342 swim platform backing plates

Black_Diamond

Replaced the stacks of washers used on the bolts to fasten the swim platform on. Used 2.5” x 5” AL plates. Plenty of support now!

Liberty44140

Nice! Would love to do this long term, don’t love the washer stacks. Is this for more support for your dinghy?

Michael T

@Black_Diamond....beautiful work! One of the most important areas of a 342 (or any boat with an added-on swim platform) to upgrade. Great example (IMO) of how it should be done...and if my eyes don't deceive me - the plates are bedded in 3M or Sikaflex to ensure even contact and load....awesome!

Black_Diamond

I did bed the plates with 4200 equivalent.  

Will help spread the load better with my dinghy. Esp with the Lk Mich waves!  I was seeing some stress from the washers, likely from over tightening when it was built. One of those things that just kept bothering me.  lol  there were (2) bolts I could not use the plates on: one was in a corner and the other was drilled thru at a bad angle thru a radius on the transom wall. So 16/18 have backing plates now. 

I got the plates cut to size from:

https://www.cut2sizemetals.com/aluminum/plate/apl/

6061 Al, 1/4” thick.  I primed and painted them too.  Just looks nicer. 

Black_Diamond

You can see one of the bolts without the plate. Left side of pic. Crappy install at factory.  

Dream_Inn

That looks great!  & I know what you mean by bothering you.  I end up having some things like that, I add it to my list and think about it for a while.  & it continues bothering me till I figure out the best way to handle it.  Good job!  (& now I'll have to look at mine )

Handymans342

What about the platform side?????

Black_Diamond

Platform side looks good.  The upper bolts go thru the thin (upper deck) section and the platform wall against the transom is probably 2x as thick. The lower bolts go thru the much thicker transom wall. 

If I ever need to tend to the platform side, I’ll pull the whole platform to seal. 

GMSLITHO

thanks ill take a look at mine hopefully real soon 

McGarnicle

Did you have to replace the bolts too, or just slide the plate on and re-tighten?

Black_Diamond

I left the bolts in place, otherwise it means resealing everything. Either use a friend to hold the platform side bolt from turning, or use a pait of nuts on the threaded side and jam them. Then a wrench can hold the bolt while loosening the lock nut. The latter is what I did. Mine were 3/8” bolts, 9/16” wrenches. Those ratchet box end wrenches with the flexible ends are perfect for this!

Stodge

I like the idea of backing plates there.  But I'd be leaning toward stainless.  Also looking for support rods to run from the end of the platform to the transom.  My platform has none.  Might be overkill but I'd feel better with them on....if it's possible.

Any ides on where to get stainless plates like BD found?

Black_Diamond

You can get SS plates from the same website.  

More $ for SS, harder to drill too.  Really no corrosion issue to be concerned with using AL. I liked the 6061 AL as it can flex a bit to deal with a non-smooth/flat surface,  SS would be quite rigid at .25” thick. 

You’ll 2-3x the cost using SS. 

Stodge

My concern would be the strength of the aluminum.  Am I over reacting or would the plates bend over time?

Black_Diamond

The only way the plates would bend is if the fiberglass behind them totally failed.  Like pulling thru. Mine fit well against the hull and I bedded them in with 4200. Washer under the self locking nut and the compression load is spread out over 11 in2 more area than just the washer alone. 

Doing the plates I used in SS was a near $500 bill. AL was like $150 or so. Or close.  

Stodge

What size hole did you have to drill into the plates @Black_Diamond?

I can save about $40 by ordering 9 plates at 2.5x10 and cutting them in half. 

Stodge

Got my plates.  Just have to drill and cut them in half.  @Black_Diamond do yo remember what size hole you had to drill into them?

Black_Diamond

They are 3/8” bolts. I went 1/16” over (7/16”). 

Stodge

Thanks!!  Time to make some holes.

Stodge

Got them put in yesterday.  Man am I sore.  

Dude_Himself

You too @Stodge?

I have the integrated swim platform (2007 280 EC), and added a grill mount to the starboard side by the cleat. I had my wife hold the screws from the outside while I wiggled on my belly, over the blackwater holding tank, to reach the backside. I watched a Black Widow crawling on her web near the rear of the 496 as I added washers, nylock nuts, then tried to spray them with lube (to prevent the stainless hardware from galling). The wife had to run off a few times to check on the kids while I laid there, waiting, in a very uncomfortable position, watching this Black Widow and wondering how fast she could really move. By the time we got all 6 tightened I was almost stuck - my core and lower back were so cramped up I couldn't wiggle back around the hatch support. That spider would be fat, dumb, and happy after eating me.

GMSLITHO

I need to do this also been down there all weekend water pump re install added a air filter for the holding tank and put in a power inverter that the seller of the boat gave me but never installed .sore back and legs and a few cuts 

mipand

I am glad I found this thread.  Thanks for the post as I am a novice to boating repairs.  I had water leaking into transom from the swim platform bolts this year on a 2005 Rinker 320. I had removed my swim platform completely to dry out the holes.  I did not like the way the washers were digging into the Fiberglass and warped,  so I had bought Starboard to use as backing plates.  After reading this post, I wonder if the Starboard will be good enough since much of the conversation was about Stainless or AL plates.  Does anyone have opinions about using starboard as backing plates? 

Liberty44140

Starboard is HDPE, it’s plastic, great stuff but it will flex and compress far more than metal. Best backing plate method would be a metal mentioned above. 

mipand

I am glad I didn't install the starboard.  Thanks Liberty. 

My thoughts were that it has to be better than no backing plates. But if I am going to add backing plates, I might as well do it right and go with AL or SS.

Liberty44140

Agree that it’s probably better than nothing, I used starboard as backing plates many years ago to back a sailboat stancion and it did work, but aluminum or SS is the right material for backing 

Black_Diamond

You really do not need the weight nor expense of stainless. You are just spreading out the load. 6160 aluminum cuts and drills easy. Polar opposite for stainless, very poor machinability. 

I used 1/4” thick aluminum plate, it is far stronger than you need. I primed and painted mine, an OCD issue on my end. You don’t even need to paint. 

www.cut2sizemetals.com

mipand

Black diamond, thanks that was my next question was if I could order a sheet of it and cut myself.  Thanks

Black_Diamond

I think you can order about any size from them. Big sheet shipping might be $ though.