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03 31 jupiter twin 300s prop size

Old 07-01-2019, 06:31 PM
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Default 03 31 jupiter twin 300s prop size

Hey guys. My 31 jupiter has twin 300s with 16x23 wheels on it right now which i know is too big. The motors are also on the lowest mark on the armstrong bracket.
With about 175 gallons and only myself and one passenger I'm hitting 5250 rpms at 42 knots and approx. 60% trim at WOT.
The boat will usually have a 4 man crew with gear, ice, and 250-300 gallons of fuel for the long haul trips. I do not want to over stress the motors and it is definitely sluggish out of the hole.
So, should i go for 21.5s or try even smaller?
thanks in advance, CJ
Old 07-02-2019, 04:21 AM
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Those props are way to big, I would drop down to 20's, this will get you closer to the 6000 rpm range where you want to be. You should be able to come up a hole or two as well with motor height from the sounds of. When up and running is the cavitation plate buried under water? Can you see it at all?
Old 07-02-2019, 05:00 AM
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Thanks for the quick response. I figured they are too big. I havent had the chance to see the cavitation plate yet. My guess is that they can also come up a hole. I dont want to worry about getting blow out in rough seas though. Do you think the 21.5 is still too big?
Old 07-24-2019, 03:22 PM
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My 2004 Jupiter 31FS runs Verado 300’s (1:1.85 gearbox) on Rev4 20” props at 5900rpm. Boat is heavy with gear.
Old 07-25-2019, 08:36 AM
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Thx for the info. My cruise right now loaded with 4 men at 4100rpm is 32-33 kts. Im pleased with those numbers for now. I wonder what rpms I would be at with 20s to achieve the same cruise speed.
Old 07-25-2019, 11:58 AM
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Originally Posted by schred86 View Post
Thx for the info. My cruise right now loaded with 4 men at 4100rpm is 32-33 kts. Im pleased with those numbers for now. I wonder what rpms I would be at with 20s to achieve the same cruise speed.
You might send Crossbones1 a PM. He runs the same set up and invested a lot of time to get it dialed in. Cruises at 40mph full fishing load getting around 1.5. I believe he tops out at 60mph light at 6000 rpms.
Old 07-25-2019, 12:54 PM
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Thx, i will reach out. Those numbers sound dam good. I top out at 52 with a light load.
Old 07-25-2019, 03:28 PM
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What's the gear ratio of the Suzi's? My cruise is 29knots at 4000, WOT is 50kn at 5900
Old 07-26-2019, 06:25 AM
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Originally Posted by Mozza View Post
What's the gear ratio of the Suzi's? My cruise is 29knots at 4000, WOT is 50kn at 5900
I believe 2.08/1 gear ration on the 300 zukes.
Old 07-27-2019, 06:50 AM
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Yes right around 2.08 if my memory serves me correctly. I cruise at 32/33 kts around 4100.

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