Advice on drilling 2 holes in hull (tomorrow pm)

yodave

yodave

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Advice on drilling 2 holes in hull (this afternoon)

Hi,

My (through the hull) Nasa Clipper Duet transducer 'catastrophically failed' when I was trying to fix it over the weekend (yep, I broke it). It had been installed at 90 degrees to the ground through the hull, surrounded by a shaped piece of wood, however it turned out that the only thing holding the wood on to the hull was the transducer itself and some SikaFlex.

I have bought a replacement transducer as well as the proper Nasa mounting system. The mounting system is angled to allow a flush fitting to the hull. It's not clear to me that the angle of the mount will allow the holes to sit at exactly 90 degrees (and so there maybe a problem with alignment to the 90 degree angle of the existing hole), but I reckon that it looks there or there abouts.

I'm fitting this tomorrow when the tide goes out. This means drilling two holes on either side of the existing (90 degrees) hole for the bolts that hold the mounting on. I'm not a natural techie and I'm nervous about drilling holes in the hull.

It seems to me that drilling the holes from the outside would be the most accurate/direct solution. However there is very little clearance under the hull as we have stubby bilge keels and she's sitting on (shallow) mud. This will inevitably make it very difficult to operate a power drill accurately to ensure that the holes that I'm drilling are at 90 degrees to the ground.

My first question is: do I drill the holes in reverse from the inside (giving me a better working space), or do I go for the outside but compromise control and accuracy?

My second question is: Do I use a drill bit that's the same size, or one that's just a little smaller?

My third question is: Should I be panicking about the angle of the holes, given the likelihood is that the mount won't be precisely aligned with the existing 90 degree transducer hole?

I'll be leaving about lunch time tomorrow, so any advice would be really welcome ...however I may not be able to respond until the following day as I'll be staying with the boat until she floats (or not).

Thanks in advance!
 
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yodave said:
Hi,

My (through the hull) Nasa Clipper Duet transducer 'catastrophically failed' when I was trying to fix it over the weekend (yep, I broke it). It had been installed at 90 degrees to the ground through the hull, surrounded by a shaped piece of wood, however it turned out that the only thing holding the wood on to the hull was the transducer itself and some SikaFlex.

I have bought a replacement transducer as well as the proper Nasa mounting system. The mounting system is angled to allow a flush fitting to the hull. It's not clear to me that the angle of the mount will allow the holes to sit at exactly 90 degrees (and so there maybe a problem with alignment to the 90 degree angle of the existing hole), but I reckon that it looks there or there abouts.

I'm fitting this tomorrow when the tide goes out. This means drilling two holes on either side of the existing (90 degrees) hole for the bolts that hold the mounting on. I'm not a natural techie and I'm nervous about drilling holes in the hull.

It seems to me that drilling the holes from the outside would be the most accurate/direct solution. However there is very little clearance under the hull as we have stubby bilge keels and she's sitting on (shallow) mud. This will inevitably make it very difficult to operate a power drill accurately to ensure that the holes that I'm drilling are at 90 degrees to the ground.

My first question is: do I drill the holes in reverse from the inside (giving me a better working space), or do I go for the outside but compromise control and accuracy?

My second question is: Do I use a drill bit that's the same size, or one that's just a little smaller?

My third question is: Should I be panicking about the angle of the holes, given the likelihood is that the mount won't be precisely aligned with the existing 90 degree transducer hole?

I'll be leaving about lunch time tomorrow, so any advice would be really welcome ...however I may not be able to respond until the following day as I'll be staying with the boat until she floats (or not).

Thanks in advance!
Click to expand...

place inside the hull in a plastic tube, fill the existing hole with CSM & resin, fill n fair ect
 
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Our transducer is the same as yours and is fitted using Sikaflex and then bonded round the edges with fiber glass.

We did'nt do it. Thats how it came. Only my oppinion but have never heard of anyone bolting a transducer to the hull.

Hopefuly some expert will come along with advice for you

Good Luck

Peter
 
Hi sailorman,

Thanks for your reply. I did seriously think about this as I read many threads on that very subject on this forum however...

1) the documentation states that it should be okay to install inside in most cases (not all).

2) I've had advice from my club to suggest that being outside is better.

3) I already have a hole in the hull and the through-hull set-up worked well previously.

4) I have a Macwester, which has a thick GRP hull and therefore that brings me back to point one; given that this was fitted externally I reckon that there's a reasonable chance that the internal solution might not be optimal.

Many thanks for taking the time to suggest an internal installation, but given the above I'm not convinced that's the way ahead.
 
Rivonia: Thanks for your input. Yes ours came broadly similar to yours, but there's a bespoke Clipper Duet mounting kit for through the hull installation and I can see the benefit of having bolts hold on the mount, rather than having the weight of the mount held only by the transducer.

Ray Dunne: Good point. I don't have a battery drill, so that's another solid point in favour of drilling the holes in reverse from the inside rather than down in the mud.

Thank you both for your input

: )
 
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yodave said:
... in favour of dirlling the holes in reverse from the inside rather than down in the mud.
Click to expand...
You need to drill from the side where you need precise accuracy - outside if I unnderstand correctly. If you drill from the other side you won't succeed in drilling exactly straight no matter how hard you try, and the bolts won't fit. If you drill from the outside and the bolts go a wee bit squew-wiff it won't really matter. (Hope I correctly understood the task.)
 
I wouldn't be too eager to drill more holes in the hull. If you choose the correct grade of Sikaflex, it is an adhesive rather than a mastic so no weight would be carried by the transducer. It will however still act as a mastic to take up any mismatch between the profiles of the hull and fairing block.

Rob.
 
Amulet: yes... that's kind of what's at the back of my mind. Guess I was hoping that it was just a figment of my imagination and nothing to worry about.

Rob2: The mount moulding is hollow, so I'd be worried about trying to bond that to the hull along the relatively thin edges (I think the drag through the water would make short work of that). The alternative being to fill the hollow mount full of Sikaflex, and I'd imagine that the weight of that would then possibly be a strain on the transducer fitting.

I think that the mount has been manufactured with the bolts for a reason. Realistically it's probably either outside with the mount OR a complete rethink and inside without the mount ...and of course the possibility that internal solution doesn't do the job.

Thank to you both!
 
Heading off around noon today; any last minute advice or opinion would be useful to hear ...as I'll be offline and alone when making decisions and doing the job.

Thanks
 
Perhaps the most important thing - have a Disaster Recovery Plan! What will you do if you find that, for any reason, you are not able to get it all installed and watertight before the tide comes back in. Have some thick, flexible plastic and Sikaflex available plus the means to hold it against the hull over any holes that you have not been able to plug more permanently? Don't leave it till the water is lapping at your feet before you recognise that you are not going to complete the job before it is lapping around inside your bilges - get the holes plugged early while the hull is still dry and will take Sikaflex...
 
NASA thru hull mount

Some quick thoughts. I remember discussion a while ago about NASA thru hulls not liking some sealants and going brittle. I notice the mount comes with its own sealant - probably best to use that only or at least check with NASA if using another.

I'd try to drill from outside after digging a hole in the mud to make some access? Use a battery drill. If you must use a mains drill, make sure there's an RCD in the circuit and have someone nearby while you drill - it will be a bit dangerous and can't be recommended. It's worth buying the right tool sometimes just for one job.

Drill small pilot holes first to check everything is in the right place. A countersink used in the pilot hole helps to stop the gelcoat chipping off the outside.

Good luck!
 
maby: Good point well made. Thank you. I have wooden bungs ready and more than enough Sikaflex. I'll be doing the job when the tide is first going out and staying with the boat until she floats again later tonight.

garvellachs: Yep it comes with it's own sealant, so I'll be sure to use that thanks. Not sure that I have time to go buy a battery drill (and charge it) at this stage, but I may try to borrow one.

Pilot holes sounds like a very sensible option ...and I'll do that. Many thanks for your thoughts.

Thanks to everyone. Getting ready to leave now. I'll check back before I go, but probably won't have time to respond to any replies until tomorrow.

Thanks again!
 
You seem to be making a rod for your own back; can you not get the boat lifted, or at least move it to a drying grid or firm surface to do the work?
 
Boathook & penfold: Thanks for your sensible advice. In the end I went ahead with the situation as it was.

It took much longer than I thought, but she floated when the tide came in without any signs of water ingress.

I laid down a plastic sheet under the hull which kept most of the mud off. There was no room under the hull to get me and a drill properly aligned. I drilled the holes three times from the inside. First time around I drilled really small holes then I went underneath and checked for position. I repeated this (enlarging the holes I had just drilled) until I had the right size of hole in the right place.

One or two quick pointers for anyone else who might be doing this in the future:

  • Make sure that the mounting kit comes with all the parts. Mine was short of a nut, and a washer (plus another two washers that I felt appropriate) - which I had to source on the spot.

  • THE KIT DOES NOT COME WITH ALL THE PARTS THAT YOU NEED IF YOU'RE FITTING THE TRANSDUCER ON AN ANGLE. Be sure you have taken the instructions into account. They state that a piece of backing wood is best practice; the truth is that it's essential if you're fitting the transducer on an angle. I had a piece of wood cut to the angle from the previous installation, however it didn't extend far enough to reach the bolts at either side of the Nasa mounting kit. I wouldn't have slept last night if a friend hadn't dropped everything to make a longer piece of suitably angled backing teak for the bolts to tighten on to. Without that bespoke wood you have two bolts going through your hull tightened with washers at an angle (to the hull interior) and just some silicon as a barrier.

  • While you can do all the prep and assembly alone, you need two people when it comes time to add the sealant and tighten everything up; one under the hull and one inside.

Thanks to everyone who took the time to reply to my post.

: )
 
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