Watertight compartments

I've searched on here and found some mention of watertight compartments but I didn't see anything that provides a guideline for sizing etc. I'm finishing up the interior layup on my first ama. While I've got it in the garage I was thinking I could at least install the bow compartment. The design does have two watertight bulkheads so the amas are split into 3 sections already, but this is a full wing deck so not completely closed off. How many should there be? I also tried to look up CE specs but didn't find anything on that either. Thanks.

 

How large is your trimaran Scuff?
I can never remember which is which, re amas and akas, I just had to look them up -
Polynesian multihull terminology - Wikipedia https://en.wikipedia.org/wiki/Polynesian_multihull_terminology

Re how she is a 'full wing deck' trimaran, does this mean that the amas / outriggers are accessible from the main hull?

 

What is the intended function of the watertight compartments or the reason for watertight compartments?

 

Bajansailor, The main hull is 28'. The amas/floats are accessible from the main hull.

DCockey my understanding is that the compartments ensure the boat floats even if flooded or damaged.

 

Are you building a complete trimaran from scratch? if so, what design is she - or did you design her yourself?

Can you post any drawings or photos of her?

As the floats are accessible from the main hull, how deep does the water have to be in a float before it 'spills over' into the main hull (assuming that the vessel does not have an angle of heel)?

 

Transport Canada does not permit an operator or builder to include watertight compartments for purposes of calculating flotation in the event of flooding or hull damage, or a leaking fitting. Closed cell foam only. So presumably where they can contribute to the structure, and not intrude obnoxiously on the livable space.

 

With all due respect DogCavalry but I find it amazing that Canada does not allow avessel, even a very, very special type, to have watertight bulkheads. It is usually the opposite, that regulatory bodies force to put more watertight bulkheads than any interior designer (not a naval architect) would like to have.
Maybe I have misunderstood you.

 

I thought it was at least recommended to put in collision bulkhead/compartment in the bow?
Bajan it's a Horstman 27-9 and I'm building from scratch. There's about 28" from the dwl of the float to the upper surface of the wing extension so I was thinking a bow compartment that high but not sure how much volume I should shoot for. Displacement is 3250 lbs. I get an error trying to add a pic

 

Scuff, have you got some photos in jpg format on your computer / phone?
You should be able to post them when you click on the 'upload a file' icon in the bottom right corner of where you type a new post.
You might have to reduce the size of the photo if you are getting an error - if you reduce it to say 300 - 400 kb in size, that is plenty - your photo(s) might currently be 10 times that size.

Re bulkheads, I think that there is a bit of misunderstanding above - TANSL, I think that what DC is saying is that if you have a watertight compartment, it has to be filled with foam, rather than simply left as an empty buoyancy compartment.
Which again does not really make sense (to me at least) - I would prefer to have accessible empty compartments that can be inspected.

Here is a link to Scuff's trimaran on the designer's webpage -
Ed Horstman Designs http://www.edhorstmanmultihulldesigns.com/triplans/tri27.php

And here are a couple of drawings from the website - the midship section shows how water in an outrigger / float could possibly spill over into the main hull if it gets filled up..

 

It sounds like DogCalvary is referring to the Transport Canada CONSTRUCTION STANDARDS FOR SMALL VESSELS TP1332E. Those standards contain floatation requirements for vessels not more than 6 metres in length. It does not contain floatation requirments for vessels greater than 6 metres in length.

 

There is nothing in the Transport Canada rules that say watertight compartments have to be foam filled, only that air filled compartments can not be used to meet the floatation requirements in vessels not over 6 metres in length except:

4.4.1.2.4 Air chambers may be used to provide the necessary buoyancy if they are not:
(a) more than 0.014 m3 (0.5 ft3) in volume, or
(b) integral with the hull structure.​

My understanding is the function of a "collision bulkhead" aft of the bow is limit flooding in the event of damage to the bow, for instance due to a collision. The bulkhead should be located sufficiently aft that it will remain watertight in likely collision scenarios, but sufficiently forward to limit the potential flooded volume.

 

@bajansailor, you are probably right because what I understand DC has said is totally crazy.
Going back to the question raised by the OP, I think that at least one watertight bulkhead at the forepeak (collision bulkhead) and one at the fore and / or aft of the engine room, if feasible, are normally required by regulations. The collision bulkhead must be at a distance from the Fpp between 7 and 9% of the LWL

 

TANSL, what size vessels do those requirements apply to?

 

It is not explicit, but it is implied.

Since there is a formula, in 4.4.1.4.2 that one is required to sue to calculate the amount of volume of buoyancy material required, ergo, a 'solid' means of providing buoyancy, to pass a swamp test. And 4.4.1.4.5 provides the calculation of Volume of buoyancy (Vb) to be used in cubic metres.

These rules assume that you must use a solid material to provide additional buoyancy - within the hull - to pass a swamp test.

 

For a more reliable answer than what I can give you, if you are really interested, consult any regulations of the Classification Societies.