I'm geting ready to instal my standoff boxes and # 3 gimbals on my 43 Scarab thunder. Does any body have any information on the prop staft to crank centre distance on a # 3 drive and any suggestion as to a suitable X dimension. I am looking to set up a decent alround performer . I want to be able to plane with a full load and see some decent speed . Any thoughts would be greatly appreciated.

Thanks Rick G.

Rick,

I have the service manual open in front of me. SSMIII has a Crankshaft to Propshaft dimension of 24.31" The supplemental manual for the IIIA lists the same exact dimension, in case you were wondering. If you ever wanted to upgrade using the same transom assembly, the IV's and V's come in varying lengths from 18.7" to 21.7" in one inch increments.

I have a single SSMIII on my boat, and it is mounted with the propshaft around 6" below the keel. It could definitely be mounted higher nowadays with 4+ blade props. If you are setting up twins, I'd target them 3" below the running surface, unless you have a transom notch or extension boxes, in which case, a little higher would be good.

Tullio

Thanks Tullio. I have both a notch and boxes. The boxes are about 8 " to 10 " and the notch pretty much ends where the drives will sit , maybe 4 " depth in front of the drive. So I am guessing you think the prop staft should be set 2 to 3 inches below the hull line.That would translate to an X dimension of 22.31 to 21.31 inches. Thanks that great info and a good staring point. I wonder if anybody else has had any experience with twins in this situation.

Rick G.

Before you start derigging you may want to find the present CG.Then calculate for the overhung load caused by the boxs to find the new CG point.The motors will probably have to go back.Next,if you have two cylinder steering you may consider four cylinder steering.The extra cylinders serve as gussets to the transom as well as reduce stress on the drive.

Ccando the boat is already derigged. So I'm not sure I can figure out the original CG. The boxes have steering ram mounts incorporated into the box level with where the gimbal mounts so I'm hoping that there will not be any excess stress on the drive. As for the motors it was my intension to mount the motors and trannys right up to the boxes via a drive coupler that way the motors would be as far back as they could go . I figured given the weight and lenght of the boat the farther back the motors the better.

Do you have any thoughts on drive height or X dimension . Any insight would be helpful.

Thanks Rick G.

Rick,are you changing to #3 drives from another model?You have said the motors are all the way back at the transom.Are the transmissions plug in or drivline?If they are plug in,how are you going to couple through the boxs? These questions are relative to the X solution.

Sorry CcanDo Idon't understand the difference . What is a borg warner tranny drive line or plug in. If the borg warner is plug in then I beleive it will be a drive line style tranny as the box has a flange to which I beleive a drive shaft must couple to. Forgive my ignorance this type of set up is new to me and I'm learning as I go along.
Thanks Rick G.

New twist to the propblem . It appears that I will propbaly not go with the extension boxes as one of them is all cracked to bits in the internal webing and not something I want to patch and reuse. So now the only factor to consider is the small hull notch. Brian on another board suggested that without the box I run the drive height with the prop shaft 2 inches below the hull line . Any thoughts.

Thanks Rick G.

set the x a little high you can always put more blades on the props or add a spacer. if your too deep your are screwed.
do a lot of research befor you cut the holes. 3,4 5 &6's like to
be run higher than bravo's .

Everything I have read or been told reffers to the cavatation plate beitng level with bottom of the hull directly in front of the drive. I am guessing that this would put the prop shaft on # 3 drive about 4 inches below the hull. From what is being suggested here that seems way too deep.

Rick G.