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Old 06-02-2015, 06:22 AM   #1
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What gear ratio to chose on P21 with 300xs

Hi All

I´m new in here, have been looking around a bit though .
I´m about to purchase a 300xs for my P21, just sold my Yamaha Vmax 200HPDI.
Was wounding what gear ratio to chose 1,62:1 or 1,75:1 Sports master.
Just want to hear from you guys, what you think would be best for P21.

Thanks

Brgds
Peter
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Old 06-02-2015, 11:22 AM   #2
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subscribing to learn about "why" one would prefer one or the other.
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Old 06-02-2015, 07:17 PM   #3
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Thanks for the nice replay Toffy, but didn't really help me much.
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Old 06-02-2015, 08:43 PM   #4
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I've googled you this link, which looks interesting. According to this it mainly comes down to turning props in a more market-available pitch range.
http://www.bbcboards.net/mercury-3-l...-62-gears.html

However, I'm sure there must be some impact on acceleration and minimum planingspeed also.

With the 1,62:1 gear the proppelershaft spins faster at a same motor-rpm. (quicker acceleration?)
With the 1,75:1 gear you must turn a larger pitch prop to obtain the same boat-speed (slower acceleration?, more stress on the lower unit?, maybe higher top end due to being more in the peak hp powerband?)

Keep in mind, I don't know sh*t and someone must chip in to back this theoretical stuff up with some first hand practical experience !
I'm just interested in this matter.

Bump +1
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Old 06-02-2015, 09:03 PM   #5
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Which is cheaper?
Would depend on what youre using the boat for. But as said, it wont really make much difference, it can be propped accordingly.

But if its top end youre after, you might find you run out of pitch on the 1.75 before anything else. No idea what a 300XS on a P21 will run like. What rpm/ pitch etc.

What speeds, gear ratio amd pitch was your yam?
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Old 06-02-2015, 10:40 PM   #6
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Thanks Toffy.

Hydrostream
With my Yam I got 70-72mph with a Bblade Blaster 26p Gear ratio was 2.00:1.
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Old 07-02-2015, 09:20 AM   #7
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I would go for 1.62 as its a light boat and you will run 27-28 pitch I think
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Old 07-02-2015, 10:51 AM   #8
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Quote:
Originally Posted by Bulibarger View Post
Thanks Toffy.

Hydrostream
With my Yam I got 70-72mph with a Bblade Blaster 26p Gear ratio was 2.00:1.
@72mph that would mean only 2,5% slip. I'm nowhere near that slip% with my very similar setup and prop (Signature Eagle 4 26P). Could it be your gearratio is off mate ? I think it should be a 1,86 ?

On topic : whatever gearratio on the 300XS you're gonna chose, you're getting a nice engine/performance upgrade there !
Keep it safe.

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Old 07-02-2015, 04:54 PM   #9
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Thanks to all, decision made 1.62 it is.

Toffy that's rigth around 2,5 slip. Bobs nose cone installed with low pickup, bullet night at bottom. So unless our garmin gps here in Denmark shows wrong :-).And yes gear ratio is 2.00:1 have had the engine from new.
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Old 07-02-2015, 05:46 PM   #10
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Could be the propp that could be a bit different. Some propps that are 27" could be 27.5 or 26.5 depending on where you mesaure the pitch.

1.62, you wont be need that big propps then

Elk here who has a P21 and 300XS has 1.75 and Amund here had 1.75 on his 250XS and P21. They ran 27" and 28"
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Old 07-02-2015, 05:57 PM   #11
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There will be a bit of prop testing and so on. Looking forward for it. ����
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Old 07-02-2015, 05:58 PM   #12
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Oh yes, I have the same "problem" lol. Lots of testing this spring! Gotta love it
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Old 07-02-2015, 09:59 PM   #13
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You'll need tabs. Mate had one on his. Ran mid 80's but have to spin a big prop which narrow phantoms don't like.
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Old 07-02-2015, 10:36 PM   #14
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Quote:
Originally Posted by Bulibarger View Post
Thanks to all, decision made 1.62 it is.

Toffy that's rigth around 2,5 slip. Bobs nose cone installed with low pickup, bullet night at bottom. So unless our garmin gps here in Denmark shows wrong :-).
That's just simply impressive ! What do I have to do to reduce slip% on my Phantom 21ft. I'm at 10% now......
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Old 08-02-2015, 03:39 AM   #15
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Guess you will have to get a more efficient prop, and spend more time on you lower unit to make the shape better, I used a lot of time to shape my lower unit, if you have a nose cone installed. You properly already have your Bullet height just at bottom V. That worked for me. Good lock.
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Old 09-02-2015, 11:10 AM   #16
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Quote:
Originally Posted by Zander View Post
Could be the propp that could be a bit different. Some propps that are 27" could be 27.5 or 26.5 depending on where you mesaure the pitch.

1.62, you wont be need that big propps then

Elk here who has a P21 and 300XS has 1.75 and Amund here had 1.75 on his 250XS and P21. They ran 27" and 28"
Elk runs 1.75 but I ran 1.62
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Old 09-02-2015, 11:39 PM   #17
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Quote:
Originally Posted by Amund201 View Post
Elk runs 1.75 but I ran 1.62

Oh damn, my bad!
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Old 10-02-2015, 05:55 AM   #18
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Old 11-02-2015, 10:19 AM   #19
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Quote:
Originally Posted by Amund201 View Post
Elk runs 1.75 but I ran 1.62
Yep. Amunds ex-P21 is currently running a 3-blade 14.75x27" Croxton or a 4-blade 15x26" Hydromotive depending on conditions. 26" runs at just over 6000rpm at WOT and the 27" just under 6000rpm. Both are labbed, so they are not standard off the shelf props. Top speed is around 85-90mph. Current pilot who is still learning the ropes has hit the 85mph mark with the 4-blade, Amund has gone 90mph+ with the 3-blade... and the motor is a 250XS. The P21 is a light weight model, not sure if that has great effect on the numbers or not...
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Old 12-02-2015, 08:45 AM   #20
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Quote:
Originally Posted by Bulibarger View Post
Thanks to all, decision made 1.62 it is.

Toffy that's rigth around 2,5 slip. Bobs nose cone installed with low pickup, bullet night at bottom. So unless our garmin gps here in Denmark shows wrong :-).And yes gear ratio is 2.00:1 have had the engine from new.
Hi Bulibarger,

I have a 1,75:1 gearcase you can try it is brand new
Where in Denmark do you live?

Mvh
Brian k
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