Outboard prop modifications

[Mr Efficiency]

In any case, the trailing edge of the prop blades have at least a little cupping, you add-on is probably going to add very little thrust, but will add drag

 

[Mr Efficiency]

The high thrust props I have seen on those engines have a hub that is wider than the lower unit "bullet", so as to be able to deflect exhaust gases forward to give better grip in reverse, what you pictured does not appear to be that prop.

 

[Slowboating]

There are 3 different highthrust props for this engine.

the one I have comes in two pitches 9” and 11”

there is a true highthrust prop which has a hub wider, like you’re saying. It comes only as a 9” pitch. Blade surface area is slightly less then the regular hub, it’s a great prop. Works better in reverse like you’re saying.

Then there is a stainless steel pontoon boat prop. Also a great prop, it’s the only one that has cupping and they go from 9” to 15” of pitch.

keep in mind these props also fit the Yamaha F115. The pontoon prop is more appropriate for the higher horsepower engine.

I’ve looked at all the prop options from all the various manufacturers too. What I’m doing, though experimental, is probably the best option. Plus it’s a lot of fun creating and building something. It serves a greater purpose down the road too. If the prop turns out to be good, and does what I say it will, it will also take to a kort style nozzle very well too. Which is something else I’d like to play around with too. The overall diameter of the blade is 14”, but more of the blade will have the full 14” instead of just the point. This will work better with the nozzle in the future.

 

[Slowboating]

Gonzella and your forum husband Mr Efficiency, you haven’t really said anything I haven’t already read or researched about, and still I have come to my experimental conclusions. Thank you for your input, though, please enjoy the experimentation process I’m going through, and do try to respond more intelligently. Thanks! Xoxoxo

 

[Mr Efficiency]

OK, I will leave you with it, I just think it is a waste of time and effort, you will get nothing worth the trouble out of it.

 

[Slowboating]

All experiments are useful for learning information and are therefore valuable beyond measure.

 

[gonzo]

One more member that gets offended when his pet idea is shown to be wrong.
@Slowboating: post your "experimental conclusions" instead of unsubstantiated claims for us to take you seriously. Personal attacks do not count as proof.

 

[Slowboating]

Oh, you run into people getting offended by you all the time, it sounds like. Hmmmm, sounds like you’re the one that needs to rethink their mode of operation, and start being more positive in this space. In almost every case, Social intelligence goes a lot farther then topic intelligence.
I’ve got props to build.

 

[gonzo]

Explaining the defects of a design is positive. Denying all previous data and scientific research is not.

 

[johneck]

It is fun to build, but I think that Gonzo has it right. Adding blade area only helps if the prop is really overloaded, this one is not. Adding cup is really only useful when it is not possible to provide enough blade area to avoid thrust breakdown; again, probably not the case here. Slip is a crude way to characterize efficiency, but reducing slip doesn't necessarily mean that the prop is more efficient, just that you are able to produce the required thrust at a lower RPM. That may actually be less efficient and worse for your engine and lower unit.
A nozzle is an interesting idea for a boat moving at less than 10 knots. I think that you will find that your prop pitch is too low once you add a nozzle. However, if you can put on a prop with the right pitch it may work out very well.
Have fun! Happy welding (and grinding).