Sunday, May 12, 2013

Building a Real Box for the Unreal Heat in Sea of Cortez and other tropical destinations

As I mentioned in previous posts it's all about insulation, insulation, insulation. That's what stops the heat leaking into the box and reduces the amount of time the refrigeration system has to run. Many production boats have totally inadequate boxes....even some new ones. So a production boat ice box may have you running the engine to keep up with electrical usage, hauling ice, looking for a marina to plug into and basically making your enjoyable cruise into a living nightmare. I know of several couples who have split up or quit cruising because of a simple comfort issue.

The following photos show a box that will yield 8.5 cubic feet of space, of this about 1.5 cubic foot will be a freezer maintained at around 10 deg. F and the rest a fridge of 7.0 cubic foot maintained at 34 to 38 deg. F. To put this in real terms, the freezer could easily hold over 30 lbs of frozen meat, fish or veg. properly packed and pre-frozen. If the fridge area was packed to its gills it would hold over 328 regular cans of beer, or over 14 cases. However there would be no room left for The amount of poured foam was about 21 cubic feet.

The first step is to gut the original factory box, 2 to 3 inches of 30 year foam in this case just would not work in tropical conditions

The holes were for drawers that have been relocated. To the left of this shot you can see the original skimpy box lids...not enough insulation.

The next step is to make a new box liner, this is a two part process, first you have to  make a wooden "plug" from which you can make a fiberglass mold which will be the box liner. Here it is cut in two so as the liner could be popped off of it. You can see the transparent PVA film which is a mold release agent.

AND here is the new box liner dropped into place

Next it needs to be correctly positioned in the enclosure so we will have 5 inches of foam around it and over a foot on the hull side.

You will see the plug as been dropped into the liner and wooden beams screwed into place. This is needed as the expanding foam creates a huge pressure and would buckle the box and force bulkheads out of shape. So the strong backs also need to be fitted on the outside of the box too.

Now to make sure of damage control. The expanding foam produces noxious gases and sticks like shit to a blanket.

Here is the foam. It's two part, mix up a two quart batch, stir for 20 seconds with a mix master fitted with a custom spray guard and pour rapidly.......don't waste a SECOND o.k..

Here is a link to the foam used, a good time to learn a little Spanish!

You will notice the foam gives of heat, so after the first 3 pours the job stopped for 20 minutes to let things cool down. If not the second level of pour will go off too quickly and make large gas bubbles instead of dense insulation.  Keep pouring foam until the void is full. Use the custom cardboard sheets to make sure it goes where you want it to go!

Note the can of Tecate beer, it is essential in the correct application of the foam!

Now the box is fully foamed all the wood is removed and excess foam trimmed off ready for the fibreglass moulded and foam cast box top to be fibre glassed to the liner. 

And the wood is gone!

It still needs detailing to accept the box top

This is the box top prior to detailing,
And the underside, all foamed and sealed with glass fibre
 It took two steps to make this, first you make the wooden plug, then you make the molding from the plug and then the same process for the box lids. As you can see here the wooden plug was broken off the molding. Each and every boat is different so it is all labour intensive custom work. Below is the plug for the top..

  The lids too are filled with foam and need to be made from a custom mold too, here it is being faired out by hand.

And the underside of the lid mold

 A tube passes through the box bottom into the bilge area. This is fully glassed into the liner and extends 9" above the box bottom, so no chance of water getting into the foam.Through this tube the pressure and suction tubes of the Mexicolder system along with thermostat wires are run. The tube is then stuffed with plastic bags and sealed on the top with aluminum duct tape and silicon caulk. Don't use polyeurethane sealants inside the box , they gas off and taint the food for weeks.
Here you can see there is 10" of foam under the box

At last the box top is fitted

No more skimpy lids, these will do the sweat, pun intended!

There are sliding bases to make easy access to the bottom of the box

The evaporator will be fixed here, the under panel helps support the weight but can slide out for access and easy cleaning

The finished job

 A carpenter will secure the original fiddle rails. Foam tape rubber seals makes the whole thing air tight. The box top is joined to the box with a thick catalysed resin paste making the entire structure "monocoque". Any holes drilled into the box liner to attach the evaporator or thermostat are caulked to keep the water tight integrity of the liner. Unless the customer specifically requires a drain we don't install one. They tend to get smelly in time. Instead a hand type pump can be used to suck water from the box and any bits of food or spilled liquids. The pump is then flushed out and left in the sun to more smelly bilged boats. I swear I can smell a boat that has an ice box drain from several boats away.

The compressor is mounted behind the aluminium grill

Note all the tubing is fully brazed up with silver copper phoshorous rod, no chance of leaks

The condenser draws air from the cabin and is sealed to the grill, warm air escapes from the louvred teak door and keeps stuff nice and dry in the locker too!

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