Ok this is probably a dumb question due to the fact that there is most likely more than enough information out there on this subject. I have just failed to find it. My question is about props. First off is copper better than carbon fiber or aluminum? Secondly, what do all those numbers mean? If I look at carbon fiber props, it will say something like dia. 29mm pitch 46mm. That is easy enough to under stand, but if I look at a copper prop it’s all crazy like X427 (1.06”) 1.4x1.06=1.484” What the crap does all that translate too? And finally how do I chose a prop. I learned the hard way what happeneds when you get a prop that’s too large. So how do I know what size to get?

if you list the size of the boat and motor that will be a big help. also, most marine motors tell you what size props are the best, this info is normally found in the description.

Its a 635 mm (25 inch) MHz Flash. Feigao 9XL and 14 cells.

I should have said earlier that im still new to rc boating and have almost no knowledge of prop range for that motor. but if it is around the same size motor as the 700 brushed that the flash is supposed to use, then it should have a 40 - 45 mm prop. but if i were you i would wait until a more experienced boater comes and gives you the right size props. plus your prop size can range in size if you want it to be fast or have good handling.
that is pretty much all i know about props.

Hi,

My son and I both run a Flash, in the 700 motor, 12 cell configuration.
The props we use most frequently are the Graupner K-series 42K, 43,5K and 45K, with an occasional 48K, milled down to 45mm.

We found the hull too small for 14 cells, it gets undrivable, specially in chop.

With your lighter brushless motor, the boat may by about the same weight as our 12 cells with a 700, so once set-up properly, the props mentioned above should work just fine.

Due to the older design of the hull, the handling will suffer once you exceed the 40-45 mph mark, the hull is too small to remain stable at those speeds, so build solid and expect brutal flips.

If you're running the boat, with the propshaft and motormount built in by MHZ, you'll be in for some 'interesting' boat behaviour...

We added a runpad to keep the boats stable when racing around our triangular course, works like a charm.
If the conditions are favourable, calm (and preferably running in the lead...), my Flash will corner like an Eco.
My son's Thick Flash has a bit more cornering issues due to the higher CoG.

The picture shows my son's Thick Flash, accelerating away from the marker, only the runpad, rudder and prop in the water, you can see the markings in the spray, made by the 45K prop.

Regards, Jan.

Does the Thick Flash right it self after a flip? And I have no idea what a runpad is. can you explain? This is great I havent talked to any one wha has run this hull yet... over all do you like it. The reason I chose it is because all the hardware is built in. I am not comftorble drilling in a $200+ hull right now. I do not know how to get thing in proper alignment. I might place things too high or low or what ever..

Oh and can you get me a pic of that runpad?

From your reply I gather you have a Thick Flash.

From experience I can tell, the Thick Flash is very stable, floating upside down, my son once flipped his boat shortly after the start (due to a ESC malfunction that kept the motor running at full throttle) and it floated with a sreaming motor for the entire length of the heat...
Even the waves from the other boats tearing by wouldn't turn it back up.

So we mounted a floodchamber and have had no problems with self righting whatsoever since.

As you can see in the pic, the twelve cells are distributed equal, my guess is, that with a 8-6 cell configuration, the eight cell pack on the left side, the boat will turn back up after a flip.
If it remains a problem, I have a template for the floodchamber wall...

Here are some pics of the Thick Flash.
The runpad end can be seen at the rear view, it extends all the way up to the step, as seen on the bottom pic of my Yellow Flash.

And yes, we are happy with this boat, even it's an older design, it handles chop much better than the newer flatter designs, which are quicker, but can't make it count in races, specially in rough conditions, as they spend more time upside down that running, than our slightly slower Flashes.
My son was Dutch champion in 2005.

We had our problems making the Flash turn at speed, without flipping it, the position of the turnfin wasn't to our likings, mounted at the transom.
As an experiment we mounted a plate, as shown in the sketch on the right hand side of the hull.
The 'turning plate' is much more shallow and barelt touches the water, running straight (=less drag), when the boat banks into a turn, the fin gets hold and does it's job very well.

Showing up at the races with this turnfin for the first time, we were laughed at.
After a few races most competitors have copied our idea...

Let me know if you have more questions.

Regards, Jan.

Thanks alot,
I do not have this hull as of yet. I am trying to figure out what hull to get and I am very close to getting a thick flash. I will be asking mre questions if you dont mind.

On the subject of props. I have a 20.5 inch mhz hotshot with a 540 8S rated at 4400 Kv. The boat is very fast on seven cell with a 36 mm carbon prop. One out of three runs results results with a flip. I have been running with six cells for a more "sane" run. Any prop suggestions? Should I go down in size?

A quick tutorial on Octura props. The "X" series are non-lifting props. The first number will give you the pitch in millimeters times the diameter. If it's a 4, then the pitch is 1.4 times the diameter.
A lifting prop wil use 2 first numbers like a 14 which is the same as the 4 but just designates it as a lifting (hydro) prop so a X-437 would be the same as a 1437 except for the design of the prop.

Ok that freakin' compicated but I am sure I can get use to that. Thanks again Ron. How do you figure out what prop you need?

Honestly, I don't know diddly-squat about electrics any more as I got out of them just before the brushless motors came out. Find a size to start out with to see how the motor likes it. If it's running too hot, go down until you find one that the boat likes.

Really? You have always had great answers! What ever I still trust your answers. Thanks