Impulse 31 Prop Mod Opinions

[rwhitfield]

All-

I have an Impulse 31 that I am preparing to make a prop mod on away from the stock. I am OVERWHELMED by the choices and the options, and could use some advice from a few pros... so I don't go broke buying 10 of these things to attempt trial and error and still not get a hit.

Based on previous research, it appears that there is some concensus on:


Prather 230
1.90" Diameter 3.0" Pitch


X445
Diameter: 1.77"
Total Pitch: 1.4x1.77=2.478


Grim Racer 42mm x 55mm
Total Pitch = 1.65" x 2.17" = 3.58 (converted mm to inches)

So the stock prop based on what I can get off the Proboat webiste is:

Proboat Impulse 31
1.6 in x 2.5 in = 4.0 Pitch

Soooooo....

What forms of speed, electrical drain, and ride characteristics can I expect between these 3 options exactly? The X445 seems like a good fit given the larger diameter, and the Prather looks like it mght be large enough to really stress the stock ESC and motor? Is the pitch on the stock Proboat prope really 4"??? I was questioning that. The Grim Racer also looks enticing, and it looks like all it requires is balancing vs polishing and balancing.

Here is my setup:

4s2p 5300 mah 30C
All stock... and only looking for a good prop choice (or two) to experiment with pushing the boat to it's limits on ocassions, accepting that run time will be whacked.

Thanks for any inputs the forum has to offer! This is a great community out here!

RW

[PapaGriz]

I had a similar dilemma when looking for a prop for my Shockwave.
Proboat lists the prop as 1.34 x 2.06 so like you I was figuring 1.34 * 2.06" = 2.76" (70mm) total pitch.
So I was confused when guys were saying that the Octura Y534 (1.5 x 34mm) was basically the same prop.
1.5 * 34 = 51mm (2.01")

What I think I have figured out is that Pro Boat lists the prop as diameter x total pitch. Not diameter x blade pitch.

So my Proboat prop is 1.34" (34mm) in diameter and 2.06" (52.4mm) total pitch. To find the blade pitch: 2.06 / 1.34 = 1.54
So to lay it out like Octura, my Pro Boat prop is 1.54 x 34mm (or 1.54 x 1.34").

I hope I figured that out correctly and someone will confirm or deny that. :cool2:

[Darin Jordan]

I'm not going to suggest anything at this point, since there ARE so many good options, but I will offer this...

Be careful trusting printed prop specs... The only way you can REALLY know what a prop measures is to measure it.

For example... The 42x55 is listed at 2.16" pitch (55mm)... I haven't measured one yet that is less than around 3.0", and with very little tweaking, they are closer to 3.5"-4.0".

[rwhitfield]

Thanks to both PapaGriz and Darin for the inputs!

I am going to try the Grimracer 42x55, and respect that the pitch measurements should be considered, and if a bit higher than specs I think that would actually be desired to some extent given the diameters between the Grim and the stock PB prop are near identical. The X445 and Prather 230 appear near equal, and I view those as yet another step "up" if the temps and electronics can handle the Grim 42x55 adequately.

Sound like a reasonable plan of attack here?

RW

[Make-a-Wake]

I'd try an x442...........or maybe an m445

[Darin Jordan]

When you say "4S2P", are you hooking a 4S pack to EACH stock connection, which would really be 8S1P (YIKES!), or have you updated the contacts and are truly running just 4S?? HOPEFULLY it's the later!!

In my experience thus far, with the stock motor, the 42x55 is an OK prop, but you might find a 45x55, or an X645, more efficient. If you do the 42x55, try lowering the strut a tad to get a little more blade in the water, especially for left-hand turns. The offset strut will tend to lift it out of the water a bit.

The 1800 motor won't like as much load as the 1500KV (MG) motor, so it won't require, or need, as much pitch. However, it should handle a pretty decent prop.

I've also had some fun with an X447/2, and tried an X447/3 as well. Less pitch-ratio, more blade area. With the stock ESC, the 447/3 is a bit too much in terms of throttle control... the ESC is just a little too "touchy" at lower RPMs and it's hard to be smooth through the turns with that much prop. The boat was a ROCKET in stock trim, however...

Once you settle on a prop, you can start playing with adding pitch and tweaking on it to get the performance in where you want it. You'll be shocked at what you can do with a simply pair of prop pliers and a little tweaking... :D

[rwhitfield]

Make-a-Wake-

Thanks for the feedback! I am still confused on the X vs M designations on the Octura props? What is the difference in the casting set up between the two? I was wondering if it had to do with the concave of the blades??

RW

[rwhitfield]

Darin-

I should have been more specific.... I am NOT stock on the original connectors! I have soldered up a true 4s2p configuration, as well as laid 5.5mm bullets on the stock motror vs the 3.5mm ones the boat came with.

I was actually wondering about that Grim 45x55 myself, but i figured your concerns of the Grim's being out of spec and delivering added pitch would mean that prop is even MORE of a strain on the stock ESC and motor vs the 42x55 due to the add in diameter? In "real boats", I have always gotten advice to try pitch up over diameter as a start?

Again.... thanks for all feedback. I am new to boats, but intend to get my expertise dialed in. One day, I hope to join some races if I can find the time and get confident enough to run with you big boys :)

RW

[PapaGriz]

Darin, with regard to my post can you confirm how ProBoat specs the props?
Is it listed as:
diameter x blade pitch or diameter x total pitch

Just want to make sure I have the right information.
Thanks

[rwhitfield]

Papa-

Darin is obviously be the gospel here.... but I think you nailed it in your post. Kinda like how Grim gives you the TOTAL PITCH in a 42x55mm item too, I think Proboat's specs are the same way and give the total pitch and you would divide them to get a blade pitch like the an Octura is speced up. I figured that Proboat stock prop could not be 4.0 pitch, and your explanation makes good sense! My inital post to start the thread was wrong.

RW

[Darin Jordan]

This forum seems to be acting weird today... I can't seem to "reply with quote" today... Anyhow... I have measured several of the stock Stiletto/Impulse 31 props, but I have my notes at home so I'll have to post the measurements later.

When I measure these, I do as much of the blade as I can reach from about 2/3rds out from the hub, and then do the tips, and in between as well, just to compare. Most of the Nitro guys will tell you ( and they ARE the true experts on this stuff... they HAVE to be, because they don't have all this extra torque/power to just pull through a bad prop choice!) that it's only the last 30% of the blade, and the last two measurements on the trailing edge that make any real difference. There is stuff going on lower on the blade than that, but I tend to agree. The speed and thrust come from what's going on at the blade tips and on the last 30% (in relation to the distance from the hub) of the trailing edge. Any pitch before that doesn't really tell you that much.

I'll try to dig out my data and post it here later tonight.

[lonneyb]

Is there a place with required reading to understand this prop stuff...it seems like no one wants to help out with an explanation of what these measurements mean...I have googled to no avail...also it would be nice to know the Pitch of the stock prop or even what the measurements mean?.....Three different companies i have looked at and they all have different numbers ...some are X445 SOME ARE 45X55 SOME SAY M445 OTHERS HAVE 1.23X2.34=1.23 THEN A PITCH RATIO AFTER IT....there seems to be no common ground....

[1truckerdan]

Here you go ,I saw this thread and thought it might help..
http://forums.offshoreelectrics.com/showthread.php?27946-Found-list-of-prop-descriptions-somewhere.......
Daniel

[Darin Jordan]

According to my notes, the stock STLO/IMPULSE 31 prop mesures 2.5475" at the outter tips of the blade (last .200" or so), and around 2.2707" in the middle of the blade. Average measures out to be right around 2.4091. You'll find this prop is essentially the same as an unfinished Prather 215.

The Grim 42x55 prop that was handed out at the 2007 Nats in Monroe, WA for the first Spec SV27 race by Grim himself measures out to be 3.1575" mid-blade, and 4.1442" at the outter tips. Considerably higher than it's specs.

By comparison, an ABC 42x55 I have, that had been detounged, but is otherwise just thinned, sharpened, and balanced, measures 2.833 mid-blade, and 3.278 at the tips, for an average of 3.0555.

[lonneyb]

Here you go ,I saw this thread and thought it might help..
http://forums.offshoreelectrics.com/showthread.php?27946-Found-list-of-prop-descriptions-somewhere.......
Daniel

Thanx That helps!