Octura vs cnc

[robbo1]

Hi guys, just wondering thoughts on octura x series props vs cnc props? For example octura x642 s&b vs cnc bronze prop 4216. Would the cnc prop give identical lift, speed and other characteristics in comparison to the octura?

[TRUCKPULL]

No difference then a real boat.
16" Aluminum prop - $200.00 - $300.00
16" Stainless prop - $450.00 - $600.00
24" Bronze Prop - $1500.00 - $3000.00

Larry

[koen]

i know cnc props give more lift then octura props

[tbonemcniel]

So my experience is no. I have a number of both OSE CNC?s and Octura?s. The Octura?s run faster.

Take this example. 33? Mono, 2100kv motor, 4S.

Using 80% motor efficiency and 25% prop slippage for mono?s

OSE CNC 4416 - Theoretical top speed of 49mph, GPS top speed 48mph

Octura M545 - Theoretical top speed of 47mph, GPS top speed of 55mph

On paper, the CNC 4416 has a total pitch of 70.4mm, and the M545 has a total pitch of 67.5mm. So the boat should have slowed down a little going from the CNC to the Octura, but instead it picked up 7mph!

Most of my OSE CNC props are pretty darn close to my calculated theoretical top speed when I use a motor efficiency value of 80%, and my Octura props are closer when I use a motor efficiency value of 90%. Yes I know, the motor is the same, it?s the prop slippage that?s changing, but the way I built my spreadsheet the slippage is a locked cell while the motor efficiency isn?t, and I?m too lazy to change that lol.

[TRUCKPULL]

Andrew
Was that M545 the one you got from me?

Larry

[tbonemcniel]

Andrew
Was that M545 the one you got from me?

Larry

Hey Larry,

Actually no. The one I got from you is in my prop box. The one in that example I bought B&S from OSE.

[TRUCKPULL]

You would have gotten the same result comparing a Octura M545 to a Octura X644
Things to remember with props Pitch is average pitch from leading edge to the rear edge.
By de-tonguing a prop you increase the average pitch, because the tip may only be a 1.1pitch.
So a 545 prop the M code(de-tongued) is closer to to a 1.6 Pitch now.

On your calculations
On paper, the CNC 4416 has a total pitch of 70.4mm,
and the M545 has a total pitch of 67.5mm.
The M545 should be closer to 72MM Pitch.

This is what gave you the higher top speed.

This is why most of my props were marked DT (de-tongued)

Larry

[tbonemcniel]

You would have gotten the same result comparing a Octura M545 to a Octura X644
Things to remember with props Pitch is average pitch from leading edge to the rear edge.
By de-tonguing a prop you increase the average pitch, because the tip may only be a 1.1pitch.
So a 545 prop the M code(de-tongued) is closer to to a 1.6 Pitch now.

On your calculations
On paper, the CNC 4416 has a total pitch of 70.4mm,
and the M545 has a total pitch of 67.5mm.
The M545 should be closer to 72MM Pitch.

This is what gave you the higher top speed.

This is why most of my props were marked DT (de-tongued)

Larry

The OSE CNC 4416 is also detounged. All of OSE?s CNC 1.6 ratio?s are detounged.

Most of the props I bought from you I bought precisely because they were detounged X?s and of course M?s.

So if you?re saying that the M545 is more like an M645, then why don?t they call it an M645, and they make an M645? Are you saying M series props essentially started life as an X, in this example X545, then were detounged to become M545?s, and they didn?t bother to relabel the pitch ratio? I would think it?s more along the lines of starting as an X445 and turning into an M545?

FWIW, I?m not arguing, I?m trying to understand what you?re saying.

I have most of this fancy pitch gauge from Germany, but it is missing one part, and the manufacturer is out of business. One day, I?ll find a machine shop to make the piece for me, and I?ll be able to measure prop pitch very accurately.

[tbonemcniel]

Actually, I have another example, but not quite as close as one set of props has a much higher rake.

A twin cat, twin 2075kv motors on 4S. Using 90% motor efficiency (twin) and 25% prop slippage for catamarans:

OSE CNC 4416 detounged props. Total advertised pitch of 70.4mm
Theoretical top speed - 54mph
GPS top speed - 57mph

ABC 17-45 1715. Total advertised pitch of 64.8mm
Theoretical top speed - 50mph
GPS top speed - 65mph

What on paper should have dropped 4mph, in fact picked up 8mph! The ABC?s are slightly less in diameter and advertised to have slightly less pitch ratio as well, but they went significantly faster.

I?m less certain about prop modifications on this example, as the ABC?s were prepped by Dasbota, and I did not order them. They came brand new with another boat I bought and later sold, but kept the props.


I should do the same test with a OSE 4214 and an Octura X442, that way both props have the same diameter and rated pitch ratio. In fact, i have a boat running an OSE 4214 on it right now, I just need an X442. Larry, I?ve been thinking of trying that 38mm Grim Racer prop I got from you on that boat in place of the OSE 4214. Hope the little 3660 can take it!

[TRUCKPULL]

ABC 17 degree rake are a different animal, we have nothing to compare them to.
I have some 47mm 3 blade props that I back-cut a 16 degree rake on them, and they have nothing to compare with also.

Also with twin -slippage is lower ( 25% prop slippage for catamarans:)

Larry

[tbonemcniel]

ABC 17 degree rake are a different animal, we have nothing to compare them to.
I have some 47mm 3 blade props that I back-cut a 16 degree rake on them, and they have nothing to compare with also.

Also with twin -slippage is lower ( 25% prop slippage for catamarans:)

Larry

Hence, why I said my second example wasn?t as good of a comparison as the first.

I know the slippage is less with a twin than a single, but also as I mentioned, in my own Excel based speed calculator, I have the slippage cell locked and not easily edited (I have given a copy to a friend who is not very computer savvy). But both sets of props were compared with the same slippage number, so as a comparison, that doesn?t matter.

Whether they?re that much more efficient, other manufacturers underrate their total pitch, or OSE CNC?s overrate their total pitch, my point remains. In my experience, Octura and ABC props outperform OSE CNC?s in the real world when on paper using advertised specs they shouldn?t.

[NativePaul]

Robbo1, can you link to the prop in question, I am not familiar with any CNC bronze props.

Neither the method of manufacture whether cast or CNC, or the prop's material effect lift or speed directly, it is all down to the shape of the blades. Only at very high power levels or very bad materials does the material strength of the blades come into play.

Several CNC prop manufacturers have a range of props that are copies of Octura X series props, and these have very similar lift and speed to the props that they were copied from, CNC copies of Graupner 2318 and ABC 1745 props are also out there, both of which have less lift than Octuras, and there are also in house designed CNC props like Tenshock and ETTI, these have less lift than Octura, and while some of Dr Props ranges are copies of Octura and ABC which have similar properties to the originals, he also has in house designs that are of much lower lift than Octuras.

I know that there is at least 2 CNC prop manufacturers who have been less than honest about their prop's pitches, one with a range of advertised 1.4 pitch props that were actually 1.2 and 1.25, that has thankfully now learned his lesson and is advertising true pitch, and another that is still advertising 1.9 pitch props that are actually under 1.4 pitch. I don't have any OSE CNC props as the rise in shipping prices made purchasing props from across the pond uneconomical before the rise of the CNC prop, or know who OSE's OEM is, but I have to wonder if you are actually seeing a big increase in prop slippage or if you are just getting less pitch than advertised. Do you have any datalogs of the prop testing, or even charged capacity after a race? A high pitch slipping a lot would be sucking more power than the Octura despite the lower speed, and a low pitch prop running out of pitch would be sipping power in comparison.

i know cnc props give more lift then octura props

Koen, when you say lift, are you talking about bow lift, ie lack of lift at the prop? Because that is the opposite of my experience when assessing lift at the prop. While there are some round ear CNC lifting props out there, I would say that at this point Octura's lettered "low lift" ranges are now of higher than average lift, and I don't know of any CNC low lift props that are of higher lift than Octura's X,M,V, or P series (the N series is an outlier as it is actually pretty damned low lift for a 1.9 pitch prop, but there is only 1 prop in the N range, and while very good is also very niche and unpopular).

[robbo1]

[QUOTE=NativePaul;759969]Robbo1, can you link to the prop in question, I am not familiar with any CNC bronze props.

Not sure how to put the link up, but the bronze cnc props I was thinking of purchasing was from rc boat bitz in Australia. (Cheaper for me as I live in Oz)
Have decided to purchase the octura s&b props from offshore electrics (a bit more coin) but reading in a post on this thread about calculated speeds I have decided to go down the octura route.