fitting floation

[The-easyrider]

I have a 650 sea legend these boats did not come with flotation so I am going to fit some. I have been informed by someone in the boat building game that the foam that is mixed and poured in can become water logged and near on impossible to dry out . So I am planing on using pool noodels as I can fit these into all sorts of tight spots. I am going to remove the kill tank then I will be able to access most of the floor and I have plenty of room in the gunnals . I figure that if a pool noodle can float my 90kgs in the pool I could work on a noodle suporting 80 kgs a piece. So boat and motor 1650 kg 210L fuel 210kg 7 people 700kg = 2560KG /80 kgs= 32 noodles fitted into the boat this will be a squeeze but should be able to get most of them in I hope as they dont have to stay as round ones they can be cut into all sorts of shapes you can even get square ones. Just after any thoughts before I make a start.
Thanks
Azza

[FNQCairns]

Hi Azza,

i think you may have your assumptions a bit off. To assume how much a pool noodle should float level with the surface calculate it's entire volume (big guess = 10L) find out what weight of salt water (guess = 1.05kg/L) it will displace.

Multiply these two together = 10.5kg subtract then the weight of the noodle (100g?).

This my example pool noodle will float only 10.4kg of anything when submerged.

Your boat weighs substantially less sunk in the water than on the trailer, there is a basic rule of thumb type equation to assume this on the US coast guard site (I think it's been a while someone may already know).

The ply used in the boat will already have positive buoyancy so you will in the end be looking to buoy only the materials that would naturally sink.

Anyway hope this helped some, from memory a light-ish foam say 2 pack polyurethane then 0.6m3 is enough to level float a 5.2m fibreglass runabout...please don't accurately quote me on any of the specific numbers i used as it's been a while.

[cbs]

Azza,

Your assumptions are way off. Think about this. A single noodle may support a 90 kg person but will not support 90kg of steel, lead etc.

The amount of buoyancy required is a function of relative densitys of every material in the boat that will be submerged with respect to seawater plus additional for the items that are likely to remain above the waterline (including people).

You might also note that buoyancy material does not need to be provided for fuel capacity. Unleaded has a density of around 750kgm-3 which means it will float on its own accord.

AS1799 has a method contained within it that will give a good answer, that will included options for level flotation in addition to basic flotation, however it is rather involved for the average person. You may be best to find a competent person to do the calculation for you.

cbs

[The-easyrider]

Yes it dawned on me after I posted that fuel is lighter than water, it was late

[Stuart]

In my opinion, and this maybe wrong. I think that the foam doesn’t and shouldn’t keep the boat afloat; it’s the displacement of water that the foam provides that helps keep a boat afloat. In having said that. I have just finished packing my 7.3 meter alloy hull with 1.7 cubic meters of buoyancy foam. Having looked at this foam packed in tight, I don’t suspect the foam itself will float the boat but the displacement of the water.

Stu

[krazyfisher]

have a read of this should help

http://www.marinesafety.vic.gov.au/doi/doielect.nsf/2a6bd98dee287482ca256915001cff0c/979a6f5d931e0c27ca2572370023848a/$FILE/Safe%20Boating%20Bouyancy%20Book_v2.pdf

[on-one]

this might help http://www.glen-l.com/weblettr/webletters-7/wl55-flotation.html

[boatie_72]

Here is the Australian standard, you have to work out the factor for fiberglass, the swamped motor weight, cubic capacity of the boat etc.

I wouldnt advise on pool noddels, the correct foam to use is polyethlene foam, which you can get from a company called foam design, isnt the cheaps of stuff but is the correct stuff approved by the NMSC.

http://www.nmsc.gov.au/media/pages_media_files/files/AS1799%20Small%20Craft%20-%20Part%2012-General%20Requirements%20for%20Power%20Boats.pdf

Hope that helps.

Cheers