Floatation – What is it and why does it belong in your boat? [PODCAST]

by Ian Kuhl on February 25, 2017

in Canoes | Kayaks, Case Study, Chandlery, Franklin Boats, Franklin Marine, Guides, Huon River, Marine Safety, Sailing Adventures, Trailer Boats, Trailer Boats Accessories

This audio is an excerpt from our weekly “Fishing and Boating Show” – click here for more about the show.

Most boats should have at least a neutral buoyancy.

This means that a boat should continue to float, even when it is full of water and upside-down.

A boat must meet this requirement for it to comply with Australian standards and receive a HIN (hull identification number).

Every boat built after 21 October 2009 is required to be fitted with a HIN plate (and thus meet a number of requirements including buoyancy) before first sale.

If your boat does not have a HIN plate mounted to it somewhere – there is a chance your boat may not meet these standards, and may not contain enough floatation to achieve the desired neutral buoyancy.

Many home made boats and boats made before 2009 are not required by legislation to contain enough floatation for a neutral buoyancy.

Ensuring your boat stays above the water in all situations is a very important safety consideration.


If you spring a leak or otherwise find yourself in grief – ALWAYS STAY WITH YOUR BOAT.

Staying with the boat, even if it is awash, makes it a lot easier for rescue authorities to locate you.

A boat is a much larger target than a person!


Most commonly, ‘pouring foam’ is poured into a number of ‘floatation chambers’ in the boat to achieve the required buoyancy level.

You’ll find these chambers under the seat in most tinnies – and underneath the floor in many runabouts.

It’s also possible to use inflatable tubes. These usually get secured to the bottom of the seat and on small dinghies, and can be used as an alternative to foam in the floatation chambers.

Obviously, you do not want to use these tubes around sharp objects, and you should keep a regular eye on them to ensure they don’t deflate over time.

Another alternative is known as Closed Cell Foam Sheeting. This type of floatation can be sliced up into blocks to be tied under seats, stuffed in floatation chambers – or even to line the anchor locker!

Polystyrene is also available, though bilge pumps really don’t appreciate the small styrofoam balls they leave everywhere. If you use this type of inflation, be very careful to keep it isolated, and keep a close eye on your pumps.

Empty plastic bottles are also a good DIY type of floatation. Just ensure they are thick and sturdy, and seal them full of air. We’ve seen this a few times in some old trailer sailors where they’ve been stuffed underneath the floor.


An easy way to test whether your boat has enough floatation (if you have a small tinny or dingy) is to try and sink it.

Take it to a shallow beach, empty it of personal gear and either bucket it full of water or roll it over until it is totally full to the gunwale.

The boat should not sink at this stage. If it does sink, drag it up the beach and add closed cell foam sheeting under the seats and lockers, then retest.


The larger the boat, the more foam you will need to achieve neutral buoyancy.

Larger runabouts should have floatation just like tinnies and dinghies, however it is worth noting that large yachts and motor boats will often not be buoyant.

This is due to the practical limitations of filling a large boat that contains ballast, keel, lockers and berths with foam.

Even when empty, fuel tanks do not ‘count’ towards the buoyancy level due to the fact they are fitted with breathers and can fill up over time.

It is very important that you replace any foam you take out while working on your boat. Don’t forget things like seats & beds!

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