ross
New Member
Posts: 31
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Post by ross on Apr 27, 2013 7:43:01 GMT -12
I noticed not a mention of propellers on the site ! and there are a few things when wanting performance that are in the water that you should be concerned with ," HULL" should be flat and light if you want to plane , GEARBOX , should be smooth allowing a good flow to prop , nose cone if in modified classes with low water pick up , PROPELLER , I have tried all and while they all need a good tidy up most will need repitching to suit your hull and set up , I used to run two blade but found that a four blade maintained a higher average speed and I use a jacking plate to raise and lower your engine to get best speed and higher rpm , if too much rpm I add a bit more pitch , I like to run around 5500 rpm, this is helped with a cav plate on engine which allows you to lift higher without cavitation , cupping on the trailing edge of your prop helps when surface proping . Top speed with stock silver century with river flow from karapiro is 14 knots gps , with jacking plate , seagull four blade prop with cav plate fitted .Best motor is silver century as is a lot lighter than 102 and has better port timings and a smaller transfer port .
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Post by thetinker on Apr 27, 2013 19:37:34 GMT -12
I have started to play with propellors. I have discovered that u need to have an accurate way of measuring propellors first. Then you can experiment. A small change in pitch can make a huge difference.
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Post by thetinker on Apr 30, 2013 7:36:15 GMT -12
Ross I wonder how the small transfer port is important. All the literature I have read suggests a bigger transfer port is important. So I am very interested in your theory on this.
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Post by chicken on Apr 30, 2013 8:54:18 GMT -12
The theory is it increases the transfer velocity, there for more air fuel mixture in to be compressed in the same time.
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ross
New Member
Posts: 31
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Post by ross on May 2, 2013 19:21:41 GMT -12
chicken is correct that you get more velocity with a smaller transfer port and with such a short time that the port is open it needs to be fast , I know you can make the crankcase pump better , then you can have a bigger or multi transfer ports but then its not standard . So a standard engine requires a small transfer port , The very last block of the 102 model used the same ports as silver century including the inlet so it made the carb sit mid way up the block and of course you get a water cooled head .
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ross
New Member
Posts: 31
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Post by ross on May 2, 2013 19:23:52 GMT -12
To the tinker , I know its a man thing but bigger is not always better !
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Post by gtfortie on Aug 18, 2013 12:23:43 GMT -12
I've been experimenting with other props, 3 blade OMC & Merc 7-1/4 diameter stock used ones & pull at least another 800- 1000rpm's.Best result is a Chrysler 6hp 7-1/4 on a feather weight 40 2-1 gearbox.GTFortie
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Post by Rex NZ on Sept 2, 2013 9:10:42 GMT -12
When you compute some performance numbers on seagull props, it emerges that they 'slip' badly Increasing the drive face area lessens this loss More blades is one way of achieving this
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