Making holes in hull

[Colvic Watson]

This is really scary, I've got a NASA Duet depth/log to fit. The transducer is pretty small diameter but the log is about 4.5cm across - what the hell do I make the hole with, where do I put it (triple keel) and how do I prevent the GRP cracking? There was a sea toilet in the forecabin (Halcyon 23) which has just got the sea cocks left - what about taking them off and using those holes?

As always, any help is very much appreciated.


<hr width=100% size=1>Are we nearly there yet?<P ID="edit"><FONT SIZE=-1>Edited by pasta_simon on 06/12/2004 12:39 (server time).</FONT></P>

 

[snowleopard]

to cut holes up to around 60mm diameter, a good quality hole saw and a big drill on low speed is the thing to use. the toy hole saws where all the blades fit into a cast metal disc are quite useless so if you don't have or want to buy a set, hire it. a good technique to get a clean edge is to cut about half way through from one side then start agin from the other side using the pilot hole to line up the drill. if you have to do it in one direction only, start from the outside as the damage is caused on breaking through at the end of the cut.

i doubt the seacock hole will serve as it's unlikely to be in the right place. the depth transducer must point pretty well straight down and not too close to a keel so the keel doesn't obscure the 'view' of the bottom when heeled. the log should be low down and in front of the keels so the water flow isn't disturbed before reaching it.

<hr width=100% size=1>

 

[john_morris_uk]

What Snowleopard says is exactly right, but if by some chance one or more of the old sea toilet holes are in the correct place but they are too small, then carve a wooden bung to fit the hole and drill your pilot hole for your hole saw in that.

To cut neat holes in GRP you do need a good quality hole saw.

<hr width=100% size=1>

 

[cpedw]

I don't deny snowleopard's observations but I can write as a registered cheapskate who has successfully cut holes in hulls using one of those "toy" hole saws.
It goes like this: Start the hole, ideally from both sides if possible, using the hole saw. Go to about 5mm depth. Go slowly as that's a severe load to put on the drill. The hole saw also will get very hot if you overload it. If you try to go right through with the "toy" you will be disappointed by the blunting of the blade.
Having made a clear impression of the hole's outline, next drill a series of small holes (say 2-3mm) right through around the pattern of the outline, checking these are square to the line of the intended finished hole. Then the hole saw can be brought back into play to remove the small amount of material remaining without getting it too hot or blunt on the way.
It may not be professional but I have found it to work quite neatly and cheaply. Some patience is required drilling all the small holes and not breaking the drill.
If you can afford it, take the purists' route...
Derek

<hr width=100% size=1>

 

[salamicollie]

You'll find it difficult to get the 42mm hole saw for the NASA skin fitting - usually you can 40 and 45mm - if you go the cheapskate way you can use a jubilee clip to squeeze down the size...

BTW why not mount the depth transducer internally if you have a solid GRP hull - one less hole.

Also do use Silicone not PU sealant and only screw the retaining nut on the log skin fitting down hand tight - to much force or the wrong sealant cabn cause the outer flange to fall off, which is why the instructions tell you to glass the fitting in as fail safe!

<hr width=100% size=1>

 

[snowleopard]

try <A target="_blank" HREF=http://www.screwfix.com/app/sfd/cat/cat.jsp?cId=100220&ts=49480>here</A>

<hr width=100% size=1>

 

[masterofnone]

Seconded, vis a vis, internal mounting of depth transducer, mine is and works ok.
Make sure you can get to the paddle wheel log as you will need to de-barnacle it constantly. Do not reduce cable lengths!

<hr width=100% size=1>

 

[macd]

Does the exhortation not to reduce cable lengths concern the practicalities of removing paddle wheels for servicing, or their electrical integrity? Reason I ask is that I spoke to a tech man at NASA just last week, who said it was OK to cut and reconnect and change the length if log cables.

<hr width=100% size=1>

 

[Colvic Watson]

Thanks for all the help!

<hr width=100% size=1>Are we nearly there yet?

 

[SlowlyButSurely]

As a further alternative cheapskate method for when you haven't got the right size holesaw and you have to get the job done on a Sunday evening when all the tool shops are closed, you can do an acceptable job by cutting the hole with a jigsaw using a hacksaw blade. Drill a small hole to get it started and cut the hole slightly undersize and finish it using a sheet of sandpaper wrapped round a can of WD40 or whatever comes to hand that's roughly the right size.

<hr width=100% size=1>

 

[gjeffery]

I drilled to 40 mm then open out using carborundum paper wound on a large wood dowel. The NASA log transducer fitting must be set in Silicone (ie not Sikaflex unfortunately), so you may think it a good idea to go make the hole slightly oversize, and seal the GRP with a wipe of epoxy resin, before fitting the log fitting.

<hr width=100% size=1>

 

[roger]

shortening cables and mountings

There are several reasons for leaving the cable alone
1. Not everybody can join coax cable to a plug and I've seen innumerable horrible bodges.
2. Coax screen wicks seawater beautifully - you can get metres of cable screen going black and useless. So do not make joints. You may have to make bigger holes to get the cable through but you are likely to get a much more relaible job.
3. Depth sounder cables are tuned and should be left severely alone or your sounder performance may suffer.
Not very relevant but I found a big Blakes seacock fitted nicely the through hull fitting for a Silva depth sounder. It might well work.
On my old boat with a NASA cheapie sounder and the sounder inside the hull in a tube full of castor oil I could get readings down to about 30 metres if the bottom wasnt soft.
Now with the Silve through hull I can get 180 metres in some places. The inside hull mounting will reduce performance.

<hr width=100% size=1>Roger