The Eventider's News
Issue Three, Autumn /Winter 2004
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 swop 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