Airmar P79 transducer installation

[MINESAPINT2]

I am about to install Airmar P79 transducer and unless I have misunderstood there seems to be a problem with the installation instructions. Ref point 1 and 4. Measure deadrise angle of hull at installation location. Draw a line on the inside of the hull at 90 degrees to the keel. This to be used to orient the base.

Whereas these instructions will be correct for some installation (or as near as makes very little difference), it does assume the deadrise of the hull is the same for the whole length of the vessel. This is not usually the case. Finding this difficult to explain. When I decided to fit a P79 I did not measure deadrise. I spilt some water (a few drips) on the inside of the hull and drew a line with felt tip pen parallel to where the water had just run down the hull. This represented the steepest slope of the hull (gravity assisted) and is at about a 60 degree angle to the keel (ie not the deadrise). The installation angle of the transducer is in fact 22 degrees so at the maximum for the P79. I am intending to install at 22 degrees and align the marks on the transducer base with my felt tip pen line, not in line with the deadrise.

If my water had made its way directly (90 degrees) to the keel this would have indicated the steepest slope was in fact the deadrise in which case the Airmar instructions would be correct.

If installation is made in accordance with Airmar instructions it is my opinion in some installations and mine in particular that the transducer will not point directly downwards, more likely forward or aft rather spoiling what seems to be a rather useful design.

Does anyone else see my point of view?

I dare say based on the information I have provided a mathematical genius may be able to calculate how far out my transducer beam would be if installed in accordance with Airmar instructions rather than on my felt tip pen line?

Thanks

Mike

 

[PaulRainbow]

Easy. decide where you want it, make a dam with some Plasticine/play dough/silicone/whatevertakesyourfancy. Make it a bit bigger than the P79 and fill this with slow drying epoxy (make sure it's slow drying so any air bubbles have chance to get out before it cures). Once it's dry, remove the dam and fit the transducer to the epoxy, well within specs.

 

[Hoolie]

I'm not sure how critical the installation angle has to be. AFAIK the P79 is only a depth transducer not a chirp scanner so it will measure the first return it gets as the the depth even if it's a bit off-centre.

In any case our boat sails bow up when it's moving so installing dead level when stationary will not be that accurate.

 

[salar]

The P79 is designed to be mounted on an angled hull with a deadrise of up to 22 degrees. As long as the bottom face is horizontal or near enough, it will work fine. On round hull forms you will find the angle may not be calculated at 90deg to the keel as the instructions suggest. I have fitted two P79s so I write from experience!