Bulkhead replacement

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Nick P
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Bulkhead replacement

Post by Nick P »

My plastic sea kayak (Aquaterra Sealion) is now over 20 years old. The foam bulkheads are now leaking substantially again - the problem is that sand eventually gets between bulkhead and hull, effectively wedging the gap open. Over the years I've removed, cleaned and refitted the bulkheads several times and to be honest, its a sod of a job, particularly the forward bulkhead 'coz theres no room to work. I also think the original bulkheads are now past it - too damaged, pitted and dirty to be worth refitting. So, I think the way ahead is to make new ones from PE foam (Knoydart sell 3" thick blocks).
Have any of you done this before on a plastic boat? (searched Almanac section but found nothing).
Given the problems of sealing the bu99ers to the hull, what about making them slightly oversized so that they can be forced into the taper of the kayak as a more physical seal? Naturally I'll finish off with Sikaflex as normal.
I'd welcome thoughts/ideas or alternative suggestions (I know - buy a composite boat!).
Cheers
Nick

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Re: Bulkhead replacement

Post by TechnoEngineer »

I had used the "Knoydart" foam as well as blocks of Plastazote in my Dagger Approach to make a bulkhead footrest (as well as other things).

The problem with making them oversize is that you have to get the shape absolutely spot on for it to seal - especially if you use the stuff from Knoydart, which is *very* stiff. You might have more success sealing if you use blocks made from Plastazote or Evazote, which are a bit more compressible. Perhaps make a wooden (marine grade plywood) bulkhead with a compressible foam rim.
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Re: Bulkhead replacement

Post by Ian_Montrose »

Just a random thought, but rather than buying solid foam blocks and cutting to size, would pourable 2-part polyurethane foam not work? Like this stuff: http://www.cfsnet.co.uk/acatalog/CFS_Ca ... m=merchant?

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Re: Bulkhead replacement

Post by TechnoEngineer »

I doubt it as a permanent solution, although it might be worth using to make templates with?
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Stuart Yendle
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Re: Bulkhead replacement

Post by Stuart Yendle »

You could take out the old bulkheads to use as a template for your new ones. Make them slightly bigger and see how they fit, afterall they dont have to go back in the exact same place. Then sand or file away any excess for a snug fit.

mick m
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Re: Bulkhead replacement

Post by mick m »

To get the balk heads to fit beter , if you router a groove about 40mm in from the edj on the face that goes into the taper thay fit beter , the groove dosent need to be deep, probably 1/3 thicnes of balkhed, and about 3mm wide.
Sikaflex probably isent a good selent for rotomold , over hear the manufacturers youse Sellies all clear , it works beter than most things iV TRIED

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Re: Bulkhead replacement

Post by CharlieS »

Hi Mick,
That sounds like a good idea but I don't quite get it. (And I'm hoping to do this job in the summer sometime.)
Where does the groove start and finish?
Do you mean a circular groove 40mm inside the edge of the bulkhead?
Or a line running from the edge into the middle?
Thank you,
Charlie

Nick P
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Re: Bulkhead replacement

Post by Nick P »

Thanks for the replies guys.

I can see the appear of pourable foam, but previous experience of seeing it used in boating applications - its basically like a sponge in the longer term - just absorbs water, gets very heavy and eventually crumbles. Not really a long term option.

Stuart has basically the same thoughts as me - to use the old bulkheads as templates for the new. Only problem is that the originals were never a very good fit to begin with! I have experience of fitting wooden bulkheads to wooden or GRP boats and am familiar with scribing and spiling techniques to get an exact fit. I just don't think I can physically get in to do that in the kayak!

Mick - I too had thought about putting a rebate in the centre of the bulkhead together with 'oilways' from the face of the bulkhead to fill the rebate - just not sure how well the sealant will flow. Does anyone know if there is an equivalent to Selleys All Clear in UK? I googled last night to no avail.

I think its just gonna be one of those slow, awkward jobs. Use the originals to make slightly oversize replacements, and gradually do some trimming/sanding to 'fit and fair' until they're the right size and shape. Can't say I'm really looking forward to it, but at the moment I'm having to keep airbags in the bow and stern compartments the leaks are so bad.

Regards
Nick

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Re: Bulkhead replacement

Post by TechnoEngineer »

If you assume that the plastic around the bulkhead is the same thickness all the way round, you can make an external template - I usually use cardboard to do that. Plus you will get an oversize shape!

I'd also reiterate that I recommend you use something other than Knoydart foam because it is too stiff.
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Re: Bulkhead replacement

Post by Hengle »

Have you asked Perception UK if they can supply you with new foam bulkheads as I am sure they will still have the templates the origionals came from just remember to specify that you have a origional sealion not a sealion fastnet.
Heng

Nick P
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Re: Bulkhead replacement

Post by Nick P »

Yes, I contacted Perception years ago. They could not supply bulkheads for mine, only the later Fastnet. As I understand, the Aquaterra brand was a US precursor to Perception.

Now trying to find a local supplier of Plastazote, Ethafoam, Evazote.
Cheers guys
Nick

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Re: Bulkhead replacement

Post by TechnoEngineer »

I'd say that Ethafoam isn't a particularly good material.

Plastazote and Evazote are both compressible, Evazote is better at springing back to shape after being compressed.

I've used LD40 grade Plastazote, and EV45 grade Evazote.
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Re: Bulkhead replacement

Post by mick m »

CharlieS wrote:Hi Mick,
That sounds like a good idea but I don't quite get it. (And I'm hoping to do this job in the summer sometime.)
Where does the groove start and finish?
Do you mean a circular groove 40mm inside the edge of the bulkhead?
Or a line running from the edge into the middle?
Thank you,
Charlie
Good morning, the groove needs to folow the shape of the balkhead ,about 40m in from the outside edge on the face of the balkhead not the edge that meets the boat ,on the side that will be the small diamiter IE towords the pointy end on the inside of the storage compartment, this lets the foam compress into the groove , so you dont have to shamfer the sides to get a good flat fit it onlu needs to be like a cut about 1/3 the thiknes of the BH and abour 4mm wide , if im still not making sence email me and il send you a drowing , this isent my idear , it belongs to Australis Canoes, the largest maker of roto kayaks and canoes in Australia

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Re: Bulkhead replacement

Post by CharlieS »

Hi Mick,
That's clear now. Thank you.
Charlie

Nick P
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Re: Bulkhead replacement

Post by Nick P »

Just thought I’d give an update on this.
I stripped the forward part of the boat of all through-bolted bits (Keepers footrests, deck fittings etc) removed all sealant and removed the forward bulkhead by pushing it aft. I’m not sure exactly what type of foam these original bulkheads are made of, but its pretty tough, incompressible stuff, about 3 inches thick. Anyway I gave it a good wash in warm soapy water, rinsed and left it to dry overnight. Turned out not to clean up too bad.
After considering the suggestions above, I decided to refit the original bulkhead, but with a modification. The basic idea was to use some more compressible foam (karrimat) as a gasket, so I cut a strip of karrimat 3 inches wide and glued it (2-part contact adhesive) completely around the foam bulkhead edges, thus increasing the overall radius of the bulkhead by 10mm. This, now much larger bulkhead was refitted by forcing it back into place (hammering, using a length of 4x2 as a drift) compressing the karrimat and forming a seal. I have not as yet put any sealant around the joint since I think the gasket will be good enough (for now!). I’m not sure what the long-term success of this method will be, but the lack of sealant to clean up, should make the job easier if I have to repeat it in the future.
Sorry I didn’t photograph all the stages, but heer are a few so you get the gist:

Bulkhead almost in position, ready to be hammered forward. Karrimat gasket clearly visible as the dark outline
Image

Boat braced against the wall ready for the bulkhead to be hammered home
Image

A couple of rather poor shots from the cockpit end
Image

Image

Forward face of the bulkhead viewed through the forward hatch. Uneven thickness of the karrimat shows the differential compression to fit the hull.
Image

I’ll let you know if this is successful or not.
Cheers
Nick

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MikeB
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Re: Bulkhead replacement

Post by MikeB »

Neat!

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