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Ask Michael Hannigan Your Own Question
Michael Hannigan
Michael Hannigan, Engineer
Category: Marine Electronics
Satisfied Customers: 11175
Experience:  25+ Years Experience in Field. Master Certified Electronics Tech and Technical Consultant
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I purchased an 899si fishfinder need to swap the transducer

Customer Question

I purchased an 899si fishfinder need to swap the transducer foer a saltwarter high def large one what are my obshions?
Submitted: 1 year ago.
Category: Marine Electronics
Expert:  Michael Hannigan replied 1 year ago.
Hello. My name is***** can help you with your question. There are a huge number of things to consider when choosing a transducer. Especially for salt water.
A couple of considerations - mounting location and specific qualities of the transducer - determine how effectively your sounder does its job. Let's look at placement first. There are three ways to mount a transducer in your boat, and the one you choose depends most on the your hull.
The most complicated is through-hull mounting, where a hole is cut in the bottom of the boat and the transducer is mounted flush with the bottom, so the transducer face is in direct contact with the water. Through-hull mounting is the most efficient way to get the best performance out of a transducer.
Direct contact with the water is the most efficient transducer mount. That way every single ounce of power that you put in the transducer goes into the water. There are some considerations, though. You have to make a hole in the hull, which some people don't want to do, though there are seldom problems with this. If the instructions are followed, you have assurance of 100-percent safety."
The beam of a transducer set to 200 kHz, left, covers less area but shows much more detail. This is the frequency that's most useful for shallow-water applications. The 50 kHz transducer beam, right, sacrifices some detail for a broader beam, useful for searching deep water.
And I think that's the most important part of what you're asking.
Not all hulls are suited for this treatment, so you must be careful when deciding.
If you are uncomfortable with cutting a hole in the hull, another option is to mount the transducer inside the hull, flush against the bottom of the boat, and shoot the signal through the hull. The disadvantage here is the power loss that occurs when the signal must pass through the hull during transmission and reception. In the past, this was much more of a problem than it is today. Even with the power loss, an in-hull mount has some advantages. One other consideration is that an in-hull transducer won't work if your hull is cored, such as with end-grain balsa or foam. In this case you'll need to go with a through-hull or transom mount.
It is not as efficient as a through-hull mount, but it is workable, and it's a lot easier to install. The newest transducers are very high-end and sport fishing models have 65- to 70-percent efficiency."
The third type of placement, on the transom, is usually reserved for smaller boats or when there is no access inside the hull for a through-hull or in-hull transducer. Transom mounting is the quickest and simplest way to mount a transducer, but it must be done properly.
You have to be very careful where you mount the transducer in proximity to the propeller with a transom mount. Try to mount it as far outboard as possible, and separate it from the source of noise.
Bubbles and turbulence can be a problem with other mounting positions, too. Both through-hull and in-hull mounts have to deal with this kind of interference.
Try to keep the block as small as possible, but also try to get the transducer away from the bottom where the disturbed water is
Choose the Right Frequency
Once you've determined where the transducer will go, it's important to buy quality.
The split-beam transducer receives in four quadrants, so we know where in the beam the target is and we can place it in relation to the boat. With a single beam, everything appears directly beneath the boat. Get a split-beam if you have the money - they run $20,000 and up - otherwise, single-beam, with dual frequency, is the way to go

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