Modernizing the Keel of a 5.5m: safe? advisable?

Discussion in 'Boat Design' started by luizebs, Dec 1, 2009.

  1. luizebs
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    luizebs Junior Member

    Dear all,

    A group of 5 people (including myself) is thinking about building a traditional long keel 5.5m sailboat. (initially we though about the Shields class from Sparkman&Stephens, because its pedigree)

    We have agreed to build the same boat.

    The problem is that I read in several forums that the boat is very slow, even in light winds, apparently due to its long keel. This would be a pitty, cause her small wetted surface had every potential to be unbeatable in light winds, which would make it easier to advocate for engineless sail, as we wouldnt be buoying around in light winds...

    I understand it has to do more with the wave resistance than to the wetted surface (since the part that most contribute to the viscous drag is the foremost part of the keel anyway).

    I was wondering if it was advisable / safe to modernize the keel to a fin one with a spade rudder (separated), instead of a long one.

    If I (we) decide to do so, what are the worries or procedures I should watch out for?
  2. Munter
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    Munter Amateur

    It seems to me to be a little inconsistent to choose a design based on pedigree and then seek to change the design! :)

    Wouldn't it be more appropriate to identify the sailing characteristics you are seeking for your fleet and then identify designs that meet these criteria? Perhaps something like an i550 would be appropriate for people interested in building a fleet of fun, fast and easy to build boats?
  3. sorenfdk
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    sorenfdk Yacht Designer

    Of course it can be done, but you should definitely contact a naval architect/yacht designer (S&S?) first!

    However, my advice would be to identify your needs and then find a design, that fits those needs. This is far better than modifying an existing design.
  4. Manie B
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    Manie B Senior Member

  5. Crag Cay
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    Crag Cay Senior Member

    I presume by 5.5m yacht you are talking of it's 'rating' as the Shields Class is around 9.5m LOA.

    Rather than mess with an old one-design why not design and build to a similar rule that is still active like International 5.5m? All the new ones have separate keels and rudders and there are plans available from various designers or you can get stuck into the class rules (see below).

    But all these 'raters' sail with a certain 'style'. Just putting a modern keel on them won't make them plane!

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  6. dskira

    dskira Previous Member

    You don't touch a 5.5. What ever the years, and they changed a lot, they are phenomenal boats (I raced on them in the sixtees).
    If you don't like them, choose an other boat. Do not transform any thing because some journalist imbecile tell that and this. Lets the trend for the fashion industry, and find the right boat for you, or learn to apreciate the beauty of the 5.5
  7. pat60
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    pat60 Junior Member

    This has been done already at least once, not on a 5.5 meter but a 30 sq metre. Bruce Schwab of Vendee Globe fame, revamped the keel and rudder of a 30sq metre (rumbleseat) and won the singlehanded transpac with her in 1996.

    Once the new keel had been designed he literally cut the old one off with a chainsaw. Sometimes we seem to discount the ease with which some changes can be made if they are planned well. It goes without saying Bruce is much more that merely competent and this should not be attempted without professional help.

    The real concerns are structural changes, the keel design can be handled by any competent designer.

    As to performance Bruce reportedly felt that the boat did not so much point better with the new keel but did track and handle much better, obviously sail carring power was much improved.

    PS- I could be wrong but my memory tells me the keel re-design on Bruce's boat was handled by Jim Antrim.
  8. Typhoon
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    Typhoon Senior Member

    Modern 5.5m boats already run a fin keel/detached rudder, why not build one of them?

    Regards, Andrew.
  9. luizebs
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    luizebs Junior Member

    which one you would suggest?
    (by the way, by 5.5m I meant the class 5.5, not the actual LOA in meters)

    Thanks a lot.

  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Fin keels have more wetted surface than long keels. It should do worse in light winds
  11. Paul B

    Paul B Previous Member

    Possibly the funniest thing ever posted on this message board.
    1 person likes this.

  12. Paul B

    Paul B Previous Member

    Seb Schmidt has been the top desinger in the class for the past decade. You should try contacting him for plans ( His recent boats sport a pronounced chine in the hull (Addam^4, below).

    The Doug Peterson designed, Melges built boat was the dominant boat for the prior decade. Maybe you can find the plans for that one. That boat was smoother, with no pronounced chine (My Shout, below)

    The other place to visit in your search is the class site (

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