The Offshore Voyaging Reference Site

Q&A: Safety of Large Pilothouse Windows



Member Tim asks [edited for brevity]: I notice you have not mentioned [in this Online Book] the integrity of windows during a knockdown and the possibility of storm covers. (I don’t mean something to fix a broken window afterwards.)

Maybe this not a significant issue for many boats but ours is a pilot house/deck saloon design…I worry that should we get knocked down and smash a window, the volume of water that could enter would be colossal.

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Marc Dacey

Well, this is a good discussion, because I have a boat with no hull portlights at all, but with large pilothouse windows, or (technically) “deadlights”, which confusingly is not only a fixed portlight, but the storm cover that can go over it. Storm covers/shutters are a necessary thing to carry, I think, but are only part of the solution. We also have the means to seal off the “downstairs” aft cabin and saloon with gasketed storm doors (also a security measure when away) and we are putting in a gasketed engine bay “clamshell” hatch: if we take a wave over the stern, the water should not get far. Lastly, the pilothouse itself has scuppers formed into the hull: if we got two feet of water inside in a worst-case scenario, it would (eventually) drain out, although I would hope that a well-designed set of storm covers and a doggable companionway hatch would keep 99% of the sea out, even in a roll. If the site allows, here’s a recent shot of the pilothouse to show what I’m talking about. The port scupper is just below the long white fender.

You can’t plan for everything, but I am often surprised at what isn’t planned for: storm shutters mounted on four or six stand-offs, threaded and backed, are really cheap insurance. Many boats seem to suffer when a portlight is stove in and it becomes impossible to keep up with water ingress. Even wooden shutters (although I prefer 1/4″ aluminum as has been suggested) could mitigate a big ‘un hitting the boat squarely.



Do you have covers that go over the forward pilothouse windows also? I was told by someone in a yard, who was relatively expeirenced, that boards were only really necessary for the p+s windows in the case of a broach / knockdown.


Marc Dacey

I do not yet have boards for the forward pilothouse windows, two of which are tempered, fixed glass and the center one, which opens up and out. I am considering Lexan boards for the fixed panes, and leaving the center pane to its own devices as it is well-blocked by the pilothouse overhang and by the substantial mast tabernacle.

But it’s definitely a consideration.

Eric Klem

Hi John,

A very worthwhile discussion that you have framed well. I actually have always considered the portholes and large forward hatch on our boat to be the weakest component structurally and am working on a plan to replace them.

A couple of thoughts on the stresses in windows/stormcovers. I suspect that the load on these can be approximated by a pressure. Unfortunately, I don’t know what pressure would be appropriate to use but there are probably people here who already know the answer to this. From there, you can take a given geometry and look at what the stress should be. In general terms, the strength in bending of a material is proportional to the square of its thickness so you would need a material that is 4 times as strong if you are going to halve the thickness. How the material is constrained at the edge makes a huge different in the stresses. Also, the geometry of the area covered is very important. If you look at a cantilevered 2D beam with a constant force per length acting on it, the stress will quadruple if you double the length. This is important because bigger windows will require thicker material or a separate support structure.

I have only ever sailed with stormcovers on once. It was on a boat that was well thought out and had clear covers so we were able to easily put them on while the weather was still nice and then there was no rush to take them off afterwards. It would seem to me that using a clear material would be advantageous as you could put them on well in advance of poor weather.


Trevor Robertson

As I understand it (and I am not an engineer), if a window or storm cover is uniformly constrained around its edge, the critical dimension for calculating the stress on it is its minimum dimension. A square window is much weaker than a long, narrow window of the same area. If I have got this right, the most important variable in specifying the strength of a deadlight is its height, assuming the fastenings are stronger than the deadlight. Perhaps an engineer could confirm this?

Given this, and the fact that most windows are rectangular rather than square, a deadlight probably only needs only to be attached along its top and bottom. However if the plate has a strongback attached along its long axis, the strongback effectively divides the deadlight into two pieces. These probably have to be attached at the ends where the strongback laps on the cabin structure. A series of short reinforcing pieces at right angle to the long axis would probably be more effective. Again, perhaps an engineer could comment?

If the deadlight is of aluminium 6061 T4 or T6 (the obvious material to use) and requires reinforcing, it may be sensible to do it with an angle section bolted or riveted in place, not welded, given the considerable loss of local strength that occurs when that alloy is welded.

As you point out John, the amount of water than comes in though a broken window is considerable. It has only happened to me once, in a previous boat off the South Island of New Zealand. I was running before a gale when a wave picked Salvation Jane up and dumped her on her beam ends, breaking the galley window on the lee side. The window was about 60cm x 12cm (2ft x 5 in). It took me about 30 minutes to get a plywood patch in place and by that time the water in the cabin was over the bunks. Salvation Jane did not have an inboard engine so at least the interior was not covered with emulsified oil, which happens quite quickly once an engine is flooded. Even without a layer of oil on everything, getting the patch in place was difficult due to the irregular, violent motion, perhaps caused by the free surface effect of a boatload of water. I baled her out and carried on to Australia, but it was a close run thing for a while.

In addition to deadlights for saloon windows, it is probably a good idea to have a precut aluminium or plywood panel to replace the acrylic section of each deck hatch. These panels are for repair only and not routinely fitted in heavy weather.

Trevor Robertson
Iron Bark
Stornoway, Scotland


Hi John: I faced this same decision when designing a 55 ft aluminun sloop with a i closed pilot light. I decided on 3/8 inch thick tempered glass windows not over 3 sf in area. Glass so they would remain clear. I know that any glass can be broken given the conditions at sea so my solution was to separate the pilot house from the interior. A self draining pilot house floor, additional conpainionway enclosure and port lights to the interior. Happy to report that after 15 years of offshore sailing they have not been needed but I know that they are there. George


I was looking at this for sale listing recently in which some of these issues seem to have been addressed for a pilothouse in a 2011 William Gardner-designed build done by a ‘professional mariner’ owner.

“From the aircraft windshields in the house to the military grade portholes in the stern..”

Images 13-15 show what appears to be a ruggedly constructed double-layered porthole (also a sealed hatch?), and image 38 shows a large part of the large ‘aircraft windshield’ comprising the front part of the pilot-house.

( I find his chart table arrangement in Images 70-71 really nifty.)

Clearly this is a custom-made job, but it appears this builder worked hard to make this a very strong ocean-going vessel. Of course this doesn’t mean he got it right, but presumably he researched this a little and might be able to contribute some specs regarding the aircraft windshield material and ‘military grade portholes’ such that an engineer contributing here might be able to evaluate if he has come up with a good pilothouse window solution.

Marc Dacey

Wow…look at that price!


That would make a great Alaska boat. Think of it as a trawler with steadying sails built like a fish boat instead of a yachty toy.
Friends who have gone to Alaska for the summer come back with spider’s nests under their sail covers——.

Marc Dacey

I forwarded the ad to some sailing friends as an example of “a bridge too far” in terms of customization. Those are definitely safe portlights, however…


I am curious to learn what aspects specifically you found ‘a bridge too far’. I have no attachment to the vessel, particularly, but am generally looking at different boats/designs in order to see different designs and solutions simply in order to learn more about how the many different issues involved are addressed. The main takeaway I got from this one is that it seems more like a working boat than a pleasure yacht, almost military-like. It also seems massively overbuilt compared to most 40′ vessels. And interesting that the hull is wooden. Looks seaworthy, but probably quite slow under sail.

Marc Dacey

CaperAsh, by “too far”, I suppose I meant “an intensely personal vision fully realized that is not going to be broadly shared”. I can see great care went into this boat structurally and (as far as I can tell) in term of equipment, access and other considerations. But it’s a damned ugly thing, is “needlessly wooden” in the sense that I associate wooden construction with beauty and “showing off that it’s wood in the first place”. Here, there’s a lot of rough lumber showing, aged three-strand for halyards, there’s no gunwhales where I would expect them, and instruments are labelled (and misspelled) with Dymo tape. It looks as if large parts were salvaged from the bins behind Home Depot, and while I suspect it’s quite strong and seaworthy, it bears the emphases of the one guy who built it to his own particular tastes. In this, it resembles a LOT of “modified Roberts homebuilt” designs I’ve seen quietly rusting in yards. *Definitely* safe portlights, though!


In ship building most side portholes have a watertight metal panel used in case of failure of the glass. This system can be found in old Hallberg Rassy too. The extra plate is connected to the main frame porthole. This solution is an extra safety with port hole that can be broken not only from a wave but manly from a jig on dock side when mooring. Other Scandinavian builders used in the past to install the mineral glass hatch ( no “plastic”, Lexan, PMMA…there are various names and quality). This good practice has been cancel from some rule standard, that see the glass to much “rigid” and the PMMA more elastic…and probably cheep. Most of actual standard hatches have thickness of 8-10 or 12mm Pmma. The most nice system is to add a couple of bar/rod under the Pmma to reinforce it. This solution is used on Bomar. The 2 rod can have a secondary (small) extra safety to make difficult enter in the boat if someone breaks the Pmma and would like to visit you…
Some ship use a small cover with a small round glass (max 20cm), so you can have light and in case of break you can close the hole with a towel.
The boat mentioned by CaperAsh has this solution on many hatches.

Regarding pilothouse glass size I can divide in:
The best is glass , so you have double or triple glasses, normally are 6mm glass,4 gap or air and 6mm glass…this will help to prevent condensation…but 6mm are a minimum standard.
If you want a extra safety or a scantling for Ice breaker you have to use 12mm or 15mm glass, that is not easy to do, specially clear. (If you think to bullet proof car they are normally dark). This will make a lot of weight that can create problem in installation.
So you have to keep your glasses small…but a pilot house with small glasses is not so much pilot house, specially when the boat is under heel, or there are spray on the glasses.
One of the main differences from glass and Pmma, is that this one can scratches quite easily.
Some like to glue, and some to screw the glass, some to have the glass on a frame, the only secret is to keep the glass or the PMMA floating on his frame with large (the seal should be scantling too) use of Sika 295 with primer,4200 by 3M .A frame can be added later but is only to protect the seal from the sun.
On large planning motor yacht, that have a lot of G acceleration when cruising at 30 to 40Kn are glued, but the risk of a column of water on top of the glass is far away, so a good pilot house is designed to flush away the major part of the water and offer less resistance.
A SAR vessel will fight against the water, but a sailboat will probably escape from big waves. Off course a roll-over or a capsize can break the windows, but major part of the water will probably enter from the main entrance, your electronics will go under water if is not water proof.
In this case a truck cloth can be the only quick solution to close the hole.
For my experience the best is to add an adhesive film when you built you glass, the same of car industry. The glass will break, but will not explode or open a hole.
The glass can escape from his frame too, so some screw can help to keep him in position. You need some clearance between the glass and the screw to compensate thermal dilatation.
The solution of the extra plate to bolt outside can be done quickly only in easy condition. Imagine to screw or bolt your 4mm plate 50x50cm in the middle of a storm. This is the time you break your glass or you fall overboard.
On my record there are more hatches broken by a winch handle or a spinnaker pole badly used, then from waves and close a hatch is possible with a piece of plywood.

George Wall

For the well described consequences of large unprotected Windows and an otherwise thrilling true story read:”OVERBOARD!” BY Michael Tougias.

Brian engle

I wonder, do any hatch and port lite manufacturers offer models with storm shutter bosses/helicoils in their frames? Might make sense. Thank you for another informative article.

Pete Worrell

Great discussion John, the proliferation of raised salons and pilothouses in the last ten years is amazing.

In our Hood Pilothouse 51, Ted Hood’s solution to the discussed dilemma was to design the pilothouse to be completely draining through its own cockpit drains, and to have the ingress/egress to the main cabin via a standard watertight sliding companionway hatch with boards. The idea is that if the pilothouse windows were compromised (in our case glass), then you still have a traditional companionway hatch arrangement keeping the water out of the main cabin and engine areas. It frequently seems a little redundant to pass through a companionway hatch from the pilothouse, but it’s simple and effective I think.

Pete & Kareen Worrell

Erik de Jong

To be honest, I do not believe in Stormshutters for pilot house windows.
Glass is tremendously strong, and water pressure is a relatively equally distributed load on the glass. Making it any stronger than the surrounding material of deck and cabin top is only adding useless weight.

I think it is much more important to focus on the details of how the glass is mounted and sealed into the pilot house itself.

Glass is horrible when it comes to point loading, so I would be more afraid to hit it with something pointy and hard (a flying halyard with a shackle or a falling winch handle) This kind of damage can easily be prevented by mounting a second layer just a quarter of an inch to an inch off the glass by clear lexan, when that bends under water pressure (and it will) it will touch the real glass and the glass will take the load. When a hard small object hits it, the lexan will absorb the load and prevent damage to the underlaying glass. A structure like this also reduces energy requirements fr heating and cooling, and will therefore make the boat more liveable.

Long story short, I think an offshore boat and any thing on it, needs to be designed to withstand these kind of situations without needing any work done to it by the crew, and from an engineering perspective, it is not all that hard to do.
To bad that only few yards/ designers seem to pay attention to these so important details.


Hi Eric,
Good to get an engineering-driven perspective on the question.

When I was construction manager on the 112′ S & S motorsailor “Venturosa” the owner requested that I devise an instrumented fixture to test window adhesives, contact areas, and glass breaking points for the substantial pilothouse windows. As I recall we ended up with a standard automotive adhesive and custom laminated 3/4″ thick glass that met the design specification for wave impact and 175 mph wind strength. So I’d tend to agree that pilothouse windows should first of all be made strong enough (which is relatively easy to calculate) before concerning oneself with metal or wood storm shutters. And your lexan idea makes a lot of sense.

In the case of the vessel I was building the owner grew tired of it and sold it before sea trials were complete. The next owner (who I’ll decline to identify) wanted us to immediately remove the pilothouse windows and replace them with bulletproof glass. He wasn’t too happy when we pointed out that the aluminum that the boat was built from wasn’t bulletproof. I can understand his concern since he found it necessary to fly a second pilot to the Sun Valley airport to have his Bell Jet Ranger helio warmed up to take he and his family the 8 miles up valley to their compound for fear of kidnapping should they be so foolish as to drive.

Life is so much simpler when you are a mere commoner—.

Eric Klem

Hi Erik and Richard,

For a new boat, what you are saying makes a lot of sense. I especially like the idea of the thin lexan outside the normal glass although it seems like thought would need to be given to preventing fogging.

How about for older boats? In your experience would it be easier to retrofit an older boat to thicker glass or would storm shutters make sense provided that the original windows are not overly weak? We don’t have a pilothouse but we have a large hatch on the foredeck which is equally vulnerable and it is definitely underbuilt. I plan to replace all of the ports with new stronger ones but dealing with the hatch would require a lot of custom work which strikes me as more complicated than making a cover.

I was aboard a steel vessel several years ago with ports in the hull and the classification society had required that they be as strong as the hull, that glass was unbelievably thick.


sharon severs

would like to know the answer as we’re getting a boat with pilot house windows and the window size is very important to know,

David Lymn

My windows are 12mm thick polycarbonate and held by 60+ small nuts and bolts. Although the forces involved are great I reckon there’s little chance of a break. Knock down implies a roll into the water on one side and a hit by a lifting wave on the other. I don’t reckon the water would have enough momentum to smash through ( I know it’s scarey when the bow smashes through a wave head on but the windows are very unlikely to be exposed to such direct blunt force). Even a wave coming over the bow would hit a sloping window with some of the forces reduced by the dispersing effect of the bow and rigging. A force great enough to break a window would probably be great enough to smash the boat entirely or at least the fibreglass that surrounds the window.


Not sure how your windows are built, but lexan is very prone to cracking. I would avoid drilling it if possible, and if so be very careful about the finish – smooth is good. Flame polishing is one solution. Uneven stress with lots of fasteners drilled will crack lexan easily.

I had to put a lexan window on a pressure housing (only needed to go 10 atm but was built with massive safety factor. We cut out a ledge with an o-ring and used a retaining frame to hold the lexan in place. Hopefully that makes sense. The bolts on the retaining piece were outside of the o-ring obviously. Wouldn’t be difficult to design boat windows that way and not even necessarily crazy expensive – you could probably just use a gasket and forego the o-rings for one.

Morgan Henry

It seems that this article and a story in today’s New York Times are destined to cross paths:

This company is developing thin glass that has a center layer that is supposed to be resistant to gunfire and other significant attacks. Maybe they can develop something for the marine industry.

Pat Kelly

As regards large pilothouse windows I recommend Michael Tougias’ book OVERBOARD – a true story and a good read. The “Achilles heel” of the boat – a Harden 46 caught in a Gulf Stream storm on her way to Bermuda -were the large forward facing pilothouse”windows” that blew out with a boarding sea. The final result was loss of the vessel.

Phil Streat

Large windows can be engineered so they are safe. The Coast Guard Motor Lifeboats are designed to punch through big breakers and roll over without damage to their windows. The classification societies have requirements for windows for different service conditions. Getting this level of design and construction in a yacht is most likely only to be found on larger custom projects.


There is very good and concise information on Steve Dashew’s site, google setsail window thickness. It is based on Lloyds & ABS requirements and years of experience from a sailor, designer and builders perspective. A selfbailing pilothouse and storm shutters are great ideas, but often hard to retrofit. 3/4″ glass in commercial frames from DiamondSeaGlaze in Canada are very nice, they have several models and thicknesses and are pretty much the standard on the Alaska fishing fleet. Damage control “blow out panels” can be carried and fitted from inside the pilothouse in an emergency. I have installed DSG windows in several vessels, and wish I could say that I got a discount on their fine products…

Marc Dacey

I fruitlessly contacted Diamond Sea Glaze to fabricate me a companionway hatch of “ocean grade” strength…I was basically told I am too small a job for the likes of them. Which is a shame, as I liked their products, but is probably true.

Any aluminum fabricator/welders out there in Southern Ontario, feel free to contact me!

Matt Marsh

This is one area where a “defence in depth” approach seems appropriate. It might look something like:
– Tier 1 is an anti-broaching device such as a JSD.
– Tier 2 is window glass and framing that can handle the dynamic water pressure encountered in a high-speed broach. (These pressures can be in the hundreds of kilopascals / dozens of PSI, so you’re looking more at submarine, aquarium or spacecraft window designs than at car or house window designs.)
– Tier 3 is an impact-absorbing outer cover such as the polycarbonate sheets suggested by Erik de Jong earlier.
– Tier 4 is independent draining and watertight separation of the pilothouse / saloon area from the rest of the boat.
– Tier 5 is a crash pump sized to keep up with the inflow through a broken window, and a stack of raw material that can quickly be used to patch the hole.

Marc Dacey

One of the reasons I put in soft mounts and an AquaDrive on my Beta 60 install is to be able to run the engine in an emergency at an angle of heel without worrying about misalignment. Oil starvation is a separate issue! But I also put in a second PTO on the front of the block in case I ever needed an engine-driven pump to supplement the existing 12 VDC bilge pumps. It’s also for a second alternator and clearly won’t go to waste, but that was the “tiered” thinking at the time, the rationale being that one might need a few minutes to find and address a bad leak. If I’m wrong, I can still have that backup alternator!

Marc Dacey

Interestingly, “defence in depth” resembles what used to be called “seamanlike prudence”. I was discussing offshore safety gear with Andy Schell ( and Paul and Sheryl Shard ( at the Toronto Boat Show yesterday and Andy is yet another JSD owner who has never deployed it, despite putting thousands of sea miles under his keel. Maybe the JSD is the talisman of sailors who are (not to get New Agey here) holistically careful and tending to the conservative in their sailing style, route planning and weather forecasting, and thus, despite having the gear to cope with very heavy weather, do not experience much in the way of heavy weather because of their extensive preparation and determination to preserve themselves and the boat. I’ve heard said that the biggest threat to small boats is not the storm, but the calendar.


It has been always a concern for me the opening ports and windows of our Hylas 56, I ahve found this Man Ship Opening Ports with Storm Covers
like a good option at keast for the opening ports

Dick Stevenson

Dear John and all,
This is a report on a large window breakage on an Island Packet 45.
Last summer this 2007 IP45 left the Pacific Northwest for a trip south. Early on, the mainsail roller furling became unworkable, and they went into port for repairs. While executing repairs, a set of small Allen wrenches, not much weight, fell from about 6 feet from work on the boom to hit the large window. An initial star grew to a crazing of the whole window able to be pushed out easily.
The above was reported first to me by one of the crew and confirmed by the owner in a subsequent conversation we had. He has made some initial work to ensure that the integrity of the boat remains OK in the event of further problems. He has not contacted IP, but intends to.
Dick Stevenson, Alchemy


Interesting verification and support for my contention that catamarans could and should be unsinkable. The Gunboat 55 Rainmaker has just been re-located after having been afloat in the North Atlantic for entire winter. Looks like she might even be sailable with jury rig after being pumped out.
Two very interesting take-aways.
1- The design is really an open bridge deck catamaran with a glass house on top. The glass house of course has been swept away. Makes one wonder how high she would be floating if the entry companionways into the hulls had been watertight doors.
2- The boat hardly went anywhere for five months! Was that due to some form of magnetic attraction to the continent where she was built? LOL

Rob Gill

Thanks for the link, what strikes me is nearly all the deck hatches appear to be missing – wow!
Is this because they have been torn off by waves, or because someone has arrived earlier and done some “selective salvage” work?
I seem to recall one Volvo skipper in the latest race saying they had concerns over their hatches breaking away when diving into deep waves at speed, and had readied their emergency covers.
Can such wave action alone rip deck hatches off without broaching or falling off a wave?


Hi Rob,
I suspect the hatches were broken out by free surface effect surge from inside. Lacking watertight closures at the companionways, the hulls rapidly filled with water once the house was gone, and the surge inside would break out almost anything less strong than the carbon hulls.

The design of this boat has always struck me as bizarre— a glass palace perched on top of two hulls. When it looses its rig or gets swept by a wave the glass palace cannot help but collapse, and pity anybody that was on deck at the time. The designer evidently never considered that such a thing could happen, and the yuppies lined up to buy them are personally immune to bad things happening because of the size of their checkbooks.

The condition of the structure is vivid testimony to the strength of modern composite materials, and to the advantage of a lightweight core that doesn’t have to float a big chunk of lead!

Rob Gill

Hi RDE, interesting thought, but yes that could do it. I agree with your thoughts on the open structure of the Gunboat, they needed a way to close the hulls off in the event of flooding the bridge deck. Like that it’s unsinkable though – and they go pretty well.

Marc Dacey

I have stated elsewhere that I draw comfort from the complete indifference of the sea to our plans and preferences: on water, you know where you stand. I find it puzzling, therefore, that while we are arguably building boats that have never been more strongly designed to survive the sea, we are putting glass boxes atop them and, in order to maintain “an airy, bright interior”, are forgoing doggable, watertight compartment doorways inside, and going for big portlights. I grasp that marketing has trumped reality here, but if I was spending millions on a vessel, it suggests I have more millions elsewhere, and I would want to preserve my life and my wealth by building a vessel as “sea-proof” as possible. This isn’t rocket science: “keep the water out” is on the “package” of this very website, and yet it seems to have fallen off the list of desirable characteristics of modern, high-seas boats.


Hi Marc,
I’ve observed that amount of money they have is inversely proportional to the amount of time owners spend on their boats. In accordance with that principle, if you are truly wealthy you stand little chance of losing your life at sea. If they have their GunBoat Glass Palace professionally delivered to the BVI and then sail it around the Drake Lake they should be fine.

(they just need to avoid web sites like this where snarky guys like me hang out and their peers will all think they are a bleeding edge genius)

nelms Graham

I simply can’t believe that no one has mentioned the technique used by countless commercial fishermen worldwide and US Navy in years gone past. Simply, very heavy wire mesh permanently mounted in heavy frames approx. an inch or two in front of the windows. This mesh breaks up the force of the wave at impact, much in the way the “bow wave breaking sticks” did on the ancient Polynesian trekking canoes.

Rob Gill

Hi John,
Latest Maritime NZ report on the loss of SY Essence off the NZ coast. As I think you know, these reports are produced after every major NZ maritime incident (commercial or pleasure craft) and are generally very well authored and researched.
The NZ Cat 1 safety rules (compulsory for every NZ yacht registered yacht and launch going offshore from NZ) have been strengthened to make the carrying and fitting of storm shutters for cabin windows larger than 2 sq foot (if no intermediate strengthening knees) compulsory. This is less area than the conservative recommendation in this post.
This was a shocking and tragic loss to the NZ sailing community of the skipper who was experienced, well known and well liked.
Br. Rob

Rob Gill

I should add the interesting lesson for me is that the windows exploded outwards, not inwards as might be expected. I had heard this rumoured around the waterfront, but this seems to be now confirmed.
Makes those increasingly large, in-hull windows seem even more vulnerable and dangerous than they look – how long before we lose a boat, and before they are banned?