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Tikis (and others) in rough seas and when beating upwind take a lot of water over the front-hatches. Does anyone have a method to build-/make them real watertight? 

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Thank you Patrick. sorry it was inadequate. Here's more detail. Note that that this design has an airspace between inner and outer restrictions like double combings and the wharram type but directs water flow away from the seal as commercial hatches do, unlike the wharram type, making the seal in fact optional as Isabel noted when I was on board wakataitea. This might be roughly similar to the traditional double combings in dryness or maybe better but simpler, cheaper, and lighter and no trash trap. Hanneke also liked it because it presents a broader more comfortable surface to sit on.

That's more like it,except there has to be a seal at the lower edge of the lid frame, otherwise solid water pressure could force the lid upwards, allowing water in.   Of course a drain from that space at the rear would relieve any pressure, but that assumes the water pressure was always coming from the front. (bows).

On my Nugget I had a small piece of angle moulding on the deck in front of the hatch cover to deflect solid water over the top of the hatch.  It worked.

I must admit I never experienced waves coming from behind, but then --as James postulates- a good multihull should run ahead of following waves.

I had a Buccaneer 28 trimaran which had convex decks on the floats. The hatch cover was  plywood with rubber seal around all the edges, hinged on one side, with snap shackle type locks on the other.  Worked fine in normal circumstances, but on one filthy black night, in the Summerville race  on Lake Ontario, it was very rough, and we took about 100 litres of water in each float. That can spoil ones whole day (or night). :(

I know exactly what you and the others mean about water coming in through those deck hatches.  I used to have to heave to and bail out the forward compartments on the Pahi 26. One of the few changes I asked for on the Tama Moana was no fore and aft deck hatches which is how it is.

I think the question of whether water pressure could lift the cover, without deflectors, would apply equally to double combings. A solid wave will always only hit the hatch from one direction at a time. A wave from astern leaves an air gap drain out the front. A seal, or deflectors, at the bottom might still be dryer although I don't think people ever put a seal in the outer gap of double combings.



Glenn Tieman said:

Thank you Patrick. sorry it was inadequate. Here's more detail. Note that that this design has an airspace between inner and outer restrictions like double combings and the wharram type but directs water flow away from the seal as commercial hatches do, unlike the wharram type, making the seal in fact optional as Isabel noted when I was on board wakataitea. This might be roughly similar to the traditional double combings in dryness or maybe better but simpler, cheaper, and lighter and no trash trap. Hanneke also liked it because it presents a broader more comfortable surface to sit on.

Thanks for the drawings. Looks good

Hi Glenn, looks good.

In the Griffith's hatches you hinge the hatch side to the outer combing, this has some advantages. How do you hinge the hatch cover in your design?

Glenn Tieman said:

Thank you Patrick. sorry it was inadequate. Here's more detail. Note that that this design has an airspace between inner and outer restrictions like double combings and the wharram type but directs water flow away from the seal as commercial hatches do, unlike the wharram type, making the seal in fact optional as Isabel noted when I was on board wakataitea. This might be roughly similar to the traditional double combings in dryness or maybe better but simpler, cheaper, and lighter and no trash trap. Hanneke also liked it because it presents a broader more comfortable surface to sit on.

The wood and string hinges on the tama moana hinge off the deck
 
Ricardo Aráoz said:

Hi Glenn, looks good.

In the Griffith's hatches you hinge the hatch side to the outer combing, this has some advantages. How do you hinge the hatch cover in your design?

Glenn Tieman said:

Thank you Patrick. sorry it was inadequate. Here's more detail. Note that that this design has an airspace between inner and outer restrictions like double combings and the wharram type but directs water flow away from the seal as commercial hatches do, unlike the wharram type, making the seal in fact optional as Isabel noted when I was on board wakataitea. This might be roughly similar to the traditional double combings in dryness or maybe better but simpler, cheaper, and lighter and no trash trap. Hanneke also liked it because it presents a broader more comfortable surface to sit on.

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