Viper/Merc 150 Setup

Randy -

Hi. My name is Don Smith and I have an 1983 Viper with a 2001 Merc 150 stock. This is my second season with the boat and I enjoy it a lot. I need some help and some tips on how to get it to perform to its potential as I am having some handling problems. I have seen other Vipers perform a lot more smoothly than mine so I know there is potential.  I've seen Vipers run at 80 + so I know it can be done with set-up and experience behind the wheel.  It's frustrating because I cannot seem to get her to run the way she should.  I was amazed at watching Ronnie H from New York tear up the CT River last fall at 90 - 95 mph in his Viper. That was quite impressive. I know these boats are capable of more than 70 mph without blowing over.  

Here's the current set-up.......

I have a hydraulic CMC jackplate with about 5" of setback, Bobs Nose Cone with low water pick-up, torque tab, dual cable steering,  foot throttle, trim on the wheel, etc. Current prop is a 25" pitch Laser from Mercury. Max RPM range is 5000-5500.  

With driver alone, the boat handles terribly above 50 - 55 mph. The porpoise is prevalent most of the time and when I add even a modest amount of trim, the chine walking gets ugly.  I can get no where near WOT with driver alone.

With driver and passenger.....especially a bigger person, the boat handles better but top speed so far has only been a tad slower than 70 on GPS before the boat gets squirrely on me. I know that it has more but I can't get there due to the handling problems. Max rpm at almost 70 is about 5100 - 5200. Maybe I am running the wrong prop.  I would think that this boat with a V-6 150, should be capable of at least 75 and maybe a little more. What do you think?

It should be noted that I have 2 batteries and a remote oil tank in the bow. Some people say this is a poor set-up, others say I need the weight in the bow. Maybe this is part of the problem with the porpoise?

Are there better props out there that will help stabilize the boat at higher speeds? What about a chopper or cleaver?  Pitch?

Last summer, I ran the engine on the transom and the chinewalk was even worse.

This is a beauty of a boat but I want to try to get it to perform better at higher speeds if possible. Any suggestions?

Also, if there are other Viper owners out there who have experienced similiar problems or who have been able to get their boats to handle great, I'd love to hear from you.  (email me at


Don Smith III



A Viper and a V6, hard project you have there. First thing  get solid mounts in the motor if you don't have them. Then get those batteries out of the nose and leave one on shore. I'd get rid of the hydraulic plate as it will cause you more problems than it's worth. Once you get the magic height you don't need all the weight and set back. I'd run the motor on a two and one half inch plate and adjust it so the propshaft is 2" below the pad. If you keep the CMC then mark the plate when the motor has the propshaft 1 and 3/4" below the pad. Slightly higher because of the longer set back. For props I'd ditch the laser and buy one of the new Hydromotive 4 blade TX-4 props. I just got 2 of them and ran them Friday afternoon. They are very fast out of the box. Most importantly it is the easiest driving  prop I've driven. I ran one on my Allison 2002 at 114mph and they made a hard to drive 2003 Gransport Allison a nice boat again. I'm not trying to sell props for Hydromotive, it's just that the things work better that most any prop I've got in the last 5 years. On your boat good handling would be a plus. 

If you set it up with the propshaft as noted and put the battery in the rear on the port side, you should have a boat that will push 80. I'd get the 13 and 3/4 X26 prop like noted. The porpoise problem is a Viper thing. Hell, they do that with 115's on them. Trim down during slowspeed maneuvers and the boat will fly on the high speed runs. With the battery in the tail you don't need to use all the trim the motor has. Just trim it till it picks the nose up and just enough to keep it elevated. After you've mastered that set up, you can go a little faster with a nosecone, some more height, and some mild engine tuning tricks. For now learn to control the chine walk as any fast v-bottom has this. The set up here should make it easier. You will find that at the engine height noted you can do just about anything with the boat. Pull skiers, go fast alone or with passengers. So mark the jack plate in case anybody plays with the buttons. Keep it simple, go fast and have fun. 

Let me know how it goes.



Please submit whatever questions you have to  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.

Mark C.


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