How Safe are Windows in the Hull

[Bobc]

I say to people "what would happen if I hit the side of your boat hard with a sledge hammer. Answer-it will bounce off. Now tell me what will happen if I hit the window with a sledge hammer. Answer-the window is gone or broken". That is the kind of force you can get coming off a wave on the bow section of a boat.

 

[Shaddickp]

Presumably as the water was knee hight before being notice there was no cheap and easy to install bilge alarm!

 

[Aja]

Here is Sirius Yachts take on hull windows .... and they have quite large ones ...

How strong are the hull windows on a boat?

That may be the case. I don't think the issue being discussed here is the windows' strength but the bond between the window and the hull.

 

[dunedin]

I say to people "what would happen if I hit the side of your boat hard with a sledge hammer. Answer-it will bounce off. Now tell me what will happen if I hit the window with a sledge hammer. Answer-the window is gone or broken". That is the kind of force you can get coming off a wave on the bow section of a boat.

In the case of the Sirius example, with bulletproof Perspex - probably break your wrist, but not damage the window

 

[Tradewinds]

In the case of the Sirius example, with bulletproof Perspex - probably break your wrist, but not damage the window

but the problem seems to be with the bond not the window material. Particularly a few years down the line.
Edit: Aja beat me to it

 

[noelex]

Here is Sirius Yachts take on hull windows .... and they have quite large ones ...

How strong are the hull windows on a boat?

One of the greatest concerns is long term durability. In five or ten years time the fibreglass hull material will be just as strong, but UV, contraction and expansion will weaken the glue bond and even the perspex itself.

The other concern is installation defects. Glue can fail to form a full strength bond for minor reasons such surface contamination. It is very difficult for owners or even surveyors to pick up these problems.

The windows can and should be periodically removed and replaced to remove the durability concerns, but few owners seem to do this. When this is done outside the original factory by a local contractor it increases the risk of installation errors, especially as it is notoriously difficult to remove all traces of the old sealant.

Small glued in hull windows well above the waterline are not a concern, but large windows close to the waterline are problem in my view.

 

[dankilb]

I say to people "what would happen if I hit the side of your boat hard with a sledge hammer. Answer-it will bounce off. Now tell me what will happen if I hit the window with a sledge hammer. Answer-the window is gone or broken". That is the kind of force you can get coming off a wave on the bow section of a boat.

I do think the (opening) portlight hull windows on our ‘89 Jen would be fine on that test - polycarbonate glazing that’s bonded as well as mechanically held into beefy cast aluminium frames. The thumb screw closures would probably fail first but we carry spares.

The owner of the boat on SLaS mentioned having had all the other windows replaced and the boat looked pretty new, so perhaps it was a warranty/build issue (cocking up the bonding somehow)?

 

[Aja]

In the case of the Sirius example, with bulletproof Perspex - probably break your wrist, but not damage the window

Perspex TM as far as I'm aware have never made a 'bulletproof' acrylic.

 

[Baggywrinkle]

I say to people "what would happen if I hit the side of your boat hard with a sledge hammer. Answer-it will bounce off. Now tell me what will happen if I hit the window with a sledge hammer. Answer-the window is gone or broken". That is the kind of force you can get coming off a wave on the bow section of a boat.

Modern boat windows are usually made from polymethyl methacrylate (PMMA) or polycarbonate (PC). PMMA is more commonly known as acrylic or by brand names, such as Perspex and Plexiglas. Older boats often have tempered glass.

Here's what happens to polycarbonate when hit with a sledgehammer.

... it's the bond, not the material that is most likely to be the problem. The take-away is get the windows checked, who knows, in time bonded hull windows might end up as like standing rigging where insurers insist on inspection and replacement after a period of time.

Perspex TM as far as I'm aware have never made a 'bulletproof' acrylic.

The Sirius example was ballistic-grade polycarbonate, not acrylic.

 

[noelex]

Polycarbonate is much stronger than perspex, but flexes a great deal. This higher flexibility makes securing polycarbonate windows very difficult, no matter what method is used. If the window pops out of its frame, the watertight integrity is lost even if the window pane is not actually broken.

For this reason when calculating the minimum required glazing thickness for polycarbonate, the required thickness to keep flexing to acceptable levels is the limiting factor. With perspex the minimum required is limited more by the inherent strength of the material.

For boat windows these factors generally cancel each other out. While it is better for a naval architect to precisely calculate the required thickness depending on the material, as a general rule the required thickness of polycarbonate, perspex and even thermally toughened or laminated glass is very similar in a marine application.

Thus polycarbonate is much stronger, but when assessing the strength and integrity of the entire window structure the same thickness of polycarbonate will be (roughly) no better or worse than the same thickness of perspex.

Perspex is less prone to scratces so is usually the preferred marine glazing material where the cost and weight of glass is not practical.

 

[mjcoon]

Small glued in hull windows well above the waterline are not a concern, but large windows close to the waterline are problem in my view.

And also surely if breached are much less likely to be sealed in any meaningful way by cushions or pillows in a splashy environment...

 

[Ceirwan]

One of the greatest concerns is long term durability. In five or ten years time the fibreglass hull material will be just as strong, but UV, contraction and expansion will weaken the glue bond and even the perspex itself.

Any professionally installed window will have a slightly overlapping frit to keep the UV off the adhesive. (Like the one you have on your car windscreen)
Assuming the correct adhesive, proper preparation & an adequate thickness of sealant to allow for contraction and expansion.

(And you can bet Sirius and probably all other manufactures do the above)
Then it should last for a very very long time. Not forever, but what does.

 

[boomerangben]

The problem I have with hull windows is they make the boat look ugly (IMO of course). But I would also be concerned about differential thermal expansion, hull flexure, quality of build, design and adhesive, not to mention effect of age, UV etc on it. But at the end of the day, it’s the aesthetics that make it a no for me. (And I don’t doubt the benefits for internal living)

 

[Aja]

Modern boat windows are usually made from polymethyl methacrylate (PMMA) or polycarbonate (PC). PMMA is more commonly known as acrylic or by brand names, such as Perspex and Plexiglas. Older boats often have tempered glass.

Here's what happens to polycarbonate when hit with a sledgehammer.

... it's the bond, not the material that is most likely to be the problem. The take-away is get the windows checked, who knows, in time bonded hull windows might end up as like standing rigging where insurers insist on inspection and replacement after a period of time.


The Sirius example was ballistic-grade polycarbonate, not acrylic.

Not necessarily the best material in a marine environment but hey-ho. As I said a few posts back its not the strength of the material that should be discussed but the bonding. "Ballistic" grade polycarb - not really sure this is pertinent to anything being discussed here.

 

[Talulah]

Do you mean windows like these ? Thanks
https://www.yachtworld.com/yacht/1986-najad-390-8678516/

No, Those are more modern. I mean these:The Najad 390 Sailboat

 

[Beelzebub]

It's not just boats that have problems with windows. Perhaps those sailing in warmer climes should take note!

https://www.pprune.org/rumours-news/655290-titan-a321-loses-windows-2.html

 

[Snowgoose-1]

What was the boat and how was the window fixed?

Apologies. Tried to post a picture but failed.

 

[ProDave]

The windows in our coachroof are on the outside with lots of sealant and lots of screws fixing them. For them to fail, it would probably be the glass plastic that fails and breaks. highly unlikely.

I suspect in this case the windows are fixed from the inside. No visible fixings on the outside so one would presume just glued in place to the inside of the hull and then covered on the inside with the trimmings of the interior.

As such that is form over function. Make them look nice but at the expense of a technically poor design, one good wave slamming against them could break the seal of the glue and the window can then just push in.

Whoever did the risk assessment of that design needs the sack.

 

[Sandy]

I say to people "what would happen if I hit the side of your boat hard with a sledge hammer. Answer-it will bounce off. Now tell me what will happen if I hit the window with a sledge hammer. Answer-the window is gone or broken". That is the kind of force you can get coming off a wave on the bow section of a boat.

Well, that really depends on the materials used.

 

[Fr J Hackett]

How do people think aircraft and car windscreens are fitted?