It's is needed because you need somthing that can take the angles you will encounter when you are not over the ballast tank. I have this under the dinette seat.
I've used a $5 tube of silicone caulk and a 50 cent plastic bowl. Angle the transducer in the caulk. Done at least 3 boats like this.
Dunno. Looks like someone took off a transom mounted deal. I just stole the photo off the internet.
Doesn't matter what kind of transducer. The principle is the same. Keep solid contact between transducer and water via a solid medium. The transducer transmits an ultrasonic ping and needs a solid (or water) medium to pass through.
So your saying the caulk works as well as water - that's seems like it would be correct - right? On mine I have it filled with glycol, but I guess i could fill it with water.
The bottom line is that the area between the channels is empty void when the ballast is empty - there are a few inches there between the top of the tank and the bottom of the hull in that area so a transducer mounted there is going to show a sounding of like .10 feet or something like that - not a good place for the sender.
There is a huge 8 inch wide rib in the later model M boats that goes from starboard to port a little behind midships, the best place I have found to mount the sounder is right next to that rib (NOT ON IT!) but either forward or aft a few inches from that big rib outside of the channel. - (on 'boat' the rib is about an inch thick and easy to find).
I guess if your dead set on mounting the sender on top of the ballast tank you could shove a bag of water in there and stuff it so it's stuck right under the sender but I think it might clog up your gate valve if it ever got loose.
I'm still trying to find a decent liquid level sensor for the ballast tank. Maybe you guys have stumbled on an idea by mounting a transducer on top of the tank.
BOAT wrote:So your saying the caulk works as well as water - that's seems like it would be correct - right? On mine I have it filled with glycol, but I guess i could fill it with water.
Glycol is better than water because it won't freeze or start to grow tadpoles.
I've installed transducers on 3 boats using clear silicone caulk. Works great and is a very common method if you google it.
If you read the posts above, it was determined that, YES, there is ballast in the middle between the ribs. The OP said his was working empty which is a mystery if there is air in there when empty.
I'm still trying to find a decent liquid level sensor for the ballast tank. Maybe you guys have stumbled on an idea by mounting a transducer on top of the tank.
Why not modify something like this.
Water alarm buzzer. You could put a switch on it or rig an LED light to replace the buzzer.
One basic setup is to have some kind of water level switch (float, hydrostatic, etc.) and a water valve. An electric valve is not great since it will not work without power. A manual valve needs to be plumbed to where it is accessible - really not that hard and it has been done.
The level switch is the hard part because of the dynamic nature of the boat and the fact the water will be splashing at the sensor. Not sure what kind of sensor would work but I do not think a float switch is at the top of the list.
On the other hand, one could put a whistle indicator like commonly used on home fuel oil tanks. Just keep the valve open while you can hear the sound. When the sound stops, the tank is full and close the valve.
Another option, drill into the tank at the floor of the forward bulkhead and plumb in a clear tube as a sight glass - and try not to break the sight glass and flood your boat.
Yeah, I'm trying to figure out how this thing works - it's not NO and NC contact so you can set it up to not use any power at all unless you send some but I'm not sure how it works:
An "upside down" float thing that would "clip" into the side of the vent hole would work - I will design the "upside down float thing clip" and make a picture of it and post it here and see if you guys can figure out what I'm thinking. I know you guys are smarter than me and will know if such a thing exists if I can make a picture of it.
BOAT wrote:I'm still trying to find a decent liquid level sensor for the ballast tank. Maybe you guys have stumbled on an idea by mounting a transducer on top of the tank.
The ballast tank is a highly irregular shape, so you're probably best off with one of these ultrasonic level sensors, although you need a Maretron control head to calibrate it:
I used a big blob of plumber's putty. Plonked it on the just behind the battery compartment under the rear berth. Pushed the transducer into it, eyeballing level, and it works a treat as long at there is water in the ballast. It has stayed there stable until now when I have moved the transducer to the locker to the aft of the table, as close as I could put it to the centerline. I am hoping this area does not have a ballast void under it. Will let you know after I try it out.
I wanted to mount mine inside the ballast tank (why not?) so as to avoid all of the concern about air in the ballast tank. I wanted it center forward, in front of the centerboard channel in order to get it as close to the actual bottom (lowest point) of the boat as possible (if it shows 1 foot then i have 1 foot beneath the deepest part of the hull)... I was going to go thru the flat spot at the top of the ballast tank directly in front of the v-berth bulkhead and mount a 4" sealed deck plate there. Big enough to put the transducer through and work in with your hand. Anyway, would drill it for a thru-deck connector like this one (which i used for my large antenna cable) big enough for the transducer plug end to fit thru. http://www.westmarine.com/buy/blue-sea- ... 94_003_008
The deck plate would give access for the transducer, the cable clam would seal the cable sticking thru the deck plate, and I'd have the transducer where I wanted it. There isn't a lot of pressure on the top layer (roof) of the ballast tank at the centerline even when heeling, so i wasn't concerned with strength of the deck plate or cable clam.
In the end, i mounted it in the laz right at the centerline by the bulkhead wall in toilet wax ring. Way easier.
mastreb wrote:The ballast tank is a highly irregular shape, so you're probably best off with one of these ultrasonic level sensors, although you need a Maretron control head to calibrate it:
mastreb wrote:The ballast tank is a highly irregular shape, so you're probably best off with one of these ultrasonic level sensors, although you need a Maretron control head to calibrate it:http://www.maretron.com/products/tlm100.php
Matt
The sensor is affordable (MSRP $195), the control head is expensive (MSRP $995). Since it is NMEA2000 compatible, would be great if it could interface with the Garmin GPSMap546s. Besides the cost, I do not know where else to add another display to my console.
mastreb wrote:The ballast tank is a highly irregular shape, so you're probably best off with one of these ultrasonic level sensors, although you need a Maretron control head to calibrate it:http://www.maretron.com/products/tlm100.php
Matt
The sensor is affordable (MSRP $195), the control head is expensive (MSRP $995). Since it is NMEA2000 compatible, would be great if it could interface with the Garmin GPSMap546s. Besides the cost, I do not know where else to add another display to my console.
Robert, it interfaces just fine, but the configuration sentences are proprietary to Maretron, and tank sensors require calibration. That said, you don't have to buy a Maretron head--you can have them calibrated once by the dealer/installer, and then just keep that calibration. Just don't buy the sensor on Defender.com and think you'll be able to install it alone. You either pay $495 for their cheapest control head, or you pay an installer $495 to install and calibrate it for you. Oh well, at least one way you get a control head.
I'm going to be using these on my four tanks on the big boat, and in that case it's worth it to put a Maretron control head on the boat since the Starboard helm needs one anyway. But it is a bit of an "FU" that NMEA doesn't at least have an arcane "Hey, you can type in these HEX sentences directly into any brand of chartplotter to configure this device if you're so inclined" minimum level of configurability. It's extremely frustrating to know that there's really no limitation other than manufacturer's deliberately being proprietary.
Could you pick up a low cost ultrasonic from dwyer instruments or omega that has a 4-20mA output and feed that into the unit somehow, like the same as the fuel tank level input? Perhaps use a low cost display and four-position selector switch? Or perhaps even a level sensor with a 1-10 bar level output or something to light up a simple 10 LED display? Just thinking...
These ballast tanks are very shallow, and an ultrasonic often has a small dead zone at the top that it doesnt read within. This might be an issue, trying to read 1-6 inches of depth...you might have to mount the ultrasonic head on a small stand of PVC pipe to get it up high enough to read properly.
this thing is the perfect solution 
thanks greatly! 
