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Old 28-12-2012, 09:54   #1
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Aerosol foam

Hi all,

In my continuing osmosis saga, I dropped my rudder off as it had larger osmosis pits in the glass, there was no gelcoat layer. I peeled the rudder, but it was very wet. Some exploratory holes showed that the rudder had water in the core.

I cut out a panel in the rudder, the core was yellow foam that seemed similar to the foam from those aerosol spray packs. As a fix, I'm planning to remove all the core, allow the rudder to dry under fans and infra-red. My question is, can I use this same type of aerosol foam to re-core the rudder, then reglue the window in? I plan to rebuild about 5mm (that was planed off) in woven glass and epoxy.

Is this type of foam open core? Would I be better trying to shape closed cell foam to fit the cavity? That seems pretty difficult. What do you think?

REgards,

Steve
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Old 28-12-2012, 10:32   #2
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Re: Aerosol foam

Some manufacturers pour a two part urethane foam into their rudders when building them. You can order this online and it is pretty easy to use though watch for rapid expansion and temperature sensitivity.

I don't think that the spray can foam will give you results of the same quality as the appropriate urethane pour foam. I'm no expert but have used both and with the urethane you should get fewer voids and you can specify a variety of densities so should be able to create a dense/sturdy core if appropriate.

Be sure to eliminate all sources of ingress with plenty of epoxy/layup done well.

Jonathan
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Old 28-12-2012, 10:44   #3
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Re: Aerosol foam

The two part foam they likely used is very water pourous. They put that cheap light foam in there just to fill the space.... I think they believed no water would ever intrude in a rudder! Ha Ha
When I rebuilt a large rudder years ago, After cutting a panel out, cleaning the interior and reglassing the panel, I cored a hole in the top and filled it with a casting epoxy called "ruddercast". It was a low density epoxy product. Heavier than foam.... but probably didnt wieght much when submerged! After that, even if the rudder happened to seep at the shaft, there was no where for the water to go!
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Old 28-12-2012, 12:57   #4
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Re: Aerosol foam

Steve,

No idea what the foam they used was, but it should be a high strength, specifically high sheer foam like corecell. And no, two part foams are not a reasonable substitute.
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Old 29-12-2012, 11:10   #5
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Re: Aerosol foam

They almost certainly used pour foam, usually the two pound foam. I've done a lot of these, I'd say 80% of the boats that come in for a bottom job have a saturated rudder. Cut it open along the longitudinal seam and pop the two halves apart. If you have ground off the paint you should be able to see the factory seam and follow it. Pop the two halves apart and scrape away the foam so you can see the armature on the rudder shaft. Have the welds inspected, and repair/add more armature. Consider coating the armature. Then carefully reinstall the two clamshell halves of the rudder and bond them in place, back grinding the external seam and glassing it heavily. At this stage I often glass the whole rudder exterior as well, yours will obviously need this if you have removed a lot of material. Be careful not to remove so much material that the clamshell halves won't retain their shape, seen it happen. Drill a few holes for foam injection, and inject pour foam in four pound or higher. Use small batches and don't overdo it, if foam gets trapped in an area without room to expand the internal pressure will become very high and potentially blow it apart. Grind and glass the injection holes when finished. If you want to go the high end route, acid etch and prime the shaft and armature, and do the pour with Chockfast Orange. Make sure to get it nice and fair, and add an extra bead around the shaft every time you haul. Good luck!
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Old 31-12-2012, 00:38   #6
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Re: Aerosol foam

Hi all,

Pour foam is not available in Turkey, I can locate closed cell aerosol polyurethane foam that I will go with. I've cut a window out of the rudder (armature is glassed to one side of the rudder and appears sound). Questions, do I spray in foam through the large window, and then level the foam. Or close up the window and inject the foam through sprue holes?

What sort of layup schedule would be good to remake the 5mm that was gel planed off?
I can access 300gsm and 600gsm plain weave cloth. Should I search for bi-axial cloth? Orient the fibres vertically?

How many layers (approx) would make up 5mm?

Thanks for all the help.

I've also found an old style yard in Bozburun which I can haul out next winter for E1400 for 6 months. Its on old time skips, and I'll be nestled in between huge 200ft Gulets, but its affordable. I've got some-one who has a gel plane and can grind offf the gel coat, so next winter (Oct), I'll grind off the old gelcoat, see if I need to double grind, and then let the hull dry over winter (I know its not the ideal time, but its the only time I can get the boat drying for 6 months?). Should I tent the boat? or does that increase the relative humidity?

I can then refinish the boat February 2014, and still get in the cruising season 2013.

STeve
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Old 31-12-2012, 01:35   #7
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Re: Aerosol foam

Hello Steve,

Others, like Minaret, have more expertise and hopefully will answer your questions but I'll throw out the following.

Whatever you use for the rudder core be sure to test it at the same temp and in the same volume/space that you will be filling in the rudder. This will help you get a feel for working time, expansion rate and other variables which can and will change as the environment etc. changes. For instance, larger amounts of foam can heat up and behave differently (at least the two part can get really exciting) and foam collapses when messed with in my experience (ie. when spreading around after it's out of the can or mixed it can flatten etc.). I've only got limited experience but am sure that pre-rudder tests will be worthwhile even if you waste some cans of foam that are expensive. You may save splitting the rudder or messing up and having to clean out the mistake.

On drying the boat from what I understand tenting the boat and then adding dehumidifiers could be a worthwhile option. This can be a broad subject and will need to start with reliable moisture readings since you may or may not need to remove a lot of moisture from the hull.

Good luck, and hopefully Minaret and others will chime in as well with more detail and guidance.

Jonathan
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