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Thread: prop slip with a 24 raker
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05-30-2018, 09:43 AM #15000 RPM
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prop slip with a 24 raker
After pulling almost 400lbs of wet foam out of my 17ft astro its running much better, but Im getting very high slip out of my 24 raker. I turned an 18 pitch no name prop to 6000 rpm and 50mph with 2 people and full tournament load before foam removal. Now I run 56 mph with my 24 raker at 5700 and 2 people. Seems like a hell of a lot of slip. Also, That is playing with the trim for best speed and lowest rpm. My jackplate is manual and a pain in the.... So I havent done much playing with it. I did lower it an inch this weekend and lost 3 mph and 250 rpm.
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05-30-2018, 02:55 PM #2
I will assume yours has the smaller V-4 gearcase with a 2:1 ratio (13 tooth driveshaft and 26 tooth propshaft gearing).
5700 rpm x .50 = 2,850 propshaft rpm
2,850 x 24 = 68,400 inches per minute theoretical forward movement
68,400 inches x .000947 (constant) = 64.77 mph theoretical mph
56 mph actual divided by (/) 64.77 mph theoretical = 86.4% efficiency (14% slip)
It takes good set-up and leverage to get 10~12% at these lower speeds. 14% slip is high, but going to 10% won't be easy. Bow lift, prop bite, 4 degrees positive attitude of the hull on the water, and driving so the hull has the least amount of wetted surface. Trim is most often the problem. Use it to push the boat forward, not plowing water.
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06-10-2018, 04:28 PM #3Screaming And Flying!
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Way too much prop change. The raker will like to be up higher.
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dompie99, phillnjack liked this post
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10-22-2018, 05:53 PM #4
Your first figures of 6,000 rpm with a 18 pitch giving 50mph were not right by a fair bit, you said it had soggy foam and you ran that with 2 people and a load of fishing gear.
According to your figures you were getting just 2% of prop slip, ha ha no chance at all with 2 people and 400 pound of wet foam from the hull..
the Raker is giving you 13.52% slip and that is more realistic with 2 people and a load of fishing gear... but you should get that down to around 7-8% slip .
The Raker props can run realy high (almost full surface) so raise it up until the propshaft is about 2 inches below bottom of the transom and try that, then go up 1/4 inch at a
time until revs go up but speed dont, then drop back down 1/2 inch....
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10-22-2018, 06:40 PM #5Screaming And Flying!
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Philln jack...... If ya ever in my woods stop by.... USA va have a drink and fast ride...Hows things where you are' boating wise? Dave S.
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