Barge-Proa once again. Videos.
Why? Let me try to explain.
I was trying to discourage the comparison to the snub-nosed Classe Mini boats and the inland racing scows because they were developed in response to rules say they cannot be any longer in length: the forward, pointy section of most hulls is elevated and released from the water when the vessel is planing and could therefore be considered extraneous [or “pointless”, ha!]... so they essentially designed longer hulls and truncated the pointy bits to still fit the rules. Some of the last crop of VOR boats did the same thing as well. The disadvantage comes when they are not sailing in planing trim and they have to fight their way through the water, but the Mini and VOR courses are mostly screaming reaches offwind and the inland scows race on placid lakes inshore so the detriment isn’t so painfully obvious.
I would consider it this way:
What is gained by ending the hull with scow-shaped ends instead of extending its lines out to finer stems allowing for a cleaner entry and exit? It only makes sense if our proas are in some way restricted in length. I often see people on these forums begin their design process by arbitrarily deciding how long the vessel will be and then trying to figure out what will fit on and in it… and then trying to figure out what they might be able to do with it. Shouldn’t we go about this the other way around and let the program decide the details?
If I remember correctly, your barge-shaped vaka is longer than your sharpie-shaped hull: the extra length has a far greater impact on speed, tracking and pitch reduction than does the different planform shape. If you carved a couple of styrofoam nose cones and stuck them temporarily on the ends of your barge proa I suspect that you would see even less gyration and better speeds.
Is the flat lee side of the barge proa hull helpful? Of course it is, but you can also put that same flat lee side on any hull, pointy-ended or not. One does not preclude the other. You could even make it a bit concave in Kiribati fashion…
My Barge-proa is 5,8% longer than my green ASP-proa. The barge is also 2 cm wider and 0,4 kg heavier. The strange thing is that is faster even though it has both more weight and is wider, with the same sail, ama and akas (total width, righting moment and driving force). And as usual I don´t have any hard factual numbers to show. This is only based on my approximatly 8 hour experience of sailing them at the same place and similar windstrength and direction. I think (again only based on my experience) that the difference in speed and general behaviour is much more pronounced than that 5,8% added length and 0,4 kg extra weight gives it reason to have. I have tried several variations on the ASP and two barges. Both barges have impressed me greatly. The old non-continous rockered barge was not very fast compared to my new red barge. It seems that a smooth continous rocker is very important for speed. he old barge had much of the same great damping effect, even though it had a shorter water-line length than any of my ASP-proas.
What is gained by ending the hull with scow-shaped ends instead of extending its lines out to finer stems allowing for a cleaner entry and exit? It only makes sense if our proas are in some way restricted in length.
The scow/barge has an disadvantage when the front of the boat slams into steep waves, but a big advantage in relesing the water in the aft. It also has an enormous advantage in damping any pitching and unwanted non-forward motion. It will move a lot of displacement far forward or backwards when going through waves. This is important in keeping the air and waterflow attached and free from turbulence. The hard chines will make he hull track very straight, even through breaking waves and surf near beaches, reducing the load and use of the rudders.
Have you compared a barge-shaped hull with a similar pointy ended hull on models or full sized boats? They both have their advantages and disadvantages, but Im very impressed by the slender and light (compared to a monohulled barge) barge. I did not believe it could be this good in so many ways. When reading all the “know all - know best” theoretical BS on forums (not here) and some designers webpages I was led to believe a barge was nothing but a crude heavy duty tool for managing large amounts of thrash or heavy ore in protected waters. This is very far from the truth. I am tempted to build a very long and slender barge-proa just to see what it could do. Imagine a 55 foot long, 2 feet wide and reasonably light barge-proa. I would start surfing just by mentioning the word “wind” out loud.
Thanks for a lengthy answer!
I agree on many things you say.
I often see people on these forums begin their design process by arbitrarily deciding how long the vessel will be and then trying to figure out what will fit on and in it… and then trying to figure out what they might be able to do with it. Shouldn’t we go about this the other way around and let the program decide the details?
Soo true! The standard solution for every problem on a proa is: make it longer!
That is of course a very simplified “solution” with some exceptions, but never the less quite true. The whole idea (as I see it) with the proa is to get the most length and width for the least amount of money/material/hours working etc…
Cheers,
Johannes
I hope that none of these discussions cause any offence, Johannes…. as that is not my intention at all. I am on your side! In my boat building career I often find myself playing the roles of the cynic and the pragmatist and I have no doubt that it is often perceived as being overly negative when it begins to interfere with peoples’ dreams. It’s never my intention, but often my job….
I doodled a little diagram that demonstrates a few things clearly: the red, barge-shaped hull is not “just” five percent longer, but has about double the displacement and much of it is dispersed into the extreme ends. I do believe that to make a good comparison between the two fors that the displacent needs to be kept similar and that some of the volume from the corners of the barge should be reallocated into the stems of a comparable canoe. I would suggest that the green sharpie hull isn’t only five percent short, but rather closer to being only half the length that it wants to be. I’m not suggesting that you build another model, but there is bit of comparing apples to oranges going on here!
The very long barge hull you describe reminds me of the Thames River racing punts which are barely a foot wide. I wonder at what point the skin friction of such an extreme hull becomes insurmountable regardless of the reductions in wavemaking drag?
I hope that none of these discussions cause any offence, Johannes…. as that is not my intention at all. I am on your side! In my boat building career I often find myself playing the roles of the cynic and the pragmatist and I have no doubt that it is often perceived as being overly negative when it begins to interfere with peoples’ dreams. It’s never my intention, but often my job….
No! You don’t cause any offence! I’m very greatfull for these discussions. I’m trying my best to develop a rather extreme and odd proa, and any and all input from others is greatly appreciated! It feels a bit lonley out here in the extreme end of simplified proas.
I hope I don’t come across as hard or confrontational. I tend to write things as short and to the point as possible, as I don’t feel comfortable expressing myself in english or in text in general. My intent and “base” is always curiosity and never any negativity.
Thanks for that picture comparing the underwater body of the two proas. Yes, it has a lot more displacement far out in the ends, and in some ways behave like it is longer. This even though the prismatic coefficient is quite low (0,5 - 0,55?)
I believe the skin-friction is less important at higher speeds, as the drag from the skin-friction is linear. Wavemaking resistans tend to increase exponetially, if I understand these things correctly.
The limit for slenderness for a barge-hull is probably more based on structural strength and usabillity, rather then skin-friction. Somewhere you get negative returns because the weight start increasing faster then the length.
A 131 foot (40 meter) barge vaka that is 2 feet wide is probably starting to push those limits of diminishing returns.
Thank you for helping me to understand the workings of the barge-hull better.. I have learned a lot today, and that makes this a great day!
I have been thinking a lot of using the same amount of plywood and epoxy but making it as slender and long as possible. 210 cm long and 7 cms wide seems to feasable. I’m very curious how that would behave.
I’m trying to finish the ama, but it is taking some time. The next hull I build will probably be a 24 foot barge vaka.
Cheers,
Johannes
How about the 24’ 3-piece Wa’apa design, so you can bolt variously shaped ends on the center section?
I hope that none of these discussions cause any offence, Johannes…. as that is not my intention at all. I am on your side! In my boat building career I often find myself playing the roles of the cynic and the pragmatist and I have no doubt that it is often perceived as being overly negative when it begins to interfere with peoples’ dreams. It’s never my intention, but often my job….
I doodled a little diagram that demonstrates a few things clearly: the red, barge-shaped hull is not “just” five percent longer, but has about double the displacement and much of it is dispersed into the extreme ends. I do believe that to make a good comparison between the two fors that the displacent needs to be kept similar and that some of the volume from the corners of the barge should be reallocated into the stems of a comparable canoe. I would suggest that the green sharpie hull isn’t only five percent short, but rather closer to being only half the length that it wants to be. I’m not suggesting that you build another model, but there is bit of comparing apples to oranges going on here!
The very long barge hull you describe reminds me of the Thames River racing punts which are barely a foot wide. I wonder at what point the skin friction of such an extreme hull becomes insurmountable regardless of the reductions in wavemaking drag?
In the realm of solo paddling craft the tipping point is around 18’-19’ unless you happen to be a very large very fit person and are mainly interested in sprints.
This has gotten to be an interesting discussion. My take on the differences between the sharpie and the barge are more in the realm of fifty percent, given equal displacement.
I’m going to be sidelined for a while building wise and will try to run some reasonable trials thru Mitchlet to get a handle on the relative goodness of the barge and sharpie in the speed range we’re talking about. Should be interesting.
Skip
I’m sorry you will be sidelined, Skip. I take it that it is due to your injury. I’ll be very interested in the results of your trials though. Would it be possible to test a hybrid? Something like the advanced sharpie hull?
There are some other things to note about scows for comparison. Since they have very little freeboard on the bow, they gain at least some ability to cut through waves when they heel.
http://www.jacomosailing.org/wp-content/uploads/2011/04/C_SCOW_angle_of_heal.pdf
Also, since crew weight can be 50% of the sailing weight in a C-scow for example, when planing, crew weight shift fore/aft is critical (and effective) for gaining efficiency (not dragging the stern) and minimizing slamming into waves forward.
Soo true! The standard solution for every problem on a proa is: make it longer!
That is of course a very simplified “solution” with some exceptions, but never the less quite true. The whole idea (as I see it) with the proa is to get the most length and width for the least amount of money/material/hours working etc…
I’ve doodled enough on proas to realize that even making it longer doesn’t help so much with accommodations volume. The problem is that the narrow hull is well… damn skinny! And the pointed ends are virtually unusable except for storage. We can get around that with hull pods or steps, though this adds weight and complexity. Many times I’ve been doodling an interior and said to myself “!f only I had a foot more beam, I’d trade 10’ of waterline for that!”
Which is why I’m excited about the barge proa hull. The full beam out to the ends permit a more usable interior in a shorter boat, and let’s face it, a cruising proa could use some of that.
That said, I’m wary as anyone about potential slamming or other bad behavior, so I think Johannes approach is good - build some models, then work up to a human-carrying test hull. I’ll be very curious about Skip’s Mitchlet trials.
I tested my barge-proa again today. The was not much wind and it was very uneven. I’m impressed by the speed considering the circumstances.
I used my cell-phone as a GPS and used an old camera to record the speed.
I post a picture to show the conditions it is sailing in.
Cheers,
Johannes
I’m sorry you will be sidelined, Skip. I take it that it is due to your injury. I’ll be very interested in the results of your trials though. Would it be possible to test a hybrid? Something like the advanced sharpie hull?
Just got back from the Orthopedic Surgeon, eight weeks immobilized after arthroscopic repair of torn rotator cuff.
I’ll have to have to see how to describe a sharpie hull in Mitchlet without too much work, barge hull will be easy. Actually a vertical cross section sharpie is trivial also. Will try to do the simulations in a week or two after everything settles down around here.
Skip
Soo true! The standard solution for every problem on a proa is: make it longer!
That is of course a very simplified “solution” with some exceptions, but never the less quite true. The whole idea (as I see it) with the proa is to get the most length and width for the least amount of money/material/hours working etc…I’ve doodled enough on proas to realize that even making it longer doesn’t help so much with accommodations volume. The problem is that the narrow hull is well… damn skinny! And the pointed ends are virtually unusable except for storage. We can get around that with hull pods or steps, though this adds weight and complexity. Many times I’ve been doodling an interior and said to myself “!f only I had a foot more beam, I’d trade 10’ of waterline for that!”
Which is why I’m excited about the barge proa hull. The full beam out to the ends permit a more usable interior in a shorter boat, and let’s face it, a cruising proa could use some of that.
That said, I’m wary as anyone about potential slamming or other bad behavior, so I think Johannes approach is good - build some models, then work up to a human-carrying test hull. I’ll be very curious about Skip’s Mitchlet trials.
I kind of like that the basic design elements of proa has spectacularly stood the test of time. Western adoption of the design form hasn’t rendered any huge advancements in performance. This tells me the Pacific folks who came up with the proa concept really got the basics right - a couple centuries before Western folks could even equal their performance.
I like Johannes’ approach - testing and validating variances from the basic form to see what results. It will be really interesting to quantify the trade-offs - i.e. 16:1 vaka results in 75% speed, 20:1 vaka is the 100% baseline or whatever the results prove. Keep up the good work.
Very brave to be willing to risk your phone without at least a Ziplock bag and a tether!
—
Bill S.
How about the 24’ 3-piece Wa’apa design, so you can bolt variously shaped ends on the center section?
That is a great idea, but I´m stupid and stubborn enough to want to do everything my own way… Why make life simple and easy?!? 😉
This has gotten to be an interesting discussion. My take on the differences between the sharpie and the barge are more in the realm of fifty percent, given equal displacement.
That seems right to me. It does not behave like it is 50% longer in every way. When I say “fast” it is within the context of a simple to build barge hull. It will rutinely sail faster then its theoretical hullspeed, but i don´t know how much faster. I have given up hope to measure the speed of my model in some wind. I hope I can measure it on my 24 foot barge-proa instead.
I’m going to be sidelined for a while building wise and will try to run some reasonable trials thru Mitchlet to get a handle on the relative goodness of the barge and sharpie in the speed range we’re talking about. Should be interesting.
I´m sorry you are getting sidelined from building your proa, but I´m very very interested in any data you get from Mitchlet regarding the barge shape. What I have seen so for tells me that the barge is better in waves and rougher conditions, but has higher drag in flat water. I builds more wake for a given speed than the ASP.
Cheers,
Johannes
Which is why I’m excited about the barge proa hull. The full beam out to the ends permit a more usable interior in a shorter boat, and let’s face it, a cruising proa could use some of that.
Yes, that combined with the ease of building such a simple shape is the two main factors in my interest of building a barge. The word “barge” in a thread about proas gives the same warm fuzzy feeling as “root canal” or “speeding ticket” 😉 soo I have had my moments of doubt regarding all of this.
I have seen what I have seen, and I will not compromise with my own perceptions in these matters.
I am very impressed by Dave Zeiger and his Triloboats. He has been sailing his simple square boats in some truely wild and exposed waters for many years. I like when people dare to go their own way, and he is very straight forward and clear about his adventures and knowledge he has gained throughout the years. It have taken me some years and quite a few experiments to dare wander out into the world of square shaped hulls. For many years I was into Wharrams, but I never got around to build anything. They still hunt me in my dreams though. The Ariki is a very beautiful design and seems to be a very capable boat.
I kind of like that the basic design elements of proa has spectacularly stood the test of time. Western adoption of the design form hasn’t rendered any huge advancements in performance. This tells me the Pacific folks who came up with the proa concept really got the basics right - a couple centuries before Western folks could even equal their performance.
They where absolutly brilliant at designing boats! I don´t think there are many people in the west who understands all the finer details about the proa today. I fear that a lot of the knowledge is lost.
I like Johannes’ approach - testing and validating variances from the basic form to see what results. It will be really interesting to quantify the trade-offs - i.e. 16:1 vaka results in 75% speed, 20:1 vaka is the 100% baseline or whatever the results prove. Keep up the good work.
Thanks! I will!! I am very curious of where this will lead. It is a very eperimental design. Very far from mainstream yaching. People I meet when Im sailing my model are usually very curious of what it is and why I have built something that odd looking.
Very brave to be willing to risk your phone without at least a Ziplock bag and a tether!
You miss-spelled “brave”. It is spelled D-U-M-B in this case. The was very little wind and I made several runs without anything onboard just to see if there was any tendency to lift the ama. I did not have a ziplock bag so I trusted “luck” this time.
Thanks everyone posting in this thread! I greatly appreciate all your comments, ideas and stimulating discussion.
Cheers,
Johannes
Do you have an idea of a good beam to length ratio?
If you were to build a 12m main hull, how wide would it be?