We have a cabin cruiser on the Kowie river witch w

[Fanie]

Best is always to stay with the boat, even if you can see the shore. Many think they can swim that far because it looks so near... Very deceiving.

My one friend told me they were a bunch of guys going out, one guy felt sick and decided to rather stay ashore. They dropped him off just behind the surf because he was going to swim out. He almost didn't make it. As tough as we are so fragile are we also.

I'm sure if the kayak capsizes and falls on you it won't be much of an issue. I have seen board surfers get pitched by a wave and that surf boad shooting up out of the water. What if it lands on your head.

 

[thika]

Found this by chance:

But still don't quite get it..must have been sick when I was a baby?

 

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DOES SAMSA HAVE THE RIGHT FORMULA? — Buoyancy and flotation simplified — by Alberto Heydenrych

THERE seems to be major confusion when it comes to clarifying the differences between buoyancy and flotation.

Simply put, buoyancy is the upward force that keep things afloat. More scientifically, it’s a principle defined by Archimedes as follows: “Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.” The definition of flotation is “the phenomenon of floating (remaining on the surface of a liquid without sinking)”.

Flotation is not the same as buoyancy. Flotation refers to items that already have a specific gravity lower than the medium they are suspended it and will therefore float of their own accord irrespective of their shape. Such objects will always float. Simply put, one cubic metre of the material weighs less than one cubic metre of water and will float. How high out of the water it will float is dependent on how much less it weighs than the water for the same volume.

Let’s consider two examples.

If we take a cubic metre of each of the following materials:
• foam (density 32kg/m3); and
• steel (density 7 800kg/m3)

If we immerse one cubic metre of each of the materials in water (for the sake of this article I will stick to freshwater density of 1 000kg/m3) it’s quite obvious that the block of foam will displace 32kg of water, and that part of the foam will be submerged. The balance of the foam (about 68cm) will be above water and will conveniently be available to keep the weight of other items above water until it also disappears below the surface if it’s weighed down too much.

It’s also quite obvious that if you drop the cubic metre of steel into the water, it will sink like the proverbial stone.

If you can roll the steel out in to a plate and make a container that’s open at the top, such as a steel barge with a volume larger than the volume it will displace when immersed (the container will need a volume of more than 7.8m3 when immersed in freshwater), it will float. Yes, it still weighs 7 800kg and displaces 7 800kg of water, but since the total volume it occupies is larger than 7 800kg of water, it floats due to the buoyancy force acting upon it.

So, although buoyancy forces are at work in both cases, only in the case of the foam (which has a density less than the medium its floating in) can the term “flotation” really be applied to the situation. If we had a cubic metre of wood that has a density of 500kg/m3 it would obviously float half in and half out of the water.

It can thus clearly be seen that the density of the material compared to the medium it floats in has a major effect on the amount of flotation available. From the buoyancy definition it can be seen that buoyancy force can also relate to something already submerged, such as a submarine.

These aspects of the physics are seemingly regrettably ignored by SAMSA when it comes to the buoyancy certificate calculations they currently apply to ski-boats. Their calculations consider that all materials have equal densities, and they simply use 60% of that weight in the calculations.

To get to a situation that SAMSA would like to approve, that is “stable level platform upon which the crew can be secured in an emergency (fully flooded, swamped or capsized)” (see http://www.samsa.org.za/siteimgs/SV%20PAMPHLET%20-%20Buoyancy.pdf), your boat should not be more than half submerged when flooded,capsized or swamped.

Read the full story in the July/August 2010 issue of SKI-BOAT. [/align]

 

[Fanie]

I saw the article.

The thing to remember is that samsa makes laws, they don't design boats. So they are trying to enforce what was specified. According to their marine notices the deaths at sea has drastically dropped to now. Not sure if this is due to the enforced safety requirements or if there just is that many less going on the water I cannot tell.

The figures are peobably supplied by some of the boat builders, and I suspect those are minimum. The 30% specified for fresh water will have most boats sink, but if you look at some boats there just isn't enough space to fit decent buoyancy.

There are two things - most guys don't think it will ever happen to them, and secondly they'll pay R2000 for a reel but don't want to spend any money on flotation. If the boat shines they're happy, wether it will foat or not is of no concern. Probably why these laws are enforced as they are, to 'assist the ignorant'.

This is why I tell anyone to first make your boat so that it will work properly then worry about if it is legal. If you did it right then it will be legal. At the end of the day it is your butt on the boat, and not samsa's. You are also responsible for the boat and the crew/passengers, so you are the only one who is going to be blamed in case something goes wrong.

Imo the whole safety thing is way out of proportion. All these laws an stuff to ensure not a single soul perrish, yet the moment when you put foot on land any of a million criminals can take a pot shot at you - and nobody cares about that. Sick eh.

 

[Mombakkie]

Another thing about flotation ....

Rubberducks have their flotation above water while fibreglass boats have most of it below deck and the waterline. (When they are at rest)
The problem here is that as you force flotation deeper the more it wants to return to the surface. So fill a ski boat with water and at some point it capsizes because the flotation wants to be on top. With a rubberduck you don't have this scenario. Not sure how cats would act but I suspect much the same as a mono.
So in a fibreglass boat one would ideally want the flotation below the gunwales above the water line which isn't practical or achievable. One could also argue that the below deck cavity filled with air would act the same as foam/bottles if it was not swamped with water.

Some food for thought ...

 

[thika]

My point made earlier exactly

A mono WILL overturn and stay that way

There is no such thing as a "stable floating platform" with mono's at sea

 

[kirk]

One of the Marine police boats here in False bay, a large rubber duck +/- 6m ,has 2x 200hp on, it has a unique set up. It has an a type  A frame on the transom much like a very high trolling board, above head hight. Atop that is a folded air bag rubber duck pvc material, attached to what looked like a 5 liter diving tank with a trip rope . Should the duck capsize all they have to do is pull the trip rope to inflate the bag from the bottle and it self rights the duck. This duck attains speeds of 60kts according to the crew. Quite a cool idea if u ask me. This probably could be adapted to mono/ cat hull cabin tops if u have the space and will to add more saftey to ur vessel.

Cheers.

 

[vanno]

I took my boat to a local boat builder in the harbour last week for inspection re buoyancy. Also supplied him with dimensions, calculations, pictures and certified copy of ID etc. Paid my monies and got back an affidavit document on their letterhead. So basically paid R450 for someone to fill in a form for me which i still need to take to a SAMSA surveyor! Going down to get my money back today! Question - does a SAMSA surveyor have to look at it anyway OR can a boat builder certify my buoyancy so i can then get my CoF? --- Update - Had a word with the guys and SAMSA. All good because it's on their letterhead

 

[Mouldz]

Doing some maths at work,you might find interesting.
Minibus Taxi(responsible for average 30 deaths a month)
MAX PAX ---30plus
DRIVERS LISCENCE-- R250.00
ROADWORTHY (once off)---R150.00
VEHICLE REGISRATION----R300.00

RIVER CABIN BOAT---max pax---5
Ressponsible for average 20deaths a year
SKIPPERS LISCENCE----R1300.00
BOAT REGISTRTION(depending on horsepower)---R400.00
MOORING FEES-----R1800.00 per annum
BOUYANCY AND COF CERTIFICATE-----R900.00
OTHER SAFETY EQUIPMENT-----R2500.00
Some thing does not add up

I am not against boat safety I am against the prices,It makes sense to me that if the rates were brought down more people will be willing to comply,the higher the fees go the more people are going to resort to illegal methods to obtain said liscenses and certificates.Why cant the guy taking your registration fee be qualified to inspect your boat and all these be included in one fee,just does not make sense,as for skippers liscence for inland waters why not have a simple competency test for a small fee once a year,paying so much for a skippers liscence that lasts a life time is simply stupid,what if that person starts loosing eyesight ,or gets brain damage then he still is classed as a competent skipper because he has a piece of paper saying so

 

[Steven13]

I had the same problem with my boat, failed the boyancy test then got a qoutation for R3500.00 to get the boyancy right.But did some research and bought some fibreglass resin and hardner +- R250 Got 4 of those yellow oil drums that they use in the restaurants from a restaurant and bought a old surfboard that i cut up.I cut a hole in the nose  and rear of my boat put the oil drums and foam in.re sealed with the fibre glass.did the boancy test and survey and passed with flying colours.