Tongue and groove has lots of problems apart from the distortion you mentioned. Normally only 19mm which is probably enough for old truck use, though a tractor might have too much concentrated weight. If you break a board it is a huge job to replace, so much so it would usually result in the tongue being cut of the neighbouring board to drop the new one on rather than unpinning the whole deck. Of course you need to get it in hardwood not pine.
Swishys shiplap is an excellent idea. Both Shiplap and T&G are subject to the edges being broken so you can finish up with gutters across the tray where the whole top of the groove or lap had to be pulled off when it was cracked and started sticking up. Probably not applicable to collector use but rocks are sure to do it a mischief.
The main problem is the boards are not nailed down to bearers like a house deck and just float across the trailer chassis only pinned at the ends by the dress timber under the coaming. If you are doing a flush deck the dress timber goes under the board ends on the coaming and you need equal size bearers along the trailer chassis to support the centre.
I think Kwila/Merbau might be a great timber looks beautiful but it is very heavy and you might be searching to get it in bigger boards without mortgaging the house to pay for it. It is very strong and weather resistant but you might have a fit of conscience about destroying the world's rain forests to get it.
Some very true info there Lang.
We used 32mm t&g tasy oak for squash courts and strong/heavy players would put a foot through those boards. They probably went back to 28-30mm after sanding but still a bloody heavy bit of wood.
As you said, only way to replace is to rip the groove out and drop your replacement in as per ship lap.
Ply on my semi didn't weather well. The actual ply layer is quite thin and typically not a terrific timber so steelwork would rip chunks out of it easily. I painted it with paving paint hoping to make it last longer, sure made it slippery, bad plan.
Have Merbau on my verandas, wouldn't go that way again. Was cheaper than Aus hardwood but it splinters dreadfully when weathered.
I have never heard of Merbau splintering and have had it on my decks for 20 years. Unfortunately Merbau is not a particular tree but a family of related species of which Kwila (from PNG is one), I am sure there is a lot of timber claimed to be Merbau which is not.
When I had my marine construction business we had to have any timber for government jobs certified as to species. The saw millers could not tell us because like fish trees have different names in different areas eg red gum and blue gum are the same in some places. We had to send samples to the forestry laboratories and those blokes, although they were pretty certain from experience, had to put it under high magnification to count the number of "pores" per square inch along with various distinctive features.
The chances of 100% identification of timber from PNG or Indonesia being correct are about zero.
Here are a few fun facts about Merbau timber decking that you may not know.
Merbau timber is imported from Southeast Asia. The species Intsia bijuga grows naturally in much of the Pacific Rim region, particularly the Philippines, Indonesia, Malaysia, the Pacific Islands and Papua New Guinea.
Merbau is a hardwood. Literally. It is one of the hardest and most durable timber species available. It is so tough and durable that special machinery — and a lot of saw blades — are needed to harvest, process and manufacture the timber.
Merbau is so tough even termites hate it and want nothing to do with it whatsoever.
The secret to Merbau timbers strength, durability and good looks is the abundance of natural oils within the wood. This natural oil also protects the timber from shrinking, cracking and splitting.
Those old oily timbers wear well.
I once converted an old Huskinson prawn trawler into a cruiser and found the decks made of tallow wood was a great long wearing timber. This old boats decks went on to be sanded and varnished as the main cabin soul where you could still see the drum winch marks embedded into the surfaces. Bloody hard wearing and oily as.
Problem was cutting it, as it blunted down every saw blade and drill bit.
The boats frames were spotted gum (no shakes) and the carvel planking was 1 1/4 in NZ Kauri. Copper sheathed below the waterline.
No wonder it lasted so well.
In order that the labour of centuries past may not be in vain during the centuries to come... D. Did
I think you ll get a shock at timber prices........Last floor I did ,the 6x1 1/2"rough boards were left loose/ish,and only secured at the edges by the coaming ,with a piece of hardwood wedged into the steel along the edge and screwed and secure nutted.....Even scrap steel didnt break the boards ,if a bit of care was used...I think it was spotted gum from memory ,dressed along the edges only....Small wheel forklifts are very destructive on steel trays,solid tyres the worst.