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  #1  
Old 03-06-2012, 06:27 AM
shakey78 shakey78 is offline
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Type of foam to use??

Question I have an aluminium boat that I'm building and need to add my floatation boat total weight 410kg, I was going to use foam sheets but was keen to know your thoughts on making my own polyeurthane foam and making moulds of the area I need to place the foam.

What's your thoughts of this liquid polyeurthane foam as floatation?
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  #2  
Old 03-06-2012, 06:35 AM
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Floatation needs to hold up the boat, any and all equipment, including full tanks, plus the crew, with sufficient reserve capacity that is can be pumped or bailed out.

A 410 kg boat needs approximately 1.35 cubic meters of foam, which will just barely float the boat and no reserve margin, but unless this is a really small boat, I think your weight estimate is off a tad.

Why do you think you need the foam? Where will you put it (really important if you expect it to remain upright when swamped).
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Old 03-06-2012, 07:12 AM
shakey78 shakey78 is offline
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Yes in Australia we have to have a buoyancy minimum for boats under 6mtrs, as my boat is only 5mtrs with Aluminium hull and not much else bar some flooring the weight of my hull so far with out the floor fuel or water and motor is 230kg, you see over here foam sheets are hard to find but i can find it in liquid form no worries
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Old 03-06-2012, 04:14 PM
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Australia is a big place - sheet foam is hard to find only in places where freight on the space taken up by foam blocks is expensive.

What is the brand of the "liquid form" your are considering ? Is it supplied from marine sources or hardware shops?

Good explanation here at

http://www.foamedinsulations.com.au/...ation-foam.seo
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Old 03-06-2012, 10:51 PM
shakey78 shakey78 is offline
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Yes i found them last night, so yer im going to look at if i use pour in or sheets, as i like the pour in foam as i can make moulds of the area i wish to place the foam and get it to fit exactly in that area, but wanted to know if i need more of the pour in foam than the sheet foam.

so i guess Pour in foam Vs Sheet foam what should i use and which one is better??
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Old 03-07-2012, 01:13 AM
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Call DuckFlat (08 8391 3988) or try http://www.duckflatwoodenboats.com/
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Old 03-07-2012, 07:14 PM
shakey78 shakey78 is offline
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well found out some stat on the pour in foam 1 cubic meter will float 965kg dead weight thats the 35 density foam wow didnt think it would hold that much but its true.
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Old 03-08-2012, 03:22 AM
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The figures from self poured foam may vary a bit if it behaves like most foams. The density can vary if it is poured in 'freeform' environment. If you pour into a container, you can expect a pooling of foam around the edges and things like that.

In practice, if you can get the sheet foam, its easier to cut and fit into position than trying to make some sort of mould to get a special shape.

The higher the displacement figure, the less solid the foam is. In a square metre of foam, only 35 kilos may mean its not as tough and solid as a bit heavier foam, and may be an indication that the poured foam ends up less dense than the 'manufactured' foam.

Best idea is to get some samples of both and see what you think.
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Old 03-08-2012, 03:32 AM
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Quote:
Originally Posted by PAR View Post
Floatation needs to hold up the boat, any and all equipment, including full tanks, plus the crew, with sufficient reserve capacity that is can be pumped or bailed out.

A 410 kg boat needs approximately 1.35 cubic meters of foam, which will just barely float the boat and no reserve margin, but unless this is a really small boat, I think your weight estimate is off a tad.

Why do you think you need the foam? Where will you put it (really important if you expect it to remain upright when swamped).
Can you elaborate?

1.35 cubic meters will float 1350 liters (or kgs) of water, minus the weight of the foam (some 50 kgs or so). Plenty to hold the 410 kgs of the boat, plus a reserve of some 890 kgs.

Placing the foam in tactical places is the key to safety. When holed, will the boat still be upright, or will it turn turtle?

I designed my racing dinghies such that when capsized, they would float low in the water, so righting them is much easier (the daggerboard would be approx on the water surface, instead of 30cm (1 ft) above), and the mast would also ly flat on the water, instead of poking into the surface, thereby reducing the risk of turning turtle.
For dinghies, capsized boats should be able to be righted by a tired crew after a day of intense sailing, and in less than perfect conditions, not just by a fit crew in the harbour.
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Old 03-27-2012, 06:35 PM
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Jasonadams, can you explain your continued insistence on asking the "yacht building experts"?

Herman, my point is the requirement requires the boat float up right, fully equipped and crewed, with sufficient reserve that she doesn't just down flood again with a passing wake. This means careful arrangement of buoyancy, as I'm sure you know, to address this as well as other considerations, such as the ability to right a capsized dinghy in a stiff breeze with building wind and waves.

As to Jason, I don't have any idea what he's talking about, particularly "holding up the boat strongly". Maybe it's a translation issue, but this doesn't make any sense.
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Old 03-27-2012, 10:01 PM
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Shakey, I spent many years helping boat manufacturers meet flotation requirements and testing boats for flotation. Also, the rules are the same here in the USA as in Australia. So just translate pounds to kilos and cubic feet to cubic meters and you will be ok

The type of boat you are dealing with is required to float when swamped, in an upright attitude, and not lean more than 30 degrees either way, and not have the bow or stern more than a foot under water (one end out of the water the other underwater)

flotation needs are:
flotation to float the weight of the boat.
flotation to float the engine.
flotation to flotation the passengers and their gear.

Each of these requires a separate calculation.
Another thing to remember is that most things don't weight the same underwater as they do in the air. Some have positive buoyancy such as wood, and some very negative such as engine blocks. So the amount of flotation has to be adjusted for each material based on it's weight underwater.

Recommended foam density is 2 lb. i.e. 1 cubic foot weighs 2 lbs and supports 62 lbs in salt water.

One of the hardest parts of this is to get the engine to float and do it without rolling the boat over. This means placing foam blocks at each rear corner in amounts enough to keep the engine afloat and stable.

The foam has to be distributed around the boat to float it level and the flotation to float the people has to be divided and distributed on each side of the boat. If you put all of it in the bottom of the boat, the boat will float level, UPSIDE DOWN.

For more info look here. As I said the rules are the same here as there,
http://newboatbuilders/pages/flot.html click on level flotation.

As for pour foam vs block (sheet) foam. Whatever you use make sure it is closed cell foam.

Block foam advantages: Convenience, availability. Usually polyurethane, not affected by gas, oils, cleaners
Disadvantages: requires strict attention to manufacturers instructions. Sensitive to temperature and humidity while being made.
Notorious for absorbing water even though it is not supposed to.
Usually 2 lb density but may vary if mixed wrong.

Block foam: Advantages: also convenient, readily available from hardware and home improvement stores (I don't know if you have Home Depot or places like it). Any place that sells materials for home building sells sheet foam. Ask for insulation foam. Usually it is in 2 X 8 ft sheets, 2 inches thick, I've also seen 4 inch thick. It is 2 lb density: i.e. one cubic foot weighs 2 lbs.
Does not absorb water.
Disadvantages, has to be cut to size.
It is almost always styrofoam (polystyrene) which is dissolved by gas and oil and some cleaners. So it has to be up out of the bilge, or sealed up in epoxy or plastic bags. If you use resin it must be epoxy. Polyester resins will turn styrofoam into goo.

None of this is rocket science. Anyone can do it. it doesn't require a lot math.
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  #12  
Old 03-28-2012, 04:13 AM
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Floatation is something people want but really dont think to much about what they are actually trying to do to make the boat float note i underlined the bit !!
What are you really trying to do ! you are dislacing the water inside the boat and force it out over the sides or the lowest place like the motor well and give the boat bouyancy again so if you use automaticly inflatable tubes you can force even more water out of the boat .
A friend and i perfected a system of auto inflatable tubes down each side of the boat and a big tube at the back to be able to suport the motor and what ever is in the back !!,most boats get air trapped under the foredeck anyway so the 2 sides and the big tube at the back did everything we asked !!.it was possible to climb up over the outboard and get back inside the boat and because the gunwhale was poking above water level could bail the rest of the water out and you have a completely refloated boat again ?? The bigger the tubes the better the system works the tubes are completely fixed to the inside of the boat so they cant come out!! made from Hypolon material same as a inblatable boat and with aircraft grade fittings with co2 cylinders that inflates in seconds . when its all back to shore the systenm could be repacked and new co2 cylinders and ready for the next mishap !!all is reuseable
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