Building 44' wooden tri with traditional planking

Hi everyone
I am thinking to build a 44 feet wooden trimaran (20-44-20) out of wood with traditional planking method mainly used in Indonesia. High density wood for keel, frames and stiffeners while softer one like cedar or teak for the planking and bulkheads etc etc.
The pre-calculated weight of the yacht comes out to be more or less 10-12 tonnes and I feel comfortable with it because I can't afford money for the plywood (also due to non availability here) or aluminum.
I plan to keep the following wood thickness for my tri
Keel = 6" by 6 (main hull)
Frames and stiffeners = 2" by 2"
Wood Planks thickness =2"
For all( the bottom, floor, deck, side amas , bulkheads etc)
Keel for side amas is kept 4" by 4" for the length of 15'.

The few main questions are,
»»»will it be ok to build such vessel according to the standard of fishing vessels with outriggers?? In my case, amas are in place of outriggers and the main hull is narrower,too.
»»»Is that boat ok to perform on speeds like 25 knots? (Deep V hulls)
Or I have to add more frames or stiffeners or other wood scantling or increase thickness?
I think we lack trimaran plans. However of anyone does have, please share in this size.

I request you all to provide useful information. Any helping material/ suggestions/ link is highly appreciated.
Thanks and regards

 

You need to get a proper set of plans to get the speed you envision. The structure is a global system and it doesn't make sense to look at an individual part in isolation.

 

Welcome to the Forum Muz.

Coincidentally OldMulti has posted this evening about power trimarans - did you see his post here?
Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-114#post-905497
(Or were you the person who was asking him about them?)

Some questions re your trimaran :

Will you be building it in Pakistan, using the boatbuilding methods employed in Indonesia?

Do you have any preliminary drawings or sketches that you can post here to show your thoughts so far?

Re the '20 -44 - 20' mentioned above, I presume that 20 refers to the lengths of the amas / outriggers?

Why do you specifically want to build a trimaran?

What will you be using the vessel for? It sounds like it will be a pleasure boat (rather than commercial) as you mention 'yacht'.

You mention a planking thickness of 2" (50 mm) everywhere - this sounds excessive to me.
Would it be feasible to use strip planking, with much thinner planks and epoxy rather than 'conventional' planked construction?
You might be surprised by the cost of all the timber that you will have to buy for this boat.
I presume that it is possible to buy basic fibreglass boat building materials in Pakistan, even if plywood is unobtainable? Good marine plywood
seems to be rather scarce almost everywhere now.

Have you seen any existing designs that appeal to you? If so, and if plans are available, it would be well worthwhile investing in a set of plans. The cost will be a tiny fraction of the overall build cost, and you will have a guarantee that the design will work, so long as you follow the plans assiduously.

 

Without knowing what the intended duty of the boat is here, just about anything said could be irrelevant, but 25 knots is very ambitious for any 44 foot boat that will be affordable to run.

 

What do they say, you can realistically have any 2 of the 3, speed, comfort, and operating economy, but not 3 from 3.

 

50mm of teak = 32.5kg/m2
3mm of steel = 23.5kg/m2
You must of course add the framework for both, but I would say steel wins.

 

Thanks a lot. I will explain your questions one by one
1. I will be building in Pakistan and luckily we have good quality hard and soft wood, abundantly found here. The reason to mention Indonesian industry is, they have documented their standards while Pakistan has not done it (bad luck). I have visited ship breaking and wooden boat building industry here but they totally operate on the experience of the builders. There are no calculations and standards to follow.
2. I have countless to show, but here is one that can sufficiently describe the main areas of plan and study. I have been doing paper work and research for almost one year about all the materials and their feasibilties for different boat types.
Q#3,4,5. Yes, 20-40-20 refers to length of amas-main hull-amas. And their respective beams are 4'-8-4'.
In fact, the confusion arose due to the non-availibility of narrow trimarans standards anywhere to my knowledge. So I implied the Indonesian wooden boat building standards which are designed for wooden yachts with outriggers, not amas in fact.
The purpose also varied here, those standards are for slower yachts, mainly for fishing, sailing or motor yachts with wider beams. That is the main confusion because I want a trimaran with narrower hull and faster speed. Main purpose is diesel engine propulsion but for get-home facility, chinese hunk (kites) sails are also in consideration.
So, definitely this is a pleasure craft but it has to be able to cover longer distances with good speed. Economy is put on second priority.
6)- Epoxy coated plywood is not available here.
I know fibreglass material is available in Pakistan but that is much more expensive to consider. You know we have to build a mold, then the costly material alone can be used, If we consider to sandwitch wood into fivreglass, that too will be a time taking as well as expensive piece of work for me. I am finalising my decision to build with planking after a detailed research.
7)- I am sharing a link of 60' trimaran. plans available in USA which could be plywood construction. These plans are obviously out of my reach. O have done some basic changes in size (reduced) to the plans and altered the option of plywood/aluminum into traditional wood planking.
60' Power Trimaran PENNYWISE http://www.kastenmarine.com/PowerTrimaran.htm
That is the least costly material availabe here.
In the last, I want to know, if I intend to increase engine hp and speed, will the built boat be able to handle the forces of pressure? Or should I increase the stiffness? Thanks

 

I believe deep v hulls in a trimaran can exceed their hull speed greatly

 

It seems I have to consider a maximum speet of 14-15 knots!

 

Muzammal. The following web site does not give you exactly what you want but provides a lot of boat plans and information about eg 23 foot to 40 foot boats whose main hulls could be used for a power trimaran. There are a variety materials used from wood to plywood to aluminum. These designs are aimed at countries who do not have easy access to the latest materials. Look at FOA designs at web site: Boat plans https://coastfish.spc.int/en/publications/posters/boat-plans

Also I have an old plan book which has timber planked designs. A 40 foot "Gundred" sailboat plan that has 30 mm thick planking on 52 x 52 mm frames at 400 mm centerlines. The next design is "Neap-tide" is a 39 foot power cruiser that has 37 x 60 mm frames (yellow pine) at 400 mm c/l with 30 mm yellow pine planking. The power boat is designed for 10 to 12 knot speeds. I may be able to scan a few pages from the book if they could be of use

 

You have to keep the basics in mind. In order to exceed displacement speed the L:B ratio at the waterline must be at least 8,5:1, or be a planing boat. There is also the option of a semi-displacement hull if you limit speed.

You should define the building technology, since that is your main limitation. Skin thickness and frame scantlings differ widely between the different wood construction techniques. Traditional indonesian techniques join the planks edgewise with wooden dowels, wich mandates a specific minimum hull thickness, regardless of what is actually required. For a boat like yours this can result in the situation that steel construction is lighter. It also matters if your builders actually know how to build that way, since it is not an easy method.

Go to the library and ask for a copy of the Lloyds rules printed before 1960, that will have scantling rules for different wooden construction methods. There are several options for you, double diagonal, batten seam, etc. You choose one your builders can do, and follow the scantling rules for planing powerboats. More modern analytical methods are not really suited, because you need to design around the wood and the fasteners (traditional wooden boats are strength limited because of this), and while it's possible, it makes no sense.

 

I’m still trying to get my head around teak being cheaper than plywood !

 

No, its not cheaper actually. But non availibility means importing!! That makes it much more expensive.
And second thing, I am considering local woods having same proven qualities like teak or somewhat less hard thatn oak. Their local names are shisham, kikar( hard woods), also, cedar, larch and other moderately soft woods are present locally in abundance at reasonable prices.

 

Thank you so much it was much helpful data provided in the given link. Those plans need little alterations in order to convert into completely timber based building in my chosen size and style.
I am looking forward to that old book's pics and I am very much hopeful that after reading those, all my headaches will be greatly reduced.
Again, thanks alot lot more!

 

Building a ssteel boat with 8' beam is totally out of question in my view because even 6 gauge(4mm) steel will be too heavy to build and I will need to get training for welding and operating machinary, etc etc. Amateurs in EU use steel, but they do so oftenly for monohulls or cats. Trimaran of this size is not feasible to be built with steel in my view.