Life of a NASA log hull fitting?

[catalac08]

Fitted by me ten years ago and at the time I thought it a bit flimsy so glassed in the inner side as per the NASA recommendation then. It usually clogs up with barnacles and I do not really use it so in time I will remove it and glass over the hole. I want to do this next winter when I have the boat out so my question is whether there is any history of these plastic fittings degrading and just failing?

 

[William_H]

I have not heard of any body failure of any paddle wheels. Certainly the wheel itself fails through loss of magnets or loss of magnetism and the wheels are to me hopeless at fouling up with weed etc. So yes do as I did a long time ago and glass over the hole. GPS is the way to go for speed and lots more. good luck olewill

 

[Bodach na mara]

I have not heard of any body failure of any paddle wheels. Certainly the wheel itself fails through loss of magnets or loss of magnetism and the wheels are to me hopeless at fouling up with weed etc. So yes do as I did a long time ago and glass over the hole. GPS is the way to go for speed and lots more. good luck olewill

While GPS is great st giving actual speed (over ground) I like to also have a reading of speed through the water. This is important in areas with tidal flows as it can be possible to get into favourable flow by going a bit off the direct line. Without the two bits of information, you cannot tell what the tide is doing. Regarding the degradation of NASA plastic log mountings, I can only say that mine was fitted about 15 years ago and is still OK. I have renewed the rotor about 5 times and the whole sensor unit last year but the mounting tube has given no problems. Yet!

 

[Corribee Boy]

When I launched last season, I promptly, and accidentally, parked the boat on a sandbank.

I used the time waiting for the tide to go and return, by checking all the fittings for leakage and was surprised to see there'd been a minor seep around the log tube. I thought I'd just see if there was any movement on the back nut and turned it by hand - cue sudden cracking noise and I was holding the tube and log unit, and admiring the (now returning) river Exe through a significant hole in my hull.

The pipe had sheered under the relatively small amount of torsion I'd been applying. I don't know how old it was, or if the plastic had been affected by the sealant that had been applied, but I can assure your they do fail!

I can also tell you the hole was significantly larger than the biggest bung I had!

 

[Stemar]

From memory, the fitting instructions do warn not to use antifouling on the plastic as it can degrade it.

If you're out of the water, I'd be inclined to give it a not too firm thump with a soft hammer/heavy stick and see what happens. If you aren't looking at the concrete under the boat, it's probably OK for a few more years!

 

[alahol2]

From memory, the fitting instructions do warn not to use antifouling on the plastic as it can degrade it.

I think in the early days they had some problem with certain sealants that degraded the plastic. The manual still states to avoid 'mastic' compounds and recommends silicon sealant. The antifouling warning relates to the echo sounder transponder and refers to a possible degradation in performance rather than damage to materials.

 

[chewi]

In a small club of max 100 cruisers I know of at least two plastic Nasa log transducers that snapped at the hull line.
Mine was afloat at the time, so I was fortunate to be able to stem the flow and run her aground in time, the other thankfully snapped in the yard.
Both appeared brittle on inspection after their demise.


It was never reliable enough to be worth that sort of risk to seaworthiness, so the hole is now plugged and I use GPS speed.

 

[Dipper]

We had a NASA log skin fitting on a boat in our club that had snapped. Luckily it was discovered whilst the boat was being launched and still in the strops.

Mine is heavily glassed in.

 

[Corribee Boy]

Glassing in wouldn't have stopped the problem: with the tube snapped at the level of the back nut there wasn't anything left to put the blanking cap on. I ended up wiring the impellor in place and relying on the 'O' ring to seal for the rapid motor to park the boat on a beach and fix it.

 

[Dipper]

My nut and halfway up the tube is glassed in.

 

[alahol2]

My nut and halfway up the tube is glassed in.

Ditto. 10+years and counting.

 

[catalac08]

Thanks for replies.
Mmmm... 4 known failures from about a dozen responses. It does look as if there is a "brittleness" possible with these transducer housings. When I fitted mine I was pretty skint having just bought the boat and only realized how flimsy it was AFTER I had bought it. Mine is well glassed in so should be alright for a while but definitely to come out next winter.