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Pontoon Engine Size

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  • Pontoon Engine Size

    Well, my wife threatened to make me sleep outside in the rain if I didn't take the deal so guess what? You guessed it!!! I TOOK THE DEAL!! lol

    Just purchased a used 18ft pontoon with hard top that needs a little TLC. It came with a 1987 Johnson 70 hp VRO installed on it. We took it for a test ride & the engine runs very good. Wide open throttle appeared(?) to be around 30 mph (guessing) since it doesn't have a speedometer installed or a tach. It WILL have very soon. At least a tach for sure. Power trim & tilt works great too although I have no idea if trim & tilt is really needed on a pontoon as I have never owned one. My question is simply this. Is 70 hp "too much" engine & is trim & tilt really needed? I have a good running Johnson 50 HP with trim & tilt on my 15ft bass boat that I personally think would be a much better engine then the 70. Again just guessing about this.

    I do not plan on towing skiers or having more then 6 people aboard at any time & bought it too just "putts around" the lake & fish out of. Any advice would be appreciated as always. Thanks in advance.


  • #2
    Re: Pontoon Engine Size

    On an 18 footer you are either at or very near the upper limit for maximum rated horsepower. That said, you are probably not going anywhere near 30 MPH although anything is possible. I would guess that combo would run in the 23-25 MPH range. With a 50 HP motor that combo would likely run in the 19 - 22 MPH range. Since pontoons are not planing hulls, more power does not necessarily translate to substantial increases in speed. It does however, translate into much higher fuel consumption so from that standpoint, the 50 would be more economical since pontoons don't generally run wide open very much anyway. I have an 18 foot Misty Harbor powered by a 40 Suzy 4-stroke and am very happy with the performance and economy. As for trim and tilt, it is just as important on a pontoon as it is on a boat. Shallow water requires tilting the engine. A slight nose high attitude makes a considerable difference with a pontoon.

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    • #3
      Re: Pontoon Engine Size

      Originally posted by Silvertip View Post
      On an 18 footer you are either at or very near the upper limit for maximum rated horsepower. That said, you are probably not going anywhere near 30 MPH although anything is possible. I would guess that combo would run in the 23-25 MPH range. With a 50 HP motor that combo would likely run in the 19 - 22 MPH range. Since pontoons are not planing hulls, more power does not necessarily translate to substantial increases in speed. It does however, translate into much higher fuel consumption so from that standpoint, the 50 would be more economical since pontoons don't generally run wide open very much anyway. I have an 18 foot Misty Harbor powered by a 40 Suzy 4-stroke and am very happy with the performance and economy. As for trim and tilt, it is just as important on a pontoon as it is on a boat. Shallow water requires tilting the engine. A slight nose high attitude makes a considerable difference with a pontoon.
      Thanks for the reply Silvertip. If I understand you correcty, are you saying I would be much better off with a 50 hp running WOT then I would the 70 running WOT? I am not looking for speed to begin with & feel like a 70 is a little too much for the pontoon. I have a 15ft Glassstream bassboat I would much rather have the 70hp on & put the 50hp on the pontoon boat. I am looking for ecomony & just want to ride around, enjoy the views & fish. My son can use the bassboat with the 70hp since he has the need for speed. I think that would be a much better combination then the way the pontoon boat is setup now. For what I paid for it & since it already has the 70 on it, I couldn't pass the deal up.

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      • #4
        Re: Pontoon Engine Size

        I'm not suggesting you are better off with the 50 over the 70 from a performance and economy standpoint because nobody on this forum can tell exactly what your priorities are. What we can do is tell you what happens when and if you make the switch. Only you can determine if the data presented is right for you. So here is what happens:

        Fuel Economy: An outboard motor in the ranges you have will burn fuel at a rate that is 10% of rated horsepower. So a 50 HP motor will burn roughly 5 gallons of fuel per hour at wide open throttle and a 70 HP will burn roughly 7 gallons per hour at wide open throttle. Since a 70 HP motor is 40% larger than the 50, you do not get a 40% increase in speed. So from a pure gallons/hour basis, the 50 HP is a no brainer. However, the 70 will be a tad faster so if you are on a really large body of water, speed to outrun a storm can make or break a trip. Since no two boats are identical in performance, a 70 HP engine on your 'toon may actually burn nearly the same amount of fuel for a given trip as the 50 because it doesn't have to rev as high (less throttle opening) to achieve the same speed the boat would have with the 50 running wide open. So you see -- things need to be looked at from multiple aspects. In car terms, I drive an Impala that routinely gets 28 -30 MPG with a V6 and its a nice roomy, comfortable car. I could drive a smaller car with a four cylinder engine and maybe squeeze 34 MPG out of it and not be nearly as comfortable. In this scenario, if one is putting on a gazillion miles a year (as I am not) then the four cylinder makes economic sense. Otherwise, I'll take comfort over MPG when there is such little difference. The long and short of this is on a pontoon you don't need lots of power unless you want to tow water toys and water ski. I'm in Minnesota and we are blessed with many very large lakes. Pontoons in the 18 - 24 foot range are almost always powered by 40 - 60 HP motors.

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        • #5
          Re: Pontoon Engine Size

          Originally posted by Silvertip View Post
          I'm not suggesting you are better off with the 50 over the 70 from a performance and economy standpoint because nobody on this forum can tell exactly what your priorities are. What we can do is tell you what happens when and if you make the switch. Only you can determine if the data presented is right for you. So here is what happens:

          Fuel Economy: An outboard motor in the ranges you have will burn fuel at a rate that is 10% of rated horsepower. So a 50 HP motor will burn roughly 5 gallons of fuel per hour at wide open throttle and a 70 HP will burn roughly 7 gallons per hour at wide open throttle. Since a 70 HP motor is 40% larger than the 50, you do not get a 40% increase in speed. So from a pure gallons/hour basis, the 50 HP is a no brainer. However, the 70 will be a tad faster so if you are on a really large body of water, speed to outrun a storm can make or break a trip. Since no two boats are identical in performance, a 70 HP engine on your 'toon may actually burn nearly the same amount of fuel for a given trip as the 50 because it doesn't have to rev as high (less throttle opening) to achieve the same speed the boat would have with the 50 running wide open. So you see -- things need to be looked at from multiple aspects. In car terms, I drive an Impala that routinely gets 28 -30 MPG with a V6 and its a nice roomy, comfortable car. I could drive a smaller car with a four cylinder engine and maybe squeeze 34 MPG out of it and not be nearly as comfortable. In this scenario, if one is putting on a gazillion miles a year (as I am not) then the four cylinder makes economic sense. Otherwise, I'll take comfort over MPG when there is such little difference. The long and short of this is on a pontoon you don't need lots of power unless you want to tow water toys and water ski. I'm in Minnesota and we are blessed with many very large lakes. Pontoons in the 18 - 24 foot range are almost always powered by 40 - 60 HP motors.
          Thanks Silvertip. "NOW" I understand fully what you mean. Like you said, the 50 is a no brainer especailly for what I intend to use the 'toon" for & since the lake I will be using it on is a small lake (10 miles long at most), the 50hp is all I will be needing at best. At my age I am not into the need for speed & even if a storm happened to come up on the lake, there are plenty of coves that I can get into & ride it out if I have to.

          As for the size of a pontoon boat?? I thought (there I go again thinking) I read somewhere on the forum that you acutally measure the size from the tip of the pontoon to the rear of it. Is that correct or not? I was told the one I just bought is an 18ft but the registration states it is a 20ft. Can you tell me the correct method of determining the size? I "thought" it was measured by the size of the decking but really don't know. Thanks again for all your help & information.

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          • #6
            Re: Pontoon Engine Size

            there are a number of measurements tossed about:

            Package Length: overall length from tail end of the motor to the tip of the pontoon.

            Deck Length: Length of the actual deck only.

            Pontoon Length: Length of the pontoon tubes from rear to tip.

            The confusing thing is that many pontoons have a foot or so of tube sticking out the rear and as much as two feet sticking out the front. If that is advertised as a 22 foot pontoon, it would likely have a 18 or 19 foot deck. My Misty Harbor for example has the deck the same length as the pontoons. It is a true 18 footer and in this example would have nearly the same walk around space than the 22 footer. The model number usually denotes the length. So use a tape to measure the deck and the tubes. Whichever measurement matches the model number is what you have.

            Comment



            • #7
              Re: Pontoon Engine Size

              Mine is a 1986 Riveria Cruiser. I'm still trying to find the model number for it. I have the registration card but all it tells me is the mfg certification number. The actual finished size of the deck is 8X16 but the tubes stick out at least 2ft in the rear & 2-3ft in the front. The NC registration has it listed as being 20 ft in length so I am not sure how they came about that mesaurement unless they are counting the tube length. I did manage to find out that the Johnson 70hp engine is the maximum size engine it is rated for. It has a 13.75X15 prop on it now with power trim & tilt & runs really well. All in all the 'toon is in excellant shape & has been stored out of the water inside a covered lift for the past 4 yrs up until this past July. A newer engine ('87) was installed as the Johnson 60hp that was originally on it has frozen up.

              My biggest problem now is trying to find a good used trailer to get it home on. Trying to locate a good used one "reasonably" priced is very diffucult right now in my area. I'm looking for a "lift" trailer but they are hard to find. At least within 200 miles of me. Again, thanks for all your help.

              Comment



              • #8
                Re: Pontoon Engine Size

                VaGent, where are you located in NC. I know of a couple of dealers who have the lift type trailers, and they loan/rent them for short times. I also know of one person who has a lift trailer and has a side business of hauling pontoons into and out of the water. I used him for several years before I broke down and bought a trailer.

                All of these are located around Kerr Lake.

                Bob

                Comment



                • #9
                  Re: Pontoon Engine Size

                  Regarding the registered length of your pontoon -- you said you have a couple feet of tube extending aft of the deck and three feet out front. If your deck is 16 feet long and you added the fore and aft tube extensions you end up with 21 feet and probably a few extra inches. The manufacturers tend to tack on an extra foot if the inches are anywhere near 1/2 foot. So you do have a pontoon whose advertised length is 22 feet. But you have a 16 foot deck. In comparison (and not to make it an issue) my pontoon tubes are 18 feet long and the deck is full length at 18 feet. So although my boat is a full four feet shorter, it has two feet more deck space. Granted, your 'toon will likely have a fair bit higher maximum load capacity because of the longer tubes.

                  Comment



                  • #10
                    Re: Pontoon Engine Size

                    I live in Petersburg, VA which is about 80 miles east of Clarksville, Va. The pontoon is located at Lake Roanoke Rapids which is 70 miles south of me. I "LUCKED UP" today at a local marina & was talking to an older gentleman & his wife who where getting ready to go out on their pontoon boat for the day. I was telling him about just buying mine & the problem was I having finding a trailer & you will not believe what happened. He told me I could use his as he has never used it but once & that was 2 yrs ago when he put his 'toon in the lake & now has a permanet slip year round for it. He told me to use it all I wanted & leave my 'toon on it until I got it restored & then bring him back his trailer. He asked for my cell phone number which I gave him & said "here is the key to the tongue lock" & got on his pontoon & went out on the lake leaving me standing there with my mouth wide open. I still haven't got over it yet. Needless to say the trailer is now at my house & I am going down to get my pontoon next Saturday. I can't beleive this happened to me today. It just proves there are some very kind trusting people still in this world & it sure makes me feel good to know them.

                    Thanks for the information you provided to me Bob as I really appreciate it very much.

                    BTW The fellow I bought the pontoon from lives in Durham. I lived there myself back in the 70s & 80s before moving to VA.

                    Comment



                    • #11
                      Re: Pontoon Engine Size

                      I measured the tubes today with a 50ft tape as I just wanted to know for sure. The tubes measure exactly 19'-4" end to end. The decking is exactly 16' long by 8' wide. This leaves me with exactly 2'-0" in the front & 1'-4" in the rear that has no decking on it now. Is there any reason since I have to redeck it anway that I couldn't add 2'-0" to the front? The only thing I don't know where to find right now is the fenceing tht I might put around the "new area" or I could just leave it open & mount a trolling motor & some pedestal seats & use it for fishing or just sitting. Any thoughts on that?

                      Comment



                      • #12
                        Re: Pontoon Engine Size

                        VaGent, glad you found a true and trusting gentleman. Bet you will never forget that experience, and you will be more than willing to pass along similar kindness to a stranger in the future.

                        In my experience, any time I have needed help, people were more than willing to help, and would never accept payment. Most said they would receive payback if I would help someone in the future.

                        Assuming we all do good deeds for each other, wouldn't this be great.

                        Best of luck with your project. Bob

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                        • #13
                          Re: Pontoon Engine Size

                          Everytime I start looseing trust in some people, someone comes along to restore that trust. I don't mind saying I was overwhelmed with this man's kindness & trust. He did for me exactly what I try to do to everyone I meet in life. It doesn't cost anyone anything to be kind to their fellowman IMO. But that all depends on who you are dealing with I suppose. If everyone else would follow that example this world would be a greater place to live in. I'm truely grateful to have met this man & his wife. I'll keep in touch & let you know how things go with the restore of the pontoon. If I can ever learn how to post pictrues I will include them as I go along. Thanks again for your effort to help out with the trailer. If ever I can be of help you know how to contact me.

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                          • #14
                            Re: Pontoon Engine Size

                            Only thing I would add on the engine swap is with the 70 running at the speed of the 50 it would be loafing and get close to the 50s gph. And of course you could cruise even slower.The 50 at any speed from wot down would be working harder than the 70.to achieve the same speed.Just a thought.

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                            • #15
                              Re: Pontoon Engine Size

                              Finally got the 'toon home safe & sound. AFTER I paddled the daggone thing for over 2 miles because the enigne quit & would not start. BECAUSE I wasn't smart enough to KNOW how to properly start it. I DO NOW!!!

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