Subject: Re: Predicting performance?
From: Mike Crawford
Date: 5/31/2010, 12:20 PM
To: Gardner Pomper

(this reply is off-group)

  Thanks, Gardner. I had some time on my hands that day and couldn't help writing (pontificating?) about harryrpoas and sail area.

  Sail area often gets me going.  I'm tired of hearing from the traditionalists who say that a boat with a mast of X meters height is overpowered, get a boat with a smaller mast, and then add on an asymmetric spinnaker that brings the SA/D up to 70. 

  What?  I've seen those guys try to handle the a-spin when the wind picks up, and that is *not* a safer option than an easyrig or swingwing rig that can be depowered, totally, by one man, by releasing one sheet.  It's possible to have too tall a mast on a traditional catamaran where the shrouds can prevent you from depowering the main, but that's not the kind of boat we're talking about here.

  So I often blather on about sail area.

---

  Fair disclosure: I'm completely addicted to having "too much" sail area. I don't have to be the fastest guy in our inlet, but I do like to move with wind in my face. I almost preferred my old 19' Starwind monohull to our current Stiletto catamaran, but it had two limitations: the cockpit was great for three people, but a crowd with four, and it bobbed like a cork on really light wind days.

  I moved up from a 110 jib to a 135 genoa, but that didn't help much. Even a 150 wouldn't have mattered. I needed a taller mast. 35' cruisers would slide past me as I sat still, their masts high enough to catch real wind.

  Now, with the Stiletto, I can sail on days that would have grounded me before. It's also nice to be able to do an easy ten to twelve knots with good wind. I've had it up to 19 mph, but I need one or two crew with me to do any better -- too many strings on too light of a boat.

  If I could have even more power, but on a boat that is far safer, I'd be in heaven. Thus, I'm fascinated with the harryproas. You know all of my safety and performance arguments by now, so there's no need to repeat them.

  I did briefly consider an Elan trimaran for a while, and was intrigued to hear that you've had one. I actually had a deposit on hand with John Elion, but eventually decided to get the Stiletto instead. The Stiletto had an acre of deck space, which is great when one has guests, or while hanging out on the hook, and it's $20k price tag was 1/4 the total cost of the Elan.

  I would love to have that nice folding option, though. Getting a Stiletto on to its trailer, collapsing it, and getting the mast down are real chores. I also miss a cozier cockpit -- it can be hard to talk to guests in the wind when they are on the other side of the 8' wide cockpit.

  How long did you have the Elan? Did you enjoy it?  I've never spoken with someone who actually owned one.  Why did you get rid of it?  Did you want the greater deck/cabin area of the MaineCat?

---

  If I could have a semi-cozy cockpit for six, like a trimaran or monohull, and still get huge amounts of deck/trampoline space, like an open-deck catamaran, on a boat that can collapse, which sails more quickly and more safely than either the Stiletto or the Elan, and which has double bunks, that would be just about the perfect boat.

  And now it turns out that this can be done!

  I was so convinced that the perfect boat didn't exist that I'd given up. And because the Harryproas can actually do the impossible, I sometimes blather on about them. They aren't perfect, and certain things are still being worked out, but I'm still wicked impressed.

  The camper sounds like a good plan. It would be a relatively quick build, a relatively inexpensive boat, should be great fun to sail, and will teach you all you need to know before committing to a larger proa.

        - Mike

 
On 5/26/2010 12:46 PM, Gardner Pomper wrote:
 
Wow, Mike, I really tickled your fingers with that question! <grin>. Thanks. I love all the feedback.
 
I have been taking the approach you suggest, which is to just put up as much sail as I can. For the 38' Contrarry, it would have to have a 2 part mast to get any useful amount of sail, so I might as well make it tall. I am restricting myself to 62' off the water because of the Intracoastal. Of course, in NJ, even 40' won't work, so you really can't use that section.
 
But, back to my basic question... according to the SA/D and Bruce calculations, Rare Bird should be nowhere as fast as she is. I think this demonstrates a fault int the SA/D particularly, since she is fast at speed. The Bruce number might be a better predictor of light wind performance, since Ono's harryproa suffered there. (I need to get the spec's of Ono to add it to my chart).
 
What I am getting at, is that increasing the sail area has more effect than just raising the mast. It also makes the boat beamier, since I don't want to get hit in the head with the boom if I am caught aback. The other option, raising the boom, makes it hard to reach. So, I would really like to be able to predict proa performance based on sail area, displacement, hull length and hull beam. If anyone has any formulas that add the hull shape to the sail area/displacement values to calculate performance, I would love to hear about it.
 
There must be a calculation based on wetted surface area and some adjustment for the hull fineness ratio. If that force could be estimated, I would think you could calculate the potential force from the sail and come up with a number that way. It would be valid up to the point where the righting moment is approached.
 
In terms of the wing sail, I think I will give it a pass. It looks interesting, but I have a few problems with it.
1) as you say, it would require a bit of experimentation
2) I dont' want to have to build all those internal shapes
3) too many control lines (like a junk rig)
4) sail doesn't hold shape between teh ribs, so I am not sure how much benefit you actually get
5) more things to break
 
I think I am going to go with a wing mast and as big a sail as I can deal with, but I do wish I could quantify it.
 
You brought up one question I had not considered: the windage of the bare mast. What should I be doing about that? While I hope to never have to sail under bare poles, I certainly can't rule out be anchored in a hurricane. What should I be looking at in terms of wingmasts and safety?
 
Thanks again for your thorough reply. I keep losing track of much of this information, so I am goign to file this thread away, and I am going back to look up some of your other posts, because they often have really great info I should keep track of.
 
- Gardner
 
P.S. the plan is to build the camper; the contrarry is probably twice the boat (cost, time) and I have to view harryproas as experimental until I can charter one for a week.