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Author Topic: HMS Cossack stability  (Read 7112 times)

john44

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HMS Cossack stability
« on: September 14, 2011, 11:49:16 pm »

Has anyone had to fit stabilizers to a HMS Cossack or is it a bad idea? Deans marine kit.
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Shipmate60

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Re: HMS Cossack stability
« Reply #1 on: September 15, 2011, 01:07:02 am »

There is no need if you keep the topweight down and use a MiNim battery pack and ballast along the hull bottom with strip lead such as flashing.

Bob
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justboatonic

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Re: HMS Cossack stability
« Reply #2 on: September 15, 2011, 11:27:07 am »

Hmmm. Long thin hulls are best ballasted with lead on the sides at water level. Sticking lead in the bottom of the hull can induce the 'pendulum' effect.
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Shipmate60

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Re: HMS Cossack stability
« Reply #3 on: September 15, 2011, 02:26:13 pm »

The lead sheeting if thin enough will go up the sides of the hull.
And certainly not at water level for these hulls.
The physical size dictates that the ballast must be as low as possible or you will have stability problems.

Bob
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john44

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Re: HMS Cossack stability
« Reply #4 on: September 15, 2011, 05:29:44 pm »

Thanks guys, I will be using lead flashing and a 6 cell NimH battery with an Mtronics esc. battery up front or middle?

regards

john
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Shipmate60

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Re: HMS Cossack stability
« Reply #5 on: September 15, 2011, 05:32:07 pm »

The battery is the heaviest so best done while afloat in the bath, should be slightly aft of the centre.
But depends on the weight of the motors, which ones will you be using?
But try her without lead as depending on battery capacity you might only need to trim her.
On my last one I used a double battery pack of 7.2 volts 2000maH and she did not need any ballast and was perfectly stable.

Bob
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DickyD

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Re: HMS Cossack stability
« Reply #6 on: September 15, 2011, 05:34:24 pm »

Inside of my Deans HMS Javelin if its any help.

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john44

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Re: HMS Cossack stability
« Reply #7 on: September 15, 2011, 09:22:14 pm »

Many thanks, Bob,Richard. The motors are MFA 385s. I will try the double battery pack as suggested in bath trials.


regards

john
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john44

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Re: HMS Cossack stability
« Reply #8 on: September 16, 2011, 09:50:15 pm »

Battery case made for twin battery pack and fitted.2000 6 cell Nicad batteries loaded, speed controllers placed in all superstructures fitted
and I still had to put quite a bit of lead flashing along the bottom of the hull to bring the bow down to water mark.
She seems very stable now. I will include some photo,s from down at the lake after this weekends sailing/maiden voyage.

regards and thanks

john
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Shipmate60

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Re: HMS Cossack stability
« Reply #9 on: September 16, 2011, 10:59:42 pm »

John,
With that set up she will be fine.

Bob
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Re: HMS Cossack stability
« Reply #10 on: September 16, 2011, 11:05:59 pm »

When you put it in the water, before you send it off, try tipping it on its side and see if it comes upright ok.   :-))
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john44

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Re: HMS Cossack stability
« Reply #11 on: September 17, 2011, 05:24:41 pm »

Thanks Bob. Hi Richard I turned her on her side as far as I could (with superstructures fitted) during the bath test, she sprung back like a good un.
I don,t think I will have a problem with her now. What do you think would be the best type & size props to run on the 385 motors?
I have fitted propshop handed 32mm 3 blade that I had spare.

john
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Re: HMS Cossack stability
« Reply #12 on: September 17, 2011, 05:53:26 pm »

I should give them a whirl John, though you might find you need 4 bladed.

Best of luck with the maiden voyage. :-))
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john44

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Re: HMS Cossack stability
« Reply #13 on: September 30, 2011, 05:35:05 pm »

Hi Richard, Bob, the maiden voyage was brilliant she sailed wonderfully with the classic slight list to either side when turning. Brilliant. Mind you her turning circle
is quite large. I will fit an oversize rudder it should help.
Once again thanks for the help and info.

regards

john
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Shipmate60

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Re: HMS Cossack stability
« Reply #14 on: September 30, 2011, 06:23:07 pm »

John,
Which way are the props turning when going ahead.

Bob
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john44

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Re: HMS Cossack stability
« Reply #15 on: September 30, 2011, 08:36:22 pm »

Hi Bob, when going ahead the L/h prop which is L/handed turns anticlockwise and the r/h r/handed prop turns clockwise.
Out in the center I think its called.

john
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Re: HMS Cossack stability
« Reply #16 on: September 30, 2011, 08:38:09 pm »

Try changing the props over John. :-))
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john44

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Re: HMS Cossack stability
« Reply #17 on: September 30, 2011, 08:43:06 pm »

Will do Richard, will be sailing again Sunday.

john
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Shipmate60

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Re: HMS Cossack stability
« Reply #18 on: September 30, 2011, 11:51:58 pm »

John,
On small models just changing the props over can have a real impact on the turning circle.
The propwash is directed on the rudder by the ships counter (stern shape)

Bob
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john44

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Re: HMS Cossack stability
« Reply #19 on: October 01, 2011, 02:59:55 pm »

So what you are saying guys is that the Idea,( propellers) displacement hulls out at the top & planing hulls inwards at the top
depends on the size of the craft, and shape of hull and that in theory they could work better in reverse?

I have swapped the props over and I will let you know Sunday how she handled.

Thanks
john
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Re: HMS Cossack stability
« Reply #20 on: October 01, 2011, 03:12:33 pm »

Only on twin screw single rudder.
The propwash is more concentrated over the rudder by the counter.

Bob
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john44

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Re: HMS Cossack stability
« Reply #21 on: October 05, 2011, 10:07:25 pm »

Hi Bob, Richard, I must say you were bang on re. changing over the props did have a huge impact on her turning circle
especially at speed, she takes a no where near the distance to turn that she used to.
Thanks again to you both for your much appreciated input.

regards

john
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Re: HMS Cossack stability
« Reply #22 on: October 05, 2011, 10:11:39 pm »

Happy to Help John, glad you have her sailing as you want her to.
It gives you more time to enjoy her.

Bob
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Re: HMS Cossack stability
« Reply #23 on: October 05, 2011, 10:16:05 pm »

Its a pleasure John.

Enjoy your sailing. :-))
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