Conference unifix::sailing

Accurate quantitative data would be virtually impossible to obtain other 
than by tank testing, and I haven't seen any published reports. Racers
strive for an ultra smooth bottom on the theory (I suppose) that it won't
hurt and might just help, but whether the difference is .001 or .01 or 
0.1 knot is anybody's guess. Unless you have a folding or feathering
propeller, flush thru-hull fittings, carefully faired bottom and keel,
etc, a really smooth, shiny bottom isn't worth the extra effort. I'd
suggest that as long as the old bottom paint is smooth (no flaking or
pits) just rolling on another coat with a roller after a light sanding 
will result in a fine bottom finish. But then I loathe sanding and 
painting bottoms.

Alan 

    Micron CSC is brand new this year, so noone is likely to have any
    empirical data on how well it works. I am in the middle of applying
    it right now, and I can tell you one very serious problem with it
    in April in New England- it must be applied when the temperature
    for the next 16 hours, while it dries, is over 50 degrees. Monday
    morning I barely made the window between the temperature rising
    enough and the rain starting. And it needs three coats.
    
    On the other hand, I used Micron 33 on my old boat, and it was
    wonderful not to have to worry about painting it at all for four
    years.
                                      TOM

    It's partly dependent on the hull form.  Low wetted surface hulls
    notice the detrimental effects of roughness much more so than heavy
    displacement full keel ones.
    
    Ditto for the effects of slime.  For a sleek hull, the slightest
    bit is noticeable.
    
    I'm convinced that at sailboat speeds there is no such thing as
    a self polishing bottom paint.  
    
    A clean bottom is like a waxed car.  Those who like it, do it.
    
    - gene ho

    I have Micron 44.  Used it last season.  Before that I used Micron
    33.
    
    The 44 is the closest cousin to CSC as far as I can tell. Even
    International recommends CSC as the no-tin replacement for 44.
    
    As for results...I think 33 is probably better for boats that
    stay under 8-10 knots and spend a lot of time in still water.
    The slime flushed off the hull quicker with the 33 than the 44.
    It was also quite evident that the 33 was doing what it is supposed
    to because the bottom came out extremely smooth at the end of the
    season.  The 44 seemed to slime up at the same rate as the 33 but
    it took either a scrub brush (the 33 would be completely removed
    with a scrub brush) or some fast sailing and a couple hours to
    have the slime flush itself off.  At the end of last season the
    44 still showed the brush marks of application, which makes me
    believe it erroded very little over the season.  I wont know if
    that is good or bad untill this year.
    
    I would hope that the CSC has been formulated to erode at a rate
    somewhere between 33 and 44.  
    
    By the way, I hate sanding bottoms too. That is what appealed to
    me first about the copolymers.
    
    I have a question too. They referred to 33 and 44 as Copolymers,
    but the term ablating is being used this year. It appears the
    term ablating applies to the paint type known as copolymer but
    I am not sure copolymer applies to paints like CSC. Does anyone
    know how they are binding the ablating paint and copper oxide in
    the new copper paints like CSC?
     

    Walt

    
    re .-1
    
    Ablation: n. 1  removal, as by surgical amputation.
    		 2  a wearing away, as of rock
    
    So, you see, your hull will wear away either by amputation or
    by rocks...  maybe you ought to try a different kind of paint!
    
       ;-)
    

    On the resistance of hulls -
    
    There are two major components of resistance for displacement hulls;
    friction drag and wave-making drag. Wave-making drag is due to the
    wave train generated by the motion of the hull through the water.
    As speed increases, the contribution of this component also increases.
    For displacement (non-planing) hulls this reaches a limiting maximum
    at so-called 'hull speed', where the bow wave has approximately
    the same length as the boat's waterline length. At this point the
    boat is essentially digging a hole in the water, and can't go faster
    unless it can begin planing. For traditional displacement sailboats,
    hull speed (in knots) is between 1.2 and 1.5 times the square root
    of the waterline length (we've all heard this one).
    
    Friction drag is largely a function of wetted surface, although
    other factors intrude. For a given wetted surface, smoothness has
    an noticeable effect, although it's not exactly what you might think.
    What really matters is the thickness of the boundary layer which
    is entrained by the surface as the hull passes through the water,
    and whether flow in the boundary layer is laminar or turbulent.
    The boundary layer is a layer of water in which the local velocity
    of the water varies between the velocity of the hull itself (i.e.
    right at the hull surface) and the resting velocity (relatively
    0) of the undisturbed water. In a sense, the boat is dragging much
    of the water entrained in the boundary layer along with it (one
    way to compute friction drag is to attempt to compute the enery
    imparted to the water in the boundary layer). The effect of smooth
    bottom paints is to reduce the thickness of the boundary layer,
    thus the extremes to which racers go to both reduce wetted surface
    and have slick bottoms.
    
    It's not all that simple. By many estimates, dolphins exhibit the
    lowest boundary layer resistance of anything which moves fast in
    the water, and they don't have smooth, slick skins. On a fine level,
    their skins are stippled and flexible. Researchers are still trying
    to figure out how they do it...
    
    For large vessels (ships) boundary layers may be 1-2 feet thick.
    For boats in our familiar sizes, they are probably more like 1-2
    inches. Another factor is whether flow in the boundary layer is
    laminar (smooth) or turbulent (boiling and burbling around). To
    confuse things, sometimes turbulent flow means lower drag, sometimes
    laminar flow does. Essentially, laminar flow is desirable at low
    speeds and turbulent flow is desirable at higher speeds (because
    it reduces boundary layer thickness).
    
    A third factor in drag is the effect of appendages. These are small
    contributors in large vessels, but major contribuors in small ones.
    The effect of a non-folding propeller is much greater than any
    variation in drag causes by different bottom finishes (although
    the effect of fouling may be greater). The effect of unfairness,
    square corners, and poorly tapered trailing edges would usually
    be included in this factor. Note, by the way, that squared-off trailing
    edges on rudders and keels (which you may find in some traditional
    designs) contribute a surprising amount of resistance due to the
    large vortices which they create.
    
    Up to about 1/2 hull speed, the major contributor to resistance
    in our boats is friction drag. Its importance diminishes thereafter,
    and may only be about 20-30% at hull speed. The quality of bottom
    finish is in fact more imporant for cruising boats than it is for
    racers because they have more surface area (or they should). It's
    just that there are so many other contributions to going slow that
    it often seems unimportant. These include high-drag appendages,
    hull forms which generate lots of wave-making resistance, and a
    more casual attitude towards fouling. I would go for the smoothest
    bottom finish I could stand working towards which offers good
    anti-fouling protection.
    
    Ross Faneuf (B.S. Naval Architecture MIT, many years ago)
    

    
    re .-1
    
    ok, making the hull smoother reduces frictional drag by reducing
    the thickness of the boundary layer, and this is increasingly
    important the lower the velocity through the water.
    
    but can you quantify this?  what is the effect (in knots) with a
    25' waterline in a 10 knot breeze, no prop in the water, with:
    
       a)  a crudely finished bottom, showing brushmarks in all direction,
           paint cracks here & there, and a gauge or two, vs
    
       b)  a glistening, hard undercoat worthy of America's Cup competition
    
    the question is largely rhetorical since I doubt anyone has hard
    data on this, but what's your best guess about the difference in
    speed, close-hauled, and the ability to point into the wind?
    
       - Jim
    

    I don't have any hard data; it may exist, but I haven't tried to
    find it. At a guess, the difference between a good, smooth bottom
    and gonzo supergloss racing is small - .1 or .2 knots. One or two
    gouges is probably unnoticeable. The difference between a hard bottom
    paint and a traditional soft one is probably some fraction of a
    knot, don't dare guess how much. A foul bottom (some small weed,
    a few small barnacles showing up) is probably .5-1 knot. A big,
    three-bladed non-feathering prop is probably nearly a knot
    
    It's probably worth spending some attention on bottom smoothness,
    fairness of appendages, and clean trailing edges on things. I wouldn't
    be suprised to see it give you .5 knots or even a little more in
    moderate breezes. These things probably mean the most whenever your
    rig isn't supplying enough power to overcome these deficits - like
    in the moderate breezes which are a steady diet in New England during
    the summer. I wouldn't be a fanatic unless you race. The same kind
    of attention to your sails and rig is probably equally productive,
    like acquiring a boom vang to reduce mainsail twist if you don't
    have one, or getting a tired sail recut to put the draft back where
    it belongs.
    
    Ross Faneuf
    

    As long as we're on the subject, does anyone know anything about
    the new super-slick paints being developed (according to PS) that
    work without toxins.  Supposedly, the little beasties can't get
    a grip on the slick surface.

    Two years ago I chrtered a boat in Yugoslavia and it had the hairiest
    bottom I've seen for many a year. The reduction is speed was
    *phenomenal*!! The boat was unable to keep up with the same type
    of boat which was clean when mine had full sails up and broad reaching
    and the other boat was on fully reefed jib and one slab in the main!!
    A smooth bottom for me any time.
    
    On non-toxic anti-foulings ; I remember a few years ago seeing for
    sale "ultrasonic antifoulings" consisting of transducers spaced
    at 6 foot intervals on the hull that made it very uncomfortable
    for beasties to want to cling to - or so the theory went. I haven't
    seen them for some time so maybe it never caught on, but then the
    main problem I've experienced is weed build-up, especially in the
    still waters of the marina, not beasties, only a few of the later
    ever having been discovered when hauling out.
    
    A good run out in a gale with a 30 minute pounding does wonders
    for shifting slime, even if you never get above 3 kts!!
    
    Brian

    Thanks, everyone.
    
    Somehow all this talk of boundary layers & turbulent vs laminar
    flows gave me more stamina this year, and I wound up making it
    smoother than I would have otherwise.
    
    Micron CSC currently costs 109 $/gallon at BLISS, but only 
    89 $/Gallon at Jamestown Distributors...  worth the trip if you're
    near Narragansett Bay.
    
    By the way, I used 60 grit paper on an orbital sander which had
    been relegated to the basement as "useless", and got much better
    results than I have in the past with not much more effort.
    
       - Jim
    

    Re: .6

    I would like to point out that the main effort when it comes to 
    achieving low frictional resistance should be in GETTING A SMOOTH
    SURFACE IN THE FIRST ONE OR TWO FEETS BEHIND THE BOW AND BEHIND
    THE LEADING EDGE OF THE KEEL.

    This is due to the fact that this is where You have laminal flow
    in the boundary layer, and the laminar flow is very sensitive
    when it comes to smoothness as it will not stay laminar if the
    surface it is flowing over is not smooth enough, perhaps 
    roughness of more than 1/10th of the boundary layer.

    The beauty of laminar flow is that it is not building in thickness 
    as fast as turbular flow, at normal sailboat speed.
    I.e. less energy, higher speed.


    /Hasse Wallin (M.S. Naval Architecture RIT, Stockholm, not so long ago)

    Hmmm...
    
    Ross, you mention that squared off trailing edges to rudders
    and keels ADDs drag.  I know a lot of racers -- me -- that deliberately
    square that surface -- about 3/16ths wide -- because it's
    supposed to reduce drag.  Any comment on this widely practiced
    trailing edge treatment.  
    
    As for "keeping it laminar as long as possible," 
    we strive to get everything forward of the keel, the keel itself,
    and the rudder sanded to a glass-like finish.  From the keel
    on aft, we are progressively less fussy -- thinking that
    turbulent flow is kicking in anyway.  Any comments or suggestions?
    What do you think about squaring off the trailing edges of control
    surfaces?

    The stuff I have heard and read indicated squared of trailing
    edges are significant in reducing turbulence or something.
    
    I remember from a SAIL magazine a couple seasons back that
    even the sharp corner from the hull to transom was important
    to speed, and the better boats had the sharper corner.
    
    Walt

    There may well be dome beneficial effect from a small squared edge;
    the energy lost to tip and trailing edge vortices is pretty
    significant, and depends on lots of tricky little details. In fact,
    only testing of your particular hull/foil form will tell you for
    sure. The squared-off edges I had in mind are those you encounter
    in some tradtional boats (1=2"), or keel trailing edges which end
    in large radius. For cruisers, fussing over sharp vs. 3/16" squared
    edges will probably be lost in the noise. There's also an issue
    of how hard it is to form and prevent damage to a very fine edge;
    most of what you see out there will be a compromise based at least
    as much on manufacturing convenience as anything else.
    
    Sharp transitions at the end of the boat may offer some benefit
    by creating completely detached flow at a well defined place, instead
    of a large area with partially detached flow and possibly large
    amounts of variable drag. This can reduce the volume in which vortices
    and turbulence are generated, thus reducing the energy lost at the
    end of the vessel. I don't know the numbers. Note that the effect
    of rating rules is at least as important in the sharp tailed form
    of boats as any other factor. This is an area in which cruisers
    are most likely to differ radically from racers, as structural
    convenience, needs for stowage space, and most importantly the amount
    of buoyancy available to react to large following seas are more
    crucial to cruisers than low ratings and the ultimate in reduced
    drag.
    
    Ross Faneuf
    

    I bought MICRON CSC at Salks Hardware in Warwick for $89/gallon
    also.   A little closer for some people.
    
    Rick
    

    Just finished the spring wet sanding ritual.  How smooth
    was smooth enough?  Well, after 8 people wet sanded with 220 for 6
    hours, we discovered that some tiny pits just wouldn't
    sand out.  Still a mystery as to where the pits came from.
    All I can say is that due to blistering, the hull was epoxy coated 
    and sanded smooth three seasons ago.  The pits appeared over time
    -- reverse blistering?  At any rate, we stripped the forward third of 
    the hull back down to the epoxy, and then hand sanded it fair.  We
    did not penetrate through the epoxy.  Three coats of paint and 
    4-people-sanding-with-220-for-5-hours later, we had a passable
    finish.  Being a fanatic, however, and feeling like we hadn't 
    truely done justice to the effort of stripping the the paint 
    in the first place, I worked an additional 6 hours to remove 
    every trace of orange peel from the forward sections.
    I then went over the leading 8 feet -- everything ahead of the keel,
    speedos, and depth transducer -- as well as the keel and rudder with 400.
    We're talking a mirror finish -- especially the forward sections.
            
    Was it worthwhile?  Who knows.  But if the Monhegan proves to be another
    early morning drifter, we may have a secret weapon!
    
    ;)

    I think you inhaled too much Micron in the sanding!  Not even a
    smooth bottom can make the Monhegan a rational race.  Last year's
    was finally the one so bad we swear to never do it again.  Two years
    ago we had an amorous whale follow us all night.  The speculation
    was that our sonic speedo was driving this poor beast wild.
    
    Do me a favor. If you see a boat named Fat Tuesday doing that race
    this year, shoot me with a flare gun.  I'll deserve it.
    
    The charity race for MS (or some such disease) the following weekend
    is a good time, however.
    
    Dave
    
    Sorry about getting off the subject.

    Oh yeah, "Fat Tuesday," I think you passed us last year.
    We were experimenting with a forward rudder configuation
    at the time.  ;)  

    RE .18 & .19
    
    Well, both you guys passed us plenty of times last season.  
    
    Somehow I doubt that the worlds smoothest bottom can make up for
    just one blown tack or sloppy spinnaker set.  Thanx for the tips
    though.  It gave us the incentive to put in a lot of extra work
    on the bottom this year.  Add that to re-cut sails and another year's
    experience for the crew and perhaps we'll be doing some passing
    of our own this season.  See y'all on the starting line ...
    
    ... Bob
    
    P.S. - Anybody else doing the JFK next week-end ??
    

    R. .20, you're absolutely right.  Sloppy crew work can very quickly
    destroy any advantage you build by having a smooth bottom.  That's
    why we are not doing the JFK regatta next weekend.  We are so late
    this season (stinky weather) and are having mandatory practice
    sessions.  We'll be  doing the Mass bay races starting the weekend
    after Mem. Day as well as Edgartown race week and Monhegan (no,
    we can't really be again, can we?).  Staying pretty local this year.
    
    Just brought Fat Tuesday down to M'head from Gloucester yesterday
    and it felt great to be on the water again!
    
    Dave
    

    Staying away from JFK -- we're rusty too.  We also have some problems
    with shaft allignment, so the iron main is useless.  Makes
    delivery a bit of a pain.  As for smooth bottoms, a prolonged
    stretch of ghosting will make a well-prepped bottom pay off
    handsomely.  Try going .2 of a knot faster than your competition
    for an hour or two.  It may be only one race all season in which
    you get a real pay off, but sometimes that one race could make
    the difference in your overall standings.  There's also the 
    psychological advantage of knowing your boat is slick.  On the other 
    hand, you have one less excuse when you loose.  ;)
    
    Think it would be worthwhile to set up a current racing events
    note -- sort of war stories and what's going on this season?  Is
    there such a note already?
    
    Dean ("Bodacious")

    Uh, Dean ...
    
    What do you mean by "ghosting"?  Isn't going .2 of a knot faster
    than your competition what yacht racing's all about?
    
    Perhaps you could elaborate.  And then again perhaps not.  We are
    in your fleet after all.   And even though you've had an easy time 
    dusting us off the last couple of years I hope to see that change
    (at least some of the time) this season.
    
    I can see we have a different attitude about racing than you guys
    though.  We're rusty, but figure we'll sharpen up quicker doing
    an early season regatta than just going out practicing.  And we
    have the mid-week races to sharpen up against some less serious
    competition in.  And it's a long ride to Boston.  We figure on doing
    a few corkscrews in the ocean practicing spinnaker sets and take-downs
    on the way to Marina Bay.  That and a coupla hundred tacks ought
    to work some of the rust out.
    
    Good luck getting that shaft aligned.  See ya on the course June 5(?)
    
    ... Bob (from WAGS)
    

    Yeah, I guess you could say that about racing.  But I was referring to 
    going .3 of a knot while everyone else is doing .1
    or dead in the water -- the type of conditions when it
    takes incredible stealth just to get the boat moving at all, and
    then someone uses the head and the wash spins the boat around,
    or you start making cracks about jet propulsion.  But enough of
    this scatalogical banter.  The point is, a really slick 
    "bottom" (oops) pays off in the zephyrs.  
    
    Of course, there's always the CRAP-shoot factor to contend with -- you 
    know, when you've "ghosted" ahead and the wind fills in from BEHIND.  
    
    ;)