Strut Pads, One Step Forward, Two Steps Back

[trace elements]

Well last night I was sanding the bilge to facilitate painting before I reinstall the fuel tank. I nicked the aft inboard corner of the starboard strut backing plate and to my surprise, water started draining out! Long story short, both strut pads were wet and rotted and will need to be replaced. The starboard strut pad was nothing but crumbled mulch. I've read the section in the tips about rebuilding the strut pads, but here is my plan of attack.

1. Double size of strut pads. Use two pieces of coosa 26 3/4" for a finished thickness of 1-1/2"
2. Lay down two layers of 1700 glass in epoxy over the area and bed the new backing pad to the new glass in epoxy.
3. Add 4 layers of 1700 over top of the new strut pad.

Any other input?

[Stephan]

Hopefully others who are wiser than I will be along shortly, until then:
Would you save the Coosa for another application and sandwich some plywood that may be better at absorbing shock?
Also, how about some collodial silica in the epoxy to make the bond between your pads and the hull?
Maybe vacuum bag the whole thing to get a confident bond to the hull?
Good luck, I hope it turns out well for you.
Stephan

[bob lico]

some years back one of our brothers whom owns a testing lab as well as a large manufacturing plant did us the service of testing a double layer of Coosa board versus a double layer of CDX plywood. well low and behold the plywood was the winner soooooo this is the procedure i took to replace the strut pads. i cut two pieces of plywood with a 45 degree angle at the transom end (because i would have to make rudder tower pads in the future) than bevel the entire perimeter of the two pieces of plywood to 45 degrees to facilitate epoxy lay up with Bi axle 1700 .i removed all the rotted plywood and ground down till all green glass was showing then a layer of epoxy/cloth to make a good adhesion to the OEM . layup.then totally covered both sides of each piece of plywood twice with epoxy then sandwich two pieces of the plywood together and place on the cloth covered hull all done while tacky . the hull at strut area required new 2" longer bronze bolts with 1/2" bronze backer plate and nut and washers.the struts pads and struts were made to be heavily abused with right angle turns at 36 knots. strut is super solid!!!!!1

[trace elements]

some years back one of our brothers whom owns a testing lab as well as a large manufacturing plant did us the service of testing a double layer of Coosa board versus a double layer of CDX plywood. well low and behold the plywood was the winner soooooo this is the procedure i took to replace the strut pads. i cut two pieces of plywood with a 45 degree angle at the transom end (because i would have to make rudder tower pads in the future) than bevel the entire perimeter of the two pieces of plywood to 45 degrees to facilitate epoxy lay up with Bi axle 1700 .i removed all the rotted plywood and ground down till all green glass was showing then a layer of epoxy/cloth to make a good adhesion to the OEM . layup.then totally covered both sides of each piece of plywood twice with epoxy then sandwich two pieces of the plywood together and place on the cloth covered hull all done while tacky . the hull at strut area required new 2" longer bronze bolts with 1/2" bronze backer plate and nut and washers.the struts pads and struts were made to be heavily abused with right angle turns at 36 knots. strut is super solid!!!!!1

Thanks, Bob. My concern is water getting into the plywood again. Given the vibration and stress at that location, I think it is very possible for water to work its way into the strut pad regardless of how well-bedded it is. What measures did you take to waterproof the penetrations in the strut pad?

[bob lico]

totally encapsulate CDX plywood twice with epoxy ,no way in hell would you get salt water penetration. ( have patients soak it in epoxy)

[Rawleigh]

Don't forget to epoxy the bolt holes.

[Ironworker]

After months of demo on my boat, I'll never install any wood on the boat. Coosa 26 laminated with glass is about as strong as it gets. Wood may very well test better when its new but give it a couple of years of water infiltration then retest against Coosa.

[Tony Meola]

I know that Capt. Pat always recommended plywood. But today's boat manufactures load that area up with glass.

When we did yours we used fiberglass pads from Mcmaster Carr and glassed them in place. Thickened epoxy them in place than used 1708 Matt to finish. Round off all the edges before you put it down.

You need to leave room for water to run aft. We left a 1/2 channel, some people use PVC pipe to create the channel.
I know everyone says the plywood gives and in that way, less damage is done to the hull should you drive a strut through it.

Once you used the Thickened epoxy, glass mat and soaked the plywood in thinned epoxy, I wonder how much give there really is.

[John Swick]

A strip of 1/2" builder's grade plywood 3" wide and 2' long breaks relatively easily over a knee. The same size strip of marine grade plywood can be broken over a knee, but you wouldn't want to do that too many times in a day (least I wouldn't). If you try that trick with the same size strip of Coosa BW26, you ain't walkin' home cause your knee cap will have been shattered. If you prop it up on the ground with a brick or over a curb and run it over with a pickup truck it might break then....maybe.
It is harder on the tools and too stiff for certain applications, but that's why they make it in lower/softer densities too.
Yeah the plywood is quick, easy/cheap to buy, and will work, but there's no way it's as strong or will last as long as coosa.

[Snipe]

https://www.mcmaster.com/phenolic-sheet ... e-e-glass/
I used glass on mine this stuff is really strong. Capt Pat posted this somewhere some time ago that he would use this as well. I used garolite g10 for backing pads as well both are bullet proof.

[Carl]

A strip of 1/2" builder's grade plywood 3" wide and 2' long breaks relatively easily over a knee.

Plywood is a laminate, once you cut it to a 3" strip you removed the tension of half the layers greatly reducing its strength. Certain materials shine in certain applications and lack in others.

I'd say the only downfall of using plywood is IF water should make its way into the wood your back to square one. Water could get in if sealant around bolts let go...hole or break in epoxy coating. I knew my old pads were shot when I was able to tight the bolts pretty easily on the struts...they were also 40 years old, unsealed and in a wet bilge.

[Ironworker]

https://www.mcmaster.com/phenolic-sheet ... e-e-glass/
I used glass on mine this stuff is really strong. Capt Pat posted this somewhere some time ago that he would use this as well. I used garolite g10 for backing pads as well both are bullet proof.

That is pretty impressive stuff.

Just so happens that I was working on my strut pads today. My plan is to put down 2 layers of 1708 in thickened epoxy on the humm, 2 layers of 3/4" coosa B26 laminated together with 2 layers of 1708 then cover the entire assembly with two more layers of 1708 wrapped around the stringers.

[PeterPalmieri]

I hate to say it, but when we surveyed Buddy Boy both strut backing pads were wet. We are going with a solid sheet of fiberglass, I forgot the thickness but we will post pics when Rob glasses it in this week.

Edit: High strength FRP sheet 84x48 3/4 thickness

[John Swick]

"Plywood is a laminate, once you cut it to a 3" strip you removed the tension of half the layers greatly reducing its strength."
Huh??
No further explanation required.

[Tony Meola]

I hate to say it, but when we surveyed Buddy Boy both strut backing pads were wet. We are going with a solid sheet of fiberglass, I forgot the thickness but we will post pics when Rob glasses it in this week.

Edit: High strength FRP sheet 84x48 3/4 thickness

Peter

Only way to guy. I know when I told Capt. Pat we used structural Fiberglass he said it was too rigid and would not give enough, therefore causing more hull damage if the strut came through the hull. We must added an inch of glass back there by the time we were done. If it works on new boats it should work on ours just fine.

[Raybo Marine NY]

All the large boats we repair that run aground have solid glass pads. Damage is, in my opinion, minimal.
Laying the pads up from glass and fiberglass is easy but we also want the sheet material to duplicate the supports for the area between the engine boxes.
This supports the hatches and side panels.
I’m not a fan of coosa for that because the panels would sit on the raw foam edge, an area not easy to fiberglass and require fairing work to get smooth.
Economically it made more sense to go with the sheet material. Took care of 2 requirements with one sheet of material especially with the ever increasing cost of fiberglass and resin.

[bob lico]

well well every once in a while you just cannot write a post without a total explanation and this is one of them. the past twenty years i always mention the fact " never allow a marine mechanic to work on your boat" this is one of those times. nobody picked up on the fact i had to use 10" strut bolts instead of 8" well think!!!!!!!! my entire deck ,hatches ,companion way, cabin floor etc is made of Coosa board so why would i use CDX plywood for strut pads? well boatyard people are there to make a buck i am not the least bit concern about labor hours or cost of material to build a project just like Bob H and the rest on this board whom built a 31 from scratch. the 1/2" plywood was methodically encapsulated with epoxy resin twice then wrap with stagger cloth joints three times for each piece of plywood then sandwich together and that composite was wrap with cloth and then biaxle 1700. the green glass hull was layed up 1/2" thick with first cloth then biax 1700 then the " sandwich was place on top by first coating hull layup and the "sandwich" is place on top with a 1" pic pipe along the stringer for water flow (totally dry my 31 is a totally dry boat" rain water has a direction to scuppers by way of channel along deck.when i put the bolts thru they were dry fitted and then remove a covered in 5200 thru holes that were first coat in epoxy. that project is over 10 years old and you can rest assure not on drop of water has intruded and you can take that to the bank ///// again labor is no object. 3" strips of plywood WHAT are you talking about????????????

[Raybo Marine NY]

Wood in bottoms get wet from the bolts loosening, not just because it’s wood
Of course if you hit bottom even a little bit all hardware should be inspected or rebedded . Just because you don’t always see water inside doesn’t mean it can’t be leaking

Another good way to tell is during winter layup, look for that tell tale stain coming out of the gear

[bob lico]

my struts are unique for a 31 Bertram . they are imbeded in the hull bottom at a angle and epoxy in place never to be removed!!!!! bronze bolts are double nutted and torque up while epoxy cures. you go aground game over!!!

[Tony Meola]

Bob

We all here you and you have built an incredible boat. We each put our own finishing touches in what we all hope is the answer to cure all problems. Sounds like you have sealed that area up well enough to prevent leakage.

But you know that old saying about things happening, and for that reason some of us want peace of mind knowing that no matter what there is no rot and can never be any rot.

There is no right way or wrong way here when it comes to using plywood or fiberglass structure. They both work if done right. We can all have peace of mind no matter which way we choose to go.

Unfortunately, I jumped the gun and became one of the few to use a Fiberglass pad when we did ours 13 years ago and questioned myself when Capt. Pat said it would not have enough give. If I was doing it again today, I would still go with the glass pad.

Who knows, if Capt. Pat was still with us today, he might agree.

I say use whatever gives you piece of mind.

[bob lico]

tony good openminded post!

[Carl]

You don't even have to run aground...I straightened out a pair of shafts for a customer, the following day he hit a whale taking out all the running gear on one side. Or did the whale hit him??

In any case, I went with epoxy coated marine ply for my strut pads, I did the best I could and pretty happy with it. IF I had Coosa I more than likely would have went that route. A quick look around I found buying small pieces was more than I wanted to spend for a small pieces. Buying a full sheet priced the stuff right...but what to do with the extra? And I really didn't want that cost either.
So I weighed the cost of coosa compared to the marine plywood and epoxy I already had, weighed several years of no problem to the cost and waiting for coosa to arrive and my choice was clear....FOR ME, at this point in my life.

I have to add I did much of this project budget-minded. For things like motor beds and shaft log I went full out. For items I could modify or upgrade later that would work perfectly fine for a good while I used my budget to heavily weigh my decisions. Pulling floor and cutting out strut pads is a couple hours if I ever wanted to upgrade or found them seeping water.

If every decision I went with doing it 100% The Best Way, I'd still be working on it and trying to pay for it. Sometimes more than adequate is fine.

[Raybo Marine NY]

so it sounds like everyone agrees there are different ways to do things

[PeterPalmieri]

So with regard to Buddy Boy. I’m sure Capt Pat did a great job and the pads looked good. When we hauled the boat we were able to summize that the boat hit something. The meter reading said the starboard pad was pretty wet. It could have been a false reading, as I didn’t end up buying the boat or ripping it apart to find out. Possibly with solid glass it could have caused more damage, who really knows.

I think when it comes to this part of the boat we all hope we don’t hit something and if we do we remain above the water. That being said I ran aground pretty hard once, thankfully on a sand bottom. When Rob removed my original wood pads they were dry and not damaged.

I’m going with the plan of whenever wood comes out of the boat I want to make the best effort to not put wood back. There are exceptions and in most cases I hope to never find out.

[Raybo Marine NY]

one important distinction with solid glass is that the boat normally make their way back to the dock. The pads have a tendency to get pushed in so they crack on both sides. WE cut the entire area out and lay up a new section of hull, sounds worse than it is- typically a 2 -3 day job tops once mechanicals are out of the way. With recessed gear the repaired side is usually able to be installed with zero shims. Usually the factory installs have shims.
at least that's what ive seen first hand repairing run-agrounds

[trace elements]

Thank all for the input. Right, wrong, or otherwise, I ended up using coosa. I would have liked to use the solid fiberglass but along the lines of what Carl was saying, it just didn't fit into the timeline and budget. I think the coosa should be just fine, and surely better than the mulch that I removed.

[Carl]

Anything is better than what was there...which in my opinion was really nothing and that nothing worked for the boats a long time.

We could debate till the cows come home which is best...but till someone decides to run two or three boats up on the hard at the same speed, load etc and qualifying the results, all we are doing is taking educated guesses and hoping.

Coosa you know is strong and isn't going to rot, I don't see it being a bad choice.

[bob lico]

i agree 100% with Robbie i have no shims and struts are recessed into the hull for two reasons , number one reduced shaft angle requires a recess and overall strength. looking at this renovation as a engineer we realize the struts are subjected to both compression AND tension thus the tendency to have the bolts loosen over time and as Robbie indicated the tell tale rust colored streak on the corner of the strut pad.whatever material you choose for lay up of the struts pads you must use the OEM. bronze plate with lock washers, double nutted and peaned the threads over the double nuts. ---------Don`t run aground!!!!!

[trace elements]

I think Bob's advice of "DON'T RUN AGROUND", might be the best advice for all of us!

[Carl]

double nutted and peaned the threads over the double nuts. ---------Don`t run aground!!!!!

Holy crap! That is some serious Locktite Right There!


Great advice on not running aground! I'd also try avoiding rocks and other none waterlike objects.