I tried one on my Baja 25 Outlaw and lost 3-4 MPH. Tried a 3 and 4 blade, about the same results.

The main reason for triming up the drive is to expose the top of the propeller to the air -- cavitate --- this loosens the waters hold on the prop where the water isn't needed. The second action is to cause bow lift. I don't believe my scarab needs a lot of bow lift since I get max speed with the props turning out for more stern lift. With the shorties I should not have to trim very much to cavitate the props so all that downward push will now be pushing the boat forward instead. Also with less positive trim pushing the stern down the boat will be efectively lighter.

They probably wont help much on the BAJA's or the CHECKMATES since they come from the factory with a high X-dim. I would think the sign that you need shorter drives would be if it takes a lot of positive trim to make your boat go fast.

cfd5,
I bet if you would have tried an neutral extention box with the shorty you would have gained what you lost.
You basically answered my question that I asked above.

I think my X is pretty low, never measured but from what I have been told they come low. I think 26 Scarab is right about the leverage, I trim out pretty good to reach top speed. With the shortie I actually had a much better holeshot. Non step boats like the Outlaw need alot of bow lift, I think the shortie just gave me too much stern lift.

CFD5 - did you ever check your bottom for hook? I will bet you have some. From what you are saying it is showing all the signs. If you have to trim a lot to get max speed on that size of a boat your drive is too low. You will loose bow lifting leverage with the shorter drive but with a properly set up bottom you shouldnt need much bow lift. My 34 doesnt need very much at all and the hull is very straight.

Tinkerboater,

the bottom on my boat is straight except for a very slight hook from the first strake out just in front of the trim tabs. The boat also has a conservative "X" , and I have to use ALOT of positive trim to get 80mph out of it and my slip numbers are 19-20% (bad) , I'm sure the Sonics, and Baja's are close to the same and require more leverage to carry the bow. I don't think it is the bottom but how the CG of the boat is. In my case I think the gas tank is a little to forward. the alternative to re-rigging the boat is to add more leverage to carry the bow. My motor is making around 670hp , so I should be 3-4 mph faster .

Never really looked for the hook, I don't trim it way up, just enough to get it on the pad. I've had problems with my trim guage, I mostly go on feel. I've heard about the ext. box and shortie. My dealer has the same boat with the box and regular drive and is not getting very good results. Only running about 65mph but they are still testing.

cfd5,
Did the other Baja you where talking about use a neutral setback or a raised one ? If it is a neutral then with the regular drive it actually lowered the "X" instead of raising it.

Does anyone know where the centerline of your
prop shaft is compared to the bottom of the boat
my 33 Avs is 6 inches below I think it is way to low
The only other boat I have checked in the last few weeks
is a 26 step hull Bluefin with a 12 in standoff box and it was
only 2 inches below single engine. I have to run my trim as high
as it will go to the trailer position.

26Scarab, I'm not sure if it was neutral or not. It came from the factory with the IMCO box. They are still messing with it, factory said it should run 72-75. My bet is it was neutral, I didn't have alot of time to talk to them, had to pick up my boat and bail.