29 August 2016 | on-the-hard, Wrangell
photo is Portage Bay, north of Petersburg
Hello boys and girls, it seems I have not posted here since completing the run south last November. Lots has happened since then, the short version being:
-lots of winter boat work
-winter holidays with family and friends in Sonoma County
-World Rugby Sevens in Las Vegas, Vancouver BC and Hong Kong
-visits with friends in Hong Kong, China and Macau
-more boat work
-cruising BC > SE Alaska since mid June
And now, here we are on the hard again in Wrangell. Warning, for those who are tech-phobes, the remainder of this post will be full of boat mechanic jargon. Along with this blog, I have posted photos of the work on my Facebook page: DavidEllis Nagle Boat.
Last winter two of our Diesel Duck sister ships, both newer and with less miles/hours than DE, replaced their propeller shafts due to anaerobic corrosion (meaning the stainless steel drive shaft, between gearbox/transmission and propeller, which lives inside the shaft log -- a seawater-filled tube between the engine room and the aft end of the boat where the propeller shaft emerges -- has not gotten enough oxygen).
We have disassembled portions of DE's drive line previously, but have not examined the whole shaft since taking possession 10 years ago. So we scheduled a lift out at Wrangell before heading south, back to Seattle. It took four people -- Dorothy, me, our frequent crew Wade and GGB "Stitches" significant other Eric, working all day (and a fifth, local welder / mechanic Ray, for a few hours) to remove the shaft. In order to get to the shaft, we first had to deconstruct significant portions of the engine room, drive line and steering locker.
Having removed the shaft, a cursory examination showed the beginnings of anaerobic corrosion; not to the degree seen in the photos from our sister-ship and we could've gotten another year or so out of it, but with the effort required to remove the shaft, it just didn't make sense to me to re-install it and do it all again next year. We're here on the hard; the shaft is out; let's deal with it. So discussions began about what to do, leading to: noting that the taper of the tail end of the shaft is not a US standard, meaning if we were to damage the prop sufficiently to need to replace it, we could not get a replacement prop with the proper taper, without providing the shaft also to whomever was going to do the work. Not real convenient if one does their cruising in say, Alaska.
After determining that the new shaft should be a proper US standard taper, it became necessary to determine if the prop hub can be re-bored to accommodate the change in taper. In the course of doing this, and checking the prop size v. shaft size tables, it appears our shaft size 1-3/4" is undersized for our 30" diameter prop, which leads to the question, what now? I am aware that several boats after DE, the builder up sized the shafts, so maybe further indication that DE's is undersize. At the same time we have 10 years of trouble-free operation as far as the drive-line is concerned, including a Pacific crossing, a greater than 90deg knockdown in the Aleutians, and several periods of significant, high RPM operation in rough water.
One possible option is the possibility, since we are replacing the shaft, to upgrade to a larger shaft, IF there exists a cutlass bearing that will accommodate a larger prop shaft within the existing shaft log. The cutlass bearing is a tube which bears the weight of the shaft/prop as the shaft exits the shaft log at the back of the keel, in front of the rudder. It turns out there is. Our current cutlass 1-3/4 ID X 2-5/8 OD can be replaced by a 2" ID X 2-5/8 OD. Great!
This leads to another consideration: at the engine end of our existing prop shaft, we have a thrust bearing and jack shaft behind the gear box / reduction gear / transmission. Connecting these to the new 2" shaft will require turning down the forward end of the new shaft in 2 steps, both greater than a 1/4" off the end of the shaft to accommodate the thrust bearing sleeve and the jack shaft universal yoke. I'm told the meatier shaft is more significant at the prop end than the gearbox end, but still it seems counter-intuitive to get a bigger/stronger shaft only to reduce the size of it. Could we get a new, larger t-bearing and J-shaft? I suppose so, but there's another option. Last winter our sister-ship Shearwater had significant work done including eliminating the t-bearing and J-shaft, replacing them with a straight shaft to the gearbox, a design found in most workboats in this area. The t-bearing, J-shaft and soft engine mounts design is frequently used by high end yachts to eliminate noise and vibration. But, they also introduce greater complexity and need for maintenance. What to do? After conversations and correspondence with knowledgeable people here, David C on Shearwater, and the shop in Pt Townsend who did David's work, I've decided to go with the new, heavier shaft -- 2" Aquamet 22 -- all the way to the gearbox, without the t-bearing and J-shaft. I am hanging onto the parts though. After all this is put back together, we'll do the 1000 mile run back down to Seattle, a good test/break-in for the new stuff and if it's not working out we can re-install the old gear, after some lathe work on the end of the new shaft.
And yes, the prop now needs to be re-bored to accommodate the new 2" standard shaft taper. So we built a shipping box up off a small pallet, and flew the prop down to Seattle where a prop shop will do the work and also tune the blades. There has always been a bit of "singing" going on from one blade at certain rpms, but recently that's grown to a whole chorus, which is not quite in harmony.
And now that all that is in motion, the next step was to replace with new, the inserts in the 'soft' engine mounts, which are 10 years old and can be seen to be flattened and cracked. I did check on the mount manufacturers website to determine that what we have is intended to handle our engine/gearbox with a straight-thru prop shaft pushing on the gearbox and the tables, North American distributor and Australian manufacturer all agreed that the mounts we currently have are properly specced for the engine without the need for a t-bearing. Great!
Changing out the inserts was a 2-day job. We removed the hatch over the engine which is the wheelhouse floor (this has not been out since we took delivery of the boat 10 years ago); placed a steel beam longitudinally across the hole and using a chain hoist lifted first one end of the engine, then the other, removing and rebuilding one mount at a time. 3 of the 4 original inserts were not only flattened but also really torn up / shredded. I wonder if the knockdown we had in '09 in the Aleutians, might be responsible, since the engine would've been hanging there in space. Anyway, despite a bit of learning curve, the core replacement of the mounts went well with lots of help from Wade and Dorothy.
And now, it's very late Sunday night. The barge from Seattle which should have our new shaft is in and the forklifts are running around the boatyard making it next to impossible to sleep. We'll work at installing the new shaft the next couple days and hope we can get the prop back as soon as possible. Everything has to be put back together to the point we can put DE back in the water and run the engine in order to be able to align the new shaft. If all goes well, and so far it has, we should be underway in another week.