31 Ao
 

Need some information.

I have a set of 2" shorty IMCO Xtreme Drives. Where should the nose cone be in relation to the bottom of the hull. As I set right now, I have not had time to play with the x dimension the nose cones are approx. 3/4 to 1" above the hull.

Thanks!

Kyle

Re: 31 Ao
 

where is the drive... is it against the transom or do you have an extension box of some type ?

Don

Re: 31 Ao
 

No extension boxes

Re: 31 Ao
 

that is much higher than we put them at the factory... we put them about 2" higher than the bottom when they are on a 12" extension box.. i would imagine that you have a difficult time getting on plane with them and your prop slip i would also think would be very high... what props are you using ?

Don

Re: 31 Ao
 

Don:
The drives are a 1:36 gear ratio and turning a 32 pitch Bravo1 4 blade. It rolls over out of the hole shot not too bad but the problem I feel is getting alot of transom lift and feels like it will not carry the bow. So that is why I felt that I needed to go down by adding a 1" spacer to get the drives deeper in the water.
Thanks!
Kyle

Re: 31 Ao
 

Are the x dimension on new boats still the same as old x dimension?? My boat is a '98.

The nose cone on the bravo drives hung down 1" below the hull.

Re: 31 Ao
 

The new boats have all had extension boxes on them.. and are almost 2" above the bottom of the boat... The 1" below that your boat was set up with originally works very well and is what we based the new x up on with the extension boxes...
Don

Re: 31 Ao
 

I would think you either need to add a spacer or extension box to your setup for optimum results... the extension boxes have proved to be very beneficial.

Don

Re: 31 Ao
 

Don:

Appreciate all the help. I will get back with you. Possibly I have my motors sold so I will not worry right now about the drives until I get the new motors built. One last question for now though, what type of extension box does AO use??

Thanks again for your help!

Kyle

Re: 31 Ao
 

They have been using the IMCO extension boxes.. but there is nothing wrong with the boxes from Stellings... With the stellings it uses a stub shaft between the drive input shaft and the engine with a u joint.. allowing for some movement of the drive upward without moving the engine up also..With this you could move your x up an additional 1-2"s without changing the engine height. I don't know how well this would work with higher hp engines running the drive shaft at an angle, but they do it..... The imco i think is easier to use but it uses a 12" longer drive shaft to reach the additional set back to the drive.. which has to be straight and aligned just like a stock setup that box is available straight or with a 3" higher setup with a 3" higher mount on the inner transom plate, allowing the hole in the transom to stay the same but the front engine mounts must be moved to keep the drive shaft in line.
Don

Re: 31 Ao
 

Try to get some slip #s before moving your drives. I have a
Chris Cat (same mold as AO)....set with props .75 in above the bottom. My setup is different being I use #3 drives and 17 in diameter cleavers.....but this can be a good guide. Remember at speed AIR should lift the nose not trim. My current setup has yielded better results than expected, hp is 736 (with 5psi boost on 509's),1.46 drive ratio and 32 pitch props, current best is 117mph on gps speedo. BAM has a great slip calcularor to help. Just my 2 cents. Good Luck! :drink:

Re: 31 Ao
 

OK now I will add my two cents worth. Without extension boxes the 3100 is slightly faster when the center of the nose cone is .25 below the bottom to .75 inches above the bottom but prop slip will be a little more than it was with the original 1 to 1.5 inches below the bottom that was used on the older boats. The lower the nose cone the greater will be the bow lift at the same trim setting. With extension boxes the center of the nose cone should be 1 to 1.75 inches above the bottom. If any higher than 2 inches the nose cone won't pick up enough water at speeds above 95 mph. Extension boxes with the right nose cone position will increase speed 2 to 4 MPH. Bow lift can be increased by cutting of the ring at the back of the bravo prop. the Lower X dimensions were used on the older boats because the 4 blade bravo props and 5 blade maxamus props which have good bite near the surface were not available.

Re: 31 Ao
 

I have a 31 foot awesome cat hp 500's I just installed 2" Mercury shorties and now I am 1" above the back of the boat with no boxes. I have bravo 1 drives with a 1.50 ratio. I tried it with a bravo 1 blade 30 pitch, which I was using before, and couldn't get it on plane. I was told that could possibly work if I go to a hydromotive 5 blade. Any suggestions?

Re: 31 Ao
 

Sounds a little high for your smaller diameter bravo propellers, My Chris Cat is setup about the same but I run 17 in diameter wheels. I have currently calculated my slip at 6-7%....736hp...32 pitch big shaft cleavers...1.46 drive ratio=118 gps mph best. On a side note I think a pointed ear prop will work best (tail lift) and My friends Awesome is heavier than my Chris and another local AO.Good luck. :drink:

Re: 31 Ao
 

thank's for the tip, But are you running a bravo dr

Re: 31 Ao
 

anything higher than 0.5 inches above the bottom without extension boxes and you will have a problem. the hydromotive 5 blade definitely bites better than the bravo 4 blade, but I would suggest the easy way out is to use a 1 inch spacer to make it just level with the bottom. only a small speed gain in going higher but it sure will be a lot more dillicult in getting the right prop to work.

Re: 31 Ao
 

thank for all tips