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There are 2 engine mounting holes drilled into the outside part of my transom ('70 Katama) that are below the splashwell. The holes extend all the way through the outer transom glass. I poked a screwdriver through and felt crunchines (is that foam?).There is no way I can think of to secure an engine in this manner since there is no access from the inside. The holes are smooth so I ruled out the idiot with lagbolts theory. I searched all articles/discussions and found nothing similar. Any ideas on how that particular setup was accomplished? It will be filled with thickened epoxy soon. I am about to install a 70hp Merc and was wondering if 2 mounting holes will suffice or are 4 necessary? Thanks, Paul

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Paul,

There is nothing idiotic about using lag bolts to secure an outboard. It was standard practice in the old days when motors needed to be mounted as low as possible. The lags were more than strong enough.

Of course today, with better propellers we can raise the motor on the transom a bit and here lies the solution to you motor mounting dilemma.

Mount your Mercury 70 using the second set of top bolt holes on the motor. This will locate the motor 3/4-1" above the transom and this should be high enough to drill through the splashwell and reach the top set of bolt holes on the lower portion of your motor's mounting bracket.

You will, of course, have filled the old bolt holes before doing this. Yes, the "crunchiness" you felt with your screwdriver was the foam core. There are other novel way to reach these lower bolt holes but I recommend against it as it involved cutting open the hull and digging out foam. I have seen some real hack jobs over the years an the as thing is there is no need for this at all.

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Thanks for all the help Tom! I would have never guessed lag bolts would hold the HP/torque. A good friend of mine almost lost his motor 2 weekends ago when he insisted that using a cheater pipe to tighten the transom clamps on his 40 hp Merc would suffice. The first turn he made saw the motor crawl up the transom and he broke the steering wheel trying to control it. He saved it but big gouges in the transom and a ruined weekend resulted. I will set up the Merc as you suggested. Thanks! Paul

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Tom,
I have a couple of questions for you on using lag bolts to secure an outboard. I have been putting off mounting a bracket for an auxiliary engine (5 hp Mercury 4 stroke) on my Montauk 170 because I cannot through bolt the bottom two fasteners and I was unsure if lag bolts would hold. My questions are if I am drilling in to ¾ inch plywood backing how long a lag bolt would you suggest I use and what size of hole should I drill for a 5/16 inch lag bolt? All fasteners will be stainless steel and will be used with 3M 5200.
Thank you,

Ian

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Ian,

Do not use 3m 5200 for your mounting as it will destroy your gel coat if you ever have to remove the bracket. Use 4200. It has the same holding strength without the finality of 5200.

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Ian,

Are you sure you have wood backing for a bracket? Early Montauk 170s did not have any provision for a kicker. Later models do. Why do you think you need to use a blind fastener (lag)?

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Thanks Jeff, I will use 4200.

Tom,
Thanks for your assistance.
My thoughts were to mount the outboard bracket directly under the HIN on the starboard side. I have a 2007 Montauk 170 and the Boston Whaler specs. indicate that there is ¾ inch plywood there, I have a swim platform on the port side of the transom.
I think I need “blind” fasteners to secure the bottom of the bracket as I do not think I have access under the starboard step. The access tunnel and above does not seem to go in far enough to allow me to access to that part of the transom.

Thanks
Ian