What are the laws for bouyancy

[archie1979]

Hi all does anyone know or where to get information regarding what the maritime laws are for bouyancy of a vessel.
Particularly what needs to be applied to a home built 20foot cruiser.
A push in the right direction would be great.

Cheers
Archie

[b.o.a.t.]

start here Archie.
http://www.nmsc.gov.au/abp.html
then follow links as seem appropriate.

according to http://www.nmsc.gov.au/documents/ABP_Standard_Web.pdf
there are several standards which may be used to calculate buoyancy.

I can't see a written requirement for any buoyancy in a vessel longer than 6M except if it is a hire boat.

and this one from Tassie gives some numbers & calculations
http://www.mast.tas.gov.au/domino/ma...e/Buoyancy.pdf

cheers
AJ

[Lewy the Fly]

Get your hands on acopy AS1799

[archie1979]

So basically for boats less than 6m you need to incorperate some sort of bouyancy

[Lewy the Fly]

I would have thought that was good idea whether the law required it or not.

[Aquamarine]

Hi Archie

you are right, the ABP standard only requires boats <6m to have either basic or level flotation. Though of course it is a good idea in >6m.

For >6m you will need to assess the stability and powering of the boat. AS1799 (which is to be re drafted this year) can be used for that. I understand that it may become available free on the NMSC website after it has been re drafted.

[b.o.a.t.]

One thing has got me scratching my head though...
a fragment of memory says something about 'x' cu.ft of enclosed air buoyancy per person, or 'x/2' cu.ft of secured foam instead of air.
My fragments suggest it was in relation to aluminium dinghies.

Does this ring any bells with anyone else ? Was it a law? Or a class rule?

cheers

[malb]

Hi all does anyone know or where to get information regarding what the maritime laws are for bouyancy of a vessel.
Particularly what needs to be applied to a home built 20foot cruiser.
A push in the right direction would be great.

Cheers
Archie

No. 1 It needs to float.

Sorry to be so flip about it, but bouyancy is what makes it float in the first place. Basically, an item placed into water will sink into the water to the point where it has displaced water with a mass equal to that of the object.

If the item is not fully submerged, then it has bouyancy, i.e the average density of the item is less than the density of water it is sitting in. If it fully submerges, it will continue to sink to the bottom unless externally restrained. In this case the average density of the item is greater than that of the water it is submerged in.

What you are actually asking about is bouyancy aids and reserve bouyancy.

Consider any small simple boat hull. when launched and loaded to it's design capacity, it should float with a reasonable degree of freeboard for the water conditions that it might encounter. Now if you tip it and recover, or take a wave, the hull will end up holding some water, increasing the weight of the unit, so it sits deeper into the water to displace a further volume equal to the volume of water sloshing in the bottom. By sitting deeper, the freeboard reduces, increasing the chance of taking more waves.

Once the hull is completely filled, there is no chance of recovering the vessel as the average density of the unit, (hull plus contained water) must be greater than that of the water is lies in.

However, if the builder had been prudent and provided air tight compartments, water should not be able to enter these compartments unless they are holed. A prudent builder would ensure that sufficient air volume was sealed into the hull to keep the hull at surface level or above it, should the boat be loaded to its design limits, and then filled with water.

Since by definition 1 litre of water has a mass of 1kg, a boat weighing 200kg, and with a design load of 250kg, needs to have a sealled air volume of 450 litres minimum to ensure that it will not sink below the surface if, in operating at design load, it is inadvertantly filled with water due to misadventure. This is termed reserve bouyancy.

The actual location of the air volume within the hull is important. If it were all placed in the bilges for instance, there would be a significant tendancy for the hull to roll over and sit in the water inverted. While the boat may not sink and could continue to support the crew to design limits, it would be significantly resistant to being righted by the crew and bailed out. Similarly, if the air volume were located forward behind a bulkhead, once the hull was filled with water, it would sit nose high and be difficult for the crew to recover.

Ideally, the reserve bouancy should be distributed about the hull in proportion to the weight distribution of the hull and fixed accessories such as motor, fuel tanks, batteries, etc and a far above the water as possible. This ensures that the distressed hull will sit near level with the water, and will provide a self righting tendancy to aid the crew.

Allowances may be permitted by controlling authorities for a range of things, such as using something other than air to prevent water ingress(foams etc), or allowing that life jackets are available to contribute support to members of the crew, so that hull may not need to provide full support for them.

I understand the nature of your question, i.e. What do I need to incorporate to legally meet the letter of the law?, but suspect that an understanding of the basics may be helpfull as well.

[Boatmik]

Below the first line looking down ... Here is some stuff on the relevant part of the Australian Builder's plate which stipulates two types of acceptable buoyancy.

Below the second line looking down ... Then an explanation that it does not apply to many boats at all.

______________________________________
http://www.waterways.nsw.gov.au/sbh/rego.html

Australian Builders Plate

Most new recreational boats will need to have an Australian Builders Plate (ABP) to be registered in New South Wales. The ABP gives you key safety information such as: the number of people and load allowed on a boat; engine rating and weight; as well as buoyancy performance.

If you are buying a new boat, the plate also makes it easier to choose one that best suits your needs.

Importantly, the maximum load information will help you to avoid overloading and possible capsize. Maximum load includes the weight of people; outboard engines; and carry on equipment such as safety gear, eskies, fishing tackle, spare parts and portable tanks etc.

A major safety characteristic of the plate is its requirement to have either level or basic flotation for boats less than 6 metres.

* Basic flotation means that the boat will float in some capacity in the event of swamping or capsize. This may allow you to cling onto the boat whilst awaiting help.
* Level flotation means that the boat will float in a level position if swamped. This will allow you to remain in the boat and possibly bail out the water whilst awaiting help.

Remember; always check with your boat’s builder or a marine professional before modifying your boat’s hull or permanent fittings, as this can impact on the boat’s flotation and other aspects vital to its safe operation.
__________________________________________

Now we discussed the Australian Builder's plates here
http://www.woodworkforums.ubeaut.com...ighlight=plate

Comes down to applying to non secondhand motor boats - unless the situation has changed.

This set of posts (thankyou Aberdeen) also has info on how you can make your own Builder's plate. The only check is when you go to register your boat is whether it has one or not.

There is also some advice about different standards - check with your state authorities - I think it is national legislation - but I am not sure.

Anyway the victorian experts said this...

2) if they don't, you need to decide which standard you will use to build your boat, my suggestion, and, it is only a suggestion is AS1799 or ISO 12217 or ABYC the later can be down loaded free almost verbatim from the USCG web page [it does take some searching to find it though] either of the other two can be purchased from SAI Global over the internet, or to avoid costs try your local library they may order it in for you if its not on the shelf.

See the link above for more complete info.

BTW most of these rules accept wooden hull material as a contributor to the buoyancy. We worked out under the US Coastguard requirements (it is one of the ones above) for the PDRacer -and with a small outboard and one person aboard it needed very little foam.
________________________________________________

Finally two words to the wise ...

1/ Having reasonable built in Buoyancy is a really good idea.

2/ If using foam - Dont use the pour-in type. It absorbs water and holds it up against the wood and creates rot and you can never get the buoyancy tanks dry. It is better to cut closed cell (and maybe fuel-proof foam and even consider giving it a coat or two of epoxy to toughen it up (polyester resin will dissolve some foams). I would also consider gluing it in place so it is not quite in contact with the bottom of the bilge to allow free drainage.

Best wishes.

Michael

[Aquamarine]

I see mention in here of using air chambers. The NMSC has released it's first Guidance Note, which deals with air chambers. In summary, the largest two chambers must be considered damaged in your flotation calculations.

[Aquamarine]

If you use ABYC, be aware of the preconditioning requirement to 'dunk' the boat for 18 hours before performing testing. This requirement has been highlighted in the NMSC Guidance Circular 07-1

www.nmsc.gov.au/documents/ABP/National%20Guidance%20Circular%2007-1.pdf

I have seen a few high volume production boats stating ABYC while thier staff are not aware of the 18 hr requirement.