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Wednesday, August 27, 2014

Kingfisher Drift Boat Build - Plascore Bottom

Plascore Board

I'm using 3/4" Plascore Board for the bottom of the drift boat. It's sort of a honeycomb plastic sheet. There have been many pros and cons discussed on various boat building forums about plywood versus Plascore. The thing that swayed me in that direction was the fact if you hit a piece of rebar or took a hard hit on the bottom and punctured the Linex coating, the Kevlar and fiberglass, with a Plascore bottom you could do a temporary fix and then flip the boat over and do the real repair when you had time. Water migrating into the core won't damage a synthetic material like Plascore. A plywood bottom would keep sucking water like a sponge. Not good! Makes sense to me anyway.

Ordering the Plascore

One problem I had when ordering the material direct from Plascore was determining what specific type of board I needed. After a few emails back and forth with the Plascore Rep we figured it out.

Here's the exact specification from Plascore. I needed 2 sheets.

Specification: 5pcf PP core with film and veil at 3/4" thick X 48" X 96".

The material was shipped from Michigan and I picked it up in Sacramento. The 2 sheets ran $98 plus about $120 for the shipping. So basically about $110 a sheet to Sacramento. Michigan is a long ways away!

Constructing the Plascore Bottom

To construct the drift boat bottom out of plascore you first have to splice together the two 3/4" x 4' x 8' boards into one sheet that is about 4' x 15' 4". You do this by creating a sort of dovetail key joint and lock the two sheets together.

Dovetail Scarf Joints Laid Out on 2 - 4x8 Sheets of Plascore

  • I used the same table that I used when scarfing the plywood. It is 5' wide x 16' long and is about 34' off the floor.
  • The plans provided by Jason Cajune has a layout for the dovetail joints. I laid out the two sheets as per the cut sheet provided.
  • The joints are cut with a razor knife.
  • Once they are cut they have to be fine tuned a bit so they lock together tightly. They sort of snap together.
  • Once they are together place a 3 mil piece of plastic under the joint, A piece about 24" x 5' is about perfect. 

I've cut the dovetail joints with a utility knife

Here's the joint locked together

Adding 4 1/2" Strips to the Sides

The Plascore sheets are 48" wide and the drift boat bottom is about 57" wide. The sides need to get extended by adding strips to each side that are about 4 1/2" wide. 48" + 4 1/2" + 4 1/2" = 57" 

  • If you're building a squared off transom you can cut 4 strips 4 1/2" x 48" from one end of the Plascore sheet. The bottom for a square transom is about 14' long so you can cut 4 of them from the end.
  • I'm doing a curved transom which will require an addition 8" or so making the bottom length about 14' 8", so cutting all 4 pieces from the end will be cutting it too close. I'll cut 2 or maybe 3 from the end and 1 or 2 from the sides.
  • These 4 1/2"  pieces will be added to the middle section only based upon the bottom layout provided with the plans. They must be placed in the correct position.
  • Being that the added strips are so close to the sides they can be butted to the larger sheets. They will be covered with enough fiberglass from the side panel/ bottom panel joint for strength. 
  • Hold the strips in place with finish nails or tape.
  • Once all the pieces are laid out and in place put finish nails around the perimeter along the sides to keep the pieces from moving apart when using epoxy peanut butter to glue everything together.
  • Mix up a batch of epoxy peanut butter that is fairly smooth and fill the gaps in the key joints. It will probably take about 3 ounces. Concentrate on the larger gaps.
  • Place additional strips of 3 mil plastic over the areas with the epoxy peanut butter and then place plywood or boards on top of the plastic and weight to hold the sheets flat against the table.

4 1/2" Strips added to both sides

You can see the "Epoxy Peanut Butter" at the dovetail joints in this photo. You can also see it on the added 4 1/2" Strips.

I'll let this set up overnight, strip off the boards and plastic and get ready to cut the bottom shape.

Next Up Laying Out The Bottom and Cutting it Out


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Have any Questions or Comments? Let me know, Clay.