steel or GRP??

[Naughty Cal]

What were her moisture readings?

 

Osmosis is more than just blistering of the hull.

[carlt]

 

Absolutely no sign of osmosis and she is somewhere between 40 and 45 years old

(Shapfell is a 25 foot narrow beam GRP cruiser built by Ormelite)

 

Ormelite hulls are about a foot thick though so osmosis shouldn't ever be a problem.

[John V]

A slight exaggeration ..................... but they are very heavily laid up

[Naughty Cal]

The thickness of the layup is irrelevant.

[John V]

What were her moisture readings?

 

Osmosis is more than just blistering of the hull.

 

what on earth would be the point of having moisture readings taken from a hull that shows absolutely no evidence of osmosis or any other problems

[carlt]

The thickness of the layup is irrelevant.

Of course it is relevant.

 

30mm of well laid up composite is going to take a lot more osmotic activity to affect it than a few mm.

 

A nice fat wodge of semi-permeable membrane is a lot less semi-permeable than a dainty thin slice.

 

If the layup is crap on the other hand, thickness is less relevant.

[gazza]

Of course it is relevant.

 

30mm of well laid up composite is going to take a lot more osmotic activity to affect it than a few mm.

 

A nice fat wodge of semi-permeable membrane is a lot less semi-permeable than a dainty thin slice.

 

If the layup is crap on the other hand, thickness is less relevant.

Indeed!

 

I can also testify that Johns Ormelite will be built like a brick sh!thouse, they are also a very high quality build - both in terms of layup and internal fit, the original joinery is top notch.

 

The only thing I dislike about my brothers is it turns like a battleship, being only 25' X 6' 10" odd and having quite a tall cabin the CoG is quite high so it leans outwards on a full lock full power turn, it's the only boat I've been on that does it. Was a bit disconcerting when it underwent it's river trials to check prop suitability and engine cooling performance.

[peterboat]

I have had a number of fibreglass cars the oldest a clan crusader built like a battleship and very well laid up fibreglass [i had to do crash repairs]. My latest is a corvette c4 made to the latest techniques [pressure, heat and vacuum] the layup is thinner but the quality is top notch not a ripple in sight. Early fibreglass cars were nearly as heavy as steel cars I have no doubt boats are the same? as in Johns case huge build thickness and very rigid due to this thickness, so little chance of delamination due to flexing. The springs on the vette are also fibreglass composite which proves GMs faith in the poduct

[Naughty Cal]

Osmosis is the passage of water through the fibreglass lay up

I suggest some of you read up on the process.

 

The thickness of layup has bugger all to do with it which is why even the earliest heaviest laid up boats still suffer with it.

 

http://www.walshsurveyor.com/yachts/articles/osmosis/index.htm

[gazza]

Osmosis is the passage of water through the fibreglass lay up

I suggest some of you read up on the process.

 

The thickness of layup has bugger all to do with it which is why even the earliest heaviest laid up boats still suffer with it.

 

http://www.walshsurveyor.com/yachts/articles/osmosis/index.htm

Correct.

 

But as discussed before, boats don't sink from it.

 

I'd rather a bubbly GRP than a teabag steel boat or rotten wooden one.

 

I've had a hand in a scabby Buckingham that literally had the gell coat flaking off, no water ingress whatsoever.

That one has been sold thank God!

[Naughty Cal]

I'd rather have a GRP boat that had been epoxy treated from new or nearly new. But you live and learn.

 

Had we known what we know now we would have treated NC when we bought her at 5 years old.

 

Now at 13 years old the moisture readings are in the range where it would cause more harm then good. And in the scheme of things they are not high but in the range recommended not to apply an epoxy coating.

[Guest]

I'd rather have a GRP boat that had been epoxy treated from new or nearly new. But you live and learn.

 

Had we known what we know now we would have treated NC when we bought her at 5 years old.

 

Now at 13 years old the moisture readings are in the range where it would cause more harm then good. And in the scheme of things they are not high but in the range recommended not to apply an epoxy coating.

I seem to recall reading that later GRP materials were modified to help slow down osmosis? That being the case, a boat as young as yours will likely be OK for many years to come. I know my late dad's one-time Dawncraft is still afloat after 45 years

Edited May 30, 2016 by Guest

[cereal tiller]

I seem to recall reading that later GRP materials were modified to help slow down osmosis? That being the case, a boat as young as yours will likely be OK for many years to come. I know my late dad's one-time Dawncraft is still afloat after 45 years

Hull mouldings have had Epoxy Resin applied to several inches above Waterline since the mid eighties.

 

Guess that production economics have limited that method to Up market Craft only

 

CT

[Guest]

Hull mouldings have had Epoxy Resin applied to several inches above Waterline since the mid eighties.

 

Guess that production economics have limited that method to Up market Craft only

 

CT

Cheers. Knew I had read something about it, but couldn't recall what

[Naughty Cal]

I seem to recall reading that later GRP materials were modified to help slow down osmosis? That being the case, a boat as young as yours will likely be OK for many years to come. I know my late dad's one-time Dawncraft is still afloat after 45 years

If only.

 

They use different resins but not epoxy.

 

There are plenty of boats at a similar age as Naughty-Cal at our marina suffering with osmosis to varying degrees.

 

In fact it is more uncommon that a boat hasn't got it that they pull out at Burton Waters!

 

Must be something in the water composition.

[carlt]

Must be something in the water composition.

Yes...It's fresh.

 

Osmosis is all about the relative concentrations of the solutes either side of the semi-permeable membrane.

 

Move your boat to to the Dead Sea and the process may well reverse.

 

All GRP boats are subjected to osmotic pressure unless their semipermeable membrane is sheathed with a non-permeable finish.

 

I'd rather have an inch and a half of well laid up fibreglass behind a bubbling gelcoat than a few mm though.

[Jrtm]

Both are wrong!!! But thats just me!

[carlt]

Both are wrong!!! But thats just me!

Both what are wrong?

 

The science of movement of water across a semi-permeable membrane from a dilute solution to a concentrated one is fairly straightforward, usually over complicated because those dealing with the occurrence in GRP boats are boat builders, not materials scientists.

 

My science is not wrong but that's just me.

Edited June 5, 2016 by carlt

[Phil Ambrose]

Both what are wrong?

 

The science of movement of water across a semi-permeable membrane from a dilute solution to a concentrated one is fairly straightforward, usually over complicated because those dealing with the occurrence in GRP boats are boat builders, not materials scientists.

 

My science is not wrong but that's just me.

Have a virtual greenie.

Phil

[gazza]

Both are wrong!!! But thats just me!

Both what are wrong?

 

The science of movement of water across a semi-permeable membrane from a dilute solution to a concentrated one is fairly straightforward, usually over complicated because those dealing with the occurrence in GRP boats are boat builders, not materials scientists.

 

My science is not wrong but that's just me.

Carl.

 

I think BillyBob is a wooden boat man.

 

I think His comment was a stab at both steel and GRP are wrong for boat building.

 

I wonder if he is aware of ferro cement....

[carlt]

Carl.

I think BillyBob is a wooden boat man.

 

Ah the insufferable intolerance of the wooden boat man.

 

You have to admire their single mindedness but also pity their endless but ultimately fruitless quest for inner peace.

 

That way madness lies...

[cuthound]

Ah the insufferable intolerance of the wooden boat man.

You have to admire their single mindedness but also pity their endless but ultimately fruitless quest for inner peace.

That way madness lies...

Surely a wooden boat man must have insufferable tolerance? I mean however else can you accept that you have a lifelong project to work on that will never be finished?

 

Edited to add a smiley, cos the one I added from my tablets library didn't show up in the post after posting.

Edited June 5, 2016 by cuthound

[carlt]

Surely a wooden boat man must have insufferable tolerance? I mean however else can you accept that you have a lifelong project to work on that will never be finished?

I was referring to the intolerance of boats made from inferior materials but your point is just as, if not more, valid.

[mustang41]

So excuse my ignorance but what is the end game with osmosis? I've read about it,think I've got a fairly good idea how it occurs, but ultimately does it sink your boat? Also while I'm here, is taking the boat out of the water to dry out every year necessary?

[carlt]

Osmosis is largely cosmetic and, unless it is causing visible delamination on a wide scale is not going to sink a boat.

 

Every grp boat has some osmosis just as every steel hull has some rust and every wooden hull has some rot.

 

Osmosis will affect the value of your boat for many years before it affects the structural integrity.