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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