A Complete Restoration, Custom Fabrication, and Carbon Fiber Make This 21 Scorpion One Bad SOB

I got to see Justin Kelly’s 21 Scorpion up close in Ontario Canada during the Tuff Marine run in the fall and after talking to Justin about it, there was no question, beyond the triple digit speeds, this was a passion project and incredibly done restoration. Justin new he wanted a 21, like many performance boaters, the 21 Linder design made famous by the Challenger is just a really well rounded boat. And, since there were plenty of copies made from many manufacturers, there are lots out there. That said, Justin’s search took him a while, but eventually a 21 Scorpion turned up close to his home and he made the deal. I really wanted to feature this build because there are some really cool things he did, and with some of the modifications, this 21 is among the faster ones around, running 102 MPH with a 300XS.

What started as a 21 Scorpion, turned into a custom composite 21 with some major design updates and plenty o carbon fiber.

This 21 needed a new core and the plan was to do everything anyway, so Justin knew he could make it his way and he had big plans. The keys to this build were making it light and modifying the bottom. I could tell immediately upon meeting Justin, he is a do it yourself kind of guy, a natural at working with his hands and not afraid to tackle projects.

One key to going fast is the bottom, the pad width and how sharp and straight everything can make a huge difference. Justin widened the pad just a little, with a large notch in the transom. More lift and moving the CG back can increase top speed dramatically.

With the lightweight theme in mind, ½” balsa was used on the running surface and foam coring was used in other areas. Epoxy resin was used throughout the boat, and a 2” Coosa transom was laminated along with a redesigned full transom extended to the deck, removing the old splashwell design. This makes it stronger and lighter. Nidacore was used for all structural pieces, including the stringers, knees and bulkheads. He also used Nida-core for the floor. To give you an idea of the weight savings, the hull with floor ready to rig was 997 lbs. That’s an incredible weight for a 21.

Justin did some really nice glass work; he used balsa, Nida-core, and Coosa for coring and structural material. He also fabricated many carbon fiber parts to lighten the build overall.

For the build Justin wanted to try resin infusion as he had seen the process used on newer boats and knew it was going to the best result when done right. He dove right in and made molds for a rear hatch, race hatch, seat mounts, side panels, switch panel and a custom intake for the 300XS. Some molds were made for just a couple parts and were constructed of MDF, primed and finished with Imron. The other parts were made with fiberglass so more could be produced.

The resin infusion process

For infusion, Justin had this advice, “If i could give advice to anyone trying resin infusion it’s great and yields an amazing strong and lightweight part. Take your time while bagging it down, even if you have the smallest leak, don't proceed, you will set yourself up for failure. Be patient find the leak and proceed.”

Parts weight specs:

Complete Nida-core carbon floor 28 lbs

Carbon race hatch 8.5 lbs

Carbon rear hatch 3.8 lbs

Carbon seat mounts 3 lbs

Carbon interior side panels 3.4 lbs

Stringers and knees out if Nida-core where 5lbs a side before glass

All of these efforts add up and make a big difference in the end. Because of the attention to detail and clever designs, this Scorpion is much lighter and stronger than it was new. Another really trick thing Justin did was adding the wind faring to update the look. He fabricated it out of foam, with a layer of glass and carbon, popped it off and removed the foam before glassing to the deck.

The faring was molded in place, then glassed to the deck. A great feature that makes this boat truly one of a kind.

With some research Justin knew he wanted to improve the performance by modifying the pad and the notch but wasn’t certain exactly the dimensions that would work. Like many of us, he’s a big fan of Tuff Marine and lives nearby, so he called them up and Mark and Thomas were glad to offer some advice on the hull, which is a testament to what great guys they are. He widened the pad a little, and made it flat and laser straight.

The perfect straight sharp edges of the widened pad are the key to the boat getting into the triple digits.

Being the true DIYer, Justin painted it himself and it turned out amazing. This build is truly inspirational, the work put in is hard to quantify. Getting ready for paint, he sanded it down and used epoxy quick fair and tried to use the minimal amount. Cromax high build primer was used before Axalta sealer primer. Justin mentioned how he was absolutely done with sanding after a while, no doubt it’s a tedious process. The bottom was painted with Imron single stage in black and finished with a clear coat. A custom color was done in dark gray with a mix of white and black Imron. I would say stealthy is what it looks like, and it looks amazing. I love the gray and black combo.

Justin even fabricated the trailer himself. The recessed nav lights are nice and the Imron paint came out amazing to give it a stealth fighter look.

By this time it was about 2 years into the project and although there might have been one or two more things he wanted to do, he had to draw the line. That’s a heck of a line to get to. This is one of the baddest 21 SOB’s I’ve seen, you can tell Justin’s blood, sweat and tears went into it. A process that was well worth it.

Here’ a list of the fabrication Justin did himself:

-All the molds for parts

-Custom trailer

-Built a new aluminum gas tank

-Machined a billet shifter, through fittings, race hatch hardware

-Machined the setback bracket

-Coned the factory torque master

-Did my own cowl mods on the 300xs

The boat hit the water in August 2023 and I’m sure Justin was elated. He had some help along the way from his significant other, his close friends, and the guys at Tuff. After getting a few runs in, Justin actually took it over to show Thomas Weigl and talk boats and props. Thomas took it for a 96 MPH pass. Justin ran a stock 32 Bravo to 97 MPH with limited seat time, and after some more prop testing, a Dewald and a 31 Mercury CNC, he ran 102 MPH at 6,200 RPM. That’s a stock Mercury Racing 300XS with a coned torque master. Absolutely incredible results. Not only that, he met some friends along the way, which is really what it’s all about.

You can see the carbon side panels and seat boxes here. The dash layout is very nice with some custom touches. A race hatch slides in right behind the seats and only weighs 8.5 lb.

Thanks to Justin for sharing his boat and all the work he did. He built almost everything himself, it’s really amazing and he’s obviously super talented. Look for this stealth 21 Scorpion flying around Ontario.

21 Scorpion Highlight

The carbon fiber race hatch. Only 8.5 lbs.