New Design for a 17' Daysailer/Racer

Discussion in 'Sailboats' started by Cleve Motley, Oct 31, 2004.

  1. TaSSie_deVil
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    TaSSie_deVil Resident Boataholic

    P17 Concept

    Just a little something that I knocked up in Rhino/Maxsurf after seeing this topic... not too bad for a first shot at Rhino!!

    This boat is way too narrow on the waterline (about 4.5 foot, 1200mm or so), but flares out to 2000mm (6.5foot). A 3/4 to 4/5ths mast high assy would be flown off the bow, with a retracting bowpole, using some 29er/49er bow gear. Estimated all up weight of about 600kgs, 450-500 in the retractable keel. Hull would be S-Glass and foam.

    Some constructive criticism would be appreciated.

    Cheers,
    tassie
     

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  2. Doug Lord

    Doug Lord Guest

    P17

    Beautiful hull!! My opinion is that maybe the cockpit is a bit large and that the foredeck could morph into a small cuddy and move aft a bit. Just two people for most sailing.. Of course, it seems that the keel could be substantially lighter if it were canting and might then add significant performance. I think you got the freeboard just about perfect ; I personally would consider bringing the max beam out to 8'(trailerable in the States)
    If you could keep the hull as light as you describe and ditch the heavy fixed keel cutting the ballast down to 160lb(72 kg) in a canting keel it would just take my breath away!
    If this boat would be designed to sail flat or nearly so there would be a lot of weight just sitting there and not contributing much to max RM. Think about it! You've done a simply gorgeus hull-my compliments.
     
  3. TaSSie_deVil
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    TaSSie_deVil Resident Boataholic

    Thanks Doug, I will do a widened version with a more substancial cuddy when I can get around to it. I'll keep the profile and freeboard along the same lines and broaden the boat further down. A bit more WSA, but a fair amount more stability. I'm not a big fan of the canting keel idea (having been given a tour of a Mini Transat once... eek!), but maybe a modified version could be done as a "Sports" edition. A lot of the influence came from 505s; a large, open cockpit, mostly aimed for racing. I was also thinking of a racing crew of 3, no trapezes and hence the larger cockpit, and bigger keel than what may be required otherwise.

    Cheers,
    tassie
     
  4. Doug Lord

    Doug Lord Guest

    P17

    Tassie keep in mind that the "customer" wanted a two person boat for daysailing and racing.Thats where the canting keel comes in: to try to give high performance in 17-18' with just two people.
     
  5. mistral
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    mistral Senior Member

    too much weight in bulb, anyway too heavy for a day-sailer; with such a long foil , canting keel, and 450 kg lead in bulb she wouldn't heel at all!!!!!
    did you make any rough calculations of righting moment with canted keel???
    I guess you may obtain values of 800-900 kgm with flat boat and 45° canted keel, isn'it too much???? I would resize bulb 'til 250-280 kg, you may still have RM about 600 kg.m with flat boat and canted keel.
    Of course these are just rough values

    fair wind
    Mistral
     
  6. Doug Lord

    Doug Lord Guest

    P17(™™)

    Mistral, I think T was showing a fixed keel not a canting keel. My suggestion was to drop the ballast to around 160lb(72kg) in a canting keel. That would be fast- with just two crew- at his projected hull weight. (assuming a canting keel)
     
  7. mistral
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    mistral Senior Member

    gosh, that sounds better, with such an heavy bulb i'd rather call her "Red October" instead of "Luna Rossa" :)))))
    how many degrees do you think can twist the keel??? about 40°???
    Hobie 16 as an approximate RM value of 580 kgm with few degrees of heeling and a 150 kg helmsman+crew, and she carries a good amount of sail; of course Hobie is not a monohull, but anyway RM=500 kgm could be a reasonable target to aim at.

    fair wind
    Mistral
     
  8. Doug Lord

    Doug Lord Guest

    p17

    Mistral, if by twist you mean cant I'd aim for a max cant angle of around 55°.That gets the bulb four feet to weather in about the same position as the third crewperson that you no longer need...
     
  9. TaSSie_deVil
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    TaSSie_deVil Resident Boataholic

    P17 Concept Update

    Oops... Sorry folks, overdid the weight estimate a fair bit. Yes, the keel is fixed, simply for ease of modeling amongst other things. Got some scales out of whack, and from there it all turned out wrong. After actually doing the sums and righting moments; the boat (provided a bulb of 100kgs, as an estimate) and the draught of 5 foot 6 inches (1.7 metres, as taken from rhino), at a heel angle of 20 degrees (roughly the heel upwind in a moderate breeze), RM=570.39 kgm, with no rig to counteract the righting moment. If the keel were to then cant 20 degrees to windward, the RM would be nearly zero, except for the moment exerted by the rig. This would result in more pace, but honestly, the fitness to be gained out of actually leaning might be beneficial, plus a fixed keel results in a cheaper boat in construction terms.

    I have redone the hull slightly, increasing the beam to 7'3; the Bwl to 4'6 and extended the foredeck further aft. I am not keen on having an obtrusive caddie on such a small boat, where it will have not much use. I modeled a version with a very high caddie, but out of disgust for its looks, I deleted it (looked a bit like a demented version of a Mini 650)! However, there is a use for a lowish foredeck in order to put your lunch under and to hide the more complex rigging gear, such as the kite launching stuff, and maybe forestay tension (unless a set-and-forget bethwaite/skiff style rig wasn't used). This is all in keeping with the KISS theory.

    For safety, a full double hull is used. I will figure out a hoisting system for the keel and the rest of the keel structure later.

    Further comments on the updated version would be good.

    Ciao,
    Tassie
     

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  10. mistral
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    mistral Senior Member

    hey Tassie come on, be more aggressive in your design, dare!!!!! or you'll end up creating something too traditional to be appealing :)))))
    Canting keel is not a black monster who will eat you at night , it's a smart way to add spice to this boat, so don't quit it!!!!! Of course it has to be properly engineered and it will raise costs, but not more than carbon wings. epoxy-carbon vaccum bagged hull, composite spar or a lot of other tricky things that every skiff has nowadays.
    How about a manual control of canting keel??? i don't like to see electrical devices in such small boats, they means weight, battery exhausted in the worst moment, water leaking on the connectors and a lot of more troubles wich will make your week-end race a suffering; with 75-100 kg of bulb it wouldn't be a problem to cant keel with a 8:1 winch, or a pair of 4-way blocks hidden under the cuddy; take a look at http://www.tom28.it/ it'a quite interesting boat for some regards (almost deck layout ), absolutely out of market because of her price.....just few of them sold...
    a very expensive way to create a traditional boat using hi-tech materials and gear

    fair wind
    Mistral
     
  11. TaSSie_deVil
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    TaSSie_deVil Resident Boataholic

    Mistral,

    Hmmmm... the Tom28's big issue was its cost... from reading the initiating post from Clive (whom I would like to hear from... he appears to have vanished from this thread), cost may be a design factor, in both money and in costruction time. This hull could be knocked out from a simple male mould, fairly quickly, by anyone who has a little bit of boatbuilding experience. Plus, I designed the boat with a one-design aspect as a future possibility for a class development. So, even if the lightweight keel were to be canting, the extra engineering involved does equate to extra cost, and it may result in the boat being overly heavy, and more of a pain to sail. The Backman 21 may suffer from the same fate, unless a few more builders can be found for it worldwide, or unless a decent class association can get in behind it. This seems to be a similar situation for a lot of these small Mini 650-like one-designs.

    Also, from a failure-mode stability aspect, what if one of the 4:1 blocks were to break through a tack (not likely with PBO and Dyneema lines available these days... but just hypothetically)? The boat would start slipping, due to a reduction in effective leeway countering, plus the crew would be fighting the "extra crew member" in the keel. I never said that a canting keel was an evil beast that is there to jump up and bite you in the bum and make life difficult; I meerly avoided it for simplicity of modelling the boat (as I am not particularly experienced with Rhino, I am only learning how to use it in my spare time for my B.Eng (Naval Arch) as a modelling tool). Plus, I am currently a first-year engineering student, so I am yet to cover the hydrostatic and hydrodynamic effects that may be caused by having a canting keel, or a winged canting keel (as on Atomic, the Murray-Dovell designed Sydney Harbour "Black Horse"). So, when I can model it in a bit more detail, and when I can predict the forces and moments generated by the forces in a bit more detail, I am certain that I could add a canting keel and feel fairly confident that it would not pose a safety issue in the case of a mechanical or material failure.

    Sometimes, safe and traditional sells better than out-there state-of-the-art flyers; just look at what is currently out there in a similar sort of market... the RS K6, Laser SB3, both of which are too big to fit this design brief, maybe the Melges 17 (when it appears, it seems to be a bit of a secret development at the moment, so it may or may not meet the bill), the Thompson 590 (but it lacks a jib and requires a crew of 3 or 4 to extract the best from it) or the Australian "Charlie" (but it is too big... about 23 foot long, and in reality it is very much like a gigantic pregnant International B14... quick, but not as exciting to race as something without hiking racks). Read: None of the above have canting keels, due to their extra embuggerance and cost. Even then, some of them are only ever going to be built in limited numbers due to certain design aspects, and the general costs of building them.

    Also, in order to complicate the boat with a canting keel, and add the extra lines to pull through the tack, it would require either making something else on the rig automatic, or figuring out something to set up in a "set and forget" manner. This would either mean a skiff-style rig, with a 1 line kite hoist, non-adjustable stays (set and forget), no backstay and a self-tacking jib, or simply putting up with another couple of lines and cleats to get caught up amongst the Macramé in the bottom of the boat. While the skiff-type rig might seem quite an attractive option, the cost makes it prohibitive, and the fact that if you are wrong in predicting the weather prior to racing, you have no option but to put up with being over/underpowered all day. There is a good reason why the skiffs have the rig the way that they do; the rigs were developed for sydney harbor, where moderate to heavy winds come in consistantly, and so it is relatively easy to pick the settings for the day, and to be pretty confident that the settings will do for the day. There aren't many places around where that can be done with a high level of confidence in the weather. So, as this boat is conceptually to be designed for the conditions found in the US, more specifically the typically lighter conditions found around Santa Barbara.

    The way that I see this boat design is as an attempt to bring the latest Aussie skiff thinking into the sportsboats by essentially creating what a sportsboat is; a big, powerful dinghy with a lifting keel in the place of a centreboard and fat men on trapezes and wings. It is sufficiently small to be raced 2-up, looks great :)D); has enough RM from a lightweight keel to make it safe to sail, provided that a rig was selected that wasn't to obsurdly large (for instance, I wouldn't go sticking a rig off an 18 foot skiff on this thing... you will end up taking it for a swim or two if that were to be done!!). This means that a canting keel is not a neccessity in order for this boat to be a fresh take upon a fairly bland design formula.

    Either way, like all design, this boat is still evolving, and frankly, I am anxious to see how far I can take this thing! It would be a miracle if it ever were built...

    Cheers,
    Tas
     
  12. Doug Lord

    Doug Lord Guest

    P17-ck

    I think the electric canting keel --well engineered --is a very good option. From what I'm told there is off the shelf hardware available today that is specifically designed for tough environments with extraordinary reliability.
    I don't think that a small canting keel like this would add significant weight but it would add RM equivalent to another person on the boat.
    In terms of ease of sailing with just two people on board I think the electrically powered canting keel would be the way to go with the backups previously discussed. And it provides more power to carry sail than an equivalent weight fixed keel by a substantial margin.
    The idea of keeping the rig simple would be important-a self tacking jib for sure.
    This whole concept has a lot of potential especially since ,as best as I can tell, there is nothing quite like it available now.
     
  13. mistral
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    mistral Senior Member

    that's the main feature of tha boat!!!!! Lorsail has focused the most essential concept: a powerful, easy-to sail, canting-keel dinghy/sportboat. a new concept in dinghy/small sportboat.
    The canting keel 'til now is been keept in a corner of the backyard by most of the race circuit, confined in the odd crazy world of ocean racers; during 2004 Pyewacket and a bunch of new generation maxi yacht have definitively proven that canting keel is tremendously effective; as a matter of fact during the last maxi rolex cup, here in Sardinia, they outsailed every trad-keeled boat, including alfa Romeo, the all-winner hi-tech water-ballastd 110 footer skippered by aussie tycoon neville Crichton, and they did it in every sea and wind condition; this will take to a new canted-keel generation of maxi in a couple of years;
    talking about costs and dinghies, costs have more to deal with shipyard's name and boat diffusion than with effective technological content of a boat; I mean: how could you pay 5000€ fo a Laser???? She's just a 70 kg GRP hull an alluminium pole a dacron cross-cut sail and a bunch of blocks; i guess that if you build one of it you may spend less than 1200€; so i think that canting keel will not make costs raise to unbearable level i a sport boat like this, but it will be an incredible added value.
    I agree with you for self-tacking jib and keep-it-simple rig, good luck and keep on tuning the project

    fair wind
    Mistral
     
  14. TaSSie_deVil
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    TaSSie_deVil Resident Boataholic

    Ok, I'm convinced. I'll stick a canting keel on her. I've seen Shockwave/Alfa Romeo in action and I can't imagine the pace that Pyewacket and the other CBTF boats must have put up to beat her. It must have been something fairly phenominal. I will figure out a way of modelling it with a canting keel; however I am considering a small hydraulic system as opposed to the potentially dangerous electrical system, or the back-breaking 4:1 block and tackle system. 505s, Australian Sharpies, Flying Dutchmans (on the odd occasion) and the skiffs have all run them at one stage on their rigs to carry huge tensions, so maybe it can be used to cant the keel from side to side. I'm not sure, however, as to how easy the hydraulics are to operate and how quickly one side can be released and a new side can be taken up... but those are only minor technical difficulties.

    The next evolution in the design should be posted within the next couple of days.

    Ciao,
    Tassie
     

  15. Doug Lord

    Doug Lord Guest

    P17-canting mechanism

    You might find ,when doing your research, that an electrically driven system is more cost effective from a weight and money standpoint at this relatively small scale. The electrical system should not,in any way, be dangerous if it is designed and installed properly.
    For a hydraulic system wouldn't you have to use electrical power as well?- unless you wanted one of these two crewpersons to have to pump like hell every so often?
    In my opinion, especially for a marketed version of this boat, the canting system has to be as simple as raising or lowering a car window-simple ,quick and very reliable-with back ups as mentioned before.
     
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