Njord Commander Hull 105

[Rico]

Thanks commanderpete. I feel better about proceeding... - I should plug those holes...

I did re-paint the mast. - Went down to Bare Aluminum... Interlux Perfection followed. (Following you very lead, if I remember correctly... )

More picts and details on the "Mephisto Cat's" (C-155) gallery page soon.

And thanks to everyone who posts on this board and Bill who keeps the board neat & tidy... This board is indeed a great resource. The bulk of the work I've undertaken has been only following and learning from other's posts on this board.

[ebb]

We did talk briefly on the thread 'Spinaker question' about this original equipment sheeve that on Little Gull is about to be taken apart.

This 6" sheeve sits in the middle of the mast in a rather too large hole.
Wouldn't mind closing it up.*
I see on some other posts masts that have a curved stainless plate that holds the block that hoisted the main on 338. The plate is positioned at the very top of the mast and kind of hangs a bit over the top of the huge slot the old frozen sheeve occupies (for but a short time left.)

OK, I can see that this plate can do the job. But I'm not happy with it either. It is fabricated of the same 3/32" plate the tangs are made from, It shows no wear and looks like it is installed properly as to corrosion showing, but it only holds the one block. I'd like a second halyard block up there - even a third.

The sheeve bolt on the sides of the mast has caused some corrosion that will have to be taken care of. When I take the sheeve out, I'll try closing the holes off with Durofix solder.
But the slots are a different matter. I'm thinking plates could be positioned over the slot on the front and back to close it off.

How does one normally rig extra main halyard blocks without their fouling? Figure the close-off/repair plate is an opportunity to create an ideal fitting to mount back-up halyard blocks AND the main halyard block. What blocks would be used?

Anybody have any ideas???
__________________________________________________ _________________________________________
One reason to close off the sheeve is to keep sweet water out. If mast wires go through the deck under the mast as they did on 338, the holes could cause balsa rot under the mast - as it did on 338.

We have solved that problem but I'm persuaded by L&L Pardey's advice that the mast must be closed off so that it does not fill with water and turn a knockdown into a disaster by keeping the boat on its side.

I would like to solve that by having no open holes in the mast. Except for the drain at the foot.

[ebb]

Been removing all hardware except main track from 338's mast.

I've noticed on pictures of other Ariel masts on this Forum that at least two have had a special curved tang fitting added to the top of the mast over the sheave to hang the jib halyard block.

Found EXTENSIVE CORROSION behind this fitting.
The aluminum has been eaten away from the sheave-box hole to the top of the mast!!!
A hard white filler* was used to pack the difference in radius between tang and mast. It is here the aluminum has been eaten away - a 3" X 3" area between the slot and the end of the spar. The slot is a 3/4" X 7" hole (repeated on the opposite side) now extending to the top.

While none of the varieties of stainless steel screws used to fasten cleats, eyes, blocks to the mast show any real galvanic corrosion, in this case the area holding the tang screws has been completely compromised.
Mild white corrosion sometimes but not always shows up between a fitting and the mast. Nothing seems to have happened IN the threaded or drilled holes (stainless steel to aluminum contact - no obvious tef-gel remnants) - only on the interfacing areas. Behind a small block used as a cheek block on a section of the extruded track flat a filler was used to stabilize it. Pit corrosion on the flat occurred here also.

The aluminum pole style spreader mounts were also mounted with goop to created a curved interface with the mast. This stuff is a hard brittle black substance that rings an old dim bell. No corrosion whatsoever - in fact where the stuff skipped the original smooth anodized surface is perfectly preserved.

Noticed that the mast track was applied over what looks like plastic electic tape, there being a piece of it still hooked into the sheave hole. No corrosion,
And because all other threaded holes turn out to be OK, I'm gonna assume the track is good to go.....another 40 years!


Urge anyone who has this halyard refit to immediately check it.
This tang must be original as it is so prevalent on our masts.
There is no provision for a jib halyard block on the mast crane.



DO NOT USE THIS FITTING TO GET UP YOUR MAST WITH A BOSUN'S CHAIR OR WEB CLIMBER.

Until you are sure it's OK. What looks like four #10 coarse thread machine screws attached this fitting. Mortified to think I could have attempted to climb the mast. Realize there is NO failsafe with this type of fitting - if it comes off so does everything attached to it. Think I'll make sure to renovate the big mast sheave!
Lucky to be lazy.
__________________________________________________ __________________________________________________ ____________
* Edit, years later (2012). I would now, having been educated by renovating the A338 mast - record found on other threads in this Forum -
that the "hard filler" was actually packed hard poultice corrosion. Hadn't seen anything like it at the time, or since!
Pretty obvious that the fitting had never been removed since the time that Pearson, OBVIOUSLY the responsible party, planted that really
badly designed halyard tang over the sheave box, carelessly mounting it so that the stainless screws would corrode the aluminum spar.
Casual inspections did not pickup on the danger lurking behind the plate.

[Tony G]

That's a noteworthy alert.

A couple of times a year I stop and look at the mast trying to figure when is a good time to begin addressing that can o' worms. Now there is a legitimate reason to start poking around at the fittings and such.

Thanks, Ebb. You may have just cost us a bunch, but, you may have saved everything!

[ebb]

Would anybody have any thoughts on redoing the masthead sheave?

There are a number of alternatives. Or very few as you see it.

The phenolic cotton Tufnol sheave from 338's 1966 mast is 6.5" D.
It is 1/32" less than 1/2" wide. (12mm?)
It has a wire groove for 3/16" max.
The groove bottom diameter is 6 1/16".
The top plus 6 feet of the mast shows wear from the long-gone wire.

There is no way that the sheave can be made over for rope (Let's call it rope for clarity here.) unless you want to go with a substantially smaller diameter than 7/16" or 1/2" rope. For hand use I require these larger diameters and I believe most people do.
There may be a quick fix in finding an O-ring to fill most of the wire groove. But the 5/16" rope that might fit would not be supported well.

I don't feel that the inside groove diameter for running wire was sufficiently wide enough.
The Delrin sheave sizing pages on www.zephyrwerks.com
allows a 5/8" wide sheave for 1/2" rope.
Depth of groove from 1/3" to 1/2". Let's say 1/2" depth.
That's a 7" grooved disk. I'd want 1/4" overhang in and 1/4" overhang out.
Adding it up: 6 1/2" diameter groove
plus 1/2" sides equals 7 1/2" sheave. I really think that groove should cup the loaded halyard best it can. It spends important time under high load in one spot,
A Harken 7" sheave will cost $750
RigRite has 7" and 8" aluminum and Micarta sheaves with oilite bronze bearings but wrong pin diameters. Didn't check the wallet waster.

Looking at Ed's Zephyrwerks Pricing Sheet as a starter: It's $120 for a 7" to 8" sheave and it comes with an oilfilled bronze sleeve bearing. Have to talk with him about the pin.

Pin material can be 316 s.s. 655 bronze or titanium. I'd argue for bronze because of the bearing. Bronze also doesn't have lack of oxygen problems that s.s has. Admittedly 316 has the best rep. of available stainless.
I'm not happy with what I found used for a pin on the mast. It was an ordinary s.s. bolt that had the threads riding in the mast hole on one side.
That side also had a tang riding on the threads. It worked... but it really irked. Smooth, sized-with-the-bronze-bearing pin is the way to go.
I'm convinced that a 1/2" rod/pin with threaded ends and castellated nuts plus cotter-pins be the most secure up there. IS THIS OVERKILL ?


Main purpose of the square aluminum pieces on either side of the sheave is to support the sheave. The sheave runs on a 1/2" hole. It's support comes from friction bearing on the aluminum sides that lines the slot. Having them easily removable cuts down on maintenance. The squares are held in place by the sheave pin. 338's are badly corroded. Not a marine grade material. The laminate sheave shows little wear on the sides. But one side is new looking, the other scuffed.
++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++

OK. How would you ladies and gentlemen proceed on this? Would you go with a new Delrin sheave and bushing. Will you go with a bronze or stainless pin or bolt? Would go with the same side pieces in the sheave slot?
Or as I suggested elsewhere make an actual box for the sheave?

Although the holes in the mast are none the worse for wear from decades of galvanic potential, they do look old (tired?) and there is that bit of rash on the wall under the tangs. Still, you vill izolate the pin from the mast it passes through.
I've looked into the possibility of bushing the pin with a plastic isolator. PEEK (polyetheretherketone) is used for sleevebearings on rotating arbors. Very hard tough stuff, and available from McMCarr. But maybe not so good - as the loads on our pin are static from the halyard on the sheave and the shrouds on the tangs pulling down.

Anybody think this is a possible idea?
There's an opportunity to shorten the mast with a raised maststep. Cutting a bit off the top of the mast would lower the sheave hole into fresher aluminum. Good thing imco. Of course the place of everything else on the mast would also move up. As the track. A regular 1/2" inch through hole could be done what? maybe 1" lower? OR the bushed holes could be enlarged in the present location. Whot you say?

What about adding TWO NEW GIANT DELRIN SHEAVES???? The slot would become at least 1 1/2" wide. That's a big hole. AH... but TWO main halyards! Can the top take it? Could it be reinforced. (I have to band with added aluminum, or do something with the nasty corrosion on top of the slot.) The top fitting, which insets the tube, is held on with machine screws and surely adds some integrity to all the busy-ness of this split-top mast.


The old Tufnol sheave shows no obvious deterioration from four decades in the sky.
Micarta and Garolite are available versions of the material in phenolic, melamine and epoxy forms.. Can't find clear enough information, from McMCarr for one, on what high pressure laminate it is that has stayed fresh as a daisy all these many years of Ariel history. I cannot make out which of a number of materials a substitute would be. I'm pretty sure the old Tufnol sheave is a phenolic linen or cotton laminate (LE) but McMCarr does not have a exterior rated LE Garolite. So it goes. Delrin may be a good way out, though it is a lot heavier.
Thanks.

[Rico]

I found that my mast did have a few markings either from a fitting on the wire, or from the wire itself. However, this was minimal and posed no issues. Once the mast was painted, this was well hidden by the shiny paint... This sort of wear could easily have been prevented by proper stowage of lines while at the dock.

I had a suspicious look at the sheave, pin, and plate arrangement while I was renewing my mast. In the end I decided that this is a pretty simple & practical solution - considering C-155 purpose of coastal cruising and hopefully SF Bay soon... I am amazed at the great condition that the sheave is in... It seemed almost new! I think that this material is most affected by the sun, as some of the original blocks made from that same material were not nearly as nice looking, although, apparently in decent shape... These were replaced.

My biggest concern with regard to the mast was the lack of compression struts (pipes) for the two thru-bolts that hold the spreader brackets and the lower shrouds.
(-I will post my solution to this issue in the 'Mephisto Cat's" gallery page shortly)

I decided to leave the sheave alone as i think it is adequate for the 3/8" line I'm using for the halyards. If you want to go with 1/2, then you may have to modify as you describe. You may resolve the wear issue by trimming you halyard to shift the area where the line meets the sheave.

I'm convinced that a 1/2" rod/pin with threaded ends and castellated nuts plus cotter-pins be the most secure up there. IS THIS OVERKILL ?

I also considered this arrangement. I agree with you thought of the pin & nuts, but considering the function in this case, the bolt works just fine. I ended-up buying a 6" or 6.5" bolt and trimmed off the excess treaded portion...

I changed nothing more since the current set-up worked fine and suffered no ill effects for 40 years+

I have to say that I did find that the same areas you indicate had a bit of corrosion, but I definitely did not find the degree of corrosion that you describe. No goop, or other suspicious substances...

I did find the plastic isolating strip behind the mast track. This did a brilliant job in protecting the Aluminum, so I followed the thought and replaced it with two layers of UV resistant sticky vinyl material on top of the thick paint and then I installed the track with SS Rivets with a generous helping of lanocote to ensure these were as inert as possible. A random few of the original ALUMINUM rivets were badly corroded, but they held well for the length of time that they were employed against the SS track. Again, some pictures and specs of this work will be posted in my Commander's pic thread.

I ended-up painting my sheave plates to keep them nice & smooth...

How to proceed?
It depends on your intent for the boat. The dual sheaves in a box would be the most innovative convenient & durable. (The box may be necessary in this case to strenthen the mast top...) but again, this is a major mod that implies that there is a differrent intent in mind. (I think you must be headed for a world cruise!)
There may be a used mast available which is in better condition if the corrosion is as severe to impact it's integrity...

I do not think that the load on the holes in the mast is an issue at all. I found no deformation at all in mine. This is from 40 years of sailing. I am relying on the paint and some dielectric to prevent corrosion. I would stick with SS for the material for the bolt /pin.

Cheers!

A~

[ebb]

Rico,
THANKS for taking this forward.
Haven't time just now to do justice for your ideas and obs.

I will pursue the double sheave box idea with a 'doorskin' mockup.
Thanks for the 'blessing'!
Nothing like a full scale 3D model to let you know if something is feasible. -or not.
I'm not sure how easy thin sheets of aluminum (6061) can be bent like guage steel can. But if it can then the box can be fixed with screws and be removable - something that down the line would be useful. A wide box would really constrict the top of the mast. Any bearing plates could be upgraded to a 'box' form by simply bending a right angle flange into the bottom and top of the plates. That certainly would close up the hole in the inside of the mast. The box could be tabbed to the out side of the mast with small machine screws. Not so simple, if I recall, AL has to be bent with a radius to avoid stressing the metal. Also across the grain and experiencial stuff like that.

The top internal sheave system doesn't really need an internal anti-compression tube. It could be designed in but the bolt or pin would have to be enclosed in a tube. I wouldn't use stainless in that upgrade. And there are other design issues like the sheave bushing. Zero wobble has to be acheived for the wide wheel.

The spreaders is a big issue imco. There should be a tubes in both bolts. But were not put in. It seems like a pretty simple upgrade until you realize you are encapsulating the bolts. One of the spreader socket bolts on 338 was obviously 304 and rusty. The other I assume was a 316 with no rust. Both nuts came off without fuss.
655 is the obvious first choice for tube encased bolts, or titanium. Don't know. Also we have an ongoing relationship with stainless and aluminum. We know how pretty much to isolate these guys. Adding bronze to the mix might get complicated. Like a menage a trois. Don't know, but how many fools do you know that are putting bronze bolts in their masts?

I'M LISTENING TO 40 YEARS OF EXPERIENCE!

I'm extremely impressed you removed and rebedded the track. I'm going to take the Hitachi to a few of those screws and see what happens. The tag end of tape that was still tucked into the sheave slot the guy used to hold the tape as he unwound it.... is very brittle. Probably should be done. sigh

[carl291]

I'm curious, What is so detrimental about using the rope/wire halyard? Also, the rope/wire when lowered to hoist main, doesn't the rope ride in the sheave? If this halyard is not the primary main halyard,but just a spare why not run a 1/4 " line and keep the rope/ wire stored below deck and just used when necessary. It seems this would be a better alternative to a $$$$$ sheave replacement. Some of the working loads on modern 3/8ths line seems plenty strong if you went that route.But then what do I know ?? I'm just a 55 yr. old kid!! As a note, on A-259 the main sail track is secured with phillips headed SS screws. Carry on!

[ebb]

Hi Carl,
Can you imagine if the sail track was put on with slotted head screws....? Wholly Jumping Jehosephat - thank you, Phillip.

I don't know why the wire to rope halyard became unfashionable. But it did. And it caused one crazed all-rope-halyard DFO to attach that stupid stainless halyard tang with 4 miserable screws that was ready to fall off with a chunk of the mast when I actually looked at it. I really went sailing with it like that!

If you are using the sheave for what it was intended, the wire holds the load in the groove with the sail up, Correct? I'd say the wire was very happy in that sheave at that time. There's no real load when the sail is being lowered. Wouldn't matter what the rope is doing in the sheave as long as it is being guided over and not hanging up like with the splice having to pass through the top. But the sheave is a wire sheave and would be OK only for 3/16" rope, nothing larger.

To me having all fat braid is a luxury for my hands. And not having a rope to wire splice is one thing less to go wrong. 3/8" will work of course but take a look sometime and you'll probably see the line gets distorted and is not supported. Does it show any wear where it rests on the sheave with the sail up? Or do you always use the wire tail? Interesting you have that choice.

But I understand not going through the change, and keeping the original set-up happening. I do. The mast in my case needs metal work done on it... so other possibilities reared their expensive little heads.

If you're thinking to convert the existing sheave to all 3/8" line, I would go to McMCarr and get a pack of 10 1/8" Buna-N 6" double-seal O-rings(they are sort of square) for $9 and try one in the groove as a filler. 3/16" square O-ring is too much rubber, and the smaller one might actually cup when stretched in the sheave groove and fill in the deep part making 3/8" line more happy. Imco. It's an idea.


Besides these what-ifs and willy-nillys bring you sober, sensible, sailing skippers to the Forum to keep us slackers straight.
And it's whole bunch more fun than sitting in the corner over there mumbling in my beer.

[carl291]

Ebb
There have been so many modifications done to my Ariel I sometimes don't have a clue what came from the factory and what came from WM. One of the main reasons I enjoy the photos.I also own a Pearson Electra that has been in storage since 1987. This little boat has no owner mods. from what I can tell. This boat has the rope/wire halyards and the halyard uses the 3/8 line for the main and jib. The mast sheave appears to have the same groove size as the Ariel only on a smaller sheave (smaller diameter mast) Even after 20 years of no use this sheave rotates freely
My Ariel mast problems are at the base, 1 foot sawed off, the top appears to be in very good shape.
Some thing for you to consider if fabing a mast sheave box is, most tight bends are done with soft aluminum and then are heat treated for hardness after being bent and shaped. I have friends in the aviation repair industry who taught me the process. I can get you the alloy numbers if you need them and also the temperatures you need for the hardness you desire. "G'day mate"

[ebb]

Carl,
I still think you could tabernackle that spar.
Build a peg leg for it.
It doesn't HAVE to lower or raise, just make the mast usable.

You know, hopefully you still have the original casting for the mast foot.
If you don't, what the hell: 'cast' a temporary one out of fiberglass.
You got the form right there.
Put it on a pedestal. Make it so it can be changed out later -
by you or the next.... care-taker!

[carl291]

Ebb,
I had convinced myself to weld the mast back together and simply have it stepped at the boatyard every year. After joining this site and reading comments form several members I'm now convinced that my thinking was flawed and costly. Your comments about a cruiser being able to raise and lower their own spar has changed my mind. Comm. Pete photos of his mast raising with a minimum of hardware cemented the idea.
My thinking now is to anchor the 1 foot stub to the deck (cabin roof) and build a tabernacle system to raise the mast from the forward position when on the water or the hard and from the rearward position if launching from the trailer.
I do have the mast heel.
What I have to do now is find the lazyist person I know, to come up with the easiest way to do this..... LOL.

[ebb]

Carl,
Your challenge may be how to fulcrum the upper shrouds with a tall tabernackle.
With a tall tabernackle you'll be able, if you want, to lower/raise aftward.

As to the materials...what the hell do aye know....you can get 6061T6* plate from OnlineMetals or probably cheaper from McMasterCarr in about the quantity you want. 1/2 plate, say, that you can inset into each mast section end and screw into place with machine screws. Might even get fancy and do it right with a nice rebate. Like the original casting has.
*T6 is the hardness rating. I don't think that I should mess with the annealing on thin sheet (for the sheave box, say). Like how to harden it back again after bending?

I have a Buzz Ballenger stainless tabernackle for my proposed masting. Calling it a tabernackle is a stretch because it is a merely plate with the usual angled up sides with holes for turning blocks - AND a couple uprights forming a 'U' for the mast to sit between - with slots in each - welded on to the plate. No moving parts.
This is a 'Santa Cruz' tabernackle. For forward lowering the front 1/3 (for our coach-roofed boats) of the mast foot is rounded with a pin put through the mast that will follow the slot as the mast is moved. It's a totally simple right-on system with two moving parts: the bolt and the mast. Nothing moves or is hinged so far as the tabernackle itself is concerned.

That foot support in the mast bottom seems to be a problem for me at the moment because it is not a simple flat plate. I don't think I'm willing to go through a casting procedure. But I think the piece should be cut from a chunk of aluminum. Don't see how the rabbet can be done - at the moment - it ought to be done that way and without welding. I'll see what Mike and the shop might be able to do here on the estate.

If you pegged the one foot piece to a solid fabricated aluminum base on deck, then you might use this modest rounded foot idea to raise and lower at the one foot height. The reason the compromise rounded foot is used is that a hinge at the forward or aft edge of the mast-foot raises the mast too much for control because you have to loosen the uppers to get over the hump. This method allows lowering without loosening (I believe) and gives the operation a 'feel'. You are coming off a flat zone that the mast bears on, using the weight of the mast going over the mild hump or round and keeping full side control with fairly taut shrouds. Sure like to see it in action.

I brought a complicated model of a full half rounded tabernackle for Buzz to see and hopefully bless. He avoided any commentary (thankfully) and I believe he raised his eyes skyward. But he did point out that from a practical standpoint the lowering and raising would be too smooth and have no 'feel'. Not his words. But that is the idea. When upright the santa-cruz mast has its foot and is stable and supported. When lowering the mast goes trough its slight hump and is eased by the small rocker of its toe.

I'm convinced. Sure like to see it in action!

Whether this hinge idea can be adapted to a mast section is a definite challenge. There are all kind s of forces that seem to make it impossible.
If you had the santacruz gizmo at the one foot level you could be home-free.
Using the cutoff may be plain impractical. But designing a pedestal that looks right is an even bigger challenge. Aesthetics raises its medusa head.

Splicing this mast section back onto itself may just be a matter of an internal collar. Or an internal collar combined with an external one. This action is all taking place conveniently below the sail track.

Tabernackle pictures from sailing photos on webshots (google)
sports.webshots.com/photo2332182000100122919gqINRS
Good luck on this coming up. Shows a typical tall euro canal type tabernackle that might jog into a good idea.



Hey you guys , help this man out!

[ebb]

The easiest way to proceed is to renovate the sheave and side plates.
Rico painted the side plates. Use the same system as for the mast.
An oilite bushing** could be added and some polyethylene sheet washers.
But the sheave itself seems good for another 40 year.
There probably would be no dimensional changes necessary when you go with 3/8" halyard and the slightly undersized 1/2" wide Tufnol sheave.
Skippers who use line alone in the combo sheave that has a deep groove for wire rope say that the profile does not harm their line.
Gotta polish up and wax the scabacious aluminum plates befor reassembling. C'pete's post #6.

There may be a scooch more room after sanding and smoothing the old plates to put in 1/32" 6"D washers of HDPE on either side of the sheave. Imco that would insure the sheave keep turning over time - but becomes a maintenance issue - have to inspect seasonally. As it is, the slot cut-out is 3/4" wide and fits perfectly in the 3/4" wide track flat of the mast extrusion.
The slot width defines the space between the plates available for additional washer/spacers and could be carefully widened a bit with a file. The sheave has to be free turning yet snuggly supported by the side pieces.
Centering the sheave for redrilling a larger hole for the oilite bearing is an exercise in precision. It can't be offcenter. Also the new bearing would have a precise 1/2" hole for the pin that may require the more exact diameter a rod can give than your usual s.s bolt. I have found modern 316 hex bolts to be very exact. The materials are available from non-marine McMasterCarr.

I've drawings to scale of an 'up grade' - to see what changes would occur. Using 1/8" 6061T6 alloy sheet from McMC an actual box could be welded up that would house a 5/8" delrin wheel* ( 1/2" line) with 1/32" thick HDPE polyethylene sheet washers.* The box ends up being slightly wider than 15/16" and 7 3/4" OD, a bit longer than the original because adding a little to the wheel diameter so that the halyard would be 1/8" further out from the mast. That's a sheave with a D of 6 1/4" inches in the groove. 6 3/4" overall diameter. The box would have radiused ends covering the sheave. This would go a long way to keep rain-water out of the mast. The box would be inserted like the separate plates are and held in place by the sheave pin/bolt.

If I'm going time and trouble and expense of welding up a single sheave box - what does a double sheave box look like? It's the same length and 1 3/4" wide.
Couple things about a double sheave option.
The lead of the halyard from the headboard on the track to a sheave is slightly skewed to one side. Would a not-so-fair lead cause some kind of chafe? The halyard does go up to the sheave top only at a very slight angle.

Anyone's thoughts on this?
[word drowning ALERT, anybody above their eyes here should exit NOW.]

The problem is that when the main is hoisted and under load, the line will end up in the same position every time in relation to an off-center sheave and be subjected to the same high tension and any wear every time.
The double sheaves are each only slightly off center in relation to the mast track. Is it a problem?

A second consideration is that a 1 3/4" wide slot is a BIG hole in a 3 1/2" wide mast.
Convinced that the box should be removable for access into the top of the mast, it can't be welded in place. It's not that access IS needed - but what if you had to get in there and it had this implant in the way?
Yet a welded in sheave box would add greatly to mast-top strength. The slot is right there at the top where everything else is happening: upper tangs, shrouds, stays, halyard blocks, wind forces yanking on all the sails terminating there, the spinnaker, masthead crane with its furniture, etc.
It's really a hard working mast-top!
All the mast-top sheave boxes I've seen on the net recently are welded in.
Not being welding compis, an aluminum welder would have to be lured to the mast, wherever it is, and that is probably expensive

Self sez to self, that a single sheave box is probably the best way to go.
What would one have to do to have a strong backup halyard block rigged permanently up there? I suppose a block could be hung from the truck?
Seriously.

It may be possible to make a tang like the one that caused the corrosion on 338's but give it a full radius coming around from the sides of the mast - a kind of hound fitting through-bolted in the manner of the sheave and spreader fittings. Good for a block and add reinforcement to the top of a tired mast extrusion.

UHMW polyethylene is a dense low friction waxy and tough plastic used by woodworkers for jigs and fences. It isn't made as thin as HDPE, which is available in 1/32" (nor is it 'Ultra') but it ought to do well as a sort of lubrication between the flat sheave and the flat aluminum box sides.
Tufnol/Garolite is the hardest laminate made.
Our sheave which has lived neglected outside for 40 years almost looks new. If the waxy plastic doesn't appeal to you, Garolite is available in 1/32" thickness. Maybe that can be buttered with something lasting and used as the buffer in the sheave box.
There must be some non-oily lube, or DRY lube in a spray can that can be squirted in there occasionally without having to take the system apart.
If you make the sheave pin assembly easy to take apart, then it'll be easy to pull maintenance on it.
Kind of a no brainer if you will haul you and your body up and down with it.

__________________________________________________ _______________________________________________
* C'Pete gives the source for a custom delrin wheel in post #7
(Ed Louchard of Zephyrwerks says no washers are recommended - his delrin wheel is fatter at the hub and a bit thinner in the body and rim.)
**ALSO checkout cjackson's 'Hull #387 "Althea" refit' thread.
post #18 shows our old sheave refitted with a new oilite bushing.
At the end of the thread are some shots of a crazy amish mast raising party using NO ropes, NO lines, NO guys or ginpole.
Maybe big guys and beerpoles is more correct!

[Robert Lemasters]

After a couple of rounds of surgery these last three years and not sailing my Commander for two years, it is in need of some maintenance. I am looking to share my boat with another/other sailors who appreciates this boat and willing to do the work or form a group to sail it. The boat is docked at Nautical Boats here in Portsmouth, Virginia. Motor has less then ten hours on it, a Nissan five horse, four stroke and is need of maintenance. I am doing very well now but need partners keeping up this wonderful sailboat and expenses.