Mahoggany deck in Indonesia - size and fitting

Hi all,
I'm building a 25m (80ft) wooden Pinisi (7 sail schooner) in South Sulawesi, Indonesia. At the widest her beam is 6.1 meters.

Her hull has been constructed according to traditional (300 yr old methods) of ironwood.

I'm now at the stage where I have to think about the deck.

I know teak is most commonly used I won't be using it but will be using Mahogany - for reasons of cost and availability of 'quality' timber. And we've had some mahogany test samples sitting out in the hot sun (30-32 degree high humidity direct equatorial sunlight!) and I do like the warm red tone it is drying into.

I have already had about 50 un-sawn plantation grown logs delivered - some up to 5m in length.

A sub-deck of 2.5cm Mahogany was laid 4-5 months ago from timber cut last January (so drying nicely) and fiberglassed it a couple of weeks ago (it is monsoon here).

So the questions I have are:

1. What thickness should I have the timber cut to? We're thinking 2.5cm
2. What plank width should I be looking for?
3. Should I go for (what they call here) 'Tongue & Groove' which isn't true T&G but an " L " - worked nicely on the sub-deck.
4. What method should I use to fix the deck to the sub deck screws or screw-less (epoxy or silicone or whatever)

..... er.... yes, I know I'm opening a whole can of worms (teak vs mahogany & screws vs screw less etc) but here's the thing........ I'm not in Europe or the USA, but literally building on a beach a 5-hour rough road drive from the nearest major supply stores for even the basics (ie screws) - so proprietary EU or US brands are impossible to find so if anyone has recommendations it would be useful to have both the brand &/or generic name / method of application so I can try sourcing in the region.

If anyone IS in Indonesia/SE Asia and has product/brand/ supply sources to recommend I'd love to hear.

Thanks

www.RajaNagaLaut.com (website up late Jan)

 

Can you get Sika products there?

 

Yes but at hideous cost and long supply chain - though it might be a consideration, since I won't actually be laying the deck for about 4 months.

My main issue this or next week is plank thickness & width

I'm in discussion now with the sawmill about having the timber quarter cut - something they've never done before, so I have a couple of videos on my phone to show them & I'll have to supervise every cut !

I have a few videos of the early stage of the lroject, last year, a lot of progress since then though:
https://www.youtube.com/channel/UC1MCjO5iQ60VkNPt33CD3OQ?spfreload=10

 

hello shoggard, On the beach in Indonesia? Got monkey's? Can I come help? The sup deck should be sealed somehow, epoxy and glass would do well but if the sub deck widths are wide your going to have some movement there so epoxy and glass may not work so well. Can you add a layer of plywood over the sub deck? Then that would need a coating of epoxy and glass. It needs to be water tight if you plan on using an overlay deck. Maybe over there you could find some sort of thin rubber sheets to use between the sup deck and finish deck or maybe heavy canvas treated with soft oil based roofing tar stuff. Traditional decks have no sup decks, they are layed and fastened to the deck beams and are always quite thick to allow for cotton caulking and seam filler. Can you put down a thicker decking? The thinnest I would go is 1-1/4 or so. the width shouldn't be too wide,say 3"+- you want to keep the swelling and shrinking down to a minimum to keep it tight. (no water dripping on your bunk!) Mahogany doesn't have the water resistance that teak does so it should be oiled often which will also help keep down the movement. Quarter sawn is definitely the way to go, also less movement and the best wear resistance. And screws should be the first choice for fasteners or maybe galvanized spikes. How big are your deck beams? Okay, I hope this helps you........................peace....g

 

Have any rubber tress down there. Cut them like you would for sap , drip in bucket . Boil the sap till thick and pasteurized . Use that as the sealant. Canvas or EDM roofing rubber underlayment. Might want to use dowel pins instead if screws or nails, just use them on main beams deck supports.

 

@GDavis: sorry, for some reason, no monkeys - plenty of goats, chickens & baby chicks milling around the boat (I'll attach some pics)
You're welcome to come if you can get to Makassar - this is Joseph Conrad country (not Heart of Darkness, more like Almyer's Folly... kind of what I sometimes think I'm in right now!!!)
To business:

She has:
- Beams: 12cm Candole (a very strong hardwood - like ironwood)
- Spaced about 70cm apart
- Sub deck: 2cm X 14cm ( 0.72" x 5 1/5".... for us old imperialists) mahogany, dried for about 8 months before going down
- + Epoxy fiberglass layer (monsoon now so we know it definitely isn't leaking)

Unless there are any other suggestions I think I'll go with 3cm X 14 (about 1 1/4 x 5 1/5") but 3cm seems to me to be a bit on the heavy side.


@ Mikeemc: Yes they do have some rubber trees - I'll send one of the guys out to scout the villages & see if anyone will sell sap
Dowels sound interesting.... the basic hull planking structure is built first & held together with dowels when they're happy with the shape only then do they fit the ribs - an interesting backwards way of going about it, but I suppose it's because the ironwood is very rigid

 

That's some boat ): if you can get sap , try to get some good canvas and impregnate the rubber solution in to it for waterproofing, my want to add funguside to the batch.

 

Hi, thanks ... we've already fiber-glassed the sub deck and it is already waterproof (or did you mean canvas and rubber sap between the planks?)
The main question for the moment is cutting the mahogany:

- what thickness & width? gDavis suggests 1-1/4 x 3" anyone got a 2nd opinion?
- should I go for tongue & groove?

 

hello sh, are you gluing down the finish deck? If you are then it can be thinner 5/8 or so then the seams will need polysulfide or the like. If the finish deck will be caulked traditional then it should be 11/4 or more. You should still bed it with something like roofing tar or some sort of sticky goo to try and keep water from sitting between the two layers. What do they use for a seam filling compound is it lime mixed with some natural fiber? Tongue and groove is very hard to make watertight but since your sup deck is already tight maybe it's not really a big concern. Again if its an overlay deck it doesn't have to be as thick and 3/4 - 1" would be pretty rugged. The pegs would work well. Are you using wedged pegs(treenails-trunnels) or stepped? The widths should be kept narrow to keep the swelling down to a minimum.3"- 4" Are you laying the deck parallel to center line or bending it in to match the curve of the hull? If its going on to the curve you'll have to see what size will make the bend. Maybe these answers will help but there are many variations here and i'm trying to also think about the way they have built boats, those ways are still good even though they may not seem familiar to us or meet some kind of western standard.(b.s.) The way of putting the planking together first was and still is (hopefuly) done in many parts of the world. The Vikings even built them that way!............................peace....g

 

A common plank dimension for a boat your size would be 50mm x 18mm. Framing..perimeters are 90mm x18

Clear stock, tight grain, quarter sawn.

18mm gives 16mm on the finished deck after sanding.

You can adhere the planks to the subdeck with any suitable structural adhesive that is used in the construction industry.

How will you develope clamping pressure when you install the deck ? Fastenings should be avoided ....these deck piercings aways supply a water path that contaminatesthe subdeck.
If you must use fasteners...remove the fasteners after bonding, epoxy fill the screw hole then wood plug it.

Compound for calking the seams ? I only use the correct stuff because of its abilty to resist UV degredation. There could be other products available for the construction industy that may be suitable . UV resistance is critical.

Regaurdless of the adhesive compoud you use for seams ou should educate yourself on its correct use. The bond breaker tape and primer to promote adhesion. https://usa.sika.com/dms/getdocumen...76-98a4-259312ac7964/ipd-marine-teak-deck.pdf


screen shot on windows

 

Heading for the mill Monday

Thanks guys.... I'll take my logs to the mill on Monday.
I'll go with 20mm thick, 70mm width - not out of contraryness, but because the sawmill here isn't particularly accurate & I'll let stack and allow the timber 3+ months or so to dry & shrink and then we can plane it more accurately on site.
I've attached a couple more pics:
Our teak stack: 14cm wide x 2cm thick... drying nicely

One of my carpenters, Nawir, yes that's an 'adze' he's using to hack away an odd piece of ironwood that was riding proud of the sub-deck - it is so hard that it couldn't be cut with a saw... he managed an acceptably flat surface that just needed sanding


BTW: I'm going to have similar questions about good sail cloth... with 2 masts and 7 sails looks like I'll need about 200 meters x 1.5 meter wide!
Of course western sailcloth isn't available here, so I'm hunting alternatives If anyone has some good ideas - canvas being the most immediate & obvious thought - but how thick? I'll probably post a separate thread

 

I envy you. Not just the boat but the adventure.

Here is another take on rubber tree sap http://en.wikipedia.org/wiki/Gutta-percha.

What about floating the boat and towing it, or add some auxiliary power to get to the nearest port where logistics is less of a problem.

Dino

 

actually she's got a 250hp Mistubishi V8 engine .... being installed at the moment.

But it is 'waving season' - height of monsoon and the seas are high so she ain't goin nowhere till that's over, March/April, so we're beached (quite literally) anyway I'm happy enough to keep her there it makes fitting out easier

 

UPDATE: We just launched our FB page... so anyone who is interested can view progress: https://www.facebook.com/Raja-Naga-Laut-475653062594414/timeline/