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Author Topic: Tug stability  (Read 3261 times)

Tom_DK

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Tug stability
« on: July 24, 2008, 04:43:12 PM »

Hi

Got a 2 hours run yesterday with my Yorkshireman. All is fine except i'm not sure if a heavy Tug like mine is suppose to "tilt over" on sharp turns?
You can probably see it, when I turn at full speed then it seems like the boat is moving towards the uppesit side as I turn to boat to. (hard to explain)

I guess its because of the position of the batteries inside the boat and how closed they are positioned to the buttom of the hull. But its it normal for a tug to act like this? or is it tilting too much?

An other funny observation I made is that when I run the boat at full speed, then stern part of the deck is diving so much that water is shortly comming onto the deck. Maybe my boat is too fast?

Data:
- 20 pc NiMh D-cells ~ 2 x 12V - 9000 mAh
- 2 Speed 550 geared motors
- weight I think more than 10 Kg
- 43mm 3 blade brass props

http://www.youtube.com/watch?v=Uai3C6vYa1U


BR,
Tom
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Shipmate60

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Re: Tug stability
« Reply #1 on: July 24, 2008, 05:34:00 PM »

Tom,
She is rather fast for a tug, scale speed of about 30 knots.
That alone will make the stern dig in, most Ocean tugs have a wet main deck when free running but not quite at that speed.
The heeling on turns is also excessive, partly due to the speed, but does indicate that your weight might be a bit too high.
Can you lower any batteries or ballast.
But most of the "problems" you mention is due to the excessive speed.

Bob
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Tom_DK

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Re: Tug stability
« Reply #2 on: July 24, 2008, 06:52:52 PM »

Thanks,

Yes i can lower the weight a bit by removing a 7.2V  battery pack and a 4.8V pack. Can use BEC from one ESC and put in a small regulator to remove the 7.2V pack. Might lower the weight by 0.5 Kg.

I don't like to run the boat at full speed either, so I think that will do it. At half speed I calculate a running time of 3-5 hoursm that should be fine  :)

Regards,
Tom
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J.beazley

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Re: Tug stability
« Reply #3 on: July 24, 2008, 06:58:59 PM »

I think what Bob was getting at is your batterys need to be placed lower inside the boat (laying on the bottom of the hull) to be able tostop some of the roll you have.

Removing batterys will only make her sit higher in the water making your troblems a little worse i think as she will bob about in the water.

Jay
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Re: Tug stability
« Reply #4 on: July 24, 2008, 07:01:20 PM »

Tom , I think Bob meant can you lower any weight not remove it. I think he thinks your weight, ballast etc is to high as in height. ;)

Sorry Jay, you just beat me. O0
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Tom_DK

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Re: Tug stability
« Reply #5 on: July 24, 2008, 07:08:52 PM »

Ah okay, yes I can lower the weight by turning both 12 battery packs 90. Thats an easy task to do

Regards
Tom
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tugmad

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Re: Tug stability
« Reply #6 on: July 24, 2008, 07:37:12 PM »

I built the Yorkshireman when the kit first came out and had stability problems with severe heeling even in moderate turns  never did iron it out.
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Tom_DK

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Re: Tug stability
« Reply #7 on: July 24, 2008, 08:10:25 PM »

I built the Yorkshireman when the kit first came out and had stability problems with severe heeling even in moderate turns  never did iron it out.

After looking into my batteries position its seems like they are so flat that turning them 90 would not change anything. I guess thats just how the kit act and I can't do anything about it. Guess its because so much weight is above the waterline  :'(
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Tom Eccles

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Re: Tug stability
« Reply #8 on: July 24, 2008, 08:23:58 PM »

Hi Tom,

I notice you are using 7.2v battery packs maybe this is part of the problem.

In my Yorkshireman I use a 12v 7ah SLA battery placed very low down immediately foward of the motors. I also have a similar sized battery which sits under the drive shafts. I found that all that was needed then were some small weights to carry out the final trimming. I use twin Viper ESCs and a Viper mixer (the build was in my pre ACTion days) .

I also found that sealing the washports helps a great deal in keeping the aft deck dry(er)

Hope this helps

Cheers
Clegg
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Tom_DK

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Re: Tug stability
« Reply #9 on: July 24, 2008, 08:43:48 PM »

No my boat is running with this equipment:

2 pc of 12V/9000 mAh packs. Both packs is made of 10 x 1.2V - 9000 mAh - D cells ( one pack for each motor)
1 pc of 4.8V/2600 mAh pack. Pack is made of 4 x 1.2V / 2600 mAh - AA cells (for the reciever)
1 pc of 7.2V/3300 mAh pack. Pack is made of 6 x 1.2V / 3300 mAh - C cells (for light and sound system)

I used NiMh cells for ALL pack since the weight is only half the weight of a SLA pack of the same size. That enables me the get a much longer running time.
The two main battery pack (12V) are place like in a T. The height of the packs is only 50-60 mm so thet are placed as much down on the buttom of the hull as possible.
The total weight of the ship should be okay since the white water marks on the hull is just where they should be.

Maybe anyone got a suggestion?

Regards,
Tom
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Shipmate60

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Re: Tug stability
« Reply #10 on: July 24, 2008, 11:11:53 PM »

Tom,
Have you tried powering her with 7.2 volts to the main motors?
If she were mine I would cut down the voltage to reduce her speed.
Make up 7.2 volt battery packs (assuming she handles ok on 7.2 volts), but with the batteries laying flat as in racing packs and replacing the lost weight with lead right on her keel.
That is about it.

Bob
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Tom_DK

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Re: Tug stability
« Reply #11 on: July 24, 2008, 11:33:07 PM »

Tom,
Have you tried powering her with 7.2 volts to the main motors?
If she were mine I would cut down the voltage to reduce her speed.
Make up 7.2 volt battery packs (assuming she handles ok on 7.2 volts), but with the batteries laying flat as in racing packs and replacing the lost weight with lead right on her keel.
That is about it.

Bob
hi Bob
It would be more easy just to set up a Dual Rate on my transmitter to reduce the speed. But I think I could try to remove the one battery pack and try improving the ballance with lead.
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Shipmate60

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Re: Tug stability
« Reply #12 on: July 24, 2008, 11:44:02 PM »

Tom,
The reason I suggested reducing the voltage is to try and get the C of G lower.
This will increase the Mettacentric height making her "stiffer" and more resistant to rolling.
As a starting point could you try removing the main batteries, ballasting her with lead along the keel and trying her on 1 x 1.7 raving Pack.
If she is more stable it will give you the option to try moving/changing the battery packs to get her stable.
I still think the excess speed is the worst culprit though.

Bob
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Tom_DK

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Re: Tug stability
« Reply #13 on: July 24, 2008, 11:48:48 PM »

I agree with you.
Will try it out tomorrow, just its not easy to break the battery pack apart again, so that would be the final thing I will try
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Shipmate60

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Re: Tug stability
« Reply #14 on: July 24, 2008, 11:50:49 PM »

Tom,
There isnt any need to YET.
Just trying to set the optimum you can expect then it will be up to you, he said sloping shoulders rapidly!!!

Bob
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