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Author Topic: Stability  (Read 21603 times)

Offline Eddy Matthews

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Stability
« on: November 21, 2006, 08:07:35 AM »
Quote from: "thewharfonline"
I was always lead to believe wheels made the boat more stable on the side...I don't know if this is only rumour though.


Exactly the oppossite Sean! The paddlewheels etc add no extra floatation, only a large amount of weight hanging on each side.... Try sitting two people in the centre of your boat - Nice and stable yes? Now move the two people so that one is sitting on each side of the boat - Nowhere near as stable then is it?

This is exactly what happens when you add paddlewheels, sponsons and paddleboxes... You DECREASE the boats stability!

Ask anyone who has modelled a sidewheeler, and most of them at one time or another will have made a model which was totally unstable, or at the very least tended to dig a paddle into the water on a turn - Even when you straighten the boat up the paddlewheel stays dug in and the boat runs with a frightening list to one side or the other!

Yet another thing to think about!

One final point - my posts are intended purely to HELP with your builds, not to put you off in any way. Yes small paddlers can be made to work, but they need careful planning and a lot of thought to be successful. Trial and error is okay to a point, but the basics must be right (or nearly right) in the first place or you are doomed to failure. Hopefully if some of the major pitfalls are pointed out you can avoid some of the issues that many of us modellers have experienced!
~ Never, ever, argue with an idiot. They'll drag you down to their level and beat you with experience ~

thewharfonline

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Stability
« Reply #1 on: November 21, 2006, 06:41:28 PM »
And the pitfalls that we discover we can write about and stop other paddler builders making the same mistake!

Attached is a photo to show the effects of bad and prove that even the big boats can do it. It's dark because of the sailpast buts it's PS Alexander Arbuthnot with everyone standing on the side of the boat that already has a room full of tools on the side....

Don't worry Eddy I'm not taking your posts as being disheartening! This advice is needed...especially for first timers like myself. And if advice isn't taken...well just take a look at Lady Rae! Michael...a photo perhaps?

Offline Roderick Smith

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Stability
« Reply #2 on: November 21, 2006, 09:09:56 PM »
Without any proof, I don't think that the proposals for Grebe or SJ will make either unstable, and certainly not in the calm waters in which they will be used.

Sean's photo of AA listing are interesting, but presumably well within stability limits (the thumbnail is black, but clicking to bring up the photo in full reveals the image).

A Sydney twin-deck screw ferry did capsize when everybody rushed to one side during a regatta or watching something famous.  IIRC the era was the 1930s, and the vessel was one of the R fleet (Rodney? Radar?).

PS Ruby was a lean greyhound.  There are published references to crew members rolling barrels of water from side to side to enhance stability around curves.  The current restoration has put only the wheelhouse back on the third deck, and not the cabins or music room.  AFAIK this is to provide stability to meet modern survey requirements.

The small PV Eliza something has two decks on a short hull.  It wears outrigger floats (like training wheels on a child's bicycle) to enhance stability.

We may laugh at PV Lady Rae being overbodied, but is it unstable?

I often ponder that PV Shiralee looks top heavy (two decks on a short hull), but that doesn'ty prove that it is top heavy.  I was cruising alongside for half an hour in July, it it wasn't listing.  I did draw a design at the time which recessed the lower deck into the hull.

Photos of all of these vessels will appear in the discussion thread in this forum in due course.

Regards,
Roderick B Smith
Rail News Victoria Editor.

thewharfonline

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Stability
« Reply #3 on: November 21, 2006, 09:56:09 PM »
Lady Rae rocks from side to side and sits in a list and now has outrigger pontoons to support her I believe...unstable I believe.

Consider PS Ellen. There were reports after lengthening that upon turning a bend she would list so much that the skipper could get a cup of water from the river (of course the river was obviously cleaner back then!) I've seen photos of Ellen...I can understand where these stories come from...her size is impressive but definately wasted.

Many steam launches carry their boiler in the front of the boat...does this assist stability...I would assume so...but I would also assume then that the quite a few people are required to sit in the stern of the vessel to balance it out...my thoughts on launches.

paddlesteamerman1

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Stability
« Reply #4 on: November 22, 2006, 06:55:23 AM »
Also the PS Marion, I have cruised on it several times now, and it as nearly always on a list to left (unless you were lodged on a sandbar at Goolwa like we were and getting towed off by the Oscar W). Always there is one paddle deeper than the other... But I wouldnt call the Marion unstable.. It would catch a lot of that howling wind down the long wide straights of the Murray in SA and it has proved stable.
Sean, that is a great photo of the AA on its classic list, I also have a few of it on a list!!
Do paddles ALWAYS decrease the stability of a vessel? Or just sometimes?
With the SJ Hull being nearly (half as wide as she is long) 6' wide and only being 14' long, it is a stable boat, and was used to row out to ships back in the 20's on the rough Southern Sea at Portland...
And paddles are the same both sides, so on flat water does it decreased the stability or is only when the boat is getting pitched around on small waves and one side goes up with a wave and the other down that the boat goes over or under???

Offline anth

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Stability
« Reply #5 on: November 22, 2006, 02:09:22 PM »
paddler's have a decrease in stability when they broad side caused by
too sharper turn under power or wind shear.
it's just the method of the beast it can't be helped when one paddle enter's the water with more float than the other unless it's a stern wheeler.

that's where the experiance's of the crew and captain are needed,it's more common with flat hull paddle steamer's than hulls with  multi chine hulls,the shape of the hull help's increase or decrease the problem.


cheers Anthony

thewharfonline

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Stability
« Reply #6 on: November 22, 2006, 06:38:31 PM »
Like Etona she has a round hull and tosses and turns in the wind like mad. I've heard stories of her on Lake Alexandrina tossing and turning like mad!

So in this way I'd say the hull shape contributes to this...random anecdote probably but I thought it was fitting!

Offline derekwarner_decoy

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Stability
« Reply #7 on: November 22, 2006, 07:57:29 PM »
Hi PD's & a quote from Eddy a few days back

"Ask anyone who has modelled a sidewheeler, and most of them at one time or another will have made a model which was totally unstable, or at the very least tended to dig a paddle into the water on a turn - Even when you straighten the boat up the paddlewheel stays dug in and the boat runs with a frightening list to one side or the other!"

The understanding behind this is pretty simple  :hammer when we think about it

Both paddles on the common shaft are in fact acting as 1/2 style gyroscopes... which have kinetic, and hence potential energy

So if one paddle DIGS in & under [water], the resultant is that this gyroscopic energy in the opposing paddle is transmitted through the paddle shaft to attempt to accelerate the wheel that is [under water] & hence increase the immersion of that wheel.......

All very important points in understanding the design of paddlers be they any scale.......Derek :)
Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op
Australia
www.ils.org.au

paddlesteamerman1

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Stability
« Reply #8 on: November 22, 2006, 08:10:58 PM »
Sorry Derek, dont have a full understanding of that  :oops:  :oops:  :oops: !!
Does that mean that if one of the paddles is under the water more the other will try and make it go faster and digging it in more??

Offline derekwarner_decoy

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Stability
« Reply #9 on: November 22, 2006, 08:52:30 PM »
Hi PD's & yes James.....

1) if one paddle is [greatly loaded or immersed]...[lower than], the opposing paddle will attempt to free wheel & hence the kinetic {rotational}  energy is transmitted via or to the fixed paddle shaft  

2) So if we think of the paddle wheel that is [greatly loaded or immersed]..., the resultant is an 'increase in rotational moment' in the opposite wheel in the attempt to 'consume' the increased kinetic energy with the water & hence to dig in even further

3) Now a secondary argument could be considered here in that both wheels are on the common shaft & the above could not happen as any attempt to overspeed by the inboard wheel would be negated by the outboard wheel

4) This is not spectulation as points 1) & 2) are fact & hence the importance of consideration of design elements prior to building in any scale - Derek  :)
Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op
Australia
www.ils.org.au

paddlesteamerman1

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Stability
« Reply #10 on: November 22, 2006, 09:03:05 PM »
Thankyou Derek!! That is now at my level of understanding, just another newbie learning along the way  :D  :D :D :D :D
Would it be a better idea to have independant paddles as to avoid this happening and doing some damage?
I have been thinking of that for a couple of hours now..
Cheers
:beer

Offline andy

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Re: Stability
« Reply #11 on: June 25, 2008, 06:14:21 AM »
Hi,

I think, a paddler is not unstable, if it has a big boiler and a fine and heavy steam engine in its hull!

But, if you fit a light Diesel engine with hydraulics instead of a steam engine, maybe!

Andy

jost

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Re: Stability
« Reply #12 on: November 05, 2008, 12:27:30 PM »
hi everyone
I'm new and I have no experience with paddlers, but when I read this stability thread so I have one question,
are there some mathematical basics for calculating the stability??????

Jost

Offline derekwarner_decoy

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Re: Stability
« Reply #13 on: November 08, 2008, 04:35:07 PM »
Hi PD's....& to answer the question from Jost... :thinking....yes when Noah built his vessel I think  :whistle he probably would have consulted with one of the local Naval Architects

These people were really only mathematical number crunchers...however the real issue for model applications is we cannot scale water pressure/surface tension/wind....... as our mother nature   :respect still controls this

So if you build a model with a high surface profile @ any scale .... :hammer....& a light breeze of 10 Km passes...your vessel is subjected not to the scale of the breeze but to the third power & hence high windage  ....which causes all of the problems

Good reading here is ...researching a thread by 'bundywrap'........

To understand basic hull stability....try a GOOGLE search on 'metacentric point of balance'........'of vessels' ....ten years worth of good reading......Derek  :beer

http://www.onemetre.net/Design/Balance/MetaCent.htm
« Last Edit: November 08, 2008, 10:22:26 PM by derekwarner_decoy »
Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op
Australia
www.ils.org.au

Scout0098

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Re: Stability
« Reply #14 on: January 11, 2009, 05:03:52 PM »
perhaps it would help to lower the center of gravity if the wheels were placed lower on the gunwales, not on level with them? In looking through the forums I saw some pics of some boats like this. One was the swiss boat and a couple of the small english boats. I like the way it looked and would like to copy the design for my boat but I am afraid the shorter height would mean smaller paddle wheels and thus less effeciancy/power (larger wheels better efficency). I notice a couple of the boats had wheels with 2 foot diameters and that seemed a bit small to me.... Does anyone have any ideas/suggestions? I just finished working the bugs out of my hull and have the material to start work on my paddle wheels/propulsion system. Thanks!

 

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