As I may have mentioned on here before I am extending an existing 2/3 beam width partial bulkhead just in front of the rudder of my North Shore 38 so that it spans the whole width of the boat to guard against rudder post or skeg damage flooding the boat. What thickness and grade of ply do you think I should use and also what weight of woven cloth to tab to the hull and are multiple layers of tabbing necessary? Presumably I should also mix up some epoxy glue/filler to glue them in place before tabbing them to spread the load and give additional strength as of course the ply shaping won't absolutely perfectly match the hull contour. I have already made up the cardboard templates. Thanks in advance for your thoughts.
This review includes the below text
www.boatsales.com.au/editorial/details/northshore-38-used-boat-review-8764/
The interior moulds and bulkheads are attached to the hull using eight-ounce cloth. All plywood is marine grade or structural 'A'.
For ply thickness would use the same or close to the thickness of the main bulkhead for the intended load case. Would expect this to be in the range 20-25mm.
There are many web links on partial bonding of bulkheads to hulls but Bluewater use full bonding which is what you need for this bulkhead.
www.bwcy.com.au/methods.htm
Would suggest 20mm Bruynzeel marine ply, epoxy biaxial 4oz glass on each face and seal all the edges with epoxy before bonding in with glue strength epoxy. Then make the radiused fillets (say 25mm radius) each side of the t butt joint on the hull and deckhead with medium density epoxy filler, sand fair and put 8oz glass biax tape strips over these fillets. Obviously secure the edge to the existing partial bulkhead in a suitable manner, including stiffeners or doublers as may be needed.
Select to expand quoter13 said..
This review includes the below text
www.boatsales.com.au/editorial/details/northshore-38-used-boat-review-8764/
The interior moulds and bulkheads are attached to the hull using eight-ounce cloth. All plywood is marine grade or structural 'A'.
For ply thickness would use the same or close to the thickness of the main bulkhead for the intended load case. Would expect this to be in the range 20-25mm.
There are many web links on partial bonding of bulkheads to hulls but Bluewater use full bonding which is what you need for this bulkhead.
www.bwcy.com.au/methods.htm
Would suggest 20mm Bruynzeel marine ply, epoxy biaxial 4oz glass on each face and seal all the edges with epoxy before bonding in with glue strength epoxy. Then make the radiused fillets (say 25mm radius) each side of the t butt joint on the hull and deckhead with medium density epoxy filler, sand fair and put 8oz glass biax tape strips over these fillets. Obviously secure the edge to the existing partial bulkhead in a suitable manner, including stiffeners or doublers as may be needed.
That's great thank you very much. Just what I was looking for :-)
Select to expand quotewoko said..
Google, joggle stick or tick stick, 
Very interesting but a little bit late for me. I just used trial and error with cardboard and radial cuts to create fingers that I bent where they met the hull and then cut off. It's quite a small bulkhead and quite tricky/convoluted where it extends up into the coaming and fibreglass toe rail recesses. Not to mention doing all this while you are bent double in the lazarette :-(
Select to expand quotejulesmoto said..lydia said..
Why use plywood?
As opposed to?
Laminate panel , sea board, pvc or airex then glassed
all easier to work and no rot issues
Cool project Julesmoto.
As Lydia mentioned, laminate panels are nuts strong and light to boot.
Here's a Aus panel with appropriate load/sizing and cost for reference (19mm). You could do better/cheaper, this is just a quick google search.
Styromax Styrofloor
My floorboards were a good example of laminate panels, a single person could carry all of them. The boat was all open cell foam, so that speaks for strength.
I've always wanted to try vacuum bagging for those little things you dream up from time to time. My wife would probably have something to say about converting a garage into a glass production line though 
.
Select to expand quotelydia said..julesmoto said..lydia said..
Why use plywood?
As opposed to?
Laminate panel , sea board, pvc or airex then glassed
all easier to work and no rot issues
Thanks
Select to expand quoteshaggybaxter said..
Cool project Julesmoto.
As Lydia mentioned, laminate panels are nuts strong and light to boot.
Here's a Aus panel with appropriate load/sizing and cost for reference (19mm). You could do better/cheaper, this is just a quick google search.
Styromax Styrofloor
My floorboards were a good example of laminate panels, a single person could carry all of them. The boat was all open cell foam, so that speaks for strength.
I've always wanted to try vacuum bagging for those little things you dream up from time to time. My wife would probably have something to say about converting a garage into a glass production line though .
Thank you
Select to expand quoteshaggybaxter said..
Styromax Styrofloor
.
Where, as in real brick-and-mortar shop or store, can you buy this stuff, or similar? Does similar include Therma-Lite? Google says I can only order an 8' x 4' board on-line (as above) for $$$$. Google also insists, unhelpfully, on directing me to the Big Green Hammerbarn/Shed, even though that particular retail chain does not list it in its stock.
What if I just want to take a look and maybe beg/borrow/buy a small swatch to take home to play with? Somewhere in Brisbane would be good. My best guess would be a trailer manufacturer or repair shop, but who and where?
Select to expand quotelydia said..
Bunnings sell HDPE panel
Search Seaboard
But will epoxy or polyester bond to hdpe as good as they do to wood. One of the benifits of hdpe is that it's hard to get stuff to stick to it
Select to expand quoteAchernar said..shaggybaxter said..
Styromax Styrofloor
.
Where, as in real brick-and-mortar shop or store, can you buy this stuff, or similar? Does similar include Therma-Lite? Google says I can only order an 8' x 4' board on-line (as above) for $$$$. Google also insists, unhelpfully, on directing me to the Big Green Hammerbarn/Shed, even though that particular retail chain does not list it in its stock.
What if I just want to take a look and maybe beg/borrow/buy a small swatch to take home to play with? Somewhere in Brisbane would be good. My best guess would be a trailer manufacturer or repair shop, but who and where?
Hi Ach,
You could try these guys?
atlcomposites.com.au/category/9/Divinycell-Foam
They look like a Gold Coast outfit, might be worth a phone call?
I know I have pieces left I brought home from a factory visit lying around in the garage somewhere, but it would be open cell foam for vacuum bagging) not closed cell. Difference is it has tiny little holes every cm for the epox to draw through. I'll try and dig it up for you if its any help?
Cheers,
SB
Select to expand quoteJolene said..lydia said..
Bunnings sell HDPE panel
Search Seaboard
But will epoxy or polyester bond to hdpe as good as they do to wood. One of the benifits of hdpe is that it's hard to get stuff to stick to it
Accept that but the proprietary brands are much better and it is not a structural bulkhead and is a wet area with poor ventilation.
Otherwise there are places like ATL which do laminate panel.
Select to expand quotelydia said..Jolene said..lydia said..
Bunnings sell HDPE panel
Search Seaboard
But will epoxy or polyester bond to hdpe as good as they do to wood. One of the benifits of hdpe is that it's hard to get stuff to stick to it
Accept that but the proprietary brands are much better and it is not a structural bulkhead and is a wet area with poor ventilation.
Otherwise there are places like ATL which do laminate panel.
Fair point that it's not a structural bulkhead
Unless I am missing something it is a structural bulkhead - equivalent to a bow collision bulkhead but at the stern.
www.cruisersforum.com/forums/f47/crash-bulkheads-on-production-boats-227151.html
HDPE is only able to be glued with Permabond which is expensive.
www.rowetrading.com.au/how-to-bond-materials-to-ldpe-hdpe-polyethylene/
Select to expand quoter13 said..
Unless I am missing something it is a structural bulkhead - equivalent to a bow collision bulkhead but at the stern.
www.cruisersforum.com/forums/f47/crash-bulkheads-on-production-boats-227151.html
HDPE is only able to be glued with Permabond which is expensive.
www.rowetrading.com.au/how-to-bond-materials-to-ldpe-hdpe-polyethylene/
All respect it is not there now so can't be too structural as in integral to the structure of the boat
Select to expand quoter13 said..
Unless I am missing something it is a structural bulkhead - equivalent to a bow collision bulkhead but at the stern.
www.cruisersforum.com/forums/f47/crash-bulkheads-on-production-boats-227151.html
HDPE is only able to be glued with Permabond which is expensive.
www.rowetrading.com.au/how-to-bond-materials-to-ldpe-hdpe-polyethylene/
You can actually glue HDPE with sikaflex and similar products provided you pass a blue tipped flame over the HDPE where you want to glue it.
That said, there are a lot of products available and already mentioned that I would use before using HDPE. (It's heavy too).
mate, there is no guarantee that if the rudder breaks and takes the back with it that the crack will stop at your bulkhead. If your yacht does not already have the bulk head designed like that, it's very unlikely that will function as you want it to
Select to expand quotelydia said..r13 said..
Unless I am missing something it is a structural bulkhead - equivalent to a bow collision bulkhead but at the stern.
www.cruisersforum.com/forums/f47/crash-bulkheads-on-production-boats-227151.html
HDPE is only able to be glued with Permabond which is expensive.
www.rowetrading.com.au/how-to-bond-materials-to-ldpe-hdpe-polyethylene/
All respect it is not there now so can't be too structural as in integral to the structure of the boat
Ok, understand that concept, likewise all respect. The original post included the text "guard against" which infers 100% security - but would suggest the plan was not expecting this but was based on doing something reasonable and proactive which would slow down the potential aftermaths of rudder system damage. That is, to not create a bulkhead which would be the same as one which was integrally designed into the hull structure and installed during the original build, but a fully sealed bulkhead nevertheless which would at least do something.
Certainly agree that rudder system damage and propagation would depend on the event.
Thanks Osco re the hdpe gluing tip.
Just be careful using epoxy in confined spaces.
When I built a similar bulkhead in my Bluebird, I had a small pot of resin in my hand, head down in the quarter berth, when it started to get hot. Very quickly it got hotter, and I only had time to wriggle backwards out of the berth and into the cabin, when it burst into flames. Threw it overboard, but boy, that was close. If it had started to burn when I was in the confined space, I could well have died.
Select to expand quoteYara said..
Just be careful using epoxy in confined spaces.
When I built a similar bulkhead in my Bluebird, I had a small pot of resin in my hand, head down in the quarter berth, when it started to get hot. Very quickly it got hotter, and I only had time to wriggle backwards out of the berth and into the cabin, when it burst into flames. Threw it overboard, but boy, that was close. If it had started to burn when I was in the confined space, I could well have died.
Thank you very much yes I will only mix up a small amount at a time and being winter I bought the slow hardener
Ok so I am pretty much done with the templates which took me forever to make so if anyone with an NS 38 wants them send me a message please. They are made from 3 mil melamine coated MDF and are the second iteration after the cardboard Originals
Gday. I love ply for this. It won't rot if it is epoxied and you don't drill holes in it willy nilly. The thickest piece of ply on my 38ft cat is 12mm. I would not go thicker than that for a bulkhead with only hydrstatic loads. But 440 gr double bias tape. It is different stuff from biaxial which is 0,90 and tabbing should only be done with +-45. Cut the ply so there is a small gap between the bullhead and the hull. Fill with thickened epoxy (use silica Powder). Then smush bulkhead on and cove, 25mm radius is on large side but okay. Clean up really well and when set, sand and then wet out double bias tape (at least 100 mm wide with epoxy resin. Make small batches but warm resin to help it penetrate fabric. Roll three coats of epoxy resin over rest of bulkhead and never worry about bulkhead or rot ever. Cheers Phil
Select to expand quoteKankama said..
Gday. I love ply for this. It won't rot if it is epoxied and you don't drill holes in it willy nilly. The thickest piece of ply on my 38ft cat is 12mm. I would not go thicker than that for a bulkhead with only hydrstatic loads. But 440 gr double bias tape. It is different stuff from biaxial which is 0,90 and tabbing should only be done with +-45. Cut the ply so there is a small gap between the bullhead and the hull. Fill with thickened epoxy (use silica Powder). Then smush bulkhead on and cove, 25mm radius is on large side but okay. Clean up really well and when set, sand and then wet out double bias tape (at least 100 mm wide with epoxy resin. Make small batches but warm resin to help it penetrate fabric. Roll three coats of epoxy resin over rest of bulkhead and never worry about bulkhead or rot ever. Cheers Phil
Thanks Phil,
Where do you get the tape?
I use Trojan at Cardiff. Their 5 to 1 epoxy is similar to West 105 which is the standard. They have rolls of db tape, get the 150wide, and about 5 litre epoxy packs. That should be enough. Also get a dozen dispoable brushes and a small pack of silica, glue powder, Not microspheres. Although some microspheres in the glue mix makes it stand up better. Cheers Phil
Select to expand quoteKankama said..
I use Trojan at Cardiff. Their 5 to 1 epoxy is similar to West 105 which is the standard. They have rolls of db tape, get the 150wide, and about 5 litre epoxy packs. That should be enough. Also get a dozen dispoable brushes and a small pack of silica, glue powder, Not microspheres. Although some microspheres in the glue mix makes it stand up better. Cheers Phil
Thanks :)
