Prop School – Part 1: Introduction

Working in performance boating is exciting: It’s fast-paced. Propulsion systems and hull designs are in continual evolution. Our customers are generally astute, technically oriented and often quite colorful characters. We’re all performance freaks! We’re all continually learning. That’s what makes my job so much fun!

The fifth edition of the iconic propeller guidebook which was first published in the 1980s.

If you are like me, your first boating experiences were in lower horsepower boats used primarily for family recreation, fishing, skiing, wakeboarding, or general cruising. And like me, your boating experiences and knowledge have evolved over time.

When working with high-end performance boats and experienced customers, one tends to assume people have basic product knowledge. However, a propeller is complicated. Because our backgrounds vary widely, our levels of understanding vary widely, too. So, we’ll revisit the basics and then dive deeper on propeller form, fit and function.

The CNC outboard cleaver propeller is an example of the advancements made in the design and production of high-performance propellers.

Back in the 1980s, Quicksilver Accessories published a book entitled, Everything You Need to Know About Propellers. It was a bible for folks like me who were learning about a very complicated and critical component that is used in diverse applications and environments. Much of the information I will be sharing is from the fifth edition of this knowledge guide.

The guide includes some interesting history on the development of propellers.

Prop Terminology.

Anyone who has shopped for a propeller has been exposed to terms describing the various design functions. I remember when props evolved from two to three blade designs. And when replacing the prop on the family runabout, all you needed to know was the diameter and pitch.

In the go-fast world of performance boating, diameter and pitch are important, but many other factors come into consideration as well. Its all about efficiency. Diameter, pitch, rake, cup, rotation, number of blades, blade thickness, blade contour, skew, ventilation, cavitation, elevation, and angle of attack all come into play when propping a boat for maximum performance and efficiency.

I’ll get deeper into these facets of propeller design that affect boat performance in my next post, Prop School – Part 2: Terminology.

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23 thoughts on “Prop School – Part 1: Introduction”

  1. Scott,
    Oh how I have waited for this topic!! I am looking forward to your next entry. We deal with all aspects of the Mercury product line so we get questions from plaining issues to diameter vs. cup vs. number of blades and their relationship to engine mounting height!
    Hope to get some insight from you!
    Thanks.

    1. Brent,

      Looking forward to sharing some ideas, seams that no matter how long we’ve been boating we’re continuously learning.

      It’s all good,

  2. Prop technology has come so far in the last decade. We have been teaching people about pitch size and speed since we first opened our shop. Bass fisherman really need to have the right prop for the job.

  3. I hope that later in this blog you will discuss the differences between area in the middle of the blade vs diameter and the effects of rpm and prop tip speed and load

    1. Great input, Sam. Yes. We plan to first address the basics of propeller design and function and then get into details regarding Lab Finishing and the effect modifications to blade configurations, diameter, etc. have on engine RPM and overall boat performance.

  4. Scott,
    Thx for sharing your Prop School. Great article!
    Concerning a T.E. Cleaver I would like to mount on a Tohatsu 40HP two stroke in combination with a 70 kg Aquarius Race Cat (3.6 m catamaran inflatable), intended to use for flat water and top speed: what diameter and pitch of the prop would you recommend? The engines rpm is 5200 – 5800. The total weight of the hull with the engine, driver and gas tank are: 222kg

    Thx

    Marius

    1. Marius,
      Thanks for the question. Yes, the TE is the prop of choice for your set up. As far as diameter and pitch, I’m going to defer you to one of the top propeller experts with this set up, Mercury Dealer Jim Merten at Merten Marine. Jim is very in tune with what you’ll require.
      All the best,
      Scott

  5. Hi Scott ive recently purchased an optimax 225hp on the back of my 21ft haines signature. We started with a 18p enertia eco but started to cavitate and over rev on the slightest bit of trim. We changed to a bravo 1 fs 20p but that has given us too much bow lift with trim fully down. I have lost the cavitation but do not like the amount of lift i am receiving with the bravo. Reading up on 19p inertia eco also states extra bow lift. What are some other options?

    Thanks Ray.

    1. Ray,
      The Revolution 4 is a 4 blade that shouldn’t offer as much bow lift as the Bravo I FS. The long barrel of the Rev 4 limits the amount of bow lift. To come close in rpm, you’re probably looking at a 19″ pitch Rev 4.
      Scott

  6. Scott,
    Love the Pro Max prop! I have a lightweight Stoker 22′ Mod-VP type hull with minimal interior and a 300X. Props are a 30″ labbed Lightning ET and a 30″ labbed Pro Max. The older Pro ET prop was always about 3 MPH slower than the Lightning, but the new Pro Max picked up about 3.5 MPH and is now faster than the Lightning! It also handles better, as the Lightning, trimmed out, has more bow lift than I need or am comfortable with at speed. (102.2 MPH GPS w/ 30″ Lightning, 102.8 w/ 30″ Pro Max)

    Maybe you have already considered it, but I’m wondering if a new “Lightning Max” 3 blade with the Pro Max style hub might also pick up that extra 3+MPH that the Pro Max did? Since I’ve also lost blades on a couple of Lightnings over the years, the larger hub might help to solve that issue, as well. I’ll be first in line if you ever develop such a prop!

    One more unrelated question. I foresee a 400R (or hopefully, even a 400ROS) on this boat at some future point. However, I have yet to see any direct comparisons of this motor with the 300XS on an identical single-engine high performance hull in the, let’s say, 21-24′ range. Have you made any such comparisons, or do you know of others who have?

    Thanks for your time and input,
    Lee

    1. Lee,
      Thanks for the comments. I’m glad to see the Pro Max is working out. You’re hitting some impressive numbers and thanks for the 3 blade tip. The only single engine comparison we have is with a Simmons Custom Boat 24’ Recon, a Texas cat made to run skinny water. The boat, with a 300XS with Sport Master gearcase, runs 68 mph all day long. Simmons swapped a 300XS for a 400R Sport Master and gained 8 mph for a top speed of 76 mph. Simmons’ customers are elated.
      Scott

  7. Hi Scott,
    We recently restored a 1987 22′ Apache Scout with a 2015 300 Optimax and were wondering what propeller would be a good choice. We are currently running a 28 pitch 4 blade Pro ET. we are only getting about 5200 to 5400 RPM out of it. The boat is getting into the low 70s. The engine is mounted on a bracket with a 24 inch offset and is mounted on the center hole. Any advice would be greatly appreciated.

    1. Chris,
      The Pro E.T. is hooking up well. The Pro E.T. is no longer available we upgraded it to the Pro Max. To gain 300 rpm, switch to the 26” pitch Pro Max It’s the same blades but with a small barrel for improved handling with high speed turns.
      Scott

  8. I have a 20ft flats boat with a 200XS Pro, boat came with Revolution 4 , 14.625 x 21. I’m on the rev limiter at 62.5 mph. Was thinking Bravo 1 XS 23?. Looking for good top end. I have 2 vent holes plugged and 2 open. Jumps on plane very good, but has to much transom lift.

    1. William,
      Consider the 24″ pitch XS, it will help get you off the rev-limiter and minimize the stern lift with the shorter barrel.
      Scott

  9. Hi Scott
    Your knowledge of props and the number of responses you have provided over that last few years is astounding. I could not find a setup similar to mine however. Hoping you can help.
    I have a Larson FX 2020 with a 300 Verado with 9.9 kicker and lots of gear. Current prop is a 21 ” Inertia. I have adjusted motor height several time to where I’m happy with overall performance however its time for a prop upgrade. RPM is about 6450 with speed around 55 mph (sometimes a bit better sometimes a bit worse). It seems like my boat is always stuck to the water (which some may argue is a good thing). I read great things about the Bravo 1 LT. I was thinking this is the route I’d like to try however the variables and prop selections are overwhelming. I’m sure you can help.
    Thnx

    1. Don,
      Thanks for your comments. Always glad to try and help. A move to the 4-blade, thankfully is limited to the Bravo I FS or Bravo I LT. The FS, with its short exhaust tube, in most cases offers added bow lift over the LT. Some boats achieve a 2 mph increase with the FS because the LT will pick the stern up pushing the bow down. Both props have great hole shot. The LT, with its longer exhaust tube – acts like a mini after-plane or trim tab. It holds the boat on plane at slower speeds which may benefit your boating. It’s your call which way to go. Hopefully, my limited explanations give you some direction. If you don’t care about the ultimate top speed – consider the 21″ pitch Bravo I LT. You mentioned engine height. Plan to raise it. In most cases – boat manufacturers mount the engine in the second hole from the top when using a 3-blade propeller. Typically, that puts the AV plate 1″ above boat bottom. If yours is like this, you may need to be in the fourth from the top (second from the bottom hole). In the end, with the 21″ LT – I would think you’ll see a 2-3 mph increase over your 21” Enertia. A 21″ pitch FS could see another 2 mph.
      Scott

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