Thursday, July 31, 2008

Steering Plan B: More Details

A reader asked for a side view of the cable steering setup (thanks for the request, it sorta forces me to think through things a bit more thoroughly). This view shows the conduit idlers and the conduit cable and how it leads up to the rudder post from under the floors. Generally, the minimum number of idlers, the smoother and more accurate the steering will be. The current design has four. The original factory had twelve. The cable-in-conduit provides this reduction as it can take up slight curves and bends (otherwise it would need to be straight line between idlers). What is not clear is how much the cable in conduit can curve. The drawing here does not really reflect the amount of space underneath the floors. There is more space than the drawing suggests. I could have the conduit snake down to the bottom of the bilge and curve up to the rudder post if needed. This is a situation where the dryfit will tell if this is ok. If I do need to add more idlers, it would likely be where the conduit comes "up" from underneath the floor, just above the prop aperture. Also, the idlers that tail out to the quadrant will need to be angled and shimmed to correctly align the grooves of the idler and quadrant to prevent any chafing of the wire from the sidewalls. Here are PDF versions of the cable steering design that may show more detail. Cable Steering Side View Cable Steering Top View
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Tuesday, July 29, 2008

Steering Plan B: Cable Steering

Here is a quick sketch of how pull-pull cable steering would look from the top. It has a total of four idlers and sheaves. Compare this to 12 idlers/sheaves that came with the original factory steering. This can be done in that the cable runs through a stiff conduit which can withstand gradual rises and bends. There will still be cable/conduit criss-crossing the engine room, but at least the cable will be protected by the conduit and have some flexibility. The conduits will have automatic "greasers" to keep the cable-in-conduit lubricated. So far, the costs of this setup is just over half on the estimate for the Jefa transmission steering. It may be less still as we await final pricing.
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Monday, July 28, 2008

Compromise Is Inevitable

As much as we would like to trick this boat out with the coolest/nicest gear, sometimes you gotta compromise. This steering design may be the first big compromise. I have been planning and working on a design for transmission steering for over a year now. Well, I finally got the details nailed down and there are two reasons now why we may not go with it and switch to traditional cable steering: 1) slight technical problem 2) price 1) The technical problem is taking up the 18 degree rake in the rudder post. While I am sure we could futz with the installation and get it to work ok, I have not been able to confidently establish the proper geometry to ensure a smooth steering action. 2) The price. This is the big one. When I started specing out parts for this transmission steering over a year ago, the price was more reasonable. These parts come from Denmark, and the US dollar has grown weaker against the Euro since then. While the setup was a bit expensive a year ago, it is even more expensive now. Enough so that I am seriously entertaining "Plan B" (cable steering). At the very least it merits getting a cable system priced out. Turns out one of our suppliers distributes a cable steering manufacturer. Note sure what kind of pricing we can get yet. So, I need to look into cable steering some more. I will be looking at the "cable in conduit" systems, not the tradition straight "cable with idlers" systems.

Thursday, July 17, 2008

Steering Linkage: Final Details

This is what the final steering linkage design is looking like. Though I am still in talks with the Jefa component distributor to verify that this is doable (and that I am not making some really obvious blunder).

In the final details are things like wheel size, wheel rotation lock-to-lock and total rudder travel. Doing some research and talking to a designer it appears that the following are "typical" on a cruising boat of this size:

  • 36 inches wheel diameter
  • 2.5 wheel rotations lock-to-lock
  • 72 degree rudder travel lock-to-lock

Getting data from other boat owners varies.

  • One W42 with 5 rotations l-to-l
  • Another W42 with 2.5 rotations
  • A Catalina 42 with 1.75 rotations l-to-l (which I did get some helm time on, very strange coming from a tiller)

The steering linkage, as currently designed, gives 2.5 rotations l-to-l. This seems like a good place to start. If more reduction is needed, the bevel linkage gears could be easily swapped out for reducing linkage gears to give 3.2 rotations or 3.8 rotations if one or both gears are changed.

Any readers out there have more data/opinions/suggestions?

What is your setup?

Would you change anything?

Please post a comment!

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Thursday, July 10, 2008

The Rudder Is In!

Yes! Can you frickin' believe it? Just a little over a year it has taken, from the engineering to the final lamination. I think this just might be the most complex part of the whole boat construction. Simply because it involved a sequence of steps involving three third parties. Getting things coordinated and timed was somewhat frustrating. Yeah, it could have been built faster, but there were sidetracks (like the small boat last fall). Thinking about remaining tasks simply involve getting the parts, perhaps modifying, and putting them together. The rudder involved sourcing material, water jet cutting, shaft machining, welding, foam shaping, and lamination.

Anyway, I will let the pictures speak for themselves. Thanks to my wife and my dad for assistance!

Wednesday, July 09, 2008

The Marelon vs Bronze Thruhull Debate

Search the Internet on this topic, and you will find all sorts of arguments.

For those not in the know...

Traditionally, ocean going boats have used bronze for their underwater metal fittings: thru hulls and seacocks. There are a couple downsides to bronze underwater fittings. First is price. Cost of the metals (especially copper) has gone up over the years. Second, is controlling corrosion. The saltwater ocean is basically a big tub of electrolyte. Insert two pieces of metal close to one another and you essentially have a weak battery (anode and cathode). Small currents will flow between them causing the metal to corrode over time. That may not be EXACTLY how it happens, but that is the general idea. The last thing you want is the metals to be slowly eaten away as that is a good way to sink the boat when the fitting ultimately fails. This is why boats are fitted with "bonding systems" that introduce a sacrificial zinc. The bronze will not corrode until the zinc has corroded away.

Enter Marelon. Been around for about ten years. ABYC certified and approved for underwater use. Basically, a composite of special resin and glass. Advantages: no metal therefore wont corrode, cheaper materials, and lighter!

Downsides? well that is the debate. Most often cited is the "sideways strength". That is if the thru hull pipe stem (on the inside of the boat) is side impacted hard enough, it can break off at the surface of the hull, letting water in.

A valid concern. What is not often included in these arguments is what "type" of thru hull/valve are we talking about. Seems it is often assumed it is just a thru-hull with a backing nut followed by a ball valve threaded, followed by a hose barb. What is often NOT mentioned is that Forespar, the exclusive maker/distributor of Marelon plumbing fittings, does make a "proper" flanged marelon seacock/seavalve. The difference in a "proper" seacock is the backing nut and ball valve are one and the flange, which bolts against the hull, provides more strength and resistance to side impacts. Effectively, the flange and ball valve housing provide more sturdiness compared to the straight thin walled pipe nipple on the end of a plain thru hull.

Why am I bringing this up? Well, we are starting the thru-hull/seacock installations, starting with the cockpit drains. There will be four of them, 1 1/2" diameter each. We have decided to go with the marelon seacocks, for the positive reasons cited above. As they will be proper thru-bolted seackcocks, I do not believe there will be much side-impact breakage risk. Regardless, I will try to position them in "safe" areas of the engine room as best as possible.

It also should be noted that, ABYC does NOT recommend ball-valved-threaded-on thru-hulls under the waterline, bronze or otherwise. Though many boat manufacturers do this simply because proper good quality bronze seacocks are getting hard to find. It used to be Wilcox/Crittenden and Groco made the "standard" tapered plug seacock. But no more. Seems the few seacock makers, including Forespar, are basing them on ball valves, which is considered less desirable because they are not easy to rebuild. The one maker of tapered plug bronze seacocks I know of is Spartan Marine.

In the end, they could always be swapped out for bronze if there is some reason to change.

Anyway, enough rambling. I am sure some of you out there have some opinions on this, feel free to post a comment.

Monday, July 07, 2008

Fill, Grind, Sand, Repeat

Much of last week was spent fairing the rudder. The general procedure is: squegee thickened epoxy (with fairing compund, West Systems 407 in this case) over the rudder, once cured, grind and/or sand with a flat disk, I used 40 grit, clean, do it again until the surface is pretty smooth to the touch. There were still a couple "slightly raised" areas over the internal stainless webs, due to the compression of the infusion process. I stopped there as I had already ground through to top layer of CSM glass and was getting down to the woven roving. I didnt want to grind through that as that is what provides the strength. It is kind of hard to see and I doubt it will affect the hydrodynamics of the boat, it is not like we are going to race this thing.

Once faired to my tastes, the final epoxy barrier coating is done. Recipe: generous layer of West Systems Expoxy (straight), followed by numerous coats of Interlux 2000E epoxy barrier coating. As many as you care to put on.
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Wednesday, July 02, 2008

Rudder Infusion: The Movie

As promised, here is the video of the rudder infusion done last weekend. Total infusion time was about 90 minutes. The video was edited down to about 25 minutes real time (removed all the boring bits). Then it was compressed into 4 minutes. Included are titles pointing out things of interest. The dork in the white shirt is yours truly. The graceful one is my wife. I expect an "Amateur Boatbuilders Guild Award" for this fine piece of production and artistry. Music is "Dust" by The Monks of Doom (now disbanded, one of my favorite bands). Enjoy.