I am lucky to live about 500 metres from the sea. I am unlucky that my home is 30 metres above sea level. No problems taking the kayak on its cart down to the sea. Much greater issue hauling the kayak and cart back up the hill to home.
I have adapted a sled harness that those gym-type people use for their pursuit of masochistic delight and added a tether to attach to the deck line (about 0.9m back from the bow). It took a little bit of tweaking to get the right length for the tether for my height.
Anyway there’s still a little bit of weight on the bow handle with the majority on the harness. It works well! What are you using to help haul your kayak cart?
I confirm that this is an actual problem, especially with a kayak loaded with several days of camping gear. One place where I camp has a very steep quarter-mile hike back up to the parking lot from the launch. The gate at the top of the hill is closed during the spring and fall off season to discourage vandalism of the park office. Your solution looks great. I attached a strap to my backpack hipbelt (a 55-liter pack with a thick hipbelt) in order to pull mainly from the hips and legs. I also pull with the handle of my kayak to add arm power. I use a hiking pole in my left hand for further assistance. I use a C-Tug with inflatable tires. Finally, I zigzag back and forth across the hill. Even with all these strategies, it’s a killer hill.
No harness. I used to live a half-mile portage from house to beach. House was on a bluff, maybe 100 feet above sea level.
What made portaging easier was to push the kayak and cart instead of pulling it. Cart under the stern as usual, but with me holding the bow in one hand and pushing the rig forward, stern-first. BIG advantage in being able to steer from behind and see if the kayak is going straight!
People joked about portaging being work, but I think loading a sea kayak onto a motor vehicle or its trailer and driving, parking, strapping, etc is a much worse PITA. I could be on the water via portaging faster than doing those things. And no worries about salt water corrosion on an auto roof.
