Watertight Compartments?

[Tom Lathrop]

Greg,

I may have the answer to your problem with the gypsum leaking problem.

A while back, a group of locals, including intrepid designer Graham, built a 20 foot trimaran which was raced in the World 1000 race from Ft Lauderdale to Virginia Beach. The bottom of the center hull was coldmolded with juniper laminations that were stapled until the epoxy set and then several coats of epoxy applied. On the big launching day with local news cameras running, the "Oriental Express" was taken out for a sail. While the cameras did not show it, she proceeded to take on an alarming amount of water.

The cause was water leaking through the staple holes. Graham and I surmised that surface tension of the low viscosity epoxy prevented it from sealing the holes. This is completely normal and should have been forseen. Surface coatings hate sharp edges and will always draw back from them, leaving the edge exposed, or hole open, in this case. Thickened epoxy or a fabric sheath will solve this problem.

I had a result just like you when my wife bought a pottery bowl that proved to be porus and leaked. I tried coating it with epoxy but it still leaked. Takes a lot for some of us to learn from our mistakes. Adding some cab-o-sil to thicken the epoxy solved the problem.

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(quote)

I do not trust air tight voids to remain free of water, so use the blue foam. To those who keep stating wooden boats float and do not need floataion, they should look at the history better. Wooden boats and ships sank and still do sink all the time. The Great Lakes are littered with thousands of them in just the last 200 years or so. (quote)

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This is a bit out of context. As I stated, I do use the waterproof blue foam quite a bit for floatation. My comment was mainly an attempt to give a jolt to the novice's belief that all floatation tanks must have foam or something else in them to make them work properly. 'Taint so, at least for the unballasted wooden boats here. I advocate multiple air tanks for the small unballasted boats that this forum is about. I like to make all my small boats so that they will float with any air tanks punctured, however that is achieved. In the Bay River Skiff that I built, there were four sealed air tanks plus the two "almost waterproof" sealed lockers in the sides and the large locker forward. To say that foam should be required in the tanks as well seems excessive to me. This boat, like all Graham's unballasted designs, will float and hold its crew up if all the tanks are flooded.

That's my story and I'm sticking to it.

Tom Lathrop

[Greg Luckett]

Tom,

Thanks for the insights about the porosity issue. I will experiment with your idea.

Actually, I was not targeting anyone specifically about the wooden boats floating, as I could not recall who the several were making those statements. Those folks were saying air tight voids were not needed on wooden boats. Sorry if you thought I was targeting you. :oops:

This thread has generated so much discussion that I am not sure what the topic should be anymore.

Thanks and Merry Christmas,

Greg.

[Guest]

To add one point of note, the grid system isolates any water intrussion and minimizes some repair work, if trouble rears its head. Sorry for addressing the epoxy problem. Thank heaven, the great one picked up the loose ends there. Merry Christmas to all and wishing a happy buildinsg season for all this winter in the northern hemisphere, and a happy summer season for the southern hemiphere.

[Greg Luckett]

I went back to the beginning of this thread and now believe we have been on topic with this discussion. It is about water tight voids and floatation.

Oyster, the grid system is smart and long proven to be a wise way to go. It adds strength and reliability. My years in the Navy and studies since then point out time and again the survivability of vessels with multiple sealed compartments over ones with only one or two sealed compartments. The Titanic is a prime example of the wrong way to build a vessel. Navy vessels have many sealed voids (all with access hatches) to improve the ability to survive torpedoes or suicide boats (like the USS Cole).

My only issue is the reliability of a sealed compartment to not allow moisture to gain entry. Looking at boat designs from the 30s, 40s, and 50s in old books, most have some sort of sealed voids. They did not have the materials we have now. I have modified the PK78 which was built about 4 years ago to have sealed voids under the seats with foam and threaded openings for air drying. A Nymph I am slowly finishing, I have done the same thing, but without the openings. I have spent a lot of time making sure the voids are sealed. Still, I am worried.

Merry Christmas Mates,

Greg.

[mustangermatt]

First as to wood floating, there are a number of species that do not float :-) Most of the ships I worked on were steel or aluminum, but we still felt quite comfortable in crossing oceans in any weather with nothing more to keep us afloat than air in water tight compartments.

I think the point is the level of survivabilty required in an open boat.

Although we need a level of safety, rarely will you find a scenario in a small sailboat where you are going to tear open all the compartments in a boat like the coresound. Given the weight and speed of the boat compared to the strength you will bounce off of most anything you hit, probably only amaging the section of impact.

The exception might be if something bigger and faster hits you, but at this point we can assume that the life jacket you are wearing will be of more use to keep you afloat than the small pieces of foam glued to broken bits of plywood :-) Assuming you survived the impact which is often not the case.

In other words a good radar reflector, nav lights, hand held vhf scaning 13/14/16 and charts with the Vessel Traffic System will go a long way to eliminate the need for foam.

[Joe Nelson CS#35]

I think that we are all correct in our assessment of foam and epoxy. There are so many variables...type of wood, use of fiberglass, quality of epoxy coating and smoothness of finish, environmental, etc.. I am sure that given a lot of experiance and the use of rot resistent wood that foam can be installed without negative effect. But without the experience, rot and moisture collection is a real potential. Oyster seems to be talking all the necessary precautions and he will most likely succeed.

Using plywood with voids for instance is more subject to expansion and contraction and this leads to cracks in the epoxy coating. Epoxy is not considered to be a 100% waterproof coating.

My vote is to leave out the foam, make wearing personal flotation devices a regular part of your float plan and get insurance on your boat...in the off chance that a major collision causes loss of multiple air chambers, your boat wont be worth much in this scenario anyway.

[Greg Luckett]

Good points Joe. Thanks for the recap.

I am trying to recall the statistics about boat swampings from the Power Squadron courses I have taken. If memory is correct, it is not from collisions that often, but rather capsizes caused by too much speed and hitting something, or too much sail, or any number of things that will cause a boat to swamp. The Coast Guard recommends staying with the swamped/capsized boat if at all possible as this increases the likelyhood of survival and rescue. This is why I believe boat floatation is so important.

I am pondering your comment about more voids increasing expansion/contraction problems. I must think about that some more. Can you offer some more insight about it?

Thanks.

[Joe Nelson CS#35]

Voids are where most of the water enters plywood. Domestic standards are much looser than the BS. The larger the voids, the more pressure difference is produced by heating and cooling. Pressure builds in the air pockets as the plywood heats up causing eventual cracks. Epoxy is more flexible than poly resin...but can eventually crack. Then, as the wood cools the void looses pressure and water is sucked back into the wood. Wood also is subject to ex/con but consistentcy of plies and lack of voids doesnt provide an isolated weak point that the forces can work on. Devlin talks a lot about this in his repair section of his book and it makes sense to me.

Please dont put me in the same catagory as the doom and gloom Wooden Boat Forum traditionalists...but I believe that you should use the best plywood you can afford. Low void content equals more long term rot resistence. Those football shaped plugs in fir plywood for instance are another source of eventual rot.

Coating everything with fiberglass is the best defense. This assures a visual and physical barrier. If you fill all the weave, you have a good consistent epoxy barrier that you can see. Cracks in fiberglass are also easier to detect than without fiberglass.

[Joe Nelson CS#35]

As far as you statistics from the Power Squadran are concerned...if most problems are from swamping or too much sail, the air tanks should not be compromised and staying with your boat should not be a problem. The area where foam has an advantage is in the case of a collision.

Its not hard to calculate the area of space needed for flotation. Figure that water weighs 10# per gallon. There are about 7 gallons to the cubic foot. Thats about 70# per cubic foot. I figure that one air tank on my CS20 is about 6 cubic feet. Thats about 420# of flotation. Of the 600# total boat weight...I figure that at least 200# of that will float. So one tank should keep her afloat. Then there are the fore/aft and side compartments that will hold water for a time. There is a lot of flotation potential on the boat!

Bottom line...do what makes you feel safe. If you are worried on the water it wont be fun. But to me that few hundred bucks doesnt buy me any piece of mind.

[Greg Luckett]

Joe,

A bit of confusion I think. :?

I am not talking about voids in plywood layers, but voids which are compartments on a boat, such as under seats, or built into the sole, etc. Navy ships have many voids which are sealed compartments. This radically increases the odds of surviving a hull breach. These are large air filled, spaces usually.

On the boats we are building, these spaces (voids) are small, usually difficult to actually get into and inspect for maintenance issues, therefore need a way to circulate air for regular drying. To actually make an air tight void which would keep water from entering while swamped for hours is the issue of using the foam....in my case anyway.

Voids in the plywood are a problem and have little or nothing to do with floatation.

Thankyou for this discussion and your help. I appreciate the jewels of wisdom and sharing that we are doing here. I agree with you completely about using the best quality plywoods. The calculation for floatation will be helpfull too. Usually I just enclose and seal any available areas without modifying the plans too much.

[Joe Nelson CS#35]

I think this dicussion has been worthy anyway.

I like your signature...There is a very fine line between "hobby" and "mental illness." I can relate.

[Greg Luckett]

I like Dave Berry. He is syndicated. Do you get him there, in the local paper?

[Guest]

FYI:The love of boats do not fit in the category of mental Illness. The love and lust of boats fits under the guidelines of appreciating well defined curves of the finearts in our society.

[Greg Luckett]

Its okay Oyster. Remember, breath deep, hold, exhale, breath deep, and so on. The drugs will take effect soon.

LOL

[Frank Hagan]

I call boat building a "magnificent obsession", both because it does become almost obsessive but is truly worthwhile, even with all the obsessive-ness (????) it entails. I learned early on that I couldn't talk too much about building a boat in front of people who hadn't done it. They tended to look at me like I was one of those unfortuneate souls wearing tin foil on my head so the aliens couldn't steal my thoughts.

[Greg Luckett]

Now it is clicking. I was puzzled by those strange looks.

:roll:

[Ambler]

I want to have access to the flotation voids on my Spindrift both for maintenence and "cargo" space. I'd like something bigger than those round plastic access plate that screw in. I see some mention earlier in this topic, of a hatch that Graham is using. Any news of it? Details?

One thing I'm wondering about is the strapped-down hatch covers I've seen on kayaks. Maybe something similar could be devised. I want to get a look at one but as yet have no opportunity. Anybody know how they work; sealing & construction details?

Alexander Miller.

[Charlie Jones]

Just spent more time reading this thread. Wow!!

First - an enclosed space, coated with multiple coats of epoxy isn't likely to "rot" I have built and still build, tanks from plywood and epoxy to hold both diesel and water. They don't seem to have any difficulties with rot.

On the Princess I'm building I have made 4 individual "sealed " compartments One on each side of the motor well, under the cockpit and under the rope locker in the bow. Each of those was heavily coated with epoxy , then filled with foam. Each also has a screw in drain at the low point that can be removed when the boat is being stored on her trailer. More to allow condensation (if any) to excape than for any other reason. Since the lower edges are all filleted and taped, and the UPPER edges are also, I really see no way water can ingress save for condensation.

Another thing I have done is make the bulkhead at the mizzen mast a water tight bulkhead, plus the two larger cockpit lockers are totally sealed from the remainder of the boat. The settees inside are also sealed off (filleted and taped) from the center of the boat.

Therefor, this boat has, by my count, nine seperate water tight sections, spread bow to stern. I'm not worried, nor is the owner, about this boat sinking Plus the centerboard trunk runs through one under bridge deck space and would take 18 inches of water in it to flood over. I guess that would make 10 spaces

There are multiple methods of obtaining floatation and part of them can be useable for other things ya know :)l

[Roger Peterson]

Ok, I finally got my pictures back and reduced in size so I can show how I framed the hatches in the seats. The photos were taken back in late January so a little more work has been completed. The first 2 shots show the side seat framing with the raised "waterproofing" lip and the third shot is the "little seat" across the back bulkhead that will have a small hatch lid for a small built in cooler. The rear deck will cover the "little seat" so people can't sit on it. There will also be a small dry storage compartment for small items like cameras, sunglasses, sunburn ointment (this is Texas after all :shock: ).

Roger

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