Yachting Monthly Senior -
options for rig re-design.
When I had sailed "Mikros" before we owned the Riptide "Thalia",
I had noticed a tendency to have to fight the weather helm on the tiller
when sailing close-hauled or reaching. Having looked at other designs (and
having obtained a degree in applied mathematics in the meantime!) I drew a
bit of a diagram of the forces involved. I determined I needed a bowsprit or
rather I needed to get some of the leeward forces further forward and a
bowsprit seemed the usual way of doing this.
One experienced helmsman I spoke with suggested that the
problem may be caused by the Senior having a flat plat rudder as opposed to
a more aerodynamic one. The flat plate ‘stalls’ in the water flow, when it
is at no more than a few degrees to the fore and aft flow. This makes it
necessary for the helmsman to have to use brute strength to place the plate
in the way of the flow to achieve the ‘straightening’ force. If the rudder
plate could be shaped like the wing of an aircraft but symmetrical more
rudder angle could be achieved before stalling and the rudder itself would
produce the force to leeward in order to keep the craft straight. This is
all good theory but I need my rudder to be able to swing up when in shallow
water or when drying. I wasn’t quite sure how I was going to achieve both. I
opted for the bowsprit but will keep the idea of an aerodynamic rudder plate
for later.
Another problem I had always noticed with regard to her
rig was the frightening sight of the mast flexing very badly about the
halfway point especially when gybing. The mast is of hollow wooden
construction and when my father built the boat, he made the mast in two
pieces. He, being an engineer, joined the two parts with a three inch
diameter 3 t.p.i. brass thread which in turn was attached to the wooden mast
parts by means of mast diameter brass ferules.
The latter over the years had slackened and regular
injections of epoxy had failed to stiffen things up.
I therefore had two problems to solve: 1) the weather
helm and 2) the mast flexure.
I
have drawn the existing (as original design) ¾ rig. Effectively things were
firmly fixed at the base of the mast and ¾ of the way up. Whilst the top of
the mast didn’t really need further staying, the centre did. I guessed that
I might need to do the one that wasn’t needed in order to achieve the one
that was.
I then referred to various books including the old eoa’s
"We built a Senior" on which front cover "Mikros" appears (c.1987 at
Lydney, Gloucestershire). I drew inspiration from Martin Lewis who for many
years sailed his "Pau Amma" with various rigs. His notes and drawings
included an idea of ‘diamond stays’.
Certainly the diamond stays would hold the centre of the
mast from lateral movement but it all seemed a bit over the top. So I
carried on with a design around a simple spreader rig. One of my local
chandlers who has mega-experience of Devon Yawl sailing suggested a
commercially available spreader from ‘SuperSpars’ but that a) sounded
expensive and b) the idea of an aluminium spreader on a wooden mast seemed a
little incongruous. I therefore came up with my own design as on the next
drawing.
The new rig would need (a) backstay(s). The Senior’s boom
almost overhangs the transom and whilst it could be shortened a tad, a
backstay from the masthead to the top of the transom would still foul the
boom and the battened out leech of the main sail. My father said, "Oh, you
need a bumpkin." I think he rather liked the sound of the word. I briefly
looked at the idea and it was feasible but complications of an already
crowded aft deck and the need for a split bobstay preventing the outboard
motor from being tilted up, etc. etc. meant that I opted to try a running
backstay for the time being. Again the idea of a bumpkin will be reviewed
later as it would reduce the number of tasks to be completed when going
about.
Other ideas I came up with are on the next three diagrams
Mikros" was re-launched at the start of the summer
without any of the above ideas being put into practice. Firstly, I then
decided that the spreaders were not needed. They, literally, got no further
than the drawing board. The main reason for this was that I had been very
successful in stiffening up the mast joint using epoxy. After drying out the
spars completely, I drilled several holes the centre brass ferules. I tapped
the holes and fitted grease nipples. I could then inject epoxy resin with a
colloidal filler under sufficient pressure from a grease gun to get it to go
absolutely everywhere it was needed (and plenty of places it wasn’t). What a
mess? But the result was so good that I do not need spreaders to cut down
the whipping for the time being.
Having solved one of the problems, I progressed the
bowsprit idea by speaking with Tony Showell (Senior "Shellduck") who has
forgotten more than I will ever know about Seniors. He went through with me
his design process for his bowsprit and told me that the length was
determined by how far he could reach from the foredeck! I then put pen to
paper and came up with the design on page 9. Basically it is a 60 x 60 mm
piece of douglas fir which is tapered and rounded to 40mm diameter at the
forward end. I made two sets of blocks out of teak to bolt to the deck using
oak pads below for strength. I had no idea of the forces involved and so I
erred on the side of over-engineering rather than the reverse. The mounts
are shown here.
Bolts pass through the blocks horizontally, sandwiching
the bowsprit. At the after end of the ‘sprit I rounded it as shown in the
side elevation above. By removing the bolt on the forward mounting and the
bobstay, you can then raise the bowsprit right up and secure it to the inner
forestay in the event of a berthing master wanting to charge more for the
64cm. extra length overall. The projection of 640mm was determined by
drawing on the original plans a line parallel to the original forestay and
measuring off accordingly. I found that Tony Showell’s criterion was also
met but only just.
The position and size of the existing stem head fittings
on "Mikros", which also has a mast lowering tackle incorporated, meant that
in order to get the forward end of the ‘sprit on the extended centre line, I
had to mount the whole thing at a slight angle across the fore deck.
For the forward end of the ‘sprit, my father made me a cranze-iron. (I
know that’s the right word but I’m not sure of the spelling.) It consisted
of a brass ferule with a piece of substantial brass strip hard soldered to
the end with one lug aimed at the mast head and another aimed at the bobstay
fitting on the waterline. The latter was already on the boat as a means of
attaching the trailer winch. The general idea can be seen in the picture
below .
.
The clew fitting for the
genoa was temporarily attached by a lashing. The cranze-iron was epoxyied to
the ‘sprit but actually a ‘push-fit’ would have been sufficient as the
rigging holds it in place.
Measuring the bobstay was simple enough but the new forestay was another
problem altogether. There was so much stretch in most of the materials I
tried and those that didn’t stretch sagged into a catenary. At a car boot
sale I spotted an old-ish Fibron measuring tape that cost the sum of 50p.
That did the job ideally. The bobstay, forestay and one running backstay
were made up by my local chandler from the drawings below.
Drawings of rigging to be made up.
I had only one running backstay made up because I thought
that with a snap shackle, I could swap sides with it as I went about but
experience later suggested otherwise. The other reason for only having one
at that stage was cost!
I had decided quite early on that I wouldn’t actually
employ any new shrouds from the masthead. Any forces down the forestay or
even that component off to leeward at the masthead were going to be
sufficiently counteracted by the windward running backstay. This proved to
be the case in practice and I was actually able to bend the masthead to
windward which wasn’t really necessary but it proved the point. See the
photo below.
At the masthead itself I made attachments for the fore
and back stays from a sheet of stainless formed into an upside down ‘U’ and
bolted through the existing two pulleys for the main halyard. It sat like a
6 inch long hat fore and aft on top of the existing derrick. The ‘hat’ was
longer than the derrick and with bolts through either end the stays were
attached via their thimbled/swaged eyes.
Fitting the whole assembly went without hitch except that
balancing the tensions of the new standing rigging with the old was a bit
time consuming. I nearly fell overboard when I first attached the genoa’s
piston hanks to the bowsprit’s forestay; such was the reach needed. After
that first time, if it wasn’t done alongside, I used the dinghy at the bow
to bend on the sail. That was less of a risk!
The first test was carried out in light breezes. I used
my existing genoa up the new forestay and a storm jib up the inner stay. The
sheets for the genoa weren’t quite long enough and I kept losing them as I
went about. Suffice to say that up to a F4 the weather helm was all but
cured and lee helm had not replaced it. Life got interesting down wind as
she appeared to yaw about quite alarmingly but I’m not sure that it was not
a lack of concentration on my part that wasn’t helping. The main difficulty
was the number of sheets to handle without proper cleats at that time. I
also found that a second running backstay was going to be needed so that
when I went about all I needed to do was to slacken the
about-to-become-leeward one off and sweat up the windward one.
I found no problems with not having masthead shrouds. In
fact I had to watch not to over tighten the backstays as you could see the
mast above the hounds bending to windward! Before fitting the bowsprit I had
already determined that spreaders had not been needed and that the firm
fixing of the ferules with epoxy had cured the tendency for the mast to whip
about when under rapidly changing forces such as when gybing.
One side benefit was that the bowsprit provided something
to which to lash the anchor when under way. In past years I had kept the
anchor and chain in a box in the cabin. When I need to anchor I would
struggle this box up to the fore deck. The box would stay on the fore deck
when I was at anchor as the unused chain was kept in it. Having been ‘big
boat sailing’ in the meantime, I changed things around and the anchor is now
kept on the fore deck. The tripping eye takes a lashing, which goes around
the bowsprit and keeps it tidily secure.
All in all it was a very well worthwhile project. The
basic lines of a Senior gunwhale lends itself to having a bowsprit and she
really ‘looks the part’ as well as sailing with a better feel.
Now when someone who doesn’t know a Senior asks how long
she is I can say "19 feet from rudder to cranze-iron".
Geoffrey Hyde Fynn.
YMS 779 "Mikros"
Senior Advisor, see Advisors Page.
March 2003, updated Nov 2004
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