• DB Marine Services

What every skiboater needs to know about buoyancy.

There is a lot of hype around buoyancy and we are here to settle it once and for all!


Don't let your ship sink!

The South African Maritime Safety Authority, affectionately known as SAMSA, refer to buoyancy as the bottles and/ or foam placed inside a boat in order to maintain flotation in a damaged or flooded state.

You can read more here


On most seagoing categories of vessels built-in buoyancy is expected to replace the need to provide a life raft, which it can only do if there is sufficient buoyancy provided to ensure a stable level platform upon which the crew can be secured in an emergency (fully flooded, swamped or capsized).


According to SAMSA the buoyancy must consist of either foam or approved plastic bottles or a combination of both. Foam should be of a suitable closed cell type, and approved bottles are HDPE (High Density Polyethylene) Grade 2 plastic bottles with secure watertight caps, or sealed six-sided boat floats manufactured of HDPE. While filling you boat hull with plastic bottles may be cheaper option, it is certainly not the safest choice!

This week a customer brought in a 28ft Butt Cat that hit a sea turtle while fishing offshore. This incident could have ended tragically, as the wounded turtle ripped the bottom of the tunnel off the boat exposing the foam noodles in the hull. Were it not for the excellent buoyancy characteristics of the cross-linked closed cell SPX 33 foam, the vessel certainly would have sunk!
The tunnel was ripped out by a seaturtle!

In an emergency like this, you really want to be confident in your ship’s ability to stay afloat! Let’s consider what could have happened had they used bottles or two-part expandable closed-cell foam. Most people just throw a bunch of empty milk bottles in the hull and call it a day. This of course, is not fantastic when your tunnel is ripped off, as all the bottles will simply float out of the boat, and you will surely sink. Should you decide to go with bottles, it is advised that you keep them in nets to keep them together. Unfortunately, bottles leave a lot of empty space in the surrounds, where water can enter, and weigh the boat down. The plastic can also deteriorate over time, rendering the bottles useless. Do not be fooled by the broad term - closed cell foam. Not all closed cell foams are created equal! Many people use 2-part expandable closed cell foam, and while it is accepted by SAMSA, it is certainly not something we would advise! This foam can easily absorb water when damaged and become waterlogged, weighing down your boat. In this particular scenario, this foam would not have been sufficient, as it is attached to the tunnel, and would have been ripped apart too, by the force. The remaining foam wouldn’t be sufficient to keep a boat with engines and 5 crew afloat! It is also more difficult to tell if there is a leak in the boat, since the foam absorbs the water.

That is why we insist on using fully cross-linked closed cell expanded polyethylene foam sheets or noodles (SPX 33) for all our deck replacements and new builds. This foam is resilient, compressible and light weight and it has excellent buoyancy characteristics - able to support approximately 1000 Kg/m3!


SPX 33- cross-linked closed cell expanded polyethylene.

Other features of this product:
  • Complies with SAMSA regulations section 9 & 9.1 regarding floatation requirements. [Category A-E: (Off-shore) as well as category R: (Inland waters)]

  • Superior tensile strength, elongation and weathering capabilities.

  • SPX 33 is fully closed-cell, and will not absorb water even if the material is cut open.

  • It is a fully cross-linked closed cell expanded polyethylene.


If you are anything like us, you want to spend as much time as possible on your boat. That is just another reason we love SPX 33: buoyancy inspections are only required every five years. However, SAMSA requires yearly inspections on PET plastic bottles and HDPE bottles require inspection every three years.


Should you need any further technical advice, get in touch with us!

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