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Old 24 May 2015, 16:45   #1
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Thundercat/ surfcat floorboards

More questions I'm afraid!
So, I've had a few hours this bank holiday to get to grips with the Ceasar Surfcat I bought a couple of weeks ago.
Engine is off, console is out and I've given the hull a good jetwash inside and out.
The trailer is in shocking condition, and was clearly of very poor design in the first place but I'm confident with welding.
Unfortunately a previous owner has had it on the collapsing, rusty trailer a few times by the looks of it and there are numerous repairs along where the parallel support parts of the trailer have chafed and rust stained the underside. What's the best glue for PVC and where do I get white repair fabric?
I've wrapped up the sharp bits of the trailer and got the completely stripped back boat back on it. Tomorrow I plan to tape up the engine bolt holes and fill the boat with a few inches of water and get underneath to check for leaks from the various repairs.

My main area of interest now is the floor. I've got it all out and jetwashed it and all the filthy hull underneath it (very satisfying job!). The floor is very, very heavy- clearly the ply wood is waterlogged. As a guestimate the three pieces of floor together weigh about half the weight of the rest of the hull/ transom. Turning the boat over etc was a real stuggle with the floor in, now I have taken it out I can do it with one hand.
The floor appears to be plywood sheathed in glass cloth and painted black. I guess it is the original floor as the zip bag bonded to the bow panel matches the stern sponson bags.
Unfortunately the previous owners had drilled a few holes in places to install various things but not sealed the wood. Because the boat has a filled in transom it's spent its life with the floorboards under rain water, although I'd imagine this would always be a problem unless you store the boat very nose up as the fabric floor seems to 'hammock' a bit of water when stored flat which will make these floorboards permanently wet.

So what are my floorboard options? I'm confident with simple wet layup techniques with polyester and epoxy resins. I'm sure the racers use carbon/ foam/ honeycomb panels but I'm hoping to find a more cost effective solution that I can do myself.
Do you need to use elite ply or do people get away with cheaper wood but fully sheathed, especially at the edges?
I guess my cheapest option is exterior ply with a sheathing of polyester/ glass fibre?
I guess people may already know with hard won experience what plywood, how many layers of reinforcement and of what weight of cloth.

Does anyone know the releative weight figures for different floors? I'll weigh mine tomorrow and see how it compares. I'm not really bothered about super stiffness, although it needs to be OK. (I'm never going to be racing it). My concern is weight as I'm hopinmg to hand launch it.
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Old 25 May 2015, 04:38   #2
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I replaced the floor of my thundercat last year, the original was the same as yours but was fairly waterlogged. The new one is a composite material (don't know exactly what it is) was custom made for me by a friend. It's much stronger, only a wee bit lighter. Make sure you cut the new ones a tiny bit wider and longer to make them a tight fit as the hull will have stretched over time.
Most folk just cut replacements from marine ply and cover them in rubber. Have a look on here - Thundercat Inflatables Forum I'm sure it's come up before.
The guys in america use honeycomb floors for flatwater racing but they couldn't stand up to racing in the surf. Carbon floors are available from the manufacturers like Ceasar and Aquarius but they really are expensive...

for repairs we use polymarine glue, like this - PVC Adhesive, 2 Part, 250ML Polymarine inflatable boat repair glue | eBay

rubber for repairs you can get most places, it doesn't have to be the same thickness as the original (Think ceasar use 0.9mm PVC) - IBS Inflatable Boat PVC Fabric | Gael Force Marine
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Old 25 May 2015, 08:13   #3
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Originally Posted by Roflhat View Post
I replaced the floor of my thundercat last year, the original was the same as yours but was fairly waterlogged. The new one is a composite material (don't know exactly what it is) was custom made for me by a friend. It's much stronger, only a wee bit lighter. Make sure you cut the new ones a tiny bit wider and longer to make them a tight fit as the hull will have stretched over time.
Most folk just cut replacements from marine ply and cover them in rubber. Have a look on here - Thundercat Inflatables Forum I'm sure it's come up before.
The guys in america use honeycomb floors for flatwater racing but they couldn't stand up to racing in the surf. Carbon floors are available from the manufacturers like Ceasar and Aquarius but they really are expensive...

for repairs we use polymarine glue, like this - PVC Adhesive, 2 Part, 250ML Polymarine inflatable boat repair glue | eBay

rubber for repairs you can get most places, it doesn't have to be the same thickness as the original (Think ceasar use 0.9mm PVC) - IBS Inflatable Boat PVC Fabric | Gael Force Marine
Thanks roflhat, I read one one of these forums that you managed to replace the three floor pieces with two. That must help the weight and stiffness. Also fewer edges to allow water in.It's the way I'll probably go. I'm guessing you mean the back two as the front one is at a slightly different angle. It must be harder to get the floor in and out now, so did you have to change the dimensions or did you simply connect the two bits of floor together, draw round them and take the dimensions that way?
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Old 25 May 2015, 12:31   #4
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Yeh mine is now a 2-piece. The reasoning behind the 3-piece floor was so that the boat could be rolled up into a smaller area (there's a rule in racing which required the boat to be rolled up into certain dimensions.) The two floorboards now are the same length, but the boat tapers towards the bow. For the thundercat dimensions were enough, for a surfcat you'll probably want a template. If you're going for less boards take into account the thickness of the bit that joins them.
I never take the floor out of my boat, but thundercat (the brand) hulls are prone to the boards popping out when the tubes go a bit flat. I did consider going for a single piece floor, but this would require either removing the transom or nose cone, which would be a lot of work...
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Old 26 May 2015, 06:56   #5
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Originally Posted by Roflhat View Post
Yeh mine is now a 2-piece. The reasoning behind the 3-piece floor was so that the boat could be rolled up into a smaller area (there's a rule in racing which required the boat to be rolled up into certain dimensions.) The two floorboards now are the same length, but the boat tapers towards the bow. For the thundercat dimensions were enough, for a surfcat you'll probably want a template. If you're going for less boards take into account the thickness of the bit that joins them.
I never take the floor out of my boat, but thundercat (the brand) hulls are prone to the boards popping out when the tubes go a bit flat. I did consider going for a single piece floor, but this would require either removing the transom or nose cone, which would be a lot of work...
Im definitely going for a two piece floor then. I recently let the boat down to take the existing floor out, and I won't be rolling it up any time soon. the hijackers are very stiff and I fear if I ever tried to fold/ roll them they would prove quite brittle and possibly sustain damage, so best not mess with that.
Also as I have a jockey console across two sections of the existing floor it will sit much better on a single piece of floor. Being able to crank its bolts down hard will add considerable stiffness to the whole structure

I measure the exising floor at just over 14mm thick, so I'm going with decent quality 12 mm marine ply with a layer of biaxial glass and epoxy each side. I'm also going to add some longitudinal carbon stiffening (unidirectional tape) top and bottom from the transom, under the lines of stress down either line of bolt holes either side of the console. I also know now where all holes etc will be so will add epoxy/ high density filler inserts for all screw/ bolt holes. The front section of the floor I will layup a bit lighter- just sealed 12mm plywood as it appears to only really serve to push the rear sections back into the transom- very rarely will anyone be standing on it. I'll finish the whole lot with kiwigrip.

I have also already added a drain plug to the bottom of the fabric floor at what looks to be the low point (about 14 inches forward of the transom). This is so that when the boat is in storage the new floorboard is not swimming in rainwater most of the time- which is what killed the last ones.

Now, back onto my fabric outer floor. I jacked the boat us and got underneath with a few inches of water covering the whole floor- the result was a bit like standing in a shower. Thanks for the link Rolfhat. I betray my money saving obsessions here, but, that fabric looks awfully expensive for what it probably is. I apreciate the glue is very specific and i won't be skimping on that. However, the floor of my boat looks exactly like the bog standard PVC sold as trailer sides/ advertising banner/ boat cover PVC of which I have lots in stock. If i was repairing the tubes that would be a different matter but the floor is a comfort item not essential for the safety of the boat.

Has anybody tried repairing boats with this much cheaper pvc?

The issue with my boat is the trailer chafe damage and future protection, so my repair patches ideally will be two 6 inch wide but very long strips almost the whole length of the boat, which would prove expensive with the 'marine markup'. There are multiple old repairs under there, in odd shapes and multiple colours, but they are all along these two straight lines. Much better I think to clean all of these off, sand back, and apply new, neat looking symetrical patches/ future wear strips. In fact, if I can get away with cheaper PVC I could consider covering the whole floor underneath and a few patches on the inside (which will be hidden by my new floor. The result should look like chafe protection rather than damage repairs.
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Old 26 May 2015, 08:21   #6
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Sounds like a good plan, very well thought out. The material covering the boards doesn't neccessarily have to be rubber I wouldn't think, just waterpoof and relatively hard wearing. Might even be worth getting an old rubber dinghy just to use the rubber for the boards, wouldn't matter if it was hypalon or PVC.
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