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Mast foot repair - Need overkill layup schedule


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As some of you who already read my other post may know, I'm re-rigging my boat.

Its a thankless task that I'll never make back in resale value, but that's boats.
Anyway, so the new mast necessitates new mast base, so as that turned up I unbolted the old mast compression post from the deck & unscrewed the 4 screws that hold into the floor that it sits on in the bilge.

When removing the screws I noticed some mushy wood clinging to the ends of them, so I decided to open them up with a larger drill bit.

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There's a distinctly 'sweet' smell to the wood I've drilled out & its definitely damp, poking around with a screwdriver it still seems pretty firm in there and there's no evidence of the floor being crushed, so I guess I have 2 options:~
- Fill oversize hole with epoxy and re-drill screw holes. Worry about it later on and just sail it.
- Cut out the top of the floor, dig out the block of wood, replace with new epoxy sealed wood & re-laminate.

If I go with option 2, can anyone recommend an 'overkill' layup schedule for epoxy that will be stronger than the original?

This is the only info I have on the existing layup:

image.png.50e6d329b4771506b0ddb9e7fffb45f4.png

Boat is 27 feet, about 2.6m tonnes (metric) and carries about 450square feet (ish) of sail.

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If it was me I'd keep drilling bigger & bigger hoping to get to dry wood.

If no joy then I'd fill the holes with high density filled epoxy and sail it - it's a 27' so the loads aren't that big.

Otherwise you have a big, ugly job to do - the kind that is best postponed if possible.

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I drilled almost through to the hull. (masking tape on drill bit so I didn't go too far)
The wet looking stuff is from the FWD holes, the dry from the aft. (Though its all damp)

If I have to replace all the wood then it will be a real pig of a job as the wood goes under the molded in bunks.

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Penetrating epoxy? Um, no. SJB's suggestions make sense so, I'd start with something like that. If you do end up replacing the whole thing (a very big job) why does it need to be stronger than the original layup schedule? Other than the water ingress the original looks to be in good condition so it doesn't appear that it was not strong enough.

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I'm in the SJB camp as well.  I'd drill the holes fairly large, and backfill with epoxy.  Can you tell how deep the wet wood goes?  I.e. only the first inch if wood in the forward holes are wet?  Or is it wet to the bottom of the drill bit? Heck, it nothing else, you've now made a bunch (4?  more?) of solid Epoxy pillars to help support the forces of the compression post.  If you really want to know how far horizontally the wet wood extends, you can drill smaller holes in ever expanding concentric circles till you get to dry wood.  Those small holes can then be backfilled with epoxy if you decide you can live with it.

The challenge to cutting off the top of the stringer and digging out the wet wood, it that any replacement wood should be scarfed into the original stringer on each side if the stringer is "structural" wood, which I suspect it is.  Can you tell from the shavings what kind of wood you have there?  I'm assuming it's not balsa...

It looks to me like the "flat plate" portion that the step sits on was added after, and the fiberglass covering the stringer was cut post construction to fit it?  The Flat portion seems to be a different color, and there is sealant around the edges. 

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It almost looks like mat layup under the mast step. But that might imply that the 4 layers of UD were cut by the mast step. Nobody would do that would they?

For a 27' boat I'm with JonB on this one.

It's survived sailing with the damp wood so far. 

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1 hour ago, Zonker said:

It almost looks like mat layup under the mast step. But that might imply that the 4 layers of UD were cut by the mast step. Nobody would do that would they?

For a 27' boat I'm with JonB on this one.

It's survived sailing with the damp wood so far. 

So from what I know of the history of the boat, when the mast was lost the first time (or maybe in a separate incident?) the original aluminum tubed compression post was damaged.
So the compression post that's on now (which is a seriously strong & heavy piece of kit) was built to replace the original. I can only guess that perhaps some of the step was cut away at this time. They almost certainly didn't have the drawings that I have as I had to ask for them from the designer especially.
Otherwise there's not much point to UD rovings across the top of a beam if you cut them in the middle.
 

@Crash I think the wood is oak. Its definitely structural, the rest of the floors are foam cored, obviously this has the timber to take the mast compression loads.

I'll take the suggestions of what most have said & sail it for this year, at the least with epoxy filled holes there is no chance of water getting in that way. And I'll just keep a close eye on it over the coming years.

The problem with this form of construction, molded liner that's then bonded into the hull mean that any water that does manage to seep in there (and I've found quite a few places it can) has no real way to escape.

 

(I said stronger than the original to compensate for the fact that I'd be doing the work as an enthusiastic amateur rather than a pro who does this day in day out.)

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58 minutes ago, MiddayGun said:

The problem with this form of construction, molded liner that's then bonded into the hull mean that any water that does manage to seep in there (and I've found quite a few places it can) has no real way to escape.

Living in a rain forest taught me long ago that you can never keep water entirely out.

You can only trap it in.

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Sounds like a reasonable plan. Mast compression loads are VERY ROUGHLY = the weight of the boat on a boat like this.  Say 7000 lbs ? = 31,000 N

White Oak cross grain compressive strength = 7400 kPA = 7.4 MPa

So required area to resist this = 31000 N / 7.4 KPa = 4189 mm2.  So if your mast step is 75mm in the fore/aft dimension, you only need 55mm in transverse direction to resist crushing loads (with no safety factor)

Therefore, a few holes potted with epoxy ain't gonna matter. You don't need much oak that is intact. Don't forget the glass on top helps a bit too (if there is UD still there)

 

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I would fill the holes with epoxy and stuff strings of pre-wetted  glass in there until i couldn’t stuff any more in there 

considering it is apart and more available / accessible than ever before, I would lay on a bunch of layers of glass. You don’t have anything to lose by sanding the top and walls and laying on ten layers of mat. The section would spread the load and you would no longer give a rat’s ass if the wood totally composted. 
so what if you spend ten bucks on materials?? Never worrying again has to be worth $10 or even $12
 

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20 hours ago, MiddayGun said:

(I said stronger than the original to compensate for the fact that I'd be doing the work as an enthusiastic amateur rather than a pro who does this day in day out.)

The composite work doesn't know if you are an amateur or a pro. It's not that complicated or difficult to do it right. Even Gouv can do it. (Sorry Gouv, couldn't help myself. Actually, Gouv has offered heaps of solid, practical advice to get people sailing again on here.) And there is plenty of information easily available to help. Surprisingly quite a good amount of that help and advice can be found right here. (Trying sooo hard not to direct you to the inexperienced couple catamaran thread to learn about boat repair...No, I won't do it. This OP seems like an okay guy...)

The Gougeon books, pamphlets etc. are one good place to start. If you truly have zero experience with this kind of thing, it will be worth the extra cost and time to do some practice before diving into your actual repairs. The worst work results come from people buying just barely enough material for the repair they need to do and then diving right in and trying to make that work. And there is plenty of poor quality work done by "professionals." (Just saying.)

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27's advice to practice is good advice. Laminating up a few small pieces on a bench will quickly learn ya how to wet out and roll out and squeegee out a lamination without having to later grind out any mistakes.

Keep in mind that laminating fiberglass is regarded as semi-skilled labour (except high tech stuff).

BITD of the SoCal and Tampa Bay sailboat industry most of the laminating was done by pickup labour who were given a few minutes to a few hours training.

Most of those boats are still floating.

I regard basic laminating as being easier than hanging wallpaper - you don't have to match seams so perfectly.

Laminating cored construction is little more difficult than making a peanut butter sandwich.

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Cheers guys.

This isn't quite my first (laminating) rodeo, I actually just finished a chain-plate relocation project which involved a good bit of fibreglassing.
Here :)

However working a drawing & deciding how many layers & the best approach to make myself are two different things. Hence the question about a good layup schedule.
I'll stick with the plan of seeing how it holds up over the year, I like Govs suggestion, but if I add any more thickness to the top of the foot then i'll have to shorten the compression post as its a tight fit as is.

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29 minutes ago, SloopJonB said:

I just checked out your thread - you should be here answering questions, not asking them. :D

Dunno... anybody who uses the term “layup schedule” when describing a simple repair job reeks of what Country folks call “all hat and no cattle.”

 

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38 minutes ago, Gouvernail said:

Dunno... anybody who uses the term “layup schedule” when describing a simple repair job reeks of what Country folks call “all hat and no cattle.”

 

Doing it is simple enough, knowing what constitutes as strong enough takes experience.
I'd rather ask and look stupid than take my chances with my own uneducated guess. Pretty sure that's the opposite of 'all hat & no cattle'.

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5 hours ago, MiddayGun said:

Doing it is simple enough, knowing what constitutes as strong enough takes experience.
I'd rather ask and look stupid than take my chances with my own uneducated guess. Pretty sure that's the opposite of 'all hat & no cattle'.

I should have said.,. “Don’t take this personally... “.  
To me “layup schedule” is in the same dictionary as forsl, larboard, marine varnish, pre-owned, black tie optional, light beer, marine surveyor, back in the day,  decelleration, underwhelmed, and some other words and phrases people use when trying their hide the fact they are unfamiliar with a subject. 
 

as this is Sailing Anarchy, I feel obligated to tease and even abuse other posters in an effort to make them feel appropriately loved and appreciated 

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48 minutes ago, Gouvernail said:

as this is Sailing Anarchy, I feel obligated to tease and even abuse other posters in an effort to make them feel appropriately loved and appreciated 

It's our duty.

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Mat is usually fine if you use 10x as much as the equivalent weight of cloth.

Oak rots kinda fast but drilling the test holes will give you a map of the damp zone. Leave the holes open for a week with a lamp down there to dry it a bit then seal with epoxy. Sail it, sell it, business as usual.

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have you tried tapping the wood inside with a metal rod of some kind to get an idea of how soft or hard the hidden wood is ( long thin screw driver or # 8-10 wire )

the condition of the wood to a large extent governs what approach to take to fix / remediate the problem ( it looks fine .. just wet )

to me it needs to be dried out before you even start to fix it .. and that may take awhile .. i would even go as far as drilling through in a couple of places at floor level on both sides to see what comes out .. these can easily be plugged or filled later .. in this case that information is important enough to justify it

then take a look around and fill the areas it might be getting in

 

as far as the actual fixing goes perhaps wetting out with evadure or epoxy thinners thinned epoxy resin ( 10 - 20 % tested to see how well it goes off first ) it may not be necessary but its always a good idea to treat wood with it .. its why its part of every boat builders supplies nowadays .. im not sure how well it works with oak you will have to research that yourself

 

if your going to overlay the glass with another laminate then i would also recommend trying to get hold of some promoted styrene monomer ( 0.2% cobalt octoate and 0.01% dma at least )

sand the area then paint on liberally the styrene mix then wipe off the first coat then reapply more and leave it ( it cleans and keys )

and leave that for 24 hours before glassing over it .. ( hint for all those repairing boat laminates over old glass .. it helps the key by quite a margin )

 

 

 

 

 

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The screwdriver test I already did and it was successful that I couldn't dig it into the wood any more than I would expect to be able to on fresh wood so that's good news at least.

For this year I'm just going to leave it, there's no sign of compression in the step, the only reason I discovered the damp was because I had to remove the compression post.
I saturated all the holes with acetone, left it a few hours to soak in, dry out. Blasted the holes with air, left it another few hours with a fanheater pointed at it. (probably all uncessary)
And then used a plastic syringe to fill it with epoxy thickened with cabosil, still pretty runny, but thick enough that I couldn't just pour it in.

Long term it may need addressing, water does seem to make it into the floors somehow, and not from the bilge area, from somewhere else, probably some leaking fitting in the internal liner.
On the other hand its lasted 30 years...

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12 hours ago, Bruno said:

business as usual.

if your going to downvote a fix at least do me the favour of explaining your logic that way i can see if my explanation needs more clarification

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I suspect it was retaliatory.

There are a number of children here who do that as a response to getting a downer.

Some will go back for days and carpet bomb all of a persons posts with downers.

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in his defense .. mine was the retaliatory one

i was just wondering why he would downvote mine .. im into research .. if im wrong in any way i want to know .. things change over time and i may be out of touch in some areas 

 

i have removed my downvote for his post .. but i am still very interested in why he saw fit to give me one

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11 hours ago, phill_nz said:

if your going to downvote a fix at least do me the favour of explaining your logic that way i can see if my explanation needs more clarification

Did I downvote your recommendation? My bad, I meant to say that's an interesting technique to improve polyester's notoriously poor secondary bonding. Why does the styrene require (vinylester) promotion? Why not just plain styrene to activate the surface? Styrene is a solvent, I guess, in this use? So it is re-solving the surface? I have had similar experiences with acetone but noted your technique above for testing the cure state of a gelcoat. My impression is styrene vaporizes in the cure?

I seem to have a problem with the reaction button provided, combination of fat fingers on the tablet and the ambiguity of the symbols. To me the up and down look identical so I can't see if I strike the wrong one.

Only improvement I'd suggest is to make sure you glove up when wet sanding the styrene into the surface and if you are making an epoxy repair then it's perhaps unnecessary. 

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no the styrene is part of the linking .. its not used as a solvent in that case

its not wet sanded with styrene .. its sanded then painted / coated / flushed with the promoted styrene

from enc britt

Styrene, liquid hydrocarbon that is important chiefly for its marked tendency to undergo polymerization (a process in which individual molecules are linked to produce extremely large, multiple-unit molecules). Styrene is employed in the manufacture of polystyrene, an important plastic, as well as a number of specialty plastics and synthetic rubbers.

 

epoxy is what i use for small repairs

it has some advantages over polyester

 

for large repairs i tend to go to polyester

it has some advantages over epoxy

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there are a few

it matches the original in flexibility and strength so when one bends the other bends with an equal amount of strain on it

it weathers better .. without uv blockers and absorbers epoxy doesn't do well under uv

it is easier to use / manipulate on large areas both in time between layers and procedure to lay it down

because it gels a lot faster large areas on verticals dont tend to slide, sag or pool ( drainage )  before they gel

 

 

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5 hours ago, Bruno said:

that's an interesting technique to improve polyester's notoriously poor secondary bonding.

the first time i came across it was when the lab i started working for ( R&D gelcoats and resins ) had a mac truck that had hit a bridge and ripped off the front left corner

the driver didnt bother picking up the bits so it was a laminate onto free space job

they asked me to " have a go "

i cleaned up the fractured bits sanded and cleaned the surviving area and pondered the procedure needed  one of the ( dam good ) resin chemists came down and said .. do this ( add cobalt and dma to styrene then wash, wipe and wash again ) and it will help the bonding

the next day i started trying to get a framework to laminate on so there were bits of glass sagging here and there and other bits being held up with masking tape .. this is what the engineers saw the next morning and promptly complained to my bosses ( ok it did look an absolute abortionate mess )  .. luckily they understood the problem .. and my explanation that i needed to start with something to laminate to ..  i started by cutting off all the bits hanging off i didnt need and then laying it up    it all took a couple of days doing it in the time i was free from my job

almost as soon as i had finished the truck mechanic right in front of me picked up a heavy rubber mallet and smashed it as hard as he could right on the corner i had just repaired   .. the rebound strained his wrist ...  the repair didnt move in any way ... and i went off my nut at him for trying to test the repair before it had time to cure properly

i also doubt the undamaged corner would have stood up to what he did .. he hit it that hard

 

sold me on the method in     " one hit  "

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  • 1 year later...

OK so 1.5 years on I need to revisit this. 
Warning, this post is wordy, full of pics & semi educated guesses.

A couple of months ago I noticed some cracking in the paint in front of the mast step, so I did a little digging and its actually a crack in the laminate.
(This section is not actually the hull, but part of the internal line)

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Now I suspect this may have existed a while, given that if you look to the right of the second picture, someone's done a shit job with finishing fabric, the thin stuff useless stuff that chandlery's sell. But I suspect its caused by the foot of the compression post sagging. Just to make it to the end of the season, I applied permanent market at each end of the crack & so far its stayed stable.

While I was in the digging around mood I decided to start poking around for the source of some bilge water that didn't seem to coming from any obvious source. 
On two of the floors glass fibre has split away at the bottom radius in the middle areas. Its actually sprung forward over the top of the backing plate for the keel bolts.
There is also evidence of a repair on the fwd edge of one as its not very true compared to the others. Water is leaking somewhere else on the boat (fresh water), getting behind the internal liner & coming out via these cracks.

 

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Not a pleasant discovery, however no evidence of anything at the very FWD end of the keel or the very aft end so I doubt its grounding damage.
Its almost as if the keel nut backing plates are too close to the radius at the bottom of the floors & have cut through it.
Anyway I bit the bullet & decided to do some more digging, by cutting out the side & bottom of the moulded in locker under the port settee to get access to the mast compression post & also to see if the floors carried on under the lockers. 

Not much of what I found was nice:
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The foam in the side of of the settee was in good condition although not particularly well bonded to the GRP. The stuff in the bottom however had a lot of sitting moisture & water between it & the hull & that lovely smell you get from GRP & polyester foam that's had water sat in it for 30 years.

A load of this crap came out, can't tell if its wood shavings or resin starved matt, it stank & was sodden.
20210916_135029.thumb.jpg.5c450139c46fefdc978981960f2e5b31.jpg

 

Yummy:
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British boat building at its finest!
So the solid hardwood core of the mast compression post is actually pretty soggy, its not one piece but three pieces, not even bonded together or at least not anymore. Its also not even fitting the hull very well at the edges, although this is possibly due to the compression in the middle springing up the edges. I would have thought they would have glassed something this important in. 
I imagine the condition of the centre of the wooden block is worse as that's the lowest point of the bilge & any water will accumulate there.

Also, as far as I can tell, the only place that the keel floors are glassed to the hull is the relatively narrow area you can see in one of the above pics, the rest is completely relying on the bond between the self expanding polyester foam & the hull.

So in conclusion need to replace the compression step, I can't see anyway to do this other than cutting open the floor & re-glassing after. Not sure if there is a better material than a solid oak block thats been soaked in epoxy. 
I also need to repair the splitting floors, which will involve at a minimum taking off the keel nuts & backing plates & hopefully working around the studs without dropping the keel. I'm thinking of using the hoist to take the weight of the hull off the keel. Afloat would probably be best for hull shape, but don't fancy unbolting the keel afloat!

 

I'm most likely getting semi-professional help with this one from a retired guy that ran a boat repair business fixing stuff like this for 40 years, but would still like to get any advice or suggestions on how you'd tackle something like this. (or just commiserations!)

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the bit that looks like toilet drain residue is probably glass ( easy test .. burn it )

is the boat made from ortho ?

that tends to rot like that

it normally takes a lot of uv and rain  to make iso go that way

look for areas where the glass looks white and opaque .. we call those problem areas

you may have to dig down in the lowest areas where the water is likely to settle and see if the glass on the hull is similarly compromised

 

there is a chance the liner and hull were laid up with different laminates

one way or another it will be fixable

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3 hours ago, phill_nz said:

the bit that looks like toilet drain residue is probably glass ( easy test .. burn it )

is the boat made from ortho ?

that tends to rot like that

it normally takes a lot of uv and rain  to make iso go that way

look for areas where the glass looks white and opaque .. we call those problem areas

you may have to dig down in the lowest areas where the water is likely to settle and see if the glass on the hull is similarly compromised

 

there is a chance the liner and hull were laid up with different laminates

one way or another it will be fixable

1986 boat. So I think  isophthalic. 
Definitely not UV due to location. 

Liner & hull were laid up separately & then the liner was locked in place while expanding foam was injected to fill all the cavities. Probably a great idea at the time, but a nightmare for access now. 
Hull laminate looks perfect, its the inside of the liner that's going like that. It looks like they may have bonded the two together with some globs of resin & fibre in places, hard to tell. 

Plan is to properly tap the saloon seat sides into the hull & then to replace the expanding foam, bond in some sort of high density core laminated panel before tapping that in as well. Basically as if I was recoring a deck, but from the side.

Looks like I'll have to cut out at least part of the mast compression step floor to put new material in, not sure if I should just cut the top out & taper the sides or if its better to cut the whole floor out & re-glass that way.

Question for those in the know.. Is it possible to use some sort of non wooden core material? Would any of them even take the compression load?

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1 hour ago, MiddayGun said:

… Question for those in the know.. Is it possible to use some sort of non wooden core material? Would any of them even take the compression load?

That wood is not installed (it appears) as a compression member. Looks like the intention was as a beam. Could be replaced with a layup of ‘glass. But the wood seems to have worked for decades so it could simply be renewed. 

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upload_2021-7-13_10-7-46.png

 

All the other floors are foam cored. Drawing specifically calls for timber blocking under compression post frame. 
Right now I'm thinking cut the very top section of that floor out but not all the way back to the outboard ends.

Template & make up new solid timber compression post. (in one piece) Epoxy soak it & probably cover with a thin layer of finish cloth for some extra water resistance.
Install into place on a thin layer of thickened epoxy to bond it into the hull, then grind a taper onto what's left of the beam & lay up with Biax. Possibly on the final two layers draping them fully over the floor and into the bilge area to tie it all in. 

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6 hours ago, MiddayGun said:

. Is it possible to use some sort of non wooden core material? Would any of them even take the compression load?

yeah. You use a sandwich of foam/glass plates. The glass plates take the load, the foam keeps the relatively thin plates from buckling

Coosa board in higher densities might be strong enough. Compare it's compressive strength to that of end grain oak and I'm sure it's lower but it might be ok even at 50%.

Assume mast compressive load = weight of boat. We'll call this "F" for force

Assume area of foot = area right under step plate. Call this "A" for area. Units are the student's choice (lbs/inches or N/mm2 because N/mm2 = MPa which is typical strength data in metric)

Compressive stress = F / A. Compare to published values and see.

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8 hours ago, Borracho said:

That wood is not installed (it appears) as a compression member. Looks like the intention was as a beam. Could be replaced with a layup of ‘glass. But the wood seems to have worked for decades so it could simply be renewed. 

This ,ala Mads on sail life. Whatever is easier for the specific situation.

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Having done a very similar repair on an SC 27, I would be inclined to scrap the enclosed wood approach and instead construct a thick laminated wood beam.  Cut out what is there and replace it with the laminated beam.  Put a rebate in the bottom of the beam so any bilge water flows underneath it and doesn't get trapped against the wood.  Epoxy the beam to the bottom of the boat with tabbing that goes up to the top of the beam where it attaches.  20200506_160949.thumb.jpg.bf87639ea41f2c28b06653d765f89877.jpg

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14 hours ago, MiddayGun said:

1986 boat. So I think  isophthalic. 

we were still making ortho for a customer till mid 90s

1999 we told him he had been getting an iso for 4 years as it was cheaper for us to supply him with an iso than cook an ortho just for him ( we checked what he was making first and decided an iso would be better than an ortho for his work )  his only reasoning was the old one where early iso's were harder to use so he stuck with ortho

 

Liner & hull were laid up separately & then the liner was locked in place while expanding foam was injected to fill all the cavities. Probably a great idea at the time, but a nightmare for access now. 

hmm yup .. they may have just gunned a layer onto the contact points and sat the liner in it till it went off then used the expanding foam .. i have heard some did it that way .. we tended to put coremat on all the contact points and wet it out before siting the liner

it would explain the handfuls of stray cut glass fibres if there isn't that much that has completely rotted away

 

Template & make up new solid timber compression post. (in one piece) Epoxy soak it & probably cover with a thin layer of finish cloth for some extra water resistance.

not sure the finish cloth ( 2oz ? ) is needed

recommended max thinning of epoxy is / was 10% with epoxy thinners

i have thinned some out 30% and injected it via needle and syringe into a shit board floor that had softened a lot .. went off and floor is hard and fine after 5 more years of use and spillage ( test to see if yours will go off if thinned that much first ) 

then let the wood drink all it can

 

not sure using anything other than wood is worthwhile

maybe sandwich with thinned epoxy 4mm thick  wood to make your own beam .....  would end up pretty much bullet proof but like the rest .. not worth the effort for the gain

 

 

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17 hours ago, Bruno said:

Not sailing related, apologies, but I have looking for information on how well polyester bonds to concrete, not much out there as the industry prefers epoxy, anyone got any experience?

we used to make the resin for a company that made concrete pipes

they used it to make the ' concrete '  fittings for pipes

was basically a really thinned down ( with styrene monomer )  standard iso

from mem the resin just replaced the water in a fairly standard concrete mix .. pretty sure the cement was still part of it .. but not 100%

they used to bond to standard concrete pipes with the mix as well as using it for casting angle etc joins

so

ummm

yup probably fine for use

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On 9/18/2021 at 8:50 PM, Bruno said:

Not sailing related, apologies, but I have looking for information on how well polyester bonds to concrete, not much out there as the industry prefers epoxy, anyone got any experience?

In my part if the world, gunnite/concrete swimming pools are often refinished with polyester resin and CSM, it seems to last for about 20 years until needing replacing

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Some rough calculations. 

Working on a weight of 3000kg (which is probably 200-300 kg over, but it seems a good idea to over rather than underestimate.
Area of the mast post base is 100x100mm. 

So that works out 0.3kg /mm2. Multiply that by 9.81 to get 2.943N/mm2. Lets just round it up and say 3MPa.

I'm struggling to find a readily available core material in the UK that has a high enough compressive strength, the best ones I can find have a density 100kg/m3, but they are short on the strength required. The only one that looked good enough was a 3d core that needed to be used with vacuum infusion to attain full strength. 

Oak seems to be 3.79MPa ish, parallel to the grain, so I'll probably just go with that & epoxy saturate it first. 
The 4x600gsm layers of uni over the top should help spread it out anyway. 

Existing layup is 300gsm CSM, 4x 600gsm UR over the very top (although in this case it looks to have  been cut) & a final 450gsm layer of mate. So the existing laminate isn't hugely thick. Can't decide if I should just cut the top section out & grind back the vertical edges for my taper. Or cut the whole thing out & laminate in a new one. 

Hard part about laminating a new one in is to try and tie it into the existing settees at the edge of the bilge as I'd rather avoid sanding and glassing any of the visible areas above the sole boards if possible. 

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22 hours ago, MiddayGun said:

epoxy saturate it first. 

Really you're just coating it. The epoxy only penetrates ~1mm or less (probably less with something like oak).

Just do 3 thick layers of resin. You can hot coat with a new layer once the first layer has cured a bit (no need for it to get super hard).

If it were me I would just taper the top and re-laminate. Throw in an extra 1 or 2 layers of uni if you're worried at all. Won't hurt and it's weight down in the bilge.
 

Rainman's solution of a laminated wood beam is probably just as good.

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Well today I did some 'exploratory cutting' to see what I'm working with. 
Took a section of the side & top of the floor & also the inner skin of the bilge area in front of it. 

First discovery was that what looked like a rebate cut into the top of the floor (and through the uni as Zonker said earlier) turned out to be something else entirely. 
Someone has covered the top with what I can only describe as polyester filler, the easy sand stuff you use on car repairs. Think you call it BOG in the USA? 

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This has literally been skimmed over the whole thing (other than where the compression post sits ) and painted over. They didn't even bother to sand it back, they bogged directly over bilge paint! 
I have no idea why, the only theory I have is that the floor had sunk due to the deterioration of the core & they added the filler so the cabin sole boards would sit on it.

20210920_182041.thumb.jpg.5dc30ae60f736f52ff8a6046e1cfe986.jpg

Pic doesn't do it justice, its that water logged than when I was chiseling the cut section out it was squirting me in the face with decades old moisture! 
You can see the thickness of the filler. & also that there is a big gap between the top of the floor and the core.

The cracked section in the inner skin of the bilge in front of this area was next.

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Again full of moisture. It was held in with blobs of filler you can see in the next pic. 
These had no bond at all.

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Crack went completely through the inner skin. 

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And the inner skin was missing its foam core, so its not even a cored structure here, just an unsupported inner skin taking all the force from the floor. 

20210920_183805.thumb.jpg.6db404508a8765b348bfa45e6fa45143.jpg

In a way its made me much more confident with my upcoming repair, because whatever I do will be way better than this. 


Current plan is to half follow rainmans advice, I will make the beam, but I'll laminate it in using the as drawn layup schedule with the UR but with biax instead of woven roving. Maybe a couple of extra layers, its in the bilge so the weight is negligible. 

Modified.thumb.png.a2d0f9971e35cb2e9972942a5bed0c91.png

Fully cut out inner skin marked in yellow to gain access to the bilge. Clean up, grind it to key it.

Cut out purple top section & recore with laminated wooden beam, epoxy it in place to the hull as per Rainmans suggestion. 
With that structure back in grind back the edges ( I may have to cut out the front face of the floor as its glassed into the inner skin not the hull. 
Glass it all back together & tab the red sections into the hull properly. 
Finally add the 4 extra layers called for in the drawings to the yellow area. 

The idea is that when finished there is no way for water to get in again.
Probably overkill, but its not much extra work while I have it all apart. 

Any thoughts on using Vinyester resin for this? I like being able to work quicker & I find its nicer to glass with than epoxy, but with me epoxy coating the beam I'm not sure how well it would bond to it?
 

 

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What's the hull cored with (other than mush?). Surprised it's held together but the inner skin with the crack right through it was a real red flag.

I'd be mentally prepared to open up a lot more hull than you have outlined if the missing/damaged core goes further than you think. 

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9 hours ago, Zonker said:

What's the hull cored with (other than mush?). Surprised it's held together but the inner skin with the crack right through it was a real red flag.

I'd be mentally prepared to open up a lot more hull than you have outlined if the missing/damaged core goes further than you think. 

Its not a cored hull as such. 
Its a solid laminate hull with an inner liner placed inside & the cavities filled with expanding foam. The idea at the time was I believe to save lots of time with building & tabbing the interior structure.

To quote the material:

Quote

The main hull incorporates chopped strand mat and woven rovings. Inside it is placed a liner moulding that includes floors, frames, bunk bases & location points for other furniture & bulkheads. Once the lining has been attached, the gap between the two is injected with foam under pressure which sets to form a dense & rigid structure. During the injection of foam, jigs lock the inner lining in place to prevent it distorting as the foam expands.

The only problem is that as can be seen, the foam doesn't appear to have actually made it to all areas. 
 

By tabbing the structure into the hull itself I can hopefully make an effective repair without ripping out the whole cabin. The hull itself seems to be a fairly thick laminate:

image.png.3ed2fd7d6f83fdd641c07d6dbce55060.png

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1 hour ago, Bruno said:

2 part polyurethane foam and the mast step, it seemed like a bad idea at the time. I am now never surprised by expedient solutions.

No the mast step was supposed to have a solid oak core. 
Unfortunately they didn't manage a good job of it.

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  • 1 month later...

Well boats out the water & well supported, so last night I did a bit more surgery. 

New section cutout, I haven't fully decided on how I'm going to tie it all back together yet, but decided to leave 150mm of the existing floor at either end as I suspect I'll have to grind a big taper on that & tie it in. 
I won't be able to fit the new oak core in once piece so I'll probably cut the middle section out with a 12:1 taper & bond it all into the bilge on thickened epoxy with glass & epoxy over everything to tie it all in. 

The wood is completely saturated. I can basically push a screw driver through it. Also note the gaps between wood and glass fibre.
20211112_165729.thumb.jpg.92e2fb463d27d9be20fae61064c08738.jpg

 

Basically held in with blobs of filler. 

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Finally bit of a cross section. Looks like there's the initial layup, some gelcoat & then some kind of repair / filler on top. 

20211112_164832.thumb.jpg.5ebf025ad8ddb5599c601abdae3b7628.jpg

 

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we used to embed the keel plank that way

do the glass layup then make up a resin, talc and microsphere bog , we just put the wood down in a bed of bog then another laminate over the top

it wasnt an unusual method to do it

that was goping down into a keel trough in the mold so flush at the top

 

looks like they used a similar method to do it to for a proud beam .. probably not the best idea for that

 

 

 

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On 11/14/2021 at 9:50 AM, phill_nz said:

we used to embed the keel plank that way

do the glass layup then make up a resin, talc and microsphere bog , we just put the wood down in a bed of bog then another laminate over the top

it wasnt an unusual method to do it

that was goping down into a keel trough in the mold so flush at the top

 

looks like they used a similar method to do it to for a proud beam .. probably not the best idea for that

 

 

 

Yeah, bedding it in bog seems to make sense to me as it bridges any gaps and ties it all in. In this case they put a preformed laminate over the top, so there are large gaps between the GRP and compression foot. 

I got the rest of the wood out today, what a mess, being squirted with stagnant bilge water every time I hit it with the chisel. 

20211114_171905.thumb.jpg.26e41a6a5a16799ecb20d951e371b819.jpg


Underneath the wood was pure resin, no filler at all, not sure how thick it is, and if its worth trying to remove back to solid laminate or just grinding it & putting the beam on top. With no glass I expect its kind of brittle.  

20211114_182230.thumb.jpg.e108dff95bf49ddaaa947adbb20f5289.jpg


Looks like water has been migrating through the internal liner & sitting there for god knows how long. Don't know what causes this next bit, lack of resin?

20211114_180952.thumb.jpg.2157ef24260c532dec4247b847c4858b.jpg

Here's a textbook example of how not to do a repair, lightweight finishing glass laminated over the  floor. No need to remove the gelcoat, in fact fuck it, don't bother removing the paint either, just slap it on! :D

20211114_183841.thumb.jpg.d0c3ad60bc9778fbd90876db146174b2.jpg

 

And finally, I cut a section out of the 'cored' area of the bilge away from the keel. 
The builders were pioneering a new weight saving composite technique by using oxygen as the core material, great weight saving, no chance of delamination & it keeps the cost down. Rigidity and strength do take a bit of a hit though!

20211114_184418.thumb.jpg.c1e4cc8ee70fdae1c4840b89a72313b9.jpg

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the resin rich area ( puddles ) usually happen at the bottom of the mold on layup ( the bottom position depends on the angle of the mold at the time ... in  normal gun layups the mold is sprayed with resin then the chopper started to deposit the glass resin mix .. it can cause wet areas esp after rolling as some resin will migrate / drain downwards as its worked through the glass layer .. there is reasons some areas get more resin during the first wetout stage than others .. this also contributes to puddles .. )

 

the white glass area looks like it has gone through many wet dry cycles where the glass will wick ( capillary action ) the wetness and debond the resin from it

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1 hour ago, phill_nz said:

 

the white glass area looks like it has gone through many wet dry cycles where the glass will wick ( capillary action ) the wetness and debond the resin from it

That would explain it then, I have survey from the boat a good 15 years ago that noted a high moisture reading from the hull, despite no signs of osmosis / blistering. 
I suspect that years of slight leaks from fittings have allowed water to migrate between the hull and internal liner, its supposed to be filled with low density foam but there are lots of voids . Once inside its basically trapped there. 

As to the resin puddles, that may be it, although I don't think a chopper gun was used to build these boats, the laminate is specified in CSM & Combi Matt layers. 

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1 hour ago, MiddayGun said:

Once inside its basically trapped there.

That is something one learns from living in a rainforest - you can never entirely keep water out, you can only trap it in.

Boats, houses in wet area etc. etc. should all be built with that in mind.

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On 11/15/2021 at 3:21 PM, SloopJonB said:

That is something one learns from living in a rainforest - you can never entirely keep water out, you can only trap it in.

Boats, houses in wet area etc. etc. should all be built with that in mind.

But then they cost more than the ones that are not built with that in mind and not enough people will pay the extra money for something they can't see.

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  • 1 month later...

This has turned in an absolute mission. 
Opening pandoras box was not a great idea. 

From the digging its been clear that the secondary bonding between the hull liner (which like a modern boat, contains the full structural grid) and the hull, has left a lot to be desired. Same for the build quality, the factory seems to have chucked in tons of chopped strand matt in the bilge area & around the structural members but without any proper prep. 

Literally large chunks are peeling away with a little bit of persuasion from a chisel, or in some cases, just by hand. Fortunately the hull underneath seems to be in great condition. 
Between the hull & the extra layer of glass is a thin layer of water, it looks like over time that the secondary bond started to seperate, which allowed water to seep in between the layers of fibreglass. Possibly a few freeze thaw cycles. 
After 30 years the whole lot is ready to just pop out. You can see how much dry glass and filler are there in the pics.

 

20211201_132720.thumb.jpg.df45ca6440eaf94320562078a2932285.jpg20211206_164824.thumb.jpg.08d0f5a7f0b2cde8d094e535db2b4e10.jpg20211206_165315.thumb.jpg.70ac727b0b923e1c21f2c709420bae44.jpg

 

Keel nuts & backing plate off for access. 
Nice chamfer on the back to hold sealant. Unfortunately the FWD most backing plate has a bow in it, will need replacing. 

20211229_130029.thumb.jpg.7d04ac3a943da1f60d9af03008f9bccc.jpg20211229_130144.thumb.jpg.5af463f25070febf001afbbc3d34f9d6.jpg

 

Had to hammer the socket onto this nut as the front face of the floor had sprung over it. 

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2nd backing plate back, not really enough material left near the edge for my liking. 
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Top cut off the next floor back. Yum. 
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Here you can really see all the trapped moisture.

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The current plan is to get back to solid glass everywhere, grind it all back. Then lay in several layers of glass across the whole bilge area & tabbed into the sides of the existing bunk structure. 
As built the drawings called for: Gelcoat - 300gsm CSM - 2x 270gsm Uni-Rovings over the keel area - 450gsm CSM.
I'm planning to put in: 600gsm CSM - 400gsm CSM - 2x 600gsm stitched biaxial - 300gsm CSM. 

I may add a 3rd layer of the biax, but I don't think it will be necessary as biax is already a superior cloth the UR & I'm putting a lot more in.

That will replace & then  some the extra laminate that should have been put there from the factory, I'll then build my structure on top of that, replacing the floors and compression foot. 

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25 minutes ago, Zonker said:

Any cardboard or paper derivatives? 

You jest. But actually if you look at the 2nd floor that I've cut out, the plywood lining in that has basically taken on the texture of wet cardboard! 

The only silver lining to all of this is that seeing that the boat has lasted 30 years without the keel falling off, despite the fact that the builders pretty much ignored the drawings and didn't bother with half the specified laminations. Unless I really fuck up, whatever I do will be a lot stronger. 

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Some hard earned experience for you.

Tape the seams of every door & drawer on the boat.

Remove all soft goods from the boat.

Drape plastic sheet before & behind the work area - tape it down fully - not just tabs.

You want to isolate your work area as much as possible but no matter how well you do it you are going to get glass in the rest of the boat so do everything you can to minimize it.

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26 minutes ago, SloopJonB said:

Some hard earned experience for you.

Tape the seams of every door & drawer on the boat.

Remove all soft goods from the boat.

Drape plastic sheet before & behind the work area - tape it down fully - not just tabs.

You want to isolate your work area as much as possible but no matter how well you do it you are going to get glass in the rest of the boat so do everything you can to minimize it.

Don't worry. 
I already did all of the above & more :). 

The inside of the boat looks like a kill room Dexter would be proud of. 
I earned that experience the hard way when I did my chain plates. 
IMG_20191106_134629.thumb.jpg.e5c63de6d1b79698280785656cdec809.jpg

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Progress update:

Got the last bits ripped out up fwd. This piece was sat underneath the keel bolt I'm undoing in a previous picture! 
It literally peeled off by hand in once piece. 
20220103_112515.thumb.jpg.fc04d7450880e8941d78df632326fab6.jpg20220103_112522.thumb.jpg.fc9e3a7ae4a46456411c951790409e9b.jpg

The boats fairly well supported, but I decided it was time to add some structure back before I rip any more out. 
Made a template from the old dust sheeting.
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Test fitting and  adjusting all the layers of cloth. Not shown are the side pieces of tabbing. 

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Annnnnnn done. Fucking horrible job. 

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Not sure who cut that backing plate, Stevie Wonder by the looks of things. 
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I went for 600gsm CSM - 600gsm Biax - 450gsm CSM - 600gsm Biax - 450gsm CSM.
Tabbing for the sides I used a 300/600 combi matt / biax combination, followed by another layer of 600 biax. The last layer of 450 that I laid in the bilge I did after the tabbing to try and give it a nicer more uniform finish. 

Since the internal molding was only a couple of layers of chopped stand & 2 layers of 200gsm woven roving that was poorly bonded in, this should be way stronger. My only concern is if I've added enough overall thickness to the hull laminate as the resin / glass slurry they used originally did bulk it up a bit. 

Started on templating up the mast compression floor. It will be 4 pieces of 26mm thick white oak. Epoxied / screwed together. (Screws just to hold it while the epoxy goes off) Would have finished today, but my jigsaw packed up. 
I think one large piece would be better, but its not practical to fit it, this is going to be way stronger than the factory did, plus it will be properly glassed in, not just bogged with some glass slurry. 
The end of the old floor don't add much in the way of structure, I mainly left them there to get the positioning and angle of the top surface correct as there aren't many good reference points in the cabin. 

Some points:
- I forgot how bad the styrene smell is, if anything Vinyl ester seems worse than Polyester. I used a proper respirator but still felt pretty weird on the  drive home. 
- Its been ages since I used CSM. Forgot how much resin it needed, plus I ended up making a bit of a mess trying to wet it out, need to practice my technique. 
- When the first batches start kicking and literally every thing you touch becomes sticky. Must have gone through 8 pairs of gloves.

Is there a technique to wetting out the matt without all the fibres pulling out & getting everywhere? I tried a roller, but it was just using up tons of resin to saturate the roller. 

20220105_132651.jpg

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Why are you using mat at all? Uncrimped fabric (biax) does not need it to fill the gaps that woven fabrics have in the crimps. IME laminates of pure uncrimped fabric can be rolled and squeegeed to a state very close to bagged laminate.

Also, can you not make those keel bolt backers larger to reduce the "point loading" or stress concentration of the bolts?

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I got a professional repair guy to give me some advice before I started. 

He recommended a layer or two of matt to help with adhesion to the bilge for the first layer, in fact he said in most cases when laying onto old fibreglass, even if the repair is in epoxy, he'll generally use a powder bound matt as a first layer. 
I'm inclined to take his advice as he's been repairing boats on the river for over 30 years and nothing he's fixed has ever come apart again, some pretty major repairs he's done are still invisible 20+ years on. 
Maybe its not necessary, but I'm inclined to take his advice as he's done it day in & out for a long time. 

The second reason is to add some thickness to the laminate, strength wise for sure what I've put in is better than the original. But I have lost some thickness which will have contributed to rigidity if not strength. 
Oh and for the final layer it makes a much nicer surface for when I eventually gelcoat or epoxy primer it. 

There will be more glass going over the whole lot when I glass in the floors. 
 

29 minutes ago, SloopJonB said:

Also, can you not make those keel bolt backers larger to reduce the "point loading" or stress concentration of the bolts?

I will make them a little larger, I'm limited by the floors themselves, before they were sat on the radius of the glass which I think contributed to the cracking. 
That said, there's no indication that the backing plate size is an issue, indeed these are larger than the standard ones. But I'm all for overkill for something like this. 

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2 hours ago, MiddayGun said:

Is there a technique to wetting out the matt without all the fibres pulling out & getting everywhere?

stipple with a throw away "chip" brush.  Don't brush. Just vertical jabbing motions. You can even trim the bristles by about 1/2 with scissors before starting to make them stiffer.

image.png.0119ec49ac2278d6d40b181638931d3d.png

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the one on the far right is the one i used for my labwork .. gave me an almost perfect 2/1 glass resin ratio

 

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I have plenty of those, I find they aren't much use in the initial wet out, just for consolidating. 
The long finned roller works great on stitched cloth, but I found that it had a tendency to pull away all the strands of mat until it was fully wetted out, I had more luck with the traditional metal roller. 
Those thin ones are really nice for getting inside a radius though.

Squeegees, the same. Great on the stitched cloth, but I found they tended to pull at the mat. 

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Zonk's advice about stippling with a short, stiff brush is the best for mat - by far.

As you point out, rollers and squeegees move mat fibers around way too much

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Since mat fibers move around so much, I usually barely wet out the matt layer, then place the next layer of cloth & work through that to get the matt wet out

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