Im retired from boating for a few years now due to old age but I have to chime in here.
Buoyancy issues are a farce in SA due to incompetent installers and I would venture to say lawmakers are not beyond question as well.
For starters, 30% buoyancy (for inland use)
does not float most of the powerboats out there, period. I made it my business about 7 years ago and informed a senior member of the then BIASA of which I was a member to take it up with SAMSA. Nothing came of it and many, if not all boaters with Category "R" are under the impression that their boats are unsinkable hence the 30% buoyancy installation if
it was correctly calculated and installed by installer I must add.
The 30% I believe was obtained by the lawmakers when one takes the submerged weight of laminated fiberglass in water, whereas the density of water comes into play, for example:
Laminated GRP SG = 1500kg/m3 (SG=specific gravity)
Submerged factor multiplier = 0.33
IOW, a cubic meter of laminated GRP submerged weights a third of its dry weight, and suddenly the 30% buoyancy requirement for Cat 'R" make sense as to how they arrived at the number. Here is a short table with conversion factors for different submerged materials - full list can be seen at http://www.uscgboating.org/safety/bo...n/table4-1.htm
However, what they seemed not to have taken into account is all the other stuff that goes onto the boat and the engine jumps at you because it is mostly made from steel and aluminum and looking at the SG's above and submerged converting factors made your hair stand up. Not to mention the battery(s) stainless steel and all other heavier than fibreglass items on a boat.
And it even get worse with boats with two outboard engines and larger the engine the worse it gets...
However, the 60% buoyancy to displacement ratio called for offshore boats makes more sense for most boats if the second engine is factored into the calculations.
But as said in my opening remarks, the problem lies with the buoyancy installer. They should have had some training which a few years ago was in the form of workshops arranged by foam manufacturer and SAMSA which yours truly attended. As a boat designer (Diploma from an accredited institution) I was not very impressed by their MO and calculations and kept mum - you know the saying about arguing with someone ...
Every buoyancy installer in SA will tell you impressive things about how it all work and most, if not all, cannot tell you why a boat floats.
I once recalculated the figures on a certificate that was suspect for a client that stated that the buoyancy ratio installed was over 60% whereas it was actually only 27%.
At least in your part of the country you can perhaps find a credible installer, (just be glad you are not in my part of the woods) but again he will only install as required by law (SAMSA) and the 30% only put you in a sense of false security in believing you boat will be OK when holed and taking on water big time.
I do not know the current state of affairs with the buoyancy issues and as I said Im retired from boats et al since 2013 and try to keep it this way, but I heard a rumour that the 30% is now replaced by sufficient and if this is true, it even gets worse. Hopefully it is just a rumour and should be treated as such.
Imagine how an owner whom had built a boat out of marineply wood that have a positive
submerged buoyancy ratio of nearly 50% going to convince a buoyancy installer that without an engine his boat exceeds the 30% required by SAMSA by far. Remember, most of these installers are boatshop workers without any "boating design" expertice and in my town the installer's main work is fencing, gates etc...
As a parting note; download the USA Coastguard buoyancy manuals (bulky and complete with sketches and calcs on how to do) etc. if you want a proper take on how it should really be done and calculated, and I would suggest SA maritime lawmakers do the same.