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Build the plug

The process is best explained by Brad Gibson, in his video  Build the hull plug   but there are some nuances which I cover below:

Click on any picture to expand the image.


Build the styrofoam hull

What you need

A  measured 1.1m flat board to lay the styrofoam frames onto. 

2 off 600x600x100mm sheets of styrofoam.  Ebay shop 

UHU POR glue to stick paper onto styrofoam.  Amazon

Hot wire cutter.  Amazon

Hot wire kit.jpg

Balsa wood planks for sanding the styrofoam  300*50*3mm and 400*20*5.   EBay shop 

Sanding boards.jpg

Builders square

600mm rule

5 minute epoxy to stick foam frames together.  East Coast Fibreglass

Sandpaper - Dry, various grades, course to fine, wet and dry 150 down to 2500 

Epoxy resin - slow cure gives about 30mins of work time

Glass to cover foam - 2 layers of 135 E cloth and 1 layer of 125 S cloth as the outer skin.  East Coast Fibreglass

Epoxy micro balloons for filling and for use later on. East Coast Fibreglass 

2 pack high build epoxy primer.  SML Paints

The process

The Foam Plug

Mark up the board with a centreline and 100mm frame positions and a 50mm and 38mm mm frame positions according to the plan.  Mark as accurately as possible and use the builders square to mark the frame lines.  


Print all the frames onto coloured card and cut out each frame.  Red or black provides good contrast to blue Styrofoam.  The colour becomes relevant later.


Cut out the red paper frames with a stencil knife.  Remember that the plan lines will mark the outside of the hull.  You need to account for the thickness of the surface of the plug and the skin of the hull, so I cut the frames two mm inside the plan line and stick to the styrofoam with UHU Por.  Cut the centre of the frame out so the epoxy can bond the foam together for a strong plug.  Only glue round the edges of the card and avoid putting any glue in the deck area of the frame.   Once the frame is stuck on the foam, cut a very narrow slit marking the deck about 2mm wide.  The use of the slit will become obvious when you sand in the area of the deck as the gap in the red paper will indicate you are nearly at deck level.

When it comes to cutting out the frames on the foam block

 Bear in mind when cutting out your frame, frame 5 is the largest.  When cutting the stern frame, mark an outline for frame 2 and cut that out.  Do the same for each frame until the central frame 5 and then do the same form the bow back to frame 5. Do this otherwise you will end up with steps rather than a fair hull. 

Hot wiring the shadows.jpg
Gluing frames forward.jpg
Gluing frames aft.jpg

Cut out the frames using a wire cutter.  As mentioned above, mark out the next largest frame and cut out.


I wedged my wire cutter into a wooden board so I could get a vertical cut all the time.  Practice with some samples first to judge how fast you can cut.  It is a smelly process so cut the foam out doors.  See image 5 above.

Carefully cut out the centre of the red card hull frame and a narrow slot on the deck line to help when finding the deck during sanding.  

To cut the 50mm and 38mm slices I marked a line on my board, held a straight piece of wood on the board and used that as a guide to get the right thickness of frame. 

Cutting the forward frames 38mm and 50mm

When you add all the frames together they should give you a length of 988mm.  However, because you have added glue and card to the foam frame the width of the frame will be slightly more so sand down now side of each frame by about a mm until the width is correct.  I only found out about this after I had glued all the frames together and ended up with a 1m boat before the bow bumper was fitted.

Starting at frame 5 in the middle, glue the frames to the board and themselves, 1 at a time using 5 min epoxy. Remove excess styrofoam with the hot wire and sand coarsely into shape as you go along.  Only stick the styrofoam with the epoxy.  

Only sand with a sanding board and always down the length of the hull to start the fairing process.  Once all the frames are in place, bring the surface down with coarse paper until you start to see evidence of the red card.  At this point move to the lighter sandpaper and carefully sand until all the red card is just exposed.  If you have been patient the hull should be perfectly fair and true.  I was amazed at the end result.   

The plug from the bow.png
Stern view.jpg

Use a saw and remove the hull from the build board.  Start at the stern and keep the cut well clear of the rising deck.  Be careful with the plug as the foam will damage easily.  Once removed I supported the hull with bubble wrap.

Sand down the deck in the same way as the hull.  Sand the radius edges on the corner of the deck as per the plan.  

Deck view.jpg

The Foredeck

Prepare the foredeck frames as before. 



Glue the frames together on the deck and chamfer the edges slightly to get a tight fit.  Protect the hull with cling film so as not to glue the foredeck to the hull at this stage.  

Guing foredeck.jpg

Glue onto the hull and sand to final finish.  Fill any gaps with 5 min epoxy and micro balloon filler.  Sand very carefully to finish.


Add a post for handling the plug and keep it a max of 50mm from the foredeck.


Epoxy and glass the hull

Rough cut 3 layers of 4-5oz glass e cloth to wrap completely around the plug. Draw a line along along the keel line on the foam plug and the cloth so you can align the cloth exactly.  


Support hull post in work bench and apply 3 layers of to 4 -5 oz glass and epoxy resin to hull and decks.  Use peel ply as a final layer.  Take care with corners and ends to make sure there are no air bubbles.  For each layer I apply the glass and epoxy to the hull and then turned the plug over and did the deck.  I applied 1 layer after the other until all three are complete.  On my second build I left each layer 45 minutes to cure which made it easier putting the next layer on.

Paint the plug in epoxy and add the first layer.  Use a roller to remove air bubbles and saturate the cloth.  Once the first layer is on, carefully paint on more epoxy and add the second layer.  Repeat for the third layer.  Once you are happy with the result, wrap the hull tightly in peel ply, which will absorb any excess epoxy and prevent an amine finish.  Images 19-21.


When working with epoxy, make sure you are in a well ventilated area, you are wearing nitril glove and  preferably glasses or safety glasses in the event of flicking epoxy in your eyes.

Epoxy will start to go stringy after half an hour or so.  When it does, throw away what's left, clean tools and gloves with acetone, reload with fresh epoxy and continue the layup.

The temperature during layup must be 10 degrees or higher and ideally cure at room temperature or higher.

Remove the peel ply and immediately add 2 coats of high build epoxy primer.  This will look really ugly but once sanded with wet and dry and polished with  t-cut, you will have a beautiful plug on which to mould your hull.

Finally apply at least 6 coats of release wax in preparation for laying up the hull.  


Next Section

First Alternative Build

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