I would like to add speed and depth gauges to my Hunter 216. The manufacturer has all but assured me of disaster should I atttempt any through-hull modifications. Can anyone with experience to back it up reccomend a transom mount sensor setup that works well for depth and speed? Thanks! Bob
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Not a Good Experience
I mounted a Ratheon speed and depth transducer to the transom of my MAC 23. I can't remember the model number, but it may be an L438. I could never get good speed indication. I moved it around on the transom. There is a calibration for the speed, but I could not get the speed high enough when compared to the GPS. I called Ratheon and they said they just do not work well on sailboats. Apparently there is not a clean enough break between the transom and the hull. I finally put it in a mode which reads kph. That is somewhat close to knots on the GPS. It reads a little low below 3k and a little high above 3k when pretending that the kph is knots. It is mounted far enough to one side to avoid the rudder swing. As a result under heeling in excess of about 20 degrees, it lifts out of the water. In order to get a cleaner break between the hull and transom, it is mounted perpendicular to the hull which means it does not point straight down. It is off by about 15 degrees or so. That is not a major problem, since for sailboats, they rarely aim straight down anyway. Other than that it works fine.
I mounted a Ratheon speed and depth transducer to the transom of my MAC 23. I can't remember the model number, but it may be an L438. I could never get good speed indication. I moved it around on the transom. There is a calibration for the speed, but I could not get the speed high enough when compared to the GPS. I called Ratheon and they said they just do not work well on sailboats. Apparently there is not a clean enough break between the transom and the hull. I finally put it in a mode which reads kph. That is somewhat close to knots on the GPS. It reads a little low below 3k and a little high above 3k when pretending that the kph is knots. It is mounted far enough to one side to avoid the rudder swing. As a result under heeling in excess of about 20 degrees, it lifts out of the water. In order to get a cleaner break between the hull and transom, it is mounted perpendicular to the hull which means it does not point straight down. It is off by about 15 degrees or so. That is not a major problem, since for sailboats, they rarely aim straight down anyway. Other than that it works fine.
Shoot through the hull
Most transducers will register depth through the hull if you mount them in epoxy with no air between the unit and the hull. For speed I use my GPS. (I became tired of fiddling with paddle wheels and such.) As a backup I bought a "Knotstick." It trails a calibrated disk in the water and is accurate, according to my GPS.
Most transducers will register depth through the hull if you mount them in epoxy with no air between the unit and the hull. For speed I use my GPS. (I became tired of fiddling with paddle wheels and such.) As a backup I bought a "Knotstick." It trails a calibrated disk in the water and is accurate, according to my GPS.
Depth Gauge OK! Forget the Speed Unit
I would be surprised if you found a speed instrument that will give you reliable information no matter where you install it. Use your GPS for speed data. There are several depth units that you will find satisfactory but they are not transom mounted. Turbulance near the transom will preclude ever getting reliable data. A puck type transponder mounted inside the hull well in front of the keel or board will provide fairly reliable data. Follow the transponder manufacturer's procedures for installation. Drop the puck in a plastic bag full of mineral oil and move it around the hull until you find a place where the unit gives you consistent reliable data, then mount the puck in epoxy as directed. Remember, air bubbles are your enemy. Jon
I would be surprised if you found a speed instrument that will give you reliable information no matter where you install it. Use your GPS for speed data. There are several depth units that you will find satisfactory but they are not transom mounted. Turbulance near the transom will preclude ever getting reliable data. A puck type transponder mounted inside the hull well in front of the keel or board will provide fairly reliable data. Follow the transponder manufacturer's procedures for installation. Drop the puck in a plastic bag full of mineral oil and move it around the hull until you find a place where the unit gives you consistent reliable data, then mount the puck in epoxy as directed. Remember, air bubbles are your enemy. Jon
GPS and through the hull transducer
No need to make a hole through the hull with a through-the-hull transducer, GPS will give you speed.
No need to make a hole through the hull with a through-the-hull transducer, GPS will give you speed.
I have both GPS
A GPS provides speed over the ground or SOG. A knotmeter gives you speed through the water. In tidal waters, the comparision between GPS speed and knotmeter speed gives you an indication of current. 6 kts through the water according to the knotmeter vs 4 kts over the ground according to the GPS means you are fighting a 2 kt current. Water is going by lickety split but the trees on shore aren't going by very quickly... That said a knotmeter, tide tables and a current atlas will do wonders to your skills in ded reckoning.
A GPS provides speed over the ground or SOG. A knotmeter gives you speed through the water. In tidal waters, the comparision between GPS speed and knotmeter speed gives you an indication of current. 6 kts through the water according to the knotmeter vs 4 kts over the ground according to the GPS means you are fighting a 2 kt current. Water is going by lickety split but the trees on shore aren't going by very quickly... That said a knotmeter, tide tables and a current atlas will do wonders to your skills in ded reckoning.
plus
a knot meter is a more immediate indicator of the effect of sail trim changes on boat speed.
a knot meter is a more immediate indicator of the effect of sail trim changes on boat speed.
do it yourself - no cutting
Take the transducer, butter up the face of it with a GENEROUS amount of silicon sealant, butter up the place on the inside hull where the transducer is to be mounted, press the transducer to the hull move it around until you are sure ALL the air bubbles are out and hold it or otherwise secure it till the silicone sets (a couple of hours) and your done. Ten years later mine works like a dream.
Take the transducer, butter up the face of it with a GENEROUS amount of silicon sealant, butter up the place on the inside hull where the transducer is to be mounted, press the transducer to the hull move it around until you are sure ALL the air bubbles are out and hold it or otherwise secure it till the silicone sets (a couple of hours) and your done. Ten years later mine works like a dream.
ACP hull transducer mounting
I know that folks have successfully used non-thru hull transducers on solid glass laminate hulls. My question is whether or not this will work for a depth sensor on my Hunter 216, which is an ABS/foam/fiberglass composite. Bob
I know that folks have successfully used non-thru hull transducers on solid glass laminate hulls. My question is whether or not this will work for a depth sensor on my Hunter 216, which is an ABS/foam/fiberglass composite. Bob
Probably not
After doing some research to replace my old unit, I've read that depth transducers won't work with a cored hull. The core material doesn't have the density the cured glass does. It runs along the same line as having air bubbles in the mounting material.
After doing some research to replace my old unit, I've read that depth transducers won't work with a cored hull. The core material doesn't have the density the cured glass does. It runs along the same line as having air bubbles in the mounting material.
Many of the new fishfinders perform the
functions you seem to be looking for, one of the Hummingbirds will even interface with or may have it's own GPS. I've used the transom mount transducers for these units on MV's and they work up to about 20 Knts or until they start breaking the surface. Mount on lower edge of transom and extend down a couple inches. There are also some that use an optional paddlewheel for STW.
functions you seem to be looking for, one of the Hummingbirds will even interface with or may have it's own GPS. I've used the transom mount transducers for these units on MV's and they work up to about 20 Knts or until they start breaking the surface. Mount on lower edge of transom and extend down a couple inches. There are also some that use an optional paddlewheel for STW.
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