In this post, Manfred (one of our readers) shares an old MULTIHULL INTERNATIONAL magazine article with us – as a follow up to comments/info he shared on a smalltrimarans post here: http://smalltrimaran.co.uk/12-tanzanian-ngalawa-style-outrigger-canoe/
Manfred writes…
“Maybe you are interested in the old design of Eric J. Manners. I´ve found some stuff after a long search in my older Laps.
There was an article in MULTIHULL INTERNATIONAL with some pictures and long time ago I bought two plans of Mr. Manners.
And .. I had a discussion with Brian Durrans, an anthropologist of the British Museum about the ngalawa boats and think I´ll find the letters again.
Kind regards, Manfred”
Many thanks for sharing this info-from-the-archives with us Manfred!
The article and drawings are contained in the following images…
I have once done this using a windsurfboard and 2 waterskis as amas. There are some disadvantages of this configuration. Most important one is the not so good “close reaching” sailing speeds. Secondly the weight of the amas is always there, also when not needed at low windspeeds. Is this then a stupid idea? No, it is not if you want to have a safe fast beam reaching sailing vessel.
Thanks Manfred for sending this along, it’s a very interesting historical document of a design approach that seems mostly forgotten.
The extreme straightness of the amas with little to no curve or rocker really stands out and seems to reinforce the idea that these were being treated more as foils than hulls or a hybrid compromise of the two. It makes me wonder how much of the trend away from this style was the result of other foils outperforming it, and how much was because of resistance to adapting to sailing foil equipped boats in general and/or judging the design as something it really wasn’t.
FWIW that is an ongoing issue in a couple of respects: there’s some dispute about the hydrodynamics of the ngalawa outriggers where some people see them as a perceptive but crude attempt at exploiting this kind of foil concept and others claim that any resemblance to a foil or ski is strictly coincidental and the shape was just a function of what was easy and available.
The other thing is that there’s a lot of assumptions made about shapes like skis and surfboards that tend to send experiments off on erroneous tangents, with the biggest one being that surfboards operate like a planing powerboat in a mostly flat orientation to the water surface. In fact they are displacement hulls and selectively weighting and unweighting them is used to induce a surfing state and develop thrust beyond that of sheer gravity as you slide down the wave face.
A perfectly flat attitude is rare; they may appear flat to the ground beneath the wave but are usually engaged in the wave surface at an angle and only go very flat when transitioning from one rail to the other being engaged (turning) or when you want to slow them down.
This design is interesting in that unlike many attempts to adapt surfboards or ski-like shapes as amas it orients them more vertically, at angles more like a surfboard to a wave face.
I’m of the opinion that this kind of shape can be optimized to transfer some of the natural weighting/unweighting of a multihulled sailboat in a seaway to also develop thrust beyond just the propulsion of a sail or motor, as well as harness and recover some of the energy that goes into wave making to assist forward momentum.
Some power tris do this by placing the amas where they will naturally be surfing on the main hull’s wake, perpetually submerged enough that they are always trying to pop out of that wake like any hollow vessel held underwater…because of the shape and location of those vessels, that thrust energy can only go forward.
The important part in this context is that this is all based on buoyancy and displacement hull principles, not foils or strictly planing. For all the foil/ski like appearance of the traditional ngalawas I’ve never seen one where the amas appear to be planing or creating much obvious hydrodynamic lift…
that is often used to support the idea that there’s little technical reasoning or physics behind their layout and shape, but I suspect that that may be based on starting from a false premise where pure hydrodynamic lift is seen as the only valid reason for that kind of shape.