Spreader problem

[hellosailor]

osiris, I can appreciate a through-bolt and compression tube, as many large boats use, but suspect that on a smaller boat, built to a price as most are, the plate with sixe screws was simply less expensive than drilling, sleeving, installing a heavy $ bolt through a mast. And apparently has held up over the years.

I used to think a real racer would use titanium sporks and coffee mugs, since they were the lightest. Then I realized, if you carry tableware and coffee, obviously you're not a real racer anyhow.<G>

[Sir Rondo Normal]

Originally Posted by hellosailor

osiris, I can appreciate a through-bolt and compression tube, as many large boats use, but suspect that on a smaller boat, built to a price as most are, the plate with sixe screws was simply less expensive than drilling, sleeving, installing a heavy $ bolt through a mast. And apparently has held up over the years.

Again...

Would a thru-bolt through the mast really be necessary? There are five machine screws holding the tang in place and the load placed on them would seem to me to be only lateral. The major force exerted against the tangs would be from the spreaders being forced (mostly) directly toward and away from the mast.

Thanks

[Blue Stocking]

A compression tube transfers 1/2 approx load to the leeward side of the mast.

[Sir Rondo Normal]

Originally Posted by Blue Stocking

A compression tube transfers 1/2 approx load to the leeward side of the mast.

Thanks Blue Stocking, what is a compression tube?

[Blue Stocking]

A tube which passes thru the mast, the length of which is equal to the o/s to o/s dimension of the mast. Usually held in situ by a thru bolt and nut, which also holds the spreader fitting base plates in position.
May not be necessary in modern multi spreader masts, but is common in older aluminum and wood sticks.

[Sir Rondo Normal]

Ok I see now. Thank-you for that and pardon my ignorance and newbie-ness

I could see that a compression tube would make it stronger but still don't necessarily see how this spreader mounting/tang system is "risky".
Maybe a couple of machine screws on the bottom side of the spreaders to keep the outer plate from lifting, would help?

[osirissail]

First, measure the angle between the bottom of the spreader mount/tang where the clevis pin captures the lower shroud. Compare this to the angle of the shroud itself from the attachment point on the mast to the chain plate down on the deck.

In other words if the spreader base/tang angle is too shallow and the shroud wire makes a steeper angle away relative from the side of the mast tube - then somehow the spreader base/tang unit got "flattened" and that is why the clevis pin is up close and personal to the mast tube sidewall.

If the shroud angle matches the angle of the bent lower portion of the spreader base/tang, then the only thing I could suggest and still keep what you have is to mount a short extension "tang" that allows the shroud eye to attach further down and away from the side of the mast tube. BUT, this would also mean shortening the shrouds, etc., and all that might just not be worth the trouble. So live with what you have until something breaks.

What is the diameter of your shroud wires? If they are less than 1/4" then live with what you have. You could add the wire clamps above and below the spreader ends, but probably they are also not needed.

[SkiprJohn]

"Again...

Would a thru-bolt through the mast really be necessary? There are five machine screws holding the tang in place and the load placed on them would seem to me to be only lateral. The major force exerted against the tangs would be from the spreaders being forced (mostly) directly toward and away from the mast.

Thanks"

If it's been working ok for a long time it might not be necessary. What I see is that the force of the lower shroud on the windward side would be pulling on those machine screws with quite some force in a high wind situation to keep the mast vertical. If they seem solid then it probably isn't an issue but if there is a little bit of vertical play then it means that the holes the screws are in have started to enlarge which could mean that eventually they could pull free of the mast under the right conditions.
kind regards,

[osirissail]

Originally Posted by SkiprJohn

. . . If they seem solid then it probably isn't an issue but if there is a little bit of vertical play then it means that the holes the screws are in have started to enlarge which could mean that eventually they could pull free of the mast under the right conditions.
kind regards,

Excellent thing to examine and look for - if the spreader base/tang assembly can be wiggled up/down left/right then maybe those mounting screws are getting loose due to screw hole enlargement. Then you might look for another way of attaching the shrouds to the mast.

If the spreader base/tank plates are solid and won't move, press on and enjoy the sailing.

[Sir Rondo Normal]

Yes that makes perfect sense and now we can go back up and have a better idea what to look for and how to test.
This boat isn't just a little coastal cruiser. The boat (as old as it is) was definitely built and outfitted for offshore use and in fact has seen bluewater cruising. The rigging and sails are all heavy duty. We will only be sailing local waters for the next few years.
What my plan is for the rigging, in the short term, is to clean it up and make sure she's fit for local sailing so that we can concentrate on other aspects of the refit..
Obviously I don't want to lose my mast or suffer any other catastrophic failures in the mean time but I'd rather leave the standing rigging part of the refit until a year or two before going offshore so that we have the strongest possible rig for for as long as possible once we're gone.
I appreciate the observations, opinions and advice from all sides. I will have a local rigger inspect though, just to be sure she's up for some good fun this summer.

[chala]

I have cap on my spreaders to squeeze the relevant shroud. Normally the fitting that holds the shrouds is in two parts held with two cap screws, with one or two pilot holes. The top spreader is normally drilled with an under size drill to squeeze the cap shroud, the lower spreader pilot hole for the intermediate shroud is drilled under sized and the one for the cap drilled over sized for adjustment reason. The spreader should bisect the angle at the shroud, harder to do for the lower spreader. I definitely would no like to have my spreaders slip up or down under load.
Spreader to mast connection. It is possible that there is a pin, bolt etc to hold the tang to the mast but the spreader conceals it.

[edsailing]

I would NEVER put a clamp on the shroud under the spreader. The reason is simple - clamping the shroud stops the strands moving and can cause metal fatigue as the flexing is stopped by the clamp. How do I know? I've had a shroud fail for this reason in mid-Atlantic - I learned my lesson!

[Cheechako]

Originally Posted by Capt Wraun

Again...

Would a thru-bolt through the mast really be necessary? There are five machine screws holding the tang in place and the load placed on them would seem to me to be only lateral. The major force exerted against the tangs would be from the spreaders being forced (mostly) directly toward and away from the mast.

Thanks

I doubt you really have an issue. Boats like the Catalina 30 had an aluminum socket with 4 little screws in them. The round spreader just fits in the socket. The spreader should bisect the angle to the shroud either side at the tip. To measure this buy a "sliding bevel square" at the hardware store. real cheap. Usually even rigging tape will hold it where you want it. or the rubber boots.

[Sir Rondo Normal]

Ya I think I'm going to go sailing this weekend and record what it looks like under sail. Maybe with just the main up first, depending on the wind. Either way, I'm going sailing

Thanks everyone!

[LH44 Anne]

Originally Posted by Capt Wraun

Ok I see now. Thank-you for that and pardon my ignorance and newbie-ness

I could see that a compression tube would make it stronger but still don't necessarily see how this spreader mounting/tang system is "risky".
Maybe a couple of machine screws on the bottom side of the spreaders to keep the outer plate from lifting, would help?

Combining the tang and spreader base gives a single point of failure for both. If one goes, you've got trouble, but with quick action you might survive the break, particularly if it's not blowing a gale.

If both go at one time, you're almost certain to lose the rig (with consequential "collateral" damage: loss of a couple of sails, potential harm to crew, etc.

Adding screws below the spreader would not be a bad thing, but it is a partial, "bandaid" approach. Comment about it being a "small boat" is well and good; getting away with it for a number of years is well and good. Getting away with it probably isn't what your wife has in mind, I suspect, whether at the masthead or back on deck. Life on the edge is exciting at times, but not as a way of life.

Good engineering and construction practice is one of the many areas that separates "common boats" from "finest kind." But "you pays you money and you takes you chances."