Building the Fire Fighter 26 Gas Rigger
From Tom Moorhouse
Over the winter months we will be building a gas rigger
Part 3
Building the front sponson
The following parts are needed to sheet the front sponsons:
2 - 1/8” plywood sponson tops.
1 - 1/8” plywood sponson back with a spar cut out.
1 - 1/8” plywood sponson back without a spar cut ou
2 X ¼ ply inside doubler
2 - 1/8” plywood sponson bottoms.
2 - 1/8” plywood sponson out sides.
2 – 1/8” plywood sponson outsides cut ½ “bigger, (the outside is on a slope so if you cut them all the same they will be too small to fit
You need to chose either carbon or aluminium for the booms I have gone with 14 mm OD X 12 mm ID and 12 mm OD and 10 mm ID Carbon fiber.
Pay close attention to be sure you are making a proper right and left side. The only change I have maid to the plans is to change from the 2 X 1/16 ply to 2 X 1/8 and the 1/8 G 10 for the turn fin spa to some 6 mm carbon fibre.
Start by attaching the 1/8 ply inside and doubler ply to the sponson inside skin. The part with the cut out is for the spar to fit inside. Set the spar inside of the cut out on the left side sponson. Glue the spar in place with epoxy glue.
Now glue the inner foam cores on top (I have used 3 pieces of blue foam as I would have had to wait for the 75mm foam). The side with the spar might need a little bit of foam removed where the spar fits against the foam. I simply pressed the foam to the spar to transfer the shape. Then I used a knife to cut away the area that was marked.
Glue the foam core ousters on.
While the sponson is flat drill the boom holes through the sides and foam making sure you are drilling square to the side,
You should now test fit the sponson tubes to make sure they fit. You can also do a preliminary
Check to see if they are square, I used a piece of 12mm rod for this, carbon out of stock for 1 week.
.Covering the front sponsons:
Sponson cores:
Glue the 1/4” ply inside doubler centre on, to save wasted glue I mark the side I am gluing with a few crosses and mix the glue on the piece, no wasted glue just the right amount used.
Sand down the sponson back to make everything nice and flat. Make sure you don’t sand too much.
The sponson back should be square with the sponson inside. Attach the sponson back
Use the sponson angle templates set the bottom piece, Glue the templates to some cardboard before you cut them out to make them more ridged.
I used our angle and glued sand paper set up; I set the angle with my template and set the angle by placing washers under the front or back.
Holding the correct template on the bottom of your sponson examine the angle you have. Determine
what you need to sand to match the template and sand it until they match. You might find it easier to
measure the bottom angle if you hold the sponson bottom in place while checking the angle.
With a sanding block sand the sponson top so that it is nice and square to the sponson inside. Attach
the sponson top
Shape the sponson outside. The sponson core needs to be shaped before attaching the sponson
outside. Use a knife to rough cut off the majority of the foam. Use a sanding block to sand the foam
nice and smooth up to the wood. You also need to sand enough of the wood so that it is angled for the
Sponson outside to be attached properly Attach the sponson bottoms when you have the bottom angles matching the templates.
All the way around the sponson outside you should create a little dent in the foam with your
Fingernail or a small stick. Use this dent to fill in with epoxy to act as a fillet to make the joint stronger.
Attach the sponson outside. Sand it flush on all sides. Be sure to keep all bottom angles sharp. Do not
Round any corners as it will slow your boat down.
Time to glue in the sponson tubes:
I chose carbon fiber tubes the tubes are 14 mm OD and 12 mm ID and 12 mm OD and 10 mm ID, there are readily available from most Hobby shops except when they are out of stock
The method I used was to glue the tubes in and keep everything straight, glue both
tubes and sponsons at the same time. Lay the sponsons on their tops on a flat surface. Dry fit
everything together first. Be careful when pushing the tubes in to the sponson. If you push too hard you
may damage the sponson outside plywood. You may need to use a round file to make slight
adjustments to the sponson core to get everything lined up correctly. The tubes should go 1.75” inside
of the sponsons. Make sure that the tubes are all square to the sponson insides. Make sure that the
sponson tops are flat on the table. The distance between the two sponsons should be approximately
13.25” The tops should be flat on the table without the need for weights to hold them down.
When everything looks good mark the tubes to indicate what part will be inside of the sponson, I cross drilled the tubes so the glue will fill the holes and make a stronger joint.
Don’t try to save weight by being skimpy with the epoxy on this step. Put the tubes in to the
holes and push in to the line you marked on the dry fit. They should lie flat on the table and be square to each other, check that they set down perfectly flat, if you have to weigh them down there is something not right.
Last thing to do was to laminate the tub sides with carbon fibre, I used 160 grams X 4” tape for this, using a piece of 10 mm SAFETY glass I brushed some resin on , laying the carbon onto the glass and brushed some more resin onto the carbon, using an old credit card I scraped the resin into the carbon and this also removes the air bubbles and excess resin from the carbon, brushing a light coat onto the tub side I just put the tub onto the carbon and clamped a 4” piece of angle down onto the tub, Just as the resin is setting use a sharp craft knife to cut round the tub leaving only light sanding when removed from the glass.
I have decided to paint the sponsons and tub red leaving the carbon look on the sides with pinstripes in red on carbon sides and black on the red sponsons, first I sanded down the wood to a fine finish spraying with a light coat of primer which will show up any marks or imperfections in the wood, I used a super light filler and sanded down with 400 wet and dry.
I used a black spray on coat as a sand of so I could see any low spots which needed a light filling. Finishing off with a final primer and 600 wet and dry sanding.
The most important think is to keep all the edges sharp do not round off the running surfaces when sanding.
Well that’s it for now next is Painting and hardware.
Next is the painting, fitting the booms and painting
