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Old 22-04-2008, 07:03   #1
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Thru hull transducer

I am going to install a new transducer in an exsisting thru hull. The directions say not to let the angle excede 10 degrees. And because it is plastic, they (Auto-Helm), recommend no fairing. It appears the angle will be about 14 degrees with no fairing. Is the only problem with this is the angle at what it reads or is there another reason not to excede the 10 degree angle? Would it really be a problem to install at 14 degrees??
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Old 23-04-2008, 08:18   #2
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Ideally, the transducer face should always be parallel with the bottom, so that the signal travels (send & receive) at a 90 degree angle to the bottom, giving an accurate depth reading.
Any mounting angle will introduce depth errors.
This is impossible, in reality, because both heeling & pitching introduce signal angles, hence depth reading errors.
Do the best you can, test & note errors (on a known depth, when level), and live with the variable errors.
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Old 23-04-2008, 10:09   #3
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Transducers have a cone measured in degrees or what might be called a beam angle or beam spread. A transducer does not need to be pointed straight down as long as a portion of the acoustic cone points at the bottom. The problem with a sailboat, especially a monohull, is that they heel and sometimes significantly.

Lets say the beam angle is 30 degrees for example. This leaves you 15 degrees for a port tack and 15 degrees for a starboard tack. If your boat heels more than 15 degrees and your transducer is pointed straight down with respect to your hull, then you will get no sound signal back..or worse yet a degraded signal from things that are not directly below you giving you a false reading that the water is deeper than it actually is.

You can buy or make a plastic wedge with a hole in it so that the transducer points downwards....but then you do take an increased risk of it shearing it off if say a log hits it. I have seen guards on large transducers on the upcurrent side of the transducer head specifically designed to protect it...but that may be going through more trouble than it is worth for you. I have four very large transducer heads located on my research boat that are flush mounted, eliminating the problem of them getting hit by something, but again, flush mounting may not be worth it for you.

If you have the option of a bronze transducer head then I would consider one because of the decreased risk of it being sheared off if something large hits it.

The manufacturers specs have the beam angle of your transducer....so that should help in knowing with certainty what you can and cannot get away with.

Transducer Beam Spread
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Old 23-04-2008, 12:10   #4
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What's the frequency, Kenneth? (apologies to Dan Rather)

Seriously, what's the frequency of the transducer?
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Old 23-04-2008, 13:01   #5
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Maren,

It is an AutoHelm ST30, I know it is an older model, however, it was new in the box when I purchased the boat.

It is a 50 Watt, 200 KHz. Is that good or bad?

Gord and Dave thanks for the reply, makes me feel better anyway.
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Old 23-04-2008, 14:08   #6
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Quote:
Originally Posted by Island Mike View Post
Maren,

It is an AutoHelm ST30, I know it is an older model, however, it was new in the box when I purchased the boat.

It is a 50 Watt, 200 KHz. Is that good or bad?

Gord and Dave thanks for the reply, makes me feel better anyway.
It means your beam angle will be more focused. Better for ... hold on, read this

As you can deduce the location will be more of a factor, if you are heeled to your favor, fine. Otherwise you might not get a reading at all.

... on the other hand ...

You only really need the transducer when it's shallow and I'm willing to bet that you aren't willing to bet your boat. As for getting good readings overall for other purposes, you might need to bite the bullet and move it.
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