[Rhodes22-list] Loose centerboard

[BillyDoc]

Greg PA wrote:
> 
> Where did you get the supplies?
> Did you machine the pin yourself or go to a machine shop?
> Why use bearings?
> 

Hi Greg,

I had all the supplies as scraps from previous projects that my business
completed.  I'm one of those guys who hates to throw anything away, and my
"junk pile" is one of my prized possessions.  I also have machine tools,
etc., and did my own machining.  If you do a Google search on "metal rods"
you will find lots of places offering to cut to length the supplies you
need, usually with a one foot minimum.  The bearing rings can be made from
PVC plumbing materials, so would cost very little.

The pin doesn't have a great deal of force on it, so using a solid pin, as I
did, is definitely excessive in terms of the strength requirements.  But
that pin should be made out of some material that is corrosion resistant,
especially in sea water, which is why I used 316 stainless steel.  The more
common 304 stainless steel is not nearly as resistant against corrosion.  If
you want to go for perfection you can get titanium rods now, and that stuff
is great in sea-water! The pin should in any case be made from a hard
material, or at least a material that is significantly harder than the
material it will be sliding or rubbing against.  This is a basic principle
of "plain" bearings, a hard material against a soft material will not gouge
one into the other, so just about any lubricant works well . . . in this
case the water.  As an aside, and to make this point further, many people
have found to their dismay that stainless steel bolts tightened with
stainless steel nuts of the same alloy will often lock up (seize) because of
mutual gouging on the sliding surfaces.  The solution here is lots of
"anti-seize," or to use two different materials with different hardness.

It was probably "engineering overkill" to use bearings at all, but my slot
dimensions were larger than my pin diameter and I didn't want the slop in
the system on the vertical axis, plus the glass part of fiberglass is pretty
hard . . . just like the pin . . . so not a good bearing surface by itself.  
So, I made the bearing rings to solve both problems.

The whole project is some pretty simple machine work, if you have a lathe,
and shouldn't be too expensive at a machine shop if you don't.  Just don't
tell them it's for a boat.  That automatically jacks the price up by a
factor of ten or so . . .

I can't think of any other details, but if you do just let me know.  The
system seemed to work well, given the shortness of the test my wife and I
gave it.  We barely got clear of the dock when we found the trunk gasket had
a pretty bad leak.  The rubber had hardened to the point it didn't seal
well, and I need to replace it.  Not wanting to go for a swim we hustled
back and pulled the boat out.  Then, of course, it got cold.  So the boat
has been sitting in my back yard, waiting for me to pull the CB trunk cap
and measure the gasket for replacement.  I'm a wimp.  I don't like the part
of traditional sailing about "Getting cold and wet and becoming ill" in
"Getting cold and wet and becoming ill while slowly going nowhere at great
expense."  So I'm waiting for spring! I'll also "de-articulate" the blocks
when I have it apart.

Good luck with it!

Bill

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