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S&S Swan Maintenance - Comments on propellers |
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Join Date: 30 January 2007
Posts: 461 |
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Dear all and especially Lars, |
Join Date: 02 January 2008
Posts: 1547 |
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Daniel Yes, I can do it, but for accurate results would appreciate if you measure the diameter in mm. Max-Props are manufactured with metric dimensions, and inches are usually an approximation. 3600 rpm is the Pleasure rating for this engine, would suggest that you consider using the Commercial rating at 3000 rpm, it is much quieter, and sufficient. The difference is in high idling = full throttle in neutral gear, for pleasure it is set to 4100 rpm, for commercial to 3380 rpm, and this can be adjusted with the injection pump rpm limit screw. I think you may after all these years adjust the screw yourself without voiding warranty. The screw is probably sealed if in original condition. Lars
Lars |
Join Date: 30 January 2007
Posts: 461 |
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Lars, |
Join Date: 02 January 2008
Posts: 1547 |
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Daniel Thank you for your comments You can sleep well, and forget about the nightmares. It is not necessary to adjust the high idling rpm, you can continue to use lower engine outputs of your preference without any adjustment. The purpose of the adjustment is to limit the maximum rpm for a pleasure rating engine in a low rpm application like yours. The adjustment prevents the injection pump from overloading the engine when a hard fisted user (not you!) slams the throttle into full position. Your particular case can well be used here as a continuation of the propeller discussion to demonstrate the effects of changing the pitch setting. It is clear from the previous Forum discussion that increasing the pitch will increase the cruising speed, or lower the cruising rpm, and you now asked what the proper setting would be in your case. The engine manufacturer's recommended pitch setting for the commercial rating specifies that the engine should be able to reach 3000 rpm, and calculation shows that the corresponding pitch setting is 20 degrees. Here it may not even be possible to try this maximum rpm in practice, as this is far over your acceptance limit. A pitch higher than 20 degrees will prevent the engine from reaching the mentioned rpm, and reduce the available power. You considered the use of 22 degrees pitch, and it can be commented that this will allow cruising at 2060 rpm, which is approx 140 rpm less than with the 20 degrees setting you used earlier. This will give about 6 knots of speed, and approx 15 hp is used. Every 2 degrees increase of pitch will lower the cruising rpm roughly by 100 rpm Let us see what happens if you set the pitch to 30 degrees, which is the Max-Prop upper limit. For cruising at 6 knots 1670 rpm is then sufficient, assume this sounds good? In calm weather this works well, and the engine still has some reserve left. At full throttle it can reach about 1900 rpm maximum, which corresponds to 25 hp, but full throttle must be avoided as the engine is severely overloaded by this. The real problem comes if there is a headwind. When the speed drops, the engine has to work harder, but there is no reserve, and the engine can not cope with the demand. It might overheat very soon, and has to be shut down. With 20 degrees pitch the available engine power in a strong headwind is 33 hp, this drops to about 15 hp with 30 degrees of pitch. The limitation with large pitches is that engine rpms are held down, and reserve power becomes severely restricted and may be unsufficient if there happens to be a serious demand. In terms of propeller efficiency increasing the pitch does not give an advantage here. The best efficiency is achieved for the cruising condition with 20 degrees pitch. The choice of pitch in this case is a balance between a wish to use low cruising rpms, while retaining enough engine reserve power for performing against headwinds. It is suggested that you consider the actual conditions where the boat is used to strike the right balance. If you count on sailing when it blows higher pitch settings can be used. Pls feel free to ask more questions if something is unclear. Lars |
Join Date: 30 January 2007
Posts: 461 |
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Thank you Lars, |
Join Date: 02 January 2008
Posts: 1547 |
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Daniel Good to hear that my comments were helpful A question referring to the engine noise - do you know if there is an induction silencer on the air intake? This would lower the noise level appreciably. These silencers were introduced around the time when your yacht was built. I seem to remember them as oval horizontal pots on the side of the engine. Should be available from Perkins Referring to your item 2) engine rpm and power, some newer diesels, particularly bigger units, have very peculiar power curves. Their power is constant over a big part of the rpm range, and the power curve is a horizontal line, while the torque curve rises linearly as rpms drop. This is achieved with electronic injection control, and these engines are intended for trucks and locomotives, where it is an advantage that the speed can be kept up also uphill. These engines must not, however, be loaded continuously at the minimum full output rpm. Best regards Lars |
Join Date: 30 January 2007
Posts: 461 |
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Lars, |
Join Date: 29 January 2007
Posts: 1019 |
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Dear Daniel, |
Join Date: 30 January 2007
Posts: 32 |
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Yes Matteo, I agree that this discussion has been very valuable and informative and really show how helpful this discussion forum is. I now start to understand why my experience with my new stronger engine in combination with the Kiwi feather prop has been so positive . The old 25hp Yanmar engine with a twoblade folding prop just had to be run at higher rpm (and noice) to give a speed of 6 knots in my Swan 40. With this new stronger engine (42 hp Vetus) and a Kiwi prop I can reach the same speed at much lower rpm and noice and the diesel consumption is almost lower. And which is also essential: there is a leftover capacity to force the boat forward even under tough condition (I had an unfavourable experience from a situation when it was impossible with my earlier setup to advance forward against strong wind and high short waves in one of the big lakes when for various reasons I had to take down the sails). This is no longer a problem, which is of course also a question of increased safety. In addition of course it is also much easier to go in reverse direction with the feather prop in comparison with the folding prop, which of course is thanks to the characteristics of a feather prop, as already discussed. However one also has to learn (from experience) about the delay when changing from forward to backwards while the blades turn around, especially if the boat still has a velocity in the water when you want to change. From the discussion I start to understand why the pitch of 22 degrees and 17 inch diameter, which was recommended from the factory, was probably the right recommendation as verified from my practical experience. One question which however remains to be answered, and where I have got different opinions from those asked, is whether it is deleterious for a diesel engine not to be run at high rpm during long periods for the lubrication or not. I have got as many opinions as the number of participants in this discussion. Although the max speed is given to be 3000 rpm for my engine, there is little use of running it above 1500-1800 rpm at which I reach a convenient 6 knots and the noice is relatively low, and most essential the diesel consumption very acceptable and almost the same as I had with my 25 hp Yanmar engine. Fair winds (which means less need of the engine) Leif |
Join Date: 16 May 2009
Posts: 252 |
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Yes Matteo, I agree that this discussion has been very valuable and informative and really show how helpful this discussion forum is. I now start to understand why my experience with my new stronger engine in combination with the Kiwi feather prop has been so positive . The old 25hp Yanmar engine with a twoblade folding prop just had to be run at higher rpm (and noice) to give a speed of 6 knots in my Swan 40. With this new stronger engine (42 hp Vetus) and a Kiwi prop I can reach the same speed at much lower rpm and noice and the diesel consumption is almost lower. And which is also essential: there is a leftover capacity to force the boat forward even under tough condition (I had an unfavourable experience from a situation when it was impossible with my earlier setup to advance forward against strong wind and high short waves in one of the big lakes when for various reasons I had to take down the sails). This is no longer a problem, which is of course also a question of increased safety. In addition of course it is also much easier to go in reverse direction with the feather prop in comparison with the folding prop, which of course is thanks to the characteristics of a feather prop, as already discussed. However one also has to learn (from experience) about the delay when changing from forward to backwards while the blades turn around, especially if the boat still has a velocity in the water when you want to change. From the discussion I start to understand why the pitch of 22 degrees and 17 inch diameter, which was recommended from the factory, was probably the right recommendation as verified from my practical experience. One question which however remains to be answered, and where I have got different opinions from those asked, is whether it is deleterious for a diesel engine not to be run at high rpm during long periods for the lubrication or not. I have got as many opinions as the number of participants in this discussion. Although the max speed is given to be 3000 rpm for my engine, there is little use of running it above 1500-1800 rpm at which I reach a convenient 6 knots and the noice is relatively low, and most essential the diesel consumption very acceptable and almost the same as I had with my 25 hp Yanmar engine. Fair winds (which means less need of the engine) Leif Leif
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Join Date: 02 January 2008
Posts: 1547 |
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Daniel For older engines without electronic injection control the main parameters indicating overload are exhaust temperature, cooling water temperature, and the colour of the exhaust gases. It is suggested that you install an exhaust temperature gauge, according to old literature Perkins recommends a maximum of 670 deg C for the 4.108. It would also be good to calibrate the cooling water gauge, and add audible alarms for both gauges. Suggest you also consult Perkins on this matter. Provided that you determine the maximum rpm that can be attained in the prevailing conditions a rule of thumb is that using an rpm which is at least 300 rpm below the maximum on each occasion means you are on the safe side. Best regards Lars |
Join Date: 03 March 2007
Posts: 241 |
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Dear all,
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Join Date: 02 January 2008
Posts: 1547 |
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Mike The newer engines with electronic injection control often have load sensing enabling them to effectively avoid overload conditions. The driving force behind this is the stringent environmental requirements on clean exhausts for new engines. Smoking must be avoided when heavily loaded, and this limits the amount of fuel injected, which on small engines may show up as a tendency to stall when gear is engaged. Perhaps the suggested 300 rpm reduction needs to be clarified further. The reference for this is the highest achievable rpm in the prevailing conditions, and there may be considerable variation. For example in a strong headwind the highest rpm as well as speed will be reduced, and therefore also the safe rpm will be lower than in calm conditions. The opposite would be ideal, i.e. to be able to use a high rpm when the resistance is high, but this requires a controllable pitch propeller. It is not advisable to increase the pitch too much in order to gain better cruising speed. One way to find out how the chosen pitch works in a strong wind is to keep the boat stationary, use full throttle and then drop the rpm by 300, and read off the available power from the propeller curve shown on the engine leaflet. This is not accurate, and will underestimate the power to some extent, but gives an indication. Measuring the bollard pull at the 300 rpm deduction would give actual information, but few yachts have equipment for this. Best regards Lars |
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