New project: A Class catamaran (2004 German Flyer / AUS849 / Saarberg)
Ian Johnson, Merricks Beach, VIC Australia
Saarberg skinny boards, Mackenzie Composite Carbon Rudders/Boxes, Harken Mainsheet System, Saarberg mast, Fiberfoam beams, Brewin big head sail, big beach wheels, bum pads, bags boat cover.
5 Altona Street
The easiest way to distinguish the German Flyers to the Auscat Flyers is in the beam connections. The front beam in the Auscat sits on top of the hull (aluminium) while the German one sits more flush (carbon).
aclass002.pdf – Harken – A Class – 2015 Cascade mainsheet system
aclass003.pdf – Tips on Sailing the A Class cat
aclass004.pdf – Landenberger Tuning Tips – Mast Setup
aclass005.pdf – A class tuning guide v3 Greg Goodall
aclass006.pdf – Tying Fibrefoam battens
aclass007.docx – Brewin Sail Tuning, Care and Rigging
aclass008.pdf – How sails work by Paul Bogataj
aclass009.pdf – Nacra A2 A class catamaran Rigging and Tuning guide
aclass010.pdf – Very general info
aclass011.pdf – Tuning your DNA
Am using marine grade ‘below the waterline’ 2 part epoxy primer and polyurethane topcoat. This stuff contains nasty chemicals absorbed through skin (and eyeballs even). Effects of exposure are cumulative. Air compressors (oil based) often have water / oil / rust in tank and require 3 stage filter (oil trap, graphite filter and moisture trap) and air hose suitable for breathing before feeding into a positive airpressure hood. If it works it is not silly.
Manual wet sanding using 240 grit paper and spray bottle / sanding block. This only takes minutes and is actually fun to do. Sheet sander and orbital sander have holes in the plate to suck in dust and do not like water (damages bearing). Also mains voltage and water = electrical hazard.
Waiting for a warm dry day for topcoat.
4m 4m 4m = 12m 5 wire
brown -> 2x tail lights
yellow -> 1x left turn
white -> 2x ground
green -> 1x right turn
red -> 2x brake
Rim: Velox 3.50B x 10 cast aluminium
Tyre: Duro HF249 5.0-10c Tubeless Trailer -> change to 145/10 or 150/10 mini radials
roller pin 240x16mm
assortment cotter pins
lacing buttons / tonneau hooks
dyneema blue 2 meter
Nairn Inspection Port – Polypropylene ABS white
Outside Diameter(145 mm): Inside Diameter(102 mm): Cut out (112 mm): Mount Screws(mm): 6 countersunk
Moulded nylon construction with screw in centres
Weatherproofing ‘O’ ring seal and wide caulking flange
EVA foam 60-75 kg/m3 blue 10mmx330mmx300mm for cradle and front beam support.
Clark Rubber has 25mm+ thick EVA foam in fitness and learn-to-swim isles.
40mm od round tube 3mm wall + jockey wheel clamp for height adjustable cradle support post.
Bostik AVS AV515 moisture curing polyurethane adhesive for gluing EVA foam
angle grinder flapper disk
angle grinder wire wheel
+1 drill brush hard plastic (drill is more versatile than angle grinder; removes grime from cold galv steel without damaging coating).
The inital goal was to sand off the blotchy faded in places blue topcoat to expose -what I thought was- white gelcoat and buff it.
[!] Gelcoat or paint won’t cover up any problems under it only highlight them. Prep is the whole / total key to a nice looking paint job.
Makita 9924DB 76mm corded belt sander 120grit belts. Wet sanding to reduce dust. Unclog belt with garden hose. Alternate five belts to allow belts to cool down and dry to prevent the backing from leaving black streaks.
AEG 300W corded random orbital sander 80 grit (yes, that is what worked best for me somehow and was not too aggressive) for curved bottom of hull. decided not to flip the boat over. lastly a light sand with 120 grit for pre-paint finish.
You can’t sand off blue top coat to expose white gelcoat and then wet sand and buff it. You will likely end up with what you see in pictures. The correct solution would have been to roughen blue paint and add another dark blue color polyurethane top coat. Or if you want white, very carefully (= orbital sander exclusively) only sand off the dark blue color and repaint with white polyurethane. This is however near impossible and will take days of sanding with fine grit paper. It is very difficult not to end up with a patchy result where the fabric weave is exposed (very bad) in places.
You start with a mold. Then PVA mold release spray or wax. Then a single thick layer of gelcoat that cures to tacky consistency, Then you lay up your fibreglass or carbon fibre weave using a vinylester / polyester resin. This will seal the tacky gelcoat, infuse the fabric weave and make it cure airtight and non-porous.
So you end up with a mix of:
Instead of a thick layer of white gelcoat you can use clear gelcoat (or just resin) for that nice carbon fibre fabric look. Or you can just paint your resin fabric weave. Paint is typically used for non-mold applications. Paint coats are thinner so less weight, don’t yellow in UV, are harder, may be suitable for below the waterline (water osmosis) but are more easily scratched and scuffed and more difficult to touch up than gelcoat.
The layers I can see in the pictures:
You aren’t painting carbon fibre, you are just overcoating the resin that was used to infuse the fabric weave. Of course if you sand down to the fabric weave itself, which is to be avoided, then there is some exposed carbon fibres. Exposed carbon (graphite) fibre weave that has no resin on it is kind of slippery and does not stick well to epoxy primers. It should stick to gelcoat:
Your typical polyester gelcoat will only adhere to fiberglass / carbon fibre, previously cured gelcoat, or polyester resin.
Never use sandpaper any coarser than 320 grit to sand finishing materials between coats.
Never wet-sand any topcoat with less than 1200 grit wet/dry paper (really?)
Do not use any stripper containing methylene chloride (aka methylene dichloride or dichloromethane). It will attack gelcoat severely.
Gelcoat is a liquid that hardens to form a thick layer that is used to protect fiberglass and give it a shiny, smooth finish. As gelcoat ages, it becomes porous. The more porous it becomes, the more easily it stains, the worse it looks and the harder it is to clean. Wet sand with soapy water to lift the dirt.
Paint over gelcoat:
Gelcoat over Epoxy primer or Epoxy resin:
You should use a vinylester or polyester resin in your fabric weave if you want to bond with polyester gelcoat. Can you use a gelcoat on an epoxy resin or epoxy primer ? Yes, but you shouldn’t.
Gelcoat over gelcoat / gelcoat repairs:
How to gelcoat:
Use a gelcoat cup gun to spray gelcoat. Alternatively use a High Volume Low Pressure HVLP spray gun.
MEK-p (1% – 1.5%)
MEK or styene to thin gelcoat (8%)
2.5mm nozzle High Volume Low Pressure (HVLP) gravity fed (= reservoir sits on top) spray gun with pressure pressure gauge / regulator at the gun (2 bar / 30 psi).
large tank high pressure aircompressor
solvent resistant paintbrush
pva mold release
glasses, suit, gloves, respirator
7-10 minutes working time
I used mylar A4 overhead projector sheets and foam brushes to apply polyester gelcoat.
100ml gelcoat = 122 grams = 1.5ml MEKp
100ml gelcoat = 120 grams = needs 1.5ml MEKp catalist applied with a small syringe from drug store / pharmacist. Wear gloves, safety glasses and non-breathing fabric long sleeves when going near MEKp. A single drop in your eye can cause irreversible blindness in 10 seconds.
Left and right patch still covered in mylar sheet hence the gloss and yellow tint.
After sanding it actually looked good except for some small flakes coming of near edges of mylar or where there was a poor bond.
“Don’t cling to a mistake just because you spent a lot of time making it”.
A comforting thought: you can always just sand it off again. Decided to remove it all and sand back to where I started from.
Alexseal Topcoat Reducer Brush R5015
Alexseal Topcoat Converter Brush C5012
Alexseal 501 Topcoat White T91xx
Alexseal rolling additive A5018 (you can see the air bubbles pop for a super smooth finish).
Can’t source these materials locally unfortunately. Specialty paint store had this instead:
Best to buy from a shop rather than order online in case you need more. This comes in 500ml, 1ltr and 4ltr tins that are in stock. Thin 10% for roller application.
Do not use foam roller. Do not use cloth roller. Do not use microfibre roller. Use mohair roller. Wrap mohair roller in masking tape and unspool to remove lint. Clean and let dry before first use.
Use professional elastic edge tape or fine line tape for a perfect seam without paint creeping underneath masking tape (bleed).
Move paint roller in slow steady movements with light pressure using short strokes keeping a wet-on-wet edge and move sideways along the hull.
Spray painter suggested apply a second coat after 1 hour when touch dry for chemical bond without sanding. Product brochure suggests the same (wet-on-wet but only once first coat has had sufficient time to cure to carry weight of second coat). Above video suggests primer coat #1 in the morning, 400 grit sanding in afternoon followed by primer coat #2. Wait a day or two for primer coat #3. Leave masking tape in place.