Help us help you select a prop

[Silvertip]

There are three posts in a row where the question was asked "what prop is best for me?" I don't know about everyone but my response is "pick one -- your guess is as good as mine!" How about giving us something to work with! Remember, we can't see your boat, we can't see your engine (year, HP and model #), we don't know what prop you have now, we don't know what your current maximum speed is, or what the recommended maximum rpm is for your engine (because we can't see it). Furthermore, without a tachometer and speedometer and some actual wide open throttle rpm and speed readings with what you consider an average load, ain't no way short of a lucky guess we can help you unless someone has exactly the same boat, same engine, same load, and same prop. Lastly, it helps to know what performance issue you want to fix. Simply saying I want more speed so should I buy a 21P? Putting that prop on an engine that currently has 19P very likely will slow you down rather than speed you up because the engine does not have enough power to turn that much pitch. I suggest you google "propeller theory" or "selecting a propeller" so you understand how a prop works and what you need to know in order to make an informed decision. Without the required information we keep answering the same old questions over and over again and quite frankly, "it gets old". There -- I feel better now but I still have a headache! :|

 

[sabastianunf]

Re: Help us help you select a prop

A little harsh but i agree and did all these people post with out reading any of the other posts first or doing any research on thier own. Sound like mods may need to pinn a "help us help you" threat to the top of this.I'd rather be surfing.

 

[Silvertip]

Re: Help us help you select a prop

Harsh? You don't know what I really wanted say. d Your point about not reading any other posts (especially when there are three in a row on the very same topic) is what prompted my response. Some posters seem to think there is a very simple and very direct answer to what prop do I need questions. They want an answer that doesn't require them to do anything or analyze anything. Asking what prop is best for my boat with no other information is like asking what size shoes do I need. There used to be a post right at the top of this forum dealing with this topic. We could refer people to that post for information about what was required and why. But that's been gone for some time now.

 

[Silvertip]

Re: Help us help you select a prop

I assume that people are reasonably internet savy or they wouldn't be on this forum. With that in mind, I did a test by typing "propeller selection" in the Yahoo search box and the search turned up 10 pages of web sites dealing with prop selection. Guess whose web site is first on the list? You got it --- iBoats. I'm not exactly a spring chicken anymore but if I can figure this out so can the young sprouts that were likely born with a mouse and game controller in their hand.

 

[Jim Thacker]

Re: Help us help you select a prop

OK I am back and see that my topic is still in vogue. I wrote a while back about my Honda 90 (1998) on a ProV Deluxe Lund (1776) and how the motor simply did not get me out of the hole as they sold it to me. So I an here again to try and get an answer, because you folks seem to be good at this stuff. So here goes.

Empty, with a 17p I will get about 35mph at 5200 rpm. With a full load (which is likely overloaded but my old 90 Yamaha 2 storke handled it) It does not get out.....

I think by the tach that it needs to get to 4400 rpm before it can get up. Full load I am at about 3900.

The answer they (dealer) gave me was a 15p which empty ran me at the redline 6200 rpm. They said that was OK but at that rpm I was still only getting about 28mph. Full load however it did get me up.....

I then looked on my own (nervous about running the red line) and came up with a Pirhana Prop (12 5/8 x 21 x B) which does sort of OK...... 4 in boat 5300 rpm and 32mph.... 2 in boat 5600 rpm 35mph.... fully loaded.... may get up, may not.... if it does I do get 5200 rpm and 30 mph.

But on this forum I was told to consider a 4 blade and wouldlike to pursue that..(I was told you needed more information)..but have no idea where to turn. The only reason I am still trying to figure it out is that my 90 hp 2 stroke Yamamha (which I never should have sheered the bottom end off of) would go 40 mph at 5400 rpm and no matter how much I put in it it would always get out of the hole........ not to that speed but up and running..............PLEASE HELP

 

[Plainsman]

Re: Help us help you select a prop

Quote ST: "There used to be a post right at the top of this forum dealing with this topic. We could refer people to that post for information about what was required and why. But that's been gone for some time now. "

I agree 100%. most of the forums would benifit from something like that. Maybe the mods could get with someone from each forum and come up with something like that. Just my .02

 

[sabastianunf]

Re: Help us help you select a prop

Jim -
I am not the guy to talk to when it comes to outboards but I think you are right in that you do not want to run any motor at redline. You may never achieve the performance you got out of your Yami since newer motors have more emission control devices on them which will limit thier perfomance. It seems odd that you got a 1000 rpm increase by droping from a 17p to a 15p usually you get 200 rpms per 1" of pitch. Was the 15p a smaller diamater?

 

[Silvertip]

Re: Help us help you select a prop

Chances are the reason for the 1000 rpm increase was the engine was being severely lugged. Get the proper prop and it can make a terrific difference in performance. Every outboard has a maximum "recommended" wide open throttle rpm. That means when the engine has the proper prop, the engire will run at that rpm with whatever load it was set up with. Anything less than that is simply not an acceptable set up. On average, a two stroke will beat the pants off a four stroke on hole shot all other things being equal. That's just a fact of life. On top end, RPM is RPM so if both engines rev to the same limit, have the same gearing, have the same prop pitch on the same boat, they should run the same speed.

 

[sabastianunf]

Re: Help us help you select a prop

I agree especially with the comment about the proper prop making a huge difference in performance. However, I am not sure that the rest aplies to this situation. these are 2 different motors probably with different rev limits, different gearing, different props and do not run the same speed.

 

[WillyBWright]

Re: Help us help you select a prop

Hondas have never been speed motors. They're reliable workhorses. If you have a big load, that may make it necesary to put on that 15 for that purpose and change back to the 17 with a light load. That's not at all uncommon. Most seasoned boaters carry separate speed and power propellers.

 

[Jim Thacker]

Re: Help us help you select a prop

Hondas have never been speed motors. They're reliable workhorses. If you have a big load, that may make it necesary to put on that 15 for that purpose and change back to the 17 with a light load. That's not at all uncommon. Most seasoned boaters carry separate speed and power propellers.

 

[Jim Thacker]

Re: Help us help you select a prop

Actually that does answer my question. I thought it odd that I would have to have two props and change them when I was taking a heavy load.......mainly because that Yamaha 90 (2 stroke) did everything with the one 17p prop. But as you say the 4 stroke is a different animal.

Changing a prop is not a big deal and that is what I will do, as the 15 does great with a full load..... I remember the salesman telling me that running it all day at 6200 rpm would not harm it at all.........but I was skeptical.....he was the same guy that told me my Honda 90 would actually perform better than the Yamaha 2 stroke............ but then he was selling me the Honda

 

[walleyehed]

Re: Help us help you select a prop

First, the 4-stroke has less than optimal performance when propped for less than 6000 with a normal load...
There is more to a prop than just "pitch".... a 21 from 1 manufacture may work, yet a 21 in a higher tech design may not.
Finding the prop that lifts properly and yet has the hole-shot you need is tougher to find for a 4-stroke than it is for a 2...Michigan wheel is coming out with some new props to address this issue, which I will be testing in the next 30 days...I'll let you know what I come up with..