Wednesday, March 14, 2012

Day 1–Naiad service

I guess its actually Day 2 but it was the first working day. 

Naiad service -5

Gray Hawk has active fin stabilizers made by Naiad.  Apparently they also make parts for Sikorski so that’s pretty good company to be keeping.  I took the photo below for future reference so we can remember where to align the lift straps for the Travelift.  The portside fin is clearly visible between the straps.  The fins are controlled by a gyro in the engine room and hydraulic actuators on the shafts that the fins fit on.  Whenever we roll the gyro sends hydraulic fluid to lower the fin on the low side and raise the fin on the high side.  It does that fast enough to damp out most of the roll as long as we are moving – obviously it can’t work without water flowing across the fins.  Its actually quite noticeable on a rough day when we flip the switch to turn on the fins – its kind of like God reached down and grabbed hold of the flybridge.  We usually take one mighty lurch in the wrong direction and then settle in more or less stable.  Unless it’s a really really really bad day like the one when we came over from Victoria.

Haulout day one -18

Naiad recommends that the seals on the fins be serviced every three years or 4000 hours, whichever comes first.  You’d have to be a serious cruiser to get to the 4000 hour interval in less than 3 years but the tech today claimed he had seen it once.  In that case he said when the guy bought his boat he didn’t bother arranging moorage because he never planned to spend that long in one place.  And with a path that had taken him through both Panama and the Northwest Passage in the same year it sounded like he had lived up to his plans.

Naiad service -3

The photo above is after the first fin came off.  The shaft is tapered stainless steel which fits into a tapered socket in the fin.  To remove it they have a hydraulic pump that attaches to the socket on the fin and pressurizes the chamber between the shaft and socket.  The tech said they usually come off at 10,000 PSI but in extreme cases he has taken them to 35,000 and then gone for coffee.  In those cases he says he usually gets a call from the yard saying that they just heard a really loud noise and when he gets back the fin is loose.  They have to be really tight because the only thing holding the fin aligned to the shaft is friction between the tapered shaft and socket.

Naiad service -22

In the photo above they are fitting the 2nd fin back on its shaft.  Its really a very simple process – if you have the right tools.  Without them I can easily see how it could turn into a multi-day ordeal.  There’s two plastic seals fit over the shaft and that is all that we had to replace.  As long as they are doing their job and keeping the water out of the bearings there’s really not much wear on the system.  Its not like the fins move that far or that fast. 

This service day was one of those that can either take a few hours or a few weeks.  As long as everything is in good shape it’s a simple matter of changing a couple of seals and putting it all back together.  On the other hand if the seal has failed and the shaft is compromised then the cost goes up more or less as the square of the time required to do the repair.

While the Naiad guy was doing his thing I was busy filling in a hole.  Generally speaking holes in boats are bad things but nevertheless holes tend to accumulate on older boats.  Over the years various owners make changes, add new gadgets, stop using old ones.  Sometimes those new gadgets involve making new holes in the hull for transducers or speed sensors or other paraphernalia.  I had one hole identified that was no longer needed so I thought while we were out of the water was a good time to fill it in.  That kept me busy today but I got it done before the paint crew was ready to cover it over. 

I was worried about it being too cold for the epoxy to kick so I used fast hardener and a heat lamp.  That worked well – maybe a little too well – my plug got hot enough to melt the plastic I used for a barrier on the outside and it gassed off pretty severely inside the boat leaving the inside surface kind of porous.  But now where there used to be a 2” hole in the hull there is a 2” epoxy plug about 1-1/2” deep.  So even if its not perfect epoxy it should be up to the task of keeping the sea on the outside.


Bob and Vivian said...

Bob, You may be interested in the referenced blog entry from "Starr" about servicing his own stabilisers

Love your blog


Jorgito's dad said...

Excellent link - thank you for that one. Dick McGrew who is referenced in that post is the tech who was here doing my stabilizers. As I said in my original posting, the work is not technically difficult, certainly easier than something like an inframe bearing roll. Nevertheless I would never tackle doing it myself because of the infrequency of the project and the need for a few specialized tools. If I were to do my own work I might do it 3 times in total in my life - Dick probably does 3 or more per week. He also has access to exactly the right parts. In our case whoever last did our seals used the wrong seals. That doesn't appear to have compromised our bearings but in the case of your link the wrong seals likely cost the owner in excess of $2000 when he had to replace the bearings. If his shafts had been damaged it would have been much worse.