My old ST30 depth transducer did not work. I have purchased a ST60 depth instrument and ordered a new plastic Airmar transducer. I have an old transducer in place on one side forward of the keel with a plywood backer inside the hull (hull is solid fiberglass). I also have another transducer hole on the other side of the hull with a dummy plug that does not have a plywood backer inside. The old openings do not leak. I will have to re-drill one of the openings for the new larger diameter (2") Airmar transducer. Which hole would you re-drill?
Which Transducer Hole?
- Thread starter StanleyJ
- Start date
Your transducer may be different, but the one I have (and a number of ones I have looked at) basically require you to mount them on the starbord side. They have an arrow that points toward the keel and a side that is supposed to be forward all due to the element inside the xducer angled to compensate for the dead-rise of the hull. so be sure to see if your new xducer is like that to help determine which hole to use.
hope that helps...
Dave in Port Charlotte
hope that helps...
Dave in Port Charlotte
Do both of these through hulls point down, or is one of them canted more sideways?
You want the more "vertical" hole in this case.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,746
That is the one I’d select. Where do Naval ships and submarines locate their sonar sensors? At the bow.
What part of your boat do you use to enter an anchorage? Where do you need the sensor to tell you there is a big rock ahead? The bow.
If the location in the bow will work and the angle is mostly flat (allowing you to position the transducer in a nearly vertical location) than that would be my select spot.
The transducer sends out a signal that radiates out in the shape like an upside down ice cream cone.
The unit then gets the rebounded signal off the bottom back up that same cone. That is why vertical alignment is best.
Thank you! The existing transducer hole is more vertical and on the starboard side. I will put it back in the same location with a bigger hole.
If the holes are of different diameter, there is an easy solution to properly center and saw out a larger hole.
First you need to properly size the existing hole with a hole saw that just fits. From the outside place solid piece of lumber ( say a 2x6x 6) against the hole and block it in place with wooden post or strong volunteer. Use the sized hole saw to drill a pilot hole in the the 2x6. Swap out the hole saws for the new correct size. Use the pilot hole to center the hole saw. Once the hole saw starts cutting into the glass, the outside aids can be removed. A good plan here is to tape over the hole to prevent blow out. Next finish sawing out the hole.
First you need to properly size the existing hole with a hole saw that just fits. From the outside place solid piece of lumber ( say a 2x6x 6) against the hole and block it in place with wooden post or strong volunteer. Use the sized hole saw to drill a pilot hole in the the 2x6. Swap out the hole saws for the new correct size. Use the pilot hole to center the hole saw. Once the hole saw starts cutting into the glass, the outside aids can be removed. A good plan here is to tape over the hole to prevent blow out. Next finish sawing out the hole.
The hole enlargement method provided by sailmate will work. If the hole diameter difference is not especially large, say 1/4", you can easily enlarge with a drill and a sanding drum bit. Select a drum as large as will fit into the old hole and with the drill running, rotate the spinning drum slowly around the circumference of the hole.
There are a number of options for enlarging an existing hole. A recent thread covered most of them.
The most important factor for a depth sounder location is clear water. If the transducer is located in turbulent water its accuracy will be affected. The second most important factor is angle, the closer to vertical the better. However once the boat starts to heel, the soundings will be less accurate because they will be shooting the bottom at an angle. That's why small deviations in the vertical angle are less important. The depth sounder can also be calibrated to compensate for any variation due to a small angle.
Enlarging hole in hull?
I am assembling parts to replace all of the above-the-waterline thru-hulls on my 1988 O’Day 322. The original white plastic one are brittle and ready for replacement. I have 4 different hose sizes and 4 different “hole” sizes in the hull. Despite my best attempts to verify the diameter of the...
forums.sailboatowners.com
The most important factor for a depth sounder location is clear water. If the transducer is located in turbulent water its accuracy will be affected. The second most important factor is angle, the closer to vertical the better. However once the boat starts to heel, the soundings will be less accurate because they will be shooting the bottom at an angle. That's why small deviations in the vertical angle are less important. The depth sounder can also be calibrated to compensate for any variation due to a small angle.
I used the wooden plug suggestion for enlarging the holes, and it worked great. No need to glue anything down (it was 28 F) and i could do it without any help.
Great tip.
Greg
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,746
As a hint, I always start a hole on fiberglass, with the drill running in reverse. This helps too mitigate chipping the gelcoat.
And of course tape the area where you will be cutting the hole. Cut through the tape. This also helps.
And of course tape the area where you will be cutting the hole. Cut through the tape. This also helps.
