How many chain plates ?

[baggywrinkle]

Hi Folks,

The rig that came with my boat has uppers and lowers. The uppers have spreaders, and they meet where the forestay attaches. The lowers attach just below the spreaders. Sound like a DS rig? Maybe not, as a previous owner 'souped up' the boat for racing mostly bigger boats. He said the boat is an 'improved' DS1. His modification was to stiffen the hull and rig for better performance. Success was asserted. When I asked him if it was an original DS, he said "Oh yeah, it's in there." (pics at link below).

The hull has one chainplate on each side, age unknown. I plan to replace both of them, plus the third one at the pointy end of the boat.
I have not seen the rig assembled. Do I need four chainplates for the four shrouds? The old ones have one small hole. I've seen chainplates with multiple shrouds attached. I could go with that type when replacing the old ones.

I thought both shrouds should be aft of the mast, for safety, should any fail. Bigger boats have groups of shrouds mounted parallel to the centerline, on an elongated chainplate fabrication, as well as groups mounted athwartships. I can choose whichever seems best, since planning to replace.

Your thoughts, please.? Thanks!

Pics are at link. Scroll to 5th pic for best chainplate view.
viewtopic.php?f=8&t=5641

[GreenLake]

We concluded (elsewhere) that your boat isn't a class-legal DS, but one of the "clones" that were produced to cash in on the success of the DS. While these are fairly similar to a DS there may be differences.

The DS has "diamond stays" with very short "spreaders" at the location you give, but with the stays terminating on the mast, a few feet below the forestay. These stays do not connect to the chain plates.

The general recommendation is to remove them as unnecessary, leaving the top part of the mast unstayed.

Since you say you haven't rigged the boat yet, make sure that you really have "uppers" that are full length and not simply diamond stays. The spreaders for true uppers would be about the same length as the lower spreaders, whereas the jumper struts for the diamond stays would be very short.

If your boat was an actual DS, I would not hesitate to recommend to you to forget about anything except what you call your "lowers". However, that not being the case, I don't know whether your mast profile is comparable. In any case, the first order of business would be to rig your boat fully with the parts as supplied to you.

That should tell you whether it can be rigged and make sure you didn't misidentify anything. Even better would be for you to take the boat on the water (close to shore in benign conditions, but enough wind to move the boat). That would expose any obvious weaknesses of the boat and rigging and give you a feel for how it is to be operated.

Only after that would I recommend any thoughts on modifications. (I know some people who have restored a number of different boats - I've observed that they always change their mind about modifications after they've sailed the boat for a bit, even though you might expect them to have the kind of experience that would let them plan ahead).

[baggywrinkle]

Thanks G L,
Your time and assistance is appreciated !

Yes, I have no diamonds, and yes, my uppers are uppers. My rig is configured just like this pic of DS1 #37

The #37 Pic: download/file.php?id=1241 (note the port upper is visible, but not attached to its spreader).
The #37 thread: viewtopic.php?f=1&t=5853

Such a nice restoration of #37 done by tomodda !

After viewing more posts and pics, I understand lowers are eschewed additions. With the four shrouds and just the two chainplates, I reckon the PO added the lowers for a stiffer rig, along with his hull stiffening modifications for racing bigger boats and all. I guess he had all four shrouds on the two chainplates, apparently.

'Mellow' has been relaunched. No leaks or drips. All five stays have been replaced. For now I will put the four shrouds on the two chainplates and see how I like it, before adding chainplates.

Mast stepping is scheduled for next week. Mast and sails will be measured for comparison with DS specs, (out of curiosity). They could be 'different', also for performance. Not that it matters to me, for just sailing around.

[baggywrinkle]

Ooops.....Correction:

I said: My rig is configured just like this pic of DS1 #37

I should have said:
My rig is configured just like this pic of DS1 #37, except that my rig does not have the diamond jumpers.

Furthermore, what I am calling 'uppers' do not reach the masthead on my rig.
My 'uppers' attach to the mast where the forestay/jibstay attaches.
These uppers have spreaders further down.
The lower shrouds attach just below those spreaders.

[GreenLake]

Thanks for the clarification!

So you have the standard shrouds (what you call the "uppers") with an additional set of "lowers" added.

In boats that do nor have swept spreaders, the shrouds are all "in plane". The function of lower shrouds would be to limit sideways movement at the point where they attach. Without them, a gust would push the tip of the mast leeward with the attachment point for the "uppers" being the pivot, the mast below could curve slightly to windward. With them, the mast can't move that way, but the tip still gives, so there would be a bit stronger bend.

When you have swept-back spreaders, their normal action is to push that point of the mast forward, leading to a bit of mast bend.
http://www.sailingbreezes.com/sailing_b ... ll0800.htm
As you can see from the diagram, if you increase the tension in the leech of the main you can increase the bend.

With lowers attached so that they also attach aft of the mast, you would limit that mast bend, because the lowers would have to stretch as the mast bends.

This leads to the question of whether that is both necessary and desirable in a boat like this. For the standard, class-legal DS it is certainly nothing that is recommended. Would it be needed for a different (slimmer?) mast profile? I'm not a marine architect, so I can't know for sure. However, the fact that you say that your Uppers don't read the mast head means that there's a bit of unstayed portion of the mast at the top. That means, your mast profile can't really be that much weaker, or it would snap off. If you accept that reasoning, then you might conclude that you could live without the lowers.

There are books on Yacht design, for example "Principles of Yacht Design", by Larsson and Eliasson, that explain how to dimension a mast and stays, and that might help you in understanding your particular setup. I keep repeating myself in that you probably want to make sure to first sail the boat (close to) the way it was originally rigged to get a feel for it. But also to have a baseline for any observed changes as result of later modifications.

[baggywrinkle]

Thanks for all that GL !

I will look up that book. As a kid I read Manfred Curry and raced in Indians and Hustlers, mostly. That seems probably a hundred years ago, in Quincy Mass, (Now it is MA).
When I was about six in 1954 or so, I shook hands with a veteran of the Civil War. He was old, in the back of a big ragtop in the Memorial Day parade. The last one of them died in 1956, if I recall.

/

Yes, thanks, I am at: "Just reassemble the rig as is, sail some...get a feel for it." No need to add chainplates. Later, maybe, ...or not. The do list is long enough as it is. Stepping mast soon.
Thanks again !

[GreenLake]

Good luck and lots of fun sailing and fixing up your boat!

[baggywrinkle]

Thanks !

[tomodda]

Hi Baggywrinkle!

Chiming in late here, but hope that I can shed some light. 1st, the bottom line, you don't need those lower shrouds going from the crosstrees to the forward chainplates. I took mine off after one test sail and never looked back. After a season, I removed the forward chainplates and epoxied all the holes, done.

Reasons? #1 reason is that the Daysailer was designed by Uffa Fox himself, and what's in the class rules is pretty much the original design. Why mess with perfection? #2 reason is that the lower shroud adds weight aloft, complication - it sits right in the middle of the jib "slot" and is just inviting a hung-up jib sheet, and expense, for absolutely no gain, no advantages to it. Just for completeness, let's unpack that statement, about no advantages. Shrouds are all about mast bend (if you have no shrouds, the mast bends to the water, haha!). Joking aside, you DO want some bend. The mast is designed to bend, both fore/aft and to the leeward:

- The fore/aft bend is to shape the draft (curve) of the sail, at the extreme you want the middle of the mast to go forward and the tips (mast head and deck partners) to go aft, curving your luff. Having another shroud attached to the lower third of the mast (at the crosstrees) does nothing to change the fore/aft bend, if anything it hinders bending the mid-mast forward.

- The leeward bend is your "shock absorber" for gusts and heavy wind. Normally, you do not want your upper mast bending to leeward at all, but if there is a gust, then the upper mast (above the hounds.... top attachment point of the shrouds) will fall off to leeward, automatically spilling some wind rather than overpowering the boat. What is "overpowering?" Well, that is when the boat starts heeling over more than is useful to drive the hull forward.... more sideways power than forward driving force. So does the lower shroud affect the leeward bend? Only marginally, it keeps the mid-mast around the crosstrees from bending off, but that doesn't bend off with a normal rig either - the spreaders hold it in place. Most of your lateral bend is in the top of the mast, above the hounds. Makes sense, that's where most of the gust's power is, up high! So I don't see where there's any advantage with lower shrouds for the lateral bend.

-I'm not going to explain all the physics of sailing here, but suffice to say that sailing is all about balancing forces. Analogy - playing the violin. You play louder by bowing harder (pressing the bow harder onto the strings), but if you ONLY do that then you'll get a horrendous screech. You need to balance your bowing with fretwork, your bowing angle, counterbalance with your chin, etc. Same with sailing, it's not JUST about windforce and how much sail you have up. Too much sail/force at best will result in the boat skidding across the water to leeward and at worst in a capsize. Balance... The boat is designed for a fractional rig, and to spill wind if it gets overpowered. These were the compromises made to have a boat that is both fast and family-friendly. Take a look at the THISTLE design for a counter-example. They are achingly beautiful boats, to the point that I get tears in my eyes when I'm around one (I tear up about strange things!) - 17' LOA, 6 foot beam, about the same as our boats, unballasted, fractional rig, and THREE sets of spreaders with diamond-stays. Pure racers, uncompromising. That mast will NOT bend to the lee, every ounce of power goes into the hull. What do you do in a gust? Hike Harder! Takes an agile crew, two at least, usually three. (By the way, the Thistle mast does bend fore/aft, but that's for draft). Anyway, I bring up the THISTLE specifically because that's what you do (multiple spreaders) if you want a stiff fractional rig on a 17-foot unballasted boat.

So what are the lower shrouds good for then? Well, for a larger BALLASTED (has a lead keel) boat, over 25' or so, where you'll have a taller mast than we do. If it's a masthead rig, then the side shrouds have to go all the way to the masthead as well. So you have a much larger span for the spreader/shroud combination (the shroud that goes over the end of the spreader like on our boats is called a "capshroud") and there are larger forces involved, thanks to the added height and the counterweight of the ballasted keel. You need extra help to control the side/side (lateral bend) of your rig:

Rigging

rigart2.jpg (28.81 KiB) Viewed 7914 times

Bottom line, our little Daysailers don't need that. And, as GL wrote, go for a sail with your lower shrouds rigged and then without, feel the difference. Should be none, except for less aggravation handling your jib.

P.S. Jumper stays on the Daysailer are a whole other story. Get rid of them! Reasons why are the same, they seriously screw up your mast bend. My mast would even bend FORWARDS (like an S-shape) before I quickly ditched them. I don't know who's brilliant idea those were, George O'Day maybe? He had a few design quibbles with Uffa Fox, some good ideas (the cuddy! Uffa didn't want it, George did) and some less than good (that rudder head....).

Well, thank you for reading, I hope was useful!

Tom