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Old 08 January 2006, 03:27   #1
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Country: Australia
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Boat name: bottomless pit
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Urethane expanding foam in RIB hulls

I've come across a couple of 3.6metre RIBS, moderate-V GRP hulls, and it appears they are prone to cracking in the 'slap-zone', within a few inches of the keel.
The most likely cause seems to be excessive flexion in this area, and I propose to use urethane pour-in expanding foam (closed-cell/bouyancy) to fill the void between hull and floor, thus stiffening the hull...

Incidently, we had to remove part of the floor to repair one of them (moved on a trailer and the roller punched a hole through said thin hull....) and found a curious 'cofferdam' - like structure,- with an aperture its full length and around 6" either side of centre. - The area in which the stress-cracks appear.
This sealed area is about 1 metre long, and 18" wide, and is glued onto the inner hull all round as well as the underside of the floor, totally sealing it from the outside world, and indeed the rest of the (empty) hull, which has a conventional bung at the back

These hulls are from South Aftrica and purchased as a single job-lot.
Apart from this minor glitch, they ride/handle well and provide much entertainment with a mere 25HP

Any ideas or advice etc would be MOST welcome !

Cheers, - 'Mature' land-lubber from Perth, West Oz
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Old 09 January 2006, 02:15   #2
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You'd be better off stiffening the area properly, the foam would add some reilience but would degrade over time as it is not in itself load bearing.

Can you post some PICs
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Old 09 January 2006, 05:58   #3
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I had an old Atlantic 21 which someone had filled the hull with foam and it caused more trouble than it was worth as over the time with hull flexing the foam must have come away from parts of the hull and when it did spring a leak to say it was difficult to get the water out again was an understatement :-(

Mark
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Old 12 January 2006, 07:52   #4
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Do It Right....

Rogue, I tend to agree..would prefer to do the job properly..and sleep well at night!
Mark, - Had started to think about that too...and did'nt particularly want to...
cheers,.
Newrib crabsnake@hotmail.com
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Old 12 January 2006, 08:20   #5
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Our lads in my boat angling club have had to cut the under floor foam out of a number of fast fishing boats in the past where the foam has become sodden and the boats would not get up onto the plane due to the extra weight. A local rib kept on a mooring had the same problem when the performance deteriorated markedly over a season. All sorts of local theories what was wrong with it, but it was underfloor foam which was soaking up water and it was a b****r to get out. Do the job properly and put some real strength in there.
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Old 12 January 2006, 08:33   #6
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I was interested in th picture to see if you could make the entry aperture into a hatch after stiffening
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Old 15 January 2006, 21:29   #7
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Some Pics

Here's a few pics, should be self-explanatory...
First pic is an overview, the bown gunk on the st'brd deck is just that, gunge from rainand dust etc, -but it illustrates the angle of outer hull. The green central 'thing' is the "bait box" - whatever.


Second pic is said 'bait box' hacked out, to reveal the inner hull surface (too thin in my humble opinion) and the unusual 'cofferdam' within, glued to hull and under-deck.

THIS is the area that the 'stress-cracks' appeared, running fore 'n aft. I propose to simply add a couple of layers of woven glass over the whole aperture.


Third is close-up of the front end of this structure...

Last pic, well, at least the seat is comfortable, ride smooth and the steering effortless. Shows hull-shape and deep chines.
The console is an add-on, most likely intended for a saddle-type seat, but I reckon a swivel-chair would make it a wonderful fishing platform!
Attached Images
File Type: psd Original deck.psd (150.2 KB, 107 views)
File Type: psd Bair bor cut.psd (152.8 KB, 73 views)
File Type: psd Front dam close up.psd (154.2 KB, 62 views)
File Type: psd Something miss ng.psd (126.6 KB, 64 views)
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Old 15 January 2006, 22:15   #8
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Country: Australia
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Expanded foam

Here's some pics of the foam, the mixture covered the bottom of the box to around half an inch (1 cm) and took about 3 minutes to reach this size.
Attached Images
File Type: psd Foam ID.psd (120.7 KB, 74 views)
File Type: psd Expanded foam.psd (153.3 KB, 69 views)
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Old 15 January 2006, 23:00   #9
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Try and post them as JPG - not everyone has photoshop!!!
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Old 16 January 2006, 11:58   #10
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Wot? - No Photoshop?

Here we go again....
For some reason, this place will NOT accept a JPG from me... - calls them 'invalid files'....

Feel free to email me on crabsnake@hotmail.com and I'd be happy to send the 'real' ones !
Attached Thumbnails
Click image for larger version

Name:	Something miss ng.png
Views:	126
Size:	107.6 KB
ID:	17027   Click image for larger version

Name:	From stern to stem.png
Views:	112
Size:	99.7 KB
ID:	17028  
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