Monohull wing mast

[capt vimes]

thank you gary!
i thought so...

the problem i have is, that you should see the winches and blocks somewhere on the mast, shouldn't you?
and the images from the here mentioned kuka light made me think, because i could not make out any winches on the mast i.e.
(see post below....)

 

[capt vimes]

here are the images:
on the first image i cannot make out any 'appendages' to tend to the lines...
on the second you may recognize that there is a sort of block arrangement at the mast, giving the lines running from it a certain amount of 'slack'...

i mean - kuka is a 12 m boat...
nobody can tell me that one sets a sail on a boat this size without winches and by muscles/weight alone?

 

[Gary Baigent]

Actually Capn, there is a way to run halyards back to cockpit but it means they have to run through the centre of the mast and the centre of the rotation bearings (a tricky job because the hole is exactly where the compression loads are highest plus it is cramped - then to turning blocks below deck and back aft.
It is far simpler to mount your winches at mast bottom and cleat/jamb off just above.

 

[Eric Sponberg]

On my free-standing wingmasts, I have a stubmast in the boat that extends from just above the keel and up through and above the deck about 10% of mast height. This stubmast has two large bearings on it, one at the top, one at deck level on a pretty massive foundation. The wingmast slips over the stubmast and its bearings. Halyards, other running rigging such as it may be, and the electrical cables come down the wingmast and through the center of the stubmast. The electrical cable harness comes out the bottom of the stubmast inside the boat. In some installations, the running rigging comes out through the foundation just above the deck and runs back to the cockpit. The stubmast is sealed at deck level so that no water can get through, and there is a pipe conduit for the electrical cable harness to pass through, but otherwise the mast is sealed. In other installations, the running rigging also comes out the bottom of the stubmast and the lines are led back through the interior up under the deck at the shear and head back to the cockpit. In this latter installation, there are more turns to make through various blocks and so the friction is greater.

In either installation, there is enough length in the running rigging, situated very close to the rotation centerline, that allows 360° rotation of the wingmast.

Eric

 

[mselle]

Wingmast positioning

May I ask the profs around to leave a comment or two about the placement of the mast in relation to the Cg or what ever it is depending on.

Cheers, Marco.

 

[Eric Sponberg]

May I ask the profs around to leave a comment or two about the placement of the mast in relation to the Cg or what ever it is depending on.

Cheers, Marco.

The weight of the mast is taken as a known weight the same way as any other element in the boat, and as in any other sailboat. It is a very important weight, and since a sailboat by definition needs at least one mast, there is not too much you can do about it other than to make the mast and rig as light as possible consistent with strength and stiffness.

In general, when I conceive of a boat design, I have in mind its general hull form and its general rig layout at the beginning. I also begin with a weight budget, meaning that I have a target displacement in mind, and certain percentages of the total are divided up into the different categories such as hull structure, deck structure, interior joinery and fixed outfit, the rig, electrical and plumbing, ballast, etc. As each part of the boat comes into focus, the weights and their centers also get defined in increasing detail. These weights, as they are defined, take up their portion of their own segment budgets. If a mast weight is getting too high, then I either have to reapportion weight from another category to allow for the increased weight, or I have to do something to the design to reduce the weight of the mast. I can't do too much about mast placement fore-and-aft as that has been defined by the concept of the boat--is it going to be a sloop, ketch, cat-ketch, or schooner??? That comes at the beginning. I can move the mast some millimeters one way or another perhaps to fit in with the rest of the elements of the boat, usually defined by the CLP or the interior arrangement. There is not too much that causes me to move the mast as a result of its weight. It's got to be there, so I live with it. At the same time, if I am designing a cat ketch, I am aware that the forward mast is pretty far forward, and so I should have a hull form that will support that weight. That means that the mast should not be too far forward, and also that the buoyancy at the waterline and the reserve buoyancy above the waterline forward should be sufficient to support the weight, consistent with other good features of making the boat sail well. I don't want the bow to be too blunt, but still be fine enough to be a respectable sailer.

I hope that clarifies matters.

Eric

 

[mselle]

Thanks Eric for a very elaborate post. But I'm still
As I understand it right, the position of the mast is foremost depending on the design/concept. If the NA set the mast at its position the boat has to be designed "around" it. The further forward the mast the wider the hull in the front to gain boyancy. Does it mean that a boat with standing rigg can't be converted to a cat rigged one?
I just happen to find a sailboat that sports both versions of rigging. Is this balanced by a different placement of the keel?

Is the load on the mast foot of a cat rigg much higher than the load of a standing rigg? I could imaging that the wires distribute some of the load.

One more question: Is the cat sail rather self-steering-pulling-along the boat or does it put more side force on the rudder which has to be corrected all the time?

 

[Gary Baigent]

Everything is a compromise, with mast movement fore and aft changes, you win a little, lose a little.
An una cat rig is way forward and because it is placed in a narrower, less buoyant section of the hull; even making compensation for this fact by increasing waterline beam in bow area, (as you point out) when the boat is overpowered with high CoE, too much sail aloft, it's going to skew its bow down and to the side purely from the normally narrow (or even slightly modified) bow shape ... and hence your weather helm-type problems trying to bring the boat back on course.
A true scow shape would be the better answer for a large una cat rig.
Another more "balanced" compromise, imo, is the "schooner/sketch" rig, but with sensible sized chord wing masts, and where the fore mast with its reduced height and weight over the bow sections, (as well as your total rig CoE being lower) - therefore this combination imparts less imbalanced "twist" on the, of necessity. less powerful bow sections. Not talking scow here.
As already pointed out, with rotating airfoil masts with such a rig, you can forget about old world gossip about two mast-ers being weak to windward; on the contrary, your "sketch" will point as high (plus the power and balance of the low CoE/CoG rig with large square top mains) - with all that area you will drive faster than most conventional competition.
But agreed, I'm a little biased here and my suggestions require a complete re-think of the boat. However if you start afresh, like Garry Hoyt did with his innovative Freedom designs ... you end up with an excellent boat, very good beating, very fast reaching. Don't know why we don't see more of them about.

 

[Eric Sponberg]

Thanks Eric for a very elaborate post. But I'm still
As I understand it right, the position of the mast is foremost depending on the design/concept. If the NA set the mast at its position the boat has to be designed "around" it. The further forward the mast the wider the hull in the front to gain boyancy. Does it mean that a boat with standing rigg can't be converted to a cat rigged one?
I just happen to find a sailboat that sports both versions of rigging. Is this balanced by a different placement of the keel?

Is the load on the mast foot of a cat rigg much higher than the load of a standing rigg? I could imaging that the wires distribute some of the load.

One more question: Is the cat sail rather self-steering-pulling-along the boat or does it put more side force on the rudder which has to be corrected all the time?

Converting designs from one rig to another: Yes, it can be done, and it's easier to do from an original design, before construction has started, than trying to retrofit an existing design. Consideration has to be given to buoyancy forward, of course, and that may affect the final placement of the mast. A designer who knows what he is doing should not have any problem with this.

On the Radford 12m examples, I can't say what Radford has done with the keel placement, you'll have to ask him. It could be that the keel has shifted aft a little bit in the cat rig design compared to the cruiser/racer design. Either that, or shifts in other weights on board, such as the batteries or tanks, may have compensated for the mast shift.

The mast heel load on a stayed rig is straight down onto the keel structure--it's the compression from the mast. There is very little loading of the mast onto or against the deck at the partners. In a free-standing cat rig, the load is sideways at the heel, not down, and it is balanced by an equal and opposite load against at the deck at the partners. The magnitude of these loads depends entirely on the geometry of the installation, and between the two cases, they all act in different directions. The two cases are totally different and the masts and boat support structures have to be designed and engineered accordingly.

As for balance, sails all work the same in that they create lift to pull the boat along. This is counteracted by the hull, keel, and rudder. No matter what rig, the balance has to be right for each. You can have boats of either rig that sail well or sail cranky. I can't say that either rig in the Radford examples would be better at self steering or not--the keels are not shown and the CE and CLP are not shown, so there is no way to judge balance from these pictures. Again, ask Graham Radford what his opinions and experiences might be with these designs.

Eric

 

[Skyak]

Some points that I think have been missed so far on this thread
-about mast rotation relative to the boom, true wing masts (and by that I mean masts with large cord relative to mast width and relative to total main sail cord) have a specific design angle that relates to the sail. The mast when rotated forms a smooth curve on the lee side , typically a NACA ~10%. The fluid dynamics section is full of evaluations of such rigs as well as evaluations of overrotation and underrotation. From what I have seen, mast rotation is used to add or reduce effective wing thickness which can not be accomplished with mast bending due to the fore/aft stiffness of the long cord wingmast.

-Short cord masts are also rotated to reduce leading edge disruption on the lee side of the sail -more is generally better. Inshore around the buoy windward/leeward racers control sail shape by bending the mast. Experienced racers are very good at it and they prefer skinny masts and lots of bending control. the Tasar is a fine example of a bending mast. The argument earlier for and against rotating wingmasts is missing the the main point -control. A wingmast rig is superior aerodynamically, but it is just one sail configuration that might not be optimal for the conditions. A well designed thin flexible mast can (in skilled hands) adjust to conditions and win the race.

-The last question about balance and rudder loading on sloop vs cat rigs I say there is a big difference in weather helm on the cat due to the center of effort swinging so far off center. You can move the mast and keel to reduce the maximum but it is intrinsically harder to balance on all points of sail.

 

[mselle]

@ Skyak: Yes, you'r right, I'm probably in the wrong thread, now that I'm realising I'm not so much interested in the wing but the free standing.
Unfortunatly, the "Rotating Free Standing Mast Design" thread is heavily involved in a wing mast discussion. I didn't wanted to interrupt it.

@ Eric: I came across your site already a while ago and read about everything. Now, I might should update myself a bit. Thanks for your comments so far, they where really helpfull.

Thanks, Gary, for your input.

It was just recently, that I found out, what type of sailor I am and what type of sailboat would fit me. It all boils down to a very easy to handle, 8 - 10 meter, cat rigged, non luxurious but well executed, lifting keel, trailerable coastline daysailor. It seems impossible to get by here in Sweden, but since I'm a (product-) designer, I have a lot of ideas, how it could look like. And maybe, one day, I get the chance to build one for myself.
Already soon, I might post my sketches for this community to review it.




Keep up the good work. Marco.