Bravo 1.5 vs 1.36
 

I will be using around 600-650 Hp and spin around 5,600 RPM.

I know the 1.36 will allow me to use a smaller pitch.

What are the advangages/disadvantages of these ratios versus props.

If I'm rehashing just refer me to a link.

Thanks.

probably not alot of help but heres a thread.

http://www.offshoreonly.com/forums/s...threadid=54938

What kind of boat are you putting these drives on and what top speed do you expect?

As a general guidline if you are running over 105 or so go with the 1.32, less than that the 1.5. Of course there are situations these guidlines don't work as every boat/motor set-up is different.

Matt

years ago when mercruiser was making our 2 blade hydroplane props, an engineer there told me for 3 blade non-surfacing props, 25" pitch was the most efficient. He said gear to try and run as close to 25 as possible. My formula311 had 1.36 drives and 25 pitch props and outran similar boats with similar power. But Ive heard plenty of other opinions lately and Im sure there have been developments in prop design too.

i thought that the optimum prop today is a 30 pitch.

also i thought that the high pitch 32 + props put extra stress on the propshaft causing them to break easier than with lower pitched props.

Don

Gear ratio has been a big issue for my boat. I started with 1.36 for the exact reasons you mentioned. I never saw the full potential of the boat until I changed to 1.5 and picked up 5mph. Unless you can run 110mph go with the 1.5

I had a bravo 1:36 that had an Imco 2" stubby on it the guy that sold me the boat swore up and down no no no I'm telling ya you need a 1:50 other wise the boat will never move. Well I bought a 1:50 switched on the Shorty and guess what... 1:36 22p Bravo1 5400 rpm, 1:50 24p bravo1 5400 rpm = same speed which also = wasted money. I called Mercury racing talked to a tech he was saying that the 1:36 is less strain on the lower due to some technical crap of which I can't remember, but he also said in most cases it won't matter 136 or 150 if you can borrow a set from someone that's your best bet and see if it matters in your setup.

I'll probably be chasing 90mph. I have some extra parts to build some extra drives.

I really like bite out of the hole and am willing to give up a few mph to do so.

Maybe I'll have poker run drives and props (1.5) and everyday set (1.36). Then I can act like I know what I'm doing:eureka: :drool:

As far as getting a lot of bite out of the hole props will have more to do with that than anything else (not counting engines, of course).

The difference between gear ratios, if any, would be seen on the top end. If you have the resources to have two sets of drives with different gear ratios then you could test them both and see which one your boat likes. Of course don't forget to test turning the porps both in and out as well.

As a starting point, figure a difference in pitch of 10% when going from a 1.5 to a 1.36 ratio. For example, you would go from a 30p with the 1.5 to a 27 with a 1.36.

Matt

Throttle up-

I’m not familiar with turning the prop in and out. Could you elaborate?

Left hand and right hand on single drive and on twins rotating in / out is Left hand on one drive and right on the other, and visa versa (LF/RT or RT/LF) Clear as mud.

Try to stay below 32" of pitch. If you can do that with a 1.5 ratio, then your decision is made.

When turning props inward....you need to take it slowly, initially. The boat may handle differently so test with caution. Some vee bottom boats tend to get light in the stern when turning inward. You may or may not see any speed increase, as this is boat specific.

Outward rotation= RH prop on Starboard Motor
LH prop on Port Motor

Inward rotation= LH prop on Starboard Motor
RH prop on Port Motor

When running props in opposite rotation, with Bravo drives put the shifter in reverse to go forward and forward to go into reverse......Be careful and cognisant when attempting this test!


Safe Testing!

Matt

props
 

chris, nice talking with you tonight and I will call you when the props get here,again Thanks for the phone call and good to do Business with you ,we will get you hooked up.:)

My last boat was single engine cat running about 800 hp with a high X. Speed was approaching 110 mph.

I started with 1.50's and a "worked" 32" prop. The boat was very hard to get on plane due to the slippage. Once on plane the setup worked great, and accelerated hard.

I decided to drop to a 1.36 ratio to avoid the planning problems. I was able to drop down to a "worked" 30" prop with the new gears, and the boat jumped right on plane. I did lose some mid range acceleration though as a result of the gear change.

That was my experience, not sure how it corrolates (sp) to your setup. Good luck.

Did you lose any top end?

Not that I could tell. The numbers were about the same on the top.

I have seen similar results with other cats. With such low drag the gear ratio is not so important especially if you already run 110mph.

On V-hulls gear ratio seems to make a much bigger difference. My boat is a great example, 1.5 ratio=5mph more top speed.

That is interesting. If it were not for the problems I had planning the boat, I would have switched back to the 1.50's. The mid range acceleration was much better with them.

Almost no one will argue that acceleration with 1.5 is better, but if planning is a problem the 1.36 should help a lot.
Just goes to show you can't have your cake and eat it too.

Havasu cig,

What props were you running with both gear ratio set-ups?

Matt

PROPS/GEAR RATIO
 

I WOULD GO TO THE 1.5 AND LET'S WORK THE PROPS FOR HOLE SHOT,SIMPLE.

AS WELL YOUR MIDRANGE ACCLERATION WILL BE BETTER.

An outboard powered boat is totally different when it comes to getting on plane due to lack of toque. With the higher pitch props if they do not break loose the boat will not plane. I tried a set of bravos 4 blades34s in place of my normal 3bl 34 cleavers and I could not plane off unless I trimmed way up to break the props loose. The cleavers come up quick. Thanks Throttle Up for all the help

Mike,

Did you get to Key West as planned?

Matt

CLEAVERS
 

[QUOTE]Originally posted by mmwalters
[B]An outboard powered boat is totally different when it comes to getting on plane due to lack of toque. With the higher pitch props if they do not break loose the boat will not plane. I tried a set of bravos 4 blades34s in place of my normal 3bl 34 cleavers and I could not plane off unless I trimmed way up to break the props loose. The cleavers come up quick.TTT