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Old 06-22-2017, 04:32 AM   #21
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Guys... Is my gear ratio 1.47?

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Old 06-22-2017, 12:34 PM   #22
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Hi guys...
I had a 21 pitch prop 14.25
Wasn't getting any take off too much... So I got a 19/pitch 14.25.
Great take off, getting 39 mph.
Do I have the right prop?
And is it my top top speed?
Or should I be getting more speed?
I seen post that say I should be getting over 40 mph...
I do trim once planed..
Wondering if I should get another prop... Not sure
Any ideas would be great.

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What is the WOT with this new prop? How many people were on board?
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Old 06-22-2017, 12:47 PM   #23
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4000 RPM.
2 people

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Old 06-22-2017, 12:48 PM   #24
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Is my ratio 1.47?
Im not sure about the ratio

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Old 06-22-2017, 02:31 PM   #25
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Quote:
Originally Posted by Jaslan View Post
I seen post that say I should be getting over 40 mph...
Speed is relative to current, wind, tide, and water conditions. Speed is not really a measurement for performance tuning.

RPM's at WOT throttle are what is used for performance tuning. The engine is rated for a target of 4400 - 4800 RPM's at Wide Open Throttle (WOT). You don't want to be outside of that range.

There are really a few main variables in this equation; vessel weight (total of boat, people and gear), prop pitch, # of blades on prop.

Ideally you would go down 1" of pitch for a rough increase of 200 RPM. overloaded gear and people will adversely impact performance. If you go too low in pitch to accommodate weight you need to be careful if the boat is empty. You don't want to exceed the upper limit of the max. rpm (4800).

Going from an aluminum to a SS prop can reduce flex and get more prop thrust, however they are very unforgiving when struck and are expensive. Going from a 3 blade to a 4 blade is the same as going up in pitch.

Call Mercruiser with your outdrive serial number and they should be able to tell you what the gear ratio is. It is sometimes stamped on the engine cowl as well.
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Old 06-22-2017, 06:25 PM   #26
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Quote:
Originally Posted by Jaslan View Post
Is my ratio 1.47?
Im not sure about the ratio

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I have no idea, do you have the serial number? if so call merc as shrew said. Problem may be someone replace the drive and if so a different ratio may have been used.
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Old 06-22-2017, 06:27 PM   #27
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Quote:
Originally Posted by Jaslan View Post
4000 RPM.
2 people

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400-800 rpms low however I would not think less than a 17" pitch would be correct.
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Old 06-22-2017, 06:55 PM   #28
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Fill in your signature so we know the boat, engine and drive you have!
It helps us give you better answers!
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Old 06-22-2017, 11:22 PM   #29
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Ok
Not sure were that is.. I'll look.
Thanks

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Old 06-23-2017, 02:45 AM   #30
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were do I fill in the signature...am I blind? hahaha
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Old 06-23-2017, 03:29 AM   #31
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Quote:
Originally Posted by Jaslan View Post
were do I fill in the signature...am I blind? hahaha
user CP

Then select edit signature
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Old 06-23-2017, 04:09 AM   #32
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Ok

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Old 07-04-2017, 01:48 AM   #33
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Hi guys... Another dumb questions... Lol...
About the prop and rpms.

I got a new 19 pitch 3 blade. 39 mph 4000 RPM max...
Then went got another
17 pitch 32 mlph 4000 RPM.

I should be getting 4400/4800. What am I doing wrong?.
The local merc dealer is selling me those and telling me it will work.... But it doesn't.....
I have a 20 pitch at home 4 blade should I try this?
Just not passing 4000 rpms....

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Old 07-04-2017, 03:16 AM   #34
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Won't hurt to try the the four blade. Maybe the tach is off, you can connect an old school auto tac/dwell meter to check it.
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Old 07-04-2017, 04:16 AM   #35
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Maybe I just have to live with it lol...
Stabilizers fins? Would that increase speed or rpms with bigger pitch?

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Old 07-04-2017, 12:29 PM   #36
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Are you talking about a bolt on fin to the drive? I don't think it will increase speed but may increase time to plane however they add stress to the transom. I would use trim tab drop fins instead but again these will not increase top speed.

Something strange about not being able to get more than 4000 rpm.
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Old 07-04-2017, 03:44 PM   #37
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Sorry I meant trim tabs... My father had fin bolt on... Worked but like you say stresses...
Ya just cant get it more then 4000.... If I make it over rev with the trim I see the tac works over 4000... But I trim back quick... Maybe I need a 16 pitch 4 blade.....
At this point I bought 2 new ones for test... I have 5 now .From 21 to 17...
Still not going higher

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Old 07-04-2017, 09:28 PM   #38
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I would think no less than 17 inch pitch would work. Something strange here.
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Old 07-05-2017, 12:44 AM   #39
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Yes very....
Im trying to find a prop rental in my area, dont seem to have any...
Might have to get 1 last prop.. 16 pitch...
I have the, 17 p 4 blade.
Then it will have to be sent to the shop.... Cause i have no clue anymore.

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Old 07-05-2017, 04:25 AM   #40
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Are all these stainless steel? SS is heavier that aluminum and decreases WOT.

None the less decreasing pitch should increase WOT unless you add blades.
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