why is there a hole in the starboard front tramp post facing forward on my mid 80's H16? Looks like machine factory made about 1/8". Anybody know if this is a breather hole for some reason or pre-owner's custom work. I plan it's maiden voyage Labor day. Please help before I sink.

It's a breather hole. You will see one on the other hull as well.

What does a breather hole achieve? Cheers

I helps equalize the pressure differences that can build inside the hull and the outside.
A hull heated in the sun which is then put into the sea can see pretty large differences in pressure. Just try putting some boiling water into a plastic bottle, seal it, wait a minute and then put it into cold water.
If the hull is airtight but flexes, pressure can build and also do damage to the hull (at least I have heard so)

Ah, okay! Yes, serious damage may result. I get round this by drilling a hole in the centre of each inspection port. I knot a cord each side of the hole and secure the cord end to the boat so I never lose the lid or drop it in the sand... or water if I am sailing and getting to my tool kit.
The area around the cord in the inspection ports equalises air.

Warbird,

You don't take on much water thru the hole in the inspection port on a capsize or turtle?

No is the answer. I pick a cords... 2ml and make a 2ml hole the cord only just goes through.

I use the same trick and it works well. But I don't have the cords, just 1.5 mm diameter holes.

Wouter

Speaking of equalization, Steve Clark's Acat has no inspection ports on it, but it has a 1/8 plastic tube out the transome that he says vents the pressure and drains the water. It comes out the top side of the transome and curls around the bottom and is about 12 inches long.

Can any of you engineers tell me how this might work?

Bill

Do you have any pictures of this Bill? Very interesting solution!

I am not an engineer, but the question sounds like "how much pressure do you need to a lift a 1/8 water column the distance from the bottom to the top of the transom". If the answer is more than the hull can withstand, or the pressure finds another hole to vent trough, you have a problem <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Bill,

This is a simple system. The tube goes from the top of the transom down to the bottom of the inside of the hull. If water does not cover the end of the tube on the bottom of the hull, then the hull vents freely. When water covers the end of the tube, then pressure is allowed to increase until it reaches a point where water is pumped/pushed out the vent hole at the top of the transom. When the water no longer covers the end of the tube at the bottom of the hull, pressures will equalize. I think this would be excellent to evacuate the water inside the hull as long as the tube in the bottom of the hull is positioned where the water gathers while resting on the beach. I don't believe it to be particularly effective while sailing, as motion of the hull would periodically allow the low end of the tube to not be submerged and vent all pressure.

The diameter of the water column doesn't have any affect on the amount of pressure required (since, as the diameter of the tube increases, the amount of surface presented to the applied pressure also increases equaly).

To raise a column of 12" in a round tube requires a little less than 1/2 psi. (.34 bar for 30 cm) - that's not much pressure.

It does make me wonder though, if the water came in from somewhere other than the tube, there is a hole somewhere else in the hull. This hole would tend to bleed off the pressure before the tube could push out the water. I'm not sure what you've gained with the tube when it comes to getting water out of the hull.

*boggle* I believe you Jake, but I have to let that mature a bit. It is easier to accept if the mass of water stay constant, while diameter of the column varies?

Our Marstrøm Tornado hulls are pretty airtight (even with the venting holes in the inspection port lids), but we still get half a cup of water in them from time to time. I suspect that the water comes from condensation.. Same might happen with Steve C's hulls.

I connect the end of the cords to one of the bolts of the port. It is a great feeling to spin the port open with one hand and let the lid fly knowing it won't drop into the sand while holding more kit in my other hand. : )

I know...that's a weird one to grasp.

Suppose you have 1psi (pound per square inch) of pressure (sorry for the English measurements) inside the hull. You also have two tubes of different size with water in them. The amount of force pushing the water up the tube is calculated by multiplying the pressure (psi) by the cross-sectional area of the inside of the tube (the exposed surface of the water that the pressure would push on).

If you have a tube that has 1 square inch of area (cross-section), at 1 psi, you have 1 lb of force pushing up the water.

If you have a tube that has 2 square inches of cross-sectional area, it has it has exactly twice the amount of liquid in it - right? If you apply the same 1 psi to this tube, you have twice the area...again you multiply the area (2 square inches) by the pressure (1psi) and get 2 lbs of force...exactly twice the pressure exerted on the 1 square inch tube - and you have exactly twice the amount of water...same lift.

I think that would be true if the leak was above the waterline as air would release easier than water. But if the leak is below the waterline the water would find the easiest way out which would be the tube??????

Thanks Jake, it makes more sense now. It is a bit counter intuitive. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

If Steve C use this system, I guess it works quite well.