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Author Topic: Floating dry dock  (Read 5001 times)

Brian Adley

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Floating dry dock
« on: February 23, 2011, 10:54:30 AM »

I am doing some design sketching of a floating dry dock.  The idea is for the dry dock to submerge, the ship is sailed into position then the dry dock is raised by discarding ballast - in this case water - with the ship in place.  I am sure someone must have tackled this before.  Any comments or tips?
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ben hall

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Re: Floating dry dock
« Reply #1 on: February 23, 2011, 11:13:06 AM »

you could begin with it submereged have 2 watter pumps either side and pump the watter out and another 2 each side to pump the watter in

the wait of the watter on each side would way it down or you could have a sub like tube underneath it and do the same but with one pump for each way(in/out) but this would be less stable
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DickyD

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Re: Floating dry dock
« Reply #2 on: February 23, 2011, 11:17:22 AM »

I am doing some design sketching of a floating dry dock.  The idea is for the dry dock to submerge, the ship is sailed into position then the dry dock is raised by discarding ballast - in this case water - with the ship in place.  I am sure someone must have tackled this before.  Any comments or tips?

Contact Ian [boatmadman] he built the Bourbon Orca, the heavy lift ship. Same principle.

http://www.modelboatmayhem.co.uk/forum/index.php?topic=17422.0  :-))
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Roadrunner

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Re: Floating dry dock
« Reply #3 on: February 23, 2011, 12:16:31 PM »

There is another Build log on the forum that is also a semi sub which would also be of intrest, which does cover a lot of the process of making the vessel submerge.

http://www.modelboatmayhem.co.uk/forum/index.php?topic=9014.0
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DickyD

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Re: Floating dry dock
« Reply #4 on: February 23, 2011, 01:48:17 PM »

Contact Ian [boatmadman] he built the Bourbon Orca, the heavy lift ship. Same principle.

http://www.modelboatmayhem.co.uk/forum/index.php?topic=17422.0  :-))

Sorry I meant Blue Marlin same as Roadrunner, same builder though.

http://www.modelboatmayhem.co.uk/forum/index.php?topic=9014.0
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Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

Roadrunner

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Re: Floating dry dock
« Reply #5 on: February 23, 2011, 02:57:12 PM »

I'm sure you have already done some googling on floating dry docks but just in case you haven't have a look at some of these. I would like to see a build log of this vessel should you get to the point of building, it would certainly be a project with a difference, something this forum needs a bit more of.
The concept of floating dry docks are not a recent invention the first were used during the 1940's but i think its only in the past 30 years they have developed into 'ships' rather then 'barge' type designs.

http://www.psm-sensors.co.uk/drydock.htm












http://www.robertwynnandsons.co.uk/terra-marique-capabilities-semi-submersible.html (website for this photo)






http://www.sealift2.com/gallery.html (website for this dock)
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dreadnought72

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Re: Floating dry dock
« Reply #6 on: February 23, 2011, 03:14:45 PM »

Earlier than the 1940s - here's HMS St. Vincent in Swan Hunter's floating drydock in 1912.



Andy
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Enjoying every minute sailing W9465 Mertensia

Umi_Ryuzuki

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Re: Floating dry dock
« Reply #7 on: February 23, 2011, 05:50:32 PM »

Here is something Roger showed up with at Foss Cup.

It will rise and fall in about a minute. He said, that any longer,... people would get bored.
The four pilings are part of a carriage set on the bottom of the pond, and keep the dock
in position, and stable.

 :-)
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Brian Adley

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Re: Floating dry dock
« Reply #8 on: February 24, 2011, 11:24:16 AM »

Thanks for the interesting comments.  Some considerations that have occupied my mind:

Don't use a valve to flood the dry dock.  If it sticks open (say something jammed in the valve preventing it from closing) you would have to get wet to recover!  Rather use a two way pump with some emergency power shut off.

My sketches show the bottom as well as the sides are water ballast containers (actually all in one). 

Keep the controls, pumps etc housed on one of the decks, above water level.  Water is pumped in and out of a sump in the bottom, protected from debris by a suitable sieve material.

In the ballast calculations careful how you take the water inside the tanks into account.

6mm plywood would probably be a good material to use for the hull.  Would have to complete the inside painting and water proofing before the second wall is built in.

etc

Happy sailing
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boatmadman

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Re: Floating dry dock
« Reply #9 on: February 24, 2011, 01:52:42 PM »

Brian,

Interesting challenge!

I recommend from experience, you use 4 off 2 way pumps, each connected to an independent chamber.

4 chambers, in the bottom of the dock, subdivided f/a and p/s each with baffles to reduce the free surface effect, this will allow you to trim the dock as it sinks/rises.

Keep ALL the pumped ballast in the bottom of the dock, use the sides as buoyancy - you WILL need them otherwise the whole thing will become really unstable and liable to capsize without even thinking about it - read my Blue Marlin build for my experience of this.

Fill the buoyancy chambers with polystyrene so that if they spring a leak you preserve buoyancy.

Dont make the mistake I did by using free flood ballast, it drastically reduces the available lift of the structure - make it all pumped ballast.

6mm ply will be plenty man enough for the job, just ensure everything is well sealed against the water.

If you lift the pumps above the waterline, the pumping rate will be reduced, if you can do it, keep them as low as possible, best would be in an airtight tank in the bottom of the structure - again, look at the Marlin build to see how I did it.

Ian
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if at first you dont succeed.....have a beer.....

Brian Adley

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Re: Floating dry dock
« Reply #10 on: February 25, 2011, 11:40:24 AM »

Hi Ian.

I suppose there is nothing against using submersible pumps, as in a fish tank perhaps.  Then they can be down at the base of the dock.  Alternatively place them at the botton of water proof shafts. 

Regarding balancing, the point on water movement causing instabillity is well taken.  Thank you.  I had in mind one pump in a sump to which all the water could flow.  Using baffles, as in a water or petrol tanker would take care of the water movement.  However, if the boat to be lifted settles of centre, it would be useful to be able to adjust the trim in the multi pump installation.  This would need 4 RC channels, but as these are probably only switched (not proportional), that would not be a problem with the modern possibility of expansion switching in RC.

I had not thought of instability as the dock will be pretty wide, byt with heavier weights this could be an issue.

Must go.  Cheers

Brian
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