In a medium-sized bowl, whisk together 1/2 cup flour, salt, baking powder, cayenne and black pepper. Add water, whisk until smooth. Let stand 15 minutes.
Meanwhile, in a shallow bowl, toss together coconut and panko.
Pat dry shrimp. Add 1/2 cup flour to gallon storage bag. Toss shrimp in flour, then one by one, dredge shrimp in flour/water mixture and coat in panko/coconut mixture, may have to press to adhere to shrimp.
Heat oil to 360 degrees, can use deep fryer or frying pan (I use cast iron) with 1" to 2" of oil. Place shrimp in fridge while oil is heating up. (This will give the coconut a chance to adhere to the shrimp)
Fry, in batches, for 1-2 minutes, until golden brown.
For Sauce: Whisk together marmalade, horseradish, rice vinegar, and crushed red pepper. Microwave for 20 seconds (to soften marmalade), and whisk until well blended. Add more horseradish, if necessary, to taste.
Do yourself a favor and double the sauce, you will be glad you did.