Dump the Coot Fat

I used to think that pour-in-place foam was great stuff. I called it Coot Fat , and extolled its virtues, even though fumes from its cure are hepatotoxic.   Molt's original idea was to use it to fill the long grooves inside the F/G hull made when the chines were first formed.   (See CBNL 28:2:6 for details.)   I suggest that such grooves could simply be covered by small, thin sheets of F/G where each bulkhead is glassed onto the hull skin, thereby creating triangular limber holes for any leaking water to pass down to the bilge.


The problem with Coot Fat is it's so easy to get carried away with it.   We used to pour it into spaces on either side of the nose wheel box at the bow, or along the leading edges of the sponsons.   A few of us filled even bigger voids around the main landing gear retraction mechanisms inside the sponsons.   This might sound clever, but the idea that the foam will always exclude water from collecting in such spaces is just wishful thinking.   Vibration from water landings will open up tiny cracks, and water will inevitably seep in, adding many pounds and obstructing your view and access later.   A classic example of this is at the hull step, where Molt recommended its use around the plumbing used to vent the step.   In case you have forgotten to read The Coot in a Nutshell (page 35), check it out and you will agree that this is NOT a good idea!   Keep the step strong with well-bonded wood ribs, not foam, and make sure that the entire step is accessible to your bilge pump.


Perhaps the worst place to use Coot Fat is near the engine pylon.   Poor Harvey had it poured around the engine control cables that run down the front, and also around the engine mounts that bolt to the pylon itself.   I suppose the idea was to reduce the amount of water that might drip down from the engine into the bilge, but on rainy days lots of water worked its way down there anyway.   The side effects that I later encountered as a result of this mistake were horrendous.   Any attempts made to replace engine cables, wires or plumbing during subsequent maintenance required many extra hours.   Worse still, large cracks in the engine mount were obscured from detection (because of the foam) until much later than would have been the case otherwise.   This could have been disastrous.


In summary, it's difficult to justify the use of pour-in-place foam in a Coot, so I suggest that you don't buy the stuff, so you won't be tempted to use it later. It should NOT be used as a substitute for good building technique.   A good Coot is strong, light and accessible .



Back to Editorials