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Sail powered Inca's Balsa Log Raft

Essence = Synopsis = Summary


The result of the Guara research


The hull of every sail-powered vessel (inclusive a Guara raft) has to be designed with high lateral hydraulic resistance - and low forward ditto.

The pointing of a Guara-raft is defined only by the positions of CE in relation to CLR.
CLR is the hold in water of the underwater-hull - and on a Guara-raft you can place your hold in water where you need it, moving CLR around on the raft by plunging in and lifting up Guaras.
CE as the wind-center is strictly bound to the canvas.

By setting sail and plunge down some Guaras you adjust your CLR, and you can point the raft all the compass around - because the wind will blow CE leeward of CLR.
Result: if the sail is adjusted for the pointing, the raft will sail.

That means, that where a ruddersystem need a helmsman as continously control and correct the course, a guara-system doesn't have this need.
It is a great self-steering system, where the raft herself act as a very stable wind vane making autocorrection in relation to the wind.
The crew could be ocupied by other - as go fishing for their next meal.

Whatever you have of rigging, the task of a sail is to divide the force of wind in a lateral and a forward force.
The lateral force is up against the high lateral resistance of the underwater-hull, and the result is the leeway - as hopefully is low, exactly because the lateral resistance should be high.

That is the forward force as push the vessel ahead, and the vessel will accelerate until the forward resistance of hull match the thrust from sail.
The relation between forward hydraulic resistance and hull speed is rather complex, and is normally defined empirically by hydraulic tank tests, as did the Norwegians.
Of course the same hydraulic rules are valid too for the leeway - and with same complexity.

The forward headway as together with the lateral leeway define the true course of the craft.

Sailing ahead, the bow is pressed into the sea, and in that way side-sliding of fore-end is restricted. More forward speed = more restriction.
When sailing with wind abeam the skippers on sail crafts are talking 'weather helm', even if the is their aft-end as slide sideways with wind.
Sailing ahead Skipper probably don't need any Guara in bow, and he can therefore lift up his front Guaras, as only brake heading.

- or more scientific we could say:
Sailing on, the water press onto lee bow is influencing on the position of CLR, as move ahead, but fortunately it is followed by the CE as too move ahead, due to the sails are sheeted out. Playing together so, the sailing will only need minor adjustments of guaras - or angeling of rudder.
The pointing of a Guara-raft in sailing situation is still defined by the actual positions of CE and the CLR - as CE still blow leeward of CLR.

Any trim on any sail-powered vessel (on rudder-steered crafts as well as rudder-less sailers) is fundamentally done by adjustments on CE or CLR - or both.
Logically it must be so, because wind and water are the only external elements, as yield forces on a sailing vessel - and they attack of course in their own centers.

Summary:
Use your Guaras to place your CLR where you want it,
and the wind will blow the Centre of Wind CE leeward of this Center of Water Resistance CLR
- and if your sail is adjusted for this pointing, you are sailing -

post scriptum:

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If you are in doubt, how wind and sea work with their CE and CLR - then ask a wind-surfer.

He has no rudder other than a fin (Guara) aft -
moving around and balancing CE and CLR is what he use for surfing -
and the rules for his wind board are the same as for your sail vessel.

 

Greetings from Lima in South America, where nearly no sail craft is present on all our Pacific coast -

klaus lynge

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Lima - August 2018