Damn!  I hate it when I have a different opinion from you Rob... it makes me feel like I'm missing something fundamental!  Since I'm counting the cost to be the carbon mast tube mast AND high-end sails.  I'm looking for cheap... for MLM.  The idea that a top quality set of sails might go $5K for this size boat to make it sing, and that doesn't count the mast at all!  I thought to myself... why don't we go whole hog and do a full wing.  I've got the analysis tools, time, but not the money...

 

I used JavaFoil to mess with the wing (and flap) to get the geometry and projected performance.  In theory (let me repeat... in theory) and just for number jocks in the group... on a reach with 20 knots true the wing should generate 445 pounds of thrust for only 790 ft-pounds of tipping moment.  MLM with crew on the ww hull can generate up to 6000 ft-lbs of righting moment.  The Godzilla analysis of the MLM's lw hull only requires 275 pounds of thrust to run at 30 knots.

 

For those interested... it uses a NACA 0020 wing with a 40% chord NACA 0012 flap.  Is 40' tall and has a 5' chord.  I'll segment it at 25' for ease of transport and to leave the top part off for really blustery days.  The top 15' will be tapered to a 2' chord at the top.

 

Structurally I've started the structural analysis and started with the beam flanges.  My assumption is I'll use carbon JUST for the flanges and use fiberglass cloth and/or tow for the webs.  Because of the relatively huge wing thickness (7.2") it makes for a very efficient use of the carbon.  As expected the analysis is stiffness critical, so I used Rob's 7% of height tip deflection as my guide. 

 

The beam bending analysis uses a mere 5.2 pounds of Carbon tow!  At the full 6000 ft-lb moment that will tip the boat.  It achieves a tip deflection of 33.6" (7%) and has a minimum tensile S.F. of 17.  Unfortunately, carbon will typically fail in compression and I don't have properties for that. 

 

Rough guestimating...

$100 Carbon Tow for wing and misc stuff for flap

$100 Fiberglass Tow and some cloth for beam web, front D-section,

$50 of those pre-made carbon tubes from Rick's suggested web site for wing ribs

$100 Epoxy

??  That shrink wrap stuff used for shipping for the wing skins.

 

All said and done... way less than $500 for a 40' wing.  Hell, replacement sails for my Mac would cost more than that.  Might have to put a wing on my MacGregor!  :)

 

Dennis

---

From: Rob Denney <harryproa@gmail.com>
To: harryproa@yahoogroups.com.au
Sent: Sun, May 22, 2011 4:37:49 AM
Subject: Re: [harryproa] Re: Rotating masts and wingmasts?

 

Cheapest is a tube mast.   Attaching the boom so it is rigid vertically, but can rotate seperately is pretty easy with tow, pvc tube and ss or glass rod as the axle.    There are performance advantages to doing this with a round mast to make a smooth junction between the mast and sail on the lee side, but it is rarely done.  With a wing mast it is essential.  Pretty easy to do, but does need some means of controlling the mast.  Relying on the boom can work while sailing, but at anchor, it needs to be locked in place.

On Sun, May 22, 2011 at 11:59 AM, Gardner Pomper <gardner@networknow.org> wrote:

 

Mike,

I just want to make 100% sure that I understand. If I go with a round mast, I can fix the boom to the mast, and just have one thing that rotates, right? I want to make sure I am clear on that. The wingmast requires the boom to rotate independently of the mast (basically +/- 20 degrees or so)?

I don't want to give the impression that I have been focusing on the cost "lately". That is, has been, and always will be, my first priority. Unless I just want to dream about a boat forever, it better end up pretty cheap!

I know you have mentioned that soft wing mast on a number of occasions, but it still just looks too complicated; too many moving parts. I don't see it being particularly cheap, if you count your time. That is pretty much how I am counting costs; assuming that I will contract out the construction. Otherwise, it is too easy to just say that labor doesn't count. I would much rather pay more for materials, to save labor time, whether I am building it myself or not.

The schooner is my preferred rig, I think. It seems like it provides a bit of a backup for the steering, which is still a concern of mine with the harryproas. It also makes it easier to keep the mast height to 40' for container shipping and maybe trailering. My problem is that it seems like the masts cost a significant fraction of the price of the boat, and having 2 smaller ones is considerably more expensive than 1 larger one.

My interest in wingmasts is more that I thought it might be less labor intensive than a round mast, even if it does use more materials. I am not primarily concerned with a performance boost, because I have ongoing worries about the behavior of wingmasts at anchor in a storm. I am just trying to keep focused on cheap, fast and comforatable.. I want all three!!

- Gardner

On Sat, May 21, 2011 at 9:44 PM, Mike Crawford <mcrawf@nuomo.com> wrote:

 

Gardner,

  The two would definitely need to be independent; otherwise, instead of a graceful foil generating lift and directing airflow onto the said, the mast would just be a big slab out there creating turbulence.

  However, as with standard rotating masts, you can find a relatively happy medium that will work for many wind angles.  With a noticeable part of the wing aft of the center of rotation, and with the sail itself pulling on the wing's trailing edge, the mast will automatically want to rotate into a reasonable angle. 

  If you limit the rotation with a rotation limiter, you'll be set for just about everything except a tight beat and a run.   And even in those cases, you'll still probably be more efficient than a standard D-section aluminum stayed mast.  If your rotation limiter were adjustable, you'd have even more chances for optimization.  I pretty much leave mine set on tight-medium and adjust it only if I refuse to let someone else out-tack me downwind.

  Of course, if you did want to race, and eek out every possible eighth-knot from the boat, you'd need a set of blocks to fine-tune the mast angle relative to the boom on all points.  But that's a lot of work.

  However, now you need to strong sets of bearings: one for the mast to rotate freely from the boat, one for the vang-less boom to rotate freely from the mast.  That's more complexity, more expense.

---

  If you're serious about keeping expenses down, another option is the swing-wing soft wing sail described by Kim and Rudolph.  One mast, no boom, no rotating bearings anywhere, no sail track.  I know you're plans haven't revolved around this rig, but I thought I'd mention it again since you've been focused on cost lately.  Unless you're going with a schooner rig (where I'm not sure the swing wing would work), it would be hard to beat in terms of price.

        - Mike

 
 
Gardner Pomper wrote:

 

I am under the impression that with a wingmast, you need to rotate the
boom independently of the mast, so that the wing is at a steeper angle
to the wind than the sail. Am I correct in this?

If so, that seems like you could no longer have the boom fixed to the
mast and use the mainsheet to adjust the angle of attack. Wouldn't you
need extra lines to trim the wing seperately from the sail, especially
in light air? If so, that seems like a major disadvantage for a
cruising boat.

Thanks for any help clearing up my confusion.

- Gardner