Depth sounder/Speed sensor placement

[GILow]

Hi all,

I’ve bought a DST810 ( they appear to have addressed the premature failure issues.)

Now I have to figure out where to put it.

Thanks to the under-floor water tanks, I can either go in alignment with the mast or I have to go well forward to clear the forward water tank.

Forward and I may run into problems with deadrise. (The DST810 says you can have a maximum of 22 degrees). But I think I can stay close to the centerline to solve that one.


In alignment with the mast appeals more from a layout and access perspective (we’ve built a utility space along there for pipes and wires), but I wonder if I’m likely to get some kind of interference from reflections from the keel?

Thoughts?

Pictures to aid in analysis.

[deblen]

Aft spot would be my choice from practical experience-retired tech.
1. You won't get reflection off keel.
2. Cleaner,less aerated water,than forward.
3.Shorter,easier? cable run to display.
4. Possible? easier access for removing & cleaning speed wheel.
IMHO / Len


https://www.cruisersforum.com/forums...el-285735.html

[GILow]

Originally Posted by deblen

Aft spot would be my choice from practical experience-retired tech.
1. You won't get reflection off keel.
2. Cleaner,less aerated water,than forward.
3.Shorter,easier? cable run to display.
4. Possible? easier access for removing & cleaning speed wheel.
IMHO / Len


https://www.cruisersforum.com/forums...el-285735.html

Good points. Glad to hear about 1, would never have thought of 2, yes to 3 and 4.

[Bowdrie]

Watch your deadrise angle, it is much more important than many would think.
The claim of ~22 degrees is misleading; it doesn't take into account heeling.
The beam width of 44 degrees is only applicable when the unit is vertical, which will allow heeling to either side of vertical.
If you install it pointing out to port at 15 degrees and the boat heels 10 degrees to starboard you've lost your depth.
Do what you can to get the sensor as close to vertical as possible, even if it means fabricating a special fairing block/housing.
I would add. You don't want a depth unit close alongside a deep fin keel, the keel interferes with the dispersion angle of the beam.

[GILow]

Originally Posted by Bowdrie

Watch your deadrise angle, it is much more important than many would think.
The claim of ~22 degrees is misleading; it doesn't take into account heeling.
The beam width of 44 degrees is only applicable when the unit is vertical, which will allow heeling to either side of vertical.
If you install it pointing out to port at 15 degrees and the boat heels 10 degrees to starboard you've lost your depth.
Do what you can to get the sensor as close to vertical as possible, even if it means fabricating a special fairing block/housing.
I would add. You don't want a depth unit close alongside a deep fin keel, the keel interferes with the dispersion angle of the beam.

I’ve been thinking about the whole deadrise thing vs keel shadow thing.

I guess I’m going to have to see how the angles pan out when I get the boat out of the water, see how far outboard I will have to put the sensor to clear the keel.

If I can avoid a fairing block for now I would be happier. I’ve got a longer slipping planned for February, if I find the depth readings are unreliable with the boat on a heel I will suck it up and square up the sounder then.

Thankfully, if depth is an issue I’m usually motoring, or at the least sailing very gently so I think we will get away with it.

[Dockhead]

Can't help you much about placement, except to say that you want the depth sensor fairly close to the centerline. I would want depth forward of the keel for sure, as far forward as you can go without running into deadrise issues. Behind the keel and you will see the shoal only after you hit it.

I would not do combined depth/speed, if I were you. Combining them in one sensor compromises both of them, and you may not necessarily want them in the same place, either. The Airmar paddlewheel sensors altogether do not have a good reputation, and STW is really hard to measure (I made a separate thread about that).

If I were you, if I were drilling holes in the boat and starting fresh, I would put in a Signet Blue Top speed log, which is what the racers use. It's actually cheaper than the crappy Airmar ones. The Signet is a pulse sensor so you'll need an adapter like Actisense sells, to get the data onto your network.

This would be a far better solution and would allow you to separately optimize the the placement for each.

[deblen]

Originally Posted by Dockhead

Can't help you much about placement, except to say that you want the depth sensor fairly close to the centerline. I would want depth forward of the keel for sure, as far forward as you can go without running into deadrise issues. Behind the keel and you will see the shoal only after you hit it.

I would not do combined depth/speed, if I were you. Combining them in one sensor compromises both of them, and you may not necessarily want them in the same place, either. The Airmar paddlewheel sensors altogether do not have a good reputation, and STW is really hard to measure (I made a separate thread about that).

If I were you, if I were drilling holes in the boat and starting fresh, I would put in a Signet Blue Top speed log, which is what the racers use. It's actually cheaper than the crappy Airmar ones. The Signet is a pulse sensor so you'll need an adapter like Actisense sells, to get the data onto your network.

This would be a far better solution and would allow you to separately optimize the the placement for each.

With respect-what is your reason for wanting ducer "close to centerline" ?
With respect-do you think having the ducer even 1/2 a boat length farther fwd(or even on the stem) will give you time to stop?
Cheers/Len


https://www.raymarine.com/en-gb/our-...art-transducer

[deblen]

Originally Posted by Bowdrie

Watch your deadrise angle, it is much more important than many would think.
The claim of ~22 degrees is misleading; it doesn't take into account heeling.
The beam width of 44 degrees is only applicable when the unit is vertical, which will allow heeling to either side of vertical.
If you install it pointing out to port at 15 degrees and the boat heels 10 degrees to starboard you've lost your depth.
Do what you can to get the sensor as close to vertical as possible, even if it means fabricating a special fairing block/housing.
I would add. You don't want a depth unit close alongside a deep fin keel, the keel interferes with the dispersion angle of the beam.

With respect-I agree that any ducer should be mounted as close to vertical as possible for best accuracy. That is why I usually recommend they be placed about halfway outwards between the keel & chine-to avoid keel shadow & stay in "cleaner,less aerated" water-at least when the boat is not heeled much.
If the boat is heeled severely,you probably should not be going that fast in water that shallow. If you need to "speed" in water that shallow,perhaps you need 2 ducers-one on each side-with appropriate auto switch. These were available in the olden days.
Cheers/Len
https://www.raymarine.com/en-gb/our-...art-transducer

[GILow]

Originally Posted by Dockhead

Can't help you much about placement, except to say that you want the depth sensor fairly close to the centerline. I would want depth forward of the keel for sure, as far forward as you can go without running into deadrise issues. Behind the keel and you will see the shoal only after you hit it.

I would not do combined depth/speed, if I were you. Combining them in one sensor compromises both of them, and you may not necessarily want them in the same place, either. The Airmar paddlewheel sensors altogether do not have a good reputation, and STW is really hard to measure (I made a separate thread about that).

If I were you, if I were drilling holes in the boat and starting fresh, I would put in a Signet Blue Top speed log, which is what the racers use. It's actually cheaper than the crappy Airmar ones. The Signet is a pulse sensor so you'll need an adapter like Actisense sells, to get the data onto your network.

This would be a far better solution and would allow you to separately optimize the the placement for each.

I understand that there may be more accurate sensors available, but I’m more concerned about the number of holes in the boat. Multiple sensors = multiple holes. Not my idea of fun.

[GILow]

Originally Posted by deblen

…
If the boat is heeled severely,you probably should not be going that fast in water that shallow

Agreed. Below 5 meters and we stay below 5 knots.

[Dockhead]

Originally Posted by deblen

With respect-what is your reason for wanting ducer "close to centerline" ?
With respect-do you think having the ducer even 1/2 a boat length farther fwd(or even on the stem) will give you time to stop?
Cheers/Len

https://www.raymarine.com/en-gb/our-...art-transducer

So, your speed transducer will work differently when you're heeled. If it's far off the centerline, it will work a lot different on different tacks. This is undesirable. Also when heeled on the side opposite where the transducer is, you have more risk of getting into frothy/aerated water, which will make it stop working.


Concerning depth -- well, you can decide yourself, but I'd sure like to know the depth ahead of the keel, more than behind it. Big ships have multiple depth sounders, for "forward depth", "aft depth", etc. It doesn't mean you can stop, if you are at speed, but picking your way very slowly can make a difference.

[Dockhead]

Originally Posted by GILow

I understand that there may be more accurate sensors available, but I’m more concerned about the number of holes in the boat. Multiple sensors = multiple holes. Not my idea of fun.

Well, they're not just more accurate, they are more reliable, and better altogether. Is 2 holes really that much worse than 1? Out of how many holes in the bottom of your boat? I think I've got 15 not counting the shaft log.


But naturally -- your boat, your priorities.

[GordMay]

Airmar, and others, suggest the following transducer locations:
• Fin keel sailboats: Mount on or near the centerline, and forward of the fin keel 300 to 600mm (1–2').
• Full keel sailboats: Locate amidships [CL], and away from the keel, at the point of minimum deadrise angle.

[GILow]

Originally Posted by Dockhead

Well, they're not just more accurate, they are more reliable, and better altogether. Is 2 holes really that much worse than 1? Out of how many holes in the bottom of your boat? I think I've got 15 not counting the shaft log.


But naturally -- your boat, your priorities.

Currently there are two holes in the boat. One for the prop and one for the engine raw water feed. This sender will be the third hole.

[GILow]

Originally Posted by GordMay

Airmar, and others, suggest the following transducer locations:
• Fin keel sailboats: Mount on or near the centerline, and forward of the fin keel 300 to 600mm (1–2').
• Full keel sailboats: Locate amidships [CL], and away from the keel, at the point of minimum deadrise angle.

Thank you, I hadn’t seen that advice. Maybe I should RTFM.