Hi Randy, I have just purchased an 86 vector in
mint cond. with a 94 135L Merc. It has a land & sea nose cone, solid
mounts 8 in. hydrodynamics jackplate, foot throttle, wheel mounted trim
& factory trim tabs. The engine has cc heads, stacks, plastic reeds,
exhaust tuner & was re done less than 100 hours ago claiming 150 to
160 horsepower. I have set it up according to the info
from this site and it is much more manageable now. It runs very solid
& controllable up to about 65. At 70 I can only stay there for a
minute or so before getting hairy. I am using a laser II 3blade large
hub.25 pitch. It looks like someone sharpened the leading edge.
Seems to slip a lot and runs about a 3 foot high rooster tail. Rpm at 70
(on the speedo) is about 6600. It seems like thatís all there is. The
prop shaft is set at 1 inch below the bottom. Is the jack plate necessary,
how do I find out what the gear ratio is? Iíve been told there are 2 possibilities.
What is the potential for speed with this motor. I also have a 4 blade
trophy 23 pitch, and a solid hub prop that has very sharp edges and
round ears. 24 pitch that I got with the boat. Any suggestions would be
greatly appreciated. Thanks for your time
Sounds like your boat is actually running quite well. You may be a little under propped, but the thing you are experiencing is what we call chinewalk. Not to be the bearer of bad news, but this is controlled by the nut behind the wheel. And contrary to what you may have heard, you cannot drive through it, as it only gets worse the faster you go. This is perfectly normal. It is what happens when the boat is reducing its wetted surface and responding to the torque and conditions it is being operated in. It is up to you as the operator using corrections in the wheel to control this chinewalk, and make the boat run flat and level. The only way to reduce chinewalk without these corrections is to slow down. I try to teach my customers how to gain this balancing act by driving at the speed at which the chinewalk just starts to occur. Then, for instance, when the left side of the boat drops down, turn the wheel slightly to the right and then back again in a very sharp movement. Do the opposite when the right side goes down. Eventually when your timing is right, you will learn to anticipate these movements, and balance your boat with the steering input. When you have mastered controlling the chinewalk at reduced speeds, slowly work your way up, as when the boat is flying level, the speed increase you will experience will be a lot more than you anticipated. A rig like yours running a 28" or 30" propeller will run in excess of 80, but you must manage the chinewalk first in order to get the speed that is already there. Last, do not try to drive faster than you are capable of controlling the chinewalk, as you will not learn a thing. This whole thing is all about timing, just like riding a bike when you were a kid. Once you have worked your way up, you will find that your boat will do things much more easily and then we can work on setup and things that will enhance it's performance even more. Don't be discouraged, just practice.
For your information, unless your motor was ported, the powerband of that motor is closer to 6000 rpm and turning at 6600 plus is actually making less power than if we held the rpm down with a bigger prop.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.
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