-2 Imco
 

What are thoughts on going to a -2 lower? When would you and what circumstance would you not? Performance vs risk?
Saber 28 Cyclone twin Hawk 525SC's Bravo drives installing an XR gear set upgrade.

It's a proven performance enhancer on the Donzi 22C. Doesn't work on all boats as bow lift is decreased. The huge water inlet sends pressure through the roof and I welded up half of mine and reconfigured it.

Maybe the better question is what is the desired X Dimension or drive height to hull bottom for maximum speed. Is there a disadvantage to going with Shorties?

It really depends and only testing will tell for sure. Best case, I would expect would be maybe a 2-4 mph gain, but thats assuming the drives are deep to start.
If the props are too high, then it will be hard to get on plane and the props will blow out easily in rough water.
In some cases the props might not have enough leverage to carry the bow, but with 2 BBC's in a 28', I don't think that will be problem for you.

What is too deep?

The kav plate from my drive is nearly a bit under the hull from my Baja 275, when it is a bit trimmed!I think this is very deep and so i try next season an -2 sportmaster!
Michael

https://cimg3.ibsrv.net/gimg/www.off...daac3463b6.jpg

https://cimg7.ibsrv.net/gimg/www.off...79bcc15ac1.jpg
Brembofreak.
That drive is way to deep - when you trim your drive up the front of the cavitation plate actually goes down into the water coming from under your boat. This pulls the transom down.
I would go with a -3 IMCO drive and I wouldn't be surprised if you gained 10 MPH. Your handling should improve also. You will have to modify the back of the upper for 1/2 inch prop clearance IF you don't buy a complete drive. My first boat had the drive mounted that low and I gained 10 MPH just by going up 2 inches. I later installed an Alpha SS drive that is 2 1/2 inches shorter and gained another 10 MPH. 18 ft Glastron Carlson CVX 18 with over 500 HP and Alpha SS - mid 90's

Thats nice to hear and sorry for highjack this tread!
Boat runs now max 80mls +- and i am happy if i gain anything like 5 mls because i think also that baja mount the drives very low in the 275! the Outlaw models have the transom all higher!
I have new upper and build an -2 sporty that gets new gears,seals and a nice podercoating!!
Cant await the new season as i also mount an addon from mayfair!
Thanks!
Michael
https://cimg3.ibsrv.net/gimg/www.off...3ac5eb4f22.jpg

New Powdercoated!

You did not hijack things at all, this is the question I think a few of us would like to know. What is the correct depth for maximum performance.

It depends on the boat.
My 26 Daytona has the prop shaft at 2 inches ABOVE the lowest point on the hull. ( catamaran - so the lowest point is 12 inches forward of the transom on each running surface.
This picture was taken during setup - I believe final was up about another 1/2 inch.

https://cimg2.ibsrv.net/gimg/www.off...61568bd1bb.jpg

Again it depends on the boat but 8 inches is way deep. I would say normal is about 5 inches.
I think you could go with a -3 safely and worse case space it back down if needed. I would not go with a -2.

The picture depicted is not my boat but thank you. I will take any other input and expieriance as well.

That is really deep. Larger non stepped single V's need the prop deep to carry the bow, but that is really deep. I had my 28 Pantera at 4.75" below with a notched transom. I would go with a -2 since a -3 needs a different upper case or needs to have the regular case custom modified.

It really depends on the boat. With your 28 straight bottom V and the power you have, I would guess you want the propshafts at about 3" below the hull. That is just my semi educated guessimate though.
I would try and compare some similar hulls like a 28 Pantera twins and maybe the 28 AT twins (only 2 or 3 of them made). For reference, my 32 AT with boxes is about 3-3.5" and I'm pretty sure I could go to a -1 lower without issue. I remember somebody with an older 32 on boxes went to -2's and he had to switch to 5 blade props. Worst case if you go -2's is you have spacer them back down part way.

I go -2 because it is much easier to find.Have only 27 feet and straight v hull.
After hear your feedback i think this is a good working option..
With -2 lower propshaft is 5-5,5 inch under hull.
By the way,i use 28 lab Bravo and a Hydromotiv p5-x so not any problem to get on plan with this light boat and 662Hp.
I have new XR upper and this is what i use next season.For savety i buy direct and driveguardian with the blowerengine last year.
Michael

Great information, thank you!