Quote:
Originally Posted by Bigshrimpin
EZ . . . The simple answer is setup and weight  My old 225 mariner carbed engine was a 1997 and had the 1.75 ratio lower. Both 3.0L 225hp and 250 are closer in hp rating than you might think. The later mercury 225EFI's were known to dyno at 242hp. You can run those Rev4 props higher without blowing out . . . less lower unit in the water means less drag (and more rpms). See the Hijacker fixed jack plate on the back of my boat with the 225.
100lbs in the wrong place can slow you down a few mph. Every 100lbs extra will make your top end suffer. Waterlogged foam in stringers can add several hundred pounds.
T Tops can be the absolute worst performance killers!!! Poorly designed Tops will catch the wind and act like a giant parachute. Just picture a 4x8 sheet of plywood flying through the air at 40mph. Tilt the front of that sheet up 5 - 10 degrees into a 15mph head wind . . . what happens?
We are talking about 25year old motors. If we were comparing both engines using the exact same hull in a controlled environment then we could say more definitively that your 250efi was tired. 46mph is respectable with a 250.
Here's a video of my boat with a 1987 vertical reed chrome bore 2.4L 175. Running light the boat would tickle 43/44mph. Those 2.4L engines weigh under 400lbs. Early fingerported 2.4L 200hp horizontal reed mercs would dyno at 218hp from the factory. That vertical reed 2.4L was real strong too . . . I'd bet money that engine was over 200hp on a dyno (despite the sticker on the cowling) and had good bottom end torque. (here's a few mods for the 2.4L . . . https://www.chattanoogafishingforum....=39864&start=1)
https://www.youtube.com/watch?v=jg7cdv1w1vE |
You make an excellent point that few discuss.
We have engine trim and trim tabs.
We have jack plates.
We have prop design.
Nobody talks about T tops.
Why not?
I have not seen a hardtop designed like a chord or wing
if you will. Think about a cutaway of an aircraft wing.
Flat on the bottom and curved on top.
Wings do not create lift.
Air wants to remain constant.
Since the distance traveled on the top of the wing
is greater than the bottom, the air has to speed up
to remain constant in its mass.
When you have an increase in air speed
you create an area of low pressure.
The wing moves from the area of high pressure
to the area of low pressure.
This is called lift, which is just an easy way of explaining
Bernoullis principle of hydrodynamics.
A t top design where you could optimize the angle of attack
and lift with trim of said top.
This is usually where Denny chimes in and says
he knows just enough to be dangerous.
Now, certainly this opens up another avenue of design failure
and operator error, but it is intriguing.
Cheers,
GFS