Suitable material as a filler under fibreglass

[Rockyscience]

Hello, you might consider "Dexpan". it is an expanding grout mainly used for breaking up rocks, concrete etc. mixes with water and increase in volume as drying. Could be just what you want, can be ordered from Home depot and others online and delivered to you. Don't have a clue to cost but easy.

Rocky

[Cheechako]

I had no idea the OP was talking that much filler. Not sure why it is necessary....? But yeah, I wouldn't put 25 gallons of concrete in. I smoothed out a concrete loaded bilge for flow with a couple gallons.

[GILow]

Originally Posted by Rockyscience

Hello, you might consider "Dexpan".

Wow, interesting stuff... just not sure I am entirely comfortable with using what is labelled as a "non explosive DEMOLITION agent" in the keel. You really wouldn't want to have that "Uh oh!" feeling half way through the stuff reacting. Somet things are only obvious after the event.

[GILow]

Originally Posted by Cheechako

I had no idea the OP was talking that much filler. Not sure why it is necessary....?

It is not ideal, but it is the only way I can see of getting the relative heights to the point where I can be certain that the area in question will drain reliably to the stern.

Normally I guess the space in question would be converted to a tank of some sort, (I pulled out the set of three fuel tanks that held around 400 litres in this area when we bought the boat because they were buggered). But either I put in full height tanks and accept that any water around them will pool as it does now, (and did before, hence the tanks were ruined) or I put in something to bring the level up to the point where it drains reliably. Once I have bought the level up I will consider some new tanks in the same place, it will still easily take 400 litres or more of tanks, even with the higher level. I was thinking some kind of generic poly fuel tanks, I can get enough in there to retire our older stainless steel main fuel tank which is getting to an age where it has be considered suspect. Then I could replace that tank with a good water tank which would balance us out better, as currently all of our fresh water is stored on the port side.

The micro balloons (or the MEGA micro balloon) idea seems the simplest solution and is waiting on my day off on Friday to get some prices.

Boats hey...?

Matt

[Terra Nova]

Originally Posted by GILow

...it is the only way I can see of getting the relative heights to the point where I can be certain that the area in question will drain reliably to the stern...

Why all the way to the stern? Why not simply to the lowest point?

[Nicholson58]

Originally Posted by UNCIVILIZED

This idea's theoretical, as it hasn't been tested yet, but...
How about filling up the space in question with ping pong balls encapsulated in an epoxy & microballoons mixture?
The mix is, I think, one of epoxy & microballoons. And it was mentioned in a rudder rebuild thread within the last couple of months. ~Odds are it was the mix, above, recommended by Nicholson58.

What you use in terms of epoxy & filler is important, as you need something which isn't going to go exothermic on you. - Which is a key point that I don't think has been mentioned yet.
However in the rudder rebuild thread, the mixture used was several inches think, but by design, took several days to cure. And didn't have any heat problems at all, despite it's thickness, & the volume of epoxy used. For which, I complimented he who suggested it.

As to ping pong balls, I know that in some classes of racing power boats, they are/were used for floatation for quite a while. As they provided the most sealed bouyancy per volume, for the lightest weight. And I gather that they did okay in terms of holding up in such applications.
IIRC, they were mostly fixed in place by sections of fishing net, & or via net bags affixed to structural members in the hulls.
So they'd be worth looking into. As would doing a test of them embedded in such an epoxy mixture. It'd let you use a lot less resin, & still fill up the space in question. Plus you wouldn't be adding that much weight.

Before you begin to apply any bonding agents:
- Pressure wash the area well a few times
- Then abrade thoroughly

Option B, might be to look into the specifics of what kind of foam surfboard makers use. And so long as it's closed cell, odds are it's cheaper than structural boat building foam. As it's a lot lower density IIRC. Plus it works well with Polyester Resins, also. Again cheaper than going to the epoxy option. Although as you're doing 2ndary bonding to resins which have long since cured, it'd be wise to use epoxy for any of that work. Especially on any glass used to hold things in place in the cavity in question.

I was the one with the thick rudder re-build. The mix I mentioned had no exothermic issues. At 5 inches thick it never even became warm to the touch. US Composites also has Phenolic balloons BTW. Tis might extend the epoxy farther. The US Composite 635 THIN is way less money than We$t. I use it for all repairs.

[GILow]

Originally Posted by Terra Nova

Why all the way to the stern? Why not simply to the lowest point?

Not all the way to the stern, but there is a section half way along the keel for the engine bay which I am trying to keep isolated from the rest of the bilge so that anything that escapes from the engine is contained.

So I have to bring the bit in front of that section up by a few inches to allow it to drain, via a hose, through the engine section and out the other side. The way the ballast is poured in the boat puts it all at the front of the keel, the aft section of the keel is empty.

A picture is worth a thousand words.

[Terra Nova]

Or you could just have a separate pump for the forward section that is lower than the engine bay.

[GILow]

Originally Posted by Terra Nova

Or you could just have a separate pump for the forward section that is lower than the engine bay.

As per my earlier post, I do have two, I am trying to bring both electric pumps to the rear together so that I have true redundancy, rather than the Clayton's redundancy the current system offerers. Also, the manual pump picks up only from the rear, being the larger volume void.

Matt

[Terra Nova]

You already have redundancy even though the bilge areas are separate, as the highest one would eventually find its way to the lower, if flooded. Or vice versa.

[Lojanica]

Terra Nova fixed it for you.

"Whatever spare parts you bring you will never be able to find when you need them."

"When your spares kit includes 5 different screw sizes the only one you can't find out of the five sizes is the one you need."

"Sometimes luck is the best item in your spares kit."

[GILow]

Originally Posted by Terra Nova

You already have redundancy even though the bilge areas are separate, as the highest one would eventually find its way to the lower, if flooded. Or vice versa.

Mate, I am loving the advice, and I hate to sound ungrateful but it would be a slightly shorter thread if you read what I have already posted.

As per my initial post, I have to ship nearly 1.5 tons of water before the water crosses the barrier.

I am not sure if anyone else finds this acceptable, but I reckon it's just a bit more than I'd like to have sloshing around.

[Lojanica]

Another cheap but good option.

Home Supply Centers sell 4 x 8 ft fiberglass sheets in 1/8" thickness. Easy to cut with tin snips. Again just cut the sheet into 8 ft by whatever width you need then pour foam (Dense pour foam is fine for a bilge and it won't absorb water unless immersed constantly even then you're gonna put glass on the top anywho. But you could cut the fiberglass and overlap. Start at the lowest point working up. That way it will be like a cascading stream flowing downhill. Then you only have to tape the seams with fiberglass and epoxy because the fiberglass sheets are waterproof and smooth.

I like this solution

[GILow]

This is a good option, but there seems to be mixed opinions on the various foams. Some people have had bad experiences with the stuff. It was certainly my initial first choice, but there are some really clever suggestions here that might mean I don't have to risk it. Didn't know about the fibreglass sheets, not sure if you can get them in Oz but I could see how they might be time savers in some situations.

Right at the moment I am feeling very optimistic about a doing something like the QCell or Micro Balloons, combined with the ping pong ball option which was too cool to pass by.

Then there's the surfboard foam idea which was also clever, but strangely I did find opinions suggesting even that stuff breaks down after a while.

Yeah, I know, you can over-think this stuff... but it is winter, and it is too cold for sailing so I am doing all the thinking and asking now so that I can hit the tasks in Spring.

Matt

[Scout 30]

What about the stuff that you pour into transoms after the rotten core has been removed? I haven't priced it but it looks like it would work well. Here's one brand: https://www.transomrepair.net/