eddystone
Well-Known Member
This is a follow on from an earlier post. I have fitted a Raymarine i50 instrument to replace an old Echopilot with an Airmar P79 in hull transducer whilst the boat is laid up ashore but I have 3 dashes on the instrument indicating there is no signal from the transducer; the boat was immersed in water, in the cradle (although not quite to waterline) but it remained on 3 dashes so the launch was aborted. Since then with the help of a marine electrics guy and a bucket of water we have confirmed that the electrical side of things is fine and the transducer is working so the problem can be isolated to the transducer installation in the hull. (spoiler alert - the S32 is not a sandwich hull, unlike later Sadlers). Firstly, the P79 has a huge diameter compared to the 38mm Seafarer that was there before and that is a problem because there is only really one place to put it under the V berth in the fore cabin. The instructions for the P79, which can be adjusted to allow up to 22 degrees deadrise, indicate fitting slightly away from the centre line and at least 600mm in front of the keel. That area of the inside of the hull has a deadrise closer to 30 degrees and inconveniently is slightly concave viewed from inside the hull. As you can see from the photo, the original transducer tube was dead on the centreline - although there was some filler to flatten the mounting point, because it was so narrow it didn't stop the transducer firing through the hull. In my opinion, building up enough width in this location for the much wider Airmar would give it a lot of material to penetrate through. (Should say at this point this area is a bit messy because I've stuck a lot of epoxy down to stop it leaking so there was a lot of work with a multi-tool to try to remove this). What I actually did was to build up a thickness of filler to bring the deadrise angle within Airmar specification. In fact think I overdid this and ended up with angle of 16-17 degrees. And, because it it was still concave, used a huge amount of silicon sealant to bridge over this. Aforementioned electrician thought there was evidence the outer edges of the transducer body were touching the sealant. Applying an electronic level to the top of the transducer indicated an angle of about 3 degrees transversely and 10 degrees fore-aft.
So I now want to describe what I plan to do and would be grateful for any critique/suggestions. I'm making an assumption here that provided there is no air between the transducer and the inside of the hull, if it is working even out of the water it will give some sort of reading even if wildly inaccurate.
1. Just to check the sealant isn't causing a problem, remove the glycol, cut away excess sealant on the inside of the mount, refill and retest. If no change proceed to:
2. The possibility the layers of hull lay up/flowcoat/successive layers of filler have left some airspaces. Remove the transducer mount, grind/sand back to glass and remount in approximately the same location but this time aim to use less filler and aim for less correction of deadrise angle to utilise tolerance of 22 degrees, focussing more on getting flat surface and therefore less filler and fewer barriers between layers. If no improvement proceed to:
3. Alternative location. Unless you are a Sadler 32 owner you'll have to trust me there are no other suitable locations EXCEPT someone on the S&SOA Facebook Group has fitted his under the chart table seat behind the bulkhead and says it works although admits doesn't do much ditch crawling. I would obviously have to build a wooden box in there to protect it. Advantages - easy cable run and relatively flat; disadvantage - behind the keel, not in front.
4. As a final resort, leave the Raymarine as a decorative feature for the time being and fit a NASA Clipper Depth. The in hull transducer is of similar diameter to the old Seafarer one and the mounting tube would I fit in the old position. I could then look forward to experimenting with the Airmar when in the water and eventually have the luxury of two depth sounders.
So I now want to describe what I plan to do and would be grateful for any critique/suggestions. I'm making an assumption here that provided there is no air between the transducer and the inside of the hull, if it is working even out of the water it will give some sort of reading even if wildly inaccurate.
1. Just to check the sealant isn't causing a problem, remove the glycol, cut away excess sealant on the inside of the mount, refill and retest. If no change proceed to:
2. The possibility the layers of hull lay up/flowcoat/successive layers of filler have left some airspaces. Remove the transducer mount, grind/sand back to glass and remount in approximately the same location but this time aim to use less filler and aim for less correction of deadrise angle to utilise tolerance of 22 degrees, focussing more on getting flat surface and therefore less filler and fewer barriers between layers. If no improvement proceed to:
3. Alternative location. Unless you are a Sadler 32 owner you'll have to trust me there are no other suitable locations EXCEPT someone on the S&SOA Facebook Group has fitted his under the chart table seat behind the bulkhead and says it works although admits doesn't do much ditch crawling. I would obviously have to build a wooden box in there to protect it. Advantages - easy cable run and relatively flat; disadvantage - behind the keel, not in front.
4. As a final resort, leave the Raymarine as a decorative feature for the time being and fit a NASA Clipper Depth. The in hull transducer is of similar diameter to the old Seafarer one and the mounting tube would I fit in the old position. I could then look forward to experimenting with the Airmar when in the water and eventually have the luxury of two depth sounders.
