Peruvian proa
Which leaves just me to come to the confessional…...
No harm or insult intended, I am too blunt too often, a lifetime habit I have struggled with. However, I will always have trouble with designs in which the major load carrying hull is shorter and fatter than the more lightly loaded one. It just seems unnecessarily slow to me. Swap them over at least, especially if you are talking about tacking as well as shunting?
That said, the big advantage of this type of layout is the inherent wind and spray protection which really is a major plus in boats likely to spend most of their time at double figure apparent wind and boat speeds.
I also like Bi-plane rigs, there seems to be other advantages other those CapnRon has mentioned:
1) No blanketing of (fore) sails deep down wind.
2) The overall centre of effort is more central than that of a schooner rig with less inherent weather helm.
And if you use one mast holding up two club footed counterbalanced “jibs” or staysails:
3) No cost, weight and windage of the second mast (but a bit extra for the second boom).
4) No need for heavier and more expensive aerofoil masts.
5) More efficient luffs due to lack of mast interference.
6) Maximum sail area for any given mast length / air draught due to the sail area gained in front of the pivot axis.
7) Lower sheet loads due to the sail area in front of the pivot axis.
The booms are admittedly much more complex in that many of the sail handling controls (especially for the weather one) have to pass somewhere near to the pivot point before going back to a more accessible point on the boat.
Cheers
Rob
This is a very interesting and constructive forum. Lots of topics discussed. Anyone who is thinking about and / or building these non conforming boats is probably not expecting a lot of hallelujahs, and should most likely have some thick skin. So I wouldn’t get too stressed.
I do think the conventional pacific proa is an amazing boat. That is well proven in history, and in current designs. I would love to have a large two cabin pacific proa in our Seabbatical Long Term Charter program. I think it would be a great boat for a couple or small family exploring the islands.
However, it seems that most of the demand is for 4 cabin larger volume boats. That is one of the reasons we are heading in the direction that we are with the Drua. I think we could have even larger cabins than we ended up with. Clearly we will be a heavier boat and probably slower boat than a pacific proa, of the same length but maybe not much heavier than a proa of the same accommodation. I think we will be as fast or faster than a lot of the high performance cats with similar accommodation. So it is sort of a hybrid between a cat and a proa.
I also think that a 50 % weight to windward, dry boat in race mode, and a 40% weight to windward fully loaded in cruise mode is not such a bad place to start. The resistance curves I have looked at seem to drop off quickly after you get to 40% and not much to be gained below 30% to WW. It is all a function of initial weight distribution, and relative lengths of hulls, balanced with how much sail area / righting moment you need. Apparently this is a touchy subject but it is what it all boils down to.
Ron
I’m pleased about the recent posts, and the responses shown. Let’s keep this a forum, for discussion, and not a platform to air issues.
That’s all I have. 😊
I like the asymmetrical sailplan, very creative. It’s a proa ketch!
So it is sort of a hybrid between a cat and a proa.
Got to wonder - would this be a croa or a prat?
The pacific proa formula just doesn’t adapt well to dealing with accommodation requirements in the real life charter world. I think this may be why it has never really been considered. The other major issue is the daggerboard/rudder issues - the Newick/Brown style effectively block accommodations and a v-berth style cabin at either (or both) end(s). Alexander’s Nixe works beautifully for his requirements - accommodations for two with day sailing for four - but this isn’t a fit with charters.
Your drua concept looks quite promising. Keep up posted.
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Bill
Ron,
I have not found information on the rudder setup of Drua. To spare the accommodation volumes they are external to the hull in the drawings. Can you elaborate? Thank you in advance.
Luc
Ron, re: hulls
The drawing provided in this topic does not correspond to the hulls pictured in the built series. It looks like each suite has its own entry now. Is that correct?
You probably also considered identical hulls. What were the main reasons to reject that choice? Thank you.
Luc
Hi Luc
We liked the Newick Brown rudders but eventually chose rudders supported by struts off the inside of the LW hull. The non opening cases are rectangular. The top of the boards are tapered so they can be pulled forward on top to balance them. Steering is hydraulic with one wheel. Rudders can both be steered even with the boards partially raised.
Cabins now have separate entrances with two heads in the LW hull and one in the WW hull. There is flexibility in the layout for future designs. The LW hull is 55 ft long and the WW hull is 43 ft long. A shorter WW hull reduces the stresses in the boat when the hulls are in different wave trains. Minimum resistance curve is when sailing with 20 - 30% weight to windward. The WW hull is still working and carrying some load, reducing the load on the LW hull. I think the difference in hull lengths could be greater but I did not want to go longer with the LW hull, and going shorter with the WW hull would not have saved much money or weight but made the boat slower when tacking or until the WW hull became unloaded.
Equal length hulls like on an atlantic proa makes sense to me on lower displacement/length boats. But then you have to worry about getting caught aback. Catamarans have their minimum resistance curve at 50 / 50 weight distribution. Resistance increases as the WW hull unloads. We have a more centralized weight distribution than a pacific or atlantic proa, but still take advantage of the one long hull one short hull.
Ron
Would the biplane layout be a suitable home for the self-trimming wingsails described by Peter Worsley ?
Has anyone used such a device on a proa ?
From my limited knowledge of the device it would seem to prevent being caught aback and driving the ama under.
I suspect I’m missing something….
Would the biplane layout be a suitable home for the self-trimming wingsails described by Peter Worsley ?
Has anyone used such a device on a proa ?
From my limited knowledge of the device it would seem to prevent being caught aback and driving the ama under.
I suspect I’m missing something….
A wingsail has been added to my to do list for the Bionic Broomstick, hope to report on first trials in 2014. Worsley’s circular cam setup for a wingsail is so simple and elegant that I’ve just got to try it, though wingsails aren’t high on my list of wantta try that. There’s always a good chance that I’ll learn something or change my mind in some as yet unknown way.
BTW I’m still in your debt for the idea of a pop a way housing on end pod rudder setup.
Thanks
Cheers,
Skip
Would the biplane layout be a suitable home for the self-trimming wingsails described by Peter Worsley ?
http://www.harborwingtech.com/products_recreational.htm shows the closest I know. I see no reason it would not work on a proa. But somehow this technology is slow to catch on. I wonder what the real catch is? It was recently used on the sail drone that sailed from California to Hawaii. It was designed to withstand full capsizing. I expect that scaling that up to an order of magnitude is far from trivial, though.
Luc
We liked the Newick Brown rudders but eventually chose rudders supported by struts off the inside of the LW hull. The non opening cases are rectangular. The top of the boards are tapered so they can be pulled forward on top to balance them. Steering is hydraulic with one wheel. Rudders can both be steered even with the boards partially raised.
...
Ron
How do you plan to prevent spray from the struts? How high is the lowest strut from the water line?
The steering wheel moves both rudders in unison? What do you mean by “non opening”? Thanks
Luc