14 foot plywood dinghy sailplan

Discussion in 'Sailboats' started by slomoshun, Sep 25, 2011.

  1. slomoshun
    Joined: Sep 2011
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    slomoshun Junior Member

    After 40 years of sailing other designer's dinghies, I decided to design my own 14 foot plywood dinghy.
    Now I need to decide on the sailplan so that I can order sails.
    I am aiming for about 10sq m to be sailed bu a heavy singlehander, or lighter 2-up.
    I have looked at a number of boats to get inspiration for the hull.
    The closest boat out there is the phantom, but I have moved the widest point back and made the entry sharper and longer.
    My considerations for the sailplan are:
    Large furl-able jib with smaller than normal main.
    A lot of mast rake to reduce the load on side stays, as the hull is fairly narrow in the side stay area.
    Loose foot like a laser.
    Full length top batten.
    Any comments or suggestions will be welcome.
     

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  2. Doug Lord
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    Doug Lord Flight Ready

    I like the looks of your hull! Can you post any numbers? You might consider going with a squaretop main. It has numerous advantages including a more effective planform and automatic gust response.
    I you might be able to go with a bit more sail w/o being over powered or difficult to sail. Good luck with the boat!
    PS-I see you sail an RC Laser-I raced one for a couple of years-it was a blast.

    Here are some collections of dinghy numbers that may or may not be helpful-and Eric Sponbergs Design ratios which can definitely be helpful:
     

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  3. slomoshun
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    slomoshun Junior Member

    Thanks for the reply and documentation.
    My hull weight is just under 60Kg and I still have to add paint, centreboard and fittings.
    L.O.A. 4200
    Width W/L 1250
    Width O.A 1400. (Maximum width is 830 from aft)
    I have made the hull pretty still with plywood frames under the side decks.
    I planned to leave my options open to add wings.
    I will go through all the data before finalizing my sail spec.
    I weigh in at 100kg, so I want to initially sail on my own, but the cockpit is roomy enough to sail as a 2 up without trapeze or spinaker.
     
  4. BATAAN
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    BATAAN Senior Member

  5. slomoshun
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    slomoshun Junior Member

    PJ 14 looks good

    Thanks Bataan
    I did look at the Dix design PJ14 before starting my project.
    I also looked at the underside of a 49er hull.
    I chose the construction method of the Phantom as I have previously built a Phantom and found it a quick and easy method.
    I had designed 350mm wide wooden wings but did not incorporate them into my hull.
     
  6. JRD
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    JRD Senior Member

    Just a couple of quick thoughts,
    Too much mast rake will affect downwind speed, and make main sail hard to set effectively down wind in the light.
    Look at the newer international 14s, they have moved the mast well aft to increase jib area, which would get your stays to a wider point on the boat.
    If you mostly plan to sail alone, I would strongly suggest a self tacking jib, or at very least lead the jib sheets further back than normal to allow you to quickly access them after tacking.
    It may just be the angle of the drawing, but the centreboard looks a long way aft for a sloop rig.
    Agree with Doug on the square top main, they are not as scary as they look handling wise. though it will require full battens throughout. (Only if your sail maker has some experince with sqaure tops though)

    Looks great though, good luck. PS have you already built the hull, if so can you post some photos?
     
  7. gggGuest
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    gggGuest ...

    On a singlehanded boat without a spinnaker a self tacking jib is very much a mixed blessing, which is why most International Canoes don't have them. However the Canoe does have the advantage that the sliding seat is used to help sheet the jib in after the tack.
    An overlapping jib is probably not a good idea since it will dump you in the water, is more difficult to set and prone to snags.
    If you don't plan to use a trapeze and your boat is well constructed with decent structure to support the rig loads then you probably don't need to worry too much about the staying base.
     
  8. slomoshun
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    slomoshun Junior Member

    A pic of the enigma hull

    Thanks for all the advice. The centreboard is about 550mm behind the mast. I thought that this was a long way back until I saw the paperjet 14, then it looked ok.
    I did not think of the mast rake being a problem running in light wind. I will reduce it a bit.
    I intend to use a jib with a long foot to make the jib sheets easier to reach.
    The ends of the sheets should also be tied with shockcord across to the weather deck to make them reachable.
    I like the idea of a square top sail, I suppose it would push the cost up.
    I have attached a pic that was taken before I finished the decking.
    Wali.
     

    Attached Files:

  9. CutOnce

    CutOnce Previous Member

    Looks good so far. I've seen a PaperJet in person, and there are two mast positions - one for jib-less usage and one with the jib. There is quite a difference between the two because Dudley Dix was moving it so the CoE was in the right spot for the CLR in either case (cat or sloop).

    The PaperJet looked like a handful to sail with jib and main singlehanded. I'd seriously consider the self tacking option - you won't lose very much benefit from the jib, but the reduction in jobs to do on tacking and gybing will make a difference. It really would not cost much more to do, and then you could function with a continuous mainsheet that connected to the self tacking jibsheet tail - so there is only one sheet in hand on maneuvers. The PaperJet would highly benefit from this and the cockpit floor spaghetti factory/crew trap would be put out of business. It also reduce the need for cam cleats and fairleads. The Swiftsolo (google it) has got a very complex (but neat) single sheeting system for main and jib. You don't need to go to that level of complexity, but I sure would look very hard at a 29er for ideas.

    Just from a glance, that fine bow doesn't appear to have huge amounts of reserve buoyancy up front - fine, but you will be able to drive the bow right into waves and have lots of water passing through & over. My boat is similar - and boy does it get wet.

    If you use a sailmaker who has experience with the squaretops - Glaser, North Suncoast etc., you should not have to pay a huge premium for the sail - square footage is square footage. Make sure the head plate is big enough and the top diagonal batten is well designed - this is the most critical area to get right if the top is going to behave right. Each batten should have individual velcro tensioning to allow control of curvature.

    Make sure your sailmaker knows exactly what tube (mast) you are using and it's characteristics. It may be better to choose a sailmaker who knows the mast well and adapts the sails to match. Get their input on standing rigging needed - it will help define if you should consider lowers, uppers and the need for a mast ram. Tuning a boat like this is critical.

    --
    CutOnce
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Here is a diagram of the Swift Solo system. It allows you to adjust the slot with a "relativity" control and works very well. I used a variation of it on my 16' foiler. The bottom line is that the mainsheet controls both sails.
    Years ago I used to race my 15' Windmill a lot but for blast out fun w/o a crew I'd sail with just the main(80 sq.ft). Never had to move the mast or board.

    Pictures-Swift Solo sheeting diagram, me sailing my 'mill in good wind w/o the jib,

    click on the swift solo image for more detail:
     

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  11. JRD
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    JRD Senior Member

    Nice work, its always great to see someone who has followed through with their plans and built something to their design.
    Something I forgot to mention with sqaure top mains is that they are generally matched with carbon fibre masts that are quite stiff. You should talk to your mast supplier and sail maker to make sure what you are ordering will work together which ever sail profile you choose.
    If you are trying to keep your costs right down, an untapered mast along with dacron sail will be the cheapest. Im not sure how Dacron would go with a square top main, as they are ussually based on film composite sails with full length battens.
    Another boat you could have a look at for ideas is the New Zealand Jollyboat designed by John Spencer. These have very simple construction and have a relatively low cost rig and plywood construction, and they are annoyingly quick to race against, with and without a crew, so have some similarities with what you are building.
    http://www.jollyboat.co.nz/

    I agree with g Guest that the self tacking jib can be a mixed blessing but my boat was originally an NS14 which I sailed one up with a standard non overlapping jib (No track). Tacking was a pain and not being able to ease it quickly in gusts also made the boat prone to being knocked down a bit in gusts.

    If you are just cruising in straight lines alot its good, but if you are racing and doing alot of manouvures then you may find that the benefits of having an overlapping simply rigged jib will be outweighed by the amount of time you spend sailing at half speed while you are trying to handle two sails at once.

    Whilst I have not seen one first hand I understand that the Swift-Solo has the jib rigged to trim in tune with the mainsail with a single sheet and some adjustments on the relative tension of both sails.
     
    Last edited: Sep 26, 2011
  12. gggGuest
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    gggGuest ...

    I would have said it was a mistake to let ergonomics affect your rig design: better to keep the two things independant. The typical setup on ICs is to have a barber hauler or similar arrangement just in front of the mast which adjusts to control leech tension and sheeting angle to get the sail to set correctly, and then have the sheets run back to a turning block and cleat much further aft to put them in the right place to sail the boat.

    Rather than shockcord the ends of separate sheets I would use a continuous sheet on a boat like yours. The easy way to rig this is to have a single long sheet which stays on the boat and a short length of line which stays attached to the jib clew by looping it through so there are two short tails. Use a sheet bend (better a double sheet bend) to attach each short tail to each end of the jib sheet. Its less string in the boat, no need to figure out which rope to pick up (its suprisingly easy to grab the wrong one even if they are different colours!) and very staightforward to rig and derig.

    I don't know I'd want to advise you on what jib setting system to use other than to have a none overlapping jib. They all have pros and cons. There are three possibilities I guess, self tacking jib on a track, self tacking jib on a spar (club foot) and non self tacking. They all have their pros and cons, depending on what you are going to use the boat for... The club foot is probably least efficient, but on a boat intended for recreational cruising sailing its really convenient and its nice to be able to just roll the sail round the spar at the end of the day (assuming a rope luff and a separate forestay with the wire in). For a serious racing boat I am convinced that the non-self tacking jib with barber hauler etc gives the best control of the sail shape and thus upwind performance. For a boat that flies a spinnaker the self tacking jib/track arrangement is best since you don't want to have to play with the jib downwind and the gubbins are clear of the kite.

    The combined jib/main adjustment on the Swift Solo has been tried numerous times on Canoes and everyone who has tried it has abandoned it. I also find it instructive that people, even Olympic sailors, don't sail two handed boats adjusting the jib exactly in sync with the mainsheet all the way up the beat.
    Apart from anything else it makes it difficult to keep the boat driving "in the groove".

    As far as square topped or whatever rigs are concerned, you need to be driven by the mast. Nothing is more important than having the sail match the mast. If you have too much area at the top for the mast bend then the sail will twist off and depower before you run out of sitting out power no matter how much kicker you use, whereas if you have too little then the rig won't dump power well and be much harder work to sail. So if you already have the mast then get the sail cut to match it...
     
  13. John Perry
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    John Perry Senior Member

    I agree with others here that its good to see someone actually building according to their ideas rather than just speculating about performance.

    One thing I dont understand is that you intend to have mast rake to reduce load on the side stays. I am not sure that is right. I can see that raking the mast back will cause the dead weight of the mast and sail to reduce shroud tension but that is a very small effect and can probably be neglected. Apart from that, the tension in the shrouds for a given wind loading depends on the angle between the two planes defined by the axis from the mast foot to the hounds and by the deck attachments for the two shrouds. As I am sure you realise, this angle is a compromise between wanting to allow the boom and sail to swing well off the centreline when sailing downwind and also wanting to give good support against the mast falling forward downwind and wanting to increase forestay tension when sailing to windward. Once this compromise has been established, I think the load on the shrouds for given sailing conditions is almost independant of mast rake.

    If you do decide to fit this dinghy with sitting out racks then you could obviously extend the racks sufficiently far forward that the shrouds can be attached to them giving a good wide shroud base. On the other hand, with such a triangular shaped hull as seen from above, you might find that you dont really use the forward part of the racks for sitting out, in which case you could save some weight and windage by having relatively short racks not extending as far forward as the shrouds. Another point is that the use of a trapeze wire reduces shroud tension.
     
  14. gggGuest
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    gggGuest ...

    Now I think of it the hull shape does remind me of something...
    [​IMG]
     

  15. CutOnce

    CutOnce Previous Member

    Plus+plus?

    --
    CutOnce
     
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