31 AO engines moved forward, thoughts?
 

Any thought on the advantages/disadvantages of moving the motors forward 12 inches in a 31 AO? Any speed advantage? Getting on plane issues? Mid range issues? My questions are relative to no boxes installed.

Installing boxes is mostly done for higher X-dim. Not because of weight.

If you go ahead and figure out the weight diffr. ,just put that much in the front of the boat and see what it does.

Moving the engines forward is alot of change to ask without testing !:rolleyes:

From what I understand adding weight to the front of the boat is not the same thing as moving the motors forward. i think all the faster AO/Awesomes have their motors moved forward.

it will help to move the cg forward on these boats... I know on the newer and lighter boats it makes more of a difference in cg therefor it helps more. I think you would be easier to add boxes and change the x would do more for added speed than moving the engines forward. at least in the amount of money spent. the kits to add drive shafts are not cheap.

Don

I agree with Chromecat

Moving the engines is OK, but yo need to find out what it does !
If you ad weight in the front of the boat to figure that out you know what it will do.
Why should it not be the same ?
What ever you add in the front is equall with moving the weight of the engines forward ,once u figured out how much weight you need to make it run better and faster. Then you know where the CG needs to be and thats how far you need to move your engines !!!!!!!!!!

And dont think you need to add more the 300 pounds.
Also dont think that 300 or even 500 pounds slow a boat down ,if thats what it takes to place the CG right then it will run better actually straighter over the water and air so it will gain speed and handling.
Alot of people dont reliase that ! they all think ballast slows you down but if properly added it makes you faster !!!!!

You can also figure out where your CG needs to be on the trailer.
Call me i tell you how,if you really whant performance with no stress.

941 592 5815

If not ,ok with me to.
Just thought i help.:ernaehrung004:

mine are not forward but i have boxes and shortened drives and mine flys good and runs fast its a older ao so its heavy anyway but 130 with the hp i have is good its all in the setup

Yea, hear you . But yours is an X-raceboat if i am not mistacen, so its dialed in correctly.

No factory boat is dialed in perfect and every boat even the same hull and weight is a little diffrent.

You have to get it right on the money and then you realy see the diffrents .:drink:

Thanks guys, I appreciate the input. It was just a thought that a couple of us were talking about as a potential spot to add some speed without adding power. The boat runs very well now with the setup I have with slip that is excellent and easy to plane. Charlie I will call you later today.

How much does your boat weigh?

tssteph,

It would help, but price the stuff to add them,

new custom tailpipes... high dollar
drive shafts ... aren't cheap
drive shaft kit for the transom assymbly and the engine kit is about $1k i think.

this is before you take the time to redo your whole rigging in the engine well.

quest has the lightest 3100 ever built.....

Well, my are moved forward and I have a 2in. spacer in my drives. Planes off instantly and I barely have any bow lift. Boat is in total control and does not feel loose! But come this summer, I will be taking my spacers out and I will be installing 30Pitch 5 blade bravo's. so god knows how the boat is going to react when I do this! Art DiNick from AO has my same exact boat but the only difference is that he has boxes. I had a two hour conversation with him. My boat hits a 138 MPH with PFaff 900's, he hits 142 -145 MPH or so. He told me to add boxes with a 1in. spacer in the drives and add a tunnel tab and I will be all set! He definately said I need a tunnel tab as well. Our hull design with the tunnel we have, the air flow I guess gets blocked or something, that our hulls around 110-115 get dragged by that triangular V in the top of the tunnel and it drags the boat down. He said the Tab will help create enough pressure to get the tunnel 100% air flow once the boat hits the 115 or so mark. I started to think about it and he's right, my boat will sit at that speed for a sec or two and then she will start to increase to her top end. The other bizzare thing is that I absolutely have no porpoise at all what so ever!

Well, my are moved forward and I have a 2in. spacer in my drives. Planes off instantly and I barely have any bow lift. Boat is in total control and does not feel loose! But come this summer, I will be taking my spacers out and I will be installing 30Pitch 5 blade bravo's. so god knows how the boat is going to react when I do this! Art Dinick also told me I need boxes and a 1 inch spacer when I add the boxes along with a tunnel tab and I'll be all set! Im hitting 138 currently with my set up with 2 people and a 1/4 tank of fuel, I can just imagine what I will hit with Boxes and 5 blade props hittin the surface! I say move the motors forward, it eliminates bow lift and gives the boat more stability with the CG ratio. If you do this without drive spacers, I dont know how she will be, but I have 2in. spacers with 4 blade 32 bravos running 1.24 gears and shes a f???ing rocket with PFaff's 900's. If you want you can call me and I will give you all of the details.

What RPM are you running at 138 MPH?

What do you think about using the imco torsion shafts (from an extension box)to move the motors forward 12"? You could make a new rear motor mount and leave the drives on the transom. A couple of stainless tailpipe extensions and move some lines around.

The torsion shaft is not riding on any bearings in the extension box, it's only supported by the gimbal bearing and the coupler, so what would it matter if the motor is moved instead of the drive. A drive shaft guard could be fabricated to go from the transom assembly to the bellhousing in case of a failure.

She spins about 5900 RPM's

Before you go making any decisions on a Tunnel Tab (or any modification to the tunnel), give Sparky a call at Vicious. He advice and wisdom could just save a life-------yours.

With all of this talk about motor position/placement, keep in mind the original design of the Chris Cat and the use the speedmaster drives. I can't think of anyone who would be more knowledgeable then George or Rich on this subject matter dealing with these hull designs.

mine has a tunnel tab and it works good mine spins 6700 rpm 1.36 gears 32 pitch hydro's labbed no diff rings it pulls hard

wow! 6700 rpms what kind of speeds are you getting? Im running 1.24's and if I went to 1:36's I would probably need 36 4 blades minimum. Right now my drives are 2 deep to run 5 blades, I would have to remove the spacers.

If I can ask, why are you saying that? DOes the Tunnel tab make the boat real loose? To be honest this boat of mine makes me nervous enough as it is, I dont need any more fear, can you fill me in a little in regards the the tunnel tab? In regards to the Chris Cat, the center of gravity point is alot different, the fuel tanks are right under the driver seat and passanger, where the AO they are in the back of the boat.

Mine are 1/2 inch below to hull with -2 Imco lowers. 1.32 drives 5200 rpm at 113 mph with 32 pitch Bravo 1 props that have been cleaned up but no pitch change. No tunnel tab no boxes.

Charlie I tried to call over the weekend, no answer I will try again tonight.

130

That's why I recommended that you call Sparky and get the info first hand. I am NOT saying that you should not consider a tunnel tab. By the way, Sparky is not the only Cat builder to have told me to NOT use a large hydro type of tunnel tab.

Do you mean that the fuel tanks in the Chris are in the sponsons, with the front leading edge just forward of the front seat? AO fuel tanks have them in the back of the boat? Any pics of these?

In a AO they are in the sponsons. They start at the rear bulkhead and run forward to the step down hole in the floor to get into the cuddy. 2 52 gallon tanks. I might be wrong but i thought a Chris Cat is the same. I know Greencards are the same size I guess I am not sure of the location.

yup thats the way mine our too but th3 1992 ao that i have that im re doin has 4 fuel tanks 2 in front sponsons im goin to use them as ballast tanks with pump to drain water and pickups to fill them when running its goin to be on 5's and boxes with crashboxes 632 blown big chief head tall deck merlins should run the number 1.24 gears

that sounds like you are gettin serious....

Don

Just leave them as fueltanks and pump the fuel back and fort,,,,,why add extra weight if you can use what you have .

:drink:

Cosmetics aside, has anyone considered bridging the sponson fronts to pack air through the tunnel rather than spilling over the deck? It seems these boats could benefit from a bit more aerodynamic lift over hydrodynamic and not have to worry about the trip effect associated with a rear tab.

Interesting subject and more reason why Sparky is the man to talk to. He knows aton about this cat size and design. And yes, the trip effect is associated with this size/design cat. A matter not to be taken lightly. Especially not at the speeds obtained by some of these cats today.

Bottom line is: I want to report to work on Monday morning. or I wish for my friends to hear from me, and not about me.

Okay, now I need specifics. lets all compare ACTUAL results. maybee we can all learn. My Chris is setup with motors way forward and has SSM3's and crashboxes. I believe the cg is slightly more forward than needed. I have driven thru the porpoise but when loaded down it will not. The props spin in(more bow lift) 32x17's and 1.5 gearing, x is .75 above and gps speed is 118@6100. I only have 4.5 lbs boost 509's dyno at 736hp . A side note my props are about as far back from the transome as a bravo on a 12in box. my slip #'s are so good I am afraid to change anything. In the roughest water it flys FLAT and even though it has a hop it never gets loose or wild feeling. tsteph and I have talked about this at length and I am interested in everyones comments. I believe boxes would allow my boat to carry the nose better when loaded.

boxes and more boost andy you know what to do

700 hp, 5 lbs of boost (B&M 250 blower) single 1050 dominator, prop shaft 1/2 in below the hull, 1.32 Imco 2 in lowers, 32 pitch bravo 1 prop spinning in. No extension box and motor at the transom. Hop is about 75 through 95 but not bad, rough water there is no hop. At WOT the nose carries very well. 113 gps at 5200 rpm. there does not seem to be much if any differnce in speed when the tanks are full. It does seem to wollar around more at slow speed when the tanks are full. It planes very easy. 113 was in fairly flat water, I think there is a couple more mph/rpm if rougher water.

One thing I wish we all knew would be the actual weights of our boats.

I think the answer to my original question about moving my motors 12 inches forward comes down to "try it and see".

mine weighs 6800 lb with me and half tanks of fuel

the previous owner told me mine was 7600 with fuel. Charlie, good to see ya here. The boxes would need to be raised to keep my prop high and not loose my X. The old merc 10 inch boxes are tough to locate and very expensive. Im already configured with driveshafts, so I only need the boxes.I hope to intercool and put the boost to 6.5 if time permits this winter.:ernaehrung004:

i know where a set are if you are interested haha in my barn

This is the situation that we all are trying to avoid. Add to this a little angle or being "crossed up" and you stick a sponson and barrel roll.
http://www.youtube.com/watch?v=h0utBfPhtjg

That headache has got excederine all over it!!!