Imco 2" Shorties
 

What improvements did you see with the shorter drives on your V bottom boat. What speed , what rpm increases, were you able to prop up.

Tinkerboater What scarab do you have???? I was going to post the same question regaurding my 28' excell.

I have a 92 34 scarab with 600hp 502's boat does 75 gps now on flat water ( havn't been out in the rough without the rev limiter in the pasenger seat -WIFE ) usually gain about 3-4 mph. Just bought two IMCO 2" shortie lowers.

sound great. keep us posted on the results.

On a application that is nothing close to yours I gained 4 mph. Hard to say how much of that was in the proping or the lower unit.

Steve did you buy complete lowers or are you putting your gears in a shorty case? I'm very interested in trying the shorter lowers also...I talked to the Sonic factory and they told me with the X they were using when my boat was made I could use the 2" shorter lowers with no problem. Did you talk to Wellcraft? the guys told me I would need a 4 blade prop.....like 26 pitch Bravo 1.
Don

we put a pair of imco 2" shorties on a customer's 97 35' fountain.i didnt expect to see much improvment over stock drives.[we thought that fountain would have had the X as high as possible already]we gained 5 to 6 mph with no other changes.this was a high 90 mph boat to begin with.you have to run 4 blade bravo props with these gearcases

What change in handling is there when changing to a shorter drive/ amount of trim/bow position etc?? Why I ask is I have a porpoise problem at speed with a Baja 208 Islander and thought it might help. I know it's a small boat but DAMN I like it!!

Dyno I am just buying the lower case and shaft and using my gears. With the drives I have I need to trim the drives up to a reading of 7 to 9 on the mech cable indicators ( K type) for max speed and I feel this is loosing a lot of potential speed as well as better handling in the rough. ( This should make my wife happier)

I am already spinning 26 BRAVO 4 blades at 5400 rpm at 75 mph gps.

On a single engine boat such as a 26 Sonic or my 26 Scarab , these boats have a conservative "X" dimension and require alot of positive trim to attain top speed , wouldn't just adding the 2" shorty without a extention box slow the boat down because your losing leverage?

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.

Installing the short drives is probably going to decrease the amount of bow lift. My Baja 210 had a lot of natural bow lift with the standard length drive and was hard to control at speeds over 70 MPH. I installed the short shaft drive and the boat flattened off and became a pretty easy boat to drive at high speeds. Unfortunately, I did a motor at the same time as the drive so I don't know how much I gained if any. One thing is for sure and that is the boat now handles better at 95 MPH than it did at 70 MPH with the standard length drive. If bow lift is what you need to go fast the SS may not work without a box. Only my opinion though.

26 scarab-my application also required full trim to run it's bestest. When I added the shortie I did end up with a surfacing drive (trimmed up it would throw a 4-5' high spray rooster). Shortening the drive resulted in a very loose ride (chine walk), which I frankly enjoyed. The hydromotive prop helped to stabilize things, but it was extreamly hard to get on plane with it. I believe that due to the drive surfacing that the prop fatigued which lead to it's failure.

When you raised your x dimeision you needed to go with the bravo prop because it has more cup then hydomotive. That is why some boats cannot run hydomotives from the factory they are all ready raised. hope this helps :)



Also I would like to know how imco shorties do against the mercs. shorties

Steve keep me posted on how the drives work for your application....I think mine is simular...hey if they work good for you I'll rent your lowers for a weekend....try before you buy????

Cat results
 

For what it's worth- check out my thread in the eliminator forum- so far 6.2 mph, probaby 8 or better to be had.

Tinkerboater I don't have a v but a 28 profile cat and I was running about 104 with the standard length and tried a friend of mines two inch shortie lower and had to prop up from a 34 to a 36 and ran 111 @ 5400 rpms but the stern was a little to lose for my taste. The prop i was spinning had the difusser ring removed and I don't know if this caused the stern to walk but it was great to gain those extra mph's but I am not sure at the price of the boat being stable! But if he is down again this summer I will sneak that lower unit out again!!!!:D

Mind if I interrupt this conversation. We just got the boat finished and I am posting pics everywhere i can. New imco extreme sc 2" shorter w/stellings 12" Extension box,polished lower.Thanks for letting me interrupt:)

elimi somebody is gettin an early start or a late finish! i see the sled in the background in thew back of the truck;)

We usually sled until early june or late may here. Its funny sometimes that we pass boaters going down to the lake while we are going up the highway to the mountains with our sleds on our trucks. This year we will be boaters though!

The polished lower -- is this just a looks thing or does it serve another purpose? I didnt get the polished lowers because I was afraid to draw that much attenion to the drives. Some kid already tried to steal the stereo out of the boat and it is parked 20 ft from my bedroom window. BIG BALLS- or just stupid. If I catch him!!!!

Im going to order a set too.
I was told that the boat gets looser with the shorties and I might be giving up some handling....don't want that on Lake Michigan ya know
We are going from about 600HP per side to 850HP.
I did have 3 bladed Mirage props on before and they ran better fully trimmed up... I want to run Bravo1's now for better curise mpg.
So with the 4's im thinking shorter again????
All this on a 93 non-step 42 Fountain.
:confused: Is there a measurement of some kind so i could ease my mind?

This is a pic with some 4's that i tried last season...they needed to be trimmed out all the way for max speed.
They look kinda low too.

They look low with that notched transom. What engines do you have now and are you supercharging them? Speed , rpm, prop pitch?

Tinkerboater-looks only is the polishing purpose

ELIMI - Thanks -- I thought so but wasnt sure. Hey nice looking boat also.

Had 600HP engines going to 850HP tall deck blower motors.
Would like to use the 1.35:1 ratio drives and 26" Bravo1's
All spinning at around 5600 WOT...Like around 90-95MPH.

Back4More,

Give Marty a call at Fountain. He seems to be the most knowledgeable about boat setup. Tim has a new mechanic formally from Everglade’s marine. He has a lot of experience with big HP Fountains and drive setup.

Dan

Dan, I was introduced to the new guy at RiverView by Tim and we talked for an hour os so.
But didn't get much out of him for the exception of boxes being a waste of effort.
I will give Marty a tryl at Fountain.
Thanks Dan;)

Mark