Floatation

Mike,

Your calculation of about 55 cu ft to float 3500 lbs is correct. To help visualize the amount of foam required, consider your fuel tanks.

An empty 25 gallon tank would provide about 200 lbs of floatation. Two empty 25's would barely be enough to float the motors!

Floating the boat doesn't require the entire 55 cu ft of foam,however. Some of the hull structure(the core) is already lighter than water.

One way to determine the amount of floatation needed would be to suspend the boat from a scale, lower it into the water, fill with water, allowing it to sink, and check the scale to see how much it weighs underwater! Everything weighs less underwater based on how much water the item displaces. But most of us don't want to use our own boat for that test!

If you look at a CD19, you can see how much of the interior has been filled in for the foam. The sides of the cockpit and hull sides inside the cabin are covered with a liner where the foam is located.
 
Larry H":34fxb2zy said:
Mike,
If you look at a CD19, you can see how much of the interior has been filled in for the foam. The sides of the cockpit and hull sides inside the cabin are covered with a liner where the foam is located.
Click to expand...

So would that make the 19 quieter than the 22?
 
Mike-

Your math is correct for 3500 lbs of flotation, which is a good number, since the loaded CD-22 can usually weigh 3000 lbs or more, and some margin is needed for safety.

To get the 56 or so cubic feet and still retain some storage, may be difficult, though.

A cube 4 x 4 x4 feet would contain 64 cubic feet. This block is very close in dimensions to the cube root of 56 which is a little over 3.8 feet.

Imagine yourself in the cockpit of the CD-22 with a 4 x 4 x 4 foot cube of rigid foam flotation and a big knife to cut it up and stuff it away for flotation.

Where will you cut and stuff it? How much of it will you be able to use? What will be left of your precious storage area?

In my mind, I not only don't think you'll find enough room for all of it conveniently out of the way, but will wind up deciding that some, perhaps much of the flotation will have to be sacrificed to retain storage space.

One good way to hide a lot of it and also get some additional benefits would be to use B~C's spray-on foam insulation system on a stripped out boat so as to include foam in the heat/sound insulation and put it up, down, and around into crevices and other unused areas that would be hard to utilize otherwise. Best to do this to a boat during production, as I've said before.

******************************************************************************

With the above in mind, why not make some of the boat's flotation available on demand by using inflatable air bags deployed electrically on demand?

It doesn't really matter if they pop out from under the transom, gunnels, v-berth or dinette, etc. (But not in the doorways, etc.)

It would be much easier to "balance" the flotation package this way to get a level float when awash, and such devices would save valued storage space.

I wonder if such units exist already? Time to go inventing?

Joe.
 
The enclosure in the bow is not only flotation but also an effective collision bulkhead. With all the deadheads & stuff floating about I like having the additional barrier foreward.
 
There have been bag flotation systems for boats around for a long time. I don't know of any people who use them. It is more usual for a boat to be lost on a reef than to sink directly. Many boats which are abandoned are found, even years later and thousands of miles away, still floating. Many of these are half full of water or even upside down.

Many small racing sailboats on up to the Flying Scot have air floatation bags, including many of the junior trainers. There was a company building large inflation tubes for offshore boats, but I cannot find it currently. One of the problems was that when the bags/tubes inflated, often they encountered a sharp object and then punctured. The "sollution to this" was a PVC or Hypalon type of material, but this was prohibitly expensive. I have never worred about a C Dory product sinking--They are very tough--and we are not crossing oceans.

I was in a racing sailboat when we hit a container at sea. The boat had a 3" balsa core and the container ruptured the outer glass (about 1/2") and impacted the balsa, but not the inner glass. This boat had enough balsa that it would self float and was 55 feet long.
 
So, the question is: does the foam in the bow actually do anything, or will the
boat sink anyway.

Yup, I did forget to take into account the bouancy of the balsa. OTOH, I did
not account for the fact that 55 cubic feet of foam must weigh something...

I'm going to guess that there are about 22 cubic feet of balsa in a CD-22.
(22 * 8 * .25) /2.

So, maybe we only need something like 30 cubic feet of foam in the bow?

Another thought:

The foam would also provide some structural rigidity between the V-berth liner and
the hull. Makes that area pretty near a single unit. I removed the access
cover one day. It was stuck on pretty good. The foam they use does have
adhesive qualities.

Any factory guys around to answer the question? If a CD-22 sinks, will the
bow remain poking out of the water, providing a holding on place, or is the
foam there for some other reason?

Mike
 
Joe,

I too thought about flotation bags - my "idea" was to have flotation tubes that would come out from a larger rub rail. I thought this would be a potentially interesting invention. Of course a patent on the same idea was already issued to somebody else a long time ago and that patent owner apparently didn't develop a financially viable product.
 
Roger-

Yup, the "float collar' is an interesting idea. I seem to remember they used it on the Apollo and/or Gemini capsules when they landed in the ocean.

If you extend the idea out to leaving the float collar on, you wind up with a RIB, or Rigid Inflatable Boat.

C-Dory could very easily have a whole second line of boats with a little modification by adding inflatabile collars.

Would be a natural on the new CD-22 Center Console.

The RIBS are great for doing rescue work with their low, padded sides.

The collars have to be quite strong (Hypalon) and very solidly atached.

Who will be the first to build a custom C-Dory RIB?

Joe.
 
On the other hand, the Coast Guard has gotten away from the RIB concept with the SAFE boats: "25-foot secure all-around flotation equipped, or SAFE boat. The boat features a rigid foam collar around the boat that provides additional flotation, serves as a fender and makes the boat virtually unsinkable"

I doubt if there is 22 cu feet of balsa in the core of the floor. The Balsa is only 1/2 or max 3/4" thick. So the at best the formula would be 22' x 8' x .04'/2 (if this is a valid formula for the bottom area). This would be 3.5 cu feet of foam if my math is correct.
 
Just a thought for those of you with 22’s, 25’s and cats. Most of you have an inflatable or dingy on the boat. If it is obvious that you are going to sink, why not get into the dingy instead of holding onto the side of a 7/8ths submerged boat?

_________
Dave dlt.gif
 
The best flotation I had in a boat was a wooden 1" flat bottom skiff I built about 30 years ago.

Cypress on oak with a 1/2" marine plywood bottom and solid oak transom. The skiff could be filled with water (totaly swamped) and the powerhead of the 15hp Evinrude would still stay out of the water. It was unsinkable. I could also steer it by standing upright, holding onto a bow line and lean left or right when it was up on plane.

It would be nice to have a boat today that is as unsinkable as my 14 ft cypress skiff was and has the capability of my CD25.
 
We had a CO2 bottle with a inflatable valve fitting, to inflate a dinghy in an emergency, rather than carrying a life raft. Definately one wants to stay out of the water!
 
Do the new 22 c-dory cruisers have a flotation compartment ?

Can you get into the hull to foam it?

You would just have to foam it beyond the differential of the boat
displacement of water under water. Sure seems as though someone
must have tried. Seats with large attached storaged boxes and a
few additional items filled with foam would go a long ways if there
is already a flotation compartment and room to add in the hull area.
 
Arthur,

Welcome to the site.

I'm guessing from your post that you have not seen the interior of a CD 22. Basically, there are no hidden spaces in the hull that are not accessible. The space under the sides and forward area of the v-berth is sealed and foam filled. The main cabin area under or inside the cabinets is storage. Other than the cabinets, there is no liner or hidden hollow spaces. It would be possible to sacrifice some storage to add floatation, but that would make the boat less useful.

Don't worry about this topic excessively. As far as I know, only one 22 has swamped off the Oregon Coast when it missed the entrance and was caught in the surf. It floated bow high and was washed ashore. The other sinking was a 25 in Cook inlet in Alaska, a dangerous place. The anchor rode became fouled in the props due to operator error, effectively anchoring the boat by the stern. The high chop then swamped the boat, but the people were rescued by nearby charter boats. One boat in SE alaska took water through the open center window (which should have been closed) in a current rapids, but that didn't sink or seriously threaten the boat.

I have operated my 22 for 16 years and over 1,000 hours including two trips to SE Alaska and offshore in Southern California and never taken any water beyond spray into the boat.

Many others have operated their boats in big water and have returned safely.

The member who started this thread is planning an expedition down the Mackenzie River in Northern Canada and his requirements are extreme and unique.

Generally, these boats can take more than the people can.

The C-Dorys shorter than 20 ft have the built-in floatation.
 
To Old Growth,

Please see the comment about what happened in the Fastnet Race in the Ditch Bag Thread. You never step into a life raft unless you step UP. The best thing to do is stay with the boat. It will be seen even if it is swamped. A swamped boat will not move as much as a Life raft, so when you let your EBERP signal, it will be easier to find you. Also, a bow up swamped boat still has the windshield to stand on.

Just one man's idea.

Fred
 
Well.... my next door neighbor who is one of the very few remaining survivors of the USS Indianapolis, .... I feel sure would speak volumes of having something between you .....and the sharks...

I also found it interesting reading his book Beyond The Depths: A Survivers Story, that the 1st food he had to eat in days.....was the inside core of a potato...and one of my best C-Dory owning friends is ol Tatter Head himself.....Roger Johnson.... a potato farmer Extraordinaire :thup :smiled

http://www.indysurvivor.com/
 
thataway":3pjv6s27 said:
On the other hand, the Coast Guard has gotten away from the RIB concept with the SAFE boats: "25-foot secure all-around flotation equipped, or SAFE boat. The boat features a rigid foam collar around the boat that provides additional flotation, serves as a fender and makes the boat virtually unsinkable"

I doubt if there is 22 cu feet of balsa in the core of the floor. The Balsa is only 1/2 or max 3/4" thick. So the at best the formula would be 22' x 8' x .04'/2 (if this is a valid formula for the bottom area). This would be 3.5 cu feet of foam if my math is correct.
Click to expand...

I thought the hull bottom had 3" of balsa.

"The next step is bonding the balsa core (1 1/2") into place in the bottom of the hull and then covering it with several more ply's of fiberglass. The bottom ends up about 2" thick."

So, I was off by 50%. But, we're dealing in rather round numbers anyhow :-)

Mike
 
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