2 blade 3 blade whats the differance ????

[magnum500sw]

:help:yeah i know the 3 blade has one more blade than the 2 blade , but the real question is what is the differance in a chopper vs a full face or round edge blade ? from what i've been reading a prop used on a mono is less then ideal or no good for a hydro . how about some explanation and some cause and effect . i have some boating under my belt but never really had any method to selecting the correct prop . i`d like to expand my knowledge base on this subject . :help:

[sailr]

good topic. I,m anxious for answers

[Fluid]

This topic is far more than can be adequately covered in a post or two, but here is a little:

A low-lift prop like an Octura X, Y or M series can work well on monos, cats and hydros. Lifting props like Octura's 1400 and 1600 series or ABC's H-series generally don't work well on monos but can work on cats and especially hydros. (A lifting prop is one which directs some of its thrust cone downwards, lifting the prop out of the water.)

A mono needs the stern planted in the water, so low-lift props do well. Hydros need the transom lifted and can use lifting props to do it, or they can use low-lift props with a bit of down angle on the strut. Cats can use either, although low lift props usually work better.

The terms "chopper", "cleaver" etc. describe the blade shape but by themselves don't say a thing about lift. Most props with these blade shapes are lifters, but a lifter can be changed into a low-lift prop by cupping the leading edges. Props with 'pointed' tips are used mostly for higher speeds but 'rounded' tips can be as fast or faster and often pull stronger out of turns.

Prop choice is not always simple, but the most fool-proof designs are the Octura X props. They usually give good results on almost any boat. Other props may work better, or not. Few props work optimally as-is, small to major mods can make a big difference in performance - or not. The most common mod is to remove the tongue of an X prop, this often results in a modest speed increase.

The best starting point is a prop that is used by others with the same hull/motor/cells...and not just one guy. If three or more folks have good luck with a certain prop - the x642 on the BJ26 comes to mind - it is a good bet to start with. Minor tweaking may increase performance a bit, or not. Prop choice is more art than science.


.

[GP73]

It would be really cool to create a chart of which props are best for certain, well-known, hulls.

Like you said: BJ26 - X642

MG - Prather S220?

[fatboyelectric]

As far as the 2/3 blade part of your question, a 3 blade offers more bite or less slip than its 2 blade counterpart as there is always a blade in the water, while a 2 blade twice in each revolution will have very little blade area in the water. It is for this reason that the 3 blade will provide a smoother yet increased torque load on the system.

[magnum500sw]

So a selection of props is a must for a competitive racer. To accommodate the ever changing conditions you may encounter in a day. So what would be used on a hydro on a slight chop ? You would want less lift from your prop correct ?

[bbosncali]

Wow what a great topic and as stated I ish there was such chart but a lot of what is said makes sense especially for someone like me who likes the higher rpms a 3 blade would probably benefit me more than a 2 blade but cause more amp draw if I'm understanding this correctly. I run a cc 1518 1800kv and usually run 6s which I know is considered way to high of rpms anyways I run either an m545 or m645 and I hit so far my best was 62.1 and I have a buddy who is running a genesis with an x642 1500kv and he hit a best 63.7 and I didn't understand why but after reading this I think I do thanks for the help

[jamie]

I have this stored as a reference ... gives a pretty simple explanation and a chart all on the same page.

http://www.astecmodels.co.uk/props.htm

[magnum500sw]

I have this stored as a reference ... gives a pretty simple explanation and a chart all on the same page.

http://www.astecmodels.co.uk/props.htm

wow!!! that is a great post :thumbup1: i am going to send that to the printer. :Peace_Sign:

[bbosncali]

I just ordered an octura 942 3 blade which is a 42mm prop just like my buddies x642 except with more pitch and an extra blade. We both have genesis he's running an 4082 1500kv and hit a best of 64.7 now I'm running a cc 1518 1800kv we wil both be running 6s but now ill be able to put that extra rpms to god use now I hope. Basically its the same prop with more pitch and an extra blade.. I hope I read this thread right i

[fatboyelectric]

I just ordered an octura 942 3 blade which is a 42mm prop just like my buddies x642 except with more pitch and an extra blade. We both have genesis he's running an 4082 1500kv and hit a best of 64.7 now I'm running a cc 1518 1800kv we wil both be running 6s but now ill be able to put that extra rpms to god use now I hope. Basically its the same prop with more pitch and an extra blade.. I hope I read this thread right i

The only things the V942/3 and X642 have in common are being made by Octura and being 42 mm diameter. V series props are basically saw props. They are very aggressive, high lift, high pitch props that are seldom used with great success on anything but hydroplanes.
Your unloaded rpms are just under 40k. Thats alot for sport running. Efficiency is the name of the game. With higher rpms look to prop down in diameter or pitch or both. This also could be good for the handling characteristics of a narrow track width single drive cat such as yours. My point is to consider that a smaller prop at good efficiancy will be faster than a bigger prop at poor efficency considering the rpms your running and would be less likely to cause damage to electronics.

Good Luck,
Kevin

[bbosncali]

That's basically what most of my runs consist of is saw runs.... I also ordered a 646/3 for my df 33 (all trial and error) but I'm running a cc 1717 so I was told to prop up. Not sure if I'm going the right direction considering I've never used a 3 blade prop I mostly stick to x642 and m 445 545 and 645 which I've had success with all at some point. Would the 942 run better running on 5s? My biggest problem is that when I'm running such high rpms a lot of them are wasted

[magnum500sw]

That's basically what most of my runs consist of is saw runs.... I also ordered a 646/3 for my df 33 (all trial and error) but I'm running a cc 1717 so I was told to prop up. Not sure if I'm going the right direction considering I've never used a 3 blade prop I mostly stick to x642 and m 445 545 and 645 which I've had success with all at some point. Would the 942 run better running on 5s? My biggest problem is that when I'm running such high rpms a lot of them are wasted

i am just a noob but it sounds like the three blade is worth a serious look

[fatboyelectric]

That's basically what most of my runs consist of is saw runs.... I also ordered a 646/3 for my df 33 (all trial and error) but I'm running a cc 1717 so I was told to prop up. Not sure if I'm going the right direction considering I've never used a 3 blade prop I mostly stick to x642 and m 445 545 and 645 which I've had success with all at some point. Would the 942 run better running on 5s? My biggest problem is that when I'm running such high rpms a lot of them are wasted

I dont think the 942 will be better running on 5s, just less load on your equipment, but if you wanna push for speed, and if you can tune that prop to work (V series props can cause strange behavior), then proceed with caution as you may find your equipments limits along the way. Remember that this is just one guys opinion. There are MANY others who are way more of an authority on these matters than I am.

I wonder what a P741/4 would do on your boat......hmmmmmm

[bbosncali]

That's how I learn.... if its not from trial and error its from everyone elses trial and error which in the long run can save me lots of money. I don't have awhole lot of experience with a lot of different props except octura x and m series and the ocassional prather which I haven't had any success with

[SweetAccord]

As far as the 2/3 blade part of your question, a 3 blade offers more bite or less slip than its 2 blade counterpart as there is always a blade in the water, while a 2 blade twice in each revolution will have very little blade area in the water. It is for this reason that the 3 blade will provide a smoother yet increased torque load on the system.

As true as this is, its the opposite for a two blade but add in top speed.

[jonjon00]

bbosncali - I think a V series prop on a high RPM cat would work awesome to whip up some margaritas. Call me when they are ready.
The blade profile on those props is designed for three point hydros. They don't have enough tongue to get the bite to bring a wetter boat like a cat or mono up on plain. And spinning them faster usually only makes this effect worse.
i would reccomend a smaller diameter for a three blade, like maybe 40MM. A coupel things that might be worth atry is a X440/3 cupped to bring the pitch up. or a higher pitched prop like your X646/3 cut down to the smaller diameter. I found it easier when I first started working props to get more consistant results by cutting the diameter down. it is much harder to get the blades to match when you are adding pitch/cupping.

[billyc42x]

Great Topic... I am also new to FE boats, and ventured out and purchased a V942/3. I did not work at all on my MG, Leopard 4074/2150 on 5s. I just cavitated, and the more throttle i gave it, the worse it got! It would not get on plane... I immediately swapped out the prop for the X642 and it runs perfect... 51.8 on a hand held GPS

[bbosncali]

Great Topic... I am also new to FE boats, and ventured out and purchased a V942/3. I did not work at all on my MG, Leopard 4074/2150 on 5s. I just cavitated, and the more throttle i gave it, the worse it got! It would not get on plane... I immediately swapped out the prop for the X642 and it runs perfect... 51.8 on a hand held GPS

Its ironic you said that cause I had the exact same problem with my mg trying the 942 this weekend it barely made it back to me almost like it had no prop at all on it.

[jonjon00]

I knew they would be good for margaritas!!:w00t:
If one of you guys wants to get rid of that V prop let me know.
I am in the planning and acquisition phase of a rigger build and wouldn’t mind trying one for that.

[bbosncali]

Shoot me a pm ill sell it

[magnum500sw]

so how is the two blade faster ? i`d think that a three would be faster due to the fact there is always a blade in the water .

[AlanN]

A two bladed prop has less load (less surface area than 3 blades) so the motor can spin a higher rpm. 3 bladed props are good for acceleration but fall off on the top end. Unless you really know what you are doing and trying a saw setup the 2 bladed prop will have top speed v.s. a 3 bladed.

[magnum500sw]

are v series props even worth having ?

[bbosncali]

Qpdefinetly not for cats

[jonjon00]

are v series props even worth having ?
If you are running a 3 point hydro they work well.

[lohring]

Lots of information in this post:
http://forums.offshoreelectrics.com/showthread.php?27065-Octura-props-quot-lifting-quot-vs-quot-pushing-quot-X-amp-other-types

Lohring Miller

[properchopper]

If you're looking for the highest one-pass straightline speed a two blade will get you there. I use 3 blade props on my P-Mono raceboats for the simple reason that they outpull two blade props coming out of turns. A heavyish P-mono needs to accelerate quickly out of turns, and that's where advantage is gained in heat racing.

[magnum500sw]

So I take it that the v series is only good for a long long straight pass.

[properchopper]

So I take it that the v series is only good for a long long straight pass.

On just about anything but a lightweight hydro, you can eat lunch while waiting for a V to hook up.

[Chris Harris]

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[magnum500sw]

I.M.P.B.A. Record Holder P-Hydro 111.001mph Q-Hydro 120.192mph S-Hydro 139.233mph


wow :bowdown:

what i am getting at is you would only ever use the v series in a saw run , never in a race setup . what i am trying to figure out now is what props to buy and what to stay away from . so far for a 1/8 hydro setup x are safe for all to use and are a good start point , 1600, 1700 and abc are more hydro props .

[Chris Harris]

wow :bowdown:

what i am getting at is you would only ever use the v series in a saw run , never in a race setup . what i am trying to figure out now is what props to buy and what to stay away from . so far for a 1/8 hydro setup x are safe for all to use and are a good start point , 1600, 1700 and abc are more hydro props .

I'm not saying that the V series can't be used in a race setup, I have certainly seen it done but in SAW setups is where they seem to do the best. When it comes to moving a big, heavy boat like an 1/8 the X series are a safe bet. The 1600 and 1700 series Octura props have high lift characteristics and will need some modding to make work.

Chris

[magnum500sw]

So if find a x series that really works good and I wanted to try a 1700 or a v series would I go to the prop chart find a similar dia and pitch. Or would I add pitch and or dia. I would think you would add some pitch because of the added lift. to me it seems like the added lift would = more rpm.

[Chris Harris]

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[lohring]

Changes in diameter change the prop load LOTS more than changes in pitch. One mm increase in diameter makes a huge difference compared to 1 mm increase in pitch. That's why people run cut down and/or pitched up props.

Lohring Miller

[martin]

If you take say a 45mm diam x 1.4 = 63mm pitch, If you cut the diam down to 40mm do you end up with a 40mm diam but pitch is still 63mm. Their for pitch ratio to diam is higher. Thanks Martin.

[Chris Harris]

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[lohring]

"Like I said above keeping the same diameter and going up in pitch increases load exponentially."

Propeller load is roughly directly proportional to pitch increases, but is proportional to around the 5th power of the diameter. See this (http://www.mh-aerotools.de/airfoils/propuls2.htm) for air propellers. The same factors hold for water operation.

Lohring Miller

[Chris Harris]

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[magnum500sw]

I.M.P.B.A. Record Holder P-Hydro 111.001mph Q-Hydro 120.192mph S-Hydro 139.233mph

This really speaks for itself. Don't abandon this thread. You've been a real help it's unfortunate that I really have no idea and experience to addequately determine the good and the bad. I'm not saying what's right and wrong with anyone's post. But your rep speaks volumes to a noob like myself and others that may pass thru this thread. I'm sure they don't shelf a rtr 139 mph hydro.

[lohring]

I'm a long way from a prop expert. However, I've been involved with attempts to scale model results to full size and have searched through a lot of information. I also race with one of the best prop men out there, Brian Buaas. We are all in learning mode with surface piercing props. Nothing beats a lot of trial and error. From this, I know you can add a lot of pitch before you need to take a tiny amount off the diameter to reduce the load. Eventually you have too high a pitch to diameter ratio and the efficiency goes down.

By the way, the link above talks mostly about the difference between two and three blade props, the topic we were discussing.

Lohring Miller

[Chris Harris]

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[jamie]

:popcorn2: Chris please continue ... Lohring please go away :blah:

[sailr]

Chris holds more records than just about anyone I know. His boat designs, setups, and obviously prop choices speak for themselves! He is the LAST person I would ever argue with but there always has to be someone of no particular fame that knows far more than the experts. Go figure.

[lohring]

I've been involved with these still standing straight line records:
NAMBA GX1 hydro 109+ mph set in 2005
NAMBA GX1 Sport Hydro 97+ mph
UIM 144 volt hydro 98+ mph set in 2008
NAMBA A Outboard Hydro 81+ mph
And these recently passed records:
NAMBA G1 Hydro 106+ mph
NAMBA GX2 Hydro 103+ mph

See UIM records (http://www.uimpowerboating.com/vsite/vnavsite/page/directory/0,10853,4916-151354-168570-nav-list,00.html) and NAMBA records (http://www.namba.com/content/records.asp?EventType=10)

The details of the NAMBA gas records with my picture are here (http://www.namba.com/content/library/propwash/2005/march.pdf) on page 12.

I'm not trying to put anyone down. I'm trying to be educational from my experience of 25 years in model and full size boating.

Lohring Miller

[properchopper]

Chris holds more records than just about anyone I know. His boat designs, setups, and obviously prop choices speak for themselves! He is the LAST person I would ever argue with but



there always has to be someone of no particular fame that knows far more than the experts. Go figure.

Gee Jim, I guess the National Safety Director of NAMBA and a veteran racer with more records than you'll ever dream of is "someone of no particular fame "

I'm sure Lohring wasn't trying to dispute Chris's knowledge and accomplishmemts but was just trying to add info from his own research.

"Go Figure"

[Chris Harris]

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[sailr]

:zip-up:

[magnum500sw]

Anyways.... I have no idea what the h@&! Just happened to my question on props. Remember 2 blade 3 blade ?

[lohring]

From the link in my post above:
I had to attach it because the pictures and formula won't post. All this applies to water propellers.

Lohring Miller

58566

[magnum500sw]

i found this .
http://www.propline.com/Propeller-General-Information/Propeller_Terminology.htm

[1truckerdan]

@ magnum500sw,
Thanks for that link
That is a really informative page for anyone to "grasp" prop terminology (like me), also there are links for rpm, sizing, installation, and FAQs.
Daniel

[lohring]

Be careful using internal combustion engine data for electric motors. Electric motors have a huge torque rise and don't loose rpm very quickly with increases in pitch or diameter. Heavy loads will stall an IC engine, but in electrics the current draw just goes up until things melt. There's a lot of data on propellers for model planes, but others experience seems to be the best for boats. Logging current draw is a big help.

Lohring Miller

[PumpedNotch]

Cool thread!!

[drwayne]

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I miss Chris ..............

[skyhighdiver]

Like you said: BJ26 - X642

MG - Prather S220?[/QUOTE]
I would have to say the x642 and the 445 are top notch MG props

[bwells]

All I get from Chris Harris' posts is a series of dashes all the way across the screen. Is there a link in there somewhere?

[magnum500sw]

Looks like he edited all his posts for some reason