Engine lift mounting question.

[Stucker]

Would love input into the best way to mount my new engine lift to the transom.  I was thinking of the plate at the bottom of the pole directly to the fibreglass and then piece of  plywood between fibreglass and backing plate on the inside.  4200 before tightening up.  Would love to hear if you had a better plan?  The end of the mop handle indicates where I plan to install the base.  Lifting a 2 stroke 9.9 so there will be a good 80 lbs on it while operating.   The other end of the lift has a mounting bracket on the stern rail.

[KWKloeber]

scott

Admittedly I am ignorant of the transom construction -- is it solid or an inner/outer skin? (mine on the 30 has a void)

Other than that it sounds like a fair plan, though not sure where you propose to use the Devil's adhesive?  Between the ply and fiberglass, not on the backing plate (I hope.) 
I'd use butyl on the topside (after properly epoxy potting and countersinking the holes of course.) 
Ply would be epoxy sealed?

-ken

[Stu Jackson]

There was a post either here on the forum or in a tech note about doing just this.

Comments about other boats is meaningless.

[Stucker]

Thanks Ken,
You bring up some good points.  I'm pretty new to drilling holes in my boat.    I had planned to use the 4200 to seal around the outside fitting But thanks for the reminder of the benefit of butyl tape.  I will def go that route.   I was under the impression that epoxy potting was for filling existing holes when resealing existing fittings.   I guess the idea for doing it would be to create a threaded almost air tight hole for the new screws?  I believe it's just one layer of glass and gelcoat without any void as it's unfinished on the inside but I'm not 100%. I was going to add a layer of epoxy over the  wood before install and then the metal backing plate after it was dry.  I just figured this would be a more solid backing than just the stainless plate?  Is this overkill when you already have a stainless plate?   Again, I'm pretty knew at this kind of install hence the post looking for guidance. 

scott

Admittedly I am ignorant of the transom construction -- is it solid or an inner/outer skin? (mine on the 30 has a void)

Other than that it sounds like a fair plan, though not sure where you propose to use the Devil's adhesive?  Between the ply and fiberglass, not on the backing plate (I hope.) 
I'd use butyl on the topside (after properly epoxy potting and countersinking the holes of course.) 
Ply would be epoxy sealed?



-ken

[Geoffreykwright]

Scott - ENgine LIft?  You mean something to lift the engine onto the boat (from the dinghy)?  If so, I've got a engine lift crane (which used to mount on my aft rail-mounted radar mast) and a bracket to store the outboard on the rail which I am no longer using.  I am based in Toronto.  Let me know if you are interested.  Save you drilling holes in your hull.

[KWKloeber]

I was under the impression that epoxy potting was for filling existing holes when resealing existing fittings.   I guess the idea for doing it would be to create a threaded almost air tight hole for the new screws?

No, not at all.  The gold standard is to pot thru-holes anywhere, whether existing or new installs. 
Even with a solid core (no plywood or balsa) you want to keep water out because fiberglass (polyester) resin is hydrophilic -- it LOVES water and water will attack and deteriorate it.  That's how hull blisters happen.

The idea isn't to get a super tight (threaded) fit.  If water gets past the caulking it's just to have the hole having been being drilled thru epoxy rather than water getting to the fiberglass.  Potting is more critical of course if there's a wooden core.  I won't get into the steps how to pot, countersinking, etc. unless you need it -- the primer on RC's aka Rod Collins' aka Mainesail's website covers it so well.

What I messed up in my reply and lost in editing was "mine had a void" [but I devised a method to pot the holes anway.]   It works well just about anywhere there's a void!  But you probably won't need it.

Is this overkill when you already have a stainless plate?

My personal opinion it's never overkill to install backing when mounting a lift, ladder, etc.  I did something similar and with that experience here's what I would do (but check the writeup Stu mentions - maybe it has a different approach.)

Whatever the backer (plywood, G10, etc.)  Butter it w/ epoxy thickened w/ microfibers (heavy peanut butter consistency.)  That additive has the highest adhesive strength -- colloidal silica is messy to mix and once I had tried microfibers I never looked back (I've epoxy'd for 40+ years.)  Before applying, wet out both surfaces w/ unthickened mix to get a good bond.  Of course, knock off any excessively high spots beforehand (have no idea the hull finish work but its probably quite level.)  Use peanut butter that squishes out (or you have extra) to fill/seal and make a fillet along the edges of the backer.  A  popsicle stick or plastic spoon makes an easy throwaway tool to make a nice rounded fillet.  Once the epoxy kicks you can wet out the back of the backer to seal it.  Then drill and pot, finish up w/ butyl under the plate/around the fasteners.