More readers' letters from the May 2006 issue
Calling Seagull/Sewmew owners
Five years ago YM printed a letter from me asking owners of Ian Proctor designed Seagull and Seamew sloops to get in touch. There were around 400 built but I only had a limited response and have a list of 30 owners. Now, with the aid of a fellow Seagull owner, Graham Tottle, we have set up a web site ‘www.seagullmew.org’ and with Graham’s assistance I am renewing my efforts to find out how many of these grand little yachts are still in existence.
I would be grateful if you would publish this letter asking any reader who is the owner of one of these yachts, or knows someone who is, to contact me.
Edwin Dewhirst (email: email@example.com)
Diesel electric propulsion
Always look out for two things when being sold something, either by a salesman, or politician. One is the word ‘compelling’. The other is the inaccurate assumption.
Nigel Calder (January issue) gives five benefits of diesel electric propulsion. They are all valid, but not in my opinion ‘compelling’. He might also have added a sixth, which is that the electric motor could be contained in a submersible steerable and retractable pod, which would increase manoeuvrability and reduce drag when sailing.
However, given a normal installation a larger slower more efficient propeller could equally well be fitted to a diesel installation. The only requirement is to increase the reduction ratio of the gearbox. The reason this is not usually done is that larger shafts and props cost more, there is generally insufficient room beneath the hull to give the required clearance, and the drag would be significantly increased when sailing.
The inaccurate assumption is the weight he gives to the inefficiency of an underloaded diesel engine. A diesel only requires a tiny amount of fuel to turn itself. The rest is injected to turn the load at a rate of about I gph for every 20BHP actually used. There will only be a marginal increase in efficiency if you take all the power available at any speed rather than half, because you will then need to inject twice as much fuel.
The final arbiter would be to run a series of tests and note the fuel consumption of two identical boats, one fitted with conventional, and one diesel electric. Maths is there to save expensive mistakes. I will happily bow to more specific, and accurate test results but as an approximation my generalised guesses would be as follows. Larger prop gain 5%, fully loaded diesel gain 2%. Conversion to Electricity lose 10%, reconversion to mechanical lose 10%, wiring and control losses 3%. Net loss in efficiency of diesel electric propulsion at normal cruising speeds = 14%. Something to carefully consider with the predicted loss of red diesel.
Graham Lascelles (by email).
Lost the plot?
I have a certain amount of sympathy for Mr Spiers (YM Letters) distrust of relying on electronic chart plotting, but it does have its advantages. You can see your position on the chart instantly, no errors creeping in by misreading or misplotting a position on a paper chart. I am sure the Yeoman plotter is excellent but my understanding is that you have to set reference points? is there a potential there for error?
His comment about not trusting himself to keep a simultaneous plot running on a paper chart is very fair. Usually I do, but on a flat calm day motoring across the Irish Sea for 60 miles it can get forgotten. However, the plotter is at the steering position and gets looked at every few minutes even when on autopilot, so failure would be noticed quite quickly. My get out of trouble card is my Navtex receiver, which prints on a paper roll. It is connected to a GPS receiver and every hour ( it could be set to half an hour ) it prints the time, position, course and speed over the ground.
The worst case scenario is having to plot a position 59 minutes ago and work up an EP. This is only going to happen in the case of total power failure or a shutdown of the GPS system and I am back to navigating by the same methods I started with 30 years ago. If it is not a power failure I still have the radar, a much overlooked navigation tool. I can foresee a time when most people rely totally on chart plotters. Is there a market for a paper recorder hooked up to them doing just what my Navtex does?
Windward Sailing: The Third Way
Tom Cunliffe’s article ‘Head to Head’ in the March Issue compares conventional foresail handling with self-tacking using a jib track I would like to draw attention to a ‘Third Way’ which provides self-tacking, and more, without all the disadvantages mentioned in the article.
By rigging the jib like a windsurfer sail it can be kept at the correct curve on all points of sailing and, if port and starboard sheets are retained, can be sheeted from the windward side with the leeward sheet slack but set up ready to become the windward sheet on the next tack. Once set up, no more sheet handling until the wind frees. When it does, ease the sheet and you are on a reach, still with a properly tensioned jib. Bear away and, bingo, you are broad reaching goose-winged (the jib gybe is trivial, – no problem). Always a well-setting jib. No foredeck work.
If you’re interested in this novel headsail, then read on?
In the March 2006 Issue of Yachting Monthly can be found an excellent article by Tom Cunliffe comparing a conventional genoa rig with a traveller self-tacking jib rig during some Force 5 sailing in two similar yachts. Amongst the conclusions drawn were criticisms of the set of the jib, particularly on a reach, the inability to heave to and of the downwind disadvantages as well as some detailed points ab out runs of sheet, winches and blocks
I would like to draw your attention to a “third way” of sailing which suffers none of these drawbacks.
Our Kelt 8.50, now 20 years old, is a very beamy swing keel cruiser which sails well if kept upright. Our self-tacking system makes use of a lightweight wishbone jib boom. Because of the light weight the thrust line of the boom has to correspond to the sheeting line of a conventional jib, that is it must pass through the mid-point of the luff, approximately, hence the perky angle apparent in the photograph. Unlike the ‘Freedom’ and the ‘Nonsuch’ the weight of the boom is negligible in determining the set of the sail. I will cover the points of sail and then talk about the construction aspects.
Tacking: The jib sets nicely, no compromises, with the port, windward sheet taking the wind force. (All the flattening stress is contained ‘within the wishbone’). As you tack the boom passes through amidships with no sail flapping, and herein lies the first advantage (the wishbone is still applying flattening stress) until the new, starboard, windward sheet takes the wind force. If the wind had increased to Force 7, I would have had to put a couple of rolls of jib round the foil meaning that the wishbone would have ridden a foot higher on the foil thus causing a bit of curve in the foot. This is not such a vice as slack in the leech and I have sailed with a curved foot with very little loss in windward performance and no flapping of loose sail. Close examination of the picture will reveal a Y-shaped downhaul attached to the bow end of the wishbone. This passes through a sheave at the stem and is led aft to a cabin top winch. To adjust the curve of the jib for the strength of the wind the tension in this downhaul can be varied (best done during a tack when the stress is reduced). Once each weather sheet has been set to give the jib the right incidence (e.g. tighter sheeted when motor-beating, – no problems with shroud obstruction) there is no further sheet handling during a beat unless the wind freshens or dies significantly. It is a great joy to be able to tack in an instant to avoid getting anywhere near close-quarters situations with other vessels whether you have right of way or no.
Reaching: To go on to a reach it is simply necessary to ease the weather sheet to let the wishbone clew sag further to leeward, the aerofoil of the jib remains unaffected and herein lies the second advantage. Clearly the wishbone angle can be set for close reach, beam wind or broad reach very easily. I have to say the Kelt performs really at her best with this rig on this point, 6 knots through the water for a bluff 28footer in a Force 5 makes us very happy. As you alter course on to a broader reach there is a moment’s hesitation and then, – bingo, the jib has gybed painlessly into the —
Goose-winged running mode, and herein lies the third advantage. Nobody has to go near the foredeck. It then pays to let the sheet out a bit more to avoid it gybing back on the next meander in course. At some stage between tacking and goose-winged the other sheet will have to be eased, of course or it will take charge instead, which you don’t want. I have gybed the wishbone jib hundreds of times and in the freshest of breezes and never had any anxieties about the gear carrying away. More of this under ‘Stressing’ below. It always surprises me how large the area of even this cut-down jib seems when it is boomed out at right angles and still held flat by the wishbone. You don’t lose much over a boomed genoa with a curve in it. (Who carries a boom long enough to hold their genoa out at right-angles and flat?).
Heaving to: If you want to heave to (and I remember sailing with a club in California where no member had ever heard of such a manoeuvre) then you still have two sheets on your jib, – go right ahead and haul in the windward one tight! (Herein lies the fourth advantage).
I have to say that we do not make a habit of sailing in anything over Force 7 and I can well imagine this rig could be an embarrassment under storm conditions, however it can instantly be handled like a normal jib, sheeted to leeward with the wishbone carrying little or no load, in an emergency.
Ideal for the ageing sailor!
Construction: The crucial development breakthrough here (achieved only at the MkIV stage) was the double claw-ring luff attachment arrangement. It uses two dinghy claw-rings small enough not to pull over the jib foil. The ones I found were still plenty big enough to accommodate the roller furled cut-down jib (but this obviously depends on sailcloth gauge). When the sail is furled they ride high up on the foil where the number of rolls is only about half the maximum at the clew. By using two claw-rings separated by a length of alloy tube, any tendency for the claw ring to twist and jam is positively suppressed. The tube length is a compromise between too much bending moment for a long tube and too much concentration of the force in one place on the foil for a short tube. (Our current arrangement errs on the short side.) The foil does assume rather a funny curve in a fresh breeze, which made Peter Lucas and Co. scratch their heads a bit when commissioning a new jib but it seems to cause no problem in practice as the picture shows.
The wishbone itself, for an 8.5m boat comprises a 190º circular bow (rolled up by Carisbrooke engineering of Fareham) 1 metre in diameter with 200mm straight ends to the curve made out of 306 stainless steel tube of 32mm o.d. and .26mm i.d. To this are attached two light alloy tubes of 38mm o.d. and 35mm i.d. of length sufficient to span from jib clew to the bow at mid-luff, (3.4m for the Kelt) with a good joint overlap. The attachment involves splitting the tube ends, like collets, into 6 by saw cuts 50mm deep (ends of cuts drilled 5mm to remove stress rising corners) and secured with stainless Jubilee clips (which have never slipped). Clew ends of tubes are simply drilled 14mm diam (at a slight angle) to accommodate a 100mm long 12mm s.s. bolt with a Nylok nut (essential) which shares the cringle in the jib clew with the twin sheets attachment. In fact, I tapered our tubes to a smaller diameter for the back metre, using the same jointing technique partly for lightness and partly to use the ‘remains’ from the MkIII! I have been cruising with this rig for four years now and these sleeved joints have never split or slipped but I think that is due in part to an original ‘good fit’ (although I did have to ‘pack’ with a short ‘C-section’ split tube) and in part to ending the splitting cuts well within the overlap region of the inside tube.
The two claw-rings are held to the tube by a piece of 8mm studding passing right down the centre of the tube (held central by bored corks). Our claw-rings already had holes just where needed, otherwise I might have been worried about weakening the back section where the bending moment is worst. The ring tapers in thickness in this region but they can be kept parallel by careful cutting of the interconnecting tube ends to slightly under 90º. I made the attachment of the tube centre to the bow by jubilee clipping a stainless steel stirrup to each which, for ease of disassembly on board, I then joined with a 90º twisted s.s. shackle wired up tight. It is advantageous to use Jubilee clips rather long for the job and to ‘figure of eight’ them by screwing A’s end into B and B’s end into A. This makes it impossible for them to slide off the end of the stirrups. High quality s.s. genuine Jubilees are essential. As can be seen by studying the picture, the downhaul is a Y-shaped rope attached at either side of the hoop with eye splices held in place (from sliding round the hoop) with a more cheap and cheerful style of jubilee clip.
Rigging the wishbone is fairly easy if there is little wind and there is a spinnaker halyard available to take the weight. The spinnaker halyard has to be knotted to the apex of the wishbone hoop with a bow knot with a long fall so that the knot can be untied, after the wishbone has been rigged, by pulling on the fall. It should be recognised that there is a danger of the wishbone falling during this manoeuvre if the knot slips, and due precautions taken (e.g. pad the forehatch, stand clear) to avoid disturbing the knot it is best to choose a calm moment, unroll the jib first and then use the spinnaker halyard (at the mast foot exit) to haul the claw rings up the foil until the dangling ends of the wishbone reach the jib clew height when the bolt can be threaded through and nutted and all is safe. Then pull on the fall of the spinnaker halyard to undo the knot and flick the halyard clear. Like this it can be rigged single handed but it is easier with two, you don’t have to hold the halyard in your teeth, for instance.
Stressing: The scantlings I chose by guess have proved adequate although there has been significant but not dangerous wear around the clew bolt holes. I can imagine eye bolts in each side (eyes on the clew sides) with a tubular tube insert to stop the eye bolt nut crushing the wishbone tube. These would then have to be attached to the jib clew, perhaps by shackles, but it is important to keep weight low here to minimise gybe trauma. Under the freshest conditions, with maximum load on the wishbone downhaul, the tendency to ‘spread’ the wishbone due to the stress is just visible but not alarming so it would seem things are about right. Concerning the ‘gybe all standing’ performance I am truly surprised at the ease with which all the gear absorbs the shock. The clew end of the wishbone is light alloy tube of small diameter and the snaking of the sheets as they come tight seems to absorb that shock very effectively. The inward pull on the sail from the sheet can pull the whole sail athwartships but the foil, not being rigid like a mast, seems to absorb that shock too with no problem. This is where the ‘figure of eight’ Jubilee clip configurations holding the interconnecting stirrups and the shackle are so important.
If anyone wishes to emulate all this, feel free to contact firstname.lastname@example.org.
All dimensions above are approximate.
Paul Cope, “Mr.Trench”, Fareham