No announcement yet.

Porpoising problem

  • Filter
  • Time
  • Show
Clear All
new posts

  • Porpoising problem

    I have recently bought a 1991 Classic 191 with a 140 Johnson. I have to run the motor trimmed all they way down or it will porpoise badly. I can't even trim it up an inch without it porpoiseing. It has a bait well built on to the back of the transom on the port side. I was wondering, if I added another baitwell to the starboard side would this help or cause it to be worse? I was also thinking about adding a stingray hydrofoil to see if this would eliminate the problem. Has anyone used these? Do they work? Any suggestions would be appreciated.[?]
    Doug[br]Montegut, LA

  • #2

    I was wondering, if I added another baitwell to the starboard side would this help or cause it to be worse?

    Yes it will make it worse. I take it the boat doesn't have trim tab's?

    I'd suggest a set of Bennett M120's for that boat.


    • #3
      Have you given any thought to adding trim tabs? They will most likely stop your problem and will come in handy in a lot of other scenarios.


      • #4
        It does'nt have trim tabs. I would have to remove the baitwell to install them and before I did, I wanted see what my options were.
        Doug[br]Montegut, LA


        • #5
          Yu could try different props, the stingray hydrofoil, and a few other gadgets that might solve the problem. But, the trim tabs definitely will solve the problem. All cost money, just a matter of where you want to spend it. A cheap solution may be to adjust the motor mounting level and see what happens. If your local prop dealer is kind enough you may be able to test a few different props to see how the boat reacts.

          Whatever you decide, let us know the results.
          Artie Sutherland[br]Rude Attitude -\'76 Mako 25 CC. - SOLD[br]1976 Mako 21[br]2002 Yellowfin 31 - 300 hp Suzukis[br]Gulf Coast, Mississippi[br]


          • #6
            You could also try wedges to trim down further.
            Richard[br]Miami[br]Pearson Flyer 30


            • #7
              I bet that baitwell is exaggerating the problem. I would ditch it, add trim tabs and add a baitwell just infront of the console.

              PS - 1991 was a great year for Mako. I have owned two 1991's and both are extremely well built.


              • #8
                The porpoising effect of your boat may be better explained as prop slip. What is happening is that when you start to trim your motor up, this pushes the bow higher in the air and the boat picks up speed. But the weight of the bow soon exceeds the lift of the prop and the bow drops causing the prop to slip or cavitate losing speed, starting the cycle all over.

                Your prop is to high out of the water when you trim up. I would try to drop the motor one hole space and test drive your boat. You may even need to drop it two holes. Has far as my experience with Sting Ray foils, this is nothing but more drag in the water thus slowing down your boat. For something cheap to try…. Try dropping the motor first. If that doesn’t work then spend some money.
                01\' Mako BayShark 2100[br]200 Optimax[br]Lakeland Fl.


                • #9
                  OK, I have been there and done that. It was on a 16' Scout with a 75 Mercury. This boat did not have a problem with a 90 on it but mine with a 75 did exactily what yours is doing. I did everything that has been stated and more. I did solve the problem and I will tell youhow I would solve yours.

                  First some questions. Is the livewell on the back flush with the bottom or is it up a little if it is up then it is not acting like a one sided trim tab, it just throws the boat off balance. So it is not the problem. Trim tabs wiil solve the problem and if you went that way I would use the Lenco electric tabs. They are the best for this size boat and very easy to install.

                  Now, what did I do to solve my problem and how would I solve yours.

                  First make sure the engine is proped right. That is, does it top out in the right RPM range for that motor. Get a good prop shop to help you do this.

                  Next, I think you might have a tired motor that does not put out enough HP to push the Mako. The factory spec for that year says the hull weighs 1900 lbs and recommends a 150. Thats is 1900 lbs without 60 gallons of gas and ice and tackle and people and more gear. The basic problems is that the motor gets the boat up and then runs out of HP and it falls down and then does it again (porpoising).

                  The next thing that I would check is that the motor is mounted correctly, look at the cavitation plate (the big plate on the motor just above the prop) with the motor trimmed all the way down it should be even with the bottom of the boat plus or minus a half inch. If this is ok then wego on to one of two fixes andmaybe both. The next easiest is to put on the motor what some call a sting ray or whale tail or a Bob's cavitation plate or I think the best choice a Cobra Stabilizing plate. I tried all of the plates made and listed above and the last one was the best. If you want one of the ones that don't work I still have them. All of the plates are designed to give more area to the factory cavitation plate so that it can put more up force on the boat. That is not a good explaination but itis good for now and it will work for you. If you go to

                  Here at Cabela's you will find the plate I speak of. It is all stainless steel has the least drag of any of the others and also has the most surface area to work with. Let me very clear I have tried ALL OF THE OTHERS and this is the BEST ONE.

                  Now the other trick is to buy what are called wedges and put these between the motor and the transom. What the will do is let you trim the motor down further then it does now. I did this on mine and it did help, but I believe that it was because Scout built the boat without enough transom angle to start with. I do not think this is the problem with the Mako.

                  So go to the propshop and make sure that is right. Then call Cabela's and order the Cobra plate and solve your problem. In fact I would get the Cobra plate first and then worry about the prop latter.

                  I will guarantee that this will work and if it does not I will buy the Cobra plate from you
                  Alabat - Cajun for \"Hey over there\"[br]1973 - 17 Mako Angler 115HP Suzuki[br]Houma, Louisiana[br]Home of the best Red fishing in the world


                  • #10
                    Something still isnt right. You should be able to trim up, at least to some degree, without porpoising.

                    My first guess would be engine height.

                    Second would be the prop...what kind of wheel are you running, and are you propped right? If the prop loses bite as you trim up, you lose lift and the bow drops.....perhaps a wheel with more cup?

                    Lastly, you could possibly have a 'hook' on the transom from improper trailer setup. Put a straight edge on the bottom and make sure its straight, particularly just before the transom. This would cause the symptoms you are describing.

                    A doel-fin or the like may help your problem, but its not a fix. Its not going to allow you to trim up, which you should be able to do. You need to investigate the above before you give up and put a fin on it!
                    1990 261 T/2001 200 HPDIs[br]Basking Ridge/Mantoloking NJ[br]


                    • #11

                      As mentioned, you've got a variety of problems. The good new is that they're easily fixed. Do you have a T-top? Many folks dismiss the impact a top has on a boat. Now some suggestions:

                      1. Remove the baitwell and start from there. That baitwell is in a terrible place -- it's impacting your ride.

                      2. Engine Installation. Is the engine properly rigged -- you won't believe how many engines are mounted improperly. With the engine trimmed down, the cavitation plate should be just above the keel.

                      3. Right prop? With the baitwell gone and after you've ensured the engine is properly mounted on the transom, determine your max RPMs with your current prop. Get you're normal load on board, say two adults and a full tank of full -- now go for a ride. If you're engine is rated for 5,500 RPMs at WOT, and you're getting 6,000 -- you need a prop with more pitch. If you're only getting 5,000 RPMs, get a prop with less pitch. If you're 2-300 over or under -- that's fine.

                      4. If you're not able to get near the magic RPM range with a reasonable prop, you may have a performance issue with the engine -- get your mechnic to check it out.

                      5. If the boat is now running well and not porposing -- GREAT! If you're still having problems, look into geting a pair of trim tabs. They will do a lot to smooth out your ride - get them anyways.

                      5. If you're deadset on having that baitwell, move it into the cockpit; preferabley centered behind the leaning post. Water weighs 7lbs/gal; if your tank is 20gal, that's 140lbs hanging off one side of your boat in the worst possible place.

                      Follow these recommendations in order and that should help smooth things out.

                      Good Luck,

                      Prop Blast[br]Mako 224, F225[br]Tampa, FL


                      • #12
                        Makorider, in some cases a cavitation plate (Cobra, Dolefin, etc ) is a fix. Just as trim tabs would be a fix. As I said I went throught this exact same problem with a previous boat. yes it could be a hook in the hull also, but that would require some other work. What we have not heard is if this problem was evident when he bought the boat or what changed since it was bought.
                        Alabat - Cajun for \"Hey over there\"[br]1973 - 17 Mako Angler 115HP Suzuki[br]Houma, Louisiana[br]Home of the best Red fishing in the world


                        • #13
                          Hopefully, not getting too technical, porposing is caused by a relationship between the lift of hull, the trim of the boat (boat steady state pitch) and the deadrize. Obviously, the center of gravity of the boat, boat hull modifications, engine configuration (height, cavitation plates, props) can effect the trim of the boat and could cause the problem. My guess is either the CG has been moved back somehow, or the engine is mounted too high. Hope this helps. The diagram below shows the relationship (CL is Lift Coefficient, Beta is the Deadrise angle).
                          72\' Mako 22\'[br]NoNeck, VA


                          • #14
                            There you go again. taking a good subject and making it into Rocket science. Change the name of this thread to "How to get from Porposing to Rocket Science in less thatn ten post"[][]

                            Thanks MakoShako that is a good tech explaination
                            Alabat - Cajun for \"Hey over there\"[br]1973 - 17 Mako Angler 115HP Suzuki[br]Houma, Louisiana[br]Home of the best Red fishing in the world


                            • #15
                              [:0][:0] "Prismatic planing hulls" ... [:x)][:x)] Ok, I'll bite... what in tarnation is that?
                              Artie Sutherland[br]Rude Attitude -\'76 Mako 25 CC. - SOLD[br]1976 Mako 21[br]2002 Yellowfin 31 - 300 hp Suzukis[br]Gulf Coast, Mississippi[br]