Thru-Bolt Motor

Discussion in 'Boat Yard Basics' started by cpauly33, May 10, 2011.

  1. It was suggested by a friend that I should thru-bolt my 15 hp Merc. Right now I just have it clamped on. It seems pretty solid. How necessary is it to bolt the motor to the transom?

    If I did want to bolt the motor, how should I go about it. I'm sure theres plenty of wrong ways to do it.

    Thank You  [smiley=1-thumbsup3.gif]
  2. mark_gardner

    mark_gardner I Love!

    absolutely yes!! you should bolt that motor down. i dont care how solid it feels it can and will walk off it's mount and you'll be left sitting in a boat going in one direction holding a motor going the other direction :eek: i was standing on the bank of this island one day watching my brother come whipping around the corner with his 15 hp merc when he encountered some wakes put off by a fairly decent sized cruiser when the motor came off the back :eek: :(, it was the most funniest thing i think i've ever seen, laughed so hard i pee'd in my pants ;D, from that day forward the motor was secured with thru bolts ;) go to the hardware store and buy some stainless steel bolts, washers ,and locking nuts that will match the diameter of the holes in your clamp, drill appropriate size holes thru the transom, pump in some sealent such as 3m's 5200 and bolt it down. the only exception to bolting down a motor would be a really small low h.p. one that i needed the ability to remove out on the water such as needing to carry the boat over dry land or loading onto a roof rack or such

  3. Gramps

    Gramps Living & Dying in 3/4 Time

    What he said. I once found myself holding on to the tiller of a Merc 25 that had popped off the transom and was dancing in the water. Scary as heck. Bolt it on!

    P.S. - Wear your kill swith/lanyard. It's just as important.
  4. out-cast

    out-cast Well-Known Member

    LISTEN TO THIS GUY!!!^^^^^^ He knows his chit.
  5. Brett

    Brett > PRO STAFF <

    Bolt holes are at the bottom of the clamp bracket.
    One at the bottom on each side...see machine screw location 24
    on parts digram in link...

    Make sure outboard is centered and clamped on transom.
    Drill, seal the insides of the hole, insert stainless bolt
    install fender washer inside of hull, thread on ny-loc
    tighten until snug, do not over tighten!
    Wipe off excess sealant...simple, eh?

  6. When I bought the motor used it came with the original bolts, washers and nuts. Never been used.

    As for drilling the holes, should I mark them and remove the motor before drilling or would you drill them with the motor attached?
  7. Brett

    Brett > PRO STAFF <

    I tilted the outboard up,
    put a section of plastic soda straw over the drill bit,
    and then drilled with the outboard on the transom.
    Plastic straw protected the finish on the clamp bracket.
    Bracket hole kept the bit square to the hull.
  8. DuckNut

    DuckNut Brandon, FL

    I found this out the hard way. I was out hunting with a buddy and I just had the motor clamped on. I pur the motor in reverse and twisted the grip to give it gas to clean off some weeds. The prop gota good bite and the motor flipped up and popped off of the transom and now is wanting to fall in the water. As I am holding on for dear life the throttle kept twisting and going faster. I was sitting in the boat, in the dark, holding on to a 25 going full throttle throwing water, weeds and muck everywhere. My buddy came and hit the kill switch and grabbed the motor and we eventually got it back in the boat and remounted.

    I do not care to experience this again...EVER.
  9. Swamp

    Swamp I Love!

    Okay, I am in no way saying you should not bolt your motor on.  Frankly it's a good idea.  That said, I have never bolted a small (<30) motor and I've never had a problem.  I also check my clamps!!!  The transom of my current boat also has a lip so that makes a big difference.  If I was in any way not confident of the setup, I would bolt it.  If I could not for what ever reason, I would attach a chain connecting the motor to the boat that could handle that kind of stress plus some extra.

    Again, you have received good advice from others and I'm not saying you should not take it.  Just wanted to give you my experiences, I'm not about to suggest you will have the same results I have had.  Having a motor come off on you would suck and be potentially dangerous.


    ETA: I just remembered I did have one jack up sideways on me once, but it did not come off the transom.  That was enough to make me check the clamps since then.  Spooked the snot out of me.
  10. Motor is bolted. Thanks for the input.
  11. backwaterbandits

    backwaterbandits Well-Known Member

    Good deal...You'll never be sorry!
    Also makes it just the slightest bit
    harder to steal. ;)
  12. Rooster

    Rooster Towee Calusa

    I made the mistake of reading this post before going to bed last night. Guess where I was in my dreams? - cornering my skiff & the motor popped off. As awful as this felt in the dream (I was looking down at my motor 10' on the bottom!); I am making the bolt on my Sunday project!
  13. cslascro

    cslascro I Love!

    I had a twenty horse clamped on the back of a Carolina Skiff for years. It never tried to come off in the water, but one clamp slid up and off during a road trip to Mosquito Lagoon. It was before sunrise, so I didn't notice it happening on the way down. I got to the ramp and went to back down and saw the motor sitting up high and off center. I went back and saw that only one clamp was holding it on. Would've been a total disaster if that thing came off in the road somewhere.
  14. noeettica

    noeettica Well-Known Member

    Interesting thread ...

    Can't decide which motor to "Commit" to or exactly where It will get bolted on :D