I finished the install of my magnetic fillet knife holder today. I wanted to make better use of the space just aft of the starboard side window. I bought some very strong magnets from
K&J Magnetics. The ones I bought are part number BY084DCS. They are neodynium magnets with about 30lb of pull force. The size of each magnet is 2" x 1/2" x 1/4" and there are two counter-sunk holes for #6 screws. They are Ni plated and won't rust. I mounted them on some 3/4" thick red oak that I stained with a red walnut stain. This approximates the color of oak. The board was then sprayed with 5 coats of Helmsman spar varnish. The magnets are held in place with stainless #6 screws. The thickness of the oak mounting board is such that even fairly thick handled knives can be mounted without the handle interfering with the wall below.
The magnets are not cheap - they were about $8/ea. So with the cost of the wood, screws, stain etc., I'm probably into this project for around $55. However, this will hold the knives VERY tightly, and I'm not concerned about them coming down when we're bouncing around over waves. It will hold 4-6 knives depending on the size of the blades and handles.