HERE WE HAVE Sure Mike II, ideally
calculated to take the largest stock
outboard motor, the Mercury Mark
55. This boat is 21 feet long with an
8-foot beam. She probably comes
closer to the size of small cruiser desired by most men than any other
boat of this type we have run in the
Boatbuilding Annuals.
She is carefully sized, having been
swimming around on my sketch pad
for a couple of years. As to her running qualities, little more can be
asked from a boat this size.
I've approached the problem of
construction from all angles and have
decided on a seam-batten job, with
planking specified in the usual manner. If it is desired, the topside strakes
may be cut from 3/8-inch 5-ply Super
Harbord marine grade plywood. I
should plank her bottom in regular
seam-batten fashion, using mahogany
or white cedar planking of the thickness specified.
I decided on this type of construction on the basis of (1) my own experience handling large plywood panels in a home shop, and (2) after
much talk with men who have tried
to plank a hull this size in "one
hunk." The condensed gist of all
thought runs like this:
The average man isn't equipped to
loft a generated surface hull this size.
He hasn't the tools or know-how to
get a fair job. A hull of smaller pieces
—that is, straked planking—will build
easier in this size boat for the average
amateur. It will take longer, but the
result will be stronger, fairer and
somewhat heavier. This latter feature
is an advantage in water that dances
a bit.
Of course, any boatbuilder who is
mechanic enough can build this boat,
planking her of plywood throughout.
It is well here to mention to the novice that when a large panel of plywood, such as a topside, is both swept
and twisted, the cross sections that
result are not straight-lined sections.
They have curve, arc, belly to them.
Hence the framing of an accurate
frame for a boat this size becomes a
job for & skilled loftsman.
The straight-framed job or a boat
with a majority of straight frames,
can be easily planked seam-batten
style in strakes. Be warned that no
design with a preponderance of
straight frames can be planked with
plywood. What you'll get is a series
of pillows between frames.
Sure Mike II can be inboard powered. The Gray Model 620 would
make an ideal installation. The Universal 60 hp Unimite would be another good choice of engine. A Chris
Craft B, 60 hp, 133 cubic-inch motor
would also turn in an extremely good
performance. Red Wing also has a
60 hp 133 cubic-inch model that has
well-engineered features.
The insert elevation section shows
enough of the inboard motor version
to enable you to install the job. The skeg and rudder on the lines drawing
give you your dimensions for this option. The Gray 620 will want a 12-inch
diameter by 10-inch pitch three-blade
wheel. The 133 cubic-inch engines,
commonly built around the Hercules
block, will swing an 11-inch diameter
by 9-inch pitch three-blade wheel.
The Universal Unimite will want a
13-inch diameter by 8-inch pitch
three-blade wheel. Differences in
torque characteristics and piston displacement are the reasons.
Speeds of around 20-22 miles an
hour can be reached if your boat is
in dry condition with a good uncluttered bottom. Under the same conditions about the same speed can be
had with the Mercury Mark 55—perhaps a shade better as the weight/hp
ratio favors this big kicker.
Though Sure Mike II is 21 feet
overall, the added length is but a bit
more than previous designs published
in the Boatbuilding Annual. She is
just three feet longer than Simplex,
published in the 1954 Annual, and but
four feet longer than Sun Dance,
which appeared in our 1953 Annual.
Both these latter boats were out
boarders, and had sufficient accommodation to allow them to be classified as "cruisers" under the modern
definition of the term. The slight
added length and beam of Sure Mike
II, however, makes her much larger
than the boats her forerunners' were.
This is because lengths vary per the
square; bulk varies per the cube.
Hence, Sure Mike II, while no leviathan, is very much more of a ship
than the outboard cruisers of the
finger-bowl-washroom and candle-
for-stove variety.
Weight and length do much the
same thing for a boat that weight and
wheel base do for a car. Where comfort and adequacy are musts there is
no substitute for either.
I believe that by extending your
purse and muscle a little to get this
boat instead of something less roomy,
you'll cure at the start the usual disease that hits home builders—"biggeritis."
Old-timers in the boating game can
tell you that you will become infected
with "biggeritis" during the first
month you're afloat in your first boat.
She'll loom like a circus tent as you
first begin to plank her, this first boat
of yours, and she'll shrink to a pumpkin seed as you begin to use her.
Why this is true is beyond me—I've
been a midwife to boating appetites
for only 40 years and have never
learned the cause. I only know that
it is true.
But I doubt that in settling on Sure
Mike II you'll suffer much from this
malady.
The information published here is
sufficient to enable anybody to build
her. Her lines must be laid down
full-sized on a smooth floor. And
an ideal floor can be made from three
panels of 1/4 inch by 4 foot by 8 foot
common grade plywood.
Old-timers at the boatbuilding
trade do not need to be told that this
full-sized lay-down and fairing up is
a must. Some beginning boatbuilders,
however, think a boat should be built
like a piece of machinery or a chair,
from a multitude of small drawings of
detailed parts. A boat cannot be built
this way. She must be watertight, so
you lay her down to get the hull
shape, the keel shape and the shape
of the knees and their bevels; also at
the same time fairing up obvious errors in scaling the original small (3/4
inch to the foot) drawings.
This gives you the shape of the hull
to the outside of the skin. This outside
shape is the important thing.
All pieces inside the vessel are then
fitted to the frames and bulkheads,
using dimensions from centerline out
as given for the accommodation plan,
and heights from the waterline for inboard fixture and joinery heights. All
boats are built this way if a fair and
easy building job is to be had.
The frames are to be diminished by
the thickness of the planking, and are
to have extensions which will meet
your building floor.
These are erected upside down over
the centerline and station line grid
marked out on your building floor.
The frames in this condition must
be created plumb, and horned square
with good bracing.
I should treat the transom cheeks
as a frame in itself, making due allowance for the fact that the projected
view on the body plan of the lines is
not the true shape of the frame: it
must be "expanded." That means to
take your half breadths for this frame
along the rake of the transom face.
This means that the transom cheeks
form a separate frame, raked. The 3/4-inch 7-ply transom can then be
scribed for shape, sawn and fastened
in place, using a good grade of casein
or semiwaterproof gunk.
The transom on Sure Mike II is
especially framed to take the largest
of outboard motors. A 16-1/2-inch
transom height will work for a Mercury Mark 55; it would be well to
procure your motor beforehand, or
measure the one you will use. It is so
easy to dope out the transom opening
and framing you want as you are at
this stage, rather than doing it the
hard way (by "unmanufacturing")
later.
Let me insert a word here about
the transom hood Idea. It seems to be
wanted by many. It does dampen
noise, but that is all. All enclosures
around outboards I have ever had
anything to do with always failed to
keep the motor running cool, despite
water circulation, and the motor always ran rich because there was no
way to get stale smoke away from the
carburetor. Cover the topside and the
forward face, but don't try to fully
enclose the motor—it is against all
principles of air circulation. Air, to a
degree, always follows a broad transom. And don't, for heaven's sake, put
the motor on a bracket outboard.
She'll load up in a following sea, also
the strain on the transom is no good.
When the frames are up, plan out
the spiling of the planking, and run
in the battens, seeing that they land
well in the gains through the frames,
and at stem and transom cheek. Battens are best streamed in after the
frames are erected, cutting the gains
at that time. Fairer planking lines always result.
When the battens are installed. I'd
commence planking the topside. Start
at the chine, work toward the sheer.
Three strakes of plywood are called
for in this topside planking. The 3/8
inch thickness will be quite light, not
too expensive. The 1/2-inch 5-ply stuff will be best, but it costs more than the 3/8 inch. I'd choose 1/2 inch if Sure Mike were my boat.
The drawings show the fastening
size and frequency for this portion.
Next apply the garboard plank, and
work out toward the chine. Use strong
1/2-inch planking here, so that when
sanded you'll finish 1/2 inch. This is
none too thick in a boat this size. The
thickness has proved serviceable) but
you can't go ramming logs with it.
Plain, good boatbuilding wood is
chosen for the bottom, because it will
swell, get tight, and can be easily repaired. It has been my experience that
3/8-inch plywood has been about the
top limit of thickness amateurs can
bend without a full crew, much experience and a goodly number of expensive clamps. This thickness is not
enough for the bottom of a boat this
size. Hence the solid planking.
Soon your hull will have taken
shape and you are ready to sand and
paint her. A good rugged disc sander
in the hands of a skilled man who
won't make gouges is the best tool;
a reciprocating sander which takes
longer and wears out more sandpaper
is the treatment for the outboard face
of the skin. Several coats of grain-filling priming paint, like Firzite, will
be needed, and the priming coat of
paint is then installed.
The cabin coaming, the deck line
and the framing of the cockpit sole
are just plain straightforward carpentry and there is no need to burn
up paper or midnight oil on that
subject here.
Work from the waterline for your
vertical heights. Work from the centerline out for your berth faces.
Individual desires always creep into
one's execution of the interior of any
cruising boat. The sky is the limit as
far as trickiness is concerned, but
don't forget that this boat, like all
other careful designs, is designed to a
weight. Performance is a matter of
horsepower per pound, and behavior
is a matter of loading the shape to
the correct angle of attack. If you
change weights, try to put in a cast iron stove, install the old family refrigerator and build a dog house for
Rover, she then becomes your design
and headache—not mine.
One 25 hp Johnson or Evinrude
would give a good 14-15 miles in this
boat. Two 15 hp motors would provide
a safety factor) furnish 30 hp for about
16 mph.
Do not eliminate the skeg shown if
you build her for an outboard. This
item is there for a purpose: to make
the boat sweet in a following sea and
to take the yaw out of her when you
have to check down to meet wild
weather. Skegless outboards work on picnic days only.
