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Variable pitch prop

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  • Variable pitch prop

    Just a curious question. Why don't they make a variable pitch prop? Variable props on airplanes have been used for years. It just seems so logical
    First they told me practice makes perfect...
    Then they told me nobody is perfect...
    So now I've stopped practicing.

  • #2
    Re: Variable pitch prop

    Google: Land and Sea Torque Shift

    Read away to your heart's content. That was the most viable attempt at producing one. Depending on who you talk to, it generally worked well. The company either folded or discontinued it...not sure who owns the patent or if there even was one.

    For that matter, why make a shifting prop when one of the big manufacturers could take the world by storm by offering a shifting gearcase...or better yet a CVT gearcase?

    Why hasn't anyone taken one of these concepts and figured it out with today's modern technology? Either in the prop or within the gearcase? I haven't the foggiest. High price, low demand, complex shifting mechanisms, lack of reliablity? All speculation on my part...


    • #3
      Re: Variable pitch prop

      They do. Not too uncommon on larger (work) boats with a straight shaft. Older (commercial) fishing vessels also had them, in some cases even without a transmission. Once you started the engine, the prop started turning (these were very slow rpm diesel or kerosene engines).

      You can even buy propellers for "our" size boats with variable pitch (http://www.piranhapropellers.com/).
      You keep the hub, just change the set of blades to a new pitch. Think they are made out of composite and there are many posts here about their benefits and potential drawbacks. Main "purpose" can be that it is easier/cheaper to replace in case you hit something, although these props might be "no better" than an aluminum prop, and you can possibly buy two alu props for the price of one composite.

      All that said, have not tested. Read posts from those who have tried them (and are running them).


      • #4
        Re: Variable pitch prop

        There is such a thing as a transmission; used in very high power sport boats. http://www.go-fast.com/cyborg_transmission.htm

        For "normal" boats, it's just too much complexity/cost/weight to be worthwhile, at least that's my assumption.


        • #5
          Re: Variable pitch prop

          I just purchased a Quicksilver Power2 Prop on E-bay for $150.00. Absolutely amazed at the performance of this prop. Very easy to adjust. It makes my 3.7 liter Mercruiser launch like a V8. My particular prop starts at a 13p and shifts to a 19p. Today I pulled my wife up on a slalom ski without any issue. My boat is a 1987 21 foot Galaxy open Bow. Worth every penny that I paid for it and then some.


          • #6
            Re: Variable pitch prop

            I think the best shot at a "shiftable" outboard gearcase was the one Merc had but never really produced. It was on a motor called Duces High. On the hood were 4 cards, all 2s, 1 heart, 1 spade, 1 diamond and 1 club. 2 hundred hp, 2 props, 2 speed, 2 cool. It had a dual prop gearcase and at low speeds only 1 prop kicked in. As the rpm increased the second prop kicked in.


            • #7
              Re: Variable pitch prop

              Pro-pulse at western marine makes a manual adjust prop.
              You have to take the prop off adjust then re install.
              I have run for 6 yrs with a merc 140hp I/O


              • #8
                Re: Variable pitch prop

                I just picked this one up. It's made by Lesnor-Maehr Marine Co. It's a OBM-1. Have not tried it. On a 13.5 foot wooden boat and a 33 pony Ski-Twin it seems I should be able to dial up the pitch and get some good speed out of the craft.

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                • #9
                  Re: Variable pitch prop

                  Years ago a neighbor had on of those props He felt that an actual prop change was more effective but the adjustable prop was convenient.
                  Keep in mind when selecting a pitch that your motor needs to be able to rev freely within its rpm rating.
                  With a light load its' wot rpm needs to be near the maximum rating.
                  Its possible that you might be able to adjust it closer to the low end of the rpm range for the best speed.
                  But hole shot and load carrying will suffer.Of course you can adjust it for best load setting.
                  The motor is rated for 4000-5000 rpm. HP is rated at 4500.
                  Raising the motor on the transom can add a couple of mph in ideal conditions. And of course
                  careful adjustment of the trim settings.


                  • #10
                    Re: Variable pitch prop

                    I never thought the composite props were an answer. The pitch was adjustable, but had to be adjusted manually. Aluminum pros were stronger, and replacement parts for the composite props were too expensive, given their fragile nature.

                    I asked an old, grizzled Merc Dealer (now deceased) about the Merc Power2 props. It was his opinion that at $500 to purchase(expensive in those days, not so much now), and their chance to be damaged in normal useage, it just wasn't worth it to buy.


                    • #11
                      Re: Variable pitch prop

                      In the very early outboards there was at least one that had a variable pitch setup controlled while the motor was in operation.
                      You could actually vary the pitch and go into reverse.


                      • #12
                        Re: Variable pitch prop

                        AeroStar Marine still make variable pitch props. They are not truly variable, rather they are two-speed props. They are a three-blade stainless prop that automatically shifts between high and low ratio depending on load. You select the high pitch to match the boat and the low pitch will be 6" less - e.g. a 21" prop will be 21" high and 15" low. There is an adjustment wheel on the hub that can be turned by hand (without tools) to adjust the sensitivity of the change point - at the extreme ends of the adjustment the prop will stay either in high or low!

                        The results are quite spectacular, launching a boat onto the plane like nothing else but the price is a little eye-watering. I had a Maxum 1900 SR3 fitted with a Mercruiser 4.3L MPI 220hp motor and Alpha drive. The standard 19" 4-blade Vensura prop would get the boat from 0-30mph in about 7.5 seconds. A 19" 5-blade High Five prop would knock half a second off that, at about 7.0 seconds but a 20" AeroStar would do it in 5.8 seconds, whilst hitting a higher top speed, running lower revs and getting about 0.5mpg better economy across the cruising range.

                        The obvious drawback is the cost but the blades were individually replaceable so repairs would be easy and, also, a spare set of blades takes up much less space on a small boat than a spare prop. The same could be achieved with a two-speed transmission and it seems odd that no-one makes one. Look through the prop section of the forum and there are no end of posts from owners who want more out of the hole performance but don't want to sacrifice top speed or fuel economy - simply not possible with a single fixed pitch prop. Whilst cost, again, would be an issue, surely this could at least be offset by being able to buy a more modestly powered boat. Most owners don't need absolute top speed and would be content with fast planing and good cruising economy - both achievable aims with the combination of a modestly sized motor and a two-speed / CVT transmission.


                        • #13
                          Re: Variable pitch prop

                          One place I could see a variable pitch or shifting prop being huge would be a twin engine boat where one engine won't plane it with a standard prop but would with a much lower pitch.... if one failed you could limp home at 25 mph instead of 6 mph

                          But, where are the reevets?
                          1981 Wellcraft V-20 CC Fisherman (FREE BOAT)
                          1989 Wellcraft Monte Carlo 28(Build thread here)
                          1992 Hotsports Jet'n'Cat Yam 701 WR3 drivetrain "SS George Washington"
                          90's Yamaha WRIII and a pair of 95 Kawasaki ZXI-900's
                          Fresh clean cheap oil is better then old dirty expensive oil any day


                          • #14
                            Re: Variable pitch prop

                            Very cool centar. A variable "on the fly" prop would be way cool on the old timer, yet it seems something like this is unobtainable for '60's Evinrudes. Top speed with the mighty 15 pony was 21 on this Droid g.p.s. Steping up to 33 ponys and a mini jack plate this year. Manually adjusting pitch for canal crusing and top speeding.... Can't wait.


                            • #15
                              Re: Variable pitch prop

                              Originally posted by TRAILN View Post
                              Just a curious question. Why don't they make a variable pitch prop? Variable props on airplanes have been used for years. It just seems so logical
                              they do! my dad had a baja boat. with a 4 cylinder i/o.... his friend had a boat with a v8...... so.. my dad is smart and he got a variable pitch prop, you change the pitch of the prop by adjusting the trim...... real cool..... no problems with it..... so the baja islander 180? late 1980's....... would pull tube, skiers, go about 50......why do they not have these anymore??? it was trouble free, and my dad's friend with the v8 only went 5 mph faster,,,,,, the baja had a small tank... the other one had a 70 or hundred gallon tank hehe..... i found this forum trying to show my friends wife how you can make a little do a lot..... now i look like an ***... i will find out the prop though..... we finally got a nice boat with v8 he didnt get the prop with it, i dunno why, because it seems it never happened,,,,, 89 88 87 86 good years!!! but now you know they made (make) variable pitch props changed by trim, to make the lil baja keep up with the v8!