Guide Point 3: Hull Type Considerations
🚤 Third Consideration: Hull Type Considerations
Fiberglass Hulls
Fiberglass hulls usually have a deep V hull shape, and due to the V nature of the boat, the boat can act as a seesaw listing to one side. By keeping the transducer as close as possible to the keel, listing effects are reduced.
The listing problem: When a deep V hull lists (leans to one side), this can significantly affect the performance and accuracy of the transducer. As the boat seesaws to one side, the sonar beam is deflected from shooting straight down to sending off at a different angle. This can either break the beam strength or miss the target and give inaccurate depth and bottom contour readings.
Critical issue: If the boat lists to the side that the transducer is not on, then the transducer can almost lift out of the water.
Deep deadrise angle challenge: Usually when a transducer is mounted on a deep V hull and transducer placement seems to be difficult, it is because of the deep deadrise angle. Using the factory mounting that comes with your transducer won't allow the transducer to get deep enough in the water, as the sharp leading edge of the boat tears the water like a giant strake. A deeper position is needed, or an aftermarket mount that will get you deeper in the water.
Aluminum Hulls
Most aluminum boats will come with a welded transom plate that has been welded to the transom as a sacrificial area. This allows transducer repositioning to be done without drilling new holes all the time and not affecting transom structure.
The positioning problem: These plates, whilst sounding beneficial, are not always welded in the correct position for optimal transducer placement. Do not assume it is welded in the correct position.
The performance trade-off: Whilst beneficial as a sacrificial plate, they can affect performance even though they may be situated in the correct position. They increase the distance from transom to transducer—the further you are away from the transom, the dirtier (more aerated) the water.
Your choice:
- Option 1 - Best performance: Remove the sacrificial plate to install your transducer hard against the transom for best results. However, this comes with a negative aspect: you must understand sealing the holes correctly as you don't want water to enter the boat and cause corrosion issues later on if the holes are not sealed properly.
- Option 2 - Easier installation: Continue to use the sacrificial plate but accept some performance loss.
So you have a choice: get the best read while ensuring holes are sealed, or lose some performance by continuing to use the sacrificial plate.