Prophets of Props & Other Realities

[Dr. Dan]

;) O.K. So when I am totally bored, I play with the Bronson Speed Calculator & the other Speed Site.....Question: In determining a reasonably accurate Pitch Size ....based on the varieables given......how accurate are these Calculators? Are they close enough to make the purchase or do ya just get involved in an exchange program until ya get it right? :p

Why am I asking this? Hmmmmmmm?

Thanks in advance...

:cool: Doc

[Digger]

I dunno Dan but when you find out fill me in... I need to be sure when I buy since its x 2 :rolleyes:

[MOP]

Dan I think the best route is prop swapping, the calculators come close but can not take into consideration all the variables. There are a ton of posts showing the difference between props of the same pitch and general configuration! Bring a wrench smile a lot and buy beers for proper testing! :D

[Ranman]

Digger,

Last year Precision Propellers (Turbo) was at AOTH III. They had a van full of props for people to try out. I tested 3 or 4 wheels on my 18. Super nice people and a great product. Maybe if you bring Freedom to AOTH IV (you are coming AND bringing Freedom aren't you?) and the Turbo guys come again, you can try a few different wheels. This was a great experience for me.



Jenn says she'll only ride in a 26 or larger...;)

[Rootsy]

and i bet if you ask really nicely of the right people they'll bring a pair or two or three of whatever you want to try...
;)

[Digger]

Randy, I definitely will be coming with the boat.

Jen would be a welcome passenger! and any other pretty girls for that matter :)

...hey MOP, why does that lady keep touching herself down there?

[boldts]

Doc, Not sure what you've done or are planning to do except as I recall, you had thoughts of adding more HP to your 22. With my boat, I used my current prop that I had as a baseline to start from. I then used the calculator to plug in different size props. In my case, I was looking for speed.

I had a 23" Mirage turning 4500 RPMs and the boat porpoised like a dolphin until she was wide open. At that point she would settle down and was running 65 GPS. I also have the 1.36:1 drive gear which is different from most of the factory set-ups which are a 1.5:1 gear.

In theory, you gain about 200 RPMs for every 1" less of pitch you run. Since my boat was only turning 4500, I knew I could drop down at least 1" of pitch with my application. When I put a 22" pitch into the calculator, I also added 200 more RPMs to the equation just as a general rule. I found that the speed did increase even though I was turning less pitch. I then tried plugging in a 21" pitch and while the RPMs were now almost at 5000, I found that the speed according to the calculator was actually less than the 22" pitch prop.

At the advice of a couple of our GA members, I then used the Internet to find the best price on a 22" pitch Turbo I prop. www.turbo-props.com I tested it all by myself with a half a tank of fuel and to my surprise, the prop was right on. I was turning 4800 at 68 GPS. No porpoising at any speed and now because I could use the trim, even the RPMs were higher than I had used in the calculator. Just for kicks, I tried a 21" Turbo I last year at AOTH. RPMs went to almost 5100, but speed fell off back to a little over 65 GPS. I found that for my application, I had the best Turbo I prop I could run.

Best thing to do, is find a shop that will work with you. Especially if your putting more HP in and aren't exactly sure where to start. Most shops will exchange prop sizes if you pay the shipping. Of course you can't damage the prop either.

Just for everyone's information, with the 1.5:1 gear, most of the 22 Classics can run a 25" pitch on a stock engine with speeds in the mid 70s GPS. One other thing about a Turbo prop is that what you get out of the box will be the best you can buy. There is no need to now have the prop labbed. Think about that next time your shelling out dollars for a Mirage Plus prop and then spending hundreds more to have it labbed and tweaked. No, I do not work for Turbo, but I am more than happy to send people their way as they have a product that really works well at a price that can't be beat. At least on the 22 Classic.

[Rootsy]

saying turbo is the "best" really leaves a disheartening feeling in me after conversations with them and hydromotive (turbo makes hydro's props)... the tolerances they allow on rake, pitch, runout, etc are pretty loose in my opinion... compared to what i endure every day on plastic components... on investment cast parts they are holding whole degrees on rake, large tolerances on average pitch... i am holding TENTHS of millimeters and fractions of degrees on blowmolded parts... c'mon i knoooow they can do better than this... least for the prices they are charging... but i guess the extra mile in quality and manufacturing control would cut into the profit margins eh... :rolleyes:

[boldts]

Sorry Roots, I didn't mean to start a this prop is better than that prop forum. All I meant when I said it was the best you can get straight out of the box was that there is no need to now send the prop to a shop to spend hundreds more on fine tuning. Sure you can do that if you want, but it isn't needed unless your using the prop for racing applications.

I agree with you about the tolerances. I've seen it from a production standpoint of a company I worked for. We had an item that we built for sale at Sears. We built the same item with lesser quality parts for other stores to sell.

I would venture to guess that the same goes on in the prop industry. Since Turbo is selling 4 blade props, why would they make the same type of prop for another company to profit from? I would think like the case with Sears, that you would want to keep your best pieces to sell through your company not someone else's. The question is from a person wanting to buy a product is why spend $500 + on a prop to then turn around and spend 2 or $300 more to make it right? When a boater needs a new prop whether it be for a 5 HP engine or a 500 + HP rig, they should get a perfectly balanced, perfectly pitched, not out of round prop the first time, every time.

[smoothie]

Root, ever watch em "check" a prop,"pretty loose" is a good way to put it.BTW did you receive the drawings I sent ya?

[Rootsy]

Rick,

yes i received the drawings i just have to get em open and stuff... just been kinda busy... but it is on the list... THANK YOU VERY MUCH for those :)

Scott,

i wasn't picking on you in any way... i agree turbo's run well, so do hydromotives, probably better than any mercury props i've run... but they are capable of sooo much more... just a general observation that you pay A LOT of hard earned money for something that you would assume and in most cases, expect, as a high performance boater, to be tight toleranced... but it is generally far from it... so then you have to spend another 200 or more to get it closer to theoretically perfect... i've spoken to hydromotive and turbo guys at decent lengths about certain issues i've had with their props... i ask some hard questions which a lot of times they try to skirt, talk over your head or down play... which frustrates and disappoints me...

the whole hub / prop runout issue is a prime example... I KNEW i had a vibration from this issue... I KNOW what it does to mechanical gear train... they say.. well no big deal...

guess in some regards this was a sore subject for me i never really voiced much in the past...

ok i'll shuddup bout it now before i get too outta control ;)

[boldts]

Jamie, no sweat! Believe me, I'm no expert on props and I only can wish I knew the Engineering profession. I admire guys like you who look out for the average Joe like myself. When I talk to a prop company, all I can ask is "Do you have this prop in a xx pitch or do you recommend this prop for my boat?" Like you said, I've never had a salesman say "No, don't run that prop on your boat. From our research, we've found this prop to work much better." It's like Mercruiser in general. When you have 98% of the boats built using your product, you don't have to worry much about the quality the general public is getting. Goes the same for their props.

BTW, yes Doc in my circumstance, the prop calculator worked for me and saved time in shipping props back and forth. At my option, I kept the 22" pitch and ordered a 23" just to try. I ended up sending the 23" back, but I didn't want to change the pitch on a prop that after trying, I knew worked very well on my 22. Like I mentioned, I later tried a 21" pitch on my boat and found almost the exact information that the prop calculator had told me before hand.