[Public-list] hull thickness

[Don Campbell]

Depending on the size and placement of the forward water tank, there 
might be room in front of the panel under the vee-birth and aft of the 
tank. I have mounted a depth sounder there on the centre line. It is not 
quite vertical, but about 11°  off,  aiming forward. That gives a bit of 
distortion but not much and is equal for both tacks. I tried this 
sounder  in an oil bath first and it would not read through the hull. I 
think it depends on who was working the day your hull was laid up as to 
how thick it is and hulls tend to be at least 1/2" in most places.  
Epoxy and fairing the installation on the forward edge has made this 
just fine for water flow around it and it is waterproof. I have not had 
a problem with slings catching the transducer on liftout with this and 
we do lift the boat every year. We do tie the straps though.
    I used a 1/4 inch drill from the inside as a locator and drilled 
with a hole saw from the outside for the final position. It is a 
compromise between vertical and easily faired into the hull line.
    Don't forget to calibrate the new instrument after installation to 
know how deep things really are when the bottom gets to be close to the 
surface of the water! If you are off centre, then any heel will affect 
the reading for actual depth.
    Having the transducer in a bath means that you need to have the 
fluid level in that box such that the transducer is always under the 
surface. This means there can be no leaks and that the "through hull" 
fitting has to be installed in the lid before the lid of the box is 
affixed. If you ever need to get the fitting out, it is a total 
deconstruction project that will leak fluid everywhere, and from what 
research I have done, oil, or at least fluids with viscosities greater 
than water are a better medium than water to transmit the signal. Your 
call though.
Don # 528

The Rochets wrote:
> I  am interested in the Raymarine ST40 depth sounder. It comes as a  
> package with a thru-hull transducer, but I want to install it in a  
> waterbox, in-hull. Raymarine has assured me it's OK to use the  
> supplied thru-hull transducer as an in-hull as as long as the hull is  
> no thicker than 1/2". Do we know what the thickness of the hull is  
> under the cabin settees about 6" away from the center line (that's  
> where I am thinking of installing the transducer)?
>
> I know the answer to this question is somewhere in the list archives,  
> but I am having trouble searching the archives. A simple search  
> returns no hit regardless of the search term, including terms like  
> "coamings" which I know have been discussed fairly recently. I also  
> tried a Google search within the archives domain (http:// 
> lists.alberg30.org/pipermail/public-list-alberg30.org/); I have used  
> it this method before, but right now this doesn't work either. What  
> am I doing wrong?
>
> Thank you.
>
> Bernard
> Sunswept #608
>
>
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