Speed and depth transducers locations

[alisdair4]

I am about to fit Raymarine i40 speed and depth transducers. The instructions are clear enough - they should both be ideally forward of the keel (the boat is an LM32), as close to the centre line as possible, and the depth transducer should be within 10 degrees of the vertical. Well and good - in the LM 32 , this points me towards an area about 18" square just off the centreline, where there is no internal moulding - and indeed where the previous (internally mounted) depth transducer was.

I am considering mounting the transducers one ahead of the other - I would presume depth ahead of the speed transducer as the reverse option would lead to disturbed water flow over the depth transducer. Does this sound right ?

 

[bitbaltic]

When I had two transducers they were mounted side by side rather than one behind the other. But mildly surprised that modern ray marine kit isn't coming with a single combined depth/speed/temp transducer e.g from airmar. This is what I have now and would think it's quite a bit simpler for you.

 

[NormanS]

Unless there was a good reason against it, I would fit the depth transducer inside. I.e. so that it fires through the hull. I'm never very sure of the correct terminology for that, as I always think that "Through Hull" is confusing, as that can be said of both methods. Anyway unless with foam sandwich or wooden hull, I don't see any advantage in having yet another hole in the boat. If you can do that, it will possibly simplify the positioning of the log transducer.

 

[prv]

I am considering mounting the transducers one ahead of the other - I would presume depth ahead of the speed transducer as the reverse option would lead to disturbed water flow over the depth transducer. Does this sound right ?

My guess would be the other way round. The depth sensor doesn't like bubbles, but I don't think it cares too much about motion. I wouldn't expect the paddlewheel to generate any bubbles, but it might just be disturbed by the slipstream off the depth head.

Pete

 

[MM5AHO]

+1
I have moved mine from one mounted to touch the water, to one firing through the hull. I could never get the one in the water to work, but now get good depth soundings in an oil mounted one inside the hull.

Unless there was a good reason against it, I would fit the depth transducer inside. I.e. so that it fires through the hull. I'm never very sure of the correct terminology for that, as I always think that "Through Hull" is confusing, as that can be said of both methods. Anyway unless with foam sandwich or wooden hull, I don't see any advantage in having yet another hole in the boat. If you can do that, it will possibly simplify the positioning of the log transducer.

 

[ghostlymoron]

I think it's possible to get a combined sensor which should make siting easier.

 

[PaulRainbow]

I think it's possible to get a combined sensor which should make siting easier.

I don't think you can with the i40, bizarrely. Even the i40 Bi-Data has two transducers. The i70 will, i think, use the Airmar DST800 triducer, which is what i suspect you're thinking of.

To the OP :
I would also read the instructions carefully for the depth transducer before considering mounting it in hull, as suggested by some here. Normally that would be good advice, but i'm sure i read somewhere (most likely another thread on here) that the i40 transducer will not work correctly in hull.

I would mount the two transducers side by, either side of the centre line.

 

[alisdair4]

Thanks for all of the feedback and advice. The I40 transducer cannot be mounted inside the hull, unfortunately - and this outfit doesn't offer a combined speed/depth transducer . Given the limitations of my budget, I have got the kit I've got, and am too mean to buy another combined transducer! Pete, thanks for that specific answer.

 

[pvb]

Like bitbaltic and PaulRainbow, I'd go for side-by-side mounting.

 

[alisdair4]

Thanks, PVB - that is the conclusion I am coming to, too.

 

[Boo2]

Is tbere such a thing as an in-hull (ie not thru-hull) combined speed / depth transducer ? I had a look but couldn't find anything.

Thanks,

Boo2

 

[PaulRainbow]

Is tbere such a thing as an in-hull (ie not thru-hull) combined speed / depth transducer ? I had a look but couldn't find anything.

Thanks,

Boo2

Can't see how you would measure speed through the hull.

 

[prv]

Can't see how you would measure speed through the hull.

If someone told me it existed, I'd assume it did it by doppler ultrasound. But I don't know whether it's actually possible, and I've never seen one.

You do get through-a-hole ultrasound logs which look similar to depth transducers and don't get jammed with fouling. Pricey though.

Pete