rotating mast stay attachment [Archive]

bob the builder

11-17-2009, 07:09 AM

hi all

need thoughts from you all.

want a rotating wing mast on my catamaran.

going to use this section with a single diamond.

http://www.boatdesign.net/forums/attachments/design-software/37445d1258459426-anybody-good-delftship-image1.png

20 x 9.5 cm, 3.8kg/m, Ix 1.4, Iy 6 (10^6mm^4)

3 x 8mm wire stays, 50m2 sail area. 13m long, boom attaches 2.1m above the deck

http://www.allyachtspars.com.au/catalogue/A1_Masts.pdf

going to sit the base on a tapered roller bearing in custom housing.

the point is to make a FREELY rotating mast (no mast spanners etc, may even drop the gooseneck and use some sort of vice, so when the boom moves it turns the mast as well.)

the question is the attachment system for the 3 stays

i'd like something that lets the wind turn the mast easily.

don't mind going custom. just whatever works.

ideas anybody?

onya,
mal.

farjoe

11-17-2009, 07:30 AM

My rotating 10m mast has a bearing placed at about 1/3 the distance from front to back. In theory the further forward you can place it the easier it will rotate.

The take off for the shrouds is a single point positioned at the front of the mast.

bob the builder

11-17-2009, 07:37 AM

thanks farjoe.

whats the single point look like? ball tang?

does it rotate easily? or do you have to do it yourself? how much sail are you carrying?

mal.

gggGuest

11-17-2009, 11:18 AM

the point is to make a FREELY rotating mast (no mast spanners etc, may even drop the gooseneck and use some sort of vice, so when the boom moves it turns the mast as well.
Are youaware that such an arrangement rather defeats the object of the section? The idea of the aerofoil sections is that the flow across the leeward size of the mast is even between spar and sail, so that the mast acts as part of the sail, hence the spanner to keep the angle between mast and sail correct...

If the mast doesn't "over-rotate", as its called, then a conventional round tube is probably better.

farjoe

11-17-2009, 01:09 PM

thanks farjoe.

whats the single point look like? ball tang?

does it rotate easily? or do you have to do it yourself? how much sail are you carrying?

mal.

believe it or not it is an adapted fitting from a Hobie 16 which has been reshaped to fit my mast. The main difference is that the pop rivets have been increased in size to 6mm or whatever is the nearest Imperial size. The single point take off has been beeefed up with 2mm SS plates on either side of the hole. This was done primarily to increase the working surface of the hole which has to take a hefty 10mm shackle. The forestay, 2 shrouds and 2 running backstays all fit into this one shackle. Initially i was wary about this arrangement but it has held up for the past 13 years so it has proved itself. I have about 23 sq m mainsail area.

I don't agree with fitting the boom solidly to the mast for the reasons gggGuest mentioned. On the other hand you will need a system to control rotation but also to stop the mast from rotating unnecessarily while moored.

Gary Baigent

11-17-2009, 04:48 PM

Nothing wrong with the boom being attached to mast trailing edge - and if the main sheeting system is aligned a little further forward of the boom/clew position, it helps to push the mast round to an over rotated position - which is what you are going to have to do anyway. There is no point in having a wing section that only rotates to be inline with the airflow, that is only slightly better than an old world fixed mast.

Munter

11-17-2009, 09:28 PM

And for convenience, have the mast adjustment controlled via a line to the boom so that it is automatically adjusted when the boom is moved. Have a look at NS14 set-ups for ideas.

bob the builder

11-18-2009, 09:09 AM

weird you should say that, i was just looking at them

fruity goodness.

points i've not come across

1/ i was not aware of forced over rotation. was expecting the mast to position itself perfectly in the direction of the apparent wind
2/ at the marina etc
3/ main sheeting system aligned a little further forward of the boom/clew position

thanks guys

"If the mast is rotated to its optimum aerodynamic position then it will be pointing approximately in the direction of the apparent wind"
http://sailns14.org/tech.aspx (Bethwaite disciples)

so, i was hoping that if the bearing is all the way foreward, then the mast would naturally set itself in the perfect position.

options so far;

1/
leave the mast to set its' own direction, leave the boom on a gooseneck, and use the traveler only.

2/
if i use mast spanners, this implies the normal ball and cup

(which i don't want to use because i've read stories about them having to be replaced after only a year or two. i want to go cruising for a decade at least without touching the mast)

3/
main sheeting system aligned a little further forward of the boom/clew position, (so as to over rotate further than the apparent wind direction)

( so, leave the mast to set its' own direction, leave the boom on a gooseneck, and have a double sheet on the main )
(i like this)

4/
use rope and cleats to hold the mast in the best position (so as to over rotate further than the apparent wind direction)

5/
set the bearing position at some percentage, say all the way forwards, so that the mast naturally aligns itself in the best aerodynamic position

6/
NS14 lever arm thingy

Attachment options (please add your thoughts!

1/ use a single 10mm shackle to attach all 3 (?(!)) stays to?

2/ hook and ring (though i haven't seen this for any larger boats, only small guys.

http://www.landenberger-onedesign.com/IMG/jpg/IMG_0011.jpg

http://www.landenberger-onedesign.com/IMG/jpg/IMG_0008.jpg

Gary Baigent

11-18-2009, 03:52 PM

You need also to use a ball and cup, plus mast spanner rotation lines - in a seaway, without spanner cleated, the mast will flap, last thing you want. On ball/socket, no problem, made of wood, then epoxied with glue/glass fibre combination coating - will last for decades, wears itself in - but periodically you need to waterproof grease the bearing surfaces.

Munter

11-19-2009, 09:42 PM

Unless you're going for a really long chord section I think you can assume that the aerodynamic forces onto the wing mast will be consistently overpowered by the forces applied by the gooseneck and battens meaning that you will need a way to control the mast position rather than just leaving it free to rotate. Playing with the fore/aft sheeting angle of the mainsheet may appear to help but will not act consistently across the full range of mainsail movement. I recommend sticking with a tried and tested set up such as a control spanner.

bob the builder

11-20-2009, 02:00 AM

Gary
mast flapping - good call

Munter
consistently overpowered - yeah

you've both changed my thinking. thanks

what about having a lever arm/spanner thing on the bottom of the mast (say 12" long) and attach a small block and cam cleat to either side?

i guess the stay attachment is no longer important, as i was looking for a freely turning attachment. so just get anything?

brian eiland

11-20-2009, 10:11 AM

bob the builder

11-21-2009, 01:24 AM

thanks brian

.

gonzo

11-21-2009, 09:34 AM

When I raced Penguins, some had rotating masts. The forestay and shrouds were all attached to the forward face of the mast. The boom had a yoke that allowed it to tilt up and down but would turn the mast which had flats on the sides.

rwatson

11-23-2009, 04:06 AM

I have sailed a couple of cats, Tornado and Hobie etc that had the 3 shrouds attached to the one point on the front of the mast.

I found it hampered the mast rotation considerably, making it difficult to trim the mast.

On my next project I am taking all the shrouds/stays to the top, and organising a rotating fixture in line with the bottom pivot, to make things betterer.

Munter

11-23-2009, 08:46 PM

Thats strange Rwatson - I've never found that style of attachment a problem. Perhaps it comes about because on the cats you mention there is no effective boom vang resulting in little forward force on the mast to rotate it? On northies there isn't a problem with getting enough rotation, rather there is sometimes a problem rotating from one side to the other because the rotation is forced in by the boom.

rwatson

11-24-2009, 03:45 AM

From memory my problem was caused by two things.

The padeye in the mast was verticle and half round, and the shackles in the eyes at the ends of the stays had to conform to whatever "lay" they could find in the limited space. Ideally, the shackles should be at right angles to the stay direction to reduce the friction, but they ended up twisted and pressured at whatever angle they found themselves in. The forestay shackle invariably lay horizontally on top of the other ones, which should have acted like a hinge, but it didnt seem to help much.

The other problem was that the "line of rotation" through the mast went from a rotating point about half way along the mast chord at the base, to just in front of the mast where the eye was fastened. The forestay (correctly tensioned and mounted on top of the other fittings) pulled the mast padeye firmly forward like a ring through the nose of a bull, and made it really hard to deviate the mast from straight ahead, mast spanner or no. Likewise, the side stays (correctly tensioned) fought each other to grab the mast eye from either side with the leverage thay had on the bottom of the mast padeye.

The answer would be a more efficient fastening on the mast I am sure, but I havnt nutted that one out yet.

I have a poor picture of a carbon fibre rotating mast off someone elses cat that illustrates the problem that I took to see what I was doing wrong. As far as I can see, they had exactly the same problem made worse by double stays (less room for shackles).

If anyone has a solution to the problem, that would be great. There is obviously a trick to it as there are a lot of boats using the method.

brian eiland

11-24-2009, 11:18 AM

This is one small catamaran that I know of that uses this two-hole hound tang. ...and it is really needed here as the Dart has no boom... to forced any rotation

Earl Boebert

11-24-2009, 04:32 PM

Well, here's how L. Francis Herreshoff did it in 1924 in his radical R boat "Live Yankee."

Cheers,

Earl

rwatson

11-25-2009, 04:06 AM

All of those drawings have me puzzled, Hereshoffs most of all. In the close up of the side stay attachment, the stays appear bolted to their respective sides of the mast, while the forestay hangs out on an arm which increases its leverage. Sure the jib halyard is rotatable, but I just cant see it helping the mast rotate.

The two pictures from the Dart cat, show two different methods. The first has the side stays fastened out in front, while the forestay is sensibly mounted close to the mast. This looks the most promising, but surely when the mast rotates, funny things happen to the side stays ?

The second Dart illustration looks like the system I encountered, with all the wires hung from one shackle. That shackle was mounted with the shacklepin inside the mast tang, so that the tang has to fight the squareness of the shackle pin and the pin hole reinforcing. Instinctively,I would have mounted it so that the round side of the shackle was inside the tang, giving some kind of pivot point.

I can see I am going to have to set up one of the old masts in the backyard and do a few experiments.

brian eiland

11-25-2009, 12:21 PM

All of those drawings have me puzzled...

The two pictures from the Dart cat, show two different methods. The first has the side stays fastened out in front, while the forestay is sensibly mounted close to the mast. This looks the most promising, but surely when the mast rotates, funny things happen to the side stays ?

The second Dart illustration looks like the system I encountered, with all the wires hung from one shackle. That shackle was mounted with the shacklepin inside the mast tang, so that the tang has to fight the squareness of the shackle pin and the pin hole reinforcing. Instinctively,I would have mounted it so that the round side of the shackle was inside the tang, giving some kind of pivot point.
The confusing aspect of the Dart dwgs is the second one with 4 wires attached is actually the two side shrouds and two trapeze wires. The forestay is not shown in this dwg, and would attach to that lower empty hole that is closer to the center of rotation of the mast...thus less leverage.

In the early days of the big French multihull building programs there were a few of those big rotating mast held up with rigging attached similar to Hereshoffs as they were concerned with the strength of the materials available at the time to carry the loads while projecting out from the mast.

Gary Baigent

11-25-2009, 04:27 PM

Cant the mast - then, if your mast won't rotate, ease the leeward shroud, mast rotates. On a decent sized chord wing mast, a tight leeward shroud will tighten across the leeward curve of the larger mast, cant the mast by tightening the windward shroud, slacken leeward (otherwise you can't cant, (poetic eh?) - but on a smaller, non canting, tear dropped shape mast, I can't see why you're having problems - except that perhaps you've set your shrouds up too tight. IMO the hounds fitting has to project at least three fingers width from mast, with shrouds and forestay attached by shackle to the hounds.
I remember Allan-Williams designed 2 metre chord wing mast on 60 foot Steinlager, had shrouds attached at the mast's widest beam point - bloody mast wouldn't rotate properly - couldn't even winch it round to over rotated position. Same with Barker's 57 foot Sundreamer when she was first launched.
Setting a rotating gantry-type system at mast top is asking for trouble, bad compression loads plus the swivel? point, a small thing, is taking these point loads and is unable to dissipate them, unlike a hounds fitting with uni directional carbon fibres running up and around the mast over a large area. Also it's weight at the highest point.

bob the builder

11-30-2009, 04:34 AM

"bloody mast wouldn't rotate properly"

i think the best idea so far is

normal hound
a shackle, then a chain link
maybe even a shackle afterwards

have to rotate easily with this

mal
.

capt vimes

11-30-2009, 04:50 AM

Well, here's how L. Francis Herreshoff did it in 1924 in his radical R boat "Live Yankee."

Cheers,

Earl

now thats a funny idea... ;)
how do you trim those sails?
they are 3 dimensional with 2 seets of canvas forming an triangle like shape and building an almost proper wing-shape with the mast...
the leeward part will flex but how should the windward part be 'compressed'... it will have a smaller chord... flapping loosely?

@rwatson
this mast will rotate... and since the sails are that strange - there is no need for overrotating it...

brian eiland

11-30-2009, 01:00 PM

Well, here's how L. Francis Herreshoff did it in 1924 in his radical R boat "Live Yankee."
Cheers,
Earl
What forward thinking fellows these Herreshoff guys were :cool:

Earl Boebert

11-30-2009, 01:32 PM

You should see the rest of the boat :-) The hull was built like an airplane fuselage, with formers, stringers, and and thin wooden skin. There was no rudder as we know it -- the after part of the fin was flexible and moved like a flipper. I must have stared at the plans for an hour at Mystic and still went home puzzled until I found a New Yorker article that said the rear of the fin flexed.

It was the fastest and most expensive R boat ever built, and killed the class in Marblehead. True to form, the NYYC banned most of its features, describing them (IIRC) as "rotating masts, double-luffed sails, and similar contrivances."

Cheers,

Earl

brian eiland

11-30-2009, 05:55 PM

They banned his father's catamaran as well...

"I can with a good whole-sail breeze, boat to windward faster, by a mile an hour at least, than any other sailing vessel afloat." -Nathanael Herreshoff , the infamous yacht designer speaking of his revolutionary 25' catamaran design, Amaryllis .....the year, 1876

http://www.runningtideyachts.com/archives/amarylis.html

http://www.boatdesign.net/forums/multihulls/herreshoffs-catamaran-reasoning-5843.html

rwatson

12-04-2009, 06:06 PM

Cant the mast - then, if your mast won't rotate, ease the leeward shroud, mast rotates. On a decent sized chord wing mast, a tight leeward shroud will tighten across the leeward curve of the larger mast, cant the mast by tightening the windward shroud, slacken leeward (otherwise you can't cant, (poetic eh?) - .

Oh yes, with sloppy shrouds, it works a treat.

I dont think 'easing a shroud' is a viable solution. You cant set a mast up with sloppy shrouds, its a formulae for mast and gear failure.

Setting a rotating gantry-type system at mast top is asking for trouble, bad compression loads plus the swivel? point, a small thing

On some big boats, thats true. I am only talking a 28ft trailer sailer, where the tip of the mast is the same size as the rest of the mast. We are only talking about moving any fittings a metre further up, and I figure I can use less shackles with a custom fitting, thereby reducing weight.

I anticipate using cross-trees and mast stays to remove the bend in the centre of a mast, like many cats do.

Should be ok ????

Gary Baigent

12-04-2009, 09:05 PM

It's simple enough RWatson, don't grind you shrouds up until they twing, just to tight, then if you're worrying about headsail luff sag, put some runners on - runners do a better job than uptight shrouds any day. Stop thinking like a fixed rig keelboater.

jfranta

12-07-2009, 01:32 PM

hi all

the question is the attachment system for the 3 stays

i'd like something that lets the wind turn the mast easily.

don't mind going custom. just whatever works.

ideas anybody?

onya,
mal.

IMO, this is a great way to attach shrouds to a rotating mast. Blocks mounted just forward of the chord, allyacht spars does this for Corsair on the C37 and sells the brackets needed. Connections can be very close to the center of rotation of the mast. The second best, imo, is thru bolted mast brackets (double tangs) on the chord. The 2 methods above will minimize chafe issues at the mast while attaching at the foestay shackle, while a lighter option, oftentimes results in contact with the mast on the shroud.

John Franta, Colligo Marine

rwatson

12-08-2009, 03:47 AM

If you get a chance John any more detail, or links to diagrams or pictures, on those methods would be very much appreciated.

brian eiland

12-09-2009, 11:56 AM

Mast Tang for Rotating Mast

Many smaller cats with rotating spars simply shackled all three (forestay & two shrouds) all together onto one tang.

I preferred to provide two separate attachment holes on the mast tang. The forestay was attached to a point that was closer to the face of the mast while the shrouds attached further out. This promoted a greater leverage by the windward shroud to firmly rotate the mast, since the forestay already had a greater angle and leverage, and would resist the rotation. This two hole arrangement necessitated the forestay hole as the lower of the two holes. (got an old drawing for my Firefly tri if I can find it)

I always found it was easier to put a rotation limiter at the base of the mast, rather than a rotation inducer.
http://www.boatdesign.net/forums/multihulls/headstay-attachment-rotating-mast-16117.html
I had occasion to rumage around an old cedar chest and found a few sketches from my old Firefly Trimaran project (http://www.runningtideyachts.com/trimaran/). So here I post the tang sketch and a couple for the mast base casting.

Note that the mast rotates on a graphiite reinfoced nylon ball. Its rotation center was placed more reward of the mast centerline so that upon rotation the trailing edge of the mast did not act to close off the slot between the main and jib sails. This casting also was designed to provide a pivot point(hinge) for rasing the mast from horizontal layout forward of the ball (mast laid out in front of boat and pivoted up from there.

This boat was also boomless so there existed no pressure by the boon to induce rotation of the mast...all the more reason to insure rotation and then limit it by a limiter. The traveler for this boomless mainsail was circular to prevent flattening of the mainsail as the traveler was let out to its extremes.

rwatson

12-10-2009, 10:27 PM

Thats looking a bit more like someone meant it to work!

The idea of the mast stays pulling the mast in the right direction seems to be a common theme in serious schemes.

I am a bit wary of systems that require the 'right' tensioning of the side stays - it complicates setup for a trailerable boat, and really shouldnt be required for a well engineered solution.

The forestay is still a problem, even though it is closer to the mast.

Thanks for that insight, it is very interesting