Stand Off Box and Lift
 

School me

how do stand off boxes like merc ITS, IMCO ext. and drive length effect transom/ bow lift

or what can do you do to them to increase or decrease lift ?

also keep in mind if you hang a box you need to go up one inch for every foot you go back, maybe more pending your current X dim.

I put a 12 inch neutral IMCO box on my Daytona but did a bunch of other stuff at the same time.
I raised the X 1 1/8 inch, installed an IMCO -3 outdrive and 598 CI engine.
adding an extension box without raising the X is going to put the prop deeper in the water.
Raising the prop will cause transom lift. The closer the prop is to the surface the more transom lift you will get.
I had to cut the bell off the prop to help negate the transom lift. My prop is FULLY surfaced as in the water goes under the prop hub at speed.

when you say raising the prop will cause transom lift,
is this in relation to any change? prop depth VS X
why is this? - in lamin terms if you don't mind. i'm googling warrior it ,
i was under the assumption that a deeper prop would want to ' climb' out of the water - lift - and a shallower one would have less "bite" due to dirty water

so if someone was to just put a box on the back of their boat - no X or leg length change - it on its own wont create more lift, just leverage?
no i didn't do this, mine came set up at the factory, just trying to understand what effects it has on the way it runs

The closer the prop runs to the surface the more it wants to surface.
Installing a box actually lowers the prop in relation to the water. Yes it increases leverage to lift the bow, It puts the prop back in cleaner water. The prop, the bell on the back of the prop and the bullet of the lower will act as a ski IF you raise the drive high enough. Mine did this and I had a BAD episode of this to the extreme when I ran the wrong prop without knowing that I had to drive the boat different with that prop.
CATS are not easy to drive like a V bottom is. I had to learn all over again how to drive my Daytona. I am still learning.
I cut the bell off the back of my props and it greatly settled the transom to the point that it was very noticeable to me.
Doing this has side effects that can make getting on plane more difficult. ( it aerates the prop )

hmm, i guess that makes sense that it wants to climb out of the water - i guess rake and cup on a propeller play into that as well as the defuser ring?

right now from the bottom of the v to prop center line im at 4.75/5". from what I've read this is pretty normal when transom mounted but with the box it making it "deeper" is their a rule of thumb on set back/ dept added with calculating?

That's why i stuck with a V for my first real go fast boat, Cats next once i get this boat sorted out haha

I always wanted a Daytona but felt that I couldn't afford one. I spent a TON of money TRYING to get a V to go fast.
I wish someone had told me to buy a boat built and designed to go fast rather than dump a ton of money into a so called fast hull trying to get it to go fast.
Set up is more important on a cat IF your goal is to go fast. Small changes can have drastic results but with proper setup can add a lot of speed and still have a boat that handles well and hooks up well.
I am very happy with the changes " I " made to my Daytona.
I have my boat going 10 to 15 MPH faster than boats set up by the professionals using the same HP.. 4% slip Some have said BS at that number but it is fact. It can be done IF you spend the time and money.
I still have more to go. I changed some things on the EFI and don't have the settings right yet because of work hours this year.

i know i' near the limits of what a 25 foot v hull should be doing. the body of water i run on is just better suited for a v hull, a cat would spend more time in the air or idling back to the doc due to the weather we get sadly

im at 13% slip right now at my current set up

did some reading and from what i gather 12'' back is about the same as one inch deeper?

so with the ITS being 7'' set back. id be about a half inch deeper?

thinking im going to try and shorty and see how she does, out drive needs a rebuild anyways and even if it doesn't help with the lift or lean it should be faster with the better hydrodynamics