Plug Making Options

[PROPGUNONE]

So we’ve come up with a new design for a 14’ flats skiff and are having the bow stations we created in SolidWorks cut at a fab place in Atlanta at the moment. Bow and sponson pieces are being 3D printed. Screen shot of the design is attached.

Our plan is to close off the “coffin box” in the middle with plywood, build a series of shelves in between the various bow stations to eliminate as much interior volume as possible, and fill the remaining cavities with an expanding foam, forming the rough plug.

Now, what does everyone recommend at this point? I’ve got a plan of attack already in mind, but I’m looking for more experienced ideas. 2lb foam, 6lb foam? Bondo, Duratec, glass, combination? How would you guys go about it?

 

[KD8NPB]

We rough shape with wood, cover with foam, then use a combination of fiberglass, ATC Polyfair F26, Duratec 707-061 EZ Sand, and 902-046 Black Topcoat.

The black topcoat ensures the mold we pull off has an excellent shine, and the black will highlight any imperfections in the pattern.

Remember, small DA sanders have no place for final sanding. Once you start spraying Duratec, you need to switch to block sanding and hand sanding in order to keep the pattern true.

 

[PROPGUNONE]

That’s pretty much exactly what we’re thinking, just with different products. 3/4oz mat to cover the sanded foam, then we were going to fair with compound and use featherfill or duratec over that, then chase it with an epoxy primer, awlgrip 545, and polish that to the final finish.

Laminating resin or waxed? Seems like you would want the hard cure of the waxed before fairing, but also wouldn’t want to have to strip the wax off before fairing.

 

[Blueknarr]

Laminating resin or waxed? Seems like you would want the hard cure of the waxed before fairing, but also wouldn’t want to have to strip the wax off before fairing.

Fairing compound will act as sufficant of laminating resin. Just as another layer of resined cloth.
Cover entirely with fairing compound and don't sand into the fiberglass, as it will cut at a different rate than the fairing. Each successive product will sand differently as well.

Good luck

 

[KD8NPB]

That’s pretty much exactly what we’re thinking, just with different products. 3/4oz mat to cover the sanded foam, then we were going to fair with compound and use featherfill or duratec over that, then chase it with an epoxy primer, awlgrip 545, and polish that to the final finish.

Laminating resin or waxed? Seems like you would want the hard cure of the waxed before fairing, but also wouldn’t want to have to strip the wax off before fairing.

I'd recommend against the Awlgrip and epoxy primers.

Stick to the Duratec line, they're designed for pattern making. They'll ensure compatibility with your choice of moldmaking systems.

Glass
Fairing putty
Rough sand and shape
Moderate sanding
Duratec 707-061 (Multiple passes to build to ~45 mils or so)
Moderate sanding

If a class B finish is OK, you can stop here and fine sand/polish up the the 707-061. If you sand through and hit the fairing putty, that's OK, it'll sand up and polish alright.

If class A finish is desired, sand all 707-061 with 220 grit, then topcoat with ~25 mils of 902-046, sand up and polish. If a little of the grey pokes through, that's OK, don't freak out, it'll all work out.

There's a bunch of application guides through Duratec that you should find useful
Available Application Guides | Duratec http://duratec1.com/duratec/application-guides/all-application-guides

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Resin ;
We use an ISO / DCPD blend for all general building here. It cures tack free. I don't think it really matters though, since you'll be sanding the heck out of it anyways.