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Old 07-09-2013, 08:56   #1
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Floating Bulkheads

Can anyone with direct construction experience define the term "floating bulkhead?" Why is this technique used in boatbuilding? If done properly, is it acceptable for an offshore sailboat?
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Old 07-09-2013, 19:37   #2
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Re: Floating Bulkheads

It sounds like with NO answers and 45 views to be a "hot potato" subject.
I was on an offshore boat which made "shoop...shoop" noises.
It was the liner sliding back and forth as we carved down swells.
I could feel the chart table seatback angle change and the base move with the sound as we sailed.
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Old 07-09-2013, 19:51   #3
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Re: Floating Bulkheads

Floating bulkheads are bulkheads which are not structural.
Some production builders mould slots in the hull into which the bulkheads are inserted and then the deck/cabin top is put on with similar bulkhead slots.

IMHO this is probably OK for daysailers in protected waters but not a type of construction sufficient for offshore passage making.
A friend of mine went offshore in a boat built like this (a well known Euro production boat).
Going to weather in 30knots, the boat launched itself off a wave and came down hard, a bulkhead came out of its slot due to hull flexing and in the process tore out the outlet from the water tank">fresh water tank and filled the bilges with fresh water!
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Old 09-09-2013, 07:54   #4
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Re: Floating Bulkheads

Albro, would the floating bulkhead be glassed into the hull on port and starboard with the top and bottom "floating" in the channel? Or, is it completely unattached to the hull?
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Old 09-09-2013, 08:04   #5
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Re: Floating Bulkheads

The new method of construction for "value boats" does not include glassing the bulkheads to the hull, rather they build a pan that is glued to the hull and the bulkheads are then attached to the pan, some glassed in others glued in. Seems to work as long as the pan stays intact. It allows the builder to prefab the complete interior and saves a lot of cost.
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Old 09-09-2013, 08:15   #6
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Re: Floating Bulkheads

I think another discription/application for what might be called a 'floating" bulkhead is when installing a bulkhead one builds a foam strip/pad along the BH perimeter to set the BH onto. The edges of the pad are pre-beveled and all is glassed as usual. It provides a cushion/soft contact point for the BH so as it won't imprint through the hull.
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Old 09-09-2013, 08:21   #7
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Re: Floating Bulkheads

Quote:
Originally Posted by robert sailor View Post
The new method of construction for "value boats" does not include glassing the bulkheads to the hull, rather they build a pan that is glued to the hull and the bulkheads are then attached to the pan, some glassed in others glued in. Seems to work as long as the pan stays intact. It allows the builder to prefab the complete interior and saves a lot of cost.
This would not be 'floating' then.

The method you describe is not reserved to what you refer to as "value boats".

I have seen this employed in expensive racers. Not sure which one it was but (maybe only) I think it was the newest VOR boat.

All boats are built to a value point. All methods, if employed correctly, are good and create a strong structure.

Problems arrive when builders cut corners or when a naive owner takes their paper boat and requires her to do things for which she was not created.

Till today I was not aware there were any floating bulkheads. Any indication of designs that have them?

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Old 09-09-2013, 09:08   #8
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Re: Floating Bulkheads

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Originally Posted by barnakiel View Post
This would not be 'floating' then.

The method you describe is not reserved to what you refer to as "value boats".

I have seen this employed in expensive racers. Not sure which one it was but (maybe only) I think it was the newest VOR boat.

All boats are built to a value point. All methods, if employed correctly, are good and create a strong structure.

Problems arrive when builders cut corners or when a naive owner takes their paper boat and requires her to do things for which she was not created.

Till today I was not aware there were any floating bulkheads. Any indication of designs that have them?

b.

Barnakiel, there are three boats that have a "floating bulkhead" according to the forums I have read: O'Day 27, Endeavour 37 and Ericson 35. However, as I research this topic, I have found that some boats tab in the bulkheads to the port/starboard hull and that the top of the bulkhead floats in a channel and the bottom allows a tolerance of 1'2" to 1" with foam cushioning to enable the hull to flex without creating a hard spot on the hull. Not being a boat builder, I would like to know if this method is acceptable for an "offshore" boat or if it is the method used by the production builders to save time and money?
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Old 09-09-2013, 10:05   #9
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Re: Floating Bulkheads

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Originally Posted by rognvald View Post
Barnakiel, there are three boats that have a "floating bulkhead" according to the forums I have read: O'Day 27, Endeavour 37 and Ericson 35. However, as I research this topic, I have found that some boats tab in the bulkheads to the port/starboard hull and that the top of the bulkhead floats in a channel and the bottom allows a tolerance of 1'2" to 1" with foam cushioning to enable the hull to flex without creating a hard spot on the hull. Not being a boat builder, I would like to know if this method is acceptable for an "offshore" boat or if it is the method used by the production builders to save time and money?
All hulls flex to be sure, however this is not considered a desirable trait and the design of a boat should be such to make the boat as stiff as possible. I would be interested to know which boats have a deck to bulkhead joint designed with foam to minimize hard spots and accommodate 1/2" to 1" of movement.

Regarding the type of construction you are referring to, it is seen in many productions boats and can be acceptable to take offshore, the caveat being that the bulkheads are not fastened with screws but are instead through-bolted. If you are considering a boat with this detail the change to through-bolts is pretty simple enough to DIY.
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Old 09-09-2013, 10:27   #10
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Re: Floating Bulkheads

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Originally Posted by rognvald View Post
Not being a boat builder, I would like to know if this method is acceptable for an "offshore" boat or if it is the method used by the production builders to save time and money?
It is both. Done correctly, with proper engineering of the hull, there is absolutely no reason why a boat with floating bulkheads cannot be just as offshore-worthy (whatever that means) as any other boat. At the same time, though, it is a way that builders are able to save time and money.
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Old 09-09-2013, 10:44   #11
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Re: Floating Bulkheads

Let's face it, It's a sign of cheap "lego" construction. You can take anything offshore, but it doesnt mean you should. JMHO.
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Old 09-09-2013, 10:54   #12
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Re: Floating Bulkheads

I will give you my two cents worth on the subject. My Catalina 30 has what you are calling a floating bulkhead.
What I do not like about them is that shroud forces are run thru them, the wood bulkheads. In other words the bulkhead acts as the connection between the shroud fitting on the deck and the hull.
The bulkheads over time can become weak at the connections (bolting thru areas on the lower end becoming soft or rotting due to wetness).
This year I am going to add aluminum straps 1/8" think and about 2 " wide from the shroud fittings below the deck to the area were the bulkheads bolt to the hull. Then there will be no reason to worry about the wood. I plan to do this to the two main shrouds and the two each forward and rear should lines.
I just think the shrouds need to be better anchored to the hull of a boat.
Remember, this is just my two cents worth here.
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Old 09-09-2013, 13:11   #13
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Re: Floating Bulkheads

" would be interested to know which boats have a deck to bulkhead joint designed with foam to minimize hard spots and accommodate 1/2" to 1" of movement." Delancey



Delancey, take a look at this forum discussion. There are some interesting comments here.


EricsonYachts.org: The Starting Point on Ericson Yachts! ... Maintenance & MechanicalJun 20, 2012 - 10 posts - ‎4 authors
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Old 09-09-2013, 14:17   #14
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Re: Floating Bulkheads

Quote:
Originally Posted by rognvald View Post
" would be interested to know which boats have a deck to bulkhead joint designed with foam to minimize hard spots and accommodate 1/2" to 1" of movement." Delancey



Delancey, take a look at this forum discussion. There are some interesting comments here.


EricsonYachts.org: The Starting Point on Ericson Yachts! › ... › Maintenance & MechanicalJun 20, 2012 - 10 posts - ‎4 authors
I read the thread. Sounds to me like the use of the foam is as a backer rod similar to the kind you would use to caulk a deep crack. To be clear we are talking about the type of construction where a groove is molded into the pan or headliner to recieve the bulkhead which on turn is installed with most commonly screws?

I didn't see anything in the thread to support the notion that the system is intended to accommodate movement except from one individual's opinion, only that it accomodates a sloppy fit.

Movement tends to beget more movement which is generally not a good thing. It promotes wears on parts and results in cyclic loading which fatigues metal and fiberglass.

My boat features this "cheap construction" method but rigging loads are carried down into the floor grid via stainless rods, my bulkheads are only in compression so maybe a little different than the Ericson.

Regardless, as before the thing to do is remove the screws and replace with through-bolts through the bulkhead and the pan/headliner groove, problem solved. Use nylon locking nuts.

If you don't, you run the risk that the bulkheads will move in a seaway, the screws will get pushed back and forth and enlargen their holes enough that they will come lose and fall out, then you have a problem!

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Old 09-09-2013, 15:09   #15
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Re: Floating Bulkheads

Quote:
Originally Posted by rognvald View Post
Barnakiel, there are three boats that have a "floating bulkhead" according to the forums I have read: O'Day 27, Endeavour 37 and Ericson 35. However, as I research this topic, I have found that some boats tab in the bulkheads to the port/starboard hull and that the top of the bulkhead floats in a channel and the bottom allows a tolerance of 1'2" to 1" with foam cushioning to enable the hull to flex without creating a hard spot on the hull. Not being a boat builder, I would like to know if this method is acceptable for an "offshore" boat or if it is the method used by the production builders to save time and money?
I would be somewhat surprised if Endeavour 37 or Ericson 35 had solutions not designed for open waters.

The foam element is likely a spacer more than a cushion.

A foam spacer between the bulkhead and the hull is a standard method on plenty of boats I sailed (mostly Scandinavian boats from 1960-1980). Our boat has the same design. The bulkhead is tabbed to the inner side of the hull. No hard spots. And the foam was there to hold the bulkhead while tabbing.

I think they gave up on this attitude when foam filled topsides became a standard - the whole foam sandwich layer acts like a huge loads absorber.

All this boat building business is so amazing. I nearly went for it when I was a kid.

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