Hidden airbags to keep a yacht afloat in case of an emergency, like in the VDS example case

Why would you go through all that trouble? Bottles are not ideal, but are already full of air.

 

The point is that the bottles hold their volume, no squeeze .
The "wise" guys argued that foam traps moisture over time and bottles are an alternative.

 

FWIW, I think that inflatable bags, that inflate during a downflooding event into the people space are a bad idea. Just look at what happened with ALM flight 980 and the rafts inflating inside the cabin. So NO, NO buoyancy bags in the occupied areas. Just to put a practical bound on the discussion.

ALM Flight 980 - Wikipedia https://en.wikipedia.org/wiki/ALM_Flight_980

 

Inflatable PFDs are supposed to be tested to hold pressure every year. Yes, yes I know, most don't. Life rafts every few years.
Imagine the logistics of testing and restowing a full-boat system.

 

How does the 'water jet pack' work? https://physics.stackexchange.com/questions/8947/how-does-the-water-jet-pack-work

A kick-@zz waterjet bilge pump. Just make sure the bilge water is ejected downward to drive the sinking boat towards the surface. A big enough jet should be able to hold the vessel at the surface regardless of the hole size.


Of course, you need power to be able to run your kick-@zz bilge pump, but if the hole isn't the same area as your waterline, it might even be able to keep your bilge mostly dry; until the jet runs out of water to expel.

The average jetski produces about 1000lbs of thrust [How Much Thrust Does a Jet Ski Produce? [Chart] - jetdrift.com https://www.jetdrift.com/jet-ski-thrust/]
Goggle's AI claims,

So several (say, 4) jetski drives could be used to lift a 40' boat off the bottom and pump it out at the surface. Using a similar pump and jet system as the water jetpacks, the pumping equipment could be on the surface while the jets and intakes could be placed on the boat itself.

-Will

 

If you compare the quality of the glued inflatables of 30 years ago , to the modern welded seams and material developments , you can have more confidence today.

 

Airbags need proper placement for stabilty when flooded, too low in the hull and they are more likely to invert a boat.
Double skin boats like Etap and Sadler are well proven with very few instances of core issues which have been bought on by owner neglect of deck hardware than factory build issues.
The water bottle flotation does work, but it needs securing behind battens or netting that is secure. I prefer closed cell foam blocks cut to size and removable to squirty foam in non accessible voids.

 

Did this system retain its buoyancy over time? I've seen a few sources advise against this approach saying that over time the closed cell foam absorbs water and thus loses its buoyancy. Also saying that a small leak will remain undetected if the foam is wedged between the hull and an inner hull. Is this true? Or is the risk exaggerated?

 

Was the concept of the double skin with a closed cell core in between successful? Both companies went out of business, as far as I can tell. You would have thought there would be a ready market for a company with a real product safety advantage.

 

They built 1,000s between them. It is not that there was anything wrong with the product. Boatbuilders go bust on a regular basis. They have good residual value second hand.

 

Carolina Skiffs are also filled with foam and are used as workboats successfully. Any type of construction has drawbacks. If you want easy access to the inside of the hull, foam or bottles are going to be in the way. Most boats fail from lack of maintenance of improper repairs and additions.

 

I would have thought that using a double skin with a foam layer in between would be a great solution but I have read others advise that closing off access to the inside of the hull is not advisable.

If using foam, is expanded PU good? Or is XPS superior?

 

Double skin and foam filled has been very successful...look at all the Boston Whaler ads. However, it only works well for a particular type of boat, not all vessels. Like all other things in naval architecture, the solution has to be selected to fit the situation and need.

 

I am not up to date with what builders would be using between glass skins at this time. I have used xps type foam boards cut to shape as buoyancy in wooden hulls, but i make sure its accessible. There are a range of inert foams on the market these days such as Diab, water absorbency would be in the spec sheet. Not all foams are equal in this respect.

 

If you don’t know anything about marine foams, you are not in the wheelhouse, swabbie.

Core boat with 1/2” 4 pound core and say 100 ounces per sqyd net resin n glass is 0.375 cuft or 1.5 pounds core. So a net density of say 8 pounds per cuft vs water of over 60. So each yard of a foam boat is contributing about 50 pound pos buoyancy