When you need a few more inches.....
 

Seems to be the story of my life. However, this time I could fix it. We are installing Stellings extension boxes on a 37 Outerlimits. We really need to get the boxes/drives as high as we can. Since the boxes are adjustable, we can move them up 2". However, that left us with a pretty steep driveshaft angle (10*). That is too much with almost 1000 hp. We have 2 choices to fix it. The first is to move the engines up. We are already sticking out of the hatch with the engines where they are currently. The owner doesn't want a scoop on the hatch ruining the hatch pad. So, moving them up isn't an option. The other option is to move them forward. By shoving them forward 4.5", I was able to get the driveshaft angle to 7*. The cleanest way to do it was to extend the mounting ears on the inner transom plate. I didn't think a rear engine plate was the way to go. Not only would it not look good, but it would be tough to work on with such limited space to the transom, since we are only moving the engine forward 4.5".

I thought ya'll might enjoy some pics of the fabrication process. I started with an IMCO inner transom plate. It is much stronger than the stock Merc unit. Not only that, but it doesn't have all the extra bs of the steering ram mount, etc. I did all of the mods with 1/4" and 3/8" 6061 aluminum.

These first pics are of the inner transom plate being cut, templates being made and mock up. We made up a temporary jig that duplicated the transom angle of the boat, the angle of the engine, etc, so that it would not only be right and fit in the boat, but so both of the transom plates would be identical.

Thanks for looking. Enjoy.
Eddie

More pics of it going together.
Eddie

Finshing up

I kept my stellings box install angle under 3.5 degrees because I wanted to be able to turn my motor 6200 (after talking to Guys there about the angles), I would be VERY nervous at 7 degrees Eddie. Make sure the front angle and rear angle match within 1 degree. I had a 4 wd jeep with a 15" rear driveshaft with 1200ft lbs at end of tcase with 10 degree angles at only about 3000 driveshaft rpms and it would snap 1350 ujoints like twigs, switched to 1410 and they bound even worse, ended up redoing everything to get angles calmer and problems went away. Looks like your working hard, Smitty. You also have to factor in driveshaft length- I attached some info I have went by for along time:
" When the transmission output shaft centerline and input shaft centerline are parallel, the u-joint operating angle permissible is length of driveshaft divided by five. Example: A short coupled driveshaft with a 15" length would be limited to 3 degrees maximum operating angle. A 30" shaft would be limited to 6 degrees.

DRIVESHAFT RPM

MAX. NORMAL OPERATING ANGLE
5000 3.25º
4500 3.67º
4000 4.25º
3500 5.00º
3000 5.83º
2500 7.00º
2000 8.67º
1500 11.5º

Did you consider gutting the stellings boxes , buying the long imco torsional shafts, angling the motors and running it that way (like a Imco), it seems to be the popular way to do it.
I used magnetic angle finders on both the crank button and Stellings flange and aligned motor till they numbers matched but I'm sure your already doing that, good luck, let us know how it turns out, Smitty

Thanks for the info Smitty.I spoke at length with a guy from Stellings. He claimed that 9* was the max and they regularly ran them in the race boats at 8+*. I really don't have much more room to go forward even if i wanted to. We can always lower the box down an inch if it causes a problem. We would prefer not to, but will if we have to.
Luckily this isn't a real high rpm deal. According to Stellings it should be no trouble at all. I guess we'll find out soon enough.Thanks Smitty.
Eddie

If we used the 3" up IMCO box, then we would have to move the engines up 3". the owner doesn't want big scoops. He would rather sacrifice the speed.
Eddie

Nice job Eddie. Thanks for sharing the pics.... Smitty are you an engineer? If not you missed your calling.

How are the Stellings boxes' design different than the Imcos?

how wil the move fwd affect the cg of the boat?

Yeah, Smitty knows his stuff. No doubt he is a very sharp guy.
The Stelllings boxes are adjustable vertically where the IMCO's are not. That is the biggest difference.


I spoke with Mike Fiore quite a bit about the boat. Originallly, he wanted me to shove the engines as far forward as i could and tighten up the drives to about 25" centers. The owner didn't want to give up the access in the front of the engine compartment. We are talking about moving them well over 1' forward. If that was ok to do and not mess up the CG, I can't imagine that 4.5" is going to affect it much. Not to mention, it's a big, heavy boat.
Eddie