I need to cut a 1inch hole in the bottom of my hull (!)

[CMJ]

Hi – following on from this thread I’ve now been able to replace my transom mount transducer for a through hull one (many thanks to ‘David2452’ for pointing me in the right direction).

I’m not sure how thick the hull will be at the lowest point, but guessing around 1inch. To fit the transducer, I need to drill a 1” hole through it.

So, for obvious reasons I need to ensure I do this properly, using all the right materials etc. At this point, my uninformed guess is that I’d need to use a 1" hole saw suitable for GRP, then seal the ‘tunnel’ created with some sort of epoxy, then fit the transducer using some other type of sealant – all this a guess and I’m hoping for some advice before I wield the power tools – so any help really appreciated

Cheers.

 

[omega2]

cut the hole with a 1" starett cutter, at a slow speed, then with ample sikaflex, offer up the transducer and tighten the nut, this will cause the excess sealant to exude around the job, do not be too fussy about the looks, if you want it smooth and lovely then a wetted finger works best.

 

[SolentPhill]

If your not in hurry to be back in water once hole is drilled apply varnish to the fresh hole to protect the wood, let it dry before going to next stage

 

[CMJ]

If your not in hurry to be back in water once hole is drilled apply varnish to the fresh hole to protect the wood, let it dry before going to next stage

Hi - sorry, should have mentioned the hull is GRP

 

[Stork_III]

You did say GRP in original post. Make sure you use the correct sikaflex product. You want the sealant not the structural adhesive otherwise it will never come out again, when you want it to.

Look it up here. http://www.bluemoment.com/downloads/sikaflexmarinehandbook.pdf

 

[SolentPhill]

Hi - sorry, should have mentioned the hull is GRP

But some grp is sandwiched with wood

 

[CMJ]

You did say GRP in original post. Make sure you use the correct sikaflex product. You want the sealant not the structural adhesive otherwise it will never come out again, when you want it to.

Look it up here. http://www.bluemoment.com/downloads/sikaflexmarinehandbook.pdf

Thanks - also seems like common sence to me to use something to treat the walls of the freashly cut hole first (even before adding the sikaflex and transducer).....

 

[CMJ]

But some grp is sandwiched with wood

Ah - ok...fair enough!

 

[David of Essex]

Also ensure you drill at right angles to the surface to get the best seal not straight down.
David

 

[jfm]

I agree the above. Cut with a starret or Bosch holesaw. You'll need a good mains drill. It will be at least an inch of solid grp there, with no wood core. Seal with Sika or Alphaseal polyurethane

But Chris, are you really really really sure you want to do this? Scuse me for calling a spade a spade, but those fancy sounders are pants. They just show you a load of blurred fuzz on a screen. Chocolate teapot. I hate holes in the hull and work to reduce the number of seacocks as far as possible (my 78 has all the sundry drains manifolded so they share one seacock. There's no way I'd cut a hole in hull for a chocolate teapot sonar. Just sell it on eBay; you know it makes sense! All imho

 

[CMJ]

I agree the above. Cut with a starret or Bosch holesaw. You'll need a good mains drill. It will be at least an inch of solid grp there, with no wood core. Seal with Sika or Alphaseal polyurethane

But Chris, are you really really really sure you want to do this? Scuse me for calling a spade a spade, but those fancy sounders are pants. They just show you a load of blurred fuzz on a screen. Chocolate teapot. I hate holes in the hull and work to reduce the number of seacocks as far as possible (my 78 has all the sundry drains manifolded so they share one seacock. There's no way I'd cut a hole in hull for a chocolate teapot sonar. Just sell it on eBay; you know it makes sense! All imho

I could put money perhaps on this being a bit of a 'told you so'........BUT, I have done quite a bit of research over the year on forums (yeah yeah yeah you're probably thinking) and although I'm probably a mug, I have been convinced this will work well at the speeds I'd want it to (<10knots)......

will you buy me a beer if it does work great though (and I've got vids to prove it)?

Sadly for me, one of my downfalls is that I have to try things for myself......sometimes I've benefitted from this though in life, but other times not.....so to conclude, I reckon you're probably going to be right, but I can't help myself - a bit like sleepwalking / hypnosis or something

Anyway, if it is craap then I'll ditch it and sellotape up the hole

 

[TSB240]

Foam or Balsa wood Cores?

You need to find out if you have a foam or balsa core in your hull lay up...

If you have either then you risk water damage and delamination without furteher work other than using a sealant to fix the thru hull fittting.

If you have either then it is recommended to drill a small pilot hole. Get a nail and bend it through 90 degrees and use this in an electric drill to hollow out the core greater than the size of your proposed hole saw.(leaving the inner and outer layer of GF )

You then use Epoxy to fill the pilot hole and the area of core that has been removed. In effect creating a plug of epoxy that bonds everything together.

You can then drill thru with your core drill and you will then have a nice hole in the epoxy with the the core of the hull lay up protected from water logging.

Then you use sealant as previously detailed..

Hope this is of help

 

[jfm]

I could put money perhaps on this being a bit of a 'told you so'........BUT, I have done quite a bit of research over the year on forums (yeah yeah yeah you're probably thinking) and although I'm probably a mug, I have been convinced this will work well at the speeds I'd want it to (<10knots)......

will you buy me a beer if it does work great though (and I've got vids to prove it)?

Sadly for me, one of my downfalls is that I have to try things for myself......sometimes I've benefitted from this though in life, but other times not.....so to conclude, I reckon you're probably going to be right, but I can't help myself - a bit like sleepwalking / hypnosis or something

Anyway, if it is craap then I'll ditch it and sellotape up the hole

Yes I'll buy you a very nice beer if it works. Sadly i think it'll be your round though . On my last sq58, an EBY stock boat specced up for SIBS2008, they had included an Echopilot FLS. The top of the range "platinum" one with a big thru hull trnasducer and video-linked to the Raymarine screens. If you look on Echopilot website and speak to them at SIBS/LIBS, you could think it is fine kit. alas, it was total junk. Just some fuzz on the screen and a rough outline of the seabed shape. Great. Not. Definitely not worth a hole in the deep part of the hull with 2m head on it constantly (which is a big deal item for me!). But I do wish you well with it and would be delighted to be shown to be wrong!

Ref TSB240 post, Azi 50 hull bottom is solid grp, no core

 

[ian38_39]

how common is this Balsa Sandwich?

Know it is often used in decks but didn't know it was used for hulls, wouldn't have thought it was strong enough.

 

[omega2]

A simple way to find out if the hull is a sandwich is to hang the transducer over the side of the boat pointing straight down into the water and note the return echo on the screen it will be the best you can expect from the unit, then put the transducer in a plastic bag with a little water and plonk it down onto the hull and note the return signal, if it's good then you can bet the hull is solid glass, if it does not return the you have a sandwich, makes no difference to your mounting though, the sika flex will seal the sides of the hole as well as the the unit.

 

[jfm]

how common is this Balsa Sandwich?

In general, it isn't common below w'line. For longevity/maintenance reasons. In an Azi 50,which is OP's boat, it's very uncommon; non existent in fact

didn't know it was used for hulls, wouldn't have thought it was strong enough.

??? For a given amount of GRP, splitting it into 2 layers with a balsa (or airex/divinycell) core properly stuck in will be much stronger and stiffer than applying it as one layer of solid GRP

 

[Mr Googler]

No chance of getting a lowrance shoot through transducer?

Save the scary " I can see the inside of my boat from underneath!!" moment.

 

[neale]

Yes I'll buy you a very nice beer if it works. Sadly i think it'll be your round though . On my last sq58, an EBY stock boat specced up for SIBS2008, they had included an Echopilot FLS. The top of the range "platinum" one with a big thru hull trnasducer and video-linked to the Raymarine screens. If you look on Echopilot website and speak to them at SIBS/LIBS, you could think it is fine kit. alas, it was total junk. Just some fuzz on the screen and a rough outline of the seabed shape. Great. Not. Definitely not worth a hole in the deep part of the hull with 2m head on it constantly (which is a big deal item for me!). But I do wish you well with it and would be delighted to be shown to be wrong!

Ref TSB240 post, Azi 50 hull bottom is solid grp, no core

My money is on JFM getting them in.

Structure Scan is a very different animal to Echopilot and, having seen it working first hand, think the OP will be very impressed.

 

[David2452]

Also ensure you drill at right angles to the surface to get the best seal not straight down.
David

No No, it must be drilled so the transducer is pointing straight down, (pilot hole from the inside first) the fairing block is then cut with a bandsaw to compensate for the angle. Don't worry, it's all in the instructions that come with the unit including which sealent to use, how to deal with cored hulls etc etc.

 

[pks1702]

(many thanks to ‘David2452’ for pointing me in the right direction).

The man himself in action on our ship



















Regrettably I don't have a shot with the fairing block cleaned up - but it was!

You can just see the fairing has been band saw cut to match the dead rise angle.





Thanks David; great job.