Newbie Prop question

[O-49]

Ron, Sam... anyone...

I have two DeWald threeblade props on Yamato 202... pitch "eyeballs" very close on both.

One is roughly 1/4 inch or slightly larger in diameter.

Given identical set up on motor height and thrust angle...what should I expect of each of these props in comparison with one another? The smaller one will drive my 10.5 foot hydro 65.4 mph.

Which should produce better top speed, acceleration, handling? (Just rule of thumb is what I'm seeking here from folks who've done this for years while I was just dreaming.)

Thanks in advance.

Dan
O-49

[Mark75H]

pitch "eyeballs" very close on both.

Looks can be very decieving.

Larger diameter can potentially aid accelleration or possibly bog your motor down.

The good Capt'n is right, there is no subsitute for testing. ;)

[O-49]

Thanks guys... I know testing is the only way to determine any given prop's performance. Just like testing is the only way to determine how a set of tires and wheels and a given differential ratio will affect "off the line" performance of a car or truck...

There, the rule of thumb is lower differential gears make for quicker hole shot, taller tires take away from that...all depends, too, on where the engine develops its torque. Now...I know those things. Boats are different to me because I haven't been around them as much, nor studied them as much--yet.

And, there's no way I'll put that new prop up against everyone else without knowing what it will do...at least measured by the GPS. What I need is basic knowledge of what prop characteristics are needed for handling in corners, powering out of corners.... better for long or short courses. Like I said, I'm new, and until now my racing was very simple--I only had one prop!

I'm just asking for generalities... a larger diameter prop... good for acceleration (if the motor has the torque to pull it). That kind of thing, as you stated, is what I'm looking for.

Now...what about corners, guts at lower speed etc.??

Dan
O-49

[Mark75H]

Oh, OK! You have the basics already:a larger diameter prop... good for acceleration (if the motor has the torque to pull it)
More pitch= more speed but less accelleration
Less pitch= more accelleration but less speed
Most of the rest of it varies so completely with each boat and set up.
basic knowledge of what prop characteristics are needed for handling in corners, powering out of corners.... better for long or short courses

What works one way on one boat quite often doesn't work the same way on a very simular boat and - props are freaky ... it is almost impossible to make 2 exactly alike in all performance characteristics. Did you see the thread where Ron had "T" welded a prop? The prop's owner had success with the prop and knew that even with the rough repair it would probably work better than an idenitcally made prop.

One thing Ron has been trying to tell people about props is that props can be "tuned" for best performance. Once you find a basic prop that suits your setup and boat .... a blade loading test is done with something like cheap lipstick (not expensive no-smear stuff). You draw lines on the prop and run it. Where the lipstick wears off - the prop is pushing hard ... where the lipstick stays the prop is loafing. You then experimentally change the pitch or rake of the blade to make it "load" all of it's surface.

A "tuned" prop can often both out accellerate and have more top end than it's identical sisters .... but change tilt angle, propshaft height, put it on a different boat or even a different weight driver and it may not remain fully loaded/tuned exactly right.

Side note: I have very good success on short courses with low pitch very low rake props. If your boat can make it around tight turns running "lighter" than my boat you wouldn't find the same advantage.

[O-49]

TNX Sam...that's the kind of thing I was searching for. I've been reading a lot of Ron's comments, trying to glean everything I can. The lipstick test I missed, but need to try that to see what's going on...

I did read about the welded prop...incredible! There went common wisdom about slick shiny polished surfaces.

Props are like women...curvy, expensive and variable at all points of measurement, and quite particular about performing in any given situation. Also, when all is right...it's a sweet situation for all concerned!

GAD!!! Now I've become a philosopher!!!

Dan
O-49