I use 2 36" bags to slow my 21' glass boat with a 350 mercruiser motor. they do the job for me.

I've tried the 5 gallon buckets with an old 18' boat I had with an 80 hp mariner I had on it and they just didn't work for me. just wouldn't get my speed down where I needed it. I tried buckets without holes and buckets with holes drilled in them and they just didn't work.