Sorry not to clarify Doug. My message related to an M17 cb. I don't go by measurement with the cb pendant on my M15, I locate the knot by feel--lower the board til it stops, then draw it up and knot it so I know for sure it's clear. I check it several times during the season to make sure the knot's stayed put, as you suggest. t
Tom Smith & Jane Van Winkle Sandpoint, Idaho M15-345, Chukar -----Original Message----- From: Doug Kelch [mailto:[EMAIL PROTECTED] Sent: Thursday, September 11, 2003 6:24 PM To: For and about Montgomery Sailboats Subject: RE: M_Boats: Centerboard Corrosion Discussion Tom, If you are talking a M15 I believe there was a posting from Jerry Montgomery indicating that the pendant is supposed to hold all of the weight. If I recall Jerry suggested a pendant stopper knot 15" above the bridge deck teak. I could't remember for sure so I have mine at 14" as the knot does tend to creep up the rope. Look up Jerry's posting to be sure. I think it was in 2001 or 2002. Thanks Doug Kelch "Seas The Day" M15 #310 --- "Smith, Tom" <[EMAIL PROTECTED]> wrote: > Informative writeup by Nigel Warren, John. Thanks > for passing it on. > > That spouting problem I was quering the group on a > couple weeks ago is due to a busted tang and the cb > positioned lower that it should have been. I dove > on the boat a couple times and positioned the cb > correctly and marked the pendant. Fixed the > problem. Now we'll see about fixing the board over > the winter. Any thoughts on fixing the tang but > rather than lowering the cb to the stopper bolt, > making the pendant carry the weight? t > > Tom Smith & Jane Van Winkle > Sandpoint, Idaho > M15-345, Chukar > > > > > > -----Original Message----- > From: John Fleming > [mailto:[EMAIL PROTECTED] > Sent: Wednesday, September 10, 2003 9:54 PM > To: For and about Montgomery Sailboats > Subject: M_Boats: Centerboard Corrosion Discussion > > > I recently bought a book titled "Metal Corrosion in > Boats", by Nigel > Warren. Really a fascinating book, with all sorts > of hints and > discussion about how to best arrange all your metal > components on a boat > and how to manage the effects of corrosion above and > below the water. > > Anyway, there's a section in the Chapter "Underwater > Problem Areas", > that should be of interest to all Montgomery owners, > especially those > with metal centerboards. I have typed this section > in for you. There > are other sections that deal with topics near and > dear to Montgomery > owners, but I'll start with this one. > > John Fleming > M-17: "Star Cross'd > > ---- > > Centreboards (Nigel's a Brit) > Most centreboards are of mild steel, sometimes > galvanized sometimes not. > That in itself does not produce special problems but > the pivot bolt and > the hoisting gear often enhance corrosion. The > bearing areas in way of > both the pivot bolt and the lifting tackle are > especially prone to a > vigorous corrosion. The actual surfaces in contact > rub together and are > immersed in salt water. Any galvanizing or other > protective coating > soon rubs off exposing the bare steel edge. The hole > in the centreplate > then enlarges quickly. The lifting tackle pin is > necessarily close to > the edge of the plate and eventually after a few > seasons can pull > through the edge releasing the centreplate. This > process will happen > even with compatible metals - in most cases a > galvanized shackle pin in > a steel centreboard - but if a stainless or bronze > shackle is used the > rate of corrosion of the hole is many times faster > because of galvanic > effects. > > With a mild steel centreboard there is no > long-lasting solution to this > problem except to use compatible materials, i.e. a > galvanized shackle on > the end of the lifting wire and a galvanized pivot > bolt, and then to > accept that steady wear will take place. Each year > the items should be > inspected and replaced when necessary. > > In the case of the lifting tackle at least the wear > of the plate itself > can easily be avoided by fitting a pair of mild > steel straps and having > a replaceable pin. With more difficulty, the hole > for the pivot bolt can > be fitted with a removable steel bush[ing]. Then at > least all the > wearing parts are easily replaced. > > Obviously the thicker the bolt and the pin the > longer their life; many > boats with centreboards are fitted with pathetically > thin pivot bolts > which while being quite strong enough when new can > tolerate very little > corrosion. [How true is this for Montgomery's? I > wonder.] > > The lifting wire itself is a problem. Constantly > wetted, neither > galvanized nor stainless wire is likely to last > long. Stainless wire > will give a short life underwater because of > pitting, and if a > coppersleeved Talurit splice is fitted this will > corrode preferentially. > Polyester (Terylene or Dacron) rope is one solution, > though with a chafe > problem, but galvanized chain is better. The lowest > link will take the > wear but if an overlong piece of chain is fitted in > the first place it > can be cut off in due course and the next link up > used instead. The > galvanizing will last only a few years so > replacement of the chain must > be considered as a matter of course. > > [My Montgomery has a little wire rope pigtail > attached to the board, and > then a polyester line going to the cockpit. I guess > he's saying I'll > have to check it every so often.] > > A complete long-lasting solution to the wear problem > at the pivot and > lifting pin on a steel centreplate is elusive. > Obviously a longer life > would ensue if the wearing areas were of a hard and > corrosion resistant > metal: this suggests stainless steel. The pitting > problem would be > reduced by the cathodic protection given by the > steel plate. So, at the > pivot, one would end up with a stainless bush fixed > to the plate and > with a stainless steel bolt, making sure that Type > 316 stainless steel > was used. The bush could be rivetted, bolted or even > welded in place. > Similarly the lifting point could be bushed, or > stainless steel tangs > could be fitted. From there a stainless shackle > would lead to a > polyester lifting rope. > > [I believe that the Montgomery's more or less follow > this advice, except > for the stainless bushing at the centerboard pivot. > He seems to say > that the pivot bolt must be pulled and inspected on > a regular basis, and > if any significant pitting has occurred, it must be > replaced. Also, it > implies that even though the centerboard is painted > to control rust, > there must be metal-to metal contact between the > cenboard and the pivot > pin.] > > Of course a centreboard of zinc-free copper alloy > would solve all the > problems because the attachments could then be of > the same > corrosion-free alloys. Suitable metals that come to > mind are copper, > gunmetal [a bronze (88% copper plus tin)] and > copper-nickel. Copper > alloys are much the same density or a little heavier > than steel. A > bonus would be that no antifouling would be > necessary. The lifting wire > could be of Monel (which is available, though at a > price). Stainless > steel for the centreplate could also be considered > (again Type 316) with > sacrificial anodes. > > [The new M23 Bob Eeg is making has a centerboard of > silicon bronze, > though he doesn't say here whether the pivot bolt is > still allowed to be > stainless.] > > Usually cost rules out such materials and mild steel > is the only > practical choice; but to avoid disaster it is wise > to consider carefully > === message truncated === __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats This message was scanned for viruses. _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats
