Herbie the Volkscruiser Proa
Hi all, thanks for the comments! I had a lovely day enjoying hernia repair surgery, and am now back home, safe and sound. I really shouldn’t post on powerful pain-killing drugs, but so it goes.
Overlaid on your sketch is a suggestion for you…...You can tune the rudder area, profile and counterbalance to suit.
Rob, that option is on the list. I did not use it just yet because I felt the exposed rudders below the keel line could inhibit beaching, and subtract from the “safety” aspect . However, if the rudders I’ve drawn are a “fail” then it would be a good fallback option. I also got a a fascinating idea via PM to reduce the hull rocker to zero, dead flat, which would permit larger rudders. On the one hand, a proa doesn’t really need much rocker because it doesn’t tack, but on the other hand, I know that moderate rocker helps to lift the bow and/or depress the stern - a good thing for a proa. How would a proa sharpie with a dead flat bottom actually sail?
Would it make sense to put the sails on different sides of the mast, fore and aft? If this was arranged so that the forward sail had a higher efficiency than the aft sail then they would have the same arrangement after a shunt.
Peter, makes perfect sense and I would always rig a standing lug proa in that way. The reason Herbie doesn’t have that feature is because was a thousand times quicker to copy and paste an identical rig than to model a new sail with the mast scandalizing the sail shape.
I also got a a fascinating idea via PM to reduce the hull rocker to zero, dead flat, which would permit larger rudders. On the one hand, a proa doesn’t really need much rocker because it doesn’t tack, but on the other hand, I know that moderate rocker helps to lift the bow and/or depress the stern - a good thing for a proa. How would a proa sharpie with a dead flat bottom actually sail?
Michael
Dead flat bottom is a simpler, safer idea in keeping with your design philosophy. Surely it can’t sail that badly??
But how would the rudder balancing work, and wouldn’t it be worst case scenario for CLR migration???
Not for me though, but then, I wouldn’t have rudders on the ends anyhow, just too problematic for me.I am a twin sidehung rudder fan which I know is too problematic for most others.
Rob
Dave, I mulled this over and tried to make a sketch. Is this what you are talking about? The dashed line represents the line of rotation of the rudder, giving some balance.
Michael,
Either way, the effective in water rudder area (shaded blue) is hopelessly small and the proportionally much larger above water rudder area will get smacked about badly by waves. Changing the pivot axis as you have will make this worse and also leave a gap when the rudder is at an angle for weed, debris (and fingers) to get jammed in…....
Overlaid on your sketch is a suggestion for you…...You can tune the rudder area, profile and counterbalance to suit.
Obviously you would also reduce the gap between the rudder and the bow to a minimum.Rob
There is one thing that I cannot get my head around with this set up of rudders…
If you steer with the aft rudder, the “shaft” of the rudder must be “at the front” of the submerged area; in other words, you must have well above 50% of the lateral surface of the submerged part of the blade on the “boat end” side of the shaft.
So what happens when you shunt?... you have now an inherently very unstable foil at the bow. I understand that you are supposed to “lock in place” the tiller in a neutral position, but for sure, the loads, with wave action, are going to be big…
Because the position of the rotation axis of the rudder make the rudder stable in one direction and unstable in the other, I do not see how those rudders could be used both as front rudder and aft rudder. It is either or.
One solution could be what Dave is alluding to, I believe; move the location of the shaft when you shunt.
Dave, for an advocate of simplicity, I am afraid you are adding a lot of complexity here!
So another crazy idea: let it roll!!!
What if instead of having the smallest possible gap between the leading edge of the aft rudder and the end of the hull, you instead consider a BIG gap here?
A gap so big that when you shunt, you just let the now forward rudder blade turn 180° and sets itself with still the same leading edge in the water flow?
The gap I was talking about earlier would then be filled by the trailing edge section of the front rudder blade.
Sure, hydrodynamically speaking, the big gap between the aft end of the boat and the leading edge of the aft rudder may create a lot of problem, turbulences, etc… But I think it would be simpler: a well balanced rudder, with a dedicated leading edge and trailing edge, rotating 180° (and more) on a fixed shaft.
Waddaya tink?
Laurent
Yes, that could work. I think instead of a tiller, each rudder could be fixed to a big, high friction pulley under the deck. Like the ones used with continuous line furlers, but bigger to get more mechanical advantage. It could be fairly large and the battleship deck would still hide it. The steering line would run around the pulley and back to amid ships along the outside of the vaka.
As Aerphydro said in the first comment, this is a ‘cool’ design, Michael!
It is above all simple and practical. It could have been simpler without the hull overhangs but for the addition of one extra panel, it adds quite a lot: extra volume inside, much wider sight lines and the added buoyancy just where you want it in a knockdown. So a lot of extra space and extra safety from both a practical and psychological viewpoint at the cost of a little extra weight, time and cost. A very good trade off, I would say.
If it was thought that the underside of the hull extensions would be too vulnerable to slamming, then a small infill panel could be added to bridge the topside to overhang panel joint to brace that joint and to lessen the clear span of the ‘pod’ underside. It would also stiffen the design as a whole as it would provide two triangular ‘rails’ for the length of the boat. But they may be quite superfluous from an engineering point of view.
The wide deck gives a very comfortable working area and again adds to the safety both practically and psychologically. The schooner lug rig also adds to controlability and comfort. All in all, I think this design has the potential to be a very easy cruiser to live in and to live with.
Being made of ply without any torturing needed, it would be relatively simple and cheap to put together, I think. Since it is symmetrical both fore and aft and side to side, it could be made in quarters. A ‘flat pack’ would be very attractive especially if it included some female forms (which could be reversed for two quarters) in which to assemble and bond the panels into the aforementioned quarters. Much furniture could be included at this stage and it could be done in a relatively small building space. It looks like the ama could be made in similar fashion. A larger space would be needed to assemble the quarters of course but it might make the difference between making it not possible to being possible for some.
It could alternatively be made with a fibreglass foam sandwich using the same quarter format but instead of just frames, a mould using a shiney surfaced panel material could be added to the frames to provide a workable mould. These panels might be supplied with tabs and slots to jig them together to ensure ease and accuracy of reproduction. Again it could be made this way in a small building space but being made of f/glass, its assembly would be more tolerant of being done outside or under a very temporary shelter.
I could go on but I think people will get the idea that, as you say, Michael, this could be a very cheap, simple, practical and safe cruiser to use and to build. 😊
The overall form of the upperworks is almost identical to the hull - just turn the top on its side and you’ve got a flat-bottomed hull. If they really were identical then it might reduce mould costs.
What if instead of having the smallest possible gap between the leading edge of the aft rudder and the end of the hull, you instead consider a BIG gap here?
A gap so big that when you shunt, you just let the now forward rudder blade turn 180° and sets itself with still the same leading edge in the water flow?
Best idea so far…....despite jammed fingers!!
Rob
Laurent and cpcanoesailor: both good ideas.
James: Thanks for the comments. That is very encouraging.
Peter: You are approaching Fullerine geometric purity. 😉
Love James’ quarter-mold idea. This is a simple shaped boat, but even so, building it in livingroom-sized pieces, let alone identical pieces, is a slice of genius. Then Peter has me reeling—now there’s a design challenge for you, Ed! If only you could repurpose portions of the shape two more times—once for the ama and twice for the crossbeams—we’d actually be *in* Nirvana. 😉
Dave
The use of a quarter mold is dependent not just on the fore-aft and side-side symmetry but also the top-bottom. The upward curvature of the keel must match the downward curvature of the deck. You’d need to be careful when molding if the keel and decks are different thicknesses….
If the keel and deck differ in curvature then the quarters of the hull turn out to be two pairs which are mirror-images of each other. If the molds themselves consist of flat panels located and shaped by C-shaped frames then the two flavors of mold could be assembled from a common set of parts.
You’re quite right, of course, Peter. But I wasn’t suggesting a standard or ‘traditional’ f/glass mould. What I had in mind was female frames (split vertically) as used for the ply build but with router cut shiney surfaced panels complete with tabs and slots so they were self jigging. What I neglected to say is that the frames would be reversed for two of the quarters (as with the plywood version) and the panels flipped over (provided they were double sided) to fabricate the other two quarters. The idea being that the mould could be supplied as a ‘flat pack’.
The mould panels could be tacked together externally to hold them sufficiently (hot melt glue?) to mould. Alternatively, the tabs could be longer with holes in them to accept wedges which would hold the panels together. If you wanted to complicate it a little further, lengths of moulded radius could be placed in the three internal corners to cover the panel joins and provide a nice looking radius to the fabricated quarters.
I really like your idea of using the one mould to make all six sections. It would be great for a version of Tom’s Box Keel Proa concept which I’ve always liked. If you put a rake on the ‘bow’, it would add a little style to the completed design, I think, by having the deck ends angled too. 😊
I modeled up a general arrangement.
From left to right: Double bunk, seating, folding table and navigation, galley, head, and another bunk (toilet beneath bunk).
I modeled up a general arrangement.
From left to right: Double bunk, seating, folding table and navigation, galley, head, and another bunk (toilet beneath bunk).
Nice and about what I hoped. My thoughts are a similar spirited boat on a careful starvation diet - about three sheets of ply (24’) long. Single 24” wide bunks at either end. Sitting headroom (fore/aft on the centreline). I’m considering using the two primary bulkheads (at 8’ from ends) for supporting structure on the aka sockets and the twin mast sockets and division of interior space. Offset mast sockets to windward to allow companionways to ends. Side mounted linked bi-directional Speer-style rudders at 4’ back from the ends (ring frame supported at midway between the primary bulkheads and the ends). Cedar stripped lower compound curve sections from 4’ to the ends - under the waterline and ply elsewhere. Wider “wings” above the lower hull starting at the ends and reaching max beam at centre - forming the buoyancy pod and also enclosed cockpit area. Single angled Bruce foil type daggerboard on the ama - providing righting moment and lateral resistance when required.
Very light- probably 4mm ply (vac’d and peel ply’d glass both sides) where I can get away with it, and 6mm where it is load bearing. Stringers where needed and panel joins by lapped ply doubling instead of scarfs. Bottom seam doubled with ply layer. Mark Gumprecht’s Drifter 17’ build is pretty inspirational. I also really like the unrockered round bottom “folded” Kelsall / Denney / KSS style hulls. I envision a pretty simple build process. I can probably use the cedar stripped ends to arrive at enough rocker to be able to turn the boat. The middle 16’ will have no rocker though. The paper models work okay so far.
Why 24’? Cost containment, trailering and driveway storage. Why the wide-ish wings on a narrow 24” hull? It’s cold here a lot and if you want more than a 3 month season, you have to deal with cold water spray. With careful arrangement I can fit what I need for weekending and coastal tripping. Maybe even a Watertribe type event. Bucket, cooler (Esky to some), mountaineering burner, 12VDC battery, trolling motor - that should about do it. Water ballast out in the ama - I’ve got a fill/empty “system” figured out in my head. 16’ (two sheet) ama, tortured ply. Aluminum tube akas, unbent for simplicity.
Schooner rigged - hope to build two wing masts, soft sails and put a nice 29er asym kite I’ve got to work downwind.
It’ll be uncompromised “form follows function” appearance - probably wallflower unpretty to most yacht club eyes. Hope enough performance can be achieved to make the ugly go away. The three sheet length lends it to building three section units and assembling once all are ready - making this fit my boatshop (garage until the temp gets up another 16 degrees C).
It’s nice to see someone else travelling down the same thought path.
—
Bill in Ottawa
I modeled up a general arrangement.
You anticipated my as yet unvoiced request. Very nice.