I made the harness from 1" tubular webbing, a short piece of 2" tubular webbing, stainless steel hardware and a plastic snap buckle. West Marine sells a child harness for about $40. After looking at it I saw that it relied on the plastic buckle to handle the load on the harness. The adjuster parts were also plastic. Otherwise it seems well made but I worried about the reaction of the plastic parts to an impact loading. Like a child reaching the end of the tether.
West Child Harness
To make my harness I got two 1" SS d rings, one 1" SS rectangular loop, and five 1" SS strap adjusters. I used only tubular webbing for the harness. It's sewn by hand (lock stitched) with #4 whipping twine. Total cost was about $30. Almost as much as the West harness but I think it's superior since there are no load bearing plastic parts. West sells 1" tubular webbing but only in blue, I think the harness should be red or yellow for better visibility. A climbing store might offer more choices. I ended up using the webbing sail ties that West sells for $9. The webbing has a dark thread running down the middle of one side and while I didn't think about it when picking the webbing it makes it easier to straighten out the harness while putting it on.
This photo shows Alex modeling the harness and showing how the tether attaches. The plastic buckle fastens the harness but the tether passes through both D rings so the buckle is never loaded by the pull of the tether. The baby end of the tether is a loop sewn into the webbing. The loop is passed through the d-rings and the snap clip end of the tether is passed through the loop. Adult tethers have a snap shackle at the harness end so that the wearer can release it. But with a child you don't want the release. You might be able to use a locking clip of some sort but if you have a child you know what curious little hands are capable of. The boat end of the tether is a snap clip to attach to padeyes, stanchion bases or a jack line.
The belt part of the harness fits up across the chest. This keeps the wearer in a heads-up position at the end of the tether (especially if the diaper is ballasted).
From the Back|
The shoulder/leg straps are sewn onto the short piece of 2" webbing (blue) on the back. There is a gap/loop for the belt part to pass through with it's adjuster buckle. I considered adding a loop for attaching the tether to the back and I may put one on. The first version of the harness had one crotch strap and it detached for ease of putting the harness on (a loop went over the belt when buckling). This version has two straps. In fact the crotch straps continue up the back to become the shoulder straps. This makes it a bit harder to get on but it's also more secure and stronger. A good trade off in my opinion. Less sewing too.
Building the harness was pretty easy and took about 1 evening of sewing while watching TV. This harness fits Alex now with a couple of inches to spare. I should have made the straps about 4-6" longer. The webbing that makes the straps is about 44", I should have made them 50" and taken up the slack with the adjusters. He'll outgrow this one sooner now. But I learned a lot building it. The belt adjusts from about 20 to 28" and seems about right. Sizing the strap lengths was the hard part. Those babies can be squirrelly. I have Alex wear the harness for a couple of hours every day or two just to get him used to the idea. He doesn't seem to mind it at all.
The harness is meant to be worn under the life jacket and I may sew in some slots to pass the d rings through the front. I may also build a harness into the life jacket.