Silicon Gasket

[Kayak Jack]

<SNIP> Let me explain what I am saying, internal pressure is easier to contain with less strength.
Simple test take a milk jug fill it with water no problem. take that same jug empty it and submerge it in water
the jug will collapse. same amount of structure just different pressures. I use to build a lot of diesel storage tanks ,even a
500 gallon held several thousand lbs of fuel but if you forgot to open the vent just ounces of vacuum would fold it up like a paper cup.
My point is a sealed compartment with our hatch system will never fracture the hull, pressure will be released long before that ,and your boat will take more pressure from inside than it will externally.

I agree that pressure will be released from your hatch long before it would explode. The hatch cover will lift and burp.

Your examples of Diesel tanks and milk bottles aren't applicable, but interesting. Their skins serve as a membrane to contain a fluid. The skin is under tension and trying to tear apart. If over pressurized they would rupture in a tear - the skin would separate under tension. Think of a penny balloon. Yes, a thin skin can hold fluids, but it isn't pertinent to boat hull design. Just more smoke screen.

Our boats, on the other hand are the exact opposite. They are withstanding pressure from the outside with a rigid skin that maintains its structural rigidity; the skin is in compression. If they rupture, it would be from a puncture. The skin would first be compressed beyond it's capacity to maintain integrity, and only then would it separate and tear.

Chuck, given enough gritz, these principles of physics work even for simple southern folks.

 

[Bellybuster]

Ummm....nice idea on the seal. have you ever seen Lexel?? It is a bit heavier than silicon and clear. Has good adhesion preoperties and I think it may flatten out better and smoother as it has a longer working time. It is also 100% water proof unlike silicon which will soften with continuous water use.
Maybe try using box tape on the bottom of the hatch as you'll be able to get it perfectly smooth and the wrinkles of the saran won't be a problem.
http://www.sashcosealants.com/home_impr ... lexel.aspx

 

[graybeard]

Ummm....nice idea on the seal. have you ever seen Lexel?? It is a bit heavier than silicon and clear. Has good adhesion preoperties and I think it may flatten out better and smoother as it has a longer working time. It is also 100% water proof unlike silicon which will soften with continuous water use.
Maybe try using box tape on the bottom of the hatch as you'll be able to get it perfectly smooth and the wrinkles of the saran won't be a problem.
http://www.sashcosealants.com/home_impr ... lexel.aspx

Careful Belly. If you keep tossing helpful info into this dogfight they'll both turn on ya.


Seriously though, thanks guys. I'm learning a lot.

 

[Bellybuster]

Careful Belly. If you keep tossing helpful info into this dogfight they'll both turn on ya.


Seriously though, thanks guys. I'm learning a lot.

those guys have been around long enuff to have a great fear/respect for us Canadians, 1812 Whitehouse thing you know....

 

[tx river rat]

Jack
This post was about using silicon to make a gasket to seal hatches, then we get off into your compression theory. you owned up to the fact it aint going to happen with our current construction of hatches.
Now the smoke you keep talking about is getting in your eyes , the diesel tank and the pressure it will hold compared to external pressure crushing it is ( now blow the smoke away so you can read this) one of the things that affect a boat hull integrity, Your boat will take a lot more stress from the inside out than pressures from the outside in. Just like you said.
So going back to the heart of this discussion ,you build a normal boat that will handle the outside water pressure it sure isnt going to have any trouble handling a pound are two of pressure from the inside,which from your own admission aint going to happen .
Again PRESSURE BUILD UP INSIDE HATCHES IS A NON ISSUE
Ron

 

[tx river rat]

Well the gaskets are going to be alright,the boat was sitting out with the hatch cover just sitting in place no straps and I got very little water in them after 24 hours of rain.
Ron

 

[john the pom]

That's probly 'cos it was rain from a low pressure weather system

 

[tx river rat]

Ron

 

[shikeswithcanoe]

Just a thought guys.

If I was looking to make a hatch seal, I think I would give strips of neoprene rubber (wet suit material) a try. Probably makes a pretty good seal if you make it a bit thick then use pressure on the hatch to compress it down a good bit.

You would probably ONLY want the hatch on tight when you are using it. Storing it that way might permanently compress it and ruin it.

Might want to look around in the hardware stores too. I think I have seen strips of stuff like that sold for doors/window seals/whatevers.

 

[Kayak Jack]

Yeah, common weather seal works well.

 

[WDfrmTN]

I decided to try laying a gasket and see how it works.
I sanded the lips just to rough them up

Then took a tube of silicon and laid down a heavy bead

Then I covered it with saran wrap

then eased the hatch cover into place and put presure on it till it was the right level

They turned out pretty good for the first try

On the next one I will wrap the plastic on the hatch cover,should make it a lot easier.
I need to trim these up but am going to let them sit overnight.
Ron

A little late here, but next time try this: prep-coat your hatch with Vaseline or beeswax as a release agent...no wrinkles like from the plastic film wrap.