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Steering Torque &
Rooster Tail
Randy,
First, thank You very much for your previous answers to my questions (Props for Merc 90). I tweaked the 14" x 30" thru
hub Mercury Cleaver as you suggested. I took off some cup and the
propeller really woke up. I gained 200 rpm on top end and even the
acceleration improved. Now it's very close to what the "2" blade
cleaver once was.
This time my questions are about boat setup. I've excessive steering
torque. My speed and acceleration are OK compared to other similar boats,
but I suspect that I could gain some speed by improving the setup. What
can I do for the steering torque? I have all the usual tricks people have
in their gearcases, a nosecone and a torque tab. I also have the engine
offset 1/2" to the port side according to boat's manufacturer's
instructions. With this setup the prop won't start to slip excessively
before blowing out. The 14" X 30" thru hub has less steering
torque than the 14" x 28" overhub, but there seems to be some
problem. Do you have any suggestions what I could do to get rid of the
steering torque? Would cutting the prop diameter help?
Now for a roostertail issue. Right now I have a CMC hydraulic jack
(5.5" setback) and additional 2" setback and it seems that I
have negative trim angle with this setup. I used to have a bit more
setback (total of 9") and this resulted to 0 trim angle, but the
speed was equal. My rooster tail is 1.5 to 2 times as high as my 20"
motor. Most people seem
to have rooster tails as high as their motors. Am I loosing hp to air as
I'm throwing lots of water to the sky? What could I do to the rooster
tail?
Regards,
Larry
Larry,
Your boat sounds like its getting better. The torque problem and the
roostertail are really the same problem. Solve one and the other goes
away. Cutting diameter at this time will most likely make it worse. If the
rooster was nonexistent then I say yes. Based on your set up description,
I'd try lowering the motor 1/2" at a time 'till the torque goes away
or the speed drops. You may find the RPM drops slightly but your speed
went up. If this happens then you found the magic engine height. Going
higher and higher with height is not always faster. All boats have a sweet
spot. If this doesn't work then, if it was mine, I'd look at the gearcase
shape. If the nosecone or tab are not shaped right what is happening to
your boat is pretty much the norm. To verify borrow another gearcase and
try it. If it's better, then you know. You're very close on this so go
slow and look for changes from
small improvements to your setup. Lastly make sure all nose weight is out
of the boat.
Randy
Please submit
whatever questions you have to IHRTechTalk@yahoo.com.
All questions and answers selected will be displayed on this page as they
come in. Note: though all boaters are welcome, priority may be given to
I.H.R.
members. Randy can not be held responsible for any advice
given. Though his information and expertise is second to none, he
has no control over what you do with your boat. It is up to you to
boat safely and act responsibly, and his advice is only to be used as a
guidance for your high performance boat/motor of which you are the one
responsible for the risks involved.
Thanks,
Mark C.
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