[Acoustics] Through the Hull Mount

Mon Feb 13 17:43:07 CST 2006

Brian,  We setup a 20 foot flat bottom Monarc boat with a well for an ADCP
mount. We have boats with front mount and side mount ADCPs but for project
work on the Missouri River we had concerns of the ADCP hitting rocks and
sand bars so we tried the well mount. We've found it works very good. The
top of the well we installed is level with the gunnels of the boat. For
travel a 'dummy plug' is installed into the well and the ADCP is installed
when the measuring site is reached. With our mount the ADCP draft can be
adjusted by shims and we have the ADCP set so the transducers are just
below the ribs on the hull, QA/QC indicated little left/right bias. To deal
with the possibility of an air lock in the well we had a valve installed at
the top of the well with a hose that expels air and water over the gunnel.
As I mentioned we use front and side mounts on four of our boats but the
'well' mount works as good or better than the mounts on our other boats.
Attached are some photos of our mount. The round well is for the ADCP  with
the dummy plug installed while the rectangular well is for our echo sounder
transducers. Hope this helps.

Joe Gorman

(See attached file: survey1.JPG)(See attached file: survey2.JPG)(See
attached file: survey10.JPG)

             Victor A Levesque                                             
             <levesque at usgs.go                                             
             v>                                                         To 
             Sent by:                  "Magee,Brian [Burlington]"          
             acoustics-bounces         <Brian.Magee at ec.gc.ca>              
             @simon.er.usgs.go                                          cc 
             v                         acoustics-bounces at simon.er.usgs.gov 
                                       , acoustics at simon.er.usgs.gov       
                                                                   Subject 
             02/07/2006 03:42          Re: [Acoustics] Through the Hull    
             PM                        Mount                               

Hello Brian,

I would not recommend mounting the ADCP recessed from the hull. The highest
part of the transducers need to be at least flush with the hull. There is
also the chance for bubble entrainment from the hull moving through the
water. There is also a good chance of flow disturbance from the hull
extending a considerable distance down into the water column. I would
recommend two mounting locations; one from the bow for calm water
conditions, and a second mount approximately mid-ships for rougher/choppy
conditions. The ADCPs will have to be mounted so that no beams have a
chance to strike the hull, which means the side mount could extend down
past the bottom of the boat. The front mount may allow the ADCP to be
shallower, but depends on the exact location and the hull shape. I have two
mounting locations on a 21 foot ocean-going catamaran that have served me
well.

Keep us all informed, as I once thought I wanted to through-hull mount our
ADCP.

Victor Levesque

U.S. Geological Survey
Center for Coastal and Watershed Studies
10500 University Center Drive, Suite 215
Tampa, FL 33612-6490
813-975-8620 extension 167
FAX: 813-975-0839

 "Magee,Brian [Burlington]"                                                
 <Brian.Magee at ec.gc.ca>                                                    
 Sent by:                                                                  
 acoustics-bounces at simon.er.usgs.gov                                    To 
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                                                       .usgs.gov>          
 02/07/2006 11:50 AM                                                    cc 

                                                                   Subject 
                                                       [Acoustics] Through 
                                                       the Hull Mount      

Before a hole is cut in the hull of a new 25' aluminium survey vessel to
accommodate a Rio Grande ADCP, I would appreciate any feed back on
operational problems that may be encountered while collecting discharge
data. The plan is to be able to insert the ADCP down a shaft through the
cabin floor to a point where the head is about 1" recessed from the hull.
The top of the shaft will be water tight at the cabin floor. We understand
the importance of a vibration free mount, beam clearance and beam
orientation. We are concerned about possible turbulence at the transducer
head when encountering high combined water and boat speeds.

Any suggestions or experiences you can provide will be greatly appreciated.

Brian Magee
Environment Canada
Water Survey Division
Burlington ON CAN
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