Confessional: admit to boat-related things you've never quite understood...

[Kelpie]

Our Graduate has a cunningham and a sliding gooseneck. So obviously not mutually exclusive.
The cunningham is set up on a 2:1 purchase with fine control possible; the halyard is just cleated. So I think the difference is that the cunningham can be tweaked much more easily whilst sailing. Makes sense as there is less friction and less rope to stretch.

 

[nigelmercier]

I just added this to get to 300 ...

Not bad for a thread started by a dead cartoon dog.

 

[dancrane]

Not bad for a thread started by a dead cartoon dog.

Ouch! I heard that. Not funny. Not funny!

 

[nigelmercier]

Ouch! I heard that. Not funny. Not funny!

I know, it's terrible news. Have you signed the petition?

 

[dancrane]

No, I just made a bitter contribution to the thread about him in The Lounge: http://www.ybw.com/forums/showthread.php?379550-Bring-back-Brian!

When you think what an imbalance of dullness & stupidity there is in that family without the dog (whatever his faults), it's hard to understand why MacFarlane made that decision.

 

[winsbury]

Our Graduate has a cunningham and a sliding gooseneck. So obviously not mutually exclusive.
The cunningham is set up on a 2:1 purchase with fine control possible; the halyard is just cleated. So I think the difference is that the cunningham can be tweaked much more easily whilst sailing. Makes sense as there is less friction and less rope to stretch.

Yes its an adjustable trim setting; nowadays sail-makers cut their fails quite full and hence massive luff tension is not required to set them correctly contrary to observed behavior of many crew as they winch the last inch of slack from the luff causing horrible creases in the fabric and stretching the luff. Instead the cunningham can be used to increase luff tension as desired to adjust the sail shape in much the same way as the backstay, ie it increases the mast precurve hence opens the leech and moves the belly of sail.

 

[MCL]

Some open 60s have 2 massive poles (spars?} sticking out the side at a 45 degree(ish) angle look like they support the rigging in some way. What are they for?

 

[dancrane]

Surely those spars are to catch their supper?

View attachment 37541

I'll get my coat.

 

[Kelpie]

Some open 60s have 2 massive poles (spars?} sticking out the side at a 45 degree(ish) angle look like they support the rigging in some way. What are they for?

Widens the base over which the shrouds support the mast, giving a stronger rig.

 

[john_morris_uk]

Widens the base over which the shrouds support the mast, giving a stronger rig.

I think you'll find its about giving a 'forward and outboard' point to sheet the reaching gennikers from as I believe they try to design the Open 60's so that the can be gybed without the runners and all the ones I've seen have shrouds to the deck.

 

[dancrane]

Here's a confession of awful ignorance...

...my boat came with a perfectly serviceable spinnaker, pole, connections, halyard and sheets, but I haven't dared hoist it yet with SWMBO as my crew.

There is a pair of little blocks, probably 25mm dia sheaves, tied to my rear deck...you can just about see them if you click the image to enlarge it:

View attachment 37543

...are they for spinnaker sheets, or for some obscure running backstay arrangement? Singlehanding, I could probably own & sail her for some years without needing to find out...

 

[Simondjuk]

Some open 60s have 2 massive poles (spars?} sticking out the side at a 45 degree(ish) angle look like they support the rigging in some way. What are they for?

The Open 60s with outriggers have spreaderless rigs. The shrouds, usually made of PBO, Vectran or similar rather than wire, run from the masthead and another one or two points further down the mast to the outboard end of the outriggers, which are then tied down to a toggle on the toerail with a pretty massive stay and bottlescrew. There are also fore and aft running guys from the outboard end of each outrigger. The inboard end of the outrigger mounts into a bracket on the mast step at deck level. Conventional forestays and running backstays and checkstays complete the rig.

The set up reduces windage and weight aloft, allows the sails to be eased further when running with no swept spreaders to ruin sail shape and cause chafe. The main feature however is that the mast can be rotated to maximise the efficiency of the sail.

 

[Kelpie]

Dan,
I would guess they are for the spinny sheets.
When I got my first boat (race rigged Wayfarer) I just used to assume that anything that didn't have an obvious purpose was attributable to the spinnaker. It turned out to be true, most of the time.

 

[vyv_cox]

Here's a confession of awful ignorance...

...my boat came with a perfectly serviceable spinnaker, pole, connections, halyard and sheets, but I haven't dared hoist it yet with SWMBO as my crew.

There is a pair of little blocks, probably 25mm dia sheaves, tied to my rear deck...you can just about see them if you click the image to enlarge it:

...are they for spinnaker sheets, or for some obscure running backstay arrangement? Singlehanding, I could probably own & sail her for some years without needing to find out...

I have two blocks in a very similar position for my spinnaker sheets. We use a lazy guy system, which means that the blocks for the guys are midships, lines going aft to the genoa winches, and the sheets come forward from those sheet blocks to their own winches.

 

[dancrane]

We use a lazy guy system, which means that the blocks for the guys are midships, lines going aft to the genoa winches, and the sheets come forward from those sheet blocks to their own winches.

I see, I think. I also have toe-stubbing cam-cleats on the cockpit floor which could grab a line from the rear deck-blocks if they rubbed over the top of the rear cockpit bulwark...

...but I expect that's their purpose. It'll be quite a cluttered foot-well! I begin to understand how purely performance-minded my boat's earlier keepers were.

I just used to assume that anything that didn't have an obvious purpose was attributable to the spinnaker. It turned out to be true...

Oh, I like that! :encouragement: Henceforth, whenever there's a domestic issue, I'll just say that SWMBO's in one of her 'spinnaker moods'.

 

[Thistle]

How does a fore-and-aft sail work?

I find I can't believe the line about it being like an aircraft wing with higher wind speed and hence lower pressure on one side: it's only a fraction of a millimetre thick so the difference between opposite sides of the sail should be tiny. And if it were down to the slot between jib and main speeding up the wind then my Laser with just one sail wouldn't move at all.

So what's the real answer?

What about air being pushed astern off the sail exerting an equal an opposite force pushing the sail forward?

 

[Buck Turgidson]

How does a fore-and-aft sail work?

I find I can't believe the line about it being like an aircraft wing with higher wind speed and hence lower pressure on one side: it's only a fraction of a millimetre thick so the difference between opposite sides of the sail should be tiny. And if it were down to the slot between jib and main speeding up the wind then my Laser with just one sail wouldn't move at all.

So what's the real answer?

What about air being pushed astern off the sail exerting an equal an opposite force pushing the sail forward?

Have a look at this: http://syr.stanford.edu/SAILFLOW.HTM

 

[boguing]

I find I can't believe the line about it being like an aircraft wing

Wings need a certain amount of stiffness, which is governed by thickness. As materials have and will improve, so wings get thinner. Up to a point.

Thicker sails would be good.

'Double luff' sails are not allowed in normal racing. The result of which is that racers can't have them, so won't stump up the bleeding edge pricing, and cruisers (other than AeroRig types) don't get to reap the benefits.

 

[Buck Turgidson]

Wings need a certain amount of stiffness, which is governed by thickness. As materials have and will improve, so wings get thinner. Up to a point.

Thicker sails would be good.

'Double luff' sails are not allowed in normal racing. The result of which is that racers can't have them, so won't stump up the bleeding edge pricing, and cruisers (other than AeroRig types) don't get to reap the benefits.

 

[JumbleDuck]

I find I can't believe the line about it being like an aircraft wing with higher wind speed and hence lower pressure on one side: it's only a fraction of a millimetre thick so the difference between opposite sides of the sail should be tiny.

If the sail wasn't there the air wouldn't be flowing in curves round it and it's flow in these curves which produces the force. even though the two sides of the sail are very close together, the flow on the two sides is very different.

What about air being pushed astern off the sail exerting an equal an opposite force pushing the sail forward?

Yup, that's a perfectly acceptable model too. In fact, you have to use it in some cases. The force on the sail comes from two effects: pressure differences in the airflow and momentum transfer of the airflow. Right at the surface of the sail, pressure is all that matters because there is no momentum transfer through the sail (unless it leaks). Far away from the sail (ten or more foot lengths away) the pressure variations induced are minimal and so all the force is accounted for by changes in the bulk air flow.

In between it's a mixture; one foot length (chord) away the two effects are roughly equal in magnitude.

You see a lot of nonsense around about "Bernouill doesn't explain lift". These claims invariably come from people who either don't understand Bernouilli's theorem or who misapply it, usually by neglecting momentum changes.