Ship launching

Kramjit

Hi!

I saw from youtube clips that dry dock ship launching use these wooden(?) contraptions. Do they cause damage to the paint coat of the ships?

Thanks

mgb_phys

No thats why you use wood.
The boats don't generally slide on the wood, the sit on cradles that slide on greased rails.

Kramjit

So you are saying that there is not a slightest damage to the coating in all cases?

Thanks

Integral

What do you propose that they use to cause LESS damage?

Kramjit

Perhaps we could use a material with low coefficient of friction as a material for the ramp, as described by Mr./Mdm mgb_phys. Eliminate also, altogether, the use of grease.
Fundamentally, I just would like to know if existing methods scratch the paintwork.

Thanks

RonL

It's been over 30 years, but when i had some involvement with boat building(intracoastal, and river pushboats) the below waterline coatings, were mixes of paints and resins, and some flourlike metals, that had to be continually stirred with a air motor while in the paintpot.
These finishes, when cured, were as hard or harder than the metal they covered.

Not sure but i would think that finishes today might be even better.

eversafe

It is an old topic I know.
For ship launching the most interesting method is air bag launching which has the least demand of ramp and related instruments.
The force analyse during airbag ship launching is very complicated because each airbag's bearing force will change in the process. According to Calculation Result from Eversafe Marine, the pressure of some airbags will double in the launch.
So it is important to control airbag initial pressure before launch.

mike99

I was wondering if airbag launching may cause the vessel bottom painting damage since there will be relative motion between air bags and vessel during their movement.

eversafe

According our experience, airbag launch doesn't cause any damage of bottom painting unless the painting is not dry enough.
When air bags roll with vessel the friction force will impact on painting but can not peel it off.

In some extreme condition we really found painting was scratched by air bags. See that Danube salvage project , airbags were intent to get out of vessel bottom, they rub the bottom at all times because the unbalanced force. So painting was somewhat scratched.

In normal launching, this never happen.

mike99

thanks for your explanation. I visited your website and found some interesting info. As a civil engineer ,i am wondering the structure launch with air bags,such as cocrete caisson,steel cofferdam,etc. So how much weight can be launched with your bags? Is there any limitation of weight or dimension?

eversafe

Mike, you are welcomed. Structure airbag launching is a very prosperous application in China. The heaviest caisson we have launched with bags are 5600 tons. The limitation of air bag launch is not only decided by structure dimension or weight but also the launch ramp and water level. With good launch condition, possible launch weight by air bags can reach 8,000-10,000 tons, we think. You may see some projects did by our engineering team:
Steel cofferdam launch with marine air bags
Caisson air bags transportation project