#StarcraftSummerFun Webisode #5 - How to Choose a Propeller for Your Boat

StarcraftSummerFun Webisode 5: How to Choose a Propeller for your Boat

How to choose a propeller for your boat can be a tricky topic. Many people can point out their propeller on their boat, but that's usually about it. When you start asking about pitch, diameter and 3-blade vs. 4-blade they look at you like you're speaking Mandarin. Well the fact of the matter is, is that the person who is going to know the most about your propeller is your local dealer. (Find my Yamaha Dealer in Canada) (Find my Yamaha Dealer in USA) But this does not mean you should't at least have a working knowledge of propellers so you can talk the talk and figure out if you're running the right pitch. 

Pitch is a great place to start as it is the most common measurement when dealing with prop choices, as well it has the most direct relation to performance. The pitch refers to the distance a propeller travels in one full roation.

      

The Propeller's pitch is going to effect your engine's RPM by either increasing it or decreasing it. The rule of thumb for this is if you go UP in Pitch you go DOWN in RPM and vice versa. 

The next thing you want to look at 3-Blade vs. 4-Blade. You can use either propeller, but choosing which one will depend on how you use your boat. 3-Blade propellers are known for their higher performance at top speed but lacking in hold shot punch. 4-Blade props have great pull out of the hole and torque but lack top end performance. Most runabouts will have a 3-Blade propeller while tow sports inboards, fishing boats and smaller engines generally rely on the use of 4-blades. Now you can also talk about stainless steel vs. aluminum but I don't want to bore you too much so we'll just stick with the basics. 

Testing Your Propeller Performance

If you're curious about testing your boat's performance to see if you could use a propeller change you are first going to want to consult with your engine's owners manual and find out what the manufacturer's recommendations are for RPM limit. My Yamaha F200 has a RPM range of 5000-6000 RPM however when I performed a performance test the max RPM I reached with my 15p stainless prop was 5600 giving me a top speed of 38 mph. Yamaha usually likes to see their engines closer to the 6000 RPM mark and that made me curious if I could squeeze a few more MPH out of my boat by going up in RPM. So since I need to go UP in RPM, I know I need to go DOWN in pitch. If I was looking for a faster hole shot or maybe I was planning on towing a skiier or tuber a lot I may consider switching to a 4-blade prop, but I'm just concerned about top speed and hitting my optimal RPM limit so sitcking with a 3-Blade is what I will do. 

Changing Your Propeller

The nice thing about changing your propeller, whether it's to put on a new one or to replace a damaged one is that they are very easy to install and remove. The only tools you will need is a standard prop wrench and a set of pliers. I reccommend bringing multiple sets of pliers to you're prepared. The plyers are used to remove the cotter pin that locks the nut onto the shaft.

  1. MAKE SURE BOAT IS TURNED OFF WITH KEYS REMOVED
  2. Use pliers to straighten out cotter pin and remove from shaft
  3. Use prop wrench to losen prop nut
  4. Use fingers to remove prop nut to make sure it does not drop in water. 
  5. Remove washer and hub
  6. Slide propeller off
  7. Insert new prop and reverse steps

This will be done easiest from the trailer but it can be done from the dock or also a shallow beach. Please, please please remember to turn off your motor and remove the keys. It seems like a silly thing to have to say, but hey, better be safe than sorry. 

Knowing I had to go down in pitch and up in RPM I tested out a 14p, and 13p along with a 13.5p Saltwater Series to see what I could get. The 14 pitch brought the RPM up to 5800, a 200 improvement however the speed stayed the same. The 13p prop brought the RPM up too high, at 6100 and the speed went down so we definitely know that is the wrong prop for this application. Testing the Saltwater Series prop was more of an experiment and it failed with a max rpm of 5600 and 36 mph - not what we were looking for. 

The Verdict

The verdict is that I decided to stay with my 15p prop. While it didn't get me to 6000 rpm, it did however give me the best performance which will result in better fuel economy. In all reality you won't have a supply of propellers on hand to test this out and do yourself. But you will however be able to now know what to look for and have a series conversation with your dealer who will know the best what you need. 

Until next time, see you on the water! 

Matt

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