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Old 09-08-2015, 12:35   #16
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Re: Suitable material as a filler under fibreglass

First, do you want the extra ballistic added to the boat...if you do then I like the idea of epoxy filler with beads it is fairly light and hard...I would find the appropriate can or bucket coat it with petroleum jelly can press in a low spot for the bilge pump. Remove it after epoxy has set.


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Old 09-08-2015, 13:25   #17
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Re: Suitable material as a filler under fibreglass

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Concrete has been used a lot in commercial fishing boats also. Simple, and cheap, easily molded to the shape you want. ...if you don't mix it too watery. Many a sailboat hull has been made of concrete. Some boats in WWll were also.
You likely want a concrete sand mix, but might google it.
.....and you wont have to put fiberglass or anything over it.
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Old 09-08-2015, 15:46   #18
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Re: Suitable material as a filler under fibreglass

Some great ideas and clearly there are many ways of skinning this particular cat that I had not thought of.

The simplicity of the concrete solution does appeal to me though I am slightly worried about anchoring the concrete well enough to to be safe in a roll over. I suppose a layer of fibreglass over the top should help, but I'd like to think of a way of connecting it to the lower surface if I were to go this way.

Thanks also for the ideas on how to do a foam layer though I take zeehag's caution about rotting foam. I wonder if closed cell pouring foam would cause the same sorts of problems... Making the bulk of the volume from a rot proof foam as suggested would surely address some concerns.

I'll check out the various fillers suggested, if they are as economical as they appear they might be the simplest solution.

Thank you all for the great advice, as always, here's to a bone dry bilge.

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Old 09-08-2015, 18:10   #19
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Re: Suitable material as a filler under fibreglass

Am I to understand you need about 100 litres (say 25 US gallons) of fill and you already have maxium displacement.

If so, I would stay away from concrete as it would add at least 1 ton or more of weight.
And to use epoxy fillers, you will need deep pockets.

Either use foam - closed cell, drop in or pour in - or create a false floor well glased and leave an air void below. Maybe with a permanent pipe just in case water does somehow get in and thus you can pump out.
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Old 09-08-2015, 18:28   #20
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Re: Suitable material as a filler under fibreglass

I'm finding a figure of 250 kg for 100 litres of concrete from online calculators. More than I'd like to add, that's for sure, and a heck of a big lump to have flying around in the case of a roll. At least if I did add that much weight it would be in a useful place, but yeah, it is a big negative. We are plenty heavy enough as it is.

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Old 09-08-2015, 19:06   #21
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Re: Suitable material as a filler under fibreglass

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I'm finding a figure of 250 kg for 100 litres of concrete from online calculators. More than I'd like to add, that's for sure, and a heck of a big lump to have flying around in the case of a roll. At least if I did add that much weight it would be in a useful place, but yeah, it is a big negative. We are plenty heavy enough as it is.
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That and concrete is best used in barges and fero cement boats.
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Old 09-08-2015, 19:28   #22
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Re: Suitable material as a filler under fibreglass

You guys are headed way down the wrong path. You don't need to fill the entire space with something, you just need to take up the space. Instead of trying to fill the void with something, just enclose it with a lightweight fiberglass tank that matches the external dimensions. Then tab the tank to the hull.

The easiest way is likely to be molding it around cheap styrafoam you can throw away afterword. It's called the 'lost foam' method, and for one off projects works great.

You can also turn this into a secondary water tank if you need it by just using more glass and adding baffles.

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Old 09-08-2015, 19:49   #23
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Re: Suitable material as a filler under fibreglass

First clean the area with TSP and knock down all the high spots, so you don't need as much material to "level" it. Then lighten the stern and weight the bow to place the boat ~6" low at the bow. A runny mix of ultra slow epoxy and microballoons will self level in the sections between frames.
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Old 09-08-2015, 20:40   #24
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Re: Suitable material as a filler under fibreglass

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First clean the area with TSP and knock down all the high spots, so you don't need as much material to "level" it. Then lighten the stern and weight the bow to place the boat ~6" low at the bow. A runny mix of ultra slow epoxy and microballoons will self level in the sections between frames.

Why 6"?
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Old 09-08-2015, 20:50   #25
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Re: Suitable material as a filler under fibreglass

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Why 6"?
Because he's being clever. Then when the boat is level again, the new cured surface will slope to the rear.

Mind you, I'd need a downward force of about a ton to lower the bow by 6 inches... but it could be done.

M
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Old 09-08-2015, 20:52   #26
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Re: Suitable material as a filler under fibreglass

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I'm finding a figure of 250 kg for 100 litres of concrete from online calculators. More than I'd like to add, that's for sure, and a heck of a big lump to have flying around in the case of a roll. At least if I did add that much weight it would be in a useful place, but yeah, it is a big negative. We are plenty heavy enough as it is.

Matt
Sorry, my error, you are right - its ~ 250Kg
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Old 09-08-2015, 20:55   #27
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Re: Suitable material as a filler under fibreglass

So back to the false floor out of plywood, coated all sides with epoxy, glassed into place and air below.
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Old 09-08-2015, 21:00   #28
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Re: Suitable material as a filler under fibreglass

In the US we can buy expanding foam in various densities. For example 2-1 gallon
containers can make 2 to 8 cubic feet depending what type you buy. It's cheaper and lighter than concrete.
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Old 09-08-2015, 21:34   #29
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Re: Suitable material as a filler under fibreglass

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Because he's being clever. Then when the boat is level again, the new cured surface will slope to the rear.

Mind you, I'd need a downward force of about a ton to lower the bow by 6 inches... but it could be done.

M
Hey thats only 1000 litres of water in plastic drums on deck near the bow.
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Old 09-08-2015, 21:48   #30
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Re: Suitable material as a filler under fibreglass

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Sorry, my error, you are right - its ~ 250Kg
Still kill ya just as well if it got loose in a rollover.
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