HK Marine Relentle SS V2

Off-shore race boat styling with speed to match!

This article was originally published in RC Driver’s June 2016 issue.

Words: Paul Onorato
Photos: Edwin Rodriguez

I am a sucker for fast electric catamarans. They are incredibly stable and agile when running flat out and I especially like how they look while ripping across the water. My latest is the newly updated version of the H-King Marine Relentless V2 from HobbyKing. driven by a potent brushless motor system that can be powered by 4S LiPo batteries.  awesome, 14.8-volts of water shredding power. It is offered as an ARR (Almost Ready To Run) where you will need to add a 2-channel radio system and batteries. The Relentless offers a lot without costing a lot. Take a closer look.

REVIEWER’S OPINION
I like the openness of the hull where you can easily access all of its internal components. I also give the Relentless V2 high marks with its sharp-looking paint job and graphics which are protected with a clear coat that will keep it looking its best over time. Driving the boat is a lot of fun due to its high speed and stability, but I don’t like how long it takes to accelerate and get on plane.

ITEMS NEEDED
• 2-channel radio system
• Two 3S 7.4V 4000mAh 30C+ LiPo battery packs
• LiPo battery charger

ITEMS USED
• HobbyKing HK-GT2E 2.4GHz radio system—9114000017-0
• (2) Turnigy nano-tech 4000mAh 2S LiPo battery pack—N4000.2S.35
• Dynamite Prophet Sport LiPo Duo 50Wx2 Dual Battery Charger—DYN4108

OUT OF THE BOX
The ‘V2’ in the name of the Relentless V2 denotes that it is the second version of this fast electric powered catamaran. H-King Marine has revamped the original Relentless with some serious upgrades like a very powerful 2815 brushless outrunner motor paired to a tough 60-amp speed control that can be juiced with 4S LiPos and an all new electronics tray to secure all its vital components. Back in the stern, the 2-blade composite prop has been swapped out for a scale-looking, 3-blade polished metal prop.

As an ARR, additional items are required to get the Relentless V2 running, like a 2-channel radio system and two 2S LiPo battery packs with a 30C rating or higher. I selected the HobbyKing HK-GT2E 2.4GHz 2-channel radio system to provide the control for this fast cat. For power, I picked up two Turnigy nano tech 4000mAh 2S LiPo battery packs. Along with the installation of the aforementioned electronics, the prop and rudder assembly need to be attached to the hull. This step takes a matter of minutes. One word of advice: Before you attach the steering linkage for the rudder, make sure the steering servo is centered and the rudder is perfectly perpendicular to the stern.

The hull of the Relentless V2 is constructed of ABS plastic. This helps to keep the cost down as well as its overall weight, but I found the hull to be a bit flimsy and it may not stand up to abuse as well as a fiberglass hull would. Like with anything, there is always a tradeoff. A big plus is the Relentless V2’s looks with its race inspired hull design and graphics complete with sponsor decals. Its finish looks as nice as a fiberglass hull thanks to a final step done by H-King Marine. After the boat is painted and the stickers are affixed, it is then clear coated to give it a rich, glossy appearance and keep the stickers from pulling up. One of the benefits of a catamaran style hull is the space inside with a large opening to easily access all the electronics. Inside you will find a large black plastic tray where all of the components are attached and where you strap in the LiPo battery packs. The tray is held in place by six screws that can be easily accessed from the underside of the hull. A large hatch is used to close up the hull and is molded to look like a cockpit to give it a scale look. A hole in the front of the hatch slides over a socket head screw installed in the hull and at the rear is a large latch to lock the hatch in place. H-King Marine added a foam rubber gasket to sit between the hull and the hatch to help thwart water from entering inside the boat.

At the heart of the Relentless V2 beats a potent outrunner brushless motor that is attached to a metal heatsink motor mount. The motor mount is kept cool with water fed from the water cooling system. Power is transferred to the motor by a 60-amp brushless speed control that is also water cooled to keep its operating temperature in control. H King Marine has the Relentless V2 setup to be powered by 14.8-volts, so two 2S LiPo battery packs. This package will make this catamaran a screamer on the water.

On the stern is a plastic adjustable strut that holds the stuffing tube in place. A flex shaft passes through the tube and spins a realistic looking 3-blade metal propeller. The rudder is offset to the right of the prop. Like the prop, it utilizes a plastic mount with the rudder itself machined of aluminum. Located just ahead of the rudder is the water intake tube that sucks up the water for the cooling system and then exits out the port side of the hull. Over on the left side of the stern is a small rubber plug which comes in very handy to let any accumulated water out of the hull.

ON THE WATER
As I got the Relentless V2 ready for its maiden run, it became clear to me that the Turnigy nanotech 4000mAh 2S LiPo battery packs will not only provide plenty of speed and runtime, but they will help keep the boat’s center of gravity nice and low since the packs are only a half inch thick. With the batteries installed and the radio system powered up, it was time to make some waves. I started driving the Relentless V2 around and I quickly discovered that it was quite slow to get up on plane. Either quick or gradual input on the throttle would yield the same result. The prop seems to cavitate as it struggles to push the hull though the water. After about a five count, the cat will finally get up on plane and then basically takes off like a rocket across the water. While up on plane, the Relentless V2 could effortlessly accelerate up to top speed. This made for some fun hot laps around the section of lake I was running on. I would drop the speed entering a relatively tight turn and then nail the throttle coming out of it and the boat would respond instantly, jumping back up to full speed. I found this cat to be very agile when running up on plane and it could change directions quickly as long as the steering input was not to severe. Overly tight turns would cause the hull to lose too much speed and it would fall off of plane. As long as you keep this in mind, it becomes less of an issue. The design of the Relentless V2 as well as most boats like this fast electric are setup to run clockwise. This means that it can carve some aggressive right hand turns, while left hand turns would unsettle the hull. During my testing of this trait, I flipped the Relentless V2 upside down taking hard left turns. I even caused it to perform a barrel role where it flipped and landed upright. Luckily nothing broke during any of these incidents and only a small amount of water entered into the hull. When the surface of the water is calm, the Relentless can run at full throttle and stay incredibly stable. Once there are some waves or when crossing back over its own wake, the Relentless V2 will get a bit out of shape and can quickly recover by slowing down a touch. I did notice the port sponson sits a bit lighter in the water than the starboard side. At speed, any steering input to the left would cause the sponson to lift some out of the water and cause the boat to get squirrely. For runtime, I averaged about eight to nine minutes of high speed running and each time the electronics were cool to the touch.

SPECS

HULL LENGTH: 28.7 in.
BEAM: 8.23 in.
HULL MATERIAL: ABS plastic
SPEED CONTROL: 60A, forward-only, water-cooled
MOTOR: 2815 brushless outrunner, water-cooled
PROP: 3-blade metal
RUDDER: Offset, knife edged aluminum
DRIVE SYSTEM: 4mm direct drive flex shaft

WRAP UP
The updates made to the H-King Marine Relentless V2 bring its performance to a whole new level. The new high power outrunner brushless motor with 60-amp speed control, 4S capability and three blade metal prop makes this cat wicked fast and oh so much fun to drive. It also looks great when out on the water with its vivid paint job and race inspired graphics. I do wish it accelerated and got up on plane quicker, but once it does it is a blast. The Relentless V2 is a fun all around boat that a newcomer or experienced person will enjoy, especially its low price tag.

LINKS
Dynamite, dynamiterc.com, (800) 338-4639
H-King Marine, hobbyking.com
HobbyKing, hobbyking.com
Turnigy, turnigy.com