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I would set it at the height that will make the drive bullet sit on top of the water coming off the bottom at speed.
my Daytona is set up this way at +2 inches using a -3 IMCO shortie and an IMCO neutral ext. box. At speed the water coming under the boat goes under the gear case bullet. I even had to lower the water pick up to just in front of the skag. I also cut the bell off the back of my prop. This made a noticeable drop in the stern. and I agree that the closer the gear case gets to the surface the more it wants to surface causing a bow down attitude. |
Page 21 post 206 (adjustable extension box pics)
https://www.offshoreonly.com/forums/...iesels-21.html Guessing you know that the stelling boxes are adjustable up and down so the perfect drive height can be acheived, Also they are nla. No reason imco boxes couldnt be modified to accept the rear hangar for a driveline and no reason the boxes couldnt be mounted on custom plates/short boxes that would allow for the boxes to be adjusted up or down a few inches The extra weight of those parts would help balance, plus the mercury driveline still uses the rubber coupler Unlike the stellings so no extra abuse on the drive. More money to go custom and adjustable on the front end of this build rather than nasa level math for a one shot Hope its right x dimension and with no spacers have to recut and rebuild an inch in either direction later |
With the prop shaft parallel to the bottom of the boat my bullet/gear case is in the water. About 1-1.5”
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I can’t find any used boxes. IMCO and ITS from mercury Racing is it. I think I need 2” maybe 2.5” to be correct. I hope 3” will work so I don’t have to redrill. |
I have done a lot of research on the blackhawks amd they run best when bullet is out of the water so You want to go higher as your now even whig the bottom problem whit this is that You have less leverage to Carry the bow but the black hawk is not designed to Carry the bow the hull need to have natural bow lift build in so might check if your hull has decent rocker in the bottom |
Originally Posted by bor
(Post 4659919)
I have done a lot of research on the blackhawks amd they run best when bullet is out of the water so You want to go higher as your now even whig the bottom problem whit this is that You have less leverage to Carry the bow but the black hawk is not designed to Carry the bow the hull need to have natural bow lift build in so might check if your hull has decent rocker in the bottom |
2 Attachment(s)
Here is a drawing I made when I figured the X on my 20 Cigarette. Unfortunately I have not run it yet. But yes I think the gearcase needs to be above the bottom.
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I did my blackhawk on my 20 with an ITS, it sits back8 inches which is approximatley 5/8s of an inch lower, i set my X at 17 3/4 and it rides like a dream.. nice and flat at 86 mph so far.https://cimg3.ibsrv.net/gimg/www.off...8b6bbc1b0d.jpg
https://cimg5.ibsrv.net/gimg/www.off...6df315dd4c.jpg |
but totally different app - not an apples to applies comparison here. Lite weight narrow short single vs far from this 29 twins and full cabin. The props are important for blackhawks as well.
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the question was about a box and the difference in the drive height and I answered it. every 12 inches you take a drive back lowers your X dim by an inch as well as changes the COG. of course props make a diff, i have multiple sets of 31s, 29's and sold my sets of 27s. the set on now was done by cutting edge and hit the 86 on its first run with minimal trim and less than 5k rpms, at 5800 it will be 100 plus.. I nailed the X dim perfectly.
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