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Bolt or clamp the best to attach motor to boat?

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  • Bolt or clamp the best to attach motor to boat?

    I just completed replacing the transom on my 15' aluminum runabout and am about to attach a 1996 Force 40 HP to it. This engine comes set up to either clamp it down like most small outboards or use 4 bolts through the hull. After all the effort to redue the transom, I'm a bit leary of drilling 4 large holes through the back, the boat previously had a 33 hp clamp on engine so there are no previous bolt holes. Is there much difference between the attaching methods? Which would y'all recommend? Thanks for the help!
    1974 Starcraft 24' Chieftan IV Express Hard top, 1984 Merc 898
    1972 Starcraft 18' Mariner, 1985 Evinrude 140HP
    >>>
    1969 MirroCraft 18.5' Center Console<<< AVOID https://forums.iboats.com/boat-restor...to-591439.html
    1965 Starcraft Jet, 1996 40 HP Force by Mercury- SOLD
    1955 Aerocraft CC-16 barrel back runabout, '67 Mercury 500
    SOLD

  • #2
    Re: Bolt or clamp the best to attach motor to boat?

    I would use both, but that's me. Keep in mind that those clamps weren't really designed to and aren't really strong enough to hold an engine of more than 20 - 25hp on a transom. I have seen an engine almost come off a boat from a hard turn and 1/2 throttle. Better safe than sorry in my book.

    Hope That Helps.

    Craig
    There are Mercury/Mariner outboards and then there are Force/Chrysler outboards. There is no such thing as a Mercury Force, yes Mercury Marine built them, but it's still the old Chysler engine with updated electronics and a better lower unit, NOTHING MORE..


    How much horsepower can I have and still go to Heaven??

    1981 Glastron SSV194, MerCruiser 228hp (305 cid), 350 hours. Cuises at 3000 RPM / 30/31 MPH

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    • #3
      Re: Bolt or clamp the best to attach motor to boat?

      I'd use the clamps with a safety chain or cable to prevent losing motor. It'll save drilling those holes in your nice fresh transom...less places for water to leak in and rot the wood! Check and re-tighten clamps now and then, and you should be fine! Good Luck!

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      • #4
        Re: Bolt or clamp the best to attach motor to boat?

        I'd clamp and use acouple bolts with a 40hp.

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        • #5
          Re: Bolt or clamp the best to attach motor to boat?

          Don't trust clamps to hold 40HP. Bolt her on.

          After you drill the holes, put some silicone or 5200 in there, then more under the washers at both ends.
          sigpic

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          • #6
            Re: Bolt or clamp the best to attach motor to boat?

            I run a chain thru the holes in the 2 clamp levers. Bolt it with S S bolt & a S S self locking nut. We have never lost or had a shift after 2 tightenings of the clamps.
            If plastic junk levers. 4 S S bolts are plenty.

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            • #7
              Re: Bolt or clamp the best to attach motor to boat?

              I would use the clamps and add a chain as security. Then when you upgrade to the motor you really want then revisit the options.


              1973 Starcraft 21 Mariner ---------------- 1966 Lone Star Medallion II --------------- 1963 14' Lone Star Big Fisherman

              A Smart Phone is one that is Not in your hand when driving!

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              • #8
                Re: Bolt or clamp the best to attach motor to boat?

                I bolt on any motor over 15hp. But if you clamp it then be sure to safety cable or chain it. 40hp is a lot of motor to be relying on clamps to hold. If you have ever seen a motor jerk itself off a transom you would always bolt from there on out lol. Holes are easy to fix and fill but motors are hard to pull off the bottom, especially in deep water. As someone said above, some 5200 or marine silicone to seal the bolt holes and no worries about transom rotting.

                I worked for a logging company for several years on the water running tugboats. Every year about 3-5 boats would hit out boom sticks (large red fir logs chained together, sometimes 2 miles long) and rip their motors and out drives off. Our shop diver salvaged countless outboards that were just clamped on when they hit the booms. Something to think about if you hit something running full throttle, think those clamps will hold?

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                • #9
                  Re: Bolt or clamp the best to attach motor to boat?

                  Would you rather have holes in transom or your engine on the bottom of the lake, I would bolt it, clamps are good for 15s but 40 is really pushing.
                  GO IRISH!!!!

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                  • #10
                    Re: Bolt or clamp the best to attach motor to boat?

                    Best performance of a boat begins with proper height adjustment (AV plate position in relation to the bottom of the boat). If you just plop the motor on the boat so it sits full down on the transom bracket the performane will almost always be less than optinum. If you bolt the motor you have the option of raising the engine to the proper height. With clamps, the motor MUST sit full down or you will certainly have it twist and possibly jump off. Bolting is also one way to secure the engine to the boat. Thieves can make off with a clamp on motor in a minute.

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                    • #11
                      Re: Bolt or clamp the best to attach motor to boat?

                      Originally posted by Silvertip View Post
                      Best performance of a boat begins with proper height adjustment (AV plate position in relation to the bottom of the boat). If you just plop the motor on the boat so it sits full down on the transom bracket the performane will almost always be less than optinum. If you bolt the motor you have the option of raising the engine to the proper height. With clamps, the motor MUST sit full down or you will certainly have it twist and possibly jump off. Bolting is also one way to secure the engine to the boat. Thieves can make off with a clamp on motor in a minute.
                      These are some good points, well made!....just the anti-theft item is worth consideration! Good Luck!

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                      • #12
                        Re: Bolt or clamp the best to attach motor to boat?

                        If using clamps, I would only do it with the clamp adapter that screws to the transom and only with lower hp engines. If the clamp is clamped to alum or anything slick, doesn't take much to get it to slide around on it. BTDT

                        On larger engines bolt for sure. Course before you bolt, you need to either have your "setup" right or know that your boat holes will allow for setup changes.

                        And obviously an engine bolted on is harder to steal.

                        Mark
                        If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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                        • #13
                          Re: Bolt or clamp the best to attach motor to boat?

                          If you do decide to bolt the engine, make sure it is perfectly centered on the transom and then mark the holes with the engine set full down on the transom bracket. That is obviously as low as the engine will go. When the holes are drilled you can then raise the motor as needed. With the engine sitting full down on the transom measure between the AV plate on the motor and the bottom of the boat with the engine vertical. Compare that measurement to the distance between the upper and lower bolt mounting holes. That will allow you to figure out how high the motor can be moved in an effort to get the AV plate flush with or an inch above the bottom of the boat. As a carpenter would tell you, measure twice and drill once. That's so you don't end up saying geez -- I cut it off twice and it's still too short.

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                          • #14
                            Re: Bolt or clamp the best to attach motor to boat?

                            There is no question that bolts will secure a motor for good and can slow a thief slightly.
                            For years the only way to mount a motor of any size was a clamp.Pretty sure E/J used clamps at least to 85 hp.
                            the in line 6 cylinder mercs had clamps.And they were up to 135 hp. They probably had bolts as well.
                            I had 2 motor jump off. a 1940's 1.5 Evinrude gone forever in 1953? and 61 Evinrude 18 for a few hours in 1962.
                            Both were from poor attention to checking the clamps on a regular basis. And I was fooling around with the 18
                            It was a tiller set up on a nice nearly flat bottom runabout.I would cut the motor and turn it hard over and the boat would do this great side slide to a stop.I can still see that motor as it entered the water and the tank hose snapped.
                            We found it standing straight up on the power head.
                            When setting up your 40 You need to get the antivent plate(just above the prop) about even with the bottom of the boat.
                            You can just add sticks to the top of the transom to hold the height while you set the clamps.If you think about it the top of the transom only sets the height and adds no security.
                            The higher the motor without venting problems(cavitation) the better.
                            I wouldn't do any bolts unless necessary to get the height safely and your happy with the motors performance.
                            To get the setup right you will need a tach(Tinytach will do and a gps for speed.
                            If you get us that info and and the prop size we can help you tell if the boat is performing as it should.

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                            • #15
                              Sign up today
                              Re: Bolt or clamp the best to attach motor to boat?

                              Originally posted by steelespike View Post
                              There is no question that bolts will secure a motor for good and can slow a thief slightly.
                              For years the only way to mount a motor of any size was a clamp.Pretty sure E/J used clamps at least to 85 hp.
                              the in line 6 cylinder mercs had clamps.And they were up to 135 hp. They probably had bolts as well.
                              I had 2 motor jump off. a 1940's 1.5 Evinrude gone forever in 1953? and 61 Evinrude 18 for a few hours in 1962.
                              Both were from poor attention to checking the clamps on a regular basis. And I was fooling around with the 18
                              It was a tiller set up on a nice nearly flat bottom runabout.I would cut the motor and turn it hard over and the boat would do this great side slide to a stop.I can still see that motor as it entered the water and the tank hose snapped.
                              We found it standing straight up on the power head.
                              When setting up your 40 You need to get the antivent plate(just above the prop) about even with the bottom of the boat.
                              You can just add sticks to the top of the transom to hold the height while you set the clamps.If you think about it the top of the transom only sets the height and adds no security.
                              The higher the motor without venting problems(cavitation) the better.
                              I wouldn't do any bolts unless necessary to get the height safely and your happy with the motors performance.
                              To get the setup right you will need a tach(Tinytach will do and a gps for speed.
                              If you get us that info and and the prop size we can help you tell if the boat is performing as it should.
                              Hey man, those are "family secrets". None of our business. Grin!

                              I have a couple of those too.

                              Mark
                              If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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