SSComp

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.

Steve_H

probably not alot of help but heres a thread.

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

throttleup

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

formula31

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.

chromecat

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

zt260

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

homan

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.

SSComp

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

throttleup

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

zt260

Throttle up-

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