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Thread: Tasar equivalent in wood?

  1. #1
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    Default Tasar equivalent in wood?

    The closest match (by eye) I know of is the Paper Jet by Dudley Dix. A bit smaller and not as much rocker forward.
    In his book, Bethwaite also mentions a design called Dribbly, from which the Tasar evolved.

    I would love to get a look at some hull lines for boats of similar shape.

    Any additional info on the Tasar would also be appreciated: waterline beam, angle of entry, waterplane area, wetted surface, anything noteworthy that is not already available on wikipedia...

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    Default Re: Tasar equivalent in wood?

    The Tasar's underwater shape was from the '60s but it's more modern IMHO than the Paper Jet. I've been lucky enough to talk to most of the world's top racing dinghy designers and the PJ ignores just about everything they have learned about how to make a boat handle well and go fast.

    The Tasar's Vee sections are dated in pure performance terms. Modern boats have more U-shaped sections that provide more planing lift, a narrower waterline and less wetted surface. The extra volume allows for narrower bows. One example is the NS14, which is the class for which the Medium Dribbly, the Tasar's ancestor, was designed. The Tasar has the same shape under the chines as the Dribbly, but the NS14 moved towards the U-sectioned shape. An NS14 is now the same speed as a Tasar although the latter has about 25% more sail.

    On the plus side, the Tasar (a boat I own and love) is more stable and can handle being sailed with a little bit of heel without losing speed like a NS14 does.

    The Bethwaites hung onto Vee shaped sections long after other people had moved to U sections, but that's partly because they were not designing to development-class rules. That allows the Bethwaite boats to be longer, all else being equal, so they don't have to pack as much volume into the available waterline length. The extra length also means they don't suffer as much from the higher form and wetted surface drag of the Vee shape; the fact that they are longer means they have a higher hull speed, which allows them to develop more planing lift before they hit their displacement speed limit. Finally, the sheer length of the Bethwaite designs means they move fast and therefore wave impact is a significant factor and the Vee shape works well there.

    I think there's some info on the angle of entry in High Performance Sailing. My boat's at the club and I won't be there for weeks due to having to travel to regattas and to work on my wooden boat so I can't measure it.

    I have simple lines plans for a Bieker Int 14 and the RS200 somewhere. The Bieker PT14 looks like a very nice Tasar-style boat.

    For more info on the NS14, see the class site. Here's an old '80s sketch showing the development in those days. It shows the shift from V shaped sections to U shaped sections. These characteristics then flowed through to 12 and 16 Foot Skiffs. Frank Bethwaite was moving this way with his last design, the 59er.

    NS14 section.jpg

    Isometric of a modern NS14 design by NA Stu Friezer. Much narrower waterline than the Tasar, very flat sections.

    queenscliffdesign NS14.jpg

    I think Stu sells plans, but they'd be foam sandwich boats.

    Here's a 2000 vintage NS14 - very flat across the centre. Note the comparatively narrow sterns - the fat sterns seen in something like the Paper Jet are something top dinghy designers tend to stay well away from these days. They don't develop planing lift, they cause the boat to nosedive, and they increase wetted surface.

    Aero 11a 2000 NS14.jpg

    Bear in mind that these are Australian boats. They don't perform as well in the lighter winds common in the USA, Europe and UK because their rigs are quite small. The NSs are also very tippy - they don't survive well when tied to docks etc as you guys often do.

    Hope I haven't raved on too much. Cheers
    Last edited by Chris249; 09-24-2018 at 08:31 AM.

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    Default Re: Tasar equivalent in wood?

    Thanks Chris,
    What I find appealing about the Tasar is the prospect of upwind planing without the need for trapeze. Not for racing, just for the tangible sense of speed.
    While the shape might not be the most efficient, it seems to have found a good compromise between performance and other trade-offs such as you mentioned, stability and some tolerance for heeling.
    How does the RS200 compare in stability?

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    Default Re: Tasar equivalent in wood?

    Which design would be the closest single-handed equivalent to the Tasar hull?

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    Default Re: Tasar equivalent in wood?

    Sorry for getting the wrong drift, WF. I agree, the Tasar has a great shape for user-friendly speed especially in the breezes I think you get around PE.

    The Impulse would probably be the closest boat to a Tasar hull, I think, with the Phantom also a contender. It would probably depend on your weight since the Phantom is a real big boy's boat. Both have the classic deep Vee entry and flattish stern on fairly light hulls.

    I've only looked at a 200, not sailed one, but I corresponded with Phil Morrison about his designs. The 200 is of course largely a National 12 development and has Phil's usual intelligent design approach, which is to use U sections and considerable rocker to reduce wetted surface to increase light air speed, and to make the boat easy to sail in high winds at the expense of top-end speed. He pretty much reckons the average British sailor likes going fast in lightish winds on short courses, and being able to stay under control in strong winds even if the hull shape drags a fair old wave with it.

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    Default Re: Tasar equivalent in wood?

    If your after a single handed planing dinghy at the 'performance' end of the spectrum, take a look over Keith Callaghan's Hadron H1. He works on CAD, and his plans are very good or you can get it CNC cut.



    http://www.bluelightning.co.uk/Hadron/Hadron01.shtm

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    Default Re: Tasar equivalent in wood?

    The Phantom is definitely my size boat (6'3", 105kg), but I once had a bad experience with a long, low boom on a Finn. I had promised myself: never again. Am I correct to assume that the Impulse will be less of a handful downwind?

    I see what you mean with UK vs Aus rocker. Even the Phantom, when scaled to the same length as the Impulse shows it clearly.
    In what way does more rocker improve control in strong winds?

    Solid line is the Impulse keel:
    Impulse vs Phantom rocker.jpg

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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by Edward Pearson View Post
    If your after a single handed planing dinghy at the 'performance' end of the spectrum, take a look over Keith Callaghan's Hadron H1. He works on CAD, and his plans are very good or you can get it CNC cut.
    Thanks for the suggestion. I have always admired his designs. I am not looking for a particular design to build, just lines for a representative hull with Tasar qualities.

    After building Flo-Mo's flywood canoe and looking at how Tornado hulls were built in ply, I realised what nice rounded sections are achievable with the correct construction approach. As a CAD exercise, I would like to design a hull that approaches the ideal compound curvature shape while still being develop-able in ply.

    The Impulse measurement rules contain sufficient dimensions to create a fairly accurate 3D model. If I use that as a starting point and keep most of the extremities the same, it might just be possible to build the new design using Impulse plans and only adjust the necessary parts to accommodate the new hull shape.

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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by whiskeyfox View Post
    The Phantom is definitely my size boat (6'3", 105kg), but I once had a bad experience with a long, low boom on a Finn. I had promised myself: never again. Am I correct to assume that the Impulse will be less of a handful downwind?

    I see what you mean with UK vs Aus rocker. Even the Phantom, when scaled to the same length as the Impulse shows it clearly.
    In what way does more rocker improve control in strong winds?

    Solid line is the Impulse keel:
    Impulse vs Phantom rocker.jpg
    The main issue is that rocker allows the boat to sort of rotate when planing downwind, so that when the boat is planing fast on the stern sections the bow is well out of the water and not going to nosedive. Following are a few of my notes on the issue;

    "
    Reducing dynamic and buoyant lift in the stern allows it to sink, forcing the boat to pivot around the buoyant mid sections and lifting the bow into a high, safe position. NS14 designer and naval architect Stuart Friezer has a rule of thumb about hull shape; “I believe that the vital measurement is the angle of an extension of the aft end of the quarter rocker. When you are going fast, the boat is just touching the water at the leeward quarter. If you extend the line of the keel rocker forward and measure how far it is below the forefoot, you’ll get a good indication of how well the boat will resist nosediving”.

    (and as an example of the rocker issue)....

    "In 1989, Australian 14 Footers met the International 14 in a world title in San Francisco. This was before the Australian boats adopted the International rules and during a period when the Australian boats had very little rocker and very low chine lines, all to create a very straight-lined hull that planed very early and was fast in medium-fresh winds. in the years before the event the Aussie boats had reduced their rocker from 65mm to 40mm. The top International 14, the Howlett 1b, had 100mm of rocker."

    "The flat Aussie boats planed early and flew in moderate conditions, but in light and heavy winds they had problems. 'Snubby' Moor, who won the regatta, reckons "In five knots the UK boats were good" because the very flat Australian boats had too much wetted surface and had the transom drag. "In 12 to 15 knots, the Australian boats were way, way faster upwind and down" says Moor. Even going upwind in 25 knots, the Australian boats were quicker."

    "The problems came after turning the corner in big winds. While the top Australians (Andrew Crisp and Peter Moor and their crews) were concentrating on staying alive, the British McDonald brothers could rely on the extra rocker in their Howlett 1b to keep the bow up and the boat safe. "Even though the British boats had too much weight and rocker, they overtook us downwind in the really strong races, which really surprised us” recalls Moor. “Downwind in the heavy stuff their boats were much faster and safer, because every time we got a gust we'd have to flag the spinnaker to stop a cartwheel. Nobody in Australia realised that downwind their boats were much faster. It was after that we realised we had gone too extreme with rocker and chine height".


    Whenever I look at a lot of Northern Hemisphere boats, I'm amazed at the amount of rocker they have. I look at their hull lines on paper, but that still doesn't drive home how rounded boats like the Flying Junior, National 12, Firefly and Merlin Rocket are when seen against comparable Aussie boats. I also didn't realise how quick it made some of the British boats in light winds - some good sources say that the National 12, for example, will easily beat the longer, lighter Tasar in light airs.

    By the way, the Impulse was designed for the enormous Port Phillip Bay, where conditions are often very similar to that of San Francisco. I haven't heard or seen of them having handling issues. However, the Sabre class is more popular around Port Phillip. It may just be because it has more critical mass and lower cost, but it's very easy to handle although significantly slower than the Laser, Impulse, OK, Phantom etc.

    By the way, the Impulse is one of the few Aussie boats that has a yardstick that is ridiculously inaccurate in my opinion; a guy who was mid pack at the nationals was normally able to beat some of the best Tasars in the world on yardstick. I mention this only to say that the yardstick is misleading about the boat's speed - in reality it appears at least as quick as a Laser, as it should be given its dimensions.

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    Default Re: Tasar equivalent in wood?

    Found a provisional Portsmouth Yardstick rating for the Paperjet. It's for the sloop rig, didn't say whether it includes that bowsprit and spinnaker.

    https://nanopdf.com/download/sas-pyh...-sa-dinghy_pdf

    The Tasar rates about the same without the trapeze shown on the Paper Jet, and with a crew of two instead of one. To me, that says the Tasar is easier to sail and is just as fast even with more weight. This doesn't seem like progress on the part of the Paper Jet.

    A wooden sloop about as fast as the Tasar would be the Windmill, which is a class that supports new wood boat construction. they plane in about 12 knots, without a spinnaker.

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    Default Re: Tasar equivalent in wood?

    The "A" in that list indicates that the handicap is for the Paper Jet with a assy spinnaker. With jib, kite and trap it's only rated 1% quicker than a Laser, or 5% slower than the Tasar and around 3% slower than the Windmill.

    The Farr 3.7 makes another interesting comparison. At just 12 ft and with a trap but no kite or jib, it's rated faster than the Laser in Australia, England and NZ. Lovely little boat.

    Farr 3.7.jpg



    Not unlike a Tasar in its hull. CAD files are available from the NZ association. The illustrations show some of the ways the lovely little Farr differs from the PJ - the Farr has curvature put into the flat sections down low in the bow and just under the chine at the stern. Many Oz/NZ designers at this time were trying to get as much flat along the keel-line aft and through the middle as they could with ply, and the Farr 3.7 seems to be no exception. Farr was pushing U shapes quite hard to get dynamic lift in his 18 Foot Skiffs, while making sure they didn't slam too much. The cleaner topsides and nice rocker also seem a major advantage over the PJ shape IMHO.

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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by Chris249 View Post
    "In 1989, Australian 14 Footers met the International 14 in a world title in San Francisco. This was before the Australian boats adopted the International rules and during a period when the Australian boats had very little rocker and very low chine lines, all to create a very straight-lined hull that planed very early and was fast in medium-fresh winds. in the years before the event the Aussie boats had reduced their rocker from 65mm to 40mm. The top International 14, the Howlett 1b, had 100mm of rocker."
    Are these dimensions along the keel or quarter-beam buttocks? Measured between transom (I assume) and which point forward?

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    Default Re: Tasar equivalent in wood?

    I modelled the Impulse and then used the Tasar rocker and chine beam approximated from the photos below (and the 22deg angle of entry mentioned for Medium Dribbly) to create a Tasar model. I reused the shear beam from the Impulse, so the topsides will not have the exact flare as a real Tasar.

    The Tasar chine, seen from the side, appears to lie in a flat plane, exactly at water level at design displacement. Both rocker and deadrise disappear at the transom. By trimming the nose down 0.5deg and adding 3deg deadrise at the stern, the Tasar has the same wetted surface area as the Impulse and 125 dinghy, all scaled to 14ft and 180kg displacement. I did "bend" the 125's back to get its wild rocker closer to that of the other two models.

    If the Farr 3.7 can be built in wood then the Tasar shape should be even easier.

    tasar hull bottom.jpg
    TASAR_LineDrawing_400_rdax_60.jpg

    Left-to-right Impulse, 125, Tasar.
    Tasar comparison1.jpg
    Tasar comparison2.jpg

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    Default Re: Tasar equivalent in wood?

    Will you design your own clone?

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    Default Re: Tasar equivalent in wood?

    Nice. The Tasar could easily be done in ply - there were many similar designs in ply. There is deadrise at the stern but I don't know how much - maybe the centreline is 40mm below the chines???

    The rocker measurements are from bow knuckle to transom along the centreline.

    Gotta go and drive a day to get the trailer out from underneath my hard-chine Spencer yacht so I can repair the trailer and start the restoration of the boat. Catch you later. I may be able to eyeball a Tasar in the club over the weekend.

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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by johnw View Post
    Will you design your own clone?
    Not likely. I might nudge the chines and keel rocker of any future plans-build project in that direction, if the application justifies it.

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    Default Re: Tasar equivalent in wood?


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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by John Meachen View Post
    Any help?
    Yes, very much, thanks. It shows the section roundness much better than the photo of the capsized boat.

    One thing that I have not figured out is why most racing dinghies have prismatic coefficients well below 0.6. Every design reference I have read suggests that higher is better for speed, with 0.65 indicated even for the upper range of displacement speed and at least 0.7 if you intend to get anywhere near planing speeds.
    In my dinghy modelling exercises I have come to realise that it becomes increasingly difficult to keep a fine entry and to minimise wetted area as Cp increases.
    Are these two factors sufficient reason for selecting a lower Cp value?

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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by whiskeyfox View Post
    Yes, very much, thanks. It shows the section roundness much better than the photo of the capsized boat.

    One thing that I have not figured out is why most racing dinghies have prismatic coefficients well below 0.6. Every design reference I have read suggests that higher is better for speed, with 0.65 indicated even for the upper range of displacement speed and at least 0.7 if you intend to get anywhere near planing speeds.
    In my dinghy modelling exercises I have come to realise that it becomes increasingly difficult to keep a fine entry and to minimise wetted area as Cp increases.
    Are these two factors sufficient reason for selecting a lower Cp value?
    .7 is fine for a powerboat, but most dinghy designs must deal with performance at displacement speed as well as planing. Chris wrote a great post on modern planing shapes here:

    https://sailcraftblog.wordpress.com/...rmance-dinghy/

    To wrap my brain around all that information, I did a design study for a 16-footer to take my Snipe rig:

    16' modern planing hull, fine ends 10-8-2018 12-46-03 PM 1484x719.bmp.jpg

    That's a prismatic of about .58. The Laser planes very nicely, thank you, with a prismatic of .57.

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    Default Re: Tasar equivalent in wood?

    When I paddled past this boat today, this thread came to my mind. So I took some photos and looked up the design.







    The drawings are from the Rigging manual and from the RS Aero Brochure.

    The photo of the capsized boat is a screenshot from this video:


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    Default Re: Tasar equivalent in wood?

    Quote Originally Posted by John Meachen View Post
    What is that? The lack of a rudder support indicates it's not a dead Laser 2000 or RS200.

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    Default Re: Tasar equivalent in wood?

    You don't have to run the chines all the way to the boa. You can develop the forward shape and introduce the chines further aft. This means you can build something like a B-14 hull shape pretty easily.final2.jpgbottom.jpg
    This canoe hull was developed out of 3mm ply with a centerline dart forward and two chine darts aft.
    If looking for upwind planing without a trapeze, the Taser is pretty old school. Most anything built light enough, and sailed aggressively will achieve this to a greater or lesser extent.
    The key from my point of view is: 1- light weight construction. 2- Length ( displacement length ratio determines the length and amplitude of the displacement wave.) Longer waves go faster than short waves. A shallow hole is easier to climb out of than a deep hole. 3- Enough flare to gain righting moment without waterline beam. Most people get antsy with less than 750mm ( ~30") waterline beam. 4- max WL beam should be well aft and the waterlines forward about as straight as you can manage. The "shoulders" of Uffa Fox style planing dinghies are way out of fashion. Whether or not the boat is self bailing has quite an effect on how far you push this.
    SHC

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    Default Re: Tasar equivalent in wood?

    Flat IC stern.JPG
    Photo of the approximate shape of the plywood that built the above referenced hull./
    There was quite a bit of violence required to get the forefoot to behave itself, but experts in the field of tortured ply suggest it was solely the result of my incompetence and in experience.
    SHC

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    Default Re: Tasar equivalent in wood?

    Steve, what is the triangular "swim platform" for? Does it extend the length? Where are the rudder fittings, are they at the pointy end, or where a transom/bulkhead might be?

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    Default Re: Tasar equivalent in wood?

    It’s a canoe. Which means it is pointed at both ends. Class rules and all that.
    ICs are 17 feet long and weigh 50 kg, so they are as long and light as any monohull on the planet.
    this combined with a sliding seat that gets the helmsman further outboard than a trapeze, creates a very dynamic sailing experience.
    I was actually calling attention to the other end and how a round section can transition into a chine within the realm of tortured plywood. Rather elegant shapes can be achieved.
    SHC

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    Default Re: Tasar equivalent in wood?

    Thanks. I'm aware of IC's. Somehow, I didn't think of them with chines, or even a modern design.

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    Default Re: Tasar equivalent in wood?

    Almost every class with a minimum waterline beam restriction, will develop chines at the height of the measurement point. This is an inevitable type-forming outcome, like plumb stems on LOA restricted classes.
    Ian Proctor first put chines on the sterns of his canoes as a way to avoid the sharp buttock rise inherent in most double ended models. The Nethercot copied this feature.

    When the rule was re-opened for hull development, Chris Maas introduced the "more or less kinked transom" as an elegant way to maximize the quarter beam waterline length.
    3.jpg1.jpg2.jpg
    And, Oh Yes, ICs are plenty "modern." They live in a unique design space that is somewhere between mono and multi hull, and between very fast displacement and planing.
    The "hump" is so low and long you don't notice it.
    SHC

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