50% luck and 50% voodoo, the rest is science

This is simply an informational thread for us to kick around some ideas on posting to technical forums. We had a recent attempt at a tutorial and it reminded me of a few things that may need discussing.

First, this thread title. While I want to make a point or two about technical issues and proper troubleshooting and diagnostics, props are far from cut and dried like we all wish they were. The best we can get is close with recommendations and then there is no substitute for actual data, from the actual boat with the actual loads, application, weather and speeds expected. Everything else is theoretical and with props it is very hard to duplicate things from hull to hull etc. Take a look at Walleyehed's data above ^^^^^ it is indicative of the variability.

Second, most of us here for very long take the validity of the technical information given very seriously. Definitive answers to squishy questions, from those of limited experience, are evident immediately. And members usually call them out quickly. That's a good thing, but it is important to refrain from definitive statements like "I know it's the flangelrod bellcrank adjustment 'cuz my buddy Jake tweaked his and it's faster now". Anecdotal info may seem helpful, but it often derails proper procedures that may seem unnecessary to many. It is funny how often we jump straight to WOT RPM and conclude that pitch is the solution. I even got sideways with another Mod on a very similar issue recently, but none of us know if it is an engine problem, a hull problem, a data problem, or a pitch problem among possibly a 100 more potential culprits.

Things like the relationship of horsepower and torque, and how each relates to performance, is so horribly misunderstood that discussion often careens out of control and becomes meaningless almost instantly. Let's all do our best to comment about that which we have have extensive experience and if we don't let's add some qualifiers to help the reader determine what he/she should do next to narrow down a problem.

Thanks

Re: 50% luck and 50% voodoo, the rest is science

A friendly suggestion:

I did read the tutorial you are referring to, before it oddly disappeared....

While it had several errors and holes within, I REALLY like the spirit and the concept behind someone posting a comprehensive and educational tutorial/propping summary. A report with many in-depth definitions, explanations, guidelines, rules-of-thumb, etc...

Strangely this forum, which is reknowned as one of the very top sites for great technical boating info, seems to be completely lacking such a document regarding boat propellers. I, for one, feel the iBoats it should have such a document, it should be the BEST one available on the internet, and it should be in a locked sticky right up there at the top of this forum. And it should be written by someone very knowledgeable and probably edited and reviewed by several other very knowledgeable people before being posted, so it's known to be of high quality and not instantly ripped apart...

Here are a few random examples of what I am talking about that can be easily found with Google searches:
http://theoutboardwizard.bizhosting.com/how_to_choose_the_correct_propeller.html
http://www.tropicalboating.com/powerboating/choosing-a-propeller.html
http://www.boatfix.com/how/props.html
and of course Iboats has a couple basic tutorials...IMO far too basic:
http://www.iboats.com/basics/choose_right_prop.html
http://boatpropellers.iboats.com/propeller-tutorials/how_to_choose_prop/

As far as I'm concerned, several of the above random links have some very good info, some are lacking, and some are too simple and missing some stuff. And I've been around here long enough to know for an absolute fact that many people on this site can do better than all of above combined...it just takes time and desire to write it.

Of course someone needs to compose the document....and moderators need to edit and approve of it...

Just thought I'd throw that idea into the suggestion box as a way to help improve this propeller sub-forum...

Thanks for listening.

Re: 50% luck and 50% voodoo, the rest is science

Thanks man. I get your point, and you're right we need a propeller basics sticky or similar. I also had issues with the different links you posted, but . . . I Googled Boat Propeller Basics just to see what else was out there, and the 1st one to come up was this: http://www.iboats.com/basics/propeller_basics.html

I don't recall seeing before and it is not the two links from here that you posted, but it is pretty dang good. Thoughts from all? Maybe we just post a link here? Maybe I post it separately here, keep the pics and edit as we all see fit for the Prop section?

Thoughts?

Re: 50% luck and 50% voodoo, the rest is science

Agreed. That one you found is indeed pretty good...and I have never seen it before either.

At the very minimum, just go ahead and create a separate sticky up there by Walleyheads results with the 3 Iboats propeller links...and any others that someone may happen to stumble across...so they're easier for people to find and people are made aware that they exist.

And you or someone else can take suggestions on other things to add, edit, or comment on. But I think it should be a locked sticky that maybe only moderators can add to. Otherwise it may become a free-for-all which results in questionable or inaccurate information...and can get confusing.

Model it kinda like the sticky's in Don's Mercruiser sections, "Adults only", etc....those are loaded with helpful tips on maintenance and repairs, resources for where to find information, etc...but random people can't get in there and muck it all up...

I think such a topic front and center up there would really be an asset to this propeller sub-forum.

Re: 50% luck and 50% voodoo, the rest is science

My first thought after reviewing the link was that it left out an explanation of Diameter, although it alludes to it. I guess I understand as diameter continues to be a hard one for me to get my head around, and there is not much a user can do with it anyway as the gear-case, and the available props to match, determines this for the most part.

A little theory might be helpful though to alleviate simple curiosity. I understand that blade surface area (diameter is a part of that) typically is increased for higher loads and lower speeds, but that is way too general to be helpful. There is no way we can solve all voodoo with a sticky, but other than Diameter what else is missing from that page?

Re: 50% luck and 50% voodoo, the rest is science

Now that I read it thru...there is quite a bit in there that I feel is missing, that should probably be discussed. Random nuggets:

Repitching can be done at prop shops up to 2" usually...cup can also be modified. You don't necessarily have to buy a new prop to accomplish small changes. Success varies with quality of prop shop.

I'm not sure I agree with their recommendation of 3 blade props for "most I/O's" etc....they make no mention of watersports, etc. They don't explain WHY extra blades offer benefits or disadvantages...only that they do. (no discussion of surface area, added/reduced drag, etc.) They don't mention that 5 blade props even exist (likely because iBoats doesn't sell 5 blade props?). They don't discuss how 3 blades can sometimes create more torque steer than 4 or 5 blades do. There is no discussion of how adding a blade may cause you to need to drop a bit in pitch to maintain a given RPM.

I feel a discussion of the usage of prop calculators would be important to include. And a link to a good prop calculator. And explain how to use it when calculating extra blades, and cupping, etc.

Deeper discussion of Stainless vs Aluminum would be good. They mention nothing about blade flex, blade thickness, etc. They do not even mention composite props at all....

How to clean/maintain your prop. Proper cleaning for stainless props that "rust", is it smart to file your own nicks & dings, guidelines for when a prop should be rebuilt or replaced...

An explanation of ventillation holes might be nice. How they work, how and where some people choose to add the holes, benefits and risks, how some manufacturers provide them and some do not, how they are completely useless if you don't have thru-hub exhaust...

The importance of having a properly tuned and running motor BEFORE trying to select a prop is never mentioned...

They do not discuss the difference/benefits/disadvantages of interchangeable hubs and fixed hubs.

Anywho....that's enough for now right off the top of my head. I'm sure there's more. There's a lot to digest here, and I think it will take substantial time and effort on the part of several people to truly be comprehensive. But anything is better than nothing...it can be a living document that changes and improves with time.

Re: 50% luck and 50% voodoo, the rest is science

The question really is what to have in a sticky and what to leave to the forum. Life is always about where you draw the line . . . So if that's true then Life = Prop VooDoo. Got it, done

The number one issue I see with props, as a starting point, is assuming that the data is right. Speed, gear ratio, pitch and RPM are all often wrong. One wrong and the whole thing is meaningless. I always discover this with Prop Calculators as you mentioned. How to spot that would be important, thanks for reminding me.

Re: 50% luck and 50% voodoo, the rest is science

likely because iBoats doesn't sell 5 blade props?

Click to expand...

They got one for my engine...http://boatpropellers.iboats.com/OM...1.00-Pitch_QST_5_QS5760X_Propeller/486/35481/

Iboats sales everything but water..

I agree.. There should be a good sticky.. Who is going to write it???

Re: 50% luck and 50% voodoo, the rest is science

Outta here for the long weekend. May check back, but thinking this is a next week project. Be safe all

Re: 50% luck and 50% voodoo, the rest is science

One thing that's very easy to forget is that not all props of the same pitch and diameter are created equal. Even within the same manufacturer. You could have 2, 14 1/4 x 19 3 blade ss props from the same manufacturer and they target completely different markets.

Not all manufacturers measure pitch in the same way. Especially progressive pitch.

All this is why it's so hard to make a blanket statement like "an inch of pitch equals xxx rpm". You have to take into account what type of prop was used to establish a baseline when making a recomendation.

There are reasons that some 3 blade props are better on a given rig than some 4 blade props. Again, you have to consider use and application. There are props that are made to run deeper in the water than some. Those props tend to work better on rigs like I/Os. There are 4 blade props that target running deeper. There are props that target pontoons and work great but don't work so well on runabouts.