Newbie platform boat build

Hi,

I am looking at building my first solo effort and for a number of reasons, have decided on a platform/pontoon boat.

I have been a sailor and motor-boater since I was a kid, so around 45 years of experience. I have also spent a lot of time working on boats, maintenance, repair, etc. so I have a good appreciation of techniques for joining stuff together.

I live on Borneo and we have some immense rivers here, with jungle and all sorts of wildlife that you just can't get to without a boat. The rivers are easy and slow - some of them 500km long! I live in a rural area and there are river access points as close as a couple of miles. I could also truck the thing 20 miles and be in a massive delta with up to 50km of navigable river to explore.

Weather is predictable - it rains We don't have much in the way of wind or storms, just heat, sun, rain and lots of lightning.

The issues I have are:

Not much of a boat-building industry - despite it being a river-based transport system for getting around (once you are off highway one, there is little in the way of interior roads!) most boats fall into two categories - massive (40-60M) river buses that do 40-50 knots, fishing/taxi boats which are all solid wood and made by the people living in the water villages. Passed down from father to son

As a result, marine ply is non-existent, marine-grade fittings and finishings are also rare, little in the way of fiberglass or composites, no foam, etc., etc.

But... we have a lot of hardwood-based ply at reasonable prices, and Maranti/Phillippine mahogany timber cheap as you like.

I also have a 4x4 CNC router... so making repetitive or complex-shaped things isn't really hard.

Which has led me to the following:

If I am going to build anything, it either has to be solid timber or construction/exterior grade ply. I can't glass it over. Cruising speed isn't an issue, so build it bigger for more displacement/safety. I am better with straight lines than compound curves. I am on a budget.

I am looking at 24' x 8' - using standard 4x8 sheets of ply (we don't get the 10' ones), have a curved-up bow, have a gradual cut-away the last third of the pontoon to the stern, to give a bit of nose-up. (sorry if I don't have the correct terminology... I am coming to grips with chines, etc.), have a torsion-box upper deck/shade - lighter than 3/4 ply with much more strength, and something I am used to making. No sides, no cabin - it's hot enough as it is! Enough ply to stabilise the top deck (sun deck/viewing platform) which will give some water/wind protection.

I took as inspiration Popular Mechanics platform boat - I know it's a few years old now, but the principles seem sound:

My questions are:

Crazy? Feel free to tell me, I'm a big boy

What should I do with standard ply - seal the edges, prime and paint/poly varnish? Just do as much as I can to seal it up.

Epoxy or mastic/sealant for joints?

Without a good source of foam, I was thinking dozens and dozens of 2L soda bottles in a net bag would work as flotation aids. There is no shortage of those here!

 

It looks like you have a good grasp of the situation, and the idea seems quote sound. Soda bottles will work ok, if they are sealed well. Getting them sealed is often a problem.

Epoxy would be the better bet for sealing chines, but thats not the only thing that would work.

You need to research what paints and other paint systems are available for protecting and fastening the ply, to get an accurate costing, and let everyone know what they are.

Once you know what your options are, there are plenty of people who can advise on the best choices.

 

Great, thanks RW.

Glad to know it's not a totally ludicrous idea

Off to the hardware store, I think.

Do you know of a good Aussie mail-order boat supplies place?

 

What part of Asia are you in ? I don't think it would be good value to order from Australia.

 

ps

here is a simple boat plan that would suit your materials

http://www.bateau.com/proddetail.php?prod=GT27

 

have you thought about using like 55 galon drums?
not sure how many u would need guessing 4 or 6,
http://en.wikipedia.org/wiki/Drum_(container)

can be found faily cheap ( from what ive looked at, ask mechanics ect they use a fair bit )
attach a plywood deck to the top ( proably with some sort of frame to get it some strenght.

 

From my research, round pontoons handle and plane like a brick.

Sorry, not meaning to be rude - I could easily make a torsion-box deck and tie it to oil drums, but that kind of negates my desire to learn how to build boats.

As I said, I have a CNC router and can make complex shapes, repeatedly, to fine tolerances. I am planning a much bigger router - 6x10 - which will allow me to make even more complex and larger components - expanding my main work by a major leap. I am a reasonable designer and can draw in 3D CAD pretty efficiently and so was hoping to bring that all together to make a prototype and (eventually) work out a process for an easily-built boat (or boats) for the local and local expat market. The platform/party style boat fulfils a lot of needs for the expat community. Living in a Muslim country, we can get away with a lot - if it is out of sight

We have a fairly active yacht club, but the racing is rudimentary - mainly because there are only a couple of very small dinghy classes of around 10 boats. Having been active in small boat racing in the past, I know what it takes to make a reliable, fast, fun boat - I just haven't ever done it myself - only worked on hulls made by other people.

This will (hopefully) bring my skills back up to speed and also give me an idea of what areas the local market is deficient (and where I can finagle stuff - for example, I just found a boat builder that exports fibreglass hulls to Australia - but doesn't sell locally. I am seeing them next week about glass, resin, etc.).

 

Borneo. We get most of out stuff from Aussie. There are four container vessels a month into the port here.

 

Thanks - I did already look at that boat, and the rest of their range - cabins aren't that pleasant in 30C at 90% humidity

That's one of the reasons for a platform/pontoon boat.

 

Yes, that's true.

One of the virtues of the GT27 is that you can build the boat without the cabin. It will function as a bare hull.

Its a much more efficient shape than the old popular bmchanics box you were looking at.

 

Hmmm... I was really wanting a floating platform - for a number of reasons.

I would like a single-hull boat eventually, but not right now.

Having found a supplier for epoxy and glass tape, I am looking at a stitch-and-glue hull. Although I am shocked at the amount of glue Do they think I'm made of money???

According to the website, the G27 needs 30 gallons of epoxy. Even using US gallons (rather than real ones!), that is 115L.

So my wooden and sheet materials would run to a couple of hundred dollars, but my composites will end up around $5000-6500 - that's bizarre!

I am planning to get in the water, painted, sealed, all-up cost of under $1000.

 

I can get resin for about $12 per litre. I don't have current f'glass prices.

But for plywood, I would have to pay around $5,000.

I presume you aren't buying marine plywood.

All the more reason for protecting it against the elements - especially the tropics

 

oh :O im jelous of you having a CNC mill haha, and yeah thats also proably true

only thing i can think of is make some sort of well point on the front of some barrels,
we have a platform made from drums at a friends place, doesnt go far so never really took notice when moving it ( just goes out like 5 - 10m when using it )

 

Hello Zootalaws,

When I read your original post and especially the parts I quoted above it sounds like you might be interested in a Jeff Spira design.

http://www.spirainternational.com/

He does not have a flat bottom design however he specializes in boats designed to be built by first timers with no previous experience. He only uses construction grade lumber so no marine ply is not a problem. There is epoxy glue involved and while minimal fiberglass is recommended it is not absolutely needed. May help keep on budget. His plans are available in either Imperial or Metric.

Good luck on your future build.



In the interest of full disclosure I am in no way connected to him, just a satisfied customer.

 

We have Maranti hardwood ply - which is pretty much void-less (no knots), and with waterproof glue, is damned close to marine ply (or better than?).

I pay AU$20/sheet for 1/2", AU$30 for 3/4, which means my sheet goods will run me about $240. I still have to sort out resin and glass - but if you are getting it for $12/L, it bodes better than I thought (no taxes or import duties here, so things aren't ridiculously expensive - I can always catch a cheap flight to KL or Singapore and carry it home )

I have been buying ply for furniture and tend to buy only 4 or so sheets at a time - but with my new CNC setup, I'm tempted to buy a whole pallet, which will bring my price right down. It helps that I have a couple of mates that are high-up in admin/sales at the plywood factory in Bintulu - All I need is a truckie to give me a good price and I'm sure I can get my base price right down.