to fix it rather than replacing it with a brand new prop?"
A prop blade cannot be filed without changing its balance which will cause the engine to shake.
We can send the propeller to a repair shop where the blades can be welded and shaped again and that labour-intensive procedure will cost 3/4 as much as a new prop and can take weeks or months to be returned. More importantly though, the rubber hub inside cannot be repaired to original specifications. So we can pay $75 to repair a prop only to later throw it in the garbage anyway. That's why we just replace the damaged prop with a new one.
 "But isn't it impossible to run the motor and not hit things?"
The best way to answer that is to note that we have guests who frequently damage props, sometimes wreck lower units and even break oil pans (the worst thing) and other guests who have never hit anything. I think this illustrates that it is the habits of the operator that are usually responsible.
We advise everyone to motor slowly toward the center of the lake until they are 100 feet off shore before opening up the engine. Within 100 feet of shore there are rocks and deadheads (logs with one end floating, the other at the bottom) galore. Red Lake is about as hazard-free a lake as you will ever find. The few "surprise" rocks at our end of the lake I mark with white bleach jugs. They are also all marked on our camp map.
The most common reasons anyone strikes an object is that they "open-up" the engine from near-shore and travel right alongside the shore for a ways, or they take a "shortcut" across the end of a point. Points always continue underwater.
Another reason is they simply aren't looking where they are going and run right over a reef that is actually above the waterline. This ends up not only wrecking the outboard but always damages the boat as well. The operator also must be vigilant for floating logs and sticks. You need to always look where you are going and for things floating on the water ahead of you.
But whatever the reason, it is important that you know we don't think less of you for damaging a prop or a lower unit or anything else. Compost happens. Just pay for the new prop, or the repairs, and away you go.
Minor damage to a prop, like the one shown above, usually comes from going to shore to get a lure snagged on the bottom or in a tree. The way to avoid this possibility is to put the engine in shallow drive before going to shore. You do this by lifting the engine until it clicks into the shallow drive position. Once you are free of the snag and have backed away from the shore you need to throw the leg position lever the other direction, lift the leg until it is out of shallow drive and let it fall all the way down to normal drive position. Then throw the lever back to the position that lets it tip forward.
We always advise not to lock down the leg of the outboard to prevent major damage when striking objects. See Lever.
Our outside worker or myself will go over all of this when we do our boat and motor orientation with you each time you come to camp.
Is it inevitable that eventually everyone will strike something? The answer is probably yes if you spend enough time on the water, however that could mean just once or twice in a lifetime. It certainly doesn't mean hitting something every time you are at camp. If you follow good habits as described above you are almost guaranteed never to hit anything.
Here are a couple of other tips on how to avoid hidden hazards. 1. Give every island a wide berth. 2. Always take the largest opening between islands. 3. Stay centered in the travel corridor 4. Expect sunken deadheads anywhere you see above-water deadheads.
Finally, there is the second common reason why one boat is slower than the other and that is because one boat weighs more. Everything inside the boat contributes to this weight: people, gear, batteries, liquids.
There are two other possibilities. One is the motor running position is not correct. This should never change since we set all the motors for the correct position. Boats travel the fastest when the outboard leg angle is set so that the craft runs parallel to the surface of the lake. It is a common myth that they go faster if the bow is lifted very high leaving just the stern to make contact. That may be true with very large horsepower craft, like bass boats. It is false when dealing with fishing boats. Sometimes people have "monkeyed" with the leg setting and we might not have noticed when re-outfitting the boat for you.
Finally, it is rare, but maybe there is something wrong with the gears in the outboard's lower unit. This could be the case where someone, sometime, clunked a rock with the motor locked down but the only visible damage was a broken prop. This is a once-in-a-decade kind of occurrence. Normally an accident of this nature will also have broken the skeg (the lowest portion of the leg, beneath the prop) and when getting this repaired the mechanic will have checked the gears as well. We wouldn't charge the current operator of the boat for the damage, of course.
It is interesting to see how other camps deal with the damaged prop issue. I always check this out with other camp operators when we are at our annual NOTO convention in the fall. Most are exactly like us, the operator pays for the damage. Some have various types of "insurance" which everybody must buy. This usually works out to be the same as the cost of a new prop! So, for us, rather than make everybody pay for a prop regardless if they damage one, we think it is fairer to just make those who commit the damage pay.
To put the whole issue in perspective, in an entire summer we may only need to charge a dozen people for prop damage, perhaps one or two for lower unit damage and one for a broken oil pan. That's a pretty good record considering the number of people who go through camp in a summer.
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