Building the Hopf Evo Nightmare Mono 2.
By Paul Williams.
Article posted 31st August 2008.
The finished Evo 2 racing with a HOR Cat.
This article details the building of Karl-Heinz Hopf's "Evo Nightmare" Mono 2 class boat. This boat was built as a demonstrator for a proposed change in the regulations for SWAMBC's "Formula 4" class. At the time of building, Formula 4 was a controlled motor class, using Graupner's 700BB Turbo motor and 12 nimh cells. I will update this article as the build progresses.
Evo 2 hull, Mega 22/30/2 motor, wire drive, Etti 150A ESC and Etti aluminium wedge rudder assembly.
Evo 2 transom.
Evo 2 stepped hull bottom.
A proposal to change to a controlled brushless motor and lithium polymer cells to reduce the long term cost of competing in this formula led me to build this boat to show what this proposed class would look like in terms of performance and run time.
The hull as delivered weighed 340 grams. It was relatively well moulded in epoxy-glass, but felt quite flimsy for a boat that would be subject to the rough and tumble of racing. I decided that I would line the interior of the hull with carbon/kevlar cloth and epoxy resin to bring the strength up to that required for racing.
The first job was to make a sturdy boat stand. This I made from a couple of lengths of 2 inch by 1.5 inch timber, joined with a couple of 3/4 inch dowels. I hunted high and low for my profile gauge to trace the shape of the hull bottom to make a stand. In the end, I resorted to using a length of electrical solder shaped into the hull bottom to get the profile at the transom and roughly halfway between the bow and the forward step. These shapes were then very carefully cut using a bandsaw.
Boat stand.
Evo on its new stand.
In order to make the Evo self-righting, it is necessary to construct a flood chamber along the left hand side of the hull. The flood chamber, as the name suggests, floods with water when the boat flips over, rolling the boat far enough to tip it upright. The flood chamber is made from two pieces of 1/16th inch plywood laminated with glasscloth and epoxy resin, both to stiffen it and render it waterproof. The hard part is getting the shape of the chamber to match the hull, a task made more difficult as the Evo is a stepped design. Once again, I used a length of solder as a profile gauge to make a rough template that I sanded to a final fit.
Flood chamber sidewall.
I compressed the wet laminate of glasscloth-wood-glasscloth between two sheets of glass to get a smooth finish, and left it to cure for 24 hours. Next, I turned my attention to adding some strength to the hull. I said earlier that I didn't think the Evo hull was sufficiently robust for racing. All racing boats suffer the odd knock from other boats or turn marker bouys, and the thin laminate of the hull as delivered simply would not have stood up to a whole season's racing.
Hull strengthened with a single layer of carbon/kevlar cloth.
I cut a length of carbon/kevlar cloth which I laid out into the bottom of the inside of the hull. This I wetted out with epoxy resin. When the entire area had been wetted through, I mopped up any excess resin with paper towels.
Etti 150A ESC.
Etti aluminium wedge rudder assembly.
1/16th plywood motor mount.
Isolation loop made from 5.5mm gold connectors.
Isolation loop.
Mega 22/30/2 turn motor installed.
Motor and Speed Controller.
Servo mount. Note the two short lengths of brass tube supporting the wiredrive, with oiling holes in each.
Lipo tray with 3 velcro straps.
Internal layout. The oiling holes for the wire drive are accessed through the strap slots in the lipo tray.
The lipo tray, speed controller and receiver mounts have had strips of 600 grit wet-and-dry paper glued to them to stop things sliding around.
Update 1
Hit a bit of a snag during the first run at Cadover Lake on Dartmoor. The water was quite choppy and the boat, which was absolutely flying, flipped and lost its hatch which is now on the bottom of the lake. Not really a serious setback, as the Evo didn't self-right with the original hatch, so I now have no excuse for not making a bigger canopy/hatch!
Update 2
Ok, I made a plug for a new canopy from a block of pink foam. I coated this with a couple of coats of epoxy resin, sanded smooth with wet-and-dry paper used wet, with a little detergent in the water. The plug was sprayed with several coats of paint, then flatted down with 2000 grit "crocus" paper. "T-Cut" paint restorer was used to restore the gloss finish, then ten coats of carnauba wax were applied prior to laying up a mould.
First off, a layer of gelcoat was painted on and allowed to partially cure until tacky. At this point, resin was painted over the gelcoat, and strips of surfacing tissue were applied, followed by strips of chopped strand mat fibreglass. It is important to use surfacing tissue first, as this prevents "print through", ie., it stops the weave of the fibreglass mat showing through the surface of the mould.
Canopy mould made from polyester resin and chopped strand mat fibreglass.
Canopy mould.
Painted canopy.
The mould was allowed to cure for 24 hours, then the plug was cracked out and discarded. Ten coats of carnauba wax were then applied to the mould to ensure the laminate would release. I laid up two layers of lightweight glasscloth into the mould using epoxy resin, then set the laminate to one side to cure for 24 hours. The next day, the new canopy moulding was cracked free from the mould, and I set to work painting it. Before painting, I poured two-part expanding flotation foam into the inside of the canopy. Now, if the canopy pops off, at least I get it back!
Transom and hardware.
Transom and hardware. Wiredrive with 1.6mm wire into 3/16ths" shaft, Etti aluminium wedge rudder canted over to reduce rudder lift. 5.5mm gold plug isolation loop.
Transom and hardware.
Update 3
I took the boat to Goodrington to try it out with the new bigger canopy. Success! With the weight biased to the left, the boat now self-rights. Mark Shipman shot some video which you can see by following the link below:
YouTube Video
You can see a YouTube video of this boat's second run here. Stepped monos are typically very fast in a straight line, but are a bit of a handful in the turns. I haven't at this point fitted a turn fin. I expect fitting a turn fin, together with a few more runs to tweak the setup, should dramatically improve the boat's cornering ability.
Conclusion
Although this boat is pretty quick in the video, remember that this is quite a tame setup compared to full Naviga Mono 2, in order to achieve the 7 minutes plus required for SWAMBC Formula 4. I'm also running 4000 mah lipos, not the 5000s that will be needed to be competitive, and the prop is the smallest 3/16th" dog drive prop I've got, an Octura X637. Also, the wiredrive needs a few runs to bed-in properly. So, there's plenty more speed to come from this boat.
The Hopf Evo Nightmare.
© Copyright Paul Williams and www.fastelectrics.net, 2010.
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Last modified: 08th July 2010 @ 09:05
