| Home | About Sailomat | Technical Info | Questions | Comments | Back to Sailomat 700 |
|
|
1) Which is the best self-steering principle?
Q: Which is the best self-steering principle? A: Definitely the so called 'servo-pendulum' principle with a servo (oar) blade suspended in a pendulum carriage, a near-horizontal pivot air vane, and pull lines to tiller or wheel. This principle offers both high steering torque and desirable yaw damping. The SAILOMAT 601 is built on this principle. Other principles, such as a vane controlling a trim tab or an auxiliary rudder, usually result in poor steering torque and unacceptable (yaw) damping characteristics, and should therefore not be seriously considered. Q: How does the 'servo-pendulum' windvane system operate? A: Sailing the correct course, the vane base is initially turned to orient the (air) vane surface to be parallel to the wind (air vane is vertical). If the yacht is falling off course, the corresponding aerodynamic force will slightly tilt the vane, and the vane-to-oar linkage to turn the oar blade. Waterflow 'side-lift' drives the oar pendulum slightly to the side ('swing' motion), pulling the pull/pull lines to the tiller or the wheel, and the main rudder to accomplish the steering course correction. The pendulum swing should be proportional to the initial course deviation. This action is usually fast, highly accurate and, if designed correctly, also properly damped to avoid course oscillations (yawing). Q: Why is the SAILOMAT 601 self-steering superior to other systems? A: Basically because it is better designed, with a much higher 'performance parameter' = steering torque per degree course deviation. But also due to the unique (patented) engineering design that goes into it, with several superior features just not available with the competitor systems. The patented SAILOMAT 601 design is state-of-the-art and highly efficient. The individual components are strong and simple, and linkages designed for durability and minimum friction. The many design parameters such as sizing of the air vane and oar blade surfaces, oar blade turning angles, variable vane-to-oar ratio , pendulum and 'tow in' stability features are all carefully optimized after years of experimentation and engineering analysis. The hardware is particularly simple and robust, requirements for high reliability and durability. The strength-to-weight ratio is also optimized, assuring best possible overall performance and function. The SAILOMAT 601 strength-to-weight ratio is currently 250% to 300% superior than competitor systems. The strength of the 'critical' high load lower section of the SAILOMAT 601 oar shaft is over 500% superior than competition, due to the a combination of (1) primarily much larger diameter tubing with much thicker walls, and (2) to a lesser extent superior yield strength for the light alloy materials used for the SAILOMAT 601 over competitor gears. The SAILOMAT 601 also comes with a vane-to-oar variable ratio, a patented exclusive SAILOMAT feature, with ability of system sensitivity tuning and better performance in light winds. The variable ratio feature offers an estimated beneficial gain of typically 50% or more in steering torque (line output) over a conventional fixed ratio. SAILOMAT 601 is currently offered in seven size versions, to guarantee the best possible matching to any the particular yacht size or geometry. The alloy casting components are identical for all size versions, but the oar shaft, oar blade or mast tube come in different lengths. In contrast, most competitor manufacturers 'try and hope for the impossible', by offering a single size to fit all yachts. Q: How is SAILOMAT 601 the safest system against blade and shaft breakage? A: In my opinion the competitor self-steering systems and systems of the past are all built too weak for demanding off shore use. This is particularly true for any stainless steel designs, where the overall weight would be unacceptably high if one would first specify and select an appropriate strength. This argument applies to all the individual components that make up the self-steering gear, and valid particularly for the oar shaft and servo blade which are both subject to potentially very high loads. Reported shaft and blade overload breakage mostly occur at the mechanical limit for the pendulum swing motion, by design limited to only 30/30 deg to each side for the competitor gears (and when the pendulum hits the limiting 'cage'). The limited pendulum travel combined with inappropriate thin-tube-wall design for the oar shaft (regardless of the material selection, including 316 stainless steel) reported strength and durability problems with these systems are not surprising. By contrast, the patented SAILOMAT 601 design permits the pendulum to 'swing' as much as 140 deg to one side and nearly one half turn or 170 deg to the other side. The total SAILOMAT swing ability is then a full 310 deg, compared to only 60 deg for some of the competitors. In an emergency situation, a rapid manual turning maneuver under sail or power would slam the competitor blade into the mechanical 30 deg limit with the possibility of fatally overloading it. In contrast, the SAILOMAT 601 blade would respond by smoothly swinging beyond the 30 deg limit, or even out of the water, thus completely avoiding equipment damage. For even further protection and superior durability, the SAILOMAT 601 shaft/blade assembly is designed to unparalleled strength - the shaft being over 500% stronger (2002 data) than the nearest main competitor! Due to the above high-strength design features used on all Sailomat pendulum steerers (first used on model 500/536 from 1984, then again used for models SAILOMAT 600 in 1992 and SAILOMAT 601 from 1995) not a single SAILOMAT pendulum component, shaft or blade has yet broken since first market introductions in 1984 for this generation of steerers- a remarkable durability record! Q: Your comments on the design philosophy of using light alloy castings and aluminum extrusions? A: As for a high-performance self-steering system one usually wants high strength in combination with lowest possible weight. Aluminum alloys are in that respect in practice the most feasible for this demanding marine application and superior to most other metals, including stainless steel (such as ss303, 304, 316 or 316L). Extruded aluminum alloy 6061-T6 (density 2.8 g/cm3), presently used for the SAILOMAT 601. Theoretically, the aluminum system weighs only 27% compared to a hypothetical similar system of stainless steel (ss 316, ss316L, density 7.8 g/cm3) for a design of 'given strength', incorporating the fact that the yield strength (maximum permissible load) for aluminum 6061-T6 is 28 kp/mm2 ( 40,000 psi), and 33% higher than for 316/316L stainless steel with yield strength 21 kp/mm2 (30,000 psi). This also means that for the same overall weight a 6061-T6 aluminum design can be built 3.7 times (!) stronger than a corresponding (hypothetical) stainless steel system. With similar overall weights, the current SAILOMAT 601 model currently has a 500% strength advantage over the competition stainless steel steering systems. This advantage is due to the combination of the selection of the superior light alloy material over stainless steel, and the state-of-the-art different SAILOMAT design. For the very same reasons we build advanced airplanes, and sailboat masts and hulls in light alloy materials - and not in stainless steel! The future points towards light composites. But we are not there yet for self-steering. Material and tooling costs are still prohibitive. Marine grade light alloys have been used successfully in all SAILOMAT self-steering designs for 25 years. It permits the use of advanced casting and extrusion techniques for compact, clean looking and highly efficient components. Q: Did Sailomat ever consider building self-steering systems in stainless steel? A: We have considered all materials. Stainless steel has been ruled out in favor of aluminum alloy, simply because our light (aluminum) alloy has 33% higher yield strength compared to stainless steel, and the aluminum density (weight/volume) is only 36% of stainless steel. In other words, for the same overall weight, an light (aluminum) alloy design can be built 3.7 (!) times stronger than a stainless steel design. The light aluminum alloy is certainly the superior choice for a high performance self-steering system. A: In using a light alloy design for the ocean environment one would have to address and carefully solve potential corrosion problems involving welding, electrolysis and fasteners. Welding is definitely banned from the SAILOMAT 601 design, thus completely avoiding the corrosion problems normally associated with welding. By design, the Sailomat 601 blade/shaft assembly and other components are electrically insulated from each other, minimizing galvanic element electrolysis for maximum corrosion resistance. Important fasteners are also secured by state-of-the-art stainless steel Helicoil thread inserts in the light alloy castings. Therefore, these stainless steel fasteners will not 'freeze up' in time. For additional convenience in disassembly we also use the new Tefgel (TM) compound. Q: Why is SAILOMAT 601 so much simpler to install? A: Installation simplicity for the SAILOMAT basically comes from our patented 'small-footprint' (170 x 300 mm, height x width) base plate concept. Only four attachment bolts are required for the base plate attachment to the transom, compared to as much as 16 (!) bolts for some competitors. Further simplicity with SAILOMAT is achieved by the rotable Universal Base (UNB), allowing simple and instant mounting to the correct slant angle (34 deg oar shaft angle, and vertical mast tube). Q: How can SAILOMAT 601 have such a small mounting base and still have high strength? A: The pendulum carriage does not transfer any significant torque to the base, basically only simple shear force. Remember that the pull/pull lines from the pendulum shoulder run to blocks that are attached directly to the yacht, and not to the base. The shear force loads (oriented parallel with the transom) on the base are rather small, less than 100 kg (200 lbs). And there are no large emergency overloads on the SAILOMAT 601, since in an overload situation the SAILOMAT pendulum can swing out of the water, in contrast to the competitor systems. Therefore the SAILOMAT 601 base can be made small. Q: Can the SAILOMAT 601 be mounted off-center, and what are the disadvantages, if any? A: Due to the compact mounting base with zero torque loads, the SAILOMAT 601 is designed to permit unique off-center mounting. Off-center mounting should be considered if you want to keep a swim ladder in original position, for yachts with walk-through transoms, for yachts with outside hung rudders, etc. Off-center mounting up to 400 mm (16 in) is common. Normally one would compensate with a slightly longer blade than for a center mounting. Performance reduction with off-center mounting is then insignificant. Q: Why is the SAILOMAT oar blade slanted 34 deg back- while competitor systems have a vertical blade? A: We designed the SAILOMAT 601 with considerable slant angle for several important reasons. One reason being the superior ability for a heavily slanted blade to rid itself and 'pump off' any sea weed that may wrap around the blade and reduce performance. Other reasons relate to 'toe-in stability' and important yaw damping. The chosen SAILOMAT slant angle also permits convenient and clean installations to modern hull configurations, e.g. with sugar-scoops and walk-through transoms. A: In principle the basic SAILOMAT 601 can be used directly as an emergency rudder, without the purchase of a conversion kit. However, the limited size of the servo blade may limit its usefulness for emergency steering. With an optional servo blade extension 'BEST' (available from 2002), the rudder area is substantially increased (+100%) to approximately 0.23 sq. meter (2.5 sq. feet), and the emergency steering ability very much improved. For emergency steering the vane-to-oar linkage is disconnected, and steering accomplished manually. The 'BEST' rudder is suspended with locking lines around the yacht's transom section, and steering performed by control lines to a special tiller. For optimum efficiency, he rudder depth is adjustable, and the rudder can be locked in a near vertical position even if the yacht is heeling. The emergency steering capability is a most valuable safety feature for bluewater cruising or racing. Q: Does the oar blade kick up? What about overload safety? A: The SAILOMAT oar blade is protected from overloads in any direction. Forward impact protection is guaranteed by a plastic sheer pin in the holding fork. Basic side overload protection by design, with the (patented) SAILOMAT full side swing motion 140/170 deg- out of water, in conjunction with built-in overload safety in the special line circuit. We have never had a SAILOMAT servopendulum oar shaft or blade mechanical failure since first introduction in 1984! A: Yes. The input signal to the SAILOMAT system is then magnetic course rather than wind vector. We recommend to use a small linear-motion 'cockpit autopilot' (e.g. Autohelm smallest tiller autopilots), with the attachment for the (linear) actuator arm connected the SAILOMAT counterweight arm. The autopilot base could be secured to the pulpit. Scheme benefits include significantly smaller electric power drain (= idle load), much less frequent battery charges, and significantly increased autopilot life and durability. Autopilot control, instead of the normal air vane, could be used when sailing in areas e.g. with many islands and disturbing directional wind shifts, narrow channels, when motoring, and when motoring in dead true or apparent wind. It is not recommended to use autopilot control when sailing very close hauled, where the windvane is always superior by sensing any wind shift and steering the yacht at optimum height and speed. Q: Can the SAILOMAT 601 be used for self-steering while motoring? A: Yes, at lower hull speeds and for limited periods of time. However, it is important that the servo blade is positioned -which is possible with SAILOMAT 601- outside any turbulent propeller slip stream to avoid damaging vibrations to the system. Adjusting the 'neutral' position of the SAILOMAT blade to be outside the slip stream is done by lengthening or shortening of the vane-to-oar pushrod (a few complete turns of the vane base on the mast tube). Q: When to select the optional Remote Course Control (RCC)? A: The all-mechanical RCC (coaxial drum on mast tube+control line to cockpit) should only be considered when you cannot easily reach the standard course control handle, which is positioned on the vane base casting. This is normally the case only for larger yachts with center cockpit, and for special situations when the Sailomat is mounted in an extreme aft position, e.g. behind an outside hung rudder. Q: Do the SAILOMAT basic bearings need lubrication? A: Basically not. The two sleeve bearings for the pendulum shaft (positioned inside the pendulum carriage), the two sets of radial-load composite roller bearings for the oar shaft, and the axial-load composite ball bearings for the oar shaft are basically all non-lubricated. They should periodically be cleaned with fresh water or a cleaning agent (or WD-40) from any salt deposits. Q: Do we need a spare part kit? A: No. The only component designed for replacement is the spherical rod end bearing. It will last 1-2 circumnavigations. A second vane may be useful. We very rarely sell or recommend a purchase of any other spare parts. Q: We have a ketch with low mizzen boom that extends aft of the transom. Can we use a SAILOMAT? A: Yes. Please contact our Design Office for a custom design solution that may include a special mast tube, special air vanes, or modified mounting platforms or other components. Q: We have hydraulic steering. Can we use the SAILOMAT? A: Normally not. With hydraulic steering it is not possible to connect any servo-pendulum system to a wheel coupling disc on the wheel, since leakage of the hydraulic fluid across the pistons will gradually cause the wheel to turn slowly under helm, which the line circuit cannot compensate for. However, special arrangements can be made to solve this problem and to still use a SAILOMAT. The solution involve coupling to a direct emergency tiller or quadrant, with a bypass hydraulic valve. Contact our Design Office for our further recommendations and assistance. Q: Do we need to reinforce the transom when mounting the Universal Base? A: Normally not. The forces on the Universal Base are generally quite small, since we have completely eliminated the overload risk from a mechanical pendulum restriction. We also have insignificant torque loads on the base plate, since the SAILOMAT is connected by pull-pull lines to blocks secured to the hull. Four 12 millimeter dia.(1/2 inch dia.) stainless steel bolts are used to secure the SAILOMAT base plate to the hull. It is generally sufficient to use conventional or slightly oversized round washers rather than back plate reinforcements on the inside. Q: How simple is it to install a SAILOMAT? A: It is quite simple. Most customers do the installation themselves. Basically, you only have to drill the four holes in the hull and follow the instructions in the manual. The fact that the SAILOMAT uses a universal mounting principle, you are always sure that the mast tube will be vertical, as required. Before selecting the appropriate line circuit, the manual should be carefully consulted, since several schemes with different features are available. Q: Which SAILOMAT size do we select? A: We offer 7 size versions. The SAILOMAT 601-S models have shorter shaft (three different blade lengths), and are normally used for 23'-39'. The SAILOMAT 601-X models have longer shaft (4 different blade lengths), and used for larger yachts 36'-65'. The SAILOMAT 601 Universal Base (UNB) should normally be positioned high up on the transom, near the deck level . Then select a SAILOMAT model that permits the servo blade to be immersed in water about 50-60% in static conditions, meaning 70-90% immersion when sailing fast. The required size can be approximately determined from the scale drawings in the brochure material. For more accurate planning and final SAILOMAT size selection a 1:10 scale drawing is available from our design office. If you fax or mail us a dimensional drawing of your yacht we will perform the size selection and best mounting recommendations for you. The man behind SAILOMAT Stellan Knöös, Swedish-American aerospace scientist/engineer and cruising sailor, with over 40 years experience in fluid mechanics and mechanical design. Over 100 inventions and patents. Original founder of the SAILOMAT company in 1974, and responsible for the professional design and manufacturing of all SAILOMAT systems. Dr. Knöös is currently heading the SAILOMAT Design & Manufacturing Office in San Diego, California, USA. |
|
 |
||
