Yacht Tender for Towing

Discussion in 'Boat Design' started by tlouth7, Jun 7, 2018.

  1. tlouth7
    Joined: Jun 2013
    Posts: 15
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: Cambridge, UK

    tlouth7 Junior Member

    I am undertaking a thought experiment to design a dinghy that is optimised for towing behind a sailing yacht and rowing.

    Where I sail there is a (fairly) lighthearted yacht race that involves sailing around a river estuary, towing a tender. The marks of the course are not buoys but pubs; each time you near a pub one member of the crew leaps into the dinghy, rows ashore, runs to the pub, downs a pint and returns to the yacht. There is a tradition in this race of bending the rules as much as possible (such that surfboards etc are now specifically outlawed as tenders). I am thus considering designing a dinghy that would be optimised for this race.

    As I see it the requirements are:

    1. Low drag when towed at up to 7kn
    2. Stable under tow (in a reasonably sheltered estuary)
    3. Stable enough to jump into from a moving yacht
    4. Fast/manoeuvrable with a single rower
    5. Rugged enough to pull onto a shingle beach
    6. Resemble a standard yacht tender (to be allowed under the rules)
    7. Reasonably cheap/low tech construction

    What hull shape would you go for?
    Is there a clever design that would minimise drag in two different speed/loading regimes?
     
  2. Richard Woods
    Joined: Jun 2006
    Posts: 2,140
    Likes: 133, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

  3. gonzo
    Joined: Aug 2002
    Posts: 13,064
    Likes: 289, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Depending on the rules to qualify as a dinghy, I would get a surfboard with built up foam sides and open transom.
     
  4. Richard Woods
    Joined: Jun 2006
    Posts: 2,140
    Likes: 133, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    The OP said "no surfboards" and I assume that includes SUPs, although they would be tricky to get on from a moving boat after a few beers

    RW
     
  5. tlouth7
    Joined: Jun 2013
    Posts: 15
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: Cambridge, UK

    tlouth7 Junior Member

    The Duo does look like a very nice dinghy, I especially like how light it appears to be. I wonder how well it tows though, given that the hull is presumably not optimised for those speeds.

    The race is on the Orwell, East coast of the UK (Fox's Two Rivers Race). I don't have a copy of the rules, but last year they made reference to the dinghy being a normal yacht tender. I assume that a monohull dinghy with transom which is not fully decked would pass muster.

    Inflatables are commonly used, as are small rigid dinghies, but these tend to squat terribly, and are designed for carrying more weight than is necessary.

    I have seen discussion of towing dinghies in a bow-up position such that the run to the transom becomes horizontal, allowing them to plane. I wonder if it would be possible to incorporate this capability at the design stage, achieving low-drag planing under tow, and then an efficient hull shape at rowing trim.
     
  6. gonzo
    Joined: Aug 2002
    Posts: 13,064
    Likes: 289, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    It depends on the definition of a surfboard. With sides it would be a dinghy.
     
  7. Richard Woods
    Joined: Jun 2006
    Posts: 2,140
    Likes: 133, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    I know it well, been to Fox's many times and the RHYC. When is the event, maybe I'll come up.

    The Duo will tow well, it has a skeg for directional stability and can motor at 7 knots no problem. Check this video of my 8ft Crayfish at 13 knots



    but I think the Duo is better suited for that sort of speed. What boat do you have?

    Richard Woods
     
  8. Chuck Losness
    Joined: Apr 2008
    Posts: 263
    Likes: 19, Points: 18, Legacy Rep: 135
    Location: Central CA

    Chuck Losness Senior Member

    When I had an Avon many decades ago I would tie the bow tight to the leeward stern cleat with only the very end sitting on the water. No drag to speak. No tow line to foul on anything. Don't have any pictures. I have thought about making my next dinghy with a rounded transom to have the same easy towing.
     
  9. Ad Hoc
    Joined: Oct 2008
    Posts: 5,692
    Likes: 248, Points: 63, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Can't go wrong with two simple slender hulls with simple cross beams and netting.
    Easy to jump in and out of, and loads of stability, being a cat!

    Cheap easy and simple.
     
  10. wayne nicol
    Joined: Dec 2009
    Posts: 135
    Likes: 4, Points: 18, Legacy Rep: 34
    Location: Queen Charlotte islands, B.C.

    wayne nicol Senior Member

    there was a guy on here a few years back- thatw as doing small single sheet origami row and paddle boats- they looked pretty good!
    but wouldnt a longer waterline be advantageous.
     

  11. tlouth7
    Joined: Jun 2013
    Posts: 15
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: Cambridge, UK

    tlouth7 Junior Member

    Richard - the race is on the 4th of August. Pursuit race starting opposite Levington.

    Chuck - Avons are a very common choice for this race, probably because they are what people have. Sadly the rules say that the entire weight of the dinghy has to be through the water (so no davits either). Technically any painter that makes an upwards angle to the yacht will be taking some of the weight though...

    Ad-Hoc - I agree that a simple catamaran would be ideal, but as they are not really used as tenders here I don't think I could get away with it.

    Wayne - Certainly I would want a long enough waterline to row at max speed without high drag, but does a longer waterline reduce drag at higher speeds under tow, when the tender will be planing?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.