Hull integrity and large windows

[psymon]

Hi all,

as some of you may know i'm in the market for a 70ft mobo, in a previous thread jfm bought up the idea of how important it is to have big windows in the central owner's cabin.

a couple of questions, how does that not affect the integrity of the hull? if there are supports worked into the design would it be possible to retrofit larger windows? (hehe)

on older boats i've been on in the past i've found that water tends to find a way into the boat through window joins? having windows so close to the water line is a little off putting for me!

what got me thinking about this is all of these new boats that have windows everywhere, as far as i'm aware the technology in materials for the majority of boats is simalar to that of 15/20 years ago so has the design process advanced that far that these newer boats really do have the durability through time?

is the trade off light for sea worthyness / durability?

sorry for the ramble and thanks for any input

psy

 

[rafiki_]

I'm guessing that the larger hull windows are bonded in, as with cars, so no detriment to the hull stiffness.

 

[jfm]

Yup, the big windows (and the little ones) on latest designs are bonded so it is close, engineeringly, to a single continuous component. Completely different from a framed opening with the glass sealed by rubber gaskets and maybe some bathroom sealant. Glass itself as a material has come on loads and is now a serious structural material (that just happens to be transparent)

As with cars, the edge of the glass components is finished with printed and fired black ceramic (with those little fade in/out dots you see on car glass), and the glue attaches to that ceramic skin surface. A very strong bond is achieved. So, nothing to worry about with big sheets of glass in the hull

 

[jimg]

Yup, the big windows (and the little ones) on latest designs are bonded so it is close, engineeringly, to a single continuous component. Completely different from a framed opening with the glass sealed by rubber gaskets and maybe some bathroom sealant. Glass itself as a material has come on loads and is now a serious structural material (that just happens to be transparent)

As with cars, the edge of the glass components is finished with printed and fired black ceramic (with those little fade in/out dots you see on car glass), and the glue attaches to that ceramic skin surface. A very strong bond is achieved. So, nothing to worry about with big sheets of glass in the hull

You are a fountain of knowledge, often wondered what that was around the edge of a car windscreen!

 

[jfm]

The black ceramic frit (to use the proper name) is a nifty bit of engineering. It sticks to the glass becuase it is ceramic. It is formulated to stick to the glue. It covers up the glue which would otherwise be visible thru the glass, and on modern cars it covers a lot of metal too so that the windows are bigger on the outside than the inside so to speak, which is the current fashionable look. More importantly, by covering the glue it stops the latter from UV attack. On a boat it also covers areas where furniture goes (sometimes caught be camera when there is back light - see the big black bit in forward part of saloon window, below, which has furniture behind it) and this allows use of window shapes outside that don't correspond to glazed areas as seen from the inside. And for good measure the little dots soften the edge look, so there's a styling bonus. Kind of kills half a dozen birds with one stone.

 

[sarabande]

jfm - are you also up to speed on impact deformation pls ? i.e. If you are rammed accidentally by a RIB, hull metal/GRP will undergo elastic then plastic deformation, at which point a permanent dent takes occurs in the hull. For glass, I imagine that the elastic phase is much smaller, yielding to fracture well before hull material.

I am trying (out of curiosity ) to get a feel for how properly engineered glazing will respond to either a wild RIB, or a solid wall of water.

thanks

 

[psymon]

thanks guys,

Soooo what your saying is that it might be a bit expensive but it would be possible to add 'larger' windows to a master cabin?

hmmm interesting stuff indeed.

your better than google

 

[jfm]

jfm - are you also up to speed on impact deformation pls ? i.e. If you are rammed accidentally by a RIB, hull metal/GRP will undergo elastic then plastic deformation, at which point a permanent dent takes occurs in the hull. For glass, I imagine that the elastic phase is much smaller, yielding to fracture well before hull material.

I am trying (out of curiosity ) to get a feel for how properly engineered glazing will respond to either a wild RIB, or a solid wall of water.
thanks

I dont know Sarabande so what follows is a bit of just guesswork, so feel free to put forward different views. I would think the glass is considerably stronger and therefore more puncture resistant than GRP. So it's like having a steel plate bonded in there: if the crashing boat hits it in a certain range of speeds the glass will just bend elastically but not break, whereas the GRP hull would puncture. I think there is only a very little phase of elastic deformation in both the glass and the GRP: they are elastic mostly then almost immediately after the material breaks, but the glass needs more force.

But of the impact is big enough to break the glass then yes it breaks. It is laminated, but at a certain point the anchor of the crashing boat will come through. But AOTBE it would have broken also if the hull had been GRP with no big window

Then there is the pointy effect. If the glass is hit by something very sharp, it is more prone to breaking than GRP, AOTBE. Like the emergency exit hammer on a train window. I guess boat builders and the classification societies must think the chance of a sharp pointed impact is very small at sea

 

[jfm]

thanks guys,

Soooo what your saying is that it might be a bit expensive but it would be possible to add 'larger' windows to a master cabin?

hmmm interesting stuff indeed.

your better than google

Retrofitting is possible but very tricky. The hull sides of almost any boat will be curved for stiffness, so you need to cut a hole on the hull and then create a flat recessed flange in new GRP. On older boats the hull side will be curved on one plane becuase the plug will have been made from plywood, but on very new designs it could be compound curved because the plugs are cut from rigid foam blocks using 3 axis cutters and compount curves are do-able. (But a new hull like that will prob have big glass already!).

If there is a knuckle in the hull that you want to straddle, it can make it very tricky - part of the window has to be very recessed, and you compromise hull strength/stiffness by removing a chunk of knuckle. Best avoided

You also need to replace the hull frames that got cut out, which is no trivial task, and probably do lots of furniture re-work inside too

Ideally you want en internal mould to create the cabin lining around the window frames, but i suppose that could be done in wood for a one-off.

A firm like Osmotech on the Hamble could do this; you wouldn't want to engage amateurs. If you do it, please share the story and photos on here!

Edit, fwiw some pic below. See in the first one how they have made flat landings for the glass, in a curved hull

 

[MapisM]

is the trade off light for sea worthyness / durability?

I don't think that's the correct way of looking at the trade off.
If you compare a similar size master cabin with or without hull windows, daylighting is not really MUCH better in the first, on one hand because the glasses are obviously darkened (while most portholes aren't), and otoh because to see inside lockers etc, - which is where more light would actually be handy - you always need lamps anyway.

The only real advantage of big side windows is the better sea view (aside from being more fashionable, but that ain't a real functional advantage).
And out of the only two activities I can think of when you're in a cabin, in neither the external landscape is so interesting, if you see what I mean...
After all, who wants to stay in a cabin looking at a stretch of water instead of staying in the saloon with an almost 360° view?!?

All that said - and even if I have no objections at all to jfm technical comments - there is one very simple reason why I've always been a bit skeptical about the comparability of a solid hull with a holed hull which is afterwards closed with a material whose tensile strength is very different: there are steel trawlers (I mean, commercial trawlers - those used to drag nets in the kind of sea which we pleasure boaters like to look at only on youtube videos) which are built with glass windshield as thick as bank doors. And in spite of that, they still have metal storm shutters with small visibility holes, that can be secured above those glasses if and when the going gets REALLY rough.
And since those guys are very much cost conscious, I don't think they would build boats with this sort of accessories if they weren't unnecessary...

 

[jimg]

Looks like you had Spiderman taking that shot!!