How to Blow a Hatch

[Bruce Brown]

I have a traditional butterfly skylight set into the cabin top of my Friendship sloop. Since it is the only way to exit the boat besides the companionway, I want to be able to remove the skylight completely in an emergency in order to exit the cabin. What method of dogs and gasketting do you recommend to allow for drip-free functioning 99.9% of the time and rapid egress for the rest?

[lupussonic]

The Maurice Griffiths hatch design is proven and dripless. But whatever design you choose, use lever catches on the inside to squeeze shut on the gaskets.

Id be interested in a design that could be opened from both inside and outside, if that's at all possible.

Ever seen the White Squall film?

You just need a few lips and corners around the edge of your butterfly hatch, with appropriate gaskets. Many fishing boats have the entire coach house able to lift off if desired to access the fish hold, haul engines out etc. Handy.

[Sailor]

I envision some sort of threaded rod in each corner with a T latch to apply downward pressure on a gasket. Opening from the outside, yes, very useful from the White Squall perspective but how would you go about it? I'd be open to suggestions as well on that one.

[Gib Etheridge]

I've never seen such a thing, but perhaps a hatch on a hatch, where the upper, maybe smaller, one opens from outside and the larger entire assembly opens from the inside.

[Bobcat]

If you're truly interested in only removing the skylight in a dire emergency, I think you need a big fire axe down below.

[Sailor]

I think Gib is right. How to make it look good though? Depends on what type of boat you're building this onto. A friendship sloop might be difficult to make it inconspicuous. A fishing boat, it would be pretty easy.

[Breakaway]

Here's one way:





Here's another:

[MN Dave]

Here's another way:
https://www.southco.com/static/Literature/m5-dcl.en.pdf

[Phil Y]

I wonder if anyone in the history of the world has ever been trapped below in a friendship sloop.

[captsct]

Something to keep in mind is the water pressure holding the hatch shut, if underwater. Fire axe/sledge hammer would be the answer then. Just be prepared for the inrush of water.

[wizbang 13]

What possible emergency can you imagine that you would have 10 seconds to climb through an overhead butterfly hatch rather than go out the companionway?
Fire maybe?Boat goin down stern first?
How do you have a leak machine on the cabin top but no fordeck hatch?

[Phil Y]

You could get one of those plastic and aluminium jobs, and put it in the side of the hull, up forward, like some catamarans have.....



Seriously, just go sailing.

[Bruce Brown]

Fire is my primary concern. Thanks to those who posted fittings. The skylight is a Maurice Griffiths design. What kind of caulking will provide the right combination of waterproof adhesion and breakaway ability: butyl tape, boatLife or 3M products?

[jackster]

You could get one of those plastic and aluminium jobs, and put it in the side of the hull, up forward, like some catamarans have.....

Those are escape hatches for when they are upside-down, right?

[schoonerjay]

Regarding Gib's suggestion, could the skylight frame be dogged or latched from the inside, and the hatch itself operate as normal from outside?

[MN Dave]

Fire is my primary concern. Thanks to those who posted fittings. The skylight is a Maurice Griffiths design. What kind of caulking will provide the right combination of waterproof adhesion and breakaway ability: butyl tape, boatLife or 3M products?

A tacky material with too much contact surface area can be surprisingly difficult to budge when it is inconvenient to have it hang on. A soft gasket or low adhesion sealant might work a lot better. The tacky butyl would have to be replaced every time you open the skylight. A low adhesion sealant can reseal. 3M makes one. It may not seal well when you close the skylight, but is will at least retain its shape. (no guarantee, you have to try it and see) A soft EPDM or silicone rubber seal should reseal well.

I specified a low adhesion polysulfide once for sealing around some parts and the shop applied it to a wide flat surface covered with freshly applied epoxy primer. It adheres pretty well to uncured epoxy and forms a very effective suction cup. Point being that you can screw anything up if you put your mind to it. Freshly applied epoxy primer is dry, but not cured for several days and can grab some things that shouldn't stick to it. Our shop was very inventive when it came to misunderstanding instructions.

[wizbang 13]

Lemme share a small fire story.
When Woodwind was newish, I had fire extinguishers in each section of the boat, 4 in all,scattered about.
Well, by n by ,my greasy dinner cooking away caught fire. Being human, I panicked a bit, and reached for a fire extinguisher. Doncha know I could not find one... I mentally slapped myself silly bla bla bla. Of course I got the fire out soon enough . Fast forward... I now keep all fire extinguishers together in one place. With a box or two of baking Sosa and a hand small hand pump water sprayed In a locker/shelf AT the companionway.

[Phil Y]

A Maurice Griffith hatch shouldn't need any sealant.