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T&T: Catamaran vs monohull (long rant)

From: Candy Chapman and Gary Bell (no email)
Date: Mon Oct 01 2007 - 15:34:25 EDT

  • Next message: Candy Chapman and Gary Bell: "T&T: Modifying a Single Screw Rudder"

    First, a disclaimer: I own and love my PDQ34 power cat. Further, I
    think it is the very perfect boat for me, and probably for just about
    everybody else as well. I must qualify that by adding that what just
    about everybody is doing is limited to what is commonly termed protected
    waters and/or coastal cruising. Power catamarans with the fuel capacity
    and storm survival attributes for ocean crossing passages are all in the
    fifty foot plus range, and don't be asking how much they cost. Truth to
    tell, the true ocean crossing monohulls are similarly uncommon, and
    similarly limited to the large and expensive models. If you want to
    get catamaran advantages and still make blue water passages, either get
    a sailing cat, or spend some serious money on Dockwise transport.

    I also choose to limit my comments to 'wide stance' (gotta be carefull
    with THAT term now!) catamaran hulls. These have widely spaced hulls
    with plenty of daylight underneath, and particularly have individual
    hull length to width ratios in the ten to one or better range. They
    rely on 'slender hull behavior' to bypass the hull length wave trap by
    minimizing the depth of the wave trap trough. By this I mean to exclude
    the power catamarans that closely resemble planing monohulls, with a
    relatively slender tunnel down the middle. They provide some nice
    improvements on planing monohulls at speed, and some limited gains in
    interior space and such, but otherwise share most of the large engine,
    poor fuel economy, rough water handling, etc. properties of their
    monohull predecessors. 'Trawlering' isn't about those high speeds, huge
    engines, high operating costs and limited boat amenities, for most of us
    anyway.

    My Admiral insists on catamarans only, based on her experiences (similar
    to yours) on a couple of scuba charters on large sailing cats several
    years ago. The rough water rolling immunity (as you mentioned),
    together with her desire to sit comfortably up where she can easilly see
    the horizon in bumpy seas are the main reasons she gives. I love the
    boat motion as well, and as the PDQ sales manager said, we don't need no
    steenking stabilizers/paravanes/flopper-stoppers/etc.. The downside of
    this (that you may not yet appreciate because it is not commonly
    encountered, and is relatively easilly manages when it does happen) is
    that the slender hull, wide stance catamaran is much more sensitive to
    pitching motion than a 'wide body' monohull. I hate to take heavy short
    period seas dead ahead or astern, because I risk some serious harmonic
    hobby horse pitching motion. The remedy is to change course and take
    such waves off the bow or quarter, and/or change speed, or of course to
    stay home. I am talking about conditions that would discourage most
    boaters, monohulls as well as cats -- eight to fifteen foot very short
    period chop in shallow water with long fetch and steady heavy winds.
    You can think of it as trading very common mononull rolling for unusual
    condition catamaran pitching. The conditions involved in hobby horse
    pitching are far less common than the waves that vex our monohull
    brethren -- maybe once per season or less for me at least. Plus, the
    remedies for pitching (changing angle of attack and/or speed when
    underway, and use of bridles, weathercock sails and/or stern anchors
    are much less costly in terms of money and of fuss than the active
    stabilizers, paravanes and flopperstoppers rolling monohulls require.

    I love the maneuverability of having twin screws twelve feet apart (we
    don't need no steenking bow thrusters). I can spin the boat in either
    direction, without moving appreciably ahead or astern. I can pirouette
    in the marina fairway and freely choose to proceed bow or stern first.

    My boat draws twenty eight inches, including skeg protected props and
    rudders. It is conveniently beached nose first, and will settle on the
    bottom in a very stable position. In the yard it sits on four wood
    blocks. I have to worry about ingesting sand, weeds, etc. when running
    generator, AC or engines in such shallow water though, and I carry a
    ladder to board over the bow on a beach. I am almost done making an
    auxilliary water source (a plastic bucket with a thousand holes and a
    big bilge pump inside, tethered with a waterproof cord/garden hose, soon
    complimented with 'T's, valves and garden hose connectors spliced into
    all the water intakes) to dip into 'cleaner' water, but haven't actually
    tried it yet.

    I can easilly get very thrrrrrifty fuel economy at trawler speeds, and
    can smoothly and easilly get up to nineteen knots without a notable
    planing 'step' or any discernable transition in performance, and still
    get about four or five gph total consumption at speed, so no need for
    big powerfull engines, or any steenking trim tabs either. Due to the
    exceptional overall beam (about half the boat length) I can rig
    anchoring bridles and towing bridles, or a strategically placed stern
    anchor to tame most boat motion issues -- I'm working on an anchoring
    sail with high hopes as well.

    You already have some experience with the roominess and light issues.
    Seldom mentioned is the particular sensitivity of catamarans to overall
    weight and distribution of that weight. Best to leave those big bow
    lockers pretty empty. Moving all your worldly goods aboard will
    similarly get you surprising degradations of performance and handling.
    Also, as relative newcomers to the market, with considerable (not
    universal!) interest among buyers, power catamarans are considerably
    more costly, and used boats are seldom found yet. Would you consider a
    good sized sail catamaran? They are hardly ever actually sailed anyway,
    and have, or can easilly be fitted to have most of the advantages of the
    power cats, plus 'free' propulsion if/when you are willing to sail.
    There are a bunch of sail cats maturing out of charter service at very
    attractive prices, even given their reputation as used up boats.

    Boat design and performance is a world of trade-offs. You can have more
    of this but you must give up some of that. I think the power catamaran,
    similar to mine, is a wonderfully optimal trade. YMMV! My advice:
    charter some power catamarans. Beg rides on them (ever find yourself
    near Portland OR? email me). Oggle power cats at the boat shows. Talk
    with lots of owners. Correspond with dealers and manufacturers. Mind
    you, bring your salt shaker, you will need to take ALL of OUR advice
    with your own grain of salt. Make up your own minds. Let your own
    experiences and preferences guide you.

    Best of luck, see ya out there...

    Gary Bell

    Mervyn Carr asked(snipping by me):

    I should explain further where the question comes from; <snip> I went out twice on a cat <snip>
    The seas were not exactly calm, about 6' waves. I was astounded at the
    difference in stability compared to my 1979 Mainship, first while at anchor
    (in my Mainship it would have been intolerable) while running head on into
    the waves, quartering the waves and even with a beam sea the movement of the
    boat was pleasant with no sudden movements. <snip> SO, I started thinking that maybe we should be rethinking
    our strategy regarding the boat we want to be on
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