Gardner,

  My decidedly unprofessional recommendation would be to go for as much sail area as you can, without driving yourself crazy in a design sense, and then rest assured you'll be fine.  Your 38' Contrarry with an SA/D of 50 should be very good.  The rest of this long post is basically to support that statement.

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  If you were located in Oregon near the gorge in Hood River, with huge average winds, I'd say that an SA/D of 25 would be fine.  Probably overkill, actually.  But you're on the Chesepeake Bay, with noticeably low average wind speeds in the summertime. 

  Dealing with those low winds would be my driving design criterion for three reasons:

  1) On a boat with an SA/D of 40 or higher, with a lot of the area up high, you'll be moving when everyone else is still.  That matters -- more days sailing per year, and/or less dependence on the outboard.

  2) Or, you'll be moving at six knots when everyone else is at three knots, quadrupling the area you can visit on a daysail, or doubling the distance you can go one a one-day leg of a cruise.

  3) Moving with wind in your face is ultimately more fun than drifting with an apparent wind of near zero.  A boat with a high SA/D will be able to tack/shunt downwind at an angle, generating a much larger apparent wind than if it were on a straight run.  You won't have a VMG much better than a run, but the trip will be a lot more fun.

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  Given the need for speed in low winds, I'd shoot for your SA/D of 50 or higher. 

  I've got a Stiletto 27 catamaran with an SA/D of 50 with two people on board and the reacher up (i,j calcs -- which is lower than total sail area), and while I love the boat, there are four issues with sail area I'd like to resolve:

  a) I'd actually like more sail on the really low wind days.  There are days that I know I could enjoy with more sail area, but can't since I don't have it (or more realistically, don't want to deal with three sails at the same time while singlehanding).

  b) Ideally, that sail area to be higher up.  It would be wonderful to have another two or three meters of mast up high to catch that delicious elusive breeze.  Some people with Stiletto's have done that, but I don't want to spend a lot of time or money modifying a lightweight unstable catamaran that has no accommodations.

  b) Dealing with high winds can be threatening while singlehanding.  Once reefed, everything is fine, but the issue is going from low winds to high and then trying to reef such a light boat alone.

  c) Too many strings to pull.  If I've got the reacher up, I've got to partially furl it to get it across the forestay.  That's a lot of work if you're not racing, especially if the wind is really, really light, and you've got the jib up too (which has to be tacked separately).  This also adds to the lack of safety when alone.

  So a boat with an SA/D of 50, or even 70, with much of that sail area high up, and which can be easily reefed, would be ideal for me.

  My guess is that this would be useful for you, too.  Maybe you'll sail with one reef in at eight knots, and two reefs at sixteen.  But who cares?  As long as your sail is designed properly, there's no reason *not* to have enough sail area to require one or two reefs in normal wind.

  Rare Bird is a good example.  It's an impressive design for a cruiser, and watching it match the wind speed in the videos is great.  But it's not quite powerful enough for light wind races when other multi's are using their spinnakers.

  You could get an outleader kite for ultra low winds, or rig up a spinnaker, and get some of the same as the taller mast, but they wouldn't give you the ability to instantly depower fully while sailing alone, or alternately, sailing with people who can't scamper all over the boat to deal with sails while you helm.  The spinnaker would also have a lot of its sail area down low, out of the best winds on light wind days.

  There's no substitute for having sail area up high that you can depower by releasing a single sheet.

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  So if it were me, i'd go for the largest sail area and tallest mast possible, regardless of whether the SA/D is 50, 60, or 80, as long as it fits within three limits:

  i) The mast(s) fit under the bridges on the ICW.

  ii) The mast(s) are within your acceptable criteria for windage under bare poles.

  iii) The mast(s) work with your travel plans.

  I personally don't think I'd bother with item iii because I wouldn't intend to ship the boat overseas very often, if at all.  But I do understand that you might insist on a container-able design.

  The ICW would then be my primary limit, keeping the mast top to 62 or 64 feet.  While I've read that there's one bridge as low as 56 feet, I don't think I'd use that as my limit, and would instead just wait around for weather good enough to travel outside the ditch for that segment.  One fellow says he's made it with an air draft of 65 fee:  http://icwcruisersguide.com/page16/page16.html

  So I'd probably just go for the largest harryrpoa with an SA/D around 70 and an air draft of 62 to 64 feet.

  It would be serious overkill on days when my monohull friends are hitting their hull speed, but I'll deal with that by reefing, as well as enjoying the mast's ability to flex and avoid a certain amount of gust energy.

  But on those days when everyone else is bobbing like corks, the breeze in my face would be exquisite.

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  If you've got a 38' containerable design with an SA/D of 50, I'd say you'd be set.  Not overreaching at all, and definitely far from underpowered.

  I'm all for max sail area, but realistically your design would still be a monster.  It would have the same SA/D of my stiletto, but would have a lot more of that area higher up, with a 12' longer waterline, much better stability due to the weight-to-windward hull, and *infinitely* easier sail handling.

  The camper design with an SA/D of 40 would also be good, though not quite as good in light air.  It should still outclass the Elan by a good amount, though, given the higher SA/D, better stability, and much longer waterline.  If the Elan was good enough for you, the camper would be even better.

        - Mike

 
 
On 5/25/2010 10:33 PM, Gardner Pomper wrote:

 

Hi,

I have been occupying myself with what seems to be my favorite hobby; designing harryproas that I never get around to building. One of the things that occurred to me, is that I don't seem to have a good way to predict performance. I have been using the typical SA/D and Bruce number calculations, but I can't get these to provide me with number I can believe, based upon my personal experience and the speeds shown by Rare Bird on the Youtube videos.

Here is a table I compiled:

Boat Type Length Disp Sail Area SA/D Bruce #

ME Cat 30 catamaran 30' 6000 500 24 1.2

ME cat w/screacher catamaran 30' 6000 720 35 1.5

Elan 7.7 trimaran 25' 2000 310 31 1.4

Rare Bird harryproa 50' 10000 774 26 1.3

Harry harryproa 40' 3500 452 31 1.4

Harrigami harryproa 35' 2500 333 29 1.3

Camper (mine) harryproa 30' 2000 392 39 1.6

Contrarry (mine) harryproa 38' 3500 728 50 1.8

It is a little hard to read, but basically it says that Rare Bird should be slower than my Maine Cat with the screacher up, or my Elan trimaran at any time. The Maine Cat never got over 12 kts, and that was surfing down a wave. With the screacher in 15 kts of wind, it would top out at about 10 kts. The Elan may have hit 15kts at one point, but that is when it was blowing 20+ kts and I was terrified of a capsize.

So, given that the longer, sleeker, harryproa hulls are the deciding factor, what metric should I use to compare a harry design with "normal" multihulls?

The reason I ask is that I may be overreaching for sail area on my designs, based on these numbers.

Thanks,

- Gardner