Prop School – Part 4: Blade Cup

Continuing from Prop School…Part 3. Here I will explain everything you need to know about Blade Cup.

An illustration of cup added to the trailing edge of a typical through hub exhaust prop.

Cup is a curl formed or cast into the trailing edge of a propeller blade.  When done correctly, the face of a cupped prop blade is completely concave.

The first three-blade aluminum props for MerCruiser powered boats featured flat blades, with 15-degree rake. The heavy, deep-vee hull ran best with the drive trimmed up (raising the bow, reducing the wetted surface, and increasing hull efficiency). We got our first experience with cupped, 3-blade aluminum props in the mid ’70s. We immediately realized greater top-end speeds. We also noticed the engine didn’t work as hard. The cupped props were more efficient. Our measurement? The paint was still on the blades at the end the season. Cavitation burns, mostly from abusive teenage kids over trimming dad’s boat, would burn away the paint. The cupped prop definitely made  a difference.

Location. Location. Location.

Originally, cupping was done to gain similar benefits as you get from progressive pitch or higher blade rake. In fact, cupping reduces full-throttle engine speed 150-300 RPM below the same pitch prop with no cup. The location of cup on the blade determines the affect it has on performance. When the cupped area intersects pitch lines, pitch increases. Cupping in this area will reduce engine RPM.  Cupping can also prevent prop cavitation or blow out.   Blade rake can be increased when the cup intersects the rake lines. Slip is a measurement of propeller efficiency as it turns through the water, the normal range is 10-15%. Most racing and performance boats slip can be as low as 5-7% where as performance vee and step vee bottom boats with high X dimension (outboard engines or sterndrives mounted high) can see slip as high as 20-22% at WOT

Cleaver Cup.

All Mercury Racing propellers spend time on the grinding wheel.

Adjusting cup on cleaver-style propellers is more difficult. The trailing edge is very thick and runs straight out on the rake line. Pitch can be altered some by grinding away some of the cup. Rake may also be altered slightly.  The rake can be reduced by decreasing the cup near the tip of the blade. Rake can be increased by reducing the cup near the prop hub. Remember that any change in cup affects engine RPM. The Bravo I propeller family is a good example of how cup changes RPM and the attitude of the boat I will discuss blade configurations and factors that effect propeller efficiency in Prop School – Part 5.

 

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91 thoughts on “Prop School – Part 4: Blade Cup”

  1. Thanks for posting. I still have the old “Everything you need to know about propellers” summary mercuryracing.com had online long ago. That document teached me the basics about the magic props. Still learning every day but reading that piece triggered my attention to prop technology.

  2. The issues I’m having is when I’m at full trim 5250 rpm I will loose about 3 mph so I back off the trim to regain my speed ! I’m running a 24 pitch lazor2 on a 17 ‘ r 78ranger sport. With a 125hp mercury. Will cupping help me or hurt me. ? Or should I try a different prop. ? This is the prop that ranger boats recommend !!! What do u think ?

    1. Eric,
      If your 125 is the 4 cylinder, it has an rpm range of 4750 to 5250 at WOT. And if you’re hitting 50 mph (or close) you may have the best set up already. It is possible to over trim; you’re in the driver’s seat. Adding cup may help the propeller stay hooked with the engine trimmed out further. However, the added cup could have a negative effect by lowering engine speed 150 – 200 rpm at WOT. There is also a good chance the speed will drop 1.5 to 2 mph.
      Scott

    2. Sounds more like you’re over propped. You could take some cup out to gain higher engine rpm or drop down to a slower prop. Being able to hit top rpm at wide open throttle is a must.

    1. Jean,
      Most prop shops increase or decrease rpm my modifying the cup height, there are a few shops that have a pitch block and will bend the prop to the pitch block.
      Scott

  3. I’m wondering if cupping will help me I’m running a Javelin Renegade 20 (20-foot foot bass boat) with a Johnson 225, 6 inch Jack Plate, 25 pitch 4 blade Renegade prop,5800WOT. Problem is I’m not getting enough bow lift trimmed all the way up I still feel like I’m plowing a lot of water and I really don’t gain any speed from 5500 to 5800RPM?

  4. I have a 1996 24 feet 5100lbs boat with a 5.7 mercruiser. Someone stole my prop. I’m having trouble finding one that works well. Do you have a recommendation. I’ve been told everything from a 14×17 to a 16×16. Boat is a deep v Hull.

    1. David,
      To close to call, but it is going to be between the 15-inch x 17-inch pitch or the 16-inch x 16-inch. With the information you’ve provided, I’m leaning toward the 17-inch pitch.
      Scott

  5. Have an inboard with a 5.7l Vortec Indmar with a Holley. Changed my prop from a cast prop with .04 cup to a CNC prop with .08. All other dimensions the same. The changes were fairly dramatic. RPMs dropped by 400 at WOT. Since we us it for skiing, the acceleration out of the hole was smooth and constant with no cavitation. Cavitation in the turns was almost eliminated. Only issue was lost about 4 mph off the top end. To be honest the acceleration out of the hole is so good now noone really cares about the top end. That’s the way skiers think. For reference this is a 1998 Malibu response. New prop was an Acme 449

  6. I have a 18′ DynaTrak fish and ski (1200lb dry). Low and wide bass type hull. It has a 1995 115hp Mercury out back. The boat came with a 22p Lazer 2 prop. I was only able to achieve 43.5mph at about 4600 RPM. It seemed to blow out rather easy in higher speed turns. I purchased a 19p Spitfire X7 to replace it thinking id gain my appropriate RPM back and gain some top speed to boot. The 19p runs me at 4800-4900 RPM at 43mph. Holeshot is much improved as is cornering. The prop starts to cavitate at high trim and goes to about 5000rpm and i lose 2mph. Am i running the wrong props? I feel like this hull and motor should be putting me really close to 50MPH at max RPM.

    1. Perry,
      I can’t seem to find a better solution for your setup. If you go down in pitch with either of your propellers, you can expect to gain rpm and hole shot, but top end will be the same or slightly worse.

      Nick

  7. Scott,

    I love these articles! You have a great way of explaining a very complicated dynamic in an understandable way!

    Here’s my situation. I have a 2016 East Cape Vantage VHP with an ETEC 150 HO. It’s a Florida style flats skiff that is 19’2” with a 79” beam and a hull weight of 950 pounds(no jack plate yet). It’s meant to go pretty fast. I expected speeds around 64mph. Unfortunately, I can’t find a prop that performs reasonably. Every prop I’ve tried thus far has either been dog slow or caused the boat to porpoise so much that I have run trim tabs even at WOT. I’ve run a 22p Raker, 22p Viper, 19p Powertech ELE, 17p Powertech OFX3, & 19p Powertech OFS4. Of those, the Viper is the best with 59 mph at 5850 rpm light and 56mph at 5600rpm with a normal fishing load and two of us in the boat. However, this prop causes the boat to porpoise quite easily even at WOT forcing me to not trim up much and keep the tabs down.

    In my research, it appears most people with my boat have success with the Mercury Tempest Plus. What pitch would you recommend 21, 22 or 23? Should I consider installing a jack plate?

    Thank you!! George

    1. George,

      I think you have a couple different options to consider. You could run a 21 Tempest but it is a bow lifting propeller and it may not fix your porpoise issue. Your other option is the Mercury Racing Bravo I LT, which has a full length flared barrel and will provide you with stern lift. Think of it as acting like a mini trim tab without you having to use your actual tabs. Consider the 21 pitch Bravo I LT for great hole shot, and a 22 pitch for maximum top-end speed.

      Nick

  8. Thank you Nick!! I was wondering how the Tempest Plus compared to the Raker because I thought it might provide similar results. Would a jack plate help my situation as well?

    1. Any time George,
      A jack plate will change your setup quite a bit. If you are going to go down that route, you should install and then test the props you have to see how it changes your handling.

      The more set back you add, with average being 4 to 6 inches, the more you will have to raise the motor. The nice thing about switching to a 4 blade prop is that it will stay hooked up at elevated engine heights where a 3 blade will not. In turn, raising the motor will add RPM, allowing you to run a taller pitch prop and see a higher top speed by up to 3 mph. For reference, if your goal is to hit 64 mph, you would need to spin a 23.5 pitch prop to 5750 RPM. A jack plate could get you there but it will change the handling characteristics of your boat and you may need to change prop styles again.

      Nick

  9. Hi SCOTT –
    I drive a Lund GL219ProV with a 350 Verado. Currently run a Bravo1 LT 22 pitch. WOT revs at 5950. Top end 60 – 62. Close encounter with a rock at slow speed. I’m thinking about a new prop instead of rebuilding the old one. Any suggestions? Thanks.

    1. Sandy,
      You can either stay with the 22″ pitch or drop down to the 21″ pitch Bravo I LT increasing 150 RPM. The 6100 to 6200 is the sweet spot for the motor but it’s hard to say if you’ll hit the same speed and possibly come in at 59 – 60 mph.
      Scott

  10. Hi scott,
    I have a couple questions. I have a Merc 115 pro xs on a Ranger 1782 and I am reaching 6000 rpms with the lazer 2 in 19 pitch but only running 37 mph, I switch to a power tech 17 and hit the same rpms but move about 40 mph, I have a 6 inch jack plate and yet I still cant reach 6300 rpms either, got any suggestions?

    1. Jay,
      If you have the new 115 XS with a 2.07 gear ratio something isn’t right. Plugging your numbers into the Prop Slip calculator 19″ pitch 2.07 gears, 6000 rpm, 37 mph give us 29% slip when it should be down around 10% for your boat/engine/prop combination. Even the other prop has 14% slip. Slip can occur either the engine to high on the transom (not enough prop in the water) or to deep (the gearcase and midsection are causing too much drag). As a rule, your AV plate should be 1.5″ to 2″ above boat bottom.
      Let me know what your current set up is.
      Scott

      1. Scott, So at the start of the AV plate at the front side of the motor its 1.5 ” and as the board runs along it goes to 1″ till it hits in the AV plate on the back of the motor, which I contribute to the transom angle, but other then that its right there. The motor was way lower before and its all raised with the jack plate now but yeah, I just keep running into a way here.

        Jay

          1. Jay,
            It sounds like your are having to use trim and engine height more than you should to achieve higher rpms, causing very high propeller slip. A larger diameter prop could remedy your situation. Consider the 17 pitch Tempest Plus. Its 14.625 inch diameter should keep you hooked up, and the lower pitch will get you into your peak power range.

            Nick

        1. Jay,
          Sorry I missed that you have a jack plate. With a jack plate, you can go higher than 1.5″. Try raising the engine .5″ at a time to 2.5″. Continue the .5″ increase to possibly 3.5″. Monitor the rpm and speed along with how the prop stays hooked up. There’s a point where the prop will not grab as you increase speed. At that point; lower the engine to the last position. I wish I could give you that perfect height but only you can do that with testing.
          Scott

    1. Jay,
      Thanks for the data of the 17″ pitch Spitefire, my mistake referencing the Tempest I was thinking you had the CT gearcase. The 115 Pro XS only comes with the standard case, sorry about that! Running your slip number using the 17″ Spitefire it looks like it’s going to be tough to beat. To get more rpm dropping down to the 15 Spitefire would increase rpm to 5900 but the speed would drop 2 mph. If you’re okay with the hole shot I think you’re there with the 17″.
      Scott

  11. Hey Scott,
    I am Currently running the 17 pitch spitfire x7 and hitting only 5600 rpms and roughly 38 to 39 mph. Just for more information.

    Jay

  12. Greetings Scott. I have a new Crownline 264R that weighs approx. 7K lbs with the 6.2L 300 HP Mercruiser. It has so much torque that it blows the props out about 1-2 seconds after hitting it. Once close to plane they grab again. Bravo III, stamp on rear prop is 14.3 X 21 P RH. I’m guessing stock props aren’t cupped. Where should I start getting that expensive torque to the ground – I mean water? Thanks. John

        1. John,

          Do you know what you are getting for top end speed and RPM? Also, what speed and RPM do you cruise at? This will help us with pitch selection. Our Mercury Racing Bravo Three XR propellers have much more cup than the standard Mercury counterparts, this could alleviate your problems with planing.

          Nick

          1. Thanks Nick. Top end is about 44-45 at around 5400 RPM. I think it is turning about 4000 at 25 MPH. (I would prefer to cruise around 30 MPH). The engine seems to have so much torque that it is blowing out the props for a few seconds while getting up on plane. I rechecked the boat weight and it is more like 7,600 lbs dry. Can you elaborate on why the XR props with more cup might help improve this? Thank you.

          2. John,

            When you look at your current props, there will be almost no cup in the trailing edge. Our Mercury Racing Bravo Three XR props have massive amounts of cup, which helps to eliminate both the cavitation you are experiencing during hole shot and the very high slip rates through the mid range. With 21 pitch Bravo Three XR props, you can expect better holeshot, a gain of 3-4 mph at your mid range cruising rpm of 4000, but you may lose about 1 mph on top end.

            Nick

    1. Nick/Scott – per our conversation above I am in the market for a set of Bravo III XR’s. My current rear prop is stamped 14.3 X 21 RH. Don’t know what front prop is stamped. As I look on your website for a set of 14.3 X 21P XR’s I don’t see any. Only 15″ and 16″. You recommended a 3-blade set. Your thoughts please? Thank you!

      1. John,

        The XR props are a four blade then a three blade, 21 pitch. This configuration combined with the added cup offers the greatest reduction in cavitation. We only offer one diameter. As we discussed, you would be looking at improved hole shot and mid range efficiency but you may lose a mph on top end.

        Nick

        1. Nick can you confirm that this is the pair of XR’s you are talking about for my boat? I think my current rear stock prop is 14.3″ diameter. Thanks!

          21″ 16″ 4 LEFT 8M0073458
          21″ 15″ 3 RIGHT 8M0073459

          1. John,

            The Bravo Three XR 21 pitch are 842939L70 and 842940L70. The numbers you listed are for the 22 pitch.

            Nick

  13. 2 more questions Nick:

    Do you recommend one 4-blade and one 3-blade prop, or 2 4-blade props?

    Asking for a friend who just got a 24′ Four Winns with same 6.2L 300 HP Mercruiser. He’d like to know if he can get his stock Bravo III props reworked and have cup added.

    Appreciate your willingness to share your expertise. I see a new set of XR’s in my future in the Spring.

    1. John,

      Having a three blade propeller in the front helps reduce cavitation, along with the Bravo Three XR’s additional cup in the trailing edge. Without these additions, cavitation burn can be a big problem on higher horsepower setups, to the point that pitting develops very quickly on these props.

      Nick

  14. I have an Everglades 360 lxc with trip Yamaha 350s. 19 /15.25 inch on outside engines and 21 pitch middle. The boat runs 58 mph at 6000 rpms. I’m hitting my rev limiters with 4 bars of trim. Would changing my pitch to 23 on all engines gain me much more top end speed? Hole shot not is increadible! Thanks for your advise.

    1. Hays,

      I think the staggered pitch setup is working well for you. You can consider going with 21 pitch on the outside and 23 pitch on the inside. Expect to pick up 2-3 mph at 5800 rpm. If you are not happy with hole shot, stepping up in pitch will actually make it worse. It takes the engines longer to spin up a taller pitch prop. If you are looking for a Mercury Racing propeller, we offer the Bravo I FS for great planing performance and top end speed.

      Nick

        1. Hays,

          Which style Yamaha prop are you running? I really can’t say how a Yamaha prop compares to a Mercury in terms of pitch and performance. Typically in an aplication like yours, the Bravo I FS provides more bow lift, thus improving your angle of attatck and requiring less trim at wide open throttle.

          Nick

  15. I have an Allison Grandsport with a 300XS 1.62 Sporty on it. I am running a 32 X 14.5 Yamaha Drag 4 copy. I am running 2 negative shim plates on my Hydraulic jack plate, to help holeshot. I seem to be having a lot of slip at top end, 6300 RPM at 92 MPH GPS and the hole shot is slower than expected with a lot of surging. With my old 2.5 225 Promax I would get 95 MPH GPS with a 30″ Chopper II. Would I be better off with a 32 x 15 Merc 5 blade?

    BTW I love the 300XS which idles like a 4-stroke and gets twice the gas mileage of my 2.5. In a year or two I might switch to a 300R when a Sporty 1.62 becomes available.

    1. James,

      Glad to hear you are happy with the repower, sounds like an awesome setup. You may think about reducing setback to improve center of gravity, going from a 2.5 to a 300xs, you are hanging more weight off the back. You will probably want to be around 4 inches of setback plus your wedges. Have you ever tried a Pro Max? A 32 Pro Max should land you over 100 mph. Our 5 blade MAX5 will generate too much stern lift for your setup.

      Nick

  16. Nick,
    I have removed everything except the C&M/Allison hydraulic jackplate [6″ setback]. I will try a 32 Promax and see how it works.
    Thanks for the good advice.
    JR

  17. Hi. Wondering if Scott or someone else at Mercury can help me with a prop question. I have a Recon 985 boat with an Optimax 200 running a Tempest Plus 21p prop. Motor is mounted about 3/4″ above boat bottom. WOT RPM is 5650 -5700 and top speed is 55 mph. Hole shot is very good, as is overall performance. However, rough water ride and handling could be better. I would like to increase top speed and acceleration and improve handling while at least maintaining hole shot. Should I raise motor height? Would the Bravo FS be a good prop? If so, what pitch?

    1. Jason,

      If your cav plate is only 3/4″ above boat bottom, you will want to consider raising your engine at least one hole. Average engine height on a boat like yours is about 2.25″ above. By both raising the engine one hole and switching to the Bravo I XS, you can expect better handling and an increase in top speed by 2-3 mph. Consider the 22 pitch Bravo I XS, that will give you the same RPM at your current engine height as the 21 Tempest. You will gain another 150 rpm per hole you raise the engine. The Bravo will stay hooked up much better and maintain performance at higher engine heights than the Tempest. The Bravo XS is our two-stroke version of the Bravo FS, it has four more vent holes for planing performance.

      Nick

  18. Hey Scott or Nick, I’ve have a 1998 Norris Craft 2000 xldv with a new 250 Pro xs 4 stroke. I’m having prop issues. I used to run a 2000 225 Pro max. With 15 inches of setback. I’m running the old 25p trophy. Hole shot is not great boat nose straight in air. Wot is 82mph at 6350. Just looking to have a good hole shot with a nice wot. Those numbers are with fully loaded boat and gas, and livewells. 12inches of setback now.

    1. Robert,

      Would love to help. Your data sounds a little bit off to me. The new 250 Pro XS has a rev limiter at 6200. If we plug in your data and a 1.75 gear ratio, we get 4% slip, which is not feasible with a Trophy. Can you double check rpm at WOT and verify speed?

      Nick

  19. 2009 triton 20×3 225 merc optimax center of prop shaft to bottom of hull 4.25″ 6″ manual jack plate 25 tempest plus 25 gallons gas 2 adults, tackle, batteries etc 575 lbs trimmed out 70 to 72 mph pending on wind 5650 rpm average. Hole shot is decent could be better. I’m more use to my other boat I had 250 xs on my 20′ ranger with the bravo 1 xs 27, hole shot top speed very good lift. What is a good prop for the triton to stay hooked up in curves? Would a Bravo 25 or a 4 blade fury 24 be better than what I have now? Thanks in advance.

    1. Ed,

      When plugging your data into our slip calculator, I only get 7% slip. That is a phenomenal number for a Tempest. I wouldn’t change a thing.

      Nick

      1. OK thanks prop was worked by a local guy at Acadiana Propeller and Fabrication in Lafayette, Louisiana. In your opinion should I try a 4 blade? And if so which one. Thanks

        1. Ed,

          I don’t see a Bravo I XS being any better on top end than your Tempest. However, it could offer better hole shot and ride quality, especially in rough water. You would want a 26 pitch Bravo I XS if you decide to go down that route. Most guys will also have the raise their engine up one hole or 3/4″ to get the most out of running a four blade.

          Nick

  20. Nick,

    I have an Optimax 200 mounted with cav plate 3/4″ above boat bottom. I’m currently running a 21 pitch Tempest Plus and achieving 5650 – 5700 RPM at WOT. I want to raise motor 2 holes, which should result in cav plate being 2.25″ above boat bottom, and then switch to Bravo 1 XS prop. Should I go with a 22″ or 23″ inch pitch on the Bravo 1 XS?

    1. Jason,

      For two holes, you will want to consider the 23 pitch. You will be gaining around 300 RPM from raising your engine and you do not want to gain any RPM at WOT since your limiter is at 5750.

      Nick

  21. Nick,

    By raising the motor 2 holes and switching to a 23 pitch Bravo 1 XS from the 21 Tempest, what are the overall changes in performance I should expect?

    1. Jason,

      Not only can you expect to gain about 5 mph on top end speed, but your handling will be greatly improved. The fourth blade helps to improve ride quality, especially in rough conditions. You will also have smoother planing and be able to stay on plane at lower speeds.

      Nick

  22. Nick,

    Thanks for the info!

    Just for knowledge sake, without any change in motor height mounting position, what generally happens to RPM when switching from the 3 blade Tempest Plus to the 4 blade Bravo 1 XS? Mercury’s general recommendation calls for going up one pitch when switching from Tempest to Bravo 1 XS. So does this mean a 22 pitch Bravo 1 would produce the same RPM as a 21 pitch Tempest Plus if no other changes were made other then the prop change? Because normally going up in pitch results in lower RPM.

    Lastly, at my current motor height, my hole shot is awesome with the Tempest. Will raising the motor 2 holes and going to the 23 Bravo 1 XS negatively affect my hole shot? If so, could the hole shot be restored by opening up some vent holes in the prop?

    Thanks again for all your help!

    1. Jason,

      You’re spot on, the Tempest usually runs about one inch of pitch taller than the Bravo family. By raising your engine one hole, you can gain as much RPM as dropping an inch of pitch, or 100-150 RPM. Your hole shot may decrease slightly, but with the vent holes open I think you will still be happy with it.

      Nick

  23. 2008 Triton TR20XHP, 2018 Mercury 250 pro xs, lower gear 1.75. 10″ manual Jack plate with hole shot plate. Merc monitor for gauge readout.
    I was running a 25p fury 3 blade at 2.5 PTP below getting 6100 rpms @ 71 mph GPS.

    Swapped to a USED 26p fury 3 blade and RPMs dropped to 5350 and speed increased to 73 mph. (These numbers make me think the prop has been modified, but I’m not sure.)
    Adjusted the the JP up .25 and now get 5500 rpms at 75.6 mph. WOT water pressure is about 20 psi. Although this setup feels good, I don’t like the RPM at the minimum 5500 rpm range. Should I consider another prop? If so, what?

    Other 20XHP owners tell me to run a 27p trophy plus.

    1. John,

      It does sound like the prop has been worked on, perhaps has cup added to it. For stepping up one inch of pitch, you should have seen a drop of 200 RPM. For top end speed, I wouldn’t change a thing. 5500 is at the bottom end of your peak operating range. If hole shot is still decent with the taller pitch prop, I think you have it dialed in quite nicely.

      Nick

      1. i have a99 ranger 461 that i just repowered with a merc 4 stroke150 i a running a fury 4 i am setting 2.5 inches under with prop shaft i have 8 inch manual jack plate it does great with just me but tournament load it struggles to get on planr with just me in boat it turnes 5800 at 60 mph gps

        1. Donald,

          Looks like your light load setup is perfect. What RPM are you getting at WOT with your heavy load?

          Nick

          1. Donald,

            If you would like a prop for your heavier loads, consider the 23.5 pitch Bravo I FS. It will bring your RPM back up to around 5700.

            Nick

          2. thanks nick can i have some of the cup taken out of the fury prop an do you think it would help

          3. Donald,

            I wouldn’t alter the stock Fury, it is performing great for you on light loads.

            Nick

  24. Mercury racing used to make a 28P Tempest Plus.

    What did the 28P start life as? Was it a 27P, with extra cup?

      1. Nick,
        What about a 29P Tempest?

        All Tempest Plus props begin life as ODD pitches then ?

        All Bravo1 XS props begin life as EVEN pitches?

        Thanks for your time!

        1. Keith,

          Racing only went up to a 28 pitch, currently Mercury Propellers offers up to a 27 pitch.

          Yes Bravos are even, every propeller family is a little different.

          Nick

  25. Nick/Scott. Thank you for your recommendation above which is dated 1-9-18. You recommended a set of 21P XR’s for my Bravo 3 on a new Crownline 264CR. A heavy boat with 6.2L engine. It just blows out the stock 21 pitch props on hole shot.

    I see you have a new 21.5 pitch XR. Are there conditions where you recommend going from a 21 XR to this new 21.5? Would just like to know before ordering a set of 21’s. Thanks! John

    1. John,

      The half inch pitch increments are all about dialing in RPM for peak performance. For example, if someone wanted to drop 250 RPM and they are running 23 pitch props, we would recommend the 21.5 pitch.

      Nick

  26. Prop pitch per rpm

    Is there a calculation to do it

    Currently running a 1995 200 xri efi with a 23’ powertech tr04 4 blade
    5500 rom wot at 62/63 mph

    Want to utilize the full power band up to 5850 rpm

    If i pitch down to a 22’ tro4 i was told i will gain 400 rpm due to prop rpm % formula

    The standard rule that most say every 1” of pitch gains or decreases rpm by 150-200 rpm. I was told that is not the correct way to look at it and guess

    Please advise

    1. Tom,

      Apples to apples comparison, brand new prop to brand new prop, 150 RPM is the most common change for one inch of pitch. If the original prop has been fixed or tweaked at some point in its life, of course that has to be taken into consideration. I can give you loads of data for Merc props, but you might want to call Powertech to verify.

      Nick

  27. nick i found the problem i wass going down with motor i started going up an it works great i just have to play with it to find happy medium

  28. nick,
    im still trying to get the right prop for my new 300R 1.75;1 hd sportmaster. the 30 promax R runs out fine but hole shot is almost non existant
    my boat is 21 Trick tunnel about 1100-1250# the prior set up was
    300XS 1.62;1 hd sportmaster with 21 signature 4 blade 14.75 hole shot was just ok, boat ran 100
    also with the added torque of the 300R it hooks harder left with the promax
    saw randy with the 21 liberator at 112mph with 5blade 34pitch CNC clever
    hole shot and top end were superb
    what are your thoughts on my set up?

    1. Stanley,

      There really is no substitute for the Outboard CNC if you are willing to spend the money. He ran a 15×34 15 degree rake I believe. Hole shot is very good, small cavitation, but the slip stays low through the entire RPM range for increased speed, fuel economy, and responsiveness.

      Nick

  29. Nick

    Looking for some advice or direction with the set-up on my boat. It is a Nitro Z19 Sport (fish&ski) with a 2018 200 Pro XS Optimax (1.75:1 lower unit), current pad to prop is 3 3/4″ with engine bolted to the transom (no jack plate) and a factory Tempest Plus 22 pitch prop. I believe it has the medium hole PVS plugs installed. Normal people load is about 450 pounds, boat will hold 26 gallons of fuel.

    The boat has a great holeshot and will pull tubes with no problem. The issue is on the top end I can not reach max rpm while trimming the boat out. I have Mercury’s vessel view and about 5450 ~ 5500 rpm is all I can get to without the boat getting extremely light and feels like its skating around. It’s not a chine walk that I have experienced with other boats, it feels like the back of the boat is on ice. It’s like a switch gets flipped right at that rpm range if I touch the trim any more. MPH per vessel view at those rpm is 58~59mph. It’s not throwing a roost, so I don’t feel like it is over trimmed.

    I will be adding a 6″ manual jack plate to adjust the engine height.

    I appreciate any help you can provide.

    thanks

    1. Jason,

      The Tempest is hooked up very well for you. For top end speed, it will be hard to beat. For improved hole shot and a slightly more stable right, consider the Bravo I XS in either a 22 or 23 pitch depending on how much throttle you have left at your 5500 measurement with the Tempest. A 23 pitch Bravo I XS will get you similar RPM to a 22 pitch Tempest at WOT.

      Nick

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