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Thread: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

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    Default Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Theres no end of information on centreboard rebuilds on the web. Some from bad maintenance, and some through a poor choice of materials, i note Catalina yachts advised against leaving their boats in salt water, due to the mix of metals in their drop keels, cast iron, bronze and steel. Bronze to bronze seems a reliable way to construct the pin and bearings, but what about if the if the ballast keel and board are from plain steel? I was searching for some inert type of material that might be used to isolate the bronze from the steel, and came across bearings made from graphalloy-bronze, used for underwater purposes and high stress applications without the need for lubrication. Sounds like an ideal use for bearing material. Anyone used this before? I would be tempted to use plain steel for everything to avoid electrolysis, but i dont see it standing up to being used with tight tolerance without some kind of forced grease lubrication.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Marmalade's stainless pin through an iron plate board stood up so well during her first four decades that when I had to replace the rusted board, I kept the pin.

    In general I think it a good idea to sleave the pin with something longer than the board is wide and jost shorter than the slot is wide. Among other advantages of this, you can't squeeze the trunk in tightening the bolt and you'll not be binding the board, at least not there. If you can't get an SS tube of sufficient thickness, go with extra heavy iron pipe. Really pack it with grease.

    If you've a wood, lead, or bronze board, you can then of course go bronze pin and sleave.

    Pete Culler and some others designed centerboards where the top/front was a semicircle on the pin hole. This put the board pivot a bit higher in the trunk for strength and put the pin above the waterline so you could drop or install the board floating. If you've ever had to dig a pit to install a board, as pictured below, the advantages of an above waterline pin are transcendentally obvious.

    Sliding to the pit.


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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Getting it up and in



    At this point I'm inside. The pin is just above the garboard/keel seam, so close that the planking is a little relieved to allow the nut to turn. Getting the centerboard hole alligned with the hole in the keel was a nightmare of me wiggling a short tapered pin while David wiggled the 500# board.

    The penent is holding the back end of the board and the front is leaning on the front of the trunk. To go up, a third person would lever the board to get it off the front of the trunk, I'd handle the pennent winch, and Dave would motivate the heel of the board.
    Last edited by Ian McColgin; 11-12-2017 at 06:47 AM.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    A friend's McGregor's swing keel pin rusted to nothing. That sail home was fun as the swing keel was in the slot but just leaning against the front and hanging all weight on the pennent. Once back at the dock, A few free dives found a hole near the hole for the pennent attachment. So, shackle there and I brought Granuaile in close with the bowsprit over the McGregor. Unshackled the anchor, lowered the chain and shackled to the swing keel, cut the pennant, and pulled the keel up with my anchor windlass.

    On a low tide we did a test roll to see if we could get her over enough that the keel could be reinstalled by sliding. Took careful measurements. I also made legs for Granuaile. Once all was ready, we went over to some firm flats off East Boston at a little after high, anchored and waited. Once the water was about knee high, we began off loading the ramp supplies - a sheet of 1" plywood and many balks - getting the McGregor on her bilge - winging the keel off Granuaile's deck and onto rollers on the ramp. From there it was just a bit of muscling followed by beer and whisky while we awaited the tide's return.

    Passing Coast Guard boats were much amused once they were sure we were not setting up something nastry - we were out from the end of 33L.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Thanks for the input Ian. The pin can go through both sides of the external steel ballast, means the pin is below the waterline, but the case will not take any board pressure, its just there to keep the water out. Looking at some hefty drop plates from Southerly Yachts and some others, the use of a large diameter pin in plain bearing, looks the best way to avoid any board wiggle. if hefty enough, but no reason the same system should not be used in a lighter board, a heavy pin is acting as ballast where it counts, and the lifting system could be simplified if the board is not excessive heavy.
    A hefty stainless pin and bearings could be used with steel if the bushes were easily replaced, from a quick search the cost difference between bronze and 316 stainless is minimal and the bronze is easier to work and a little closer to steel (compared to stainless) in the galvanic series.
    I have seen a board and casing made entirely of stainless, not something i could weld up myself, and the materials would be expensive.......not sure i would trust it either long term, come across too many fuel and water tanks suffering from micro holes.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    My old Alden 43' centerboard schooner Goblin was unlike the Goody&Stevens in a key respect: The G&S had a conventional built down keel with a lump of lead at the bottom and the board went through all that. By the time I came into Goblin in the early 80's, any surviving G&S centerboard Aldens that I heard about were keeled over and maintaining that slot was just impossible. Goblin, by contrast, has a massive cast iron keel with the slot well supported by 3' deep by 1' thick iron on each side. Because it was so long, the weight was distributed more fore and aft than the earlier 43's. Comparing the lines was fascinating.

    Anyway, despite that massive structure that really did save her, the trunk was still considerably stronger than just holding the water out. This proved a good thing when on a fast tight reach I was a little late in tacking and smacked Egg Island just opposite Kalmus. The board could not just go up because hard over that way the pressure of the sand basicly bound the board in the slot. The strength of that drifted oak board structure of the centerboard itself was proven - the board obviously bent some under the impact and when we were fully stopped and the lateral pressure reduced, the board straightened with a twitch and wiggle that the whole crew felt. Very saucy of old Goblin.

    A metal board would have stayed bent. A glass composit board would likely have broken.

    The cast iron keel took most of the twisting strain but the trunk also took its share.

    I think the best in trunk design looks at the trunk and bed logs as a box beam for strength - it should enhnace the fore and aft strength of the keel and should be laterally so robust that when the boat's grounded or hauled out the slot won't pant or deflect at all. For that to happen, the trunk must be robust up from the bedlogs to the top.

    The whole point of a centerboard boat is to go in shallower water than a keel boat of that size can go. With that in mind, design for smacking the hard brown stuff around the edges.

    G'luck

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    I wonder if a lignum vitae bushing would work between pin/board of dissimilar metals.
    CLC Skerry = "Vingilothiel"

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Hi Skara ( what is your name?)

    My centreboard is 7/8” steel and i bought a length of Acetal plastic rod about 40mm in dia. I took board to a metalworking place and they bored a hole to take it, and at the same time put a 25mm hole in the acetal. The pivot pin is 25mm bronze. I cut a length off the acetal and glued it into the centreboard with epoxy as a bearing. All up pretty easy and hopefully it’ll work.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Thanks Ian, agree the case and keel/slot should be able to take severe grounding. The lower end of the case will be out as far as the keel apron and thru bolted to the ballast/grounding plate. Something similar to this.....





    Though i would prefer to see more vertical webs and bigger triangulation plates on either end.

    Andrew, its another Ian, did you have pics on your thread? Im thinking at present a 1/2in (12mm) plate with timber/foam each side to gain a foil shape. Its more for windward assist. My current thoughts are that a heavily ballasted board will put way more stress on everything, and i have never been keen on the idea of cutting a long slot in the backbone of a boat; the only reason im thinking about it is the fact there will be steel fabrications either side of the slot,top and bottom, acting very much like Ian suggested, like a girder.
    I have not run any sums on righting moment yet, but given the relatively shallow depth of the board, i see more issues with a heavily ballasted board. Jury is still out on that....

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    the use of a large diameter pin in plain bearing, looks the best way to avoid any board wiggle.
    I'll argue that the board to pin fit should be loose to ensure that the board can wiggle - enough so that the side stresses are taken by the keel and case. All the pin does is carry the weight and serve as a pivot. Why concentrate high loads on a single point when you can spread them out? And you won't get any wiggle when sailing -- the board will lock itself in quite securely as soon as the sails fill.

    I've done a couple of light boards like this image from a Jamestown Distributors blog. The case isn't squeezed when the caps are installed and the loads on the pin are minimized. A similar approach can be taken with bronze or other metals if the weight of the board demands it.

    -Dave

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Ian S photos with not much detail are on #520 & #658 showing c’board with the hole and bearing glued in.

    #320 shows the 2” diameter epoxy slug I cast into the keel Timbers to have a 25mm hole drilled in for bronze rod.

    The Acetal bearing sticks out each side of c’board about 1/8” so its a loose fit in centrecase. This system hasn’t been tested yet but I got my fingers crossed.

    Ive routed a housing in each side of keel timber over those epoxy slugs that will have a 1/4” plate of bronze ( 2”x3” ) captive for the rod.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Thanks Dave. I confess i never owned a centreboard boat. My reason of thinking of putting the pin thru the ballast plate is that is the last thing that is going to twist. My thoughts were going away from a heavy board until i saw the Southerly set-up, this is no dinghy style.



    If there is over an inch of steel plate either side of the board,(steel ballast shoe) im thinking its better to use that as a pin carrier. The Southerly keel is supported by the one pin only, and that weighs more than the entire calculated weight of my (unladen) project boat. Having "wiggle room" might be ok on a lightweight board, but im not sure i would be happy with anything that weighs over 200lb being anything other than a smooth slick action, if possible.

    And yeah, i think Lignum Vitae would make a good bearing if the wall thickness was adequate enough. The only reason i bought up the question of graphalloy bronze, was that they are availiable as bushes, allowing plenty of area around the hole and still a good sized pin.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Thanks Andrew, i check it out.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Quote Originally Posted by andrewpatrol View Post
    Ian S photos with not much detail are on #520 & #658 showing c’board with the hole and bearing glued in.

    #320 shows the 2” diameter epoxy slug I cast into the keel Timbers to have a 25mm hole drilled in for bronze rod.

    The Acetal bearing sticks out each side of c’board about 1/8” so its a loose fit in centrecase. This system hasn’t been tested yet but I got my fingers crossed.

    Ive routed a housing in each side of keel timber over those epoxy slugs that will have a 1/4” plate of bronze ( 2”x3” ) captive for the rod.
    Looks the same as what im thinking, just replace your deadwood with steel. I will have to look up acetal, your board is way heavier than i might construct, how did you come to the choice to use that, and at that size? Seems there is no end to wonderfull modern plastics, but i do not fancy being a test dummy......hard to move away from time tested materials.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Quote Originally Posted by skaraborgcraft View Post
    Looks the same as what im thinking, just replace your deadwood with steel. I will have to look up acetal, your board is way heavier than i might construct, how did you come to the choice to use that, and at that size? Seems there is no end to wonderfull modern plastics, but i do not fancy being a test dummy......hard to move away from time tested materials.
    The steel board is as specified in plans by Mr Oughtred. It’s $%^&^% heavy. When i went to the plastics supplier I explained what I was doing with it and they said that Acetal wont expand in a permanently wet environment, its self lubricating and its an ideal bearing material under weight.
    I know what you mean about being a crash test dummy, but the plans were very light on info in the centreboard and case and bearing dept. Only info I had was to use a 25mm pin.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    For my Joel White 23, I used a 3/4 inch titanium pin from eBay. It rides in a red brass bushing in the 150 pound board. After three years there is no detectable corrosion on pin or bushing. The eBay seller cut the rod to length for no charge.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Thanks Andrew. Lots of acetal being sold on the web, i was looking for information on water absorbtion without luck, but you have answered that, so sounds like an option.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Quote Originally Posted by CundysHarbor View Post
    For my Joel White 23, I used a 3/4 inch titanium pin from eBay. It rides in a red brass bushing in the 150 pound board. After three years there is no detectable corrosion on pin or bushing. The eBay seller cut the rod to length for no charge.
    Red brass? Is your board steel? Its the mix of metals that are a concern to me. It seems many steel boards will use a stainless pin, but that will be oxygen starved, or go with bronze and face the electroylisis factor. I think polymer bushes are the way to go to avoid at least metal to metal contact, and a small zinc can always be put on the boards head, out of the waterflow but always submerged.
    How about lifting tackles. How many lift from the board head, compared to lifting from the tail end with a wire? Not looked at that yet, but dont fancy a wire humming in the water.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    My board is wood. Red brass is widely used for pipe in marine service as it is very resistant to salt water corrosion.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Quote Originally Posted by CundysHarbor View Post
    My board is wood. Red brass is widely used for pipe in marine service as it is very resistant to salt water corrosion.
    Thanks, i will make a note of that.

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    After describing some of the options, I looked for an example online and found this https://www.mcmaster.com/#plastic-sl...rings/=1a98awd Pick a material and look at the load rating for the same size bearing in each material. It will be found by clicking on the part number and then click on product detail. McMaster might not be a good source in the UK, but the information available there is good. The bearing information on this site looks accurate.

    I would probably just go with a bronze oilite bearing. Maybe the PTFE filled, but oil should be OK. In a plastic, I would start with either Delrin AF or Ertalyte. -- Or the PTFE fabric lined fiberglass if the loads are too high -- and if I had the patience to find a source. Teflon fabric lined fiberglass has a very high load capacity, but you have to assemble carefully. Pound in a pin with a burr that catches on the liner and the liner will peel and bind up. Good help is hard to find.

    PTFE filled acetal (Delrin AF) is extremely wear resistant and doesn't swell. Unfilled acetal does not absorb water or swell, but is not the highest load capacity bearing.

    Ertalyte PET-PE is as good or better than acetal, especially if the gearing will get hot. (Not an issue here, obviously).

    Carbon filled PEEK aside from the ridiculous price and galvanic compatibility with nothing but titanium, is bulletproof.

    The only problem with the Graphalloy bronze is that it is brittle, so be careful with the hammer. You can run Graphalloy dry in an application that will melt Torlon in a heartbeat. I don't know enough about galvanic corrosion with the bronze filled Graphalloy to comment, but the straight graphite version is for titanium only.

    Polyimide (Vespel), Polyamide (Nylon) and Torlon all absorb a lot of water and swell, which can cause a bearing to bind.

    Stainless steel can be well protected by carbon steel anodes. That would explain Ian's good result. 2205 stainless is more corrosion resistant and twice as strong as 316 for the same price, at least the McMaster-Carr price. https://www.mcmaster.com/#2205-stain...-rods/=1a981f2

    I have to disagree in part with Woxbox as far as the load on the bearing surface is concerned. [quote]I'll argue that the board to pin fit should be loose to ensure that the board can wiggle - enough so that the side stresses are taken by the keel and case. All the pin does is carry the weight and serve as a pivot. Why concentrate high loads on a single point when you can spread them out?[quote/] When a round shaft or ball contacts a support with a larger diameter, all of the load is concentrated on a very small area. A close tolerance fit spreads the load much better. As for the rest, he may be right.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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    Default Re: Reliable/bombproof centreboard pin construction. Graphalloy-bronze?

    Dave, thanks for the links and info. Stainless 2205 sounds right for a pin. I might be able to increase the pin diameter to decrease surface loads if polymer bearings are at risk. I will check out that calculator/comparison chart dreckly.....

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