bertram31.com

as usual i work ass backwards . i have my 31betram 11 years and finally decided to rip out the struct supports and reinfore from inside. the problem is i have removable kill boxes that are flush with cockpit floor. i am now confined to keep finish struct support at current thickness above bilge including the 1/4" bronze backing plate which i will retain, so i want to use the strongest material possible with epoxy (mainly resistance to puncture from struct coming thru.) i would like to use a combination of epoxy and kevlar or carbon fiber in a 90 degree build up approx 2' square.has any body ever used these?

STOP!!!!!

Carbon fiber needs special resin and needs to be cured in an autoclave. It doesn't wet and cure like fiberglass. I don't know about kevlar, so I can't help with that.

Epoxy and carbon fiber would be no stronger than epoxy alone........

thanks mike now i narrow it to kevlar. i just need the strongest layup possible within 3/4". ok does anybody have first hand knowledge of working with kevlar and west marine epoxy possibly 1/2' coosa board in between.

Bob

I used a half inch think piece of glass sheeting from Mac masters but the good Capt. Says that works but Plywood is better because it will not shatter. All I know is that by the time we got down, we had close to an an extra inch of glass running from the transome to just past the struts.

I don't have the brnze plate anymore but thinking about putting it back in.

why not just use a 1/4" thick stainless steel plate; cut to whatever size you are looking for, bent a little to match the hull curve, and bedded in place?

I'm not real big on composites, but I would think that would be a lot stronger than any of those other materials you mention.

Titanium would be better........ Sorry couldn't resist

You could go back with roven encapsulated substrate. Marine Ply or Coosa board. The glass is the answer you just need the substrate to absorb the impact;

dead trees break, live trees bend.

If its a late 70's hull then your not working with a whole lot of glass in that area any way, same thickness of new glass top and bottom and a good filler like ply or coosa and you should be good to go.......Rebolt the old brass washer in place and wallah....

We are talking about the strut pads correct???

And you are going to include the rudder post supports as well, sorry for asking my speed reading classes tend to have me skip things.

yes the stuct pads. i through about titanium or 6062 1/4" plate --no kidding but figured even if i sand with 60 grit the titanium may not ahere to layed up biaixl . tensile strengh of stainless is 250,000lbs/sq. in and kevlar 49 is 400,000 . i am using ss for comparison instead of 6062 because it is even stronger. titanium scares me at the through of drilling 12-- 3/8" hole on the money-----ouch. serious capt. patrick i know you use plywood in your tips section . i wanted both your and jp opinion IF you could not use two 1/2" pcs and could build up no more then 3/4". kevlar 49 seems to meet the specs. but i don`t know how it combines with regular west marine 105 epoxy.did you ever use it ?what if money was no object (a couple of yards)

i am making the strut pad 24" long and from stringer to stringer wide ,about 22" i will use small pvc tube for drainage as you indicated.

IF you could not use two 1/2" pcs and could build up no more then 3/4".

Bob,

You never struck me as a mathematically challenged... How 'bout 2 pieces of 3/8" ply, or if you're really squeekin' in at a true 3/4" final result, use 2 pcs of 1/4 marine ply and double up on the middle layer of fiberglass.

As to any thing metal ---- won't work. Not so much of a bonding issue as it is the strength of a composite build up and the cross plys will exceed the strength of the same thickness of metal. Also a metal plate will readily bend and has no memory, so once it bends, it stays bent.

A well built fiberglass and plywood composite has both the strength and memory to absorb a heavy impact and return to it's original form. The size of the strut pad is the key to spreading the impact force across a larger surface area, thereby increasing the overall strength.

Forget the Kevlar and carbon fiber. Too much trouble for the small potential gain.

Coosa board is good stuff, but thickness for thickness is not as strong as plywood.

The ONLY perceived disadvantage to using plywood is that it may rot out.

Consider that most of the totally untreated and polyester bonded plywood that Bertram liberally threw into the bilges of these boats has lasted for close to 20 years and more. Done correctly with epoxy and PVC bolt sleeving, it's not inconceivable to expect a minimum of twice that amount of life out of the plywood.

Review the nature of Basic Composite Structures and think plywood as the core material. Review also Sleeving Through Bolt Mounts and other hardware mounting in composite materials

But if you're really determined to not use plywood what so ever, do the strut pad in solid 3/4" fiberglass, laid up entirely of alternating layers of 0/90 24 oz roving and 45/45 17 oz biaxle. Or go the McMaster route, pay a lot more, and use 2 laminates of 3/8" Structural Fiberglass (FRP) part #8537K37.

Bob,
You plan on jumping some jetties or ram some whales?

Bob,

I did my strut pads a couple years ago.

I'll give you a ring. I am pretty happy with the way they came out, and confident they will hold up to anything that does not remove the rest of the bottom. I used the Patrick method, and it is a beefy new area.

I'll give you a ring on your cell later today. It would be good to catch up anyway!

Dug

In case you ever wonder, when I purchased Tailhook, one of the first projects was to replace the cutlass bearings. Given that I had a friend with a machine shop, I decided unbolting the strut would be the easiest way -- he could then press them out in his shop. so I unbolted the strut, used a little Anti-Bond and it came right off.

However, when I crawled back inside the boat, boy was I surprised to see that I could remove the backing plate with my left hand. It was exactly as Capt. Patrick described. Free Floating!!!!

Anyhow, I used Capt. Patrick's method and it was stronger than I could ever imagine when complete!

My 2 cents!

Bob,

listen to Capt Pat

but if you dont already have the resin use a different epoxy, that west is terrible for wetting out

Thanks for the 6 Robbie...

i guess the problem in my thick skull is the lingering sight of two 1967,one 1972 and one 1979 31 bertram with water soaked ,delaminating plywood used for the raw water thru hole in addition to quite a few others in 50 years of boating. i am so anti plywood in the bilge it would just not sit to well in my brain .i will forget any metal because it would be to rigid but i would love to hear something on kevlar 49 with coosa board in between . robbie i also have gallons of the expoxy from dyna-grout in deer park .i don`t know the brand .the skater cat (24')that i saw repaired was made of kevlar 49 and i know you work on them. did you ever use kevlar???

I have a kevlar 28 skater here now, its awful to work on, and 3 different epoxy resins, one I buy from Skater- its the worst if you are not vacuum bagging and don't have good heat in the shop. To be honest I see no difference in the way this boat has aged compared to any of the non-kevlar ones we have worked on, and we have worked on at least 8 of them in the last 2 years. For what we are doing- filling holes, lining the gas tanks, recoring some of the bottom, replacing some of the wet deck, and full paint including the bottom- we have no need to use any kevlar in the repair process

As UV says the enemy of good is better.

Glass and Wood-- its pretty unanimous from the folks that do it for a living.

Good Luck....

Ahh, what the hell Bob, Kevlar, epoxy, and Coosa Board?

Go for it it! I mean really, go for it and keep us posted on your progress.

But I would seriously suggest that you get real friendly with Google Search and spend some quality time researching information available on the use of Kevlar in composites.

Good luck, I'm outa' here...

now now capt. just asking questions not arguring. i did a search and not counting a facility for perfect temperature and humidity , patients with attempting to cut kevlar with sissor or the ' pre-preg' . i was taken back to find out that althrough kevlar is much better then glass in tension it is much worse in compressive and thats what concerns me impact with the bottom of the bay!! in so many words kevlar is for a pro like robbie who may have to match a crash area on a skater cat . i will go with wovenroving cloth 24.5oz. and biaxle but i would like your blessing on the coosa board with the knowlege we learned from brother rocky`s test with both plywood and coosa.

thickness for thickness, plywood is stronger than Coosa board.

It's all about naturally bundled cellulose fibers laid in 0/90 layers. Other than a light weight fiberglass layer or two, and some chopped strand, Coosa board is little more than a bunch of ground up carbon by product fused into a light weight sheet. Excellent for decks, bulkheads, cabinetry, and such, but still not as strong as plywood.

Don't take my word for it.

Take a piece of Coosa and a piece of plywood, both the same dimensions, and break them. See which is stronger and what their breaking characteristics are. Do the same test on laminated fiberglass composite pieces, one made with Coosa and one with plywood as the core material.

As I said before, if you want the strength of plywood, thickness for thickness, but without wood involved, go with a solid layup of fiberglass, alternating between 0/90 roving and 45/45 biaxle. In fact, that would be stronger than a plywood/glass composite if you have the proper ratio of resin to glass. For roving and biaxle, the ratio should be between 60/40 and 50/50 glass to resin. Tough to achieve an air free layup of that ratio without vacuum bagging. And that's a whole other bucket of worms.

Bob, you're not building a space shuttle on unlimited government funding...

BTW, the trailing thwart ship edge of the strut plate is where the most force will be directed upon a forward movement impact. Sort of like an axe hitting at a 60 degree angle.

The initial fiberglass break is a shearing action, which then transfers forward as the boat's weight settles onto the strut. Most floating objects will be deflected by the shaft, strut angle, and prop.

Hard grounding force will be generated aft of the strut by the prop and transmitted back up the strut, trying to push the aft end up, while pulling the forward end down. This is why the rectangular bronze backing plate is very important. Without it, the forward two bolts will try to tear down through the backing pad.

thank you for being very considerate taking time out to explain everything in your (fiberglass) world. you explain the conditions under impact and that what i really wanted to base my decision on.

Yeah Bob, I initially had the resistance to use the Coosa board after seeing how easy it was to break comparitively to same TH ply, but promptly got retesting after Capt Pat said I was testing on the wrong plane. The Coosa had great strength (more) than the ply but on end. I have confidence it would deflect well though in your application if laminated correctly but as I tested and Capt Pat says the ply is stronger on THAT plane. I'd go for the McMaster structural glass and save labor time with the strength you want, then you can keep your "no wood in bilge" in effect! Thank you too Capt for explanation in detail on why we need to do rienforcing here. By the way, what about the G-10 circuit board sheets that's supposed to be so strong, laminated together?

G-10 circuit board sheets that's supposed to be so strong, laminated together?

Too costly, no appreciable advantage... Nix

Bob Lico, I see you mentioned plywood for the thru hull fittings. I just replaced the plywood with 3/4" pvc board. It does not rot and will last forever, not to be used in a structural format. Just squeeze it down, it goes nowhere.

the ply will last you years and years, figure it this way: how many other items on your boat will last 20-25 years? How many electronics upgrades, cushions, canvas, engine and transmissions maintenance, etc.

for such a small item I think you may be putting too much thought into it

Got a question.. Other than the crappy bonding and the fact they are not big enough. is there any problem with your OEM ply strut pads?

Coolair,

If they are truly OEM, then odds are what you see as a strut pad is really just a hard outer shell of fiberglass with a soft center of wet 25 year old plywood. Kinda like an M&M. There was no real attention paid to the bolts and thats where the water comes in, every one I've seen is wet. Hell ours came out by hand after zipping the glass off.

The pads were marginal at best as original. They would barely absorb enough impact as designed to prevent the strut from coming through the hull, as would be the case in a hard grounding. Now think about that plywood pad and the M&M situation that exists today and imagine a hard grounding. Ouch..

Most every boat I've seen redone including ours has had this strut area redone as the first upgrade, its relatively cheap and provides a great deal of safety.

Before I found this site I hit a whale shark and pushed the whole strut right through. If I did not have all the pumps I do and shoring material I woulld have sank.

coolair basicly what jp indicated , of course i did not remove mine yet but the tell tale brown streaks are coming thru from rotted plywood . the awlgrip paint is cracked around the pad.my structs are inbedded in expoxy at a slight changed angle to match reduction of shaft angle so raw water is not leaking in but i imagine the only structure holding it is the broze plate squeeze down on the m&m`s

ok but the point of my initial spart as remark was those crappy ass pieces of wood imporperly installed lasted 25 years... so why wouldn't Capt. Pats method with work last at least that if not longer... :)
I wasnt questioning they why jus the how :)
and i guess i better go a head and do it now too.. crap! one more project on the list
dumb question but you will have to realign the shafts right?

go with a solid layup of fiberglass, alternating between 0/90 roving and 45/45 biaxle.

Allright Bob... how 'bout doing just what Patrick said, but sneak a single layer of kevlar cloth in the laminate.
Doubt it'd be very beneficial, but you could then tell eveyone you've got aramid reinforced strut pads.

I've worked with it very minimally, in conjunction with WS epoxy. No it doesn't wet out like glass, but it isn't too dissimilar or foreign to work with.
And if you kept it to a single layer, I think it could be accomplished with minimal 'pullin your hair out' frustration.

I've seen people laying up the lightweight kev/epoxy canoes- that process seems very straightforward.

well i started the struct job today . first of all as capt. patrick indicated the top layer of cloth installed by bertram never ahered to the plywood . east to peel off.

plywood was completely intack and they used a 1/2" layer of resin/additive that completely ahere to both the plywood and the boat layup. i had to resort to a diamond wheel on 4" grinder to remove . one layer of the plywood stuck to the additive! very differcult to remove.

you got to love grinding out that beautiful awlgrip painted bilge perhaps we have a planning problem here.------------paint as a last project!!!

Bob, make sure it's big enough...Russ





http://s851.photobucket.com/albums/ab75 ... 240017.jpg

russ this is just the prelimenary where the plywood used to sit . i just extended the sanded area a little bit with 6" sander to get the "feel" of removing all that awlgrip paint at least 1' forward and 6" towards stern.i do all work on my bertram myself so i get tired i walk away! great project in winter i would die with the itch grinding fg. in the heat!!

Looks good bob! If your down there on a weekend and need an extra hand give me a call 516-606-0962. I'm not a skilled laborer but would appreciate some on the job training if I don't get in the way.

Pete

Bob,

That dark half circle on one end of the 6 holes may indicate some glass delam from a past bump. I know it never happened during your watch, but you may not be accountable for the 20+ years before you.

Just a question or a hint to check it out...

Dug

dug i have never gone aground i am very in tune with that ugly side of boating because i am always at the wheel of a trade in or new boat check out however this boat came with a pair of beast diesels in it (cummins 504) with oil continuously in the bilge well there was a slight seperation between the plywood struct backer and the layup the oil layed in there and permeated the glass i will have to grind it out. b.t.w. i have not made a decision on backer yet but i will vacuum bag the hold layup just waiting for "sticky tape" and details on the amount of vacuum to be looking for.

i will vacuum bag the hold layup just waiting for "sticky tape" and details on the amount of vacuum to be looking for.

Only gonna' say this once and let it be... Don't waste time, money, and headaches on bagging the strut pad & layups. You won't gain enough advantage to offset the expense, and if not done very correctly can be less effective than just straight hand layup. Leave the bagging to the "big boys" and their factories.

The learning curve to successful vacuum bagging is long & steep.

that sounds like a word to the wise from a good friend. ok i will abandon that though . this was going to be done with a heater below enclose the hull in a enclosure and heat from above not a controled situation so i will take your word as gold.

bob- if you can get weight on the area put wax paper or peel ply and weights on the repair ( cinder blocks ) , it will be as good as you can get it and fool proof.
You still have to steel roll the glass out before the paper and weights, but it will add strength and will yield a smoother repair, use another piece of wood or something under the blocks so you dont end up with the print from the blocks



I somehow think you wont listen to anyone and go ahead with the vacuum bagging, I predict you will regret this decision if you choose to head down that path

Boy Bob, that ply looks amazingly in good shape for were it's been the last 40 years! What material are you leaning towards? Did you upset the struts or are they still adhered to the bottom? I ask because I could very well be right behind you on this "little project" while I put engines on back burner for a while, but don't want to upset the strut's position as I lost my reference (engines) for aligning struts back into place. When I do mine I think I'm going mcmaster structural glass, 1/2" laminated together.

we repair a few run agrounds a year, 50' searay with solid glass strut & rudder pads, 20-25 layers glass, no shims needed when complete- they are not that hard

at least you dont have to spray it Bob!

robbie i am not like that honest to GOD. when sombody says no it means he already put his hand on the hot stove!!! like mike answer to carbon fiber----no ok thants dead capt. patrick on vacuum bagging ----no
ok drop it but your comment is great for a guy with limited experiance---me! that would be easy to do (the use of a cement block on plywood and wax paper) and i appreciate the tip. now i don`t have to go to your shop and look over your shoulder and ask a hundred questions.
thanks again!

rocky my structs are still embetted in epoxy under the boat with the bolts out but supported for safety.they have not moved. rocky now is the time to do this job .inexpensive and necessary. i may not go aground but i sure as hell have a great chance of running over something in the dark going to the canyon!! yes i have great radar but thats not going to see a whale, log,tree, shipping crate,etc.
peter i will be at the boat this weekend and would be glad to have you cut the woven-roving,etc and nand me the cement blocks thur that hole in the shrink wrap tent.!!

Let me know and I'll be down there

Ok
i have to ask.. and NOT because i am questioning the advise but because i am curious about vacuum bagging and want to learn about it Why or what is the reasoning for the curve being so bad? to me it would seem something simple like 2 piece of of wood would be easy to do.

oh and when you referance 12 oz. 45/45 biaxle fabric are you talking about 1208? and the 32 oz. 0/90 fabmat is 2408?

after removing bilge paint i ran 60grit over area to be glassed . i removed bolts and took measurement of bottom of hull as i did with one 1962.two 1967, one 1972 and my 1973 they all are 5/8" on botttom of hull . core sample from middle of hull (raw water intake area) reveal the same thickness also as well as water tank area. back on subject i layed up 1 layer of cloth,one layer of biaxle,one woven roven and top off with biaxle. the hull is now flat and 15/16" thick. next i took a mop handle and molded a waterway were some use pvc pipe i wanted the rest of the process to adhere together.