I’m about to install a forward scan transducer and looking for some advice/reassurance.

The sounder is more or less the same as a normal depth / speed transducer, ie a 50ish mm threaded tube with flange and removable inner plug. Unlike a depth/speed fitting it needs to be installed horizontally athwart ships (there can be a small angle fore/aft).

The hull is almost completely horizontal very close to the centreline so installing it there would save me messing about with fairing inside and out to get the fitting horizontal. So less work and less drag.

I have two queries really:

1. General install method. I’m planning on drilling a hole with a hole saw, removing the antifoul from around the hole, applying plenty of sikaflex in and around the hole, push the fitting up, tighten the nut. The housing is either stainless steel or chromed bronze. Seems pretty straight forward but is there anything else I should be doing or not doing or looking out for?

2. Location. The proposed location is quite far forward and offset slightly from the centreline. About an inch or two to one side of the fore/aft glassed in bulkhead and very close to where the baby stay terminates on that bulkhead. The baby stay hydraulic ram is bolted to the bulkhead about 3 inches above the bottom of the hull and the proposed hole. I’m wondering if there are any potential issues, structural or otherwise, in drilling the hole so close to the bulkhead and/or the baby stay connection point?

Thanks in advance

Pete

+x

 

pete.holt - 31 Dec 2022

I’m about to install a forward scan transducer and looking for some advice/reassurance.

The sounder is more or less the same as a normal depth / speed transducer, ie a 50ish mm threaded tube with flange and removable inner plug. Unlike a depth/speed fitting it needs to be installed horizontally athwart ships (there can be a small angle fore/aft).

The hull is almost completely horizontal very close to the centreline so installing it there would save me messing about with fairing inside and out to get the fitting horizontal. So less work and less drag.

I have two queries really:

1. General install method. I’m planning on drilling a hole with a hole saw, removing the antifoul from around the hole, applying plenty of sikaflex in and around the hole, push the fitting up, tighten the nut. The housing is either stainless steel or chromed bronze. Seems pretty straight forward but is there anything else I should be doing or not doing or looking out for?

2. Location. The proposed location is quite far forward and offset slightly from the centreline. About an inch or two to one side of the fore/aft glassed in bulkhead and very close to where the baby stay terminates on that bulkhead. The baby stay hydraulic ram is bolted to the bulkhead about 3 inches above the bottom of the hull and the proposed hole. I’m wondering if there are any potential issues, structural or otherwise, in drilling the hole so close to the bulkhead and/or the baby stay connection point?

Thanks in advance

Pete

Hi Pete,
It is not a complex job, but it is good that you are doing research ahead of time.
I would extend your research: I believe RC Collins on his web site, Marine-how-to, (https://www.google.com/search?q=Marine-how-to&oq=Marine-how-to&aqs=chrome..69i57j0i30l4j0i8i30j69i65l2.663j0j7&sourceid=chrome&ie=UTF-8
has an article on this and could be a good resource. I am sure there are lots of others such as Nigel Calder’s books.
I do notice you did not mention a backing plate which is probably wise for any hull skin but may be required if the hull is particularly thin. And, I assume it is not a cored hull.
And if the angle of the hull off-horizontal exceeds the recommendation of the sounder’s manufacturer, then it is easy to make an angled plinth of g-10 or the like and epoxy it in.
And, consider access, you may want to be able to pull it out and put in a plug in the water at some point.
And, then there is the question I suspect only a structural engineer could answer definitively, although a surveyor or boatyard may give opinions.
If you go by just building up the area to compensate for the hole you drill, then find a way to remind yourself after commissioning the boat to power up the hydraulic ram and look for movement/cracks, etc. Do the same after your first sail and then after the first boisterous sail in seas where you bang around a bit.
Random thoughts, Dick Stevenson, s/v Alchemy

Hi Dick,
Thanks for your input.
That marinehowto site is a superb resource, it’s a shame it may not grow any further due to the owner’s health. He has a really comprehensive guide to installing seacocks, however I think I can afford to be less diligent for a simple thru-hull only, with no seacock to potentially lever or twist the through-hull out of place.
I hadn’t considered using a backing plate as I assumed the hull would be quite thick in that area but I’ll take some G10 just in case.

I’ll do some more digging about any potential structural implications of making a hole in that area. Although as you say this is probably just guess work for anyone other than a structural engineer.

Cheers
Pete

+x

 

pete.holt - 4 Jan 2023

Hi Dick,
Thanks for your input.
That marinehowto site is a superb resource, it’s a shame it may not grow any further due to the owner’s health. He has a really comprehensive guide to installing seacocks, however I think I can afford to be less diligent for a simple thru-hull only, with no seacock to potentially lever or twist the through-hull out of place.
I hadn’t considered using a backing plate as I assumed the hull would be quite thick in that area but I’ll take some G10 just in case.

I’ll do some more digging about any potential structural implications of making a hole in that area. Although as you say this is probably just guess work for anyone other than a structural engineer.

Cheers
Pete

Hi Pete,
RC has returned to active involvement in certain areas, but it is unclear whether he will return to his previous output of his superb pictured how-to articles.
With regard to a backing plate and your concern of integrity in the area, you might consider thinner G10 stacked a bit and taper it out- well bonded to each other and to the hull- from the seacock. Try to avoid an abrupt support edge that could “hinge”.
And agree, as described, yours is an easier install.
Let us know how it goes.
My best, Dick Stevenson, s/v Alchemy