HarryProa Style Hulls

Discussion in 'Multihulls' started by ThomD, Aug 4, 2010.

  1. ThomD
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    ThomD Senior Member

    I'm curious about the new hulls that have central, apparently parallel running lines, and then a nosecone section to part the water. Most hulls use as much length as possible to part the water. I can see the attraction of this style for building, max displacement, etc... Probably why party cats use it, but I was wondering what it's merits relative to resistance are. Or other factors. If deemed good, why not use it on other multihulls, particularly those that are not going to be maneuvered rapidly. Say for ocean crossings, or other long passages.
     
  2. Alex.A
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    Alex.A Senior Member

    Proa hulls thread - page 2.
     
  3. rob denney
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    rob denney Senior Member

    The new hulls are parallel for most of their length( 16m and 6m). The final metre on each end is bent to form the bow. The sides are flat, so are bent into the stem. The compounded area above and below the decks is made from polystyrene foam and glassed over.

    Reasons for this are:
    1) It is very easy, light and cheap to build using simple but very accurate infused flat panels. The weight savings are huge, and I originally hoped they would make up for any hull shape deficiencies. Then Rick Willoughby ran them through Michlet/Godzilla for me. Results showed these hulls to be relatively low drag compared to more conventional shapes. Given that they are lighter than conventionally built hulls, the results are even more favourable. Comparison drags are attached. Hull lines for the comparison are at http://au.groups.yahoo.com/group/harryproa/ under Solitarry 2 drag curves. There are some build pictures of the hull in the Photos section.
    2) The bows on some previous harrys have been quite bluff and the boats have been very easily driven, albeit wet. As the spray is away from the crew, I can live with this.
    3) The hulls are quite narrow.
    4) The hulls have very high prismatics (~0.95) so have a lot of buoyancy in the ends. This will allow lower freeboard forward, resulting in less weight and windage. The first iteration is approx twice as high at the bows as I think they should be. There are a few reasons for this but pretty high up the list is that it is easier to reduce them than increase them.
    5) I like trying new things.

    The hulls are an experiment in an experimental boat (rudders mounted on the beams close to the mast, unstayed, telescoping wing mast, sail shape controlled by individual batten manipulation). The hulls are small in cross section so if they don't work, it is easy to increase the taper zone either a little, or all the way back to the middle.

    I doubt this shape would work for conventional cats which draw more, are wider and need rocker to tack and for light air reduction of wetted surface. Be fun to try it though.

    rob
     

    Attached Files:

  4. terhohalme
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    terhohalme BEng Boat Technology

    Just wondering, what was the reason to pick 16 knots as optimizing speed. Is it really the most propable sailing speed, for the most of the time?

    I have used lot of time optimizing racing wooden rowboats. Gozilla is an excellent tool for optimizing thin long hulls. I just made one major mistake: I choosed the average speed of best time rower as an optimizing speed. This made Cp too high and the boat too hard to row even for the master rower. The boat just felt too laborious to practise and row. I decreased optimum speed significantly and the next version was "possible the best ever" as the rower says. Big changes in speed during the stroke can of course have an influence.

    In low winds when driving force is small, we need to have the right Cp to keep the boat going on. When the wind increases there is lot of driving force and small increase in resistance doesn't make the boat significantly slower.

    Your building method developement and experimental reasons are still very notable.
     
  5. ThomD
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    ThomD Senior Member

    I was working on a Trimaran design with a somewhat similar hull, inspired by your earlier hulls, Rob. The similarity was in the idea of bent shapes high pc, and straight keels, but the assumption was that there would be torturing, and keel shaping involved, even if less that what is considered normal. I was thinking the boat might have longi stability and be easier to build out of plywood.

    The brief for the boat was to be capable of long passages, rapid tacking was not an objective, though the ability to tack certainly is. I also wanted a boat with extremely easily driven hulls, and very secure accommodations, sorta a Jester for one person with all central controls, no flooding in an open cockpit. The huge open secure area the trimaran and nets provide. That said, it doesn't need to be a trimaran, I have considered other types, podcats, proa, cats.

    Needs to be cheap end of construction spectrum, since there might not be a return ticket from some of the voyages I have in mind, or maybe for everything other than the main hull.

    On tacking, I understand what shunting is vs. tacking except to the extent of the dynamic of a shunt vs. a tack. Tehro has mentioned the fact a proa was not practical for his tight waters. But would a trimaran with HP hulls be any worse, would it all come down to horses for courses. Would the trimaran with HP hulls be better at holding a course on the open sea?

    When designing the long parallel HP hull does it mater whether the nose cone, and tail cone, assembled would have a shape like an 8-1 hull or whatever one takes as threshold non-waveforming?
     
  6. Alex.A
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    Alex.A Senior Member

    Not the same but similar - Wharram pahi cant tack with main only but tacks fine using jib. His child of the sea uses a mizzen. Similar long straight hulls?
     
  7. ThomD
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    ThomD Senior Member

    Yeah, I was thinking of Wharram also, the hulls do have rocker, but they are sharp so not so turny. A lot of cruising monos of the old school had lots of longi bite, but they were pretty unsophisticated foil wise, and not consistent with my low resistance objective.

    Another inspiration is TF Jones. Not the boats, but the idea of building a platform and going for a ride, then selling it up and coming home without spending too much on it.
     
  8. mcollins07
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    mcollins07 Senior Member

    Are there any pictures or line drawings of these hulls, perhaps already posted?

    I checked the yahoo groups link but did not find them.

    thanks.
     
  9. ThomD
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    ThomD Senior Member

    The solitary build in the pictures files of the hp yahoo groups is a hull of this type. The central section is a folded U of material and then the ends are pointed in with normal like hull sections.

    What I was thinking of was more a standard tortured section, folded where the central section is between 160 and 180 degrees and the cutting of the keel back at the bow was limited so that while the hull would have taper, the rocker would be minimal. I haven't done a model yet, not at home for the moment. The purpose in my mind was less just the fast build, but also to see if a fatter section could be made for tris. Obviously if the section where U shaped bow to bow, there wouldn't be any max beam/length ratio, as there is with tortured hulls. But some pointing is required. I'm not up for the nosecone approach yet.

    Another option to get the type of hull Rob is now working with might be the forward section on this kind of boat:

    http://www.glen-l.com/designs/canu-row/robroy-notes2.html

    These do not produce the nicest transition, but it's fast and not all that bad.

    For me to be interested, resistance of the middle sections would have to be no worse than doing a hull in multi chine, since that method is fine enough for cruising hulls.
     
  10. Alex.A
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    Alex.A Senior Member

    What are your dimensions/requirements - hull length,beam and depth?
     
  11. ThomD
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    ThomD Senior Member

    I guess it shows the degree to which I am just dreaming on this concept, that I don't really have a number in mind for any of this. I would figure something in the order of 4K pounds displacement, not more than 40 feet. So that would be a beam of about 2 feet at the WL, if the pc was near one. That is pretty much an ama. :) Doesn't need to be that long either.
     
  12. basildog
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    basildog basildog

    I've read this thread with interest and wonder why laying up a flat fibreglass panel and torturing it the same way you would with plywood would not work.

    The potential for hull explosion when folding may be reduced due to the panels having no imperfections. If it could work it would eliminate all the stigma of a plywood boat and you could achieve hulls with rocker etc.

    Or is this essentially what Derek Kelsall does already?
     
  13. rob denney
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    rob denney Senior Member

    Plywood will work, but to do it from a flat sheet, you will need to score the panels in the bent areas, then figure out how to get inside to glass them. Experiment a bit with this before you do a full length piece. Tortured ply for the hulls will be ok (ish), but results in a lot of work and weight for the rest of the boat, compared to the single sheet of bent panel method. Also, the scarf joins may not bend the same as the rest. You will have to glass and fair the exterior, and I would also glass the interior as it stiffens the ply significantly.
    Check out what John Tetslaff in NZ does with 4mm ply 8.5 cat and tri hulls. You will need some extra frames and stringers.

    A table and vac bagged or infused foam/glass/vinylester panel would be quicker and easier. Also lighter. Possibly more expensive(depends on materials, but in Aus, decent ply ain't cheap), but you can then use the table for the beams, rudders and mast(s).

    Pretty much what I wanted with Solitarry, plus it had to be fast and cheap. Long passages are much easier with a quick boat, so 12m is good. Short boats are also less comfortable and feel more scary in a big sea. Design whatever accommodation you need, then build the longest hull(s) you can. The tri will be heavier, so needs to be bigger and stronger. Plenty of long voyages in F 27's though, so could certainly be done. 4,000 lbs would give you over a tonne of payload on a 12m harryproa, nothing on a 30' Farrier.

    A tri won't be at the cheap end. Twice the materials for a start.

    $10 grand (plus a little as your hulls will be bigger to carry the extra weight) plus rig for Solitarry will be hard to beat You also need to get to grips with an unstayed mast in either wood, alloy, glass or carbon. Cheaper, more reliable and feathers in a gust. In a proa, a una rig would work, which saves a bucket of cash.

    No idea. Hull shapes are pretty secondary compared to rig and daggerboard/rudder placements. Harrys track well, but they are skinnier and shallower hulls than a tri or cat, plus the fore and aft rudders make balancing the proa very easy.

    A rockerless tri may need the jib to be backed when you tack. With a self tacking jib, this won't be onerous for a solo sailor.

    Hopefully, a shunter can be made to go up a narrow channel as my 7.5m will live at the end of a 300m x 25m canal, with boats and jetties each side, with the prevailing wind blowing straight down it. I am confident it will, but will keep you posted.

    Don't know yet, but it is not as blunt as the 15m harryproa hulls we have previously built, so should be ok. The lee hull bows in the photos are all foam due to table length limitations, which we don't have any more. The ww hull ends give a better idea of how it was done.

    Terho,
    Rick will probably tell us why he chose those particular hulls as comparisons.

    I agree with you about low speed drag being more important than high speed. However, I did not think the differences would be noticable enough to justify the extra weight from using a conventional build method. Time will tell! Guess I should ask Rick to add another line. The harry shape a hundred kgs lighter.

    rob
     
  14. ThomD
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    ThomD Senior Member

    "Tortured ply for the hulls will be ok (ish), but results in a lot of work and weight for the rest of the boat, compared to the single sheet of bent panel method."

    I'm certainly finding your pics very interesting. Not all of personal boat building comes down the what is best. That method looks like it wouldn't fit onto my current shop! I am tempted by an all foam and glass boat. Price isn't all that daunting (for most projects) because of resale.

    " Also, the scarf joins may not bend the same as the rest."

    I have had problems with scarfs, print through for instance. But bend has not been one of them. It could happen if the underlying material was right at the threshold of max bend, but you could bend 3/8 right next to 1/4, if the bend was within the capability of both, so scarphs are pretty easy. actually, even though I have a vac scarphing jig, I once built without scarphs, just hung the panels from a shear, then bent them, then butted the joints with bog and tape afterwards.

    "You will have to glass and fair the exterior,"

    Remarkably little is required, but it won't be as easy as what you are doing for sure. Are you using a table, how large, costly, time to build? That stuff cuts into a one-off.

    " I would also glass the interior as it stiffens the ply significantly"

    I sometimes core it also, though that is throwing pearls at swine, it just can be a good deal, particularly down the road 20 years if one sticks with it that long.

    "A table and vac bagged... rudders and mast(s)."

    I would love to know how to do that. I must try infusing something, it clearly rocks. I have a small foil in mind, maybe I will infuse that. Where to find info...

    "The tri will be heavier, so needs to be bigger and stronger."

    "A tri won't be at the cheap end. Twice the materials for a start."

    Maybe. gougeon 35 footers 2200 pounds, lots of accom, ply, only trick part is the core in the decks. No vac bag at least on Adagio, as far as I know. I like vac bag, just saying that is the era. Beams not really offshore. They did an interesting 60' OSTAR Stressform design for Phil Steggall. Sadly it was never built but it did involve low weight and resistance principals, small side rig.

    "You also need to get to grips with an unstayed mast in either wood, alloy, glass or carbon. Cheaper, more reliable and feathers in a gust."

    Even on a tri? Sounds like a lost opportunity to use the staying base. What is so great about a freestanding spar, more loaded. Serious question, I hear good things, just not getting it yet.

    "In a proa, a una rig would work, which saves a bucket of cash."

    Time out for proas for a sec... I need to have a look at that potential, vs the ballestron. Strengths weaknesses. I have an idea for a lightish all wood mast, but it would need to be directional like the ballestron.

    "A rockerless tri may need the jib to be backed when you tack. With a self tacking jib, this won't be onerous for a solo sailor."

    This is what I was thinking, no biggies on long legs, and it would make a virtue out of a "D'oh!"

    Thanks!
     

  15. rob denney
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    rob denney Senior Member

    What you want can be built with any of the common systems and you will end up with a workable boat at a reasonable price. Based on my experience with the 50'ter, if you want the easiest, cheapest, lightest fastest way, it will be vacuumed flat panels using polyester, pvc core and e glass.

    My guys have a very good 8m table and are putting the finishing touches on a 15 x 3.8m table which is a work of art. For one offs, all you need is a flat, airtight surface. Melamine covered mdf with epoxied biscuit joins (or just packing tape) mounted on sawhorses is fine. 100 x 25 alloy bars make good lengthwise stiffeners. It all costs, but there are no building frames or strongback required, and it is all reusable, so not so bad.

    Infusing does rock, but if you are using epoxy (eg you dislike the styrene smell), then vac bagging a hand laid laminate will have less waste. And different sorts of stress. Flat panel rudders and daggerboards are very simple, mine will be happening in the very near future, pics will be on the chat group.

    No maybe about the materials. A 12m lee hull proa and a 6m ww hull will have less material than 3 x 35' tri hulls. I have not seen any numbers on the Adagio build, but I bet it takes longer than the 300 hours to infuse, bend and bond the full size flat panels. Again, a tri will do your job, as will a cat or a mono, but if ease of building, cost, weight and speed are parameters, the proa will be better, based on my experience.

    What don't you get?
    Raise, lower and reef the sail on any point of sail in any strength of breeze?
    Ability to completely depower and/or stop the boat on any point of sail?
    No rigging to check each time you go sailing?
    Nothing to replace every x years? Automatic first reef due to the bendy mast?
    No rigging for the sail to chafe against?
    No deck gear?
    Localised loads which are both lower and easer to resist than a stayed rig?
    Build the mast and most of the fittings yourself and save money?
    Let me know which of these you don't get, and why. Also, whether the aspects you point out negate the others.

    As for the tri staying base, half of it is wasted on a given tack, so why not ditch it?

    Wood is good, but reality is that carbon is stiffer, and a mast needs to be stiff.

    You will build what suits you. I am just keeping you up to date with options and my experience.

    rob
     
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