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Old 20-01-2014, 04:33   #31
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Re: Kelsall Method

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Originally Posted by beiland View Post
...and definitely not balsa core,...
how come not balsa core?
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Old 20-01-2014, 08:46   #32
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Re: Dudley Dix 470, 550

The only advantage balsa has over foam is perhaps cost, period, but the rot issues associated with balsa can not be ignored. When you are buying a used boat you really don't have much choice as most production boats are balsa cored, at least in the decks but when building your own boat you do and there is no reason other than perhaps cost to choose balsa over foam. I think the only arguments I have ever seen on this viewpoint come from boat owners who own a balsa cored boat or those amature boat builders who have built their own using balsa and feel a need to justify their choice. Very few professionals who have built or repaired in both mediums would choose balsa for their own build.

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Old 20-01-2014, 16:16   #33
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Re: Dudley Dix 470, 550

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The only advantage balsa has over foam is perhaps cost, period, but the rot issues associated with balsa can not be ignored. When you are buying a used boat you really don't have much choice as most production boats are balsa cored, at least in the decks but when building your own boat you do and there is no reason other than perhaps cost to choose balsa over foam. I think the only arguments I have ever seen on this viewpoint come from boat owners who own a balsa cored boat or those amature boat builders who have built their own using balsa and feel a need to justify their choice. Very few professionals who have built or repaired in both mediums would choose balsa for their own build.

Steve.
I'm boatless at the moment so I have no dog in this fight so to speak, but the subject interests me. I've been told by several people I would regard as experts that the above is not true at all and instead has become a bit of myth based on some poor balsa efforts in the past, but I'm keen to hear from people who actually have data to share on this rather than just the "its bad" brigade. Its said that over 70% of all cats produced every year are balsa cored (lagoon, leopard and others) and modern balsa builds have had very little problems in the last 10-15 years or so. Balsa cores result in a much stronger / stiffer structure. I've been told a lo of the major race boats (monos and multis) now use balsa for high stress areas and honeycomb elsewhere....ie no foam. The cost diff I hear is not that much anymore either so its interesting the majority of builders (by volume) have stuck with balsa rather than move to foams. Keep in mind the production balsa builders are using ester resins as well, epoxy over balsa would be even better, especially with the individual square end grain cut balsa (like duflex) which can not spread moisture past each little square and is very easy to repair. Balsa, I'm told, only rots if is over 30% moisture and has ready access to oxygen, I think if you had damage and the both the above symptoms and still left it to rot then ones maintenance standards would probably result in problems no matter what the core....

Is there someone here who actually knows about this stuff that would care to comment?
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Old 20-01-2014, 17:14   #34
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Balsa Core

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I'm boatless at the moment so I have no dog in this fight so to speak, but the subject interests me.
If you are really interested in learning of this subject then I would suggest that you use the 'search button' of several of the various boating forums and look up 'balsa' or 'balsa core'.

You will find lots of such discussions of this subject right on this forum. You will find boat yard managers that report the repairs that they have seen in numerous situations.
Here is just one discussion on this forum:
Are Cats Made from Duflex Panel Kits Strong ?


If you go over to the Trawler forums you will find MANY trawlers that were produced in Asia that have had to have their balsa cored decks redone.
Trawler Forum

Here is but one discussion of many that turns up on Boatdesign.net:
Choosing a deck core - Boat Design Forums


The basic problems are that you very often never really get a perfect bond at the skins and the core, and that eventually this leads to water migrating along this 'seam. And secondly many folks end up adding equips/structures onto their decks, and the improper or failing bedding of these pieces allows water into the core structure. The third basic problem is the 'impact resistance' that a balsa core structure lacks that can lead to delamination with its skins.

Go do some reading, there is LOTS of discussions and testimony.
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Old 20-01-2014, 18:00   #35
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Re: Dudley Dix 470, 550

Thanks Brian, I have already done a lot of reading on the subject (on forums etc) and the problem with the search button is it most often returns a truckload of conjecture and very little in the way of hard facts/numbers. Up to date facts/numbers I mean, not for cases dating back to the 70' and 80's or for bad techniques when installing deck equipment or folks pointing at particularly dodgy yards using dodgy materials, which the same can be said re issues with (in fact a larger proportion by % of total units produced per annum) some foam construction projects. I'll keep looking though!
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Old 20-01-2014, 18:24   #36
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Re: Dudley Dix 470, 550

Foam core and epoxy would be the only way to go for a multihull these days. Anything less is just settling or bargain shopping. You don't want to be doing either when you embark on a project this scale. If you are Interested I would be happy to discuss making available the male plug and molds for the Maltese 52 design. It could help kick start the process... The completed and painted shell for the first cat took the good part of 11 months with weather delays. Fit out time all depends on systems and how light you want to keep her... Feel free to contact me through Maltese catamarans dot com.
Regardless, good luck on your venture and keep the momentum rolling.
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Old 20-01-2014, 19:01   #37
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Re: Dudley Dix 470, 550

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Thanks Brian, I have already done a lot of reading on the subject (on forums etc) and the problem with the search button is it most often returns a truckload of conjecture and very little in the way of hard facts/numbers. Up to date facts/numbers I mean,.....
I do understand what you are saying here. it does require a lot of reading between the lines. But over the years I've just seen and heard of too many problems with balsa cored vessels.

On the other hand I had rejected the use of polypropylene honeycomb products (Nidacore, etc) for years just based on the fact that 'nothing' likes to stick to this stuff.

But more recently as I took a more serious look at how the scrim layer (bond-to-layer) is THERMOFUSED to the ends of that PP honeycomb, ....and the fact that this PP plastic is TOTALLY rot proof,...and the manner in which impact loads are (are not) transferred through the sandwich cored structure,...and the fact that they now supply a PP honeycomb product that can be utilized with Kelsall's resin infusion method....
I've become convinced that this is a very good solution for many cored structures on boats, other than underwater portions. Here are the 'vertical cells' that the balsa guys claimed for so many years as preventing water migration thru their cores, yet here those cells are built of a totally waterproof and rot-proof plastic material.

...just saying
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Old 20-01-2014, 19:15   #38
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Re: Dudley Dix 470, 550

now that's very interesting...who makes it?
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Old 20-01-2014, 20:06   #39
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Re: Dudley Dix 470, 550

Im sorry, after 40 years of custom building and repairs including dozens of recoring jobs I guess I just dont have enough experience yet. There is nothing wrong with balsa from a structural standpoint, I dont think anyone will dispute that but it does not make for a stifffer panel than any other core, the biggest contributing factor in panel stiffness in a sandwich panel is core thickness. One thing ive learned over the years through actual experience is that water will migrate from block to block just fine and rot out huge areas from quite small penetrations even though the "experts" will claim otherwise.Now I agree that with the use of infusion the resin will fill all the gaps between the individual blocks and largely alleviate many of the rot issues as long as every other precaution is taken during the build and of course by owners adding or subtracting hardware, hell, ive seen substantial areas rotted out from the stupid little snaps from the canvas guy installing a dodger. Btw, I own 3 boats at present, 2 with balsa and 1 with foam. One of the balsa boats is totally dry, no issues at all,, the other has some small areas of moisture in the deck which I will deal with. The foam boat is an interesting case, the builders had screwed down teak slats in the cockpit sole and also on the sole in the head, the boat had sat with water over the sole for months before I bought it so of course the foam was wet, I cut out an access hole to install a transducer and in doing so the jigsaw was throwing water from the core in my face, the interesting thing is that over the course of a few months the foam dried out completely and there is zero decay or delamination, its as good as new, I know without a shadow of a doubt from years of experience that if that sole had been balsa it would be compost. The bottom line is well proven structurally and much more damage tolerant.

Steve.
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Old 20-01-2014, 21:48   #40
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PP Honeycomb

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now that's very interesting...who makes it?
Here is one manufacturer right here in the USA:
http://www.plascore.com/pdf/PP_Honeycomb.pdf

Nidacore was bought out by 3M so I imagine more expense by some fair amount.

Just for kicks here is a guy who build a whole boat out of PP honeycomb:
Building a cat with Polycore
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Old 20-01-2014, 22:04   #41
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Impact Resistance & Delamination

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Im sorry, after 40 years of custom building and repairs including dozens of recoring jobs I guess I just dont have enough experience yet. There is nothing wrong with balsa from a structural standpoint, I dont think anyone will dispute that but it does not make for a stifffer panel than any other core, ....
Steve.
Agree with just about all that you said, except for this portion concerning 'structural standpoint'.

Nigel Irens was once talking about some delamination problems the big French racing tris where experiencing. he spoke of some of the 'incompatibles' that came about between various hi-tech skins and various cores as being a problem to be aware of.

As I looked thru numerous discussions on this same sort of subject I became aware of some problems that can arise between the very strong balsa core and its skins. In many cases it can be advisable to use a somewhat 'compliant' core...a core that is 'tough' rather than just strong in compressive strength like balsa is. Then when the boat's hull/skin gets hit with a sudden impact, that force is not all transferred to the inner skin as well as the outer one. It can result in less delamination. Less delam means less structure damage,...and less chance of skin separation from the core,...thus less chance of water entering and traveling along the core-to-skin bondline.

I've mentioned this on several forum discussions, but I can not recall where specifically at this time.
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Old 21-01-2014, 07:50   #42
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Re: Impact Resistance & Delamination

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Agree with just about all that you said, except for this portion concerning 'structural standpoint'.

Nigel Irens was once talking about some delamination problems the big French racing tris where experiencing. he spoke of some of the 'incompatibles' that came about between various hi-tech skins and various cores as being a problem to be aware of.

As I looked thru numerous discussions on this same sort of subject I became aware of some problems that can arise between the very strong balsa core and its skins. In many cases it can be advisable to use a somewhat 'compliant' core...a core that is 'tough' rather than just strong in compressive strength like balsa is. Then when the boat's hull/skin gets hit with a sudden impact, that force is not all transferred to the inner skin as well as the outer one. It can result in less delamination. Less delam means less structure damage,...and less chance of skin separation from the core,...thus less chance of water entering and traveling along the core-to-skin bondline.

I've mentioned this on several forum discussions, but I can not recall where specifically at this time.
I actually totally agree with you on that, I used to and sometimes still club race and every year there are a few T bones so ive seen and repaired a lot of these impacts, most of them are balsa boats only because most production boats are built this way but a few years ago my son was the recipient of such an impact, his boat is a 24 ft uldb which I designed and built launched in 1987, it is H80 klegecell with 1 layer of DB120 each side and AME 4000 resin, the impact which was significant did not damage the inner skin and was not repaired until the following winter.

Steve.
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Old 21-01-2014, 16:10   #43
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Re: Dudley Dix 470, 550

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Originally Posted by beiland View Post
I do understand what you are saying here. it does require a lot of reading between the lines. But over the years I've just seen and heard of too many problems with balsa cored vessels.

On the other hand I had rejected the use of polypropylene honeycomb products (Nidacore, etc) for years just based on the fact that 'nothing' likes to stick to this stuff.

But more recently as I took a more serious look at how the scrim layer (bond-to-layer) is THERMOFUSED to the ends of that PP honeycomb, ....and the fact that this PP plastic is TOTALLY rot proof,...and the manner in which impact loads are (are not) transferred through the sandwich cored structure,...and the fact that they now supply a PP honeycomb product that can be utilized with Kelsall's resin infusion method....
I've become convinced that this is a very good solution for many cored structures on boats, other than underwater portions. Here are the 'vertical cells' that the balsa guys claimed for so many years as preventing water migration thru their cores, yet here those cells are built of a totally waterproof and rot-proof plastic material.

...just saying
I have played with a few samples of polycore, and while I think it is great for furniture etc, I would never use it for structure. Laminated polycore can have the laminations stripped off by just digging your nails under it. Impossible with duflex. The same thickness duflex is stiffer to bend and harder to snap in half. Also (apparently) thanks to the geometric shape of cells it does not want to bend fair either.

You encourage people to look at anecdotal evidence such as your unbelievable story where a poly core boat was dropped 5 stories by a crane for 2 days and did not break. Yet its also possible to find stories where someone has drilled a hole in to structure for wiring etc and had water pour out of the holes on a polycore boat.
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Old 22-01-2014, 09:31   #44
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Re: Dudley Dix 470, 550

Hoping to get this back on topic without offending anyone. Has anyone on this forum built the DIX 470 I would like to see some real numbers like cruse under power with your engine chose and what can be achieved under sail say in 10 and 15 kts. and what construction proses you used. Will she sail up and how see handles a big quarter stern sea. Can she be made to sail buy a two person crew with ease? Thanks!
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Old 25-01-2014, 14:14   #45
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Re: Dudley Dix 470, 550

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The only advantage balsa has over foam is perhaps cost, period, but the rot issues associated with balsa can not be ignored. When you are buying a used boat you really don't have much choice as most production boats are balsa cored, at least in the decks but when building your own boat you do and there is no reason other than perhaps cost to choose balsa over foam. I think the only arguments I have ever seen on this viewpoint come from boat owners who own a balsa cored boat or those amature boat builders who have built their own using balsa and feel a need to justify their choice. Very few professionals who have built or repaired in both mediums would choose balsa for their own build.

Steve.
Balsa has far higher compression strength, and far higher sheer strength. The skin to core bond is vastly better.
It's much easier to delaminate the glass from foam and polypropylene cores. To get similar panel stiffness you need thicker cores or heavier laminates.

I know professional boat builders who have chosen to use balsa cored Duflex for their own boat, based on their experience with the product.
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