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Author Topic: Prop Question  (Read 3666 times)

Killerinc

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Prop Question
« on: August 19, 2011, 03:53:43 AM »

Hey all,
I have a 32" Robbe Blue Marine MKII and i asked Robbe what type of prop comes standard on this boat and this is what they sent back....standard prop: 1-1497  Surface Screw 2-Bl.R D33.
So with that knowledge can someone help me to know what size that is and what would be a good upgraded prop to get.
Below is a Pic and here is a youtube video of the boat and gives info on what's in it..
http://www.youtube.com/watch?v=dJlv1RCse6A


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Martin [Admin]

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Re: Prop Question
« Reply #1 on: August 19, 2011, 08:55:12 AM »

Hi Killerinc,
I've used those Robbe strudder units on my Robbe 'Scarab' & 'Little Devil'. They are basic units and you may find it and the
UJ (universal coupling)  might not stand up to  huge increase in power put through it, ie. you fit larger props and motors.

 Although, having said that, I have run a 2cc IC engine through a Graupner Strudder I and a 3.5cc with a tuned
 pipe through a Strudder II !!!

http://www.modelboatmayhem.co.uk/My_models/04%20hydrospeed.htm
http://www.modelboatmayhem.co.uk/My_models/06_arrow.htm
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Killerinc

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Re: Prop Question
« Reply #2 on: August 19, 2011, 05:33:07 PM »

Is that the stock prop? if not how do you read that info on my prop(what does it mean)
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MikeA

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Re: Prop Question
« Reply #3 on: August 20, 2011, 12:26:42 AM »

standard prop: 1-1497  Surface Screw 2-Bl.R D33.


2 blade

right hand

diameter 33mm

if you up the diameter or the pitch youl get more push BUT will require more torque from the motor and martins saying that the strudder will fail if you over do it.
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bikerdude666

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Re: Prop Question
« Reply #4 on: August 20, 2011, 08:36:33 PM »

Anyone got a link to somewhere that sells those 'strudders' I had a quick google and can't find anywhere.
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pompebled

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Re: Prop Question
« Reply #5 on: August 20, 2011, 10:58:49 PM »

Hi Killerinc,

The robbe speedprops are in general only good for one thing, binning it...(they are not very good)

For the motor you've chosen, a Graupner 2318.40,5K would be a better choice.
The motor can handle more, but you'll have to buy the universal coupler in wholesale to be able to run the boat more than once a day, as the motor will shred it very quickly, specially if you 'floor' the throttle from a standstill.

The Robbe Blue Marine MKII wasn't designed with motor-upgrades in mind, the universal coupler in the steering outdrive is a dead give away for that...

Be careful and gentle on the throttle with bigger props!

Regards, Jan.
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Killerinc

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Re: Prop Question
« Reply #6 on: August 21, 2011, 03:43:22 AM »

If anyone knows a good alternate way or metal hardware to beef up the unit let me know, also what is " Binning it "?
if i do change up the strudder what would be the next step up from my prop?
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MikeA

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Re: Prop Question
« Reply #7 on: August 21, 2011, 09:26:05 AM »

binning it = put it in the bin lol
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pompebled

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Re: Prop Question
« Reply #8 on: August 21, 2011, 05:22:16 PM »

Hi K,

The 1640KV motor on 4S gives you 24.000rom unloaded, with a motor this size (and length) you should be able to turn a 42K and maybe a 43,5K - 45K if the boat is dialed in correctly.

Had the motor been longer (74 mm = more torque) you would be able to turn even bigger props, as the rpm under load are on the low side.

The steering outdrive won't handle such prosizes for very long, so changing to a stinger with an offset rudder would be the way to go.

You'd have to decide if a plastic hull is worth all the fuss, as it will need reinforcing to keep the hull (bottom and transom) from flexing when the speed increases...

Regards, Jan.
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Killerinc

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Re: Prop Question
« Reply #9 on: August 22, 2011, 07:52:41 AM »

Hi K,

The 1640KV motor on 4S gives you 24.000rom unloaded, with a motor this size (and length) you should be able to turn a 42K and maybe a 43,5K - 45K if the boat is dialed in correctly.

Had the motor been longer (74 mm = more torque) you would be able to turn even bigger props, as the rpm under load are on the low side.

The steering outdrive won't handle such prosizes for very long, so changing to a stinger with an offset rudder would be the way to go.

You'd have to decide if a plastic hull is worth all the fuss, as it will need reinforcing to keep the hull (bottom and transom) from flexing when the speed increases...

Regards, Jan.

Hey Jan,
i get the unloaded equations, but how did you get to 42k to 45k ?
Also what size Stinger and rudder sizes would you suggest for a 32" boat.
would you also be able to suggest a different motor if i upgrade the above mentioned parts?
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pompebled

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Re: Prop Question
« Reply #10 on: August 22, 2011, 05:14:02 PM »

Hi K,

The propsizes are from my experience with this size motors and the rpm's they generate on 4S, (rule of thumb so to say).
If you go up in Voltagem reduce the propsize untill you're syre the motor, Lipo end ESC will cope without overheating, than go to the next size prop.

For a surface piercing drive, you'll want the prop at 10-13% of the hull length behind the transom, so that's the size stinger you'll be looking for.

To counteract propwalk, you'll want the rudderblade next to the prop, as in the picture of my 65 cm BK Xcalibur;



Sideview:



To be honest, I would not go for a more powerful motor, your hull won't cope.
The Xcalibur in the pictures has an epoxhull, very stiff and runs up to 65 - 70 km/h (40 - 44mph) on smooth water and is a handfull to steer, with a wobbly plastic hull you'll be more floating upside down due to the bad handling...

The boat on the left is the Xcalibur, accelerating out of a turn:



Regards, Jan.
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Killerinc

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Re: Prop Question
« Reply #11 on: August 22, 2011, 06:51:42 PM »

Hi K,

The propsizes are from my experience with this size motors and the rpm's they generate on 4S, (rule of thumb so to say).
If you go up in Voltagem reduce the propsize untill you're syre the motor, Lipo end ESC will cope without overheating, than go to the next size prop.

For a surface piercing drive, you'll want the prop at 10-13% of the hull length behind the transom, so that's the size stinger you'll be looking for.

To counteract propwalk, you'll want the rudderblade next to the prop, as in the picture of my 65 cm BK Xcalibur;



Sideview:



To be honest, I would not go for a more powerful motor, your hull won't cope.
The Xcalibur in the pictures has an epoxhull, very stiff and runs up to 65 - 70 km/h (40 - 44mph) on smooth water and is a handfull to steer, with a wobbly plastic hull you'll be more floating upside down due to the bad handling...

The boat on the left is the Xcalibur, accelerating out of a turn:



Regards, Jan.


Hi Jan,
Cool, thx for all the great info and the pics, they are worth a thousand words.

As for the voltage, if i get the new drive/rudder system and reinforce the transom, should i try a 5s Lipo, cuz my watercooled motor and watercooled 125a ESC are super cool and the Lipo is warm after a 30 min straight run, thats why i was told somewhere that if it's cool up the prop size. I dont get propwalk now but who knows after the upgrade, so thx for the tip.
i was also told that you want to be within 25k - 35k rpm, so with the 4s like u said i am about 24k.

For the Drive Strut i took the middle point between 10-13.... 11.5 percent of 32" = 3.68, Does that sound right, over 3 1/2" past the transom?
I dont have a Flex shaft, so should i just get a Drive Strut or a Stinger and order a Flex Shaft?
The prop should be flush with the rudder? and how deep of a rudder should i get for a 32".
Thx
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BJ

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Re: Prop Question
« Reply #12 on: September 15, 2011, 07:52:07 PM »

You could try this for a solution, see the pictures attached
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Killerinc

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Re: Prop Question
« Reply #13 on: September 20, 2011, 06:51:14 AM »

Hi Jan,
Cool, thx for all the great info and the pics, they are worth a thousand words.

As for the voltage, if i get the new drive/rudder system and reinforce the transom, should i try a 5s Lipo, cuz my watercooled motor and watercooled 125a ESC are super cool and the Lipo is warm after a 30 min straight run, thats why i was told somewhere that if it's cool up the prop size. I dont get propwalk now but who knows after the upgrade, so thx for the tip.
i was also told that you want to be within 25k - 35k rpm, so with the 4s like u said i am about 24k.

For the Drive Strut i took the middle point between 10-13.... 11.5 percent of 32" = 3.68, Does that sound right, over 3 1/2" past the transom?
I dont have a Flex shaft, so should i just get a Drive Strut or a Stinger and order a Flex Shaft?
The prop should be flush with the rudder? and how deep of a rudder should i get for a 32".
Thx
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