Foam Install

120 Cubic Feet of Insurance...

Foam, pillowed up out of the hull and cured.

Another hot topic out in the boatbuilding community is whether or not to use 2 part expanding polyurethane flotation foam. This is really only an issue among the amateur boatbuilding folks because USCG rules require professional boat builders to provide positive flotation or the ability for the vessel to float if swamped.  The counter-argument to this practice is that some installation practices provided water intrusion into the foam that is naturally water resistant and with continual immersion can begin to hold water. 
Now, basically, water weighs between 62 to 64 lbs. per cubic foot dependent on salinity (additional weight of dissolved salts and mineral). So every cu ft. of foam we add will give us that much flotation less the actual weight of the foam itself.  Typically 2lb. flotation foam is used in these applications.  It is not considered structural but can serve to stiffen floors and insulate as well.  We calculated that to fill the floor and space between the frames we would need 80 cu ft.  That's around 500lbs of flotation. The plywood itself is around 36 lbs. per cu ft. so there is a difference of 26 pounds so the hull itself is providing some buoyancy. She would still sink if holed and its a risk I will not take with love ones aboard.  Heck, I don't have a death wish if it were just me.  So, an 80 cu. ft. foam kit was ordered shipped in 10, 1 gallon part B cans and 2, 5 gallon part A drums.

Bow chamber with bag liner - View from up top

Interior view

We started at the bow.  There were three chambers starting at Station 2 through 6.  On the rest of the boat, the chambers were lined with plywood, the hull serving as one side and the pilot house's interior and coaming as the other side with the frames themselves boxing the chamber in. The bow was different because the chambers were open to the under berth area around the tanks.  In order to provide some containment, we used large plastic bag drum liners that were stapled in at the deck and foam poured in around the water tanks and water heater set in place.  Once done, relief will be cut away and sealed with epoxy resin.  All of these pours were mixed in 24 oz. batches. Leave plenty of time between pours so that the subsequent pour doesn't melt the last pour.  Also, mix with precision and the hotter the better.  Those two factors are the most important to get the maximum amount of expansion, approximately 25 to 30 times the volume.  The interior  view shows how this bag worked as it molded around the tanks.  The plastic bag peels easily from the foam.
With this part completed we moved on to the floor and worked our way back toward the stern.





Foaming Sequence in pictures...



Port side pours.  cups can be reused

The following sequence shows how we get the foam in the floor and walls.  The floor was hole sawed in various places and pours were made as we watched for foam-out to know that it was completely filled.  Once the foam had progressed up the wall cavity we continued to make pours until we reached the bottom edge of the pilot house wall where we then stapled heavy plastic sheeting with battens to bring the foam to the top of the deck.  One thing to remember is that all of the foamed out cups can be removed and thrown back in the "to be foamed" chambers.  Once there, we used a combination of saws and sanding boards to flush the foam with the deck. 
Around the fuel tank, we bagged the tank and plugged any of the conduit turning up for control, steering cable, and wiring.  We also built dams where space needed to be left for the fuel fill, tank sending unit and vent out of scrap pink board.
The following sequence of pictures should be self explanatory.  Note that the fuel tank requires room to expand.  I cut about and inch of relief where foam touched the rear quarters of the tank.


Holes cut in floor and foam poured.  Note the foam out in the bilge sump.

Trimmed and flush sanded foam deck.

Foam scrap everywhere.

 Fuel Tank and Blocking for Cleats...

Carved with 4" grinder and sanding disk.

One last piece to handle before the decks are added is to block under the cleats for additional reinforcement and to provide access to those cleats.  The front cleats will have 6" inspection ports in the cabin wall to access the cleat studs.  The amidships cleats will be accessed through the cabinets to be installed via a notch between the pilothouse wall and hull liner in the PH.  The stern cleats will have wells carved out, epoxy coated and painted with 6" deck mounted inspection ports.  The following pictures show this...

Cleat installed and ring in basic position.  Location is noted on hull exterior.

Amidships Cleat before 1" pine blocking is added and sealed with thickened epoxy resin.

The fuel tank was mentioned previously.  The back wall of the coaming is installed and will be opened up with two long hatches after the deck is installed. There will be an emergency 500GPH Bilge pump installed in the fuel tank compartment along with a blower to vent.

Tank installed.  Foam was sealed with epoxy and painted with 100% acrylic as further protection.
Neoprene pads under tank hold down straps (Moeller).

Coaming installed.  Glued and screwed.

 At this point we are ready for the deck.  Cleats are in, foam is removed from the wood surfaces for proper bonding of the deck.


By the way... It took another 40 cu ft to fill it all. That's 7400 lbs. of flotation in a fully loaded #5000 lb boat. Over 150 24 ounce batches mixed and poured.