Hatchea for watertight craah compartment

[Cyrus Safdari]

Recomendations for hatches for watertight compartments? Commercially produced or diy. Many monohull cruisers have modified the area under their vberths into watertight crash compartments, with access hatches that I assume are actually watertight and can hold back the pressure of a flooded compartment.

I am pretty sure the standard boat hatches even woth gaskets aren't actually up to the task, and they hold water out not in, and then really can only deal with rainwater and occasional waves.

But I know of only one manufacturer of plastic (not heavy aluminum thank you) hatches that are dogged-down with a screw-type turning handle that tightens cross beams across the hatch (Armstrong). But their biggest version 10x20 isn't as large as id like. I would.make my own if I knew where to source the screw handles
Any tips appreciated.

[coopec43]

It would be quite easy to make up a lid out of fiberglass

There's plenty here but I suppose they'd be pricey?

https://www.google.com/search?q=Wate...w=1024&bih=626

LATCHES

https://www.google.com/search?q=Wate...nt=firefox-b-d

[RaymondR]

It's a contingency item and they don't need to seal completely as long as the bilge pump can handle the leakage volume.

Sort of thing you could implement using sliding closures on the underside so that water pressure forced the hatch up against the say a !/8" rubber gasket if one had the room to slide them side ways to open.

[Cyrus Safdari]

The regular deck hatches are not designed to hold water in, they are designed to hold water out. And even then they are weather tight not really water tight. Same with the latches they use.

Wven the Armstrong hatches are not really suited since the lip goes on the outside not inside. Ideally there shoukd be a gasketed lip on the inside so the water pressure compresses the lid gasket and makes it seal better.

A hatch lid with a lip on the inside of course would make opening the hatches a little hard because you have to press the lud inwards first, tip it a little then pull it out of its hole.

As far as latches: This can be easily done with with a longish bolt passing through the the hatch and a cross beam which is tightened by a butterfly nut on the other side, but then you can't put a mattress over the protruding bolt end.

(Im not a submarine or tanker of course so the water pressure isnt huge, i dont need one of them heavy metal inspection hatch jobs. The hatch lid need only be as strong as the rest of the hull material, structurally.)
I guess Im going to have to get creative...

[Cyrus Safdari]

[QUOTE=RaymondR;3213223].

Sort of thing you could implement using sliding closures on the underside .[6hTLXfLC/QUOTE]

I'd like to keep the water out as long as possible. If there ever is a crash up there, it will probably be a big one!

And yes to the interior lip, that's a problem with using Armstrong lids because their lips are on the outside (again, meant to keep water out, not in), and the crossbeam is on the inside. Putting the lip inside would of course make it more difficult to open the lid since you have to press the lid in a little, turn it and then jiggle it out. (But thats just the cost of an interior gasketed lip.)
I could easily make a lid that is slightly larger than the hole, put a gasket around it, with a thrubolt that passes through a crossbeam on one side and a wingnut on the other. Tightening the wingnut compresses the hatch against the interior of the space, but then you cant put a mattress over the bolt end protruding up on the outside.

[barnakiel]

Latches and other devices can be fabricated to your design. You can copy a design that you like.


Welded SS fittings are easy to build as long as you find a welder who can fluently read your drawings.



b.

[singlespeed]

The bigger the hatch, the heavier the weight and the chance of leaks increase. The gaskets are always a weak point, easily damaged and larger hatches have larger gaskets. If it's a dedicated crash box, there is no real need for a large hatch. Water ingress can be pumped out of ever small hatches. I have seen owners who cut Styrofoam into small cubes and push these through small round hatches to give them more flotation if the crash box suffers a failure. Crash boxes should not be used for storage.

[waterman46]

How far aft does your V-berth extend? Think about where you might have a breach in the hull due to collision. I bet it would just as often open up the hull aft of the V berth, likely in a nearly inaccessible place.

Perhaps it would make more sense to figure out a point in your boat where a temporary watertight bulkhead could be incorporated into the existing interior bulkheads. In many boat this would be just aft of the head and any lockers across from it, where existing transverse bulkheads already extend nearly across the width of the interior. Seal all openings under the floors at that point. In an emergency the whole boat forward of that point can be sealed off. You could have a panel about four feet high that could be inserted into the cabin floor, fitting into the existing bulkheads on each side, to form a nearly watertight compartment if needed, in the forward part of the boat.

As noted, you don't need a watertight seal, just one that will reduce the flow to what bilge pumps can easily handle.

[Cyrus Safdari]

Originally Posted by waterman46

As noted, you don't need a watertight seal, just one that will reduce the flow to what bilge pumps can easily handle.

I'm shooting for watertight. If there's ever a crash big enough to take on water in the bow it wont be sonething tbe bilge pumps will keep up with.

Under the vberth and the two settees will be watertigjt compartments in addition to cockpit lockers plus vberth port and starboard. The settees are integral water tanks so no need for any hatches, just a regular inspection port. However I want access to area under vberth so need hatches that can be opened but also are watertight enough to withstand force of flooded compartment. Regular hatches do not. Regular hatches keepwater out,not in,and not very well either.

The point i to keep the lid lip with gasket on the inside, not outsode. Regular hatches have a gasket but on the outide so water can get by. It is possible to make a reverse version of the latches on the Armstrong hatxh but thays too much work. I may just go with regular hatches and jigger a way to keep their lids down extra tight with my own added cross bar over them.

[Cyrus Safdari]

Originally Posted by singlespeed

. Crash boxes should not be used for storage.

Converting the space under the vberth as a crash compartment is a prettt standard matter, not unusual at all. Im just curious what hatches people use. The hatches dont need to be particularly heavy or stronger than the rest of the boat which is keeping back the same water pressure. It just needs to be stiff enough not to flex, and the lip should be on the inside so water pressure closes the lid shut more tightly.

Seems like people who do this conversion rely on regulat deck hatches and assume they're watertight both ways. They're not.

[barnakiel]

Our boat displaces 4t and we can pump out 8t of water each hour.


How big are your pumps? You may have undersized pumps.


It is not about ultimate tightness. It is about blocking the flow to one easily dealt with by the pumps.


Mind ultimate tightness need to be matched with ultimate structural strength of the bulkhead. Or else calculated the pressure from this amount of sloshing water onto this bulkhead. Will it stand it?


barnakiel

[Matt Johnson]

Originally Posted by Cyrus Safdari

Converting the space under the vberth as a crash compartment is a prettt standard matter, not unusual at all. Im just curious what hatches people use. The hatches dont need to be particularly heavy or stronger than the rest of the boat which is keeping back the same water pressure. It just needs to be stiff enough not to flex, and the lip should be on the inside so water pressure closes the lid shut more tightly.

Seems like people who do this conversion rely on regulat deck hatches and assume they're watertight both ways. They're not.

How often do you want access? We made ours watertight with a simple plywood hatch and gasket that was bolted down flush to a recessed lip. It took under two minutes to unscrew the roughly 16 machine screws whenever I need to get into the area.

Matt

[NorthCoastJoe]

Might sound crazy but if you are that worried. Fill the area with expanding foam, making it solid foam. If you crash there is no place to fill with water.
My Macgregor 25 came packed with foam under the V berth.

[RaymondR]

If you can put a plywood hatch with a soft rubber seal around the edge through the hole and into the compartment and pull it against the surround any water pressure inside the compartment will tend to force it into the seal. For example if the hatch is 24" x 12" and it has 1 psi of water pressure against it the force against the seal will be 288 pounds. 2 Psi 576 pounds etc. The hatch just needs to be held against the in place to get the initial seal and the water pressure will do the rest.

This is how the over wing emergency exits in air liners work.

[Nani Kai]

Originally Posted by RaymondR

....... if the hatch is 24" x 12" and it has 1 psi of water pressure against it the force against the seal will be 288 pounds. 2 Psi 576 pounds etc. The hatch just needs to be held against the in place to get the initial seal and the water pressure will do the rest........

RaymondR is correct. I was a professional underwater cameraman for many years. Underwater camera housings work on this principle. The latches that attach lens ports and the backs of housings just hold them in place. Water pressure as you descend compresses the "O" ring seals making them watertight.

If it were me I would make the hatch lids with a 1/2" rabbit around the perimeter, then rout out a slot to accept a 1/8" 'O' ring. Then install flush deck marine hatch cover latches such as these on Amazon: Slam Latch Hatch Round Pull Latch (OWACH AL-958- if you prefer plastic or Amarine Made Marine Boat Stainless Steel 2" Flush Pull Hatch Latch - YI-0357 for SS.

Or you could just rout out a slot in the hatch surface and a matching one on the berth deck and install simple flat SS dogs to hold the hatch in place until water pressure seals them tight.