Which gear ratio is better???
 

Is one faster or more reliable? - everything else constant between 1.36:1 with a smaller prop pitch (26p) or 1.5:1 with more pitch (29p) with both of them spinning 5,600 rpm's.

Re: Which gear ratio is better???
 

It's Not That One Is Better Than The Other. Bigger Heavyer Boats Use 1.36 Which Puts Less Stress On The Drive. Most Boats Use 1.50. Where The Weight Limit Comes Into Play Im Not Sure But 6-8000 Lb Boats I Know Use 1.50. My Ol Weighs 12000 Lbs I Have To Use 1.36.

Re: Which gear ratio is better???
 

I am sure there is alot more technical information that will be posted on this, but from what I know about this subject, you should be runnung a 1.50 gear until you run out of prop. By this, I mean that should run a 1.50 gear until you have enough horsepower to be able to over rev the motor with a large pitch prop.

Re: Which gear ratio is better???
 

I've talk to a lot of people about just this subject.. They all tell me the same thing. It depends on the hull shape... the hull speed .. the weight of the boat... how much HP... what speed you are looking for... etc etc etc... I've asked if it is better to run a 1.36 with a prop that has less pitch... or run a 1.5 with a prop that has more pitch.. I get the same damn answer... It depends... Bottom line is it is all subjective to how the boat acts with the different gearing. Same thing with running the props "in" or "out"... grrrr... Same thing with prop diameter and style.. I can't get a difinitive answer on any of those questions........ :mad:

Re: Which gear ratio is better???
 

Whatever gets you closer to a 30" prop.

Re: Which gear ratio is better???
 

One thing that all the drive manufacturers are in agreement on is if you run a taller gearing (1.36) with a lower pitch prop ( 28 instead of 32).... you theoretically should have the same top speed... but if you factor in the additional drag of having to spin the prop more in the water to achieve the same speed.. you lose efficiency. But.. the trade off is you have better acceleration in the midrange. So midrange acceleration is better... but top end is slightly slower. Bottom line... what do you want out of the boat? Some of the turbine powered boats run a lower pitch... but rpm's aren't a problem with a turbine. They build more HP the faster they spin. Not always true with BBC's..

Re: Which gear ratio is better???
 

Is 30" a special number for your boat GL?.... I had 32's... I also had a hard time getting out of the hole. But I had a great top end. 100 mph for 1.5 gearing.

Re: Which gear ratio is better???
 

the application is a 38 Fountain 8,900lbs dry looking for top speed more so than mid range punch. Anticipating ~85mph top speed

Re: Which gear ratio is better???
 

John, how can you stand having a boat that only runs in the 80's now?? LOL Is that why you're tinkering with it?

Re: Which gear ratio is better???
 

I had a 40 foot fountain ... a little heavier... I had 1.5 gears in #3's 17X32 three blade props... I could just barely hit 100 at 5800 rpm's. I'd say stick to the 1.5's Just my guessing. Anyone else have an opinion?...

Re: Which gear ratio is better???
 

This thread is one of the topics I planned on tackling this spring. I just bought a Formula 312 and was wondering about the props on the boat. It has 502's with what looks like 1.65 Bravo's and a labbed 30 pitch prop. Could that be right? It pulls 77mph on speedo, haven't run to GPS yet. If correct, what would that do to mid-range speed/RPM?

Re: Which gear ratio is better???
 

30" props are suppose to be the most efficient... therefore you want to gear towards alway using a 30 if possible... at least that is what i was told

Don

Re: Which gear ratio is better???
 

Chromecat, I ran a 30"p on my eliminator daytona and did not see any more efficiency verses a 26, 28 or 31. I tried a 32 and it was the most efficient, but I could not turn it as hard enough. I think it would have been about the same slip 14-16%.

Bob - I am shooting for mid to upper 80's with heads and shorties. I would rather go with 1.5's because the used prop selection is better, but have been finding more 1.36 lowers for sale than 1.5.

Re: Which gear ratio is better???
 

Gear ratio doesn't really matter until you are running out of prop. I have heard 34 and 36 Bravo props are poor out of the hole so it may be better to run a 30 or 32 with 1.36 gears than a 34 or 36 with 1.5 gears. Aside from this it really is splitting hairs and may not have any difference on the performance of the boat. What is the difference between turning a 30 pitch 6000 RPM through 1.5 gears vs a 27 pitch 6000 RPM through 1.36 gears? Not much, and that is consistent throughout the RPM range. Many people say 1.5's have better acceleration than 1.36 and we typically select a prop for a desired WOT RPM. The 1.5 will accelerate better than the 1.36 if the same prop were used, but the 1.36 will require less pitch to give us the desired WOT RPM and thus it will accelerate the same or very close to the same as the 1.5. :cool:

Re: Which gear ratio is better???
 

I would go with the 1.5's especially for a boat that is going to run in the mid 80's. Depending on your engines you should only need a 28-29 pitch prop in a V bottom boat to run low to mid 80's. Like GLH said this puts you close to a 30 pitch prop which is a great pitch in a 15" diameter prop.

There has been a trend lately to put the 1.65 ratio behind the 496HO motors. Some manufacturers have found the boats have a better top end speed than with the 1.5 ratio.

Like everything else in boating the only way to know which is the best for your particular set-up is to try it. But if you don't have the time or money to buy two sets of lowers, one with 1.5's and one with 1.36's, the 1.5's would be a safe bet on your application, John.

Matt

Re: Which gear ratio is better???
 

I have always heard that the 1.5 gears are stronger. Don't know how true that is.