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Old 12-08-2010, 10:12   #1
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Leeboard Pivot Bearing Material

I have a question concerning the deck mount of the leeboard pivot:

As originally designed, the leeboard pivots fit through the side of the hull, very much like the pics on the Sea Pearl website. In fact, that's where the original builder got the inspiration for the rig and boards once he had the hull built. (It's a Culler Sharptown Barge with Sea Pearl-like rig and boards.) The pivot hardware was a 1-1/8" diam. bar fit through the hull, with inner and outer blocks added so that total shaft-to-mount length was about 2-1/2". Originally, it was simply this thickness of bare wood drilled for a snug fit around the brass. It evidently worked well enough, as the wood pieces I have from that installation were not rotted or worn badly. My guess is that what little water they saw both swelled the wood against the brass to prevent leaks, and lubed the joint sufficiently for movement.

Before I took possession, he had moved the mounts topside and plugged the original holes in the hull. And he made new mounts for on top of the deck. I believe these to be too small, and they look cobbled together, so I'm looking at something larger to spread the load better, as well as to look more appropriate.

My questions:
For the same bearing surface where the brass shaft fits through the oak mount, is bare wood to brass a good enough prep? I am shy of it, because I think the wood would not be sealed, and could swell and rot.

So, to me I need to at least seal it in a layer of epoxy. I envision needing at least to over-bore the hole, fill with epoxy, then re-bore to shaft size.

Is a simple 1/16" or 1/8" layer of epoxy around the shaft sufficient? Should I also line it with say, 660 bearing bronze?

For reference, the boards are about 50 pounds or less. They rotate 90 degrees. I can see the boards maybe going down and up say 20 times in a day of sailing.

If a inner layer of epoxy would be sufficient, it sure might keep life easier
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Old 12-08-2010, 11:43   #2
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Have you got any pictures of the present installation you can post...I'm having a hard time visualizing this.
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Old 12-08-2010, 12:04   #3
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Quote:
Originally Posted by bassman1956 View Post
...Is a simple 1/16" or 1/8" layer of epoxy around the shaft sufficient? Should I also line it with say, 660 bearing bronze?
...
I'd overdrill at least 1/2" diameter, allowing a minimum of 1/4" epoxy all around (for 1.125" shaft).
It's a bearing surface, so a bearing material (660 Bz) would be prudent.
If it's an assymetrically loaded bearing surface, as I believe (from desciption) it is, then a bearing material would be REQUIRED.
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Old 12-08-2010, 19:28   #4
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Rotationally, there is little loading beyond the weight of the board. Axially, when down, and the board is under the load of leeway, it pushes against the board rest on the hull as a fulcrum, and then applies an axial load outward from the CL of the boat. If the board is under windward loading, it is free to rotate away from the hull, and again, no significant loading.

This joint is really over-designed. For a similar but larger boat, let's compare with Phil Bolger's Black Skimmer, a cat yawl with leeboards. Bolger's, 25.5' x 7' x 9" with a displacement around 1 ton, vs my boat, 24' x 5' x 8", and about 700# + load. He used loops of 3/8" line as the pivots, where the boards would be in a loose state while up, and tighten the line while being lowered, and the top of the board would move out on a brace and snug up the line. I have the prints. Very simple. It would take me much more to convert my boat to a similar setup than simply finish what is there.
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Old 12-08-2010, 19:59   #5
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I'd be inclined to recommend HDPE or UHMWPE as bearings. I'd suspect an epoxy bushing would eventually chew on the shaft or at least wear it slowing with time, while the HDPE surely not. I'd also incorporate a flange on the outboard edge of the bushing so it could accept the side loads. Or possably, use two pieces, a bushing, then a washer (the flange part), both of HDPE, this way you could replace the washer if necessary, as I'd expect it to wear at a faster rate. Maybe HDPE for the bushing, and the high modulus stuff for the washer.

Of course bullet proof would be a bronze bushing/flange, maybe with a Zerk to keep things happy.
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Old 18-08-2010, 20:52   #6
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Here are some pics:













Considering Bolger used only a loop of 3/8" line for the Black Skimmer, a boat 1' longer, 2' wider, and 3 times the displacement, this seems way overkill. But, I think at least sealing the bearing surface with epoxy is a good idea for the wood mount. And maybe bearing bronze. The mounts I will swap out. As you can see, these look small and cobbled together. First, I will make a full partner for them under the deck. Then enlarge the topside mount, especially coming inward. The only thing that really concerns me about the design is the outward pull of the pivot shaft when the board is under leeway load on that side, and it's moment and stress on the deck. Otherwise, it seems way overdesigned.

That brass bar is 1-1/2" OD by about 10" long, the pivot is 1-1/8" OD with 1" UNF threads. The undercuts are for the SS straps to hang the boards with. BTW, any on know of a good source for polished 316SS plate, about 0.1" thick?
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Old 24-01-2011, 14:57   #7
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Okay, I now have new pivot blocks in progress, out of white oak. You can see them below compared with what was there. Increases the base area by about 8+ times, and should work great to spread any stresses. (Also are a couple pics of the new grab rails in progress.)

Anyways, replacing the missing brass kingpin (or whatever you'd call it), it's just as easy to get all new material and make 2 new matching sets.

The old pins are unidentified brass.
The old bearings were a snug fit through the wood hull, with spacer blocks both inside and out.

Am looking at using:
C485 leaded naval brass for the pins
CDA932 bearing bronze or 316T SS for bearing bushings inside the white oak
316T SS x 0.075" for the 2" x 10" straps that wrap the pins and hold the boards onto them

This design borrows heavily from LF Herreschoff's Meadowlark, even in sizes, and this boat is about 1/8 the displacement of that one.

Comments, criticisms?
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Old 27-01-2011, 17:17   #8
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CDA932 is the choice.
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Old 28-02-2011, 09:28   #9
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Re: Leeboard Pivot Bearing Material

C464 vs. C485:

The C464 unleaded naval brass is very expensive. C485 leaded is half the price, but not weldable. I discussed this with the weld shop boss to confer. The lead destrys the weldability. I need weldability. So C485 leaded naval brass for the pins is out. C464 naval brass is the most direct alternative.

So, I'm studying C954 Aluminum Bronze in the place of the C485 leaded naval brass for the kingpins. It's weldable, strong, very resistant to corrosion, in fact, often recommended for marine use, and about 1/3 the cost of naval brass. For the materials for these pins alone, that's $100 vs. $300.
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Old 08-03-2011, 19:51   #10
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Re: Leeboard Pivot Bearing Material

After speaking with other engineers at work, and the weld shop, I'm opting for the 6061-T6 aluminum for the kingpins, staying with the C932 bronze for the bushings, and 14 gage SS316 for the straps that wrap around the kingpins and hold them on to the leeboards.
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Old 08-03-2011, 20:14   #11
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Re: Leeboard Pivot Bearing Material

Aluminum, bronze, stainless and seawater, sound like a good battery to me!
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Old 08-03-2011, 21:27   #12
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Re: Leeboard Pivot Bearing Material

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Originally Posted by capngeo View Post
Aluminum, bronze, stainless and seawater, sound like a good battery to me!
I've been looking into that.

It's all at the sheer line or above. At this time, fresh water, although estuaries are not out of the question for the future. Trailer sailor.

6061-T6 aluminum is one of the most noble aluminums, good for corrosive atmospheres, and non-galvanic reactions. And, I'll investigate getting them hard anodized. Still far far cheaper than naval bronze. And about 10 pounds lighter, if it matters. 316 as simple straps, without welds, I have no fear of. Nor the bronze. All three are within about 0.2 to 0.25V of each other on the galvanic series. 0.15V is fairly safe. 0.5+ is bad. So this is a good sign.

All are easily visible, rotating fits are not at all critical, and mating surfaces will be lubed.
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Old 11-04-2011, 20:31   #13
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Re: Leeboard Pivot Bearing Material

Atlas Bronze out of New Jersey had some much better pricing on naval brass than what I had found, and didn't mind small orders, and not being much more pricey than some of my other options, so I wound up revising my plans

So I actually went with C464 naval brass for the king pins, CDA932 bearing bronze for bearing bushings inside the white oak mounts, C464 plate for the straps, more naval brass for the washers on each side, and only SS nuts.

The one thing I ran into is that 1"-14 is replacing 1"-12 as standard fine thread. Most charts and references refer to UNF being 1"-12. My days as a machinist say this is good. I have a 1"-12 die. We have 1"-12 die and tap at work. No 1"-14. But apparently, 1"-14 is becoming the standardly stocked components over the last few years. So, I had to order a die also. D'Oh!
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