Bolger Advanced Sharpie Proa, now with Videos.
I would like a much lighter build, but since im not a trained naval engineer, i have to overbuild instead. My experience with sharpies is that weight matters. They should not be to light, as that leads to pounding and excessive leeway. I need that weight to get enought of the hull down below the surface. The chines need to be at least on foot down, to get a good “grip” without heeling. When testing the model i found it to actualy sail better when loaded down a bit more.
I know multihulls “should” always be as light as possible, but this is the way i have found to “marry” the proa and the sharpie and combine a lot of their best characteristics. There is probably a lot of different ways one could build an advanced sharpie proa. This is an easy way i have found.
Obviously i did not have a moment of clarity yesterday…
I tested with a paper hold by hand close to the mast. I did not think it all the way through. Thanks for pointing that out. I guess i have to use a boom. But i still think a Wharram soft wingsail is good idea. Not having to turn the mast around simplifies the rigging and building a lot. I guess i get some of the same high efficiency and clean airflow around the mast as a turning wingmast, but without having to turn the mast.
With best regards
Johannes.
I wouldn’t worry about the pounding on a narrow proa hull. It’s never been a noticeable problem and is unlike pounding in a wider hull. You really have the bottom of a waterski in the water where that little bit of pounding equals lift equals speed. Please build it light like a model aircraft.
Gary
We have been sailing in our monohull this weekend, and i pulled the proa behind us. I removed the rudder to see how the hulls behaved in the waves. I think it handles them very good. We are doing about 4,0 - 4,5 knots when filming this. That is about twice the theoretical hullspeed for this proa. That would equal 18 knots if i scale the speed up to a 46 feet vaka.
I think the advanced sharpie hull manages to keep the bow clear of the water most of the times. In real life a proa sailing in waves this large, would be reefed down and slowed down a bit.
My thoughts:
HULL
Rocker: I had always assumed, a good rocker was beneficial as it give ease of turning, useful in a cat. Not so in a proa, as lack of rocker gives good longtitudonal stability and reduces pitching. (pitching being a huge loss of drive in choppy seas, as Sven confirms). Also with a sharpie, rocker causes the water to flow around the (sharp) edge.
18mm ply sounds heavy, but scaling up Pacific Bee I think you get 16mm so not far off. Are you covering with glass? For the bottom I would add extra glass. If this is a home and for cool climates, a sandwhich, two layer of ply with foam filling, would keep you warm and cut condensation.
SAIL
I do like the soft wing, and no reason for not having a boom, it swings away from the crew in any case. But: with no boom very high sheet loads are needed to give sail shape, and are still high with a boom. Also not easy to reef. Have you considered a junk or junk derivative?
MODELLING
Small models are good for seeing shape in 3D, but how useful when sailing? Do scale factors of wind waves and speed make it very dificult to see realistically what will happen to the real thing? (I I correct that the wind is a square-root factor?)
At 16ft, you can be a onboard, so get a feel of what is happening, that said, for a 46ft full size, your scale weight is nearly 2 tons! Also difficult to put yourself at the same centre of mass as the real thing. I noticed when I had a 16ft proa, the speed of change is much faster, one minute sailing next minute on your side!
Looking forward to comments and delevelopments.
Mark
Not so in a proa, as lack of rocker gives good longtitudonal stability and reduces pitching. (pitching being a huge loss of drive in choppy seas, as Sven confirms) .
I think rocker is very much needed in an advanced sharpie proa. The rocker is part of a lifting foil (the hull), like a wing on an airplane. There is no aircraft with totaly flat wings. There is always a rocker in a lifting foil. The hull (vaka) on my advanced sharpie hull is the main lifting foil, resisting leeway and enabling the boat to sail all other courses other than straight downwind.
The sharp 90 degree chines damp out pitching very well, and is one of the key points in why i want this kind of proa. All unwanted motion like pitching and hobbyhorsing, is very damped. A very low Q, ( = unwillingness to to resonate with any kind of wavelenght ).
I have compared the pitching motion in the youtube-videos of Jzerro and my AS-Proa, and i must say that my seems better at damping the pitching motions. Now this is a model and i know scale has its non-linearitys, so one can not just “translate” the behaviour of a scale-model with a large proa in an easy and simple way.
I think one can observe a lot of different aspects of the behaviour of a hull from a model and draw quite accurate conclusions, but its not always a linear relationship between the model and the large hull.
(pitching being a huge loss of drive in choppy seas, as Sven confirms)
Looking at Open 60 and similar monohulls, one can see that their forefoot is vertical (or very close to) and without any flare. This is partly to maximize waterline-lenght, but also to minimize losses due to pitching. Bows with a lot of flare will throw a lot of water far forward everytime it pushes down into the surface. A straight bow without flare will not do that. I think this was part of the success with Teamwork Evolution and its scowbow. It didnt throw much water far forward and out to the sides. The large scowbow damped the pithing motion, but at the same time let the boat ride very smooth on top of the waves. It doesnt try to plow its way through the waves, and it doesnt pitch very much. There is no resonance. Just a short well controlled motion.
As i mentioned before. I think we will se a lot of work going into the scowbow in a lot of different areas of sailing in the near future. Its a wonderful time ahead of us. A lot of evolution. We will see the proa really taking of and showing its potential, and we will see a lot of old dogma fall in the process.
Also with a sharpie, rocker causes the water to flow around the (sharp) edge.
The advanced sharpie solves the problems with crossflow over the chines. Just use the same rocker on the sides as on the bottom part of the hull. This is the reason Phil Bolger created the advanced sharpie.
18mm ply sounds heavy, but scaling up Pacific Bee I think you get 16mm so not far off. Are you covering with glass? For the bottom I would add extra glass.
My panels is only bent in one direction. They are not double-bent like in Jzerro or Pacific Bee.
I need stronger panels to compensate for the lost stiffness in double-bent plywood.
I dont think 18 mm plywood is soo much overkill in a 46 feet and 3,2 tonne Vaka. the bottom will have two layers of 18 mm plywood = 36 mm thickness. I will glass the outside of the hulls.
The bottom need to withstand a lot of grounding and cruising i shallow waters. There is kinds of barly visible junk laying around and just waiting to hole a careless boat.
Johannes.
two layer of ply with foam filling, would keep you warm and cut condensation.
That would be very nice. I think it would be very quiet to. But its too expensive and too much work. Plywood will have to do.
Have you considered a junk or junk derivative?
Yes, i have thought a lot about junk-rigs and lugg-rigs, but i dont like them in a shunting proa. I would like to re-hoist the sail everytime i shunt, so that i dont get a “bad tack”. I like the power and the versatility of the bermuda on a proa. I still consider it a bermuda, even if use a soft gaff-wing-sail as main-sail. I like to be able to fly big genoas and similar sails.
I dont want to experiment with too much different things. Some things i just want to work. I want to follow Russell Browns example in many ways, even though i am using a very unorthodox kind of hull. I think the Wharram wingsail and the daggerboard-rudders is proven in many circumstances.
Thank you very much for interesting points and thoughts!
With best regards.
Johannes.
Johannes,
While I do appreciate the simplicity of the box-sectioned, pram-ended sharpie style hull I think it is important to acknowledge the underlying mechanics behind a few of the merits that you appear to be witnessing with your models; you are seeing some great results, but there may be some illusions misleading you. I’ll try my best to explain and ask that you please understand that I am attempting to be supportive and not critical at all.
The rocker. Your tow tests indicate that your model’s bow is inclined (yes, pun intended…) to rise when towed, but it has little to do with “dynamic lift” as a result of the forefoot’s angle of attack. “Lift” is force created by inducing a region of negative [relative] pressure on one side of a surface such as above an aircraft’s wing or to leeward of a boat’s sail which is not the case here. There is indeed an upward force under your bow being created as your hull attempts to move forward as easily as possible, but there is also an opposite effect attempting to draw your stern down at the same time and the net upward pitch is really just the result of your model trying to overtake its displacement wave system; the bow is trying to climb up it’s bow wave and it’s tail is sinking down into its trough. There is no appreciable lifting force. Many features that make for an effective bow unfortunately don’t translate well into an effective stern when simply turned around the other way, which will always be one of the banes of proa ponderers everywhere!
The scow bow. There have been more blunt-nosed boats built in history than there have been pointy ones and with good reason: it does a lot of things better. It gives a greater displacement for a given amount of building material, making it a more efficient load-bearer. It’s more resistant to pitch and to roll, making for more stability in many cases. It’s often easier to build. It can create a hull with a length limited by a class rule that is might be inclined to plane a little bit sooner than it’s pointier competitors as demonstrated by Teamwork Evolution’s Mini and the current crop of Volvo Ocean Race entries; they focus on sailing in planing mode and they have hulls that are optimised for reaching that condition sooner and staying there longer at the expense of being atrocious sailers off-plane. All reasons save the last are applicable and beneficial to a proa in some way; I would encourage you to appreciate the recent scow-bowed racers as a source of inspiration for their creative thinking, but discourage trying to apply their reasoning to a cruising proa beyond that.
I quite like your approach to using pram-styled ends on the vaka and I think it is important for us all to remember that proas are just boats with two identical bows, but two identical sterns as well. There is another thread of discussion on the forum currently regarding a cylinder-moulded hull’s affinity to be built with a transom; perhaps it would be even more appreciative of being built with two of them?!?
Thank you for your entusiasm Johannes; I find it both refreshing and inspiring.
MTP
Thank you for your entusiasm Johannes; I find it both refreshing and inspiring.
Thank you very much! As i said before. I only want to contribute back to this site and everyone active in proa-development. I have been thinking about this proa for the last two years now, and i thought i needed a realitycheck.
I fint this forum very supportive and encouraging. There is a lot of knowledge here! Thanks everyone, and thanks MTP for a realy insightful comments!!
I quite like your approach to using pram-styled ends on the vaka and I think it is important for us all to remember that proas are just boats with two identical bows, but two identical sterns as well.
I think the wider stern is a really good thing. In my tests i can see that it flatens the sternwave and relese the water in a very smooth way. Its very similar to surfing, and sometimes it looks like it starts to plane. The first hint of a sternwave starts about half a hull-lenght aft of the actual stern.
The rocker. Your tow tests indicate that your model’s bow is inclined (yes, pun intended…) to rise when towed, but it has little to do with “dynamic lift” as a result of the forefoot’s angle of attack. “Lift” is force created by inducing a region of negative [relative] pressure on one side of a surface such as above an aircraft’s wing or to leeward of a boat’s sail which is not the case here. There is indeed an upward force under your bow being created as your hull attempts to move forward as easily as possible, but there is also an opposite effect attempting to draw your stern down at the same time and the net upward pitch is really just the result of your model trying to overtake its displacement wave system; the bow is trying to climb up it’s bow wave and it’s tail is sinking down into its trough. There is no appreciable lifting force.
It might be wrong, but i tent to see it as “lift”. Not exactly the same way as a foil or birds wing. It does however lift the bow out of the water, and thats what i want. When the blunt bow hits a wave it throws some water around, and that is opposite to what i want it to do. The lifting action of the pressure under the forward part of the bottom works together with the low pressure under the aft part of the bottom - to lift the blunt bow out of the waves.
There is another thread of discussion on the forum currently regarding a cylinder-moulded hull’s affinity to be built with a transom; perhaps it would be even more appreciative of being built with two of them?!?
That seems like an great idea!!! I really like it!
With best regards.
Johannes.
I am not sure of your idea with applying the advanced sharpie to a proa. Does a slow moving mono inshore have much in common with a fast moving multi, especially off shore?
The scow bow only works because it has little height, in other words it is still sharp, though turned through 90 deg when viewed head-on.
The fast multi has to be wave-piercing, if it not wasting energy pitching or unsafe in falling off tops of waves. Proa is long, the rig is low, therefore the bow not pushed down too much, so works very well. A blunt bow is not too good for wave piercing!
As previous contributer added, a proa has two bows and two sterns. So too much rocker does hold it back. I first read of the minumum rocker on the Harry proa site. I believe Russell’s later designs have less rocker.
Regarding sharp chines at the hull ends, they are not good for slow speeds, but very good for planning. A bit of rocker does help here. As an (ex) windsurfer, I do appreciate the planning hull. Whether it has much advantage in a long thin hull, I do not know. The cross flow over the (Bolger) chine only happens when it is healed over, hope this is not the case with your proa!!
When (if?!) I build, it wil probably be a simple dory / sharpie hull shape, being so easy to construct and fit-out. It would have a small rocker, say about half the hull dpeth*. There is a question whether the chines are sharp or rounded, probably stick with sharp and accept the small loss is slow speed performance.
*Crash protection by building in a 45 deg slopeing bulhead.
Cheers
Mark
I am not sure of your idea with applying the advanced sharpie to a proa. Does a slow moving mono inshore have much in common with a fast moving multi, especially off shore?
I think the “advanced sharpie” has more to do with an even distribution of pressure around the hull to offset the cross-flow over the chines. Cross-flow gives a lot of eddies and friction = less speed. I’m not building a short fat 3:1 or 4:1 AS-hull. Its still very slender and light compared with a mono-hull. I cant see any problems with a boxy cross-section off shore?! I have to build it strong and durable, but its built out of large arches, so there is a lot of stiffness in the geometrical shape.
As previous contributer added, a proa has two bows and two sterns. So too much rocker does hold it back. I first read of the minumum rocker on the Harry proa site. I believe Russell’s later designs have less rocker.
The rocker is part of a whole. If one just thinks about the rocker, it might seem a little much for a for and aft symmetrical slender hull. But one has to view in the right circumstances. Its part of the whole “offset crossflow - even pressure distribution - lifting body” idea. Just as one shouldn’t remove one wing from a Boing 747 to lower the “wet”
surface, one can not just pick one piece of this hull, and say its wrong. I can agree that to much rocker would not be a good thing. My tests are partly to find out whats too much and whats too little rocker. The new model i am building is longer with less rocker. The downside is that the blunt ends will be wider and closer too the surface. I will have to test it before i can say anything about it.
Regards.
Johannes.
Johannes,
The cross flow and subsequent eddies aren’t really much of a problem with such lean shapes as you are building. My tamanu hull has slight (I think 10 degrees) flare, but reasonably sharp edges. I did router them slightly to get glass to lay around the corner. While you are building little models, you should also try a low rocker boat with a pointy bow. Having seen a Martha Jane pound upwind on the Texas 200, it’s a wet experience. Even getting the CP too high can thrwo some spray as well as seen on the Harryproa videos. If in fact this is to be a cruiser, the directional stability of the lower rosker hull would be a good thing. The pointy bow would slice cleanly through waves going upwind. The pram bow on the Moni you are enamored with is to encourage the planing that a super narrow proa hull probably will never achieve—nor does it need to since it simply leaves behind it’s own wave like you are seeing on your models. Minis are not designed to go upwind really at all. I’d be inclined to say neither are the AS boats judging by their foil package and rigs. I think the AS series are designed to be ruthlessly functional, offer huge interiors, and be super easy to build. That said, some of those same traits whould be very appealing to you. Easy build? Check. Big interior volume? Check. I just don’t think the mono background translates to the multi reality of super slim hulls. The rocker you are building into the hulls will help keep the bows out of the chop, but once they start to hit it’s going to be quite a sight. While you are toying with the model phase, try something contrary to your AS approach. Maybe mess with a pointy bow, or a very low rocker hull or something. Either way, you’ll have learned something valuable to add to your knowledge base going forward to your cruiser.
I like that!!!!!
This thread ist a real blast. Our opinions are very similar, because I also favour a flat bottom/hard chine configuration. I did not catch every detail of this thread in the moment, but want to respond on some.
You said that you want to learn sketchup for your design. Scetchup is good for the general overview and details like pod and cockpit. Download free!ship as well and design your hulls with it. Its a free design programm für designing hulls and you have all the relevant Data and hydrostatics. It also gives you the plate developments for the hull.
Rocker of sharpie hulls: “Mbuli” of Cheasapeake Light Craft has the right amount of rocker. The 20’ boat has been proven to be fast and safe, with no tendency to pitchpole. The forefoots are just below the waterline with a (thoretical) trim of full displacement and ama flying. In the habour (with the ama taking some of the displacement) the front of the bow is above the Waterline. When sailing the forefoot is out of the water as it should be in a sharpie.
Your rockerline seems to be a part of a circle, thats the wrong line, because it does not support a stable fore and aft trim. Flat it out in the middle a little until you get a soft curve and add a part of a circle at both bows to bring the two forefoots near the waterline. Easy to do with freeship.
Wheight and Displacement: Don’t go with your superheavy structure and keep the boat lightly built. I agree with making the botton of the boat stronger than the sides, but don’t double it. If you are afraid to build the boat fragile keep an eye at the scantlings of similar sized plywood multihulls (wharram for example).
In the last weeks I had a private chat about cruising proas and I made some rough design studies for a (2 - 4 people) offshore cruising proa. I calculated a needed displacement of 4000 kg. 1000 to 1500 kg of that displacement is payload, so the boat should not be heavier than 2500 - 3000 kg. I managed it to put everything together in a 12,8m long vaka ( 42’ ). If you are interested I can spoil your thread and post a basic linesplan of the vaka here.
Ratio: I ended up with a LWL / BWL ratio of ~11 and I’am quite happy with it.
Length. Playing around with the length is a funny game at the design stage but it is a lot more hard work and high costs if you are building the actual boat. Its definetly not the addition of just another plywood panel. A longer boat means higher weight, more sail area, heavier and more expensive deck gear, higher docking costs and so on and so on. Keep the boat as short as possible without spoiling the lines and numbers. 46’ is the hell of a big boat and very expensive to build, equip, sail and maintain.
Ok, thats it for the moment, let me hear your opinion..-
Best wishes from The German North Sea Coast, Michel
Yes, i have thought a lot about junk-rigs and lugg-rigs, but i dont like them in a shunting proa. I would like to re-hoist the sail everytime i shunt, so that i dont get a “bad tack”.
That doesn’t seem to be much of an issue with Slieve McGalliard’s split junk rig. Have a look at http://www.junkrigassociation.org/slieve
The Junk Rig Association had a meeting in Stavanger in August several times. I could check whether there will be a meeting this year. Slieve’s Poppy is unlikely to travel there from the Solent, but there normally are several boats with cambered panels. Try it before you decide. The simplicity, low loads, low cost and easy reefing very much fit with what you are aiming for.
But i still think a Wharram soft wingsail is good idea. Not having to turn the mast around simplifies the rigging and building a lot. I guess i get some of the same high efficiency and clean airflow around the mast as a turning wingmast, but without having to turn the mast.
Not rotating also simplifies using a (pair of) tricolour lights on the mast. But a proa gets the clean lee side for free, without a rotating mast, at least on the wind, when it matters most. Your mast track is on the lee side anyway. You would gain less from the Wharram wingsail than a catamaran.
I once read a claim that the Wharram wingsail tends to have more friction between cloth and mast than a more conventional setup. I don’t know whether that claim was based on experience, or just someone’s expectation. I recommend arranging to sail on a Wharram, and to try reefing. It would be ideal if you could arrange that both when mast and sail are dry and when they are wet.
Regards
Robert Biegler
While you are toying with the model phase, try something contrary to your AS approach. Maybe mess with a pointy bow, or a very low rocker hull or something. Either way, you’ll have learned something valuable to add to your knowledge base going forward to your cruiser.
I have way to little time to build all the permutations of this proa i would like to do. It takes a week at the least to build a simple model.
Matt Laydens Paradox has differing rocker in the sides and bottom of the hull. but its only one part of a really clever way to get good windward ability without any foils or keel. I really dont like it outside the Paradox-design, as i am more afraid of cross-flow and added resistance than of some additional rocker and associated problems.
I understand the idea of using as little rocker as possible to resist hobbyhorsing and excessive pitching especially in a multihull, but im not convinced that is the only way to avoid those problems. I think too little rocker makes the hull behave much worse in heavy seas.
The traditional Polynesian and Micronesian proas has lots of rocker. There must be some reason why they did so.
Its a very interesting problem. I will test my latest model soon (i hope). It has 32:1 in Length/Rocker ratio, instead of 24,2:1 as my current model.
This thread ist a real blast
Thank you! I hope we all learn something from this. I have learned a lot already! Its going to be very interesting times ahead. I hope we all will see the Proa start gaining momentum, qnd really show its potential.
I will answer more of your questions soon. I need to find some papers i have copied out of a book.
Regards.
Johannes.