New SS prop

[kheidebrecht]

I am going to buy a new SS prop this spring and wanted to see if I could get some specific advice from the knowledgable guys here.<br /><br />Data:<br />2005 Bennington 2575RL (25 ft)<br /> - Performance Pkg - 3 logs, lifting strakes, etc.<br />Mercury Optimax 225<br />Prop: Merc Alpha 4 - 14 1/2" x 18", 4 blade Alum (Merc #834852A45)<br /><br />Current Performance: Great hole shot (pop skiers up easily), Top Speed 37mph, RPM@WOT = 5200rpm<br />Uses: Family fun, water sports (tubing, skiing, etc.)<br /><br />Problem/Issue: Too low in WOT range (5000 - 5750rpm). I want to upgrade to a SS prop and have narrowed it down to several options but I have some detailed questions.<br /><br />Potential Props: (all Mercury)<br />Mirage Plus - 15 1/2 x 17, 15 3/8 x 18, 15 1/4 x 19<br />Rev 4 - 14 5/8 x 17, 14 4/8 x 19<br />Enertia - 14 2/3 x 17 thur 14 1/4 to 20<br /><br />Bennington tested Rev 4 19" @ 45.5mph @ 5300rpm, but recommended the Mirage Plus, 19" for light loads and max speed and 17" for a loaded boat and better acceleration. They also mentioned there would be slight compromise in acceleration and top speed from the Rev 4. I am also considering the new Eneria prop coming out this spring.<br /><br />I know that a 1" change in pitch changes rpm by 200rpm in the opposite direction (increase pitch - decrease rpm). Do you get a similar change in rpm with a change in diameter? Will a SS prop of the same dimensions spin faster than aluminum? Will a 3 blade spin faster than 4 blade of the same pitch and diameter?<br /><br />I am looking for an increase in top speed, but more importantly, I want to get up to the top of WOT (5750rpm). My ultimate goal is to maintain about 36mph for slalom skiing and reduce prop blow out in the corners (yes, I do trim down in the corners).<br /><br />Thanks for your advice and expertise.

 

[WillyBWright]

Re: New SS prop

Welcome to iboats. <br /><br />The Mirage prop is my first choice. It's made to lift the back of stern drives. Your toon would have similar characteristics. You might also consider a 4-blade Alpha prop. It'd be a whole lot cheaper and it's also designed to provide stern lift. They come in even number pitches. I'd try the 16 for heavy loads and the 18 for speed. That motor will run 6000rpms and like it.

 

[kheidebrecht]

Re: New SS prop

Thanks for the input Willy. I am currently running an Alpha 4 18". I want to change to SS and I'm just not sure whether a 3 or 4 blade is the best for my specific situation.<br /><br />"Current Performance: Great hole shot (pop skiers up easily), Top Speed 37mph, RPM@WOT = 5200rpm"<br />"Uses: Family fun, water sports (tubing, skiing, etc.)"<br /><br />Price is not a huge issue, I have resigned myself to spending $500 - $600. I do think that the Mirage would be a great choice, I am just not sure of all of the differences in performance from a 4 BLADE ALUMINUM to 3 BLADE SS. I understand the 200rpm change with 1" change in pitch but I am not clear on the other variables noted.<br /><br />Thanks again, I am confident from reading all of the other posts on this site that I will get some solid advice.

 

[Texasmark]

Re: New SS prop

Something that I didn't see in Willie's reply was features of the SS.<br /><br />Blades don't bend, are thinner for less drag resulting in higher performance over comparable pitched alum. Blade tips are cupped which helps to reduce cavitation under load and in turns.<br /><br />I think it's equivalent to 2" of pitch change. So, since you want to up your rpm's you are going to have to go down at least 2" with your ss from your current prop. Now, with the ss running more efficient you may then be able to bring your rpm's up too. Otherwise it is drop more pitch to accomplish this; back to your 200 rpm's per inch.<br /><br />Best thing to do is to get your dealer to sell you a prop with a swap out option so that if it doesn't do what you want you can exchange it.<br /><br /> If you don't ding it up and return it after the first outing I don't know why they wouldn't go for that.<br /><br />Mercury and Michigan wheel both have web sites that help explain these things although some folks on here aren't real happy with the sites.<br /><br />Other thing is porting. Don't know if the recommended props are ported or not, but all will tell you that if you want to get up fast, get a ported prop. It lets air out across the blades during the hole shot, resulting in deliberate cavitation that gradually disappears as speed increases. <br /><br />This gets your rpm's up rapidly in the hole causing hp to increase rapidly causing you to get out fast. <br /><br />Once you get on top, water pressure essentially covers up the hole and all the exhaust goes out the rear like a normal prop.<br /><br />I had one on a Ranger and once she got rolling and the air cleared out it was just like overdrive. The rpm's dropped and the boat speed jumped in a step fasion. Don't know if you boat is too heavy to do that or not but it worked for me and was so cool.<br /><br />Sorry for the long reply. Fingers tired; signing off.<br /><br />Mark

 

[kheidebrecht]

Re: New SS prop

Mark,<br /><br />Thanks for the info. Just to make sure I understand correctly, a SS prop of the same blade number (4 blade) and same pitch (18") will lower rpm by approx 400rpm compared to aluminum. Therefore, to get the same rpm (5200rpm) I need to drop to a SS 4 blade 16" pitch from Alum 4 blade 18". To get my rpm up to the top of WOT of 5750, I would then need to drop to 15" pitch or maybe even 14" pitch. Am I thinking correctly?<br /><br />Do you know what difference going from a 4 blade prop to a 3 blade has on rpm? I am guessing it should increase rmp, but how much?<br /><br />Next, does diameter affect rpm in a significant way? Again, I assume that smaller diameter should increase rmp, but how much?<br /><br />I will be checking with my local marina about buying a prop with a swap out option. Thanks for the advice.

 

[Silvertip]

Re: New SS prop

Look at engine height before you begin spending money on props. Where is the AV plate in relation to the bottom of the hull. As a minimum it should be flush to one inch above. Less lower unit in the water = less drag = higher revs = higher speeds. You need to keep an eye on water pressure though so don't go too high. Secondly, of all the props you listed most have MORE pitch than your current prop so using any of them will LOWER engine rpm. Stainless props of same diamter and pitch will likely drop RPM somewhat as well. Four blade over three blade will drop rpm. You definitely need to work with a shop that can help you sort this out. But get engine height set right with the existing prop. You may be surprised that you already have a great prop.

 

[Texasmark]

Re: New SS prop

Kenny is your prop pro as he tests them all the time......"Walleyehed".<br /><br />Manufacturer's data indicates that since the ss is more efficient, it will produce more thrust at a given rpm which has to be factored into the rpm curve; hence the reasoning for having to drop your pitch if you want to keep the load on the engine (WOT rpm's) in the correct area....at the top of the recommended range under normal load measured atWOT. Things making it more efficient I indicated in my reply.<br /><br />Having run OEM aluminums and then ss I totally agree with their data.<br /><br />Never ran a 4 so I can't say. Merc says the fewer the blades, the more the efficiency....cause of water turbulence generated by multiple blades adds to "slip".<br /><br />I think that 4-5 blade props came about with the bassing community running their mils half out of the water to reduce lower unit drag and get more speed for a given setup. More blades gives them more water contact and when you're going that fast, the water moves by fast enough that you don't have to worry about cavitation caused by multiple blades (opinion).<br /><br />The larger, heavier, and slower the boat the larger the dia and lower the pitch. Converse is true.<br /><br />In selecting props of a given series, you will notice slight diameter changes. I think this is just because the blade area is kept pretty much constant and as the pitch increases, the blade essentially lays down on the hub reducing the dia. I think pitch has a more dramatic impact than minor changes in dia.<br /><br />Best bet is as you say. Get the guy to loan you a prop, run it out and test it and come back for another....till you get what you need.<br /><br />Mark

 

[kheidebrecht]

Re: New SS prop

Thanks for the additional info. <br /><br />Upinsmoke...<br />I will check the engine height as recommended and make sure that it is "flush to one inch above the bottom of the hull" OR in my case the bottom of my center pontoon.<br /><br />Mark...<br />Makes sense that ss is more efficient than alum. with thinner blades and less flex. As far as "The larger, heavier, and slower the boat the larger the dia and lower the pitch"...well a pontoon is not a "perfomance" boat so a lower pitch makes sense and the larger diameter of the Mirage Plus completes the equation.<br /><br />I am leaning toward 3 blade SS props at this point, but may include one 4 blade.<br />Current Prop - Alpha 4 - 14 1/2 x 18" (Alum)<br />1st Test - Rev 4 - 14 5/8 x 17"<br />2nd Test - Mirage Plus 15 1/2 x 17" OR the next one down is a 15 3/4 x 15"<br />3rd Test - NEW Enertia - 14.5 x 18", 14.65 x 17", 14.82 x 16" and potentially even 15.0 x 15"<br /><br />Results I am looking for....THE prop that will run as close to 5750rpm at WOT. Any reason I should look at any props other than Mercury? I like the idea of the Flo-Torq II system, several other brands I have looked at have one piece construction and I don't like the idea of potentially having to rebuild the bottom of my new 225 Opti. <br /><br />From the info that I have found on the Enertia, it sounds like better all around performance with "Better acceleration and top speed" This may end up being my choice once it is released this Spring. Maybe I can get through the Rev 4 and the Mirage Plus props by the time it is released.<br /><br />Walleyehed - any thoughts?<br /><br />Thanks again, I am trying to learn as much and as fast as I can. I know that my education will go a long way once I get out on the water and start testing a few props.

 

[walleyehed]

Re: New SS prop

3, or 4 blade in the same pitch, IF we have the same blade design, will usually drop about 100-150 going from alum to SS.<br />As for which prop to choose, I think testing is the only way to know....all 3 of the props you speak of are designed for heavy load with heavy rear-ends, so You're not shooting in the wrong direction, but be careful of limiting yourself to 1 manufacturer.

 

[kheidebrecht]

Re: New SS prop

Thanks Kenny,<br /><br />Any other specific manufacturers that you would suggest or recommend?<br />Additionally, any other specifics that you would recommend?<br /><br />Thanks

 

[walleyehed]

Re: New SS prop

Don't over-look the Solas Lexor..It's a Mirage replacement and it shows good numbers in comparison.<br />I've always been a fan of Turbo and always will for good reason, but there are many others out there that may provide an edge in one area or another, and lack in others...<br />A guy can get by with many props, but if you're like me, I always wondered...."is there one out there that might be better yet???"<br />It's very hard to give a recommendation for that one perfect prop when we really don't know how it will work with your style of not only boat, but "boating" as well.<br />If you're running on lakes where long runs in rough seas are not an issue, I think I would rule out the rev4, but if you run a heavy rig (loaded) and need lots a push,(not speed), keep the rev4 on the list....for sure if you're not running the max allowable HP.<br />Testing with many is the only true way to know.<br />You do want to stick with props designed for your application to narrow it down...such as a Laser or Tempest...not good choices for the rig you have

 

[kheidebrecht]

Re: New SS prop

Thanks for the info Kenny.<br /><br />I will definitely check out the Solas Lexor, I have seen them here at iboats. I will also look further at Turbo, I looked at them briefly after seeing you mention them on some other forums here but didn't know if they would be good for my application.<br /><br />Although I am fairly new to boating, I definitely have that perfectionist attitude like you, I want to find that "perfect" prop. I just want to narrow it down as much as possible before Spring gets here so I can ultimately enjoy boating and not fuss with changing props all season. I may be kidding myself, I may always be wondering, like you, about one that performs even better than the one I am currently running. Oh well, the "hassle" of boating is still better than the "joy" of work.<br /><br />Re: the Rev 4, we spend all our time boating on lakes near Kansas City... Perry, Stockton, Table Rock. We don't make long runs generally (maybe up to 5 miles) and generally fairly calm water. Boat weight fully loaded is approx. 4000 lbs. (boat, engine, 52 gal. gas, gear and family) I will definitely have to drop to the 17" with the Rev 4 to get the rpm up. My thoughts of changing to 3 blade SS would be to increase rpm #1 and if I can get some increase speed as well that would be great.<br /><br />Stay away from Laser and Tempest due to the high pitch? small diameter? blade design? or what?<br /><br />Thanks again.