No depth reading with ballast out

[Mac26Mpaul]

Hi all,

My Hummingbird 767c fish finder worked fine for the first three or four years but then then started giving readings of .2 or .3 metres no matter the depth. I payed the service agent a few hundred to look at it and he declared he could find nothing wrong but reinstalled the software. I thought it was fixed as all was well the next time out.

Coupla months later we used the boat again and the probem was back but we realized it is only when the ballast is out, but works fine when ballast is full.

Anybody got any ideas? The transducer is not over the ballast tank. It is in the rear left compartment on the hull and had been there for about 7 years and used to work fine.

It is a bit annoying because when not sailing we mostly prefer to run with ballast out...

[Russ]

Interesting that it's related to ballast.

So you are sure it's not over the ballast?

Maybe the boat sits lower with ballast in and that affect something.\
Is it mounted through the hull or in a putty bed? Maybe re-seat it.

[tlgibson97]

My only thought is if it is an external transducer it could be out of the water when there's no ballast. If it's bonded tot he inside of the hull, is it bonded over top of the ballast tank?

[Crikey]

That would be true enough for an outside exposure. Also, if it was firing through the ballast, any bubble or partial fill would interfere with the high frequency signal.

R.

[yukonbob]

I would also have to suggest that it is coming out of the water frequently with the ballast out. Also could be a different loading of the boat contributing?

[Mac26Mpaul]

Boat is out on the mooring so cant get a decent photo, but you can sort of see the transducer in this photo. Its the black bit in the starboard side rear compartment, its not over ballast.


It did work fine for years. I see the PO has used epoxy to bond the transducer to the hull and it has slightly lifted at one end. However the transducer itself still seems to be hard against the hull.

Anyway, yeah, I think I'll take Russ's advice - Might pry it u and try and cut away some of the epoxy from the transducer and reseat it. What is best to use to bed it?

[Russ]

I see the PO has used epoxy to bond the transducer to the hull and it has slightly lifted at one end.

That is likely the problem. If it's lifting up, then it's not making solid contact with the hull. That location seems perfect.
Now if it's epoxied, you may have to work to get it off. Why would someone use epoxy? So hard and permanent.
If you get that loose, clean it very well to remove all the epoxy possible. Any air voids will affect the transducer.

I've installed several of these and bed them in silicone caulk. Easy to work with and easy to cut off with a knife if it doesn't work. Absorbs vibration well. They key is to keep bubbles out of the caulk. Simple clear bathroom caulk worked well for me.

You could just squeeze out a large amount and sink the transducer into it flat.


Caulk doesn't have to be clear, however I like to be able to see if there are bubbles.

Let us know what you find.

--Russ

[Crikey]

The clear silicone idea is good. Though I don't have one yet, I've read about many manufacturers bedding them in 4200. The silicone can be immensely strong as well and spotting bubbles in the setup (or afterwards) is a great advantage.
I want to get one of those side-scanning imagey thingys.

[Obelix]

If your sensor is located between the 2 ballast-channels, I think there is water ballast below and you wouldn't get a reading if the ballast is empty.

Obelix

[Russ]

The clear silicone idea is good. Though I don't have one yet, I've read about many manufacturers bedding them in 4200. The silicone can be immensely strong as well and spotting bubbles in the setup (or afterwards) is a great advantage.
I want to get one of those side-scanning imagey thingys.

Yea, 4200 is $20 a tube and you can't see through it.
I've installed several transducers in a bed of clear GE silicone caulk. Works great. I've used it as a great adhesive to mount wood to fiberglass to make a mounting platform. Absorbs vibration and it can be cut away with a razor.

If your sensor is located between the 2 ballast-channels, I think there is water ballast below and you wouldn't get a reading if the ballast is empty.

He said it was working, so I doubt there is ballast there.

This photo makes the ballast channels seem to run on either side and around the dagger trunk.

[Obelix]

When you look closely at the drawings, you'll see a double bottom in this area.


Obelix

[Crikey]

This shot is through here:

Looking port/ahead, the upper grey area is the 'U' shaped channel:

Just about all of the removable ballast is positioned forward.

[Mac26Mpaul]

Why did he use epoxy (lots of it) to bed it? He was a stock broker...

Now I'm a little left handed myself, but even I was shaking my head at a lot of stuff, like his wirering job And the fact that he had had the boat for 2 years and the mast was so out of tune, it would just bind up hard to port and not move. Took me half a day climbing up and down to get that working right.

I think it will come away from the hull with a bit of prying as it is already coming up at one end. Looks like he may have poured the epoxy on around it so hopefully not underneath.

Okay, clear silicon is the plan, thanks

The drawing does seem to show a bit of ballast under there but I don't think that is correct - pretty sure that is the hull. And yes, it certainly worked fine for a long time and we mostly have no ballast in.

Thanks all, will get onto that job shortly then.......

[Hamin' X]

The side tubes must be connected in some way toward the stern, else all of the ballast would not be able to be drained from only one side.

~Rich

[Mac26Mpaul]

The two tubes are joined at the stern with a tube going across I believe. Look at the photo Russ posted.