Maybe, maybe not

Discussion in 'Boat Design' started by valery gaulin, Oct 23, 2021.

?

Should I build?

  1. Maybe

    88.9%
  2. Maybe not

    11.1%
  1. valery gaulin
    Joined: Jan 2017
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    valery gaulin Senior Member

    You have describe exactly my sailing area!

    Trailer is not for me, I tried it and it is alot of work! I am more of a marina type of guy.

    Lenght is costly at marina amd I figured that 26 feet is the maximum I want to pay for a berth at a marina!

    Also at 26 feet my house insurance cover it!

    I am the owner of a 1973 Grampian 26 that I love but want a little more space and a little more protection from the element. 26 feet seams to be the magic number, 10 foot beam make it possi le to trailer if needed at the end of the season with only a day permit for wide load but nothing else special is needed.
     
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  2. CT249
    Joined: May 2003
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    CT249 Senior Member

    Not really. High aspect keels have less wetted surface than low aspect keels, but making keels "high aspect" does not make them better at reducing leeway per se.

    The keels in your design are still dramatically limited in effectiveness by their very shallow depth. The fact that they are high aspect means that they are highly likely to stall when heavily loaded, which will be the case when coming out of tacks or gybes or when reaching or trying to go upwind.

    A high aspect but shallow keel like this does not prevent leeway better than a low aspect keel of the same depth; in fact in a craft like this, with very high sideforces and low speeds, the high aspect foil is extremely likely to spend much of its time stalled out.

    Sure, high aspect keels have lower wetted surface but given the other facets of this design that's not here or there.
     
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  3. valery gaulin
    Joined: Jan 2017
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    valery gaulin Senior Member

    Well, my twin keels right now are 36 inch long with a chord of 24 inch at an angle of 15 degree.

    At low speed the keel will most likely stall like any other airfoil profile. Now the question that we need to answer is at what speed do I want the airfoil to start to be effective or creating lift? I would say at 2.5 knots! In reality below 3 knots of hull speed I will motor. Therefore low speed is not as critical. At higher speed 3 knots to 7 knots the foil need to create as much lift as possible with the least amount of drag. The other compromise is how much thickness the foil need to be for descent structural strenght? Right now I believe that my keel size with a foil NACA 0012 are a good compromise for the purpose.

    Don't forget that when heeled twin keel show their full profile were a regular keel when heeled loose some effective profile cosine of that heeled angle.

    Look at the RM yacht and their twin keels or another French designer Brouns that do twin keel.
     
  4. valery gaulin
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    valery gaulin Senior Member

    1/10th Scale model of my 26 foot motrosailer showing the ergonomie with a scale 6.25ft human.
     

    Attached Files:

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  5. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    That is a very impressive model Valery!
    Are you going to put a keel(s), rudder and sailing rig on it to do some trials before building the full size version?
     
  6. valery gaulin
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    valery gaulin Senior Member

    That is the goal, keel, rudder,etc to do some trial before I make one of the biggest mistake in my life!!!
     
  7. Tops
    Joined: Aug 2021
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    Tops Junior Member

    Varely,
    Nice progress on the model. Have you considered 3D printing for the model rudder and fin keels? I know I don't trust myself to foil small parts (OK any parts) accurately. Perhaps make them so they be changed easily to see the affect of one versus another.
     
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  8. valery gaulin
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    valery gaulin Senior Member

    YES, I will consider 3D printing some part if needed for this project as I own a 3D printer. Probaby the rudder is one of them.

    But not the keel as I want them to be in steel the same as it is in the full scale boat. To get the actual weight for ballast.

    Thanks for the input.
     
    Last edited: Nov 21, 2021
  9. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    just a reminder that boats - and other things don't scale right in terms of masses and righting moments etc.

    mass/volume scale in power of 3
    Areas in power of 2
    etc.

    scale sailboats for example use ridiculously large (if real sized) bulb keels to keep them upright in wind.
     
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  10. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Valery,

    Looking relaxed here:)

    I like the style, I'd prefer up around 40' & with an open to the stern cockpit or a boarding platform that lifts to close.
    Great to get the shelter there. Your raised deck and beam reminds me a little of a Hartley silver image https://hartley-boats.com/product/hartley-30/ Hartley 30 (Steel Version) - Hartley Boat Plans https://hartley-boats.com/product/hartley-30-steel-version/
    My Dad built one of these- very roomy and comfy "big for length" yacht
    Regards from Jeff.

    upload_2021-11-22_19-56-49.png
     
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  11. valery gaulin
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    valery gaulin Senior Member

    You are so right about that!
    But I think I will at least be able to test the actual vanishing stability, since everything is the scale.
     
  12. valery gaulin
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    valery gaulin Senior Member

    Never heard before of the Hartley 30! Nice line...

    How long your dad kept the boat?
     
  13. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    Valery, I'm building my own design of 26' by 10' boat. So of course I think you should too.
     
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  14. valery gaulin
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    valery gaulin Senior Member

    Cool! Do you have photos or a site where I can see the design and the construction?
     
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  15. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

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