Extension box?
 

I have a question for the extension box experts. I'm running ITS boxes on my Formula. The ITS box has a 7" offset vs 12" on an IMCO. I believe that the general consensus is that on the imco the water will rise 2" by the time it hits the drive. By this I mean when the water leaves the hull, it will come up 2" by the time it gets to the prop. If this is true, I'm assuming an ITS box would have a 1.2" rise? Would everyone agree with this?

I'm going with IMCO -3's this summer, last year I was 5" below the hull with a -2 set up and I was still too deep. -3 will put me at 4" below which I would think would be optimal on my boat.

Thoughts?

I have tested many stand off boxes. 12" box is closer to 1" lower. There are so many variables, speed, angle of boat when running, spacing of drives,ect.. Most boxes will give you the option to bolt gimble at different heights. I found the major benefits to a box was control when you trim up or down the boat responds better, like a larger breaker bar more leverage.

Are you referring to the actual measurement of the box and the propshaft to the hull? I'm talking about the water coming back up due to displacement of the boat. I agree that a lot has to do with a variety of factors, but on average, I thought it was 2" for 12" box. If it's only 1" for a 12" box, that is better than I thought.


I started at 7.5" below the hull with no box, with box and -2 I'm 5", with -3 I will be at 4" below.

I set my boat up,bravos,a 2" spacer added,then put my boxes so w/ the spacer prop shaft was 2" below the bottom of the hull.the control was awesome,I could put the nose of the boat,up or down quickly.It was easy to plane this way but not the fastest set up.
I took the spacers out and yes the boat is faster,,but and a big but,,the boat likes to fly more,,which means,,in rough water,its not as fast as when the drives are deeper.of course the videos now are better,,more hang time.
this summer the spacers are going back in.
I also have 380 kplanes.

A up 3 box will net you 2". water rises 1" at 60+ mph, more at slower speeds

I think it all depends on the hull and speed.
I had this conversation with Dave Wesseldyke and his answer was at speed the water doesn't come up much at all.
I was at 7/8 inch above the lowest part of the hull bottom without the box ( with the -3 drive ) and then added the neutral box ( but installed it 1 1/8 inch higher )
Running the same prop the boat is harder to get on plane but the speed and handling is much better. My slip numbers are low ( < 5 % ) at top speed but my cruise speed is slower at the same RPM. I also can't stay on plane at the same speed I used to unless I trim the drive way down. ( I have a lot more negative trim than stock)
I have been told by BBlades that my boat is one of few 26's that can run my combo and have it work.
Right now I am running an OLD Bravo 28 that is stock.
I bought a labbed 30 from BBlades but haven't run it yet.
I have a 28 Maximus that the boat DIDN'T like that is going to BBlades to make it friendly to my boat.

My info is on V-Hulls

Class6
I agree with what You said. I have heard the 1 inch from many people. BUT the faster you go the less the rise. Also the faster you go the less the boat sinks into the water.

and another factor is how rounded or sharp were the bottom of the hull meets the transom. A rounded edge the water will curl up against the transom. A very sharp edge will release the water at that point and IMO will probably be a 2 inch rise. Other factors play in the mix that was already mentioned.

Gopro off back of boat to see where drives are in relation to water while running top speed? If hard to measure, maybe some bright paint marks that are measured out on frt or side of drive ?