Nasa Log impellor hole

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emearg

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Hi all,

I have a wee problem with my sadler 32. I noted that my log tube had a wee leak so when I lifted out I would investigate it. ……………..went into the locker and removed the big plastic nut from the log tube, yes it should be epoxied in…it wasn’t!!!!!!!!!!! Next I thought I would remove the tube housing, expecting myself to ruin it when I removed it, imagine the shock when it just falls out and even worse it was held in with ordinary house hold silicon…and worse again the diameter of the log tube is approx 40.5 mm and the hole in the boat was 50.5mm in diameter…….and even worse again the big plastic nut only had a diameter of 51mm…how I never sunk my boat I will never know. But anyway…..


The questions I have to ask are.

1. Why was the hole in the hull so big…was there any old log in there which had a different diameter or was it just cowboyed.
2. If I am now going to fix it, is it best just to re epoxy the hole and redrill the correct size or would sicaflex fix it……think the best way would be to epoxy it and re drill.
3. If I am going to epoxy it then I have a counter bored the hole from the inside so that the epoxy bung will not fall through the hull, should I then do the same for outside the hull so the epoxy “bung” will not fall out into the boat. How do I make sure it is properly “keyed” into the hull……..a 50mm hole lets in a lot of water.

Opinions and answers welcome.

Graeme.
 
Have a look at West's guide to glass fibreing. Basically the hole needs to be chamfered on both sides then several layers of glass mat built up. Redrill and refit log tube. You've been lucky, I think.
 
The NASA log is smaller than the majority of other log transducers. I expect the previous owner found out during fitting the NASA replacement. Bit of extra work over the winter for you!:o
 
emearg said:
and the hole in the boat was 50.5mm in diameter……
Click to expand...

This sounds as if it could be the NAVICO DL150 log fitting, which would probably be around the correct era for a S32. I fitted one to my S29 in 1984 and was faced with the same dilemma when I wanted to change to a NASA with much smaller thru-hull.

I decided that the best way would be to leave the original thru-hull in place; grind off the outer flange and excess inner. The new thru-hull was a decent fit inside the old one.
Unfortunately you don't have this option as the old thru-hull has been removed.

(In fact I abandoned the idea because the the NASA fitting is too short for the S29 hull thickness without serious surgery, and anyway I have given up on paddle-wheel logs and am quite happy with GPS SOG. I just fitted the blanking plug and left it at that).
 
You should laminate the hole shut with epoxy and glass an then make a hole the right size for your log through hull.Bear in mind that silicone sealant is what Nasa recommends for their plastic through hulls because polysulphides and polyurethanes can attack the plastic.The way to epoxy the fitting is to laminate around it and over the nut with resin and glass.
 
seem to think I've read other info regarding this fix and one thought was to fit a brass through hull fitting-think ply / epoxy layers were recommended-I am thinking what to do on our own s29 which has the old log fitting etc -unusual diameter to replace-at present we use a stowe trailing log and just fit the old paddle annually even though it don't work !!! -
 
30boat said:
.Bear in mind that silicone sealant is what Nasa recommends for their plastic through hulls because polysulphides and polyurethanes can attack the plastic.The way to epoxy the fitting is to laminate around it and over the nut with resin and glass.
Click to expand...

Early Nasa through-hulls were notorious for the outer flange breaking off. From a visual inspection of mine - which I never fitted - there seems to me to be an obvious weakness in the design. The suggestion that only silicone sealant should be used is pathetic.....silicone is the ONE sealant I would NOT use under water. Perhaps their choice of material could have been different?

As for 'glassing in the fitting over the nut' ...... do you do this for any of your other skin-fittings?
 
VicMallows said:
Early Nasa through-hulls were notorious for the outer flange breaking off. From a visual inspection of mine - which I never fitted - there seems to me to be an obvious weakness in the design. The suggestion that only silicone sealant should be used is pathetic.....silicone is the ONE sealant I would NOT use under water. Perhaps their choice of material could have been different?

As for 'glassing in the fitting over the nut' ...... do you do this for any of your other skin-fittings?
Click to expand...

My Nasa log fitting did just that. Came away in my hand as I removed the transducer for cleaning, very little pressure.
It does concentrate the mind to see daylight through the bottom of your boat. Considering the response from Nasa when ordering a new tube, it wasn't an unusual occurrence.
They do tell you to glass the tube in but few people do. I did ,after that but am going to infill the hole and manage without a log. Seldom worked properly anyway.
 
VicMallows said:
Early Nasa through-hulls were notorious for the outer flange breaking off. From a visual inspection of mine - which I never fitted - there seems to me to be an obvious weakness in the design. The suggestion that only silicone sealant should be used is pathetic.....silicone is the ONE sealant I would NOT use under water. Perhaps their choice of material could have been different?

As for 'glassing in the fitting over the nut' ...... do you do this for any of your other skin-fittings?
Click to expand...

I've used silicone on my Nasa through hull and in 11 years no leaks.
I only glass over Nasa skin fittings.It strenghtens the fitting making up for any shortcomings in design.All my other skin fittings are metal.
 
The best fix is to completely fill the hole again with epoxy and fibreglass cloth. Chamfer the outer and inner edges and ensure that the cloth laid from outside is in good contact with the cloth layers from inside. Build it up to a thickness similar to the original hull. Then if you really want to drill a correct sized hole either in the plug or in the hull at a suitable spot. But I am with the others leave it out and use GPS. good luck olewill
 
seascape1 said:
seem to think I've read other info regarding this fix and one thought was to fit a brass through hull fitting-think ply / epoxy layers were recommended-I am thinking what to do on our own s29 which has the old log fitting etc -unusual diameter to replace-at present we use a stowe trailing log and just fit the old paddle annually even though it don't work !!! -
Click to expand...

A bronze, DZR or plastic one might work. A plain brass one - and there are plenty sold in chandleries - would be more likely to sink your boat than the the bodge the OP found!
 
Thank you for all your replies.

Think the best way for me would be too counter sink both sides of the hole (nearly 2" think at this point of the hull) and fill with cloth and epoxy then redrill for new fitting. Though I do like the idea of just filling in the hole and just use the gps speed, then its one less hole to worry about letting in water....believe some people glass up every hole in their boat.....be nice and reassuring that you are not going to sink because of a failed seacock.

Graeme.
 
emearg said:
Thank you for all your replies.

Think the best way for me would be too counter sink both sides of the hole (nearly 2" think at this point of the hull) and fill with cloth and epoxy then redrill for new fitting. Though I do like the idea of just filling in the hole and just use the gps speed, then its one less hole to worry about letting in water....believe some people glass up every hole in their boat.....be nice and reassuring that you are not going to sink because of a failed seacock.

Graeme.
Click to expand...

The disadvantage of GPS SOG is that it's slow to respond, so it's harder to see the effect of sail trim changes. If you lie awake at night worrying about through hull failure, you'd better do a Dylan and get rid of the inboard engine - and the toilet!
 
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