Kort nozzle/hull clearance question

I’m trying to get a feel if I am pushing things too far on my kort nozzle design. Our current 18’ boat has a 12” dia. nozzle with the top 1.5” from the hull. In order to reduce draft is there any reason not to push it right up to the hull? I realize doing so will disrupt the flow around the nozzle but it be significant enough to out weigh the benifit of less draft? The shaft is running parallel with the waterline. Any comments or experience would be greatly appreciated. Thanks.

 

Tom, I,m currently on a job fitting the engine beds, stern tubes & rice nozzles to a 50' x 20' motorized crane barge of low draft, part of the decision to go with the nozzles was for a reduction in draft due to no tip clearance allowance had to be made from the hull although the top(outside) of nozzle is still 1 3/8" fom the bottom plating( for framing attachment to hull plate & internal framing), the prop dia is 22", the only thing I can think is that maybe some bubbles flowing along/under the hull get drawn through the nozzle if its set right against the hull bottom although they may get in any way with more clearance, the other reasons for fitting are that the vessels being set up with push knees & tow post for inshore light towage work & stores transfer to ships & the nozzles should increase efficiencys in bollard pull & close manouvouring in twin propulsion fwd/rev turning. I'd say go for it & see what happens, all the best from Jeff.