But a key issue with proa is also the rudders an daggerboard, having to work both ways or lifted (lifted for rudders clearly)
Sure is. Harryproas use oversize rudders (no daggers required) mounted on the side of the long hull or on the beams so there are no holes in the hull below the waterline and the boards can kick up in both directions. The beam mounted rudders rotate through 360 degrees, the hull mounted ones are 2 way sections designed by Tom Speer, which work almost as well as NACA 0012.
Sorry for the thread drift. Maybe ask more proa questions at http://forums.sailin...oa#entry4709952 Make the lee hull 3-4 times as long, scale up the rig and beam accordingly and make the little hull just big enough for 3 crew, their gear and a half a ton of water and have a go at the JV. ;-)
Make the lee hull 3-4 times as long as what?
as IdecSport? 96...128 metres long?
What's the scaled rig height and beam ?
This conversation is carried over from the Transat Jules verne thread where people get stroppy when thread drift occurs. For the fastest boat around the world, NotSoFast advocated a maxi cat with minimum beam and 3 tonnes of water ballast on a strut out the side of the hull, with strings fore and aft and to the mast to support it. I (believe it or not) thought a harryproa would do a better job.
Answers to BSF's questions above:
If a harryproa accidentally tacks or gybes, it is a no stress event. The rig weathercocks and the boat drifts downwind, is steered back onto course and gets sailing again. Sheet action is minimal. Compare this to an accidental gybe on a fully powered up cat with 3 tons of pod hanging 17m off the wrong side, the boom against the runners and the headsail sheeted on the wrong side. Sailing with both pods full to avoid problems seems to defeat their purpose. An unstayed wing mast with stays to the pod would not weathercock.
Covering 6 degrees of freedom is pretty easy, although keeping everything tight while scooping up 3 tons of water at 20+ knots will be a challenge. I don't doubt it could be done. My point is that it is easier and less windage to do it with an extended beam and the ballast in the windward hull on a harryproa.
A leeward pod is not only weight in the wrong place it is in danger of hitting the waves, which would increase the loads a lot. It would also be a lot of drag if the boat flew a hull far enough to immerse it. Consequently, I assumed it would need to change sides.
Afaik none of the maxi cats weighed less than 20 tons, plus crew, fuel, food and water, so 10 tonnes for your boat seems ambitious.
250 kgs would get you 4-5m of streamlined beam on a JV harryproa.
3-4 times as long as Bucket List. ie, 40m lee hull. Other dimensions are wild guesses, loosely based on the cruising harry weights. Maybe 2,5 tonnes for the lee hull, 1.5 for the beam (25m long, 3m wide), 1 for the rig, 0.5 for the rudders/steering and 1.5 for the ww hull (9m long) incl 3 crew etc. 7 tonnes. Bruce number (imperial) to be competitive, say 2.5. So sail area (probably an unstayed wing masted schooner for ease of handling) 360 sq m. 180 per rig, so masts are 28m high x 1m wide, booms 6m long. Righting moment (1.5 +.75) x 25 = 56 ton metres. Maybe add a ton of water ballast to get 81 ton metres, but this ioncreases the boat weight by 15%, so is probably too much. RM is less than Idec but so is the weight, sail area, rig height, windage and effort required to sail it so not really relevant.
Bucket List update:
I decided to build the mast and beams myself to play with a build method that needs neither moulds not mandrels. Took 3 of us 10 days to build 3 x 6m mast sections and 2 x 8m beams. The first one was ordinary, the last one pretty good. Decided that I would rather experiment with the rig than build what i already knew would work, so the mast telescopes. It works ok against the side of the house, but there are some challenges, most of which have been met, but some we are still working on. In particular, how to avoid paying $7k for a sail.
It is unlikely the telescoping will be used on the charter boats if they happen, but it is more fun to play with.
The long hull comes up at the end of the month, assembling it at Maritimo, (about half the price of Boat Works and enthusiastic people), so things are getting closer. Photos, videos, weights and updates at http://harryproa.com/?cat=2
"Compare this to an accidental gybe on a fully powered up cat with 3 tons of pod hanging 17m off the wrong side, the boom against the runners and the headsail sheeted on the wrong side. "
That has nothing to do with what I proposed. A rigid wing like in most C-cats do not have any jib thus can't be sheeted on the wrong side. No boom, but the whole wing can be aganist the shrouds, but only when apparent is aft, not supposed to happen in a truly fast boat unless sailing in a storm, which is intended to be avoided by means of weather forecasting and routing.
"Sailing with both pods full to avoid problems seems to defeat their purpose"
In most places yes, but if wind is totally unpredictable like I assume it to be in doldrums (with no personal experience), it is something that can be done to keep it from breaking up.
" An unstayed wing mast with stays to the pod would not weathercock"
Unstayed with stays ??? Not what was talking about.
Rigid wing in C-cats do weather cock, but not through 360 degs, but as long as apparent is enough forward it should be fine.
"A leeward pod is not only weight in the wrong place it is in danger of hitting the waves, which would increase the loads a lot. It would also be a lot of drag if the boat flew a hull far enough to immerse it. "
Yes 250 kg in the wrong place in a 10+ ton boat, don't consider that to be a major problem. Hitting waves yes, can be kept higher up if wanted to easily to prevent it. It wouldn't increase loads any more than to the low level of a small beach cat windward hull. Only way to make it immersed when empty is to capsize the whole boat on it. There is no string to make it go under when tensioned, as all of them either lift it up or are horizontal and none of the strings can be put on compression for obvious reasons. Again, the deck spreader is never on bending loads due to both ends having ball on cup connection not capable of transmitting bending loads. Thus can't push the small hull under. In addition, the fore/aft position of the deck spreader is adjustable +- 90 degs, therefore can be kept directly aft on the lee side and would be for most cases at speed.
"Afaik none of the maxi cats weighed less than 20 tons, plus crew, fuel, food and water, so 10 tonnes for your boat seems ambitious. "
Compare with the tris and you should see the reasoning it can be much lighter than them with same RM. The beams of those tris are heavy items, and with both 45% shorter and with much less load on them from the mast can be built much lighter. Rigid wing with no foresails can also be built much lighter than conventional masts due to less compression at least in big size. C-cats are evidence it works well in smaller size as well, but not sure if they are also massively lighter. No mainsheet load, no forestay load to keep them tight help a lot for less loads. Pretty much just the weight of all the boat equals mast compression in a wing. I think my suggested weight is very conservative compared to the newer tris for RTW route, like yet to be built Banque Populaire ??? (IX if I remember correctly) with all up 15 tonnes with soft sails, higher mast, longer hulls, more sails, and more beam than IdecSport.
Those maxicats were heavy due to all traditional mast compression loads put on a single unstayed wide beam, no such thing on my suggestion.
"RM is less than Idec but so is the weight, sail area, rig height, windage and effort required to sail it so not really relevant. "
But not on the same proportion less. ~84 % rig height and over 87% sailarea upwind with less than 34% RM. That's massively more oriented for lighter winds than IdecSport.
Only reasonable for rtw route with fully 360 degs weathercocking rig which you do have.
I would like to see what your HarryProa suggestion would look like if scaled up or ballasted to have same RM as IdecSport, 160 tonne metres, and same size rig height 33,5m from the water, and sail area 411 m^2 upwind. Or at least close enough to be comparable.
All descriptions on this or previous messages (6 degrees of freedom etc) assumes boat frame of reference, not inertial one. That also means term "horizontal" (*) heels with the boat, which might be misuse of terms. I hope that doesn't make it less understandable. * = in context with how no string pulls downwards, means then pulls below "horizontal" as defined above.