What's my gear ratio?...if...

[loadnet]

24 foot Searay 240 Fly Bridge<br />Mercruiser 233hp Ford 351W<br />Pre-Alpha 1976 (roughly)<br /><br />My upper unit vertical gear has 20 teeth.<br />My upper unit horizontal gear has 16 teeth.<br /><br />Anyone know what gear ratio I have in this thing?<br />Is this a 1.32r? <br /><br />I've already been to www.mercstuff.com and do not see a thing about 16 teeth gears over there..<br /><br />I see 17 on one gear set but mine is 16 teeth for sure on the horizontal gear.. duh?<br /><br />WOT is at: 4100 RPM - running a 12 pitch prop, so I'm thinking my ratio must be off.<br /><br />I've been told I should have a 1.50r to move this application past 4100... top speed is like 24 to 25... that's it.<br /><br />Thanks for whatever you can tell me.<br /><br />CaptainWhere'dMyTeethGo? customerservice@401hosting.com

 

[CRT Skiff Crafter]

Re: What's my gear ratio?...if...

Howdy Capn'.<br /><br />I believe that gear ratio would be 1.25, but I may be incorrect in my thinking. <br /><br />I believe the method of calculation would be <br />20 divided by 16.<br /><br />If this is whacky thinking, I'm certain someone will give us the correct info and I'll go hide my red face in the bilge. <br /><br />Regards, crt.

 

[Ralph 123]

Re: What's my gear ratio?...if...

Did you see this page?<br /><br /> http://www.mercstuff.com/drivegearratio.htm <br /><br />It says 16 = 1.32

 

[CRT Skiff Crafter]

Re: What's my gear ratio?...if...

Ah, I get it.<br />Good show Ralph!<br />regards, crt.

 

[loadnet]

Re: What's my gear ratio?...if...

Yep!... saw that page on mercstuff.com however had to make sure I was thinking correctly here.<br /><br />My boat has been out of WACK all summer.<br /><br />If I change the ratio to 1.50 from 1.32 how many more RPM's will I pick up at WOT?? 200, 300, 600, ??<br /><br />Thank you,<br /><br />PB

 

[johnkc]

Re: What's my gear ratio?...if...

your going to think this is crazy but my neighbor has the same boat as you .it has a 305 engine though.it would take a loong time to plane with correct prop and 1:50 gears.so to get it on plane faster we put on a 1:98 ratio and a 17 pitch prop.gets on plane very good now and there is a lot less stress on the engine and it still runs 28 gps mph on top end.

 

[loadnet]

Re: What's my gear ratio?...if...

John, I talked to a mechanic who just installed a 305 in a 24 Fly Bridge Searay model 240 like a 1976 - same exact boat I have and he has 1.50 gears - 4 Barrel Carb...<br /><br />He took the boat out for a test drive and it did 32 knots at 4600 RPM Sorry but I don't remember the prop pitch.<br /><br />If THAT one did 32 knots with a 305 your neighbors should do the same, and mine has 233hp compared to 190hp 305 so mine should literaly fly at WOT...<br /><br />With 233hp my boat should be fine with 1.50 I just want to find out how many rpms I'm going to pick up by going from 1.32r to 1.50r thru this forum board if someone out there knows the answer.<br /><br />What is your neighbors WOT RPM please?<br /><br />Also, how many more RPMs did you pick up on WOT after going from 1.50r to 1.98r ??

 

[johnkc]

Re: What's my gear ratio?...if...

captain ,the wot rpm is 4800. if i remember corectly it was running 3800 with the 1:50 and i believe a 19 wich is the way it was when he bought it.it was a real pig out of the hole.that is the reason we went the drastic measure of the 1:98.and come to think of it, we are probably fighting a real tired engine in his boat also.

 

[loadnet]

Re: What's my gear ratio?...if...

OK... thank you for that info John.<br /><br />I'll be changing my ratio to 1.50 before next season hits and hopefully before this season is over.. to give it a try.<br /><br />I'll let you know how I made out with it.<br /><br />PB