Prop School Part 7: Barrel Length

The obvious function of the barrel, or outer hub, of a propeller is to be the attachment point for the propeller blades. What is often overlooked, however, is that the length, diameter and shape a propeller barrel can have a direct effect on boat performance.

Mercury Racing propellers currently have three barrel sizes. The smallest-diameter barrel is found on solid-hub props with broached splines like the Mercury Racing CNC Cleaver model. Barrels also come in different lengths and some have a flared trailing edge.

Mercury Racing offers different barrel lengths and shapes on the Bravo I, Maximus, and MAX5 propeller families. The longer and wider the barrel, the more stern lift the propeller will generate. Adding flare to the aft end of the barrel also generates stern lift; a long barrel with a flare acts as a miniature trim tab, providing lift and improving hole shot. This is why, for example, the Mercury Racing Bravo I XC has a longer barrel with a flared trailing edge – both features help fishing boats used in the Texas Gulf Coast market plane off quickly in very shallow water, and hold plane at lower speeds as anglers sight fish.

Maximux ST versus LT barrel length

The different barrel length options for the Lab Finished Maximus LT and ST propellers have been a used for years to fine tune stern lift on boats powered by twin sterndrive engine.

A long propeller barrel can negatively impact top-speed performance in many fast boat applications when stern lift created by the barrel causes the boat to run too flat. The Mercury Racing Bravo I FS, Bravo I XS, Bravo I OC, MAX5, MAX5 ST, and Maximus ST all feature shortened and tuned barrels to dial back stern lift. The Bravo I OC and MAX5 ST represent the most extreme versions of this treatment, featuring very short barrels that perform especially well when an ultra-lightweight boat is paired with high-horsepower outboard power.

If you are up to speed on our previous Prop School Blogs, you will know that the barrel is not the only part of the propeller that provides lift. But if a propeller is generating too much lift due to diameter or blade count, the barrel is often the first part of the propeller to “hit the chopping block.”

MAX5STThe MAX5 ST is suitable for lightweight bass boats and catamarans featuring the 250R, 300R, and 450R outboards.

The Bravo I OC is specifically designed for twin engine two stroke powered catamarans.

 

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19 thoughts on “Prop School Part 7: Barrel Length”

  1. So does the Bravo LT have more stern lift than the Rev 4 XP. If so which prop is faster & easier to turn on a non step hull the Bravo LT or Rev 4 XP?

    1. Phil,

      The Bravo I LT does have more stern lift than the Rev 4 XP. Both props are great for hole shot, however, the smaller diameter of the Rev 4 often allows it to spool up quicker. It’s hard to say which is the best for a non stepped hull without knowing size, number of engines, etc. But, typically it is the Rev 4. The Bravo I LT is mostly for the Walleye market- boats that feature an outboard, a kicker, a power pole, and 5 batteries all in the rear of the boat.

      Nick

  2. I have a 25ft catamaran with 2x400HP Mercs running 118MPH (just off of the rev limiter) with 36in Bravos 48-832124 – absolutely no slip coming out or the hole. I also have a set of 38in 5 blade cleavers running 128+ (just off of the rev limiter) but slip like crazy coming out of the hole. Does Mercury make any prop of any pitch would come out of the hole without slipping and give me a little more top end than the bravos?

    1. Walter,

      Typically the MAX5 is the happy medium between the Bravo and Cleaver but Mercury Racing only offers up to 34 pitch. It would net you about the same top speed as the Bravo due to the reduced slip. For anything faster than that, we recommend the 5 blade CNC cleaver. Most of the new cats cavitate a small amount coming on plane, it is crucial to back off the throttle and ease the boat on plane to avoid propeller and gear case damage.

      Nick

    1. Chris,

      The Maximus ST is typically the prop of choice for your setup. I recommend you talk to Brian Forehand at Marker 17, he is one of the best in the industry at setting up Fountains, 910-821-0190.

      Nick

  3. I have a 36′ 2008 Deep Impack with quad Mercury 300 Verados, it has bravo 1 28p 4 blade on outside 2 engines and Mirage 27p 3 blade on center 2 engines, it turns 6200 @ 75 mph, do you think Bravo fs would be better choice for this boat and if so, what pitch?

    1. Bill,

      Yes to my knowledge the new Deep Impacts are all coming with Bravo I FS props from the factory. Running the FS on all four engines should give you similar lift to your current setup because you are getting bow lift from the Mirages and stern lift from the stock Bravos. With the tuned barrel on the FS, you get a happy medium. Consider stepping up one inch of pitch across the board when switching. The Pro Finish on the FS gives you more RPM over stock, which is part of where your speed increase will come from. Which dealer would you purchase the props through? We can work through the dealer if the pitch ends up being off.

      Nick

        1. Bill,

          Great, please give me a call if you have more questions. I’m happy to work with you if you end up needing a different pitch.

          Nick

    1. Terry,

      Beautiful boat, do you know which propellers the boat used with the 400R? My guess would be 18 or 19 pitch Rev 4 XPs. A safe bet would be 20 pitch Rev 4 XPs for your 450R motors. Any further data on how the boat runs with other engine packages would be helpful in determining pitch but the 20 pitch XPs will be close.

      Nick

  4. Hey guys,
    I have a step hull 32 ft cuddy center console Glasstram call it 8200lb wet. I recently replaced A pair of 250 pro XS OptiMax gold blocks… with twin mercury 300 pro XS V8’s. There’s a set of four blade revolutions on the boat now… borrowed. I had a set of bravos on the 250s (which were faster than the new set up) I’m wondering if I should try those and what you would recommend other than the revolutions. The revolutions are a great whole shot and mid range Prop, and the torque will throw people off the back of the boat if they’re not holding on. I just feel like it’s missing out on the top end… how can I get a good balance of hole shot, mid range, and top end? By the way these V8’s are crazy amazing!!!

    1. Wes,

      Great to hear the new motors are working out for you. Do you know what pitch the Revolutions are and what RPM/speed you are seeing at wide open throttle? If you like the feel of the revolutions, you could go with the Rev 4 XP, possibly stepping up an inch of pitch and gaining some top end speed. The Bravo I FS also work well for top end speed on some center consoles that require more bow lift.

      Nick

      1. Nick,

        The revolutions are 25’s and spin up to 5800
        The second run out with flat conditions my speed was 55mhp…I was trimming up one push of the button at a time we got trimmed up to a point and it felt like the wheels grabbed and launched us up to about 64 mhp in an instant. With that being said the XP might be a good choice based on your recommendation.
        Your thoughts

        1. Wes,

          What were the Bravos that you ran on the previous setup and what were the performance numbers? No doubt the rev 4 XPs in a 25 pitch would be a great option. Most guys gain 150 RPM and 2 mph over the standard 25 pitch. I’m just trying to feel out if your boat would benefit from a little more bow lift, in that case you could go with the Bravo I FS.

          Nick

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