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Posts: 24
| looking for some type of reference guide for props and what they can do for my performance. I have a 95 200hp evinrude vindicator. Looking for something that can explain it to a uneducated person on the things different pitches and such Do and mean towards the performance of my motor...... not really looking for top speed just something to get me a outta the hole and on plane alot faster. I am curently running a four blade renegade stainless prop. No clue as to the pitch or and specs of the prop itself. It has some dings and nicks on the baldes could this be my problem?. Can i get my current prop repaired?. Anyways just looking for a reference site that would steer me in the right direction without trying to push selling their product to me. | |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
I will do my best to lay out the basics of things..hopefully in a way it makes sense...
On any prop, there are two numbers, usually listed as something like this: 13 x 19
The first number is the outside diameter of the prop and the second number is the pitch of the prop.
Pitch: Defined as the amount of distance your boat would travel in one full turn of the prop. So...a 19 pitch prop would theoretically move your boat 19 inches forward in one rotation. The actual amount the boat moves is less than this due to the prop having to slip a little in the water in order for it to turn. The lower the pitch number, the slower the prop will be, but a lower pitch will also make it easier for the motor to turn, giving a better hole shot. Higher pitch will increase speed, but it has a limiting factor as well...too much pitch and your motor will not operate in it's designed RPM Range.
Cupping: On many steel props, if you look and feel from the tip of the prop fin and along the back side of the fin, there will be a curl upward (if the prop is sitting on a bench). That curl is what cupping is... What it does is helps force water in certain directions to do different things with handling characteristics of the boat.
Tip cupping: Adds bow lift. The more tip cupping, the easier it is to bring the bow up with less trim(or tilt outward of the lower unit from the boat). Tip cupping also allows a prop to grab the water better when turning since it carves into the water at a different angle than a prop that does not have it.
Rear edge cupping: Allows the prop to lift the stern more. The more rear edge cupping (toward the center of the prop) pushes the stern of the boat upward as the prop travels in it's rotation.
Many props that have tip cupping also have rear edge cupping which helps overall performance of the boat.
Blade Design: There are many different designs out there to choose from. In a nutshell, a prop with big and wide ears (almost like elephant ears) are designed for high thrust. Usually these props are used on boats that push heavy loads and are very slow. They also have a very low pitch number as well. A prime example of this type of prop: Look at anyone with a Yamaha T8 Kicker motor.
There are various style of fins in between, all depending on what you are looking for. Many props have what is called higher "rake" which you see on many props with more of a swept-wing style that you can see looking at the back end of the prop. A standard white yamaha propeller has very little Rake (the back edge of the prop is connected to the prop at close to a 90 degree angle) A prop with high rake would be like an OMC/Bombardier "Raker" brand propeller. As you look at the prop from the side, a high rake propeller has it's fins bent back toward the back of the hub more...
What rake does is this: It is another way to help lift the bow and help in overall handling of the boat.
Number of blades: The more blades, the more surface area the prop has to contact the water. Props with 4 blades usually are designed for heavier boats and/or walleye boats. They usually have a bigger and more rounded fin in many cases.
Vent holes: Vent holes are holes drilled into the hub not too far from the blades. What these do is allow exhaust gasses to escape through the holes in lower RPM ranges on the motor. when the motor is put into gear, the extra exhaust gasses allow the blades to turn easier (more slip in the water). What this allows is a higher RPM to be obtained by the motor when you accellerate. At a certain RPM level, the exhaust gasses are at a high enough pressure they go right past the vent holes, the prop then grabs the water abruptly, and up pops the boat out of the hole. Good in some cases (like bass boat applications), but not good in others (heavy wind where you may not be able to be up on plane).
I hope I have been able to help in the understanding of the bigger items for props with this... It is not the greatest in detail, but hopefully a start.
Couple of things many on here can help you out with... If you have your current RPM's, and can find the brand, diameter and pitch of your prop (either on the side of the hub, or on the front or back side of the hub next to the where the spindle goes through the prop itself), we can help find something to get you started. Also, what are you looking for in your prop? Better handling, speed, hole shot?
Edited by VMS 9/28/2011 10:23 AM
(Cupped and vented propeller.jpg)
Attachments
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 High thrust prop.jpg (3KB - 166 downloads)
Example of rake.jpg (5KB - 150 downloads)
Vented propeller.jpg (5KB - 147 downloads)
Cupped and vented propeller.jpg (4KB - 165 downloads)
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Posts: 24
| Hey thanks alot that explained a bunch. I'm looking for a better hole-shot first and foremost, and possibly better handling (seems like im wrestling with the steering wheel at times) I have a Four blade Renegade not sure of diameter and pitch yet. My rig is currently at the shop getting some work done. Should know by this weekend......... Also there are some nicks and dings on the tips of my blades, will this cause damaging vibrations and or effect the performance? | |
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Posts: 3508
Location: Elk River, Minnesota | Hi again,
depending on the severity of the dings and bends, the vibration could do damage to the seals and innards of the lower unit. The vibration is due to a prop that is out of balance, and thus as it turn, will balance on its own accord, which is not in balance with the outboard...thus the vibration and steering torque you might be feeling.
The renegade prop is a good prop and designed for bass boats with higher motor heights but really excels in rougher water conditions (thus the 4th blade) without too much loss in top speed.
I'd be interested in what type of boat you have, as this can play a big role in the type and design of the prop that would best suit your needs.... so...when you find out the numbers (RPM, pitch and diameter), then we can start to work with some things... Sometimes, a prop change is the right thing to do, and other times, some tweaks to engine height, torque tabs, etc. can help as well...
All part of tinkering until you get your desired performance out of your rig for how you want it to run.
Steve | |
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Posts: 433
Location: Cedarburg, Wisconsin | Now that you know more about the ins and outs of prop design, you need to look at your rpm range with the curent prop at a normal load. Your '95 has an rpm range of 5000-6000rpm listed on the web. Look at the wide open throttle (WOT) rpms with the motor trimmed up as far as it will go and still run without porpoising. If you aren't running very close to 5800 I'd think you are losing holeshot performance, so you'd need to change pitchs to get there. A good vented 4 blade prop that runs 5800 WOT, tuned to let you spin say 3500rpm on take off, would be great for holeshot and handling. | |
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