Adapted design, 40 ft pacific proa

Discussion in 'Boat Design' started by Vortiseas, Apr 20, 2018.

  1. Vortiseas
    Joined: Apr 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Ladysmith BC

    Vortiseas Junior Member

    Cold molded 40 ft LOA pacific proa, similar in many ways to Jzerro including main hull rocker and lee pod. Sani-tred hydrophobic paint w/o glass, (lighter, lower maintenance). Black walnut exterior layer for toughness. Longer outrigger hull with better wave piercing but similar buoyancy relative to scale.

    I appreciate your insights. I do not have the great benefit of prior boat builds and thousands of sailing miles on pacific proas. I’m checking with the top guys to see if I’ve got this about right.

    1, a)Why not combine an oceanic sail on a track with a jib foresail? The oceanic sail would then be about 25% less than max versus traditional. The oceanic would then be manageable singlehanded at that size. This combination would facilitate scaling the sails to the conditions. It would also allow for autopilot use, storm jib only, and better reaching. That’s where my research took me.

    1. b) Oceanic boom and yard...Delta wing concept at work....Finer wind entry angles = greater sail force according to wind tunnel testing. Round is strong and easy, but not the most effective. Why not an elongated triangle shape for yard and boom? A couple of folding supports between the yard and boom might be needed to counteract twisting forces. I intend to try this out. Your thoughts?

    2. Foresails: Why not interconnect jibs/foresails with a winch in between....raising one lowers the other.

    3. Foils. I haven’t seen any low drag small foils used primarily for trim. This would apply more to proa designs with hull rocker, a fairly narrow application.

    All of these 3 features promote ease of use from the control center.

    I have intended to build a pacific proa for about 7 years. Read everything I could find. Hydrodynamics of ejection vortices, fluid dynamics, supersonic modelling and relative hull behaviour plus forum threads, all of Russel Brown and Harmen Hiekamena’s info, Jim Antrim's site on proas, traditional info and more. My thanks to all for sharing information.

    My design includes 2 inches of keel protrusion to lessen the needs for daggerboard/rudder use while also acting to lessen hull damage potentials in beaching, trailering, launching and unexpected debris (like logs in the water). Lots of debris in the Georgia straight and further north. The design allow for local boat launch use, (folding AKAs). The pivoting drive system should allow adequate steering. I accept a minor drag gain may occur due to the keel depth addition, but a decent trade for added safety. And yes, folding AKAs will be larger at the hinge points so the AKAs will be a little heavier, but a trade-off that allows launching from a standard boat launch, hauling on a trailer, self-righting with airbags maybe, and even, heaven forbid, berthing at a marina. 14 ft total width when folded.

    West system, black walnut outer hull layer because of toughness, sani-tred hydrophobic paint, (rubber, low maintenance, poor marine growth adhesion), no glass layer except on keel, bubble channelling on lower aspect of hull, my own design retractable pod drive electric, (neodymium magnet motors provide high torque at low rpms and are very efficient), airbags for self-righting is a potential I am considering. A folding outrigger design that includes folding when turtled and auto-dismasting without breakage seems to be an attainable and worthwhile goal.

    2 sets of eliptical wing foils, each at 25% of hull from each bow. Foil specs: lateral dimension 10in, width of 6in. Paired, one each side, on through hull pivoting shaft. Oval outer edge. Located a few inches above keel.

    Sail plan of oceanic plus jib foresail. Sail track for oceanic sail across lee pod, doubles as a railing, except across pod. Moved by hand winch on endless line from the control station. This facilitates single sailing. Railing meets a more prominent bow rise similar to the traditional Chamorro design. Because of this the apex of the oceanic sail is elevated by about a foot. A little improvement in pilot visibility is good.

    The primary objective of the foils is trim. Other benefits may be realized. These were my thoughts as to why to add foils.

    1) Hull rocker aids in sail steering. (The bow or stern can be "skidded" by loss of depth in the water). If what I read was correct, this also allowed tighter sailing to the wind. In native tradition, weight shift was used to accomplish this. Foils can do the same with no-one extra to feed. Foils would react faster than a weight shift. Less weight = more speed. This does not overlook the ability of sail positioning to impact steering, it is just an additional aspect that applies to proas with hull rocker.

    2)Russell Brown includes the tendency of Jzerro to “bury the nose” in some sailing conditions. Other sources agree. Jzerro has similar hull rocker to my design. I believe that trim foils would act to counteract this. He also includes using the stern rudder drop to counter-act this tendency. He wrote about having a foil incorporated into his rudders. I believe that being able to trim the nose up with foils adds safety and improves sail-ability in some conditions. This is not a criticism of RB's design, just a different approach.

    3) If the trim foils eliminate much of the cruising rudder use needs in steering, the rudder/daggerboards would be up. Rudder drag is eliminated at those times. This would offset most of the drag loss related to the foils when looking at the total time when both are used. Traditionally, the crew moved to shift weight to aid in sail steering or to lift the bow. Foils don’t add the weight of a crew or ballast and don’t fall overboard in moving about.

    4) I expect that the foils would be quieter than the noise of the daggerboards as well.

    5) Some braking effect may be realized by near vertical positioning of the four foil planes for the occasions when slow is best. This would be an assist to sail repositioning for braking.

    6) I also consider that a minor sea anchor effect may occur in storms with this design. (my design includes ballast tanks both hulls and I will have multi-cone sea anchor onboard).

    If three of the above reasons are incorrect, that still leaves 3 valid reasons to use trim foils on this design. (That doesn't make this applicable to proas with little hull rocker).

    I am presenting the how and why of the foils to share ideas and learn where I can. I am not invested in the foil plan. I have discarded many design ideas already regarding this build. But to discard a well researched design requires that my understanding change so I can recognise my error. I prefer to recognise errors ahead of building a design. This design affects the hull shape so it is a bigger issue than some. The foil question needs a bright and open mind balanced by experience. If this is you, I would appreciate your input.

    My approach to the complex design questions is: research in depth, understand, design it, research further, redesign it multiple times, ask the right people, finalize and build. I have a couple of great local boat builders/sailors who have already added their insights. I am close to finalizing this design.

    My understanding is that shaft stuffing boxes and waterproof shaft seals, these are not complex. West system allows for custom (home built) graphite bearings. Making the foil weaker than the combination shaft/hull allows for safety on impact. A pivoting straight shaft with a foil on each end is about as basic as a system can get. The location just above keel allows for very strong attachment points. Replaceable foils allows for design changes. A little mechanical advantage makes for easy operation. A sleeved shaft on the pivot arm that allows passive extension/retraction would connect to an actuator rod. This rod would pass through 2 bushings to maintain the position of the actuator rod through a seal in the stuffing box lid. A mechanical, closed hydraulic or electric system would then be attached. An electric window motor from a car would do just fine, waterproofed of course. (They are already water resistant). Not much more of challenge to use than operating a trim tab button.

    DRAG and FOILS
    An oval ended elliptical set of 4 wing-foils with an area of 200 sq inches should create little drag when neutrally positioned. The following design applies:
    Supersonic air/fluid dynamics are transferrable. A small waisting-in at the foil exit point should reduce and dissipate the related shock wave of the foils at the hull exit points. This is what is done at the wing/fuselage attachment point on supersonic aircraft. This waisting-in will allow hull clearance for effective foil positioning. It may be that efficient foils will add very little drag when neutrally positioned if the related shock waves are effectively dissipated. The drag created would be offset most of the time by lessened rudder use secondary to more effective sail steering.
    These are not large foils. 200 sq inches is small compared to the overall hulls wetted areas. Final foils size could include trial and error as they are removable. As a comparison, RBs, (now Ryan's) rudder on the Jzerro is small, but effective at moderate-high speeds. His rudders on proa builds incorporate a small foil as he wrote. Harmen Hielkema used elliptical daggerboards.

    My design allows for foil angling which would be difficult to build into a rudder design. (I tried to sort this out can be done, but very complex to build. The simplest way I found was to pivot the dadderboard. Other approaches weakened the whole structure).
    Foil angling works on subs and on supersonic aircraft.

    I am a 35 year paramedic, about to retire. Main and side jobs include being able to do just about anything with a car or a house, sawyer, lumber grader, heavy equipment operator on 5 pieces of equipment, welder/fabricator, faller. Jack of all....master of a few. I have completed 4 big individual projects that ran between 2 and 4 years. I have been quite successful under the design and build category. This boat design/build is my next big project once I finish the next 4 years of commitments, (a property development included).

    So....would you be interested in adding your thoughts?

    And I am staying out of the whole Atlantic/Harry/Pacific debate, especially since my boat currently consists of a bunch of clear red cedar, d-fir and the black walnut is still logs. I researched in depth and designed my own boat. Others are entitled to their beliefs without acrimony.

    All the best and thanks for your input in advance, T
  2. chinaseapirate

    chinaseapirate Previous Member

    Well congratulations on choosing the best sailing design, bar none, in the world. Will this be a racer/cruiser? I'm imagining more cruiser than racer because of "folding" akas. Feel free to try anything you want on cruiser (comfort) but the "trim foils" seem dubious on a racer (ultimate speed), that 3 feet squared of wetted surface is significant compared to 50 feet squared or so of the wetted surface on a 40 ft racing multihull, maybe your design has 80 feet squared if it is 4,000 lbs (and flying theweather hull). Pivoting, implies some form of active control, but (and probably missing the point without a drawing) what do you want to chieve with the "fins"? Do you want it to squat on the back of a wave and plow through the front of one to "level out" ? Other foil systems do this trick in the air not in the water...

    Unfortunately, even though I have sailed on a couple of outrigger trimarans with their native owner/builders the both had pretty much standard triangle lateen rigs and no jibs or crab claw shape...they were faster the wind in 5-8 knots of it, slower in <4 and I have no idea in over 10 knots. For me I have always wanted to try a symmetrically cut, foot and leech are equal, large windsurfer (flexible tapered wing mast) type rig suspended and balanced mid mast "oceanically". Either one or two, probably just one on a forty footer. Seems perfect for a proa. I've been to CNMI, plenty Chamorros but zero proas did I see.

    Sorry I cant help much there with rig or foils. However, I strongly suggest that, excluding extraneous criteria, you do not cold mold it. Strip plank it. If you can't devise a method (dowels epoxied through the strips) without relying on the glass in/out that you don't can still double strip plank it, technically double diagonal cold molding;), just orient the strips 30 degrees from each other LENGTHWISE. Faster (construction), easier (materials to obtain), lighter (less frames), and stronger (roughly twice because of grain orientation). Not to mention less epoxy, ease of applying the strips, and hoards less of fairing. I have used both methods not just relating what I have read. Also, I'm not in favor of water ballast as opposed to having more weight initially in the windward hull. Use a foil or two on it, keeping the windward hull high and dry. It (windward hull) should be in an ideal negative feedback loop with foil lift vs heeling moment and gravity. Ignore waves just build wider.

    Good luck, you won't regret building any type of Pacific proa.
  3. Vortiseas
    Joined: Apr 2018
    Posts: 5
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    Location: Ladysmith BC

    Vortiseas Junior Member

    Cruiser with long race potentials. The intent is fast with comfort potentials, single sailor capable, durable, low maintenance, blue water after trials.
    I plan for the 4000lb range. Jzerro pulls 21 knots, longer should be a little quicker in the same conditions if I've done my homework right.
    My design is unlikely to beat a full on racer. They have reliability issues that I can't tolerate with my sailing plans, and liveaboards are heavier with all that is needed. Shelving, a stove, fridge, etc. That said, if unloaded for a race it might surprise a few bigger boats and do it with less crew. Then back to reload it all. Why not, I'll be retired anyway.

    The foils...Running, "bury the nose tendancy" occurs according to RB. When running before the wind bow trim up would counteract this. I didn't consider squatting the stern as well. My research says that hull rocker changes the dynamics of sailing a pacific proa in regards to sail steering. Bow up position will cause an off wind yaw of the bow. Bow down position will cause a stern yaw. Both change point of sail. In a very light proa with medium hull rocker, the difference is significant. Sail steering in this boat type includes sails and hull position for best performance.

    The ballast tanks are for very heavy weather with a storm jib up or a bare pole with the sea anchor down. Mid ocean can deliver the worst and I intend to be as prepared as I can be.

    The folding Akas will add about 15lbs per joint, 4 "knuckles". A modified hinged leaf spring will overlay the top of each hinge. The spring's curve will be reverse to the akas. I can have these galvanized. The hinge side bolted through a plate, then the aka into a plate below. The mid point of the leaf spring crosses a piece of rubberized belting to focus pressure directly on the hinge and avoid wear. The other end is modified to receive a through bolt that dogs the hinge down like a freighter hatch cover. A three ft spring section should do fine. My minor blacksmithing interest allows for all of this. The joints will be overbuilt so that they are not weak points. Roughly 60 extra lbs is the trade off for many advantages.
    That puts racing back on the table.

    The sail combination is changeable as it is all above deck. Oceanic and jib in combination seems untried. Unless I find information that says it won't work well I will give it a fair trial that includes trialing the elongated triangular yard and boom on the oceanic mainsail. I can handle being wrong that much, especially since I'm building almost everything.

    I am fortunate in having access to logs and a mill. My wood costs me time and minimal other expense. I currently fall timber as a side job.

    The hull plan is currently 3/8ths thickness in 3 layers. Cedar at 30 degrees lengthwise, next cedar layer opposite, black walnut lengthwise. This on integral 5/32 x 2 inch flat ribs of clear bluff grown d-fir. Bluff grown d-fir is exceptionally tough stuff. It almost rivals yew. I trialed it when running a single band sawmill. Except for 2 bulkheads, all the frames will be removed at the end of the build. 3/4 d-fir square strips lengthwise on the frames 6 in apart. Now it changes from normal. I want more strength to just above the waterline, less above. The D-fir strips are now run vertically. They begin two inches apart in the bilge. At the waterline every third strip stops. 18 inches higher and now every second strip stops. There is now 4 inches between the rib strips. The average is one rib strip every 6 inches, but stronger where more strength is needed at the waterline and just above. The effect is tapered plywood. I may need to do some steam setting to get what I want.
    1/4 inch topsides, everything incorporates curves. Built in strong points where required of course.
    The flat ribs are a variation on strip canoe building. Monocoque design allows for less structure. Cedar strip canoes are 1/4 inch plus flat ribs. My approach is 3/8ths plus flat ribs, more to the waterline and less higher.

    All hulls need a form of ribbing or frames so I exclude this part and focus on the hull sheeting.

    Two rows of strip planking =1/2 in. I don't see how strip planking can be used without glass. Glass adds weight.
    This compares to:
    3 rows of 1/8 strips = 3/8 in.
    Epoxy adds weight, but a lot of strength.
    This method allows for a horizontal layer of black walnut for toughness.
    This toughness does away with the need for glass - saves weight

    If I am correct, because of the weight of epoxy in cold moulding, 3/8ths cold moulded = 1/2 inch of strip planking. But there is no current method of sealing strip planking without glass. The strip planking method is then about 20% heavier, and it is not likely to be stronger. That would turn my 4000 lb boat into a 4600 lb boat as this only applies to the hull. Or I missed something somewhere. It's easy to see why plywood is so popular.

    The Chamorro design is fairly recent as I recall. I found it online. Part of a resurgence of interest in traditional sailing. Strip planked, with a higher bow rise with flare at deck level and substantial hull rocker. I am incorporating a similar bow rise and some of the flare. This may be enough to offset the issue of "burying the nose".

    I've read threads on ama hull foils and seen the pictures. But in all conditions was the question left over. Are they capable of keeping the ama down when in big seas and gusty high winds? I agree that they are quicker in flat to choppy conditions, or in large swells, but are they safe in the worst of it?
    That's a "bet your life" question that no-one has answered as far as I know.

    I appreciate your input. Thanks, T
  4. chinaseapirate

    chinaseapirate Previous Member

    Well I like your described construction method. Scale it up to 5/8" (with a couple 15 degree layers in it 2nd and 3rd) and 72 feet, explain to the 49 pax rating retentives that it is 30% stronger than the Kurt Hughes scantlings and warrants the extra 7 feet. I would not classify it as cold molding though. Technically it is, but once you find (or possibly already know) out that your veneers fit best at 1/8" x 3/8" for the cedar and maybe get away with mostly 1/8" x 3/4" for the walnut, you may start to refer to them also as "strips". Just taper the D-fir strips 1 1/2 to 1/2 inch and set them 1 1/2 inches apart same weight and wont look like a digital equalizer from inside. If you need the 2" gap for clamping space or something then 1 7/8" by 5/8" 2" apart.

    I was thinking 9/16 x 3/4 bead and cove cedar pinned together with 3/16 fir dowels every 8 inches or so you wouldn't have to glass it. Honestly I don't see the problem with 3.2 oz glass in/out only for reassurance. It is not 675 lbs heavier. Its only part of the main hull . 1/2" wood epoxy - what 200 feet square? 240? 300 lbs 20% = 60lbs over at 1/2 inch. another 30 lbs over with the extra 1/16 of cedar. And if it was (2) layers of 1/4 x 1/2 inch (STRIPS) then no bead and cove, no dowels, and possibly no glass - up to you- (I convinced myself long ago to go with the flow and glass at least outside:)) then its the same hull as yours just no walnut and one less layer. That's why I like your 3 ply better but its just semantics to say that double planked hull needs glass whereas a triple "planked" one doesn't.

    I found some "old style" proas from Chuuck and Guam - 2" solid "logs" but not the newer design you referred to. I don't believe your in an immediately life threatening situation even if you picthpoled/capsized you're proa. Just have an in-case plan. Jzerro has a full marconi rig up to the pulpit. This drives down the bow further than what the type of rig you are describing would, significantly. If you are really worried , place the fins at 5 degrees positive angle of attack just below the shearline near the bow, or 2-3 degrees just above the waterline, or both. lots or early proas had "spoons " up there. I like fins (foils) (mga palikpik) better.
    Last edited: Apr 22, 2018
  5. Vortiseas
    Joined: Apr 2018
    Posts: 5
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    Location: Ladysmith BC

    Vortiseas Junior Member

    Tapered d-fir I had not considered....a much better option to achieve the desired goal. I will incorporate this change. Curved in place plywood is phenomenally strong and resilient. The 3 million stress cycle comparison tests that I found are the proof. 70% strength retention for this type of construction versus 22-25% for glass. All of the other common materials compare poorly. Then add that wood is lighter, is not rot prone with epoxy, will absorb medium load side impacts without denting or cracking, and has low thermal transfer properties, (less sweating). I am very fortunate to have access to the very best of materials at low cost, (family logs, work trades, mill access). I agree regarding a lot of frames to construct this properly. By using tying wire through small drilled holes in the 1st layer of ribbing the frames will be easily removed afterward. Part of the reason I chose this ribbing method was hard point avoidance. The hull is most likely to be damaged where the hull cannot give on impact, next to a frame or stiff rib. Integral light ribbing has better load transfer properties. This isn't telling you anything you don't already know, but rather explaining that I have a good understanding of this aspect.

    After reading your last post, I agree with you as to the weight of each method. I don't have the background to make a fair comparison between the methods as to weight. I have studied one design quite a lot for a first builder. That means I know just how much I really don't know. My design isn't really my design at all. It is an incorporation of many elements of others proven designs. Those designers are all a lot more developed in their fields of expertise than I am. I learn where I can.

    What I did not understand is that the construction method I came up with for this boat is maybe a "between" method. Not quite cold moulding or strip planking. I agree with your point about strip widths, and thanks for that. I admit that I was scratching my head a little in considering how to have the strips conform to the complex curves involved without creating gaps that would require thickened epoxy fills. My primary goal is the right combination of light and strong as this so greatly affects all the potentials of a proa, regardless of the quality of the hull shape or sail plan choice. Unnecessarily added epoxy weight doesn't fit this goal.

    As with foils, daggerboards create drag. That loud hum they create is the outcome of drag. This design does not incorporate daggerboards. That said, I can build them into the design later if I am am wrong. I did a lot of research of hull shapes. A square has the least waterline per cu ft. (when the beam is constrained), while ovals have better hydrodynamics. A pacific proa has the wind from one side only of course. An asymetrical hull has some advantages in proas. The deep micronesian proa hulls have a lot of wetted surface but don't use daggerboards. Rounded hulls need daggerboards more often to avoid excessive yaw.
    What I settled on is a near flat lee side on the main hull to the keel. The bottom begins laterally at the keel and curves in a round shape to the windward side. The roundness of the windward side allows for good hydrodynamics. The hull is tapered of course, and transitions to a fine bow form. The flat lee side should be a benefit in "gripping" the water while also reducing the wetted area. If I am correct, this will eliminate the need for daggerboards and thereby reduce drag. A lower wetted surface area should also reduce drag. If I later find that I need daggerboards, they can be smaller in comparison with other hull shape designs. What this hull shape also does is add 1/2 the advantages of a square to a round hull in reducing the wetted area. This also reduces the complexity of the build as it is easier to build a nearly flat side. Allowing a hull side to move on purpose might cause some fits amongst traditional boat builders, but I am confident in the 3 million stress cycle tests and how this applies to a 3 layer wooden hull with integral ribbing. Besides, all boat shapes twist and otherwise deform in the water, it's just a question of how much is tolerable within the design parameters.

    I will have retractable windward side mounted rudders available.

    As for sail plan and burying the bow, I agree that by using the oceanic mainsail I will have less of this tendency in downwind runs. I also theorize that if I can counteract this tendency I can fly more sail. I have read in many posts that pacific proas have less success downwind than many other designs. This leaves me with an interesting question: Will the combination of trim foils with more sail area and no daggerboard drag make this design a competitive downwind sailer?

    What remains to be seen is the effect of dynamic hull shape changes that will occur on the lee side of the main hull. Being near flat with integral ribbing, high speed pressures are likely to create a degree of convex in the lee hull shape. The hull may create it's own foiling advantage through this. I am leaving this hull area free to move inward by design, at least between the two bulkheads. I can do this by cantilevering the cabin floor bracing off of the keel. This would leave a gap between the cabin floor and the lee hull. I can later temporarily brace the lee hull side against the floor for a comparison and see what is faster.

    I expect to get some bubble production from the fin/foils. Not from cavitation but from wave action creating pitch. The 50% center area would benefit from bubble channeling IMHO. How much gain through this aspect is up for debate. Perhaps 3-4%. The choice of a hydrophobic paint should help control the water adhesion, the bubbles should help and the surface ejection vortices should be reduced overall. This is part of the reason I am avoiding glass. I am attempting to make this hull "slipperier" in the water. It would be difficult to maintain the shape of small oval bubble channels if glass is used. The combination of bubble chanelling with hydrophobic paint should reduce the size of the hull ejection vortices.
    Use of the "kirabati dimple" has been trialed with success in real life by Harmen Hielkema. It theoretically dissipates a mid hull shock wave on asymetrical hulls. I plan to incorporate this as well.

    Improving the wind entry angle of the oceanic main has been wind tunnel tested. As compared to round "spars" the finer entry angles created elongated triangles improves sail force by over 25%, and as much as 50% theoretically. At the same time the heeling force or CE is lower than other commonly used sail types. This allows more sail to be carried. One system uses a middle zipper to section a triangle out of an oceanic sail so scaling an oceanic sail to the conditions is possible. The oceanic sail can be larger for light winds without changing sails as a result. When correctly rigged, they can be made to spill wind force as well. The foresail adds to the benefits of sail selection.

    Do all these little things brought in from other's designs make this boat faster? Theoretically it does. I'm shooting for 25 knots in a 40 ft pacific proa that is live-aboard capable. I believe this is conservative. Only by building it will I know.

    I began my search for the best design to serve my end goals without preconceptions. It was pure research with the goal being: build the best design available that allows the widest degree of travel in a design that allows speed, comfort, safety, low cost and low maintenance.
    The mystique of this design is something I find captivating. I'm hooked on completing it. It should be a blast to sail, regardless of top speed. I settled on Pacific proas for good reason. The science backs it up. Real world experience backs it up. Past speed records do as well. Speed with comfort and safety, durability, and the potential of low maintenance if appropriately built. Adaptable for using a boat launch, not hurt by sitting on a trailer, comfortable for crew when at anchor in normal conditions, but also safe in the worst of storms if appropriately prepared. Race capable in the "racer's" category.
    Beachable on a sandy bottom, low draft allowing access to more areas. Can carry a few extra items like sea kayaks, a good scuba platform with low entry/exit over the ama.

    All of this comes from something that can be built yourself at relatively little cost. I have priced out the higher ticket items. I should come in under $30,000. There are a lot of advantages to be found in the design of a pacific proa. Yet it is widely seen as a "niche" boat, even an eccentricity. Their loss.

    It's a lot of words to describe what is a design that is mostly not drawn. Sorry, no CAD here, just a pretty good memory. Progress pictures will be taken at all stages.

    Thanks for your valuable input, it is much appreciated, T
  6. chinaseapirate

    chinaseapirate Previous Member

    Yeah, I realized that you were well read on the subject of boat construction. I read your last post three times before opening my yap (maybe a record for me). A lot of do it yourself boatbuilders like to get into details of types of wood, use old wooden shipbuilding terms, use chisels, hand planers, awls and what not, but you were describing actual construction techniques and dimensions. Although I barely qualify as as a "top guy" in even the construction aspect, much less hydrodynamics or sail theory, I do have both thousand of miles of "bluewater" experience (2 to be excact ), and more thousands of sailing miles coastal wise. I was like you - completely confident to build my own boats based upon what I liked reading of other designs. I developed my own "myopic" style - stringer (heavy)/(wide)frame spacing, slab sided full length flat panel(single curvature), with various shapes of below waterline strip plank- imagine a Filipino bangka with 1/3 of the frames and a strip planked (usually) keel. This would work, but it is not competitive with your proa concept. You want the lightest/strongest hull design you can get with a bit more displacement than a full on racer, to pitch camping gear in it and go wherever RV style, correct? If so have you looked at stressed skin construction?
    Its almost what you have with your 3 x 1/8 custom plywood hull but in my opinion, and that of quite a few race results, the extra stiffness resulting from forcing the plywood to make the compound curve shape whether it likes it or not, allows a lighter hull at nearly a magnitude less of effort. Cold molding was the standard one off racing hull design, but then numerous techniques were always competing to get a lighter and stiffer boat by orienting more of the wood grain fore/aft as opposed to keel/gunwale and getting away from the whole tedious process by using preformed ply panels (the better ones molded full length). The easiest was the Gougeon's description of "compounded plywood" the closet predecessor of "Stitch & Glue". The most sucessfull was Hughes's "cylinder mold". It introduced a slightly "precompounded" full length one piece sheet of plywood at the same time allowing fuller hull shape, "less wetted surface". I'm describing cold molding as using 2"-4" veneers laminated over a mold or tight group of longitudinal ribbands or even your novelty(to me) left in-place ribs. Either way it had been found that the sweet spot for typical multihull shapes was 30-35 degrees from vertical, not even the 45 degrees most monohulls could achieve. It is still common in larger boats to cold mold a last veneer or two over a single or double strip planked boats as it goes pretty quick against a solid "mold"(the existing hull) and eliminates the fiberglass cross grain requirement (although everybody glasses nowadays-even if just to reinforce the epoxy believe it or not). The 60 degree - or 30 degree from longitude is heavily compounded on a long skinny hull. A 3 inch veneer set there would look something like the backbone of a mahi mahi if you sanded it "fair" again. Forget filling it. 18 x 3/8 is about as small as i figured you can go, i was thinking staples, and that you would be able to force it "flattish". If wire ties...I wouldn't even attempt that. It would be superior, but ...well you can count better me probably.

    If I were you and had all that wood and tools, I would make a "tube mold" with an imperceptible amount of CONCAVE curvature (to avoid patent conflicts) out of 7 or 8 beams on sawhorses leveled over 40 foot. Get about 2 inches of "bend" across the width of your full length hull panel by using different height beams, lock the beams together and attach your ribs - the tapered 2" ones. An eye drop of hot glue should be enough. Then run your two cedars, and you can use 4-6 inch veneers now, and finish with the "zanzibar walnut", not that "black walnut" stuff. That's for my boat. Then I would make a 16 foot flat table and start producing 6,8,10,11 and 12 mm "Maritime Plywood" full epoxy (from china or make my own out of wood oil). And sell 20 x 3 foot sheets of it for $75.00 a sheet day and night. The only reason stress skin plywood eventually lost out to carbon fiber was the cheap plywood becoming unusable and the "good" plywood overpriced. Just a thought.

  7. Vortiseas
    Joined: Apr 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Ladysmith BC

    Vortiseas Junior Member

    I'll choose wood over carbon fiber for boats hulls as well for reasons of resiliency. Wire was for the 1st set of ribs, to hold it to the frames so they can be removed later. I agree, staples from there on. I agree regarding stressed plywood veneers, to a point. I understand that each strip is itself stressed into position. Isn't the effect essentially the same, but on a smaller scale? And don't wider sheets confine aspects of hull design relative to how they will lay up? I chose the method I did because I can build it myself with the materials I have available while keeping the costs down. Are there better material's, of course there are. If I could harvest yew wood it would excel in every area regarding resiliency. Works for bows, works for boats. I may find enough to make the mast, boom and yard out of it. I appreciate that there is a great time savings to be had with veneers. Boatyard cost relative to time make them the right choice for most. It's just not the right fit for me. And feel free to "open your yap". My skin is thick enough and I appreciate an honest perspective.
    The tube mold is an interesting approach that I will have to give some thought to. I am not aware of the patent issue applying to my design. Am I stepping on someones turf regarding design, or does this only relate to the tube mold you included?
    Thanks again, T

  8. Vortiseas
    Joined: Apr 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Ladysmith BC

    Vortiseas Junior Member

    A variation of the tube mold perhaps? I can have boards inside the initial ribs between the frames. I have some saved used c grade d- fir flooring that I could insert on edge to the ribs. Wedges would fill between these and the longitudinal ribs. (Doubled wedges, one from each side, as when hanging doors). This would allow more precise fairing while using less frames. The effect of the rib backing combined with wedges would be the same as having a frame every 3-6 inches that is itself adjustable. The 1st set of ribs would then not be shifted by the second set. This would allow me to use the process you described to lay up the second set of ribs. That is better than frames alone, and may be as good or better than a tube mold for a one off build because of the adjustability. And I reread your last post, and understand that the patent issue applied to tube molds.
    Manufacturing marine plywood is an interesting and quite viable potential for many on the BC coast that have woodlot licenses or timber holdings. 15 years ago I would have very seriously considered it. But at this point I have 4 shifts left and then retirement from paramedic employment. Then the final commitments: fall and buck 40 loads of timber to grade, 2 home renos, a 50 acre property development and then, finally, my shop goes up. Then I can build this boat. Marine plywood, great idea, bad timing for me personally.
    Hey, thanks a lot. I appreciate your input. I'm going to be away for a good bit doing everything I need to so I can actually start building this boat before I am too bloody old. It's been a real pleasure, T
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