Saturday, July 28, 2007

Upper Rudder Bearing

Pics of the upper rudder bearing and housing.
The bearing is a Jefa self-aligning roller bearing, as spec'd by our engineer. The original plan provided to us had the bearing directly glassed to the hull above the port for the rudder stock. But, we modified that slightly...
Anticipating that there may be a need to replace the bearing in the future, we opted to instead build a bearing housing and have THAT glassed into the hull. The housing is a piece of G10/FR10 tubing (very dense/strong epoxy/glass tubing) with the inside turned to recieve the roller bearing. A matching "cap" made of the same stuff, with the outside turned, fits in the top to hold the bearing in place. The assembly is of the order...
  • glass lower assembly to hull
  • insert bearing
  • insert cap
  • glass cap to lower assembly
Should the bearing ever need replacement. Simply cut along the outer seam where the cap and lower assembly meet. Pull out the inner piece of the cap that was just cut. Remove the roller bearing.
Replacing the bearing will require a new cap as removing the original will require destroying it.

Friday, July 27, 2007

Final Battery Box Design

We have come to a final design for the battery box. It can accomodate up to six size 4D batteries or fourteen golf cart batteries. The overall height is about 15 inches which means it can handle the taller golf cart batteries (like the Trojan T-145).
Now T-145's weigh about 80 lbs each. In order to ensure the weight will be supported, extra and beefier crossmembers, between the lower tank and the box, will be installed. The box itself will be thru-bolted to the framing supports all around it. Cleats attached inside the box will keep the batteries from sliding, and there will be five hold downs bolted across the top. Attaching different size blocks as "shims" will hold down the different height batteries. The inside of the box will be glassed with reinforcement in the corners.
Cutting down the center tank to make room for this box reduces the tank to 37 gallons. With the wing tanks at 69 gallons each, that still leaves a total of 176 gallons for fresh water. With a water maker on board, I think this should be ok. Heck, we seem to get by with 20-30 gallons on the small boat.

Monday, July 16, 2007

Aquadrive/Final Drive is IN!

...with the mounts compressed to recommended tightness. I had to remove a couple shims and flatten the back of the stern tube a bit (with a file) to get things precisely aligned. But the shaft now free-spins on it's cutless bearing, indicating minimal resistance, a good indicator of proper alignment. The mounting plate was painted with bilgekote and the thrust bearing and shaft coupler were painted with a more durable engine paint (Volvo green, they gotta look nice ya know!).
This area wont be touched again until engine and prop selection has been made. Whereupon the final items are
  • new prop shaft machined
  • Aquadrive extension shaft (custom length with CV joints)
  • goop up the stern tube with sealant and install permanently
  • install shaft seal
  • install propeller
Most will be done just before splash-down.
For all pictures of this installation, click here.

Saturday, July 14, 2007

More Heavy Metal

Recall that the Westsail did not come with a rudder and we had a new one designed. Well the first parts are in. The large center plate and seven "cross section" webs were cut this week. They were cut by local waterjet cutter JetPoint Technologies. Waterjet cutting uses a sharp stream of high pressure water with dissolved abrasives to get a clean precise cut. Simply cutting these pieces by a torch would not be possible as there is a 1/4" slot in the 5/8" thick webs that must be close tolerance to fit over the center plate. The waterjet process is driven by CAD files for each piece cut. The CAD files were created by copying objects directly off of the rudder designe CAD drawing (plus a little cleanup). A couple more stainless parts to be machined and things will be ready for welding.

Wednesday, July 11, 2007

Dry-fitting the Aquadrive

Completed the dry-fit of the Aquadrive thrust bearing. Why do this now? Well, access. Everything is open in the stern. As things get built up back there access will be more difficult. Reminder that the Aquadrive is a device which separates the thrust of the propeller from the engine. A typical straight shaft installation pushes on the engine to move the boat forward. With an Aquadrive the thrust is transferred directly to the hull. The primary advantages are:
  • less noise. Since the engine is not bearing the thrust, softer engine mounts can be used, dampening noise and vibration.
  • alignment is less critical. With a straight shaft installation, the 300lb+ engine needs to be precisely aligned with the prop shaft otherwise premature failure of the cutless bearing (in the stern tube, supporting the shaft) may result. The Aquadrive uses CV joints between the thrust bearing and the engine. The CV joints are flexible and can allow up to an 8 degree deviation between engine and the thrust bearing.
However, the alignment of the thrust bearing with the final drive is critical for the same reasons mentioned above. Compared to a retrofit of a finished boat, things are easier here as nothing is yet permanent and everything in the driveline can be tweaked if necessary.
There were a few gotchas of course.
The instructions suggest installing the bearing to a 3/4" plate. This could be made of plywood, steel, etc. But it is emphasized that it be strong and the attachment to the hull should be very robust as it will be bearing the thrust of the prop.
Well, I anticipated an aquadrive during the design of the aft floors and planned to use one of the floor supports as the plate for the bearing.
To beef it up, I made it about two inches thick (two 3/4" pieces laminated with glass in between).
Turns out this extra thickness made it impossible to get the bearing in there with the rubber bushings and necesary shims to get the right angle.
In the end I had to route out 3/4" in the forward side to provide the necessary wiggle room(see picture).
In the end the shaft and coupling match the thrust bearing spot-on.
As it is still even a pain to get in there I may simply make the install permanent.
This simply means rounding over some sharp edges, smoothing out some surfaces and applying
a little paint.
Then I will wrap it up in plastic in place until we get to the engine installation (a ways away yet).
More later...

Tuesday, July 10, 2007

Update on Mechanicals...

Here is a quick update on latest mechanical designs. Placement of most of the major components is done. That is, it has been determined that there should be enough space. Referring to the 3D model...

  • orange - sanitation. Both heads will have their own holding tank (20-30 gal each), vacuum generator (for vacu-flush system) and thru-hull discharge. There is even room for a lectra-san (on board sewage treatment) for each head if we so desire (undecided right now).
  • purple - Propane cylinders, dive cylinders, dive compressor and A/C. That is a small 7000 btu A/C unit. Not shown in the model is a 16,000 btu unit under the fore dinette settee, serving the main and forward salon. Again, the dive and a/c stuff are optional. We are making room for it should we decide.
  • olive - diesel tanks
  • dark green - batteries, room for 14 tall golf cart batteries or six 4D batteries.
  • dark blue - water tanks, not shown is another water tank under the batteries

Still working on the plumbing runs a bit.

Saturday, July 07, 2007

Aligning and Centering the Final Drive

The design of the final driveline calls for a 4 degree downangle for the propshaft. This is closer to "horizontal" than would be if the stern tube was mounted flush against hull surface as it came from the factory (it would be about 8-10 degrees is my guess). It is desireable to have the shaft closer to horizontal as possible, getting the most forward thrust. But, this is a Westsail and it has a canoe stern, which have a tendency to "squat" under power.
Using laser tools, it was fairly easy setting up the marks to align and center the shaft. The goal is to mark a target on the inside support where the propshaft will intersect, at the 4 degree downangle. It must be lined up and "shoot" through the shaft opening. The opening was cut at the factory and is a little offset to starboard. I dont know if that was intentional or not. It could be to allow shaft removal easier (with rudder installed). Modern fin keel performance boats have propshafts significantly off center for this very purpose. Anyway, the slight offset shouldnt affect handling when under power.