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A 90 degree turn increases the load by 41% if the block has zero friction (not possible in the real world). Please make sure that your home-built block is up to the load. A failure of that block would be life-threatening to anyone in the path. We had a racer at our club killed by a spinnaker snatch block that gave way under load.
Spend a couple of dollars on a block that has a tested safe working load and make sure that you calculate the actual working load based on the angle of deflection. Most turning blocks are intended to slightly change the angle to align with a winch or a stopper, not to dramatically change the direction.
Scary story. Spinnaker snatch blocks have a nasty failure path when they go. A classic case. The safety tip is to NEVER stand inside the sweep of a highly loaded block. Failures happen. This bit of wisdom goes back to the dawn of sail.
Yes, the load is 141% of line tension at 90 degrees and 200% of line tension at 180 degrees. However, most blocks are rated at 180 degrees (Spinlock, below, for example), so actually, 90 degrees is 71% of rated load. The most common service for winch feeder blocks is a 90 degree deflection (cross sheeting), but 180 degrees is commonplace.
The article did not quote a load limit, nor did we give an exact design. In this case, the breaking load a 3/8-inch center bolt in such an installation would be about 5,000 pounds and the working load with a 4:1 safety factor would be about 1,250 pounds. It would bend and jam long before that. The equivalent Spinlock Winch Feeder (1/2-inch center bolt) has a working load of 1,500 pounds. Makes sense. Most likely, in both cases, the limiting factor is the deck reinforcement and backing plate. On this boat (24 feet) exceeding a working load of 600 pounds would require a gorilla on the winch. A complete failure would cause the line to snap forward about 8 inches into an area no one stands. This is a safe installation.
But rlemoine make an excellent point. As always, the installer should understand the maximum load. If you are not an engineer, ask one.
You mentioned ‘blowing’ dust away. It’s important, (to U’re lungs), to blow one good blow, rather that take a 2nd breath, (of dust U just disturbed), or turn away to take a 2nd dust free breath. Also with 1 wrap of spin sheet on lee winch, we had a slippery semi tube between to winches (because of curve & nonslip on hatch), so crew on windward net could use windward winch, (with more wraps). My best idea?, is a second release position, near the mast for quick release while foreword. It can be made to double the main sheet power, (inside the boom forward to the gooseneck, then down to deck cleat). I.E. if one release is on the aft traveller, & U are working near the mast, U have a 2nd release point at U’re feet, (as long as it’s pulled in some).