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Author Topic: Correct rpm for 60mm props??  (Read 3180 times)

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Correct rpm for 60mm props??
« on: September 06, 2014, 12:40:40 PM »

Hi all,

I've been speaking to Andy Griggs regarding
The Typhoon/Tempest hull,
Andy informs me that she has 60mm props at the scale avaliable.

I'm curious if the motors I have will be ok rpm wise for driving the props?
There 4000rpm at 24volts with plenty of torque.

Any help or comments gratefully accepted

Regards
Adam
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Shipmate60

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Re: Correct rpm for 60mm props??
« Reply #1 on: September 06, 2014, 12:49:56 PM »

A lot will depend on the pitch and type of prop.
What type of hull is it?


Bob
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Re: Correct rpm for 60mm props??
« Reply #2 on: September 06, 2014, 01:11:02 PM »

Hi Bob,

It's models by design

Typhoon salvage tug, unsure of the pitch of prop but since she is kort nozzle I'll go to simon at prop shop,

Have not purchased the hull yet as had a few I really like but it's more the size
38.5" x 11.5"

Adam
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Re: Correct rpm for 60mm props??
« Reply #3 on: September 06, 2014, 01:33:57 PM »

2 x 60 mm korts will not need any more rpm than 4000.


Bob
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Re: Correct rpm for 60mm props??
« Reply #4 on: September 06, 2014, 04:08:23 PM »

I would say you could afford to drop RPM to between 2-3000RPM. Simon documents the spec of his props quote well. Website is down, but I think from memory the pitch of the kort props is about 1.2-1.3 times the diameter.

At 4000RPM, with 25% slip the props will try and push the tug along at about 8.5mph!

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Re: Correct rpm for 60mm props??
« Reply #5 on: September 06, 2014, 04:53:03 PM »

Bob Andy,

Thanks for the info gents, so perhaps I should use a belt drive and gear them down say a 1.5 reduction would that be a better rpm figure to match the prop pitch?
And would there still be enough top end grunt to get out of the way if need be?

Regards
Adam
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Re: Correct rpm for 60mm props??
« Reply #6 on: September 06, 2014, 05:08:22 PM »

I would go that way, and you may find you need to reduce further. Recommending drives is always tricky as there are so many factors thatcan influence how they work.

I like to test motor and prop combos in a bucket, with an watt meter attached, and also monitor the RPM, if the motor can't turn the prop at 75% of it's free running RPM or greater, then the combination is inefficient and you eityher need a more powerful/bigger or slower turning motor or gearing.

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Re: Correct rpm for 60mm props??
« Reply #7 on: September 06, 2014, 09:32:49 PM »

The motors are out of Brian Roberts
Severn lifeboat, I run them up and it seems they run a lot better on 24v
I'll end up using belt drive with alloy pulleys.

Thanks for the info Andy.

adam
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Re: Correct rpm for 60mm props??
« Reply #8 on: September 08, 2014, 04:12:51 PM »

Hi Adam
 
Most of the props of that size for tugs etc are rated at a maximum of 5500 revs, dont know if this is about cavitation etc or its the max revs the prop can stand.
My Amsterdam has an 80mm prop and a 24v motor from Mobile Marine, doing about 5000rpm, just throttle back!!!!!
 
Mark
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Re: Correct rpm for 60mm props??
« Reply #9 on: September 10, 2014, 11:11:43 AM »

if it were me I would wire up your motors to your speed controls and see if you have good low speed control if yes then go direct drive providing amps are not a problem and if too fast don't push so far forward if you are going to tow with this model you will be glad it has extra power believe me
Steve
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Re: Correct rpm for 60mm props??
« Reply #10 on: September 10, 2014, 01:29:24 PM »

Hi Steve,

Just the chap to join in, curious about 1 of your bow thrusters..?
Also I originally wanted to build a wolradd woltenmade but having difficulty finding plans of her, well hull lines anyway.

So started looking at svitzer Maltby hull but can't get a defo answer regarding what kort size etc.
So figured go for typhoon,

The scooter motors I have are 6v - 48v with an 8mm output shaft.
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Re: Correct rpm for 60mm props??
« Reply #11 on: September 10, 2014, 02:46:17 PM »

I have a maltby it will be having 70mm Kort's direct drive with the same motors as my tug powerful that pulls 12 pound constant pull the motors were out of a Mk5 Astra internal blower/heater unit props from propshop the best I have used bow thruster will be 40mm waste pipe with a cut down shaft to 2.5inch and a sanded 45mm speed boat prop I think an x prop is what its called I have made many many to this spec and all work better than anything you can buy. unless I sold you one lol
Steve
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Re: Correct rpm for 60mm props??
« Reply #12 on: September 10, 2014, 03:41:57 PM »

Re Bow thruster lol.

I was emailing Brian close re his svitzer and a couple of other tugs
Incl 1/24 nederland
But I'm havering between The Typhoon and models by design wolradd or kingston lloydsman,
No offence to others but I prefer ocean going tugs, but not a lot anchor handling tugs have character, I guess it's all upto the modeller,
Brian did say that almost all tug towing is at 1/32 scale,
But there is nothing up here regarding towing events so it makes me think I should just get what I fancy.

Fingers crossed the motors I have will give as much pull as yours
adam
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