New bottom for 7m platey

[Cam-82]

Hi all,
About three months ago i bought a 7m plate alloy fishing boat that was supposed to have a 4mm bottom. I have recently found out that it is only 2mm. As the bottom is pretty trashed i have been thinking about replacing it with 6mm.
Any ideas about the best way to go about this would be greatly appreciated

Thanx,
Brendan

[Bonus]

Cam-82, A 7 metre plate boat would have 5 or 6 mm thick bottom depending on how it is braced and strengthened. It is very dificult to just replace the bottom because that is where all the work is. Give Jason Norup a ring at Offshore Marine Master - 0438778330.

[FNQCairns]

What???? you serious!!!!!!!!!!!!!!! a 7m plate boat - not pressed?? and it is 2mm thick! death trap comes to mind. Did you buy new. How do you know it is only 2mm, never heard the likes of it before.

cheers fnq

[Jackinthebox]

What turkey would build a 7 mtr platey with a 2mm bottom???????

That's a big, nasty job to replace the bottom sheets.

Good luck matey

[Cam-82]

I couldn't believe it myself when i seen it. It could have been a death trap 4 sure me and a couple of mates went out to have a go at some snapper at a mark about 40 kms out. We were about half way there when we noticed that we had alot of water coming in. Decided to head back and just made it. When we eventually pulled the boat out of the water we had to sit on the boat ramp for a half hour before the trailer could be moved. The weight of the water had it sitting down hard on the ramp. When i got home i cut a hole in the hull with a 25mm holesaw and noticed it was only 2mm.

[Cam-82]

fnq i bought the boat second hand

[peterbo3]

Cam,
I do not want to be a prophet of doom, but if that rig has a 2mm bottom, there could be all sorts of other shoddy work. Get that sucker checked out by a reputable alloy boatbuilder before you invest any more $$$.

[seatime]

Another option is to sandwich a 3-4mm bottom onto the existing one, it's been done before!
What's the internal framework like? was it built as a plate boat or a pressed boat? that'll determine how you can fix it.

[FNQCairns]

That's a nightmare, makes me feel better about my badly built boat...you know what I mean, Brendan what brand??

cheers fnq

[Cam-82]

There is nothing on the boat to say who built it i have a fair idea it is a home made special. From what i have seen the internal frame is all solid i have pulled all the floor and floatation out of it so i could have a good look. If it would help i could try to put some photos on here 4 you to look at.

Thank you all,
Brendan

[FNQCairns]

Yeah throw up a "do you know what type of boat this is" thread.

cheers fnq

[GAD]

Shite mate , I reckon u is lucky you got home by the sounds of it .
In an older post one of the blokes got a new bottom put on his boat , fairly old.

[Lovey80]

Thats amazing. At 2mm it's actually not a plate boat. I'm not Sheety but i thought anything under 3mm was sheet and over was plate.

Can't wait for the pics.

Cheers Chris

[whichway]

Hi

You might think about the welds. I would get some NDT done, maybe X ray to check weld penetration.

Whichway

[Getout]

Another option is to sandwich a 3-4mm bottom onto the existing one, it's been done before!
What's the internal framework like? was it built as a plate boat or a pressed boat? that'll determine how you can fix it.
Wouldn't corrosion be a big problem?

[seatime]

Wouldn't corrosion be a big problem?

7-8 years on and no corrosion evident. it's all sealed, a new hull in effect. why would you consider corrosion to be a big problem?

[gofishin]

7-8 years on and no corrosion evident. it's all sealed, a new hull in effect. why would you consider corrosion to be a big problem?

Gelsec, the new bottom sheet needs to be stitch welded 'x in every y' mm to every stringer and girt, hence the existing bottom sheet would end up looking like a fish net. In addition you now have a 2mm gap between the existing structure and the new bottom sheet. To me it sounds like a whole new can of worms.

In this case i would certainly not state that it can, or could, be 'totally sealed' with this method of refurbishment. Oxygen & salt laden moisture = corrosion. In an oxygen deprived process, as this would be between the sheets, the corrosion process would be accelerated.

More importantly, the question i would be asking is what 'other shortcuts' were taken when this boat was built?

Cam-82, photos 'all over' would be a help here, but I would seriously consider obtaining the advice from a professional ally boat builder, not just a guy that can weld ally!
cheers & good luck

[seatime]

Gelsec, the new bottom sheet needs to be stitch welded 'x in every y' mm to every stringer and girt, hence the existing bottom sheet would end up looking like a fish net. In addition you now have a 2mm gap between the existing structure and the new bottom sheet. To me it sounds like a whole new can of worms.

In this case i would certainly not state that it can, or could, be 'totally sealed' with this method of refurbishment. Oxygen & salt laden moisture = corrosion. In an oxygen deprived process, as this would be between the sheets, the corrosion process would be accelerated.

More importantly, the question i would be asking is what 'other shortcuts' were taken when this boat was built?

Cam-82, photos 'all over' would be a help here, but I would seriously consider obtaining the advice from a professional ally boat builder, not just a guy that can weld ally!
cheers & good luck

gofishin, good info thanks. I'm not a welder and don't want to be one either.
Ideally Cam should speak to a boat builder, if you're one why not offer him your advise. I suggested an option not advise. The boat I referred to was fixed with a new bottom sheet added over the top of the old, the details of how weren't my concern as it wasn't my boat. It worked and there isn't any corrosion.

[Getout]

My concern would be the cavity between the sheets becoming be a ticking timebomb.

[Cam-82]

Thank you for the help but does anyone know an ally boat builder that would talk about this to me as most seem to act like it is a black art.


Thanks again,
Brendan