Commander 93 - Unholey

It sounds from the angles you are describing that perhaps you are measuring the angle between the spreader and the mast above and below the spreader. Sorry in advance if this is the wrong assumption, but those angles are pretty divergent. The angle that is supposed to be the same above and below the spreader is the angle between the spreader and the shroud.

The intent is to prevent a reaction force that attempts to push the spreader up or down, since the firmness of the connection between shroud and spreader tip is tenuous at best. It also prevents putting the spreader under bending strain, when it should be loaded only in compression. I think the angle of the spreader bracket is really only a guide to get things set up.

Example: if the spreader is set dead horizontal, the smaller angle between shroud and spreader above the spreader tends to push the spreader down. If it slips too far, the shroud goes slack with possibly disastrous results.

So lay out the geometry bases on a scale drawing or mathematical calculations taking into consideration the width at the base, height of the mast, length of the spreader and height of the spreader. For those fixed pieces of information the variable will be the angle of the spreader to the mast, which is what it is, and will NOT be the same above and below the spreader. Of course any of the above bits of data can be varied to change the outcome, but the primary ones you COULD change if you already have the boat and mast (which you do) are the length of the spreader, height of the spreaders from deck, and spreader angle.

I gather your mast is slightly different than original in at least one or 2 of above (length, width of mast section, height of spreader mount), but if it is any help, I have my rig down on various parts of my property, so I could give you the dimesions of the above if needed (such as spreader length or attachment height).

I still have one of my original spreader brackets (cracked) and a replacement that was made from non or cheap stainless about 25 or 30 years ago. Very heavy, but caused some corrosion on the mast underneath. I would like to have some new ones welded up out of heavy aluminum of the same type as the mast, and perhaps annodized, though I may make due with a set of the available aftermarket cast ones which I found online somewhere.

The spreader are just heavy round aluminum tubes Suprisingly thick walls, which turned out to be good, since one of the metal halyards has been rubbing through it for may years prior to my getting hold of her. If it had been as thin as it could have been, it surely would have worn right through.

As a non-sequitor of sorts, I exprience my first dismasting on a sailboat last year, on my brother in law's wooden catboat. It was an unstayed wooden mast of several decades vintage, glued up, but punky at the core. Very dramatic, but nobody was injured. Luckily no kids on board at the time, just 3 able and resourceful friends. We managed to retrieve it in tow to Cuttyhunk island, where it was quickly adopted by a local fisherman as a flagpole. We just wanted to avoid creating a hazard to navigation. Last time I was on the boat it was sporting a very stout metal mast, which I appreciated when reefing the big gaff sail.

And I am not really an expert, so if any other members of the group have a differing opinion, please advise.....

-Frank

Also, just noticed the above picture of Mephisto Cat. Love the Cat, but the starboard spreader is doing exactly what I was talking about in my reply, being almost horizontal. The spreaders are very strong on these boats, and the brackets are stiffer than they need to be. On some sailboats they actually have a pivot at the mast to allow the angle to adjust, but the A/C brackets angles are fixed. That is what is keeping the Mephisto Cat's rig up, but I THINK those spreaders should be pointing up several degrees more.

I will try to find a picture to save me the next thousand words. I know I have seen a diagram somewhere.

Bingo, this is what I was looking for.Attachment 7373

The associated text from the image:
<TABLE summary="Position photo and caption" cellPadding=10 width="90%" align=center><TBODY><TR><TD>FIG. 8-1 I - Spreaders should not be "cocked" or canted from each other. They should be exactly opposite each other to counteract equally the forces imparted to them. When spreaders are raked, ideally Angle "A" should be equal to Angle "B", while Angle "C" and Angle "D" must be equal.
</TD></TR></TBODY></TABLE>
<HR width="70%">and the source:
http://www.glen-l.com/free-book/rigg...ilboats-8.html

Rico, I'm glad that question is directed to you, I don't see how the angle could be the same as well, unless the shrouds were bolted to the base of the mast.

The way the angles are the same is by having the spreaders point upwards until they are the same.

Just think of the spreaders as the arms of a christian reaching upward and saying "praise the lord" or something along those lines. If the arms are pointing DOWN, then the praise is going in the direction of the other place.....and we don't want THAT.

Ahhh... Hence the discrepancy!

Yes - this is indeed a difference in the arguments... - In order to have the spreaders in absolute compression (zero bending moment) you do need to bisect the angle that the shroud makes with the spreader... This would be the ideal.

Just as 'ideally' a boat's chainplates would match the angle of the shrouds - they are often designed like that - but they rarely do...

In most production boats (just looked at some pictures of Cals, Catalinas, a Crealock, Moores, etc. ) you'll see that the spreaders are horizontal. seems Mr. Alberg and many other boat designers (likely urged on by the manufacturers...) have gone this route of horizontal spreaders. Even when the rig incorporates swept-back spreaders, they tend to stay horizontal.

The resulting bit of bending moment is simply accounted for by the spreader's resistance to bending...

My comments above assumes a spreader at 90 degs to the mast. Straight and plainly horizontal as originally produced by Pearson for the Ariel or Commander & other boats.

Frenna- If you note on the picture, the masts (The Mephisto Cat's & the other boat's) are not parallel to each other - likely due to water movement, or the boats may not be sitting perfectly on their lines (they rarely do!). It looks like the spreaders are a bit tweaked - but in reality they are straight. At least they were when I climbed up my mast for a pre-singlehanded-race inspection last weekend!

Incidentally- I hit a bird (actually the bird hit me!) and part of my incentive to climb up was to un-tweak my windex!

I do see what you mean on the photo of Mephisto Cat, the spreaders do seem perpendicular to the mast now that I am focusing on it.

I do wonder, though, if Alberg really intended them to be truly horizontal. I don't have the drawings to verify, but I would have thought one of his ilk would not have stood for such heresy, even from a paying client. Perhaps there was a bit of Pearson-eering going on, along the lines of the keel voids.

Just to verify, I did schlep up to my shed where my spreader bracket is sitting on a shelf (man, I gotta clean up that shed) and my original cast aluminum bracket is in fact made with a 2 degree pitch upward. (43 degrees above, 47 degrees below) However, my old fabricated replacement is horizontal. I even seem to recall the previous owner commenting on how that one had a bit of a "droop", which he felt it should not.

I suspect that even the 2 degree angle is less than it should be, but I have not done the math (geometry?) on it to verify.

When I get around to making new ones, I will get that right.

Also, though the spreader itself seems to be bullet proof oversized extrusion, the brackets take the real bending load, and there have been many failures of that part on these boats, suggesting that the angles should be revised for the future.
I'm not normally such a perfectionist, but when it comes to big heavy things over my head (and my crew's heads) I like to be fussy. Besides its all part of sailing lore, no?
Attachment 7376

[SIZE=2][SIZE=2]Wow looks like I've started a big discussion here. Thank you all for taking the time to discuss, Freena you've just confirmed my understanding, the angles in my initial post was the angle from the spreader to the shroud using a spreader length of 33 1/4. I consider my spreader height fixed (centre of hole is 15ft 2 inches) as there is currently a throughhole and I don't want to go and drill two more holes as I'm sure more holes in the mast reduces the structural integrity more than having spreaders at angles that don't exactly bisect. So using the following measurements:
Mast length 357.25" (29ft 9 1/4 inches)
Spreader height 182" (15ft 2 inches)
Edge of mast to centre of chainplate (at level) 37.625"
Spreader length 33.25" (plus probably about 1/4 inch of the thickness of the spreader base but I imagine the effect on the angles would be negligable)
Height of mast base in relation to the deck 21.25"
Assuming a perpendicular spreader to the mast that means that if you were to drop a plumb line from the edge of the spreader to the deck there would be about 4.375" (37.625 - 33.25) distance from where the plumb hits the deck to where it meets the centre of the hole.
Using good old trig to determine the angles between the spreader and the shroud gives about 91 degrees below the spreader and 79 degrees above the spreader. Even moving the spreader height down a foot (as I believe most of the commanders existing mast bases are) doesn't change the angles that drastically (maybe 1-2 degrees) and you're still left with a disparity in angles. Also changing the spreader length by 4-5 inches doesn't do much either (still assuming a perpendicular spreaders to the mast).
So this is where having the spreaders having a 5 degree upward angle from the horizontal starts to change it...but again not drastically enough to make the angles bisect. I've put the equation to a few physics and math forums to basically find the spreader length assuming a 5 degree upward angle and according to them changing the length by a foot doesn't change the angles that much.
So my initial conclusion was to use whatever spreader lengths were currently on the Commander, put them at perpendicular to the mast and make the angle below the spreader at 90 degrees to atleast take some of the tension off. And just looking at most sailboats out there I can easily tell that most of them aren't bisecting the angle. Given this will be a simple cruising and not pushing it hard I'm hoping the design will hold up (atleast for the year and a half that I'm on the island :) ).
But if you think I'm playing with fire I'll revise....thoughts?
[/SIZE][/SIZE]

Spreader length should not be longer than designed because they'll interfere with your foresails.

Shroud angle over the spreader should be the same above and below spreader to equalize
pressure on the spreaders, on the wire, and on the attachments.
Equal angles is so totally accepted as correct that anything else looks hokey or in need of adjustment.
Some may point out that you can't tune your rig with the angle over the spreaders not equalized.

Good luck, tho!

Ebb is right on all counts, and made it short and sweet too!

Commander 93, it seems like you are definately clear on the concept and the geometry. I agree there is no reason to compromise the mast by adding extra big holes, even though their impact that close the spreader would likely be minimal, they are still ugly holes.

The challenge you are facing is that your spreader height is a bit higher than standard (just measured mine at 14' mast base to spreader attachment centerline) and your mast is small bit shorter, but the real challenge is that the typical commander spreader does not have as much up angle as it really should, either by design or production. It works because the spreaders take it, but for no good reason.

In the older days of wood spars and spreaders it was impractical to expect the spreader to support bending loads, so they tend to be much closer to the ideal.

I will be making my new ones with equal angles too - why not?

Also, 5-7 degrees of lift, even more if necessary, seems fine to me. Expected, really.

Here is a picture of my boat in the water before I purchased her. The port spreader is up 2 degrees, the starboard is perpendicular to the mast. As you can see it is pretty darned hard to even notice it. 5, 7, even 10 degrees up would just look appropriate to my eye. Go look at some boats in the water with wooden masts and spreaders, I bet you will see what I am talking about.



Attachment 7377


Here is another web image of the ideal, and as you can see the upward angle is quite noticable, I would guess at least 7 degrees:


Attachment 7378
it came from here:
http://www.answers.com/topic/spreaders (some good text to support it)

I agree that extending the spreader length starts to interfere with the headsails, and you have to go awfully far to change the angle much.

Or to simplify, I suppose if the 2 degree original bases work, a 5 degree one should be better without the need to get TOO acurate.

Also, it is worth noting that the original spreader sockets, though cast and prone to failure eventually, are fairly hefty in proportion, and heavily through bolted across the mast, so they really can take a bit of bending load (for a while). If you were for some reason going with anything wimpier, the angles become more critical. The heavy bolting (one below, one above the spreader) is nice.

Look forward to hearing what you come up with for a spreader support, and seeing some pictures of whatever angle you decide on.

Firstly, here is a link to an old spreader socket failure discussion, complete with pictures to justify why the original pearson solution is somewhat flawed:

http://www.pearsonariel.org/discussi...-Socket-Broken

And here is a link to a viable replacement, which seems not to be the ideal angle, but is available and expedient, at $68.00 bucks a piece. Not being pre-drilled, you may be able to easily adapt it to your current mast holes. (original holes are half inch diameter)

http://www.drmarine.com/proddetail.asp?prod=P26%2D200
Used on many Pearson masts! 3"x6" Cast Aluminum

Ok this all makes sense and the thought of my spreader bases falling apart makes me extremely nervous, especially for someone who's never sailed before. I've attached an image of drawings I can up with last night. (let me know if that works)

The only thing I imagine I'll need to do now is determine the degree of the upward angle of the spreader brackets and should be good to go. My guess is 10 degrees at a minimum just based on my spreader height being a good foot heigher than most other Pearsons. Or do you think I should just drill two new holes about a foot down then determine the spreader angle from that point?

Hopefully this thing will be even stronger than the original off the line!

I don't know if the masts are EXACTLY the same on Commander and Ariel.
A-338's mast is in the driveway so I went out with a tape to add some numbers here.
The bracket holes in the mast are 4" center to center.
Don't know what happened to the brackets, but they were a mess.
The holes are indeed 1/2" as no compression tube was put in by Pearson.
It is arguable whether they are needed.
The lower hole is 13' 10" from the bottom of the mast extrusion.
Add a little more for the original maststep casting. It flanged under the mast maybe 1/4" (?not sure)
This lower bolt holds the tangs for the four lower shrouds strung on the bolt.
This bolt does a lot of work.

Can't tell if the pictured cast aluminum bracket is a replacement for the original.
Imco we ought to keep that 4" spread between the 1/2" bolts going thru the mast.

Can't make out if the bracket socket is at an angle for the spreader tubes on our boats.
If not, or if the angle is too small I might fill the socket with thickened epoxy,
let it set and then redrill the hole at the correct angle.

Imco the bracket base should fit the radius of the mast, It should be a match so that
water and dirt doesn't get behind the sealant/caulk and a plastic membrane that should also be included.

My original cast brackets were also cracked. The lower holes in the mast slightly egg shaped.
I believe this happened beause the lower 1/2" bolt is being pulled down by the shrouds. This may have actually pulled the bracket apart!
Being a purist, my solution would be to put the lower bolt in a compression TUBE and have that tube drilled exactly to size thru the mast. It would provide a larger bearing surface in the hole. That tube is more "quiet" than the bolt that goes thru it.
And also allows better loading of the tangs on the bolt. You could actually tighten the nut on the bolt without fear of distorting the mast.
In case there is any confusion, the compression tube is flush with the outside surface of the mast. There have been guys on forums trying to figure out how to squirrel the tube up inside the mast!

RICO has beautiful close-ups of this upgrade on his Gallery thread.
RICO is a genius and does everthing right!!!!

On page 146 in the Association Manual there is a line drawing of Ariel sail dimensions.
There is a schematic of the mast next to it showing one spreader that looks like spreader position splits the shroud angle. J.L.Lee has signed the drawing.
Could take a school protractor and get the angle.

I think using a 10 degree upward from horizontal angle gives 89 degrees above and 91 degrees below (very rough estimate). This is very rough math and I imagine there's a few variables I'm not considering that may make this even out so I imagine that 10 degrees is the magic number. Time to get these puppies made!

Thank you all again for your help! Saved me a ton of time!

I checked out your drawing. Looks about right, but I might suggest the following adjustments:

The socket tube is a bit thin on your drawing. Original is solid 3/16", but then again it is a fragile casting. Good quality extrusion might do with less.

It looks like you are indicating a 3/8" diameter hole through the socket and spreader to make a connection. The original does have a small pin to keep the spreader from falling out, but it is tiny. 1/8" is all. Some kind of tinky metal pin drifted in with friction if I recall. I would not be tempted to drill a big hole, since there should normally be quite a bit of pressure holding the spreader tube into the socket anyway. Its really just to help with mast stepping etc.

Double check your spreader tube and socket tube diameters. If somebody is welding it up, you should be able to find available sizes that nest nicely.

Another thing to consider in that selection is the availability of a fitting for the shroud end of the spreader. Original is a casting that sits inside the spreader and has a groove to receive the shroud and a couple holes for seizing wire. If you can find a readily available fitting online that fits a certain size tube, that would be a good guide.

And yes, the spreader base should fit well to the mast. If your mast has much curvature as the originals do, it will be necessary to accomodate that in the design or find a way to add something underneath, which I would discourage. Perhaps the base plate could be formed into the desired radius before attaching the socket tube, or ground out afterwards.

So much effort for one little part, to be sure, but I suppose we all hope to be able to get our cash back on these thought investments when the weather is stinky and are we are not frantic with fear of the rig coming down!

Or so we hope......