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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41 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

  5. I have a 39 Cigarette TG Unlimited with staggered 525’s. Bravo 1’s with speedmaster lowers. I currently have Hering 5 blades. 31 pitch with added cup. The boat is hard to get on plane and has 13 to 14% slip at wide open throttle. What props would you suggest. Max 5 or the new 600hp cleaver. Thanks. Mike

    1. Mike,

      Awesome setup. What are you currently seeing for RPM at wide open throttle? The 15.25 diameter MAX5s will be the best option. Slip should be around 8-9% on top end.

      Nick

        1. Mike,

          Have the engines been chipped? Typically 5200 is the red line. Either way, you could expect top end speed improvements with the MAX5s. The 15.25 diameter is the way to go for further reducing slip. Comparing Mercury Racing pitch with modified Hering pitch will be a little tricky but 32 pitch would be a great place to start. Part numbers are 8M0156480 and 8M0156481. If needed we can tune the pitch down for you. You can expect 3-4 mph gain on top end. The MAX5s are typically great on hole shot as well.

          Nick

  6. Nick

    The engines have been chipped. Thanks for your time and help. Sounds like the max5’s are the best option. Thanks again.

    Mike

  7. I have a 2004 Prosports Baykat single engine Catamaran. It has a Yamaha 225 4S. I have tried a OFX418 and an OFS417 prop, and get a ton of porpoising with both from 28 mph up. I understand that i need a large prop with a ton of bowlift, as the it helps the porpoising issue and bowsteer. Would the Bravo 1 FS be my best choice to get the grip i need along with the most bowlift?

    1. Mike,

      Cool boat. Yes I do believe the Bravo I FS will improve your ride. The shortened barrel offers great bow lift, but the fourth blade and larger diameter still support the stern for great handling and hole shot. Are you able to achieve full throttle with the current setup? If so, what RPM are you seeing? The Bravo I FS will turn slightly higher RPM than your current propellers, you may need to step up in pitch.

      Nick

  8. I get between 5800 and 5900 rpm, and the top speed was around 49 mph. It is very hard to run at that speed, and the nose is down and the bowsteer make it very unsettling. The OFS 4 blade had a slight tip cup, but it did not help. I think a 20 or 21 in the Bravo FS would be a good staring point. I had talked to owner of a Baykat with a Suzuki 250 that had an Enertia Eco, Does the Bravo FS or Eco give the most bowlift?

    1. Mike,

      I would say the ECO gives you more but it also lifts the stern up too. The ECO is a total boat lifting prop designed to reduce drag for optimized fuel economy.

      Nick

  9. I also see Mercury Racing sells the Bravo 1 OC, with a shorter barrel and added tip cup, but samller diameter. What would be your recommendation between the FS and the OC?

    1. Mike,

      The Bravo I OC is a substitute for the old solid hub three blade cleavers. Designed to run on single or twin engine cats with two stroke power. The very short barrel and reduced diameter keep lift to a minimum since these hulls naturally generate lift at speed.

      Nick

      1. OK, how does the Bravo FS compare to a Rev4 worked for extra bowlift, with additional tip cup and a shortened barrel? Would the FS be able to lift the bow more?

        1. Michael,

          The Bravo I FS does generate more bow lift, it is mostly due to the shortened barrel. The Rev 4 does have quite a bit of cup out at the tip.

          Nick

  10. Nick,

    I’m not certain if this is the best spot to ask this but I’m struggling to get advice so here it goes:

    I’ve got a 2020 Ranger 621cFS with a Verado 400XL I ordered last year, took delivery of in November 2019 and I’m exploring a new prop. Boat is rigged with a 15HP Mercury Pro Kicker, one Talon and 4 batteries in the back and an Ultrex in the front. The boat also has a Bob’s Hydraulic jack plate with 6” set back. It also has Zipwake trim tabs installed which really help keep the bow down when getting out of the hole and keep the boat level when running swells. The boat came with a Bravo I 22 prop with the p/n 48-831910 22P stamped on the barrel. I’m not sure which model Bravo I have. I believe it’s the LT, since it’s got a flared barrel, but it could be an FS. It does have four PVS installed.

    I boat mostly at about 4,000 feet in elevation and my max RPM is 700 low at 6,100 with a full tank (56 gallons), two adults, tackle, etc. With that RPM I’m running about 58 to 59 MPH. I can get to 6,300 if I lift the jack plate and max out the Verado’s tiller but boat control isn’t great. The best performance and control seems to be Verado tiller raised about 10% to 12% under max and the jack plate about 2.5” up from the lowest setting. With those settings the boat runs flat and level in the 50 MPHs and handles 18” chop well up to 40 MPH so I believe the prop has the right amount of stern lift. That said it might be running a little bow down. It definitely runs more horizontal and level than my last boat which was an 18’ Crestliner with a 150 Mercury 4S.

    I’ve tried lifting the jack plate with a neutral tiller to gain more RPM and I really haven’t noticed much difference but once the jack plate settings exceeds about 4” high the back end of the boat begins to drift back and forth. Further, the Zipwake is set so the trim tabs shut off and fully retract once 45 MPH is exceeded.

    All that said, I believe I need to step down to a 20 pitch prop and based on all other factors I think I should stay with the same model of Bravo but I’m open to suggestions. Can you provide some guidance on which Bravo I have and I appreciate any other advice or suggestions on which prop might best suit my needs.

    1. Scott,

      Happy to help. The model of prop should be stamped on the top of the hub inside in the barrel, right next to where the prop nut would be. Since you have been running it, you may have to clean off the exhaust dust to see it. Judging by your handling characteristics, I would assume it is an LT. I do think you would benefit from going to a 20 pitch Bravo I FS. You are experiencing a lot of stern lift at speed, causing bow steer. Hole shot will also improve by stepping down in pitch, and you will get into the peak power band on top end.

      Nick

  11. Just a couple additional items I thought to add. Gear ratio is 1.75.

    At WOT, my boat veers right and I constantly need to nurse the wheel to the left to stay on course. It also seems as if I’ve got too much hull in the water and it sort feels like the boat is being held back or pushing something uphill.

  12. Nick,

    Thanks for the response. The back of the prop is stamped with FS * CS. The asterisk represents a recessed dot that separates the FS and the CS. I can send a picture if needed. Based on this would you still recommend I try a Bravo I FS in 20 pitch?

    1. Scott,

      Yes your hole shot and acceleration will be much improved with the 20 pitch. All in all, it should wake the boat up considerably.

      Nick

  13. Nick,

    I got the 20 pitch pro finish Bravo 1 FS we discussed above. After a couple of days on the water the hole has improved but I didn’t gain many RPMs, maybe 100. I don’t know if it matters but on the break in day I was able to get to 6,500 RPM and 61 MPH with the 22 pitch Bravo 1 FS the boat came with. I’ve never been within 200 RPM of that since with either prop. Is it possible the Verado’s throttle or computer needs to be recalibrated? It’s hard to describe but it just feels like there’s more there and the engine isn’t getting to full throttle. Engine only has 23 hours on it now….

    I’ll probably go to a Mercury service center and have them take a look too.

    Thanks!
    Scott

    1. Scott,

      I think that’s a good idea. A Mercury dealer will be able to tell you if the engine is making full boost under load.

      Nick

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