Conference unifix::sailing

    I dont know how accurately the cutter will float on her lines or
    what the effects of loading stores, gear, water, etc. might have,
    but here is my experience so far:
    
    My first boat was a true light displacement flyer.  The water line
    was WAY off at the stern and some off at the bow from the factory.
    By the time I added additional batteries, lockers, tanks and filled
    them, the line was even further off.  
    
    I ended up raising the boot top 6" at the stern and 3" at the bow
    over 3 seasons. Fortunately, I had chosen a black bottom/black boot
    top with no contrasting color between. Thus I was able to keep raising
    the masking tape each year on both the boot top and bottom paint.
    To allow for loading of stores, water and fuel I had about 3" of
    bottom paint above sea level when "light" and about 1" when loaded up 
    (for a week, not for crossing oceans).
    
    
    The boat we have now (an S&S design) came from the factory perfect.
    She is also a light displacement (D/L about 180) boat and has about 
    3" of bottom showing forward and 2" aft when "light".
    With all the gear, food, fuel, water and ice aboard for a 2-week
    get away, she sits right at the top of the bottom paint.   She has
    a molded-in, 1" wide, mark all round which identifies both top of
    bottom paint and bottom of boot top. This mark is white (hull color)
    and serve to accent the boot top indigo blue vs. the bright blue
    bottom. There are also molded reference marks (metal + ) at the
    bow and stern, 6" above the molded mark, which allows recreating
    the waterline, should the 1" mark be ground off.
    
    I saw an article in Sail or Cruising World some time back which
    described using a visable light laser, on a tripod, to find a straight
    line from bow to stern.  I think a pencil or felt tip was used to
    mark the path of the laser. Once marked and painted, it should be
    easy to remask when repainting, unless you take it all off.
    
    In general, I think boats should allow for more waterline range forward
    because the lower bouyancy forward is affected more by added weight
    than aft.  I would say that you would want to set the water line
    an inch or so above "fully loaded" weight - if you can figure that
    out.
    
    Walt

    As a one-time naval architect who fell into computing early-on,
    I have had a little fun during construction of this boat. I have
    computed the displacement from data lifted from the lofting, which
    is probably a bit more accurate than the results of using a planimeter
    on the 3/4"=1' design drawings. I have done my own weights and ballast
    calculations based on standard commercial practice, which requires
    computing all weights on board - e.g. if you are planning to carry
    3 anchors, figure them all in at their most likely locations. And
    figure 50% of all consumables (water, fuel, food etc), plus reasonable
    live crew weights. The latter may be no small item; on my boat with
    its 160 gallon water capacity, live weights are over 1000#, and
    amount to nearly 6% of the total displacement.
    
    The result is that the boat will certainly float at least 2" lower
    than the designer computed if it is to retain its ballast ration.
    He claimed a 45% ballast ratio on about 16,000# displacement. On
    his original lines, I computed about 15,300# displacement from my
    lofting data. To maintain that displacement with my computed weights,
    (which were about a ton over his), I would have had to drop the
    ballast ratio to about 30-some %. Instead, I sank the boat 2", upped
    the displacement to 17,200#, and ended up with a ballast ration
    of 42%.
    
    The lesson in all this is NOT that my designer was a klutz. I spent
    a LOT of time doing this - even with the assistance of a Macintosh.
    The point is that he didn't have a computer, and in order to complete
    the design at a reasonable cost, probably did a lot of estimating
    rather than exact computation. Contemporary designers SHOULD be
    able to do better; for instance, a superb design package which runs
    on the Mac is available for about $2500; I don't know how many
    effectively use such aids.
    
    For production boats, the commonest technique is to use the actual,
    floating waterline of the first boat built to mark the rest. Designers
    and builder who are willing to mold the waterline mark into hull
    #1 are VERY gutsy.
    
    As an indication of what accuracy means, the following might
    illustrate. A 36' boat like mine has a sinkage of about 1000# per
    inch at her designed waterline - an additional 1000# will sink the
    boat an inch. I haven't computed the moment to trim one inch, but
    at a guess it's about 1500-1700 ft lb. When my wife and I go aboard
    a boat for a cruise, with all our gear and 2 weeks worth of food,
    the boat probably sinks between 1 and 2 inches. If we all go forward
    to heave on a fouled anchor, our weight + hauling may pull the bow
    down 3-4 inches. This sort of sets the background for dealing with
    waterlines. I suspect that if I were fussy, I might habitually trim
    the boat to look good on her mooring :-).
    
    Maybe the prudent course is NOT to permanently mark the waterline,
    and keep shifting that tape. But meanwhile, any marking notions??
    
    raf
    

    The reference marks on my boat at the bow and stern, might make
    a good system for you.  You could place each, lets say 6" above
    the design waterline.  From there on you could use them both to
    recreate the waterline from scratch (if necessary) and as reference
    points when changing (lets say raising the line at the stern 2",
    which would leave the mark 4" above at stern and 6" above at the
    bow).   The visable laser-felt tip idea strikes me as a good way
    to gwt a straight waterline.
    
    By the way, I dont know how to describe the reference marks above
    except as some sort of metalic disk with a + in the center. It is
    about the size of a #8 screw head, and added to the hull at layup.
    The boat is an '83 Tartan 33. There are lots of Tartans around, stop
    by one at a yard sometime and take a look at this thing. I suppose
    there are other boats that use similar systems (one just has to
    know what to look for).
    
    Walt

    Sounds remarkably like a phillips drive screw or the equivalent.
    Strikes me as real easy to simply sink a few nails or screws at
    an appropriate line, and mark the heads with a punch if needed.
    Sounds neat and easy. Thanks.
    
    Ross Faneuf
    

Ross,

Thoughts on placement and marking:

I agree that the waterline should be higher forward than aft, and each 
end should also be above the aft-of-midship height.  Most designers agree
that with some sheer at deckline, an inch or two of swoop at the waterline 
goes a long way to adding pizazz to a yacht's appearance.  Just offhand,
I'd guess the aft end might be 3/4"-1" above the low point (which should
actually be somewhat aft of amidship) and the forward end 1-1/2"-2" above
the low point.  Exact proportions depend on the amount of sheer, hull
shape near the waterline, flare, etc.  Probably the best means of
determining the waterline sheer is trial-and-error with a large-scale
drawing (1:6 perhaps). 

The boottop should also follow the sheer, swooping proportionately higher 
fwd and aft more than the waterline by a smidgeon.  It also should 
be wider forward and aft than in the middle, all for the same 
proportioning reasons.  For a boat of your size and type, I'd have the
boottop adjacent to the bottom paint -- I think it looks a lot better. 

Does Skene's have a discussion of this?  It's the sort of thing Francis 
Kinney loves to fuss about endlessly in search of perfection.  (He 
designed Pipedream, a 36' sloop.)

Having owned a boat with a white boottop moored in Gloucester's outer 
harbor, I would absolutely raise the lowest part of the waterline (top of
the bottom paint is what I mean) at least 1-1/2" above the at-rest-
unoccupied-but-partially loaded state.  Various cultures of scum 
seem inevitably attracted to the sides of a hull, and on a quiet sunny day
can chemically metamorphize into an unremovable substance epoxy chemists
would do well to study. 

Lastly, marking a waterline.  In practice, rarely will you ever remove 
*all* the paint to where you can't tell a line at all.  But JIC eng'g
(just in case) demands a back-up.  Presuming the dynel covering and epoxy
are essentially clear, or at least highly translucent, why not paint a
contrasting line -- the entire white boottop would be perfect -- on your
dark hull over the cold-molded sheathing, but underneath the dynel &
epoxy?  I doubt you'll ever sand it off accidentally.  For preservation 
and appearance, paint the true waterline and boottop over the dynel, 
knowing you've always got a complete permanent record of the original
position underneath if needed.

John.