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On the topic of foils, inside facing foils will cavitate earlier than outside facing foils because of the superposition of low pressure areas from the vertical and horizontal parts. This can be mitigated to some degree by increasing the transition radius between the horizontal and vertical parts.

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Finished the revamped 15.5 metre wing mast for Groucho. Could only obtain 4mm ply for the skin so took belt sander and reduced thickness by a mm or so ... to reduce weight by a ridiculous and minimal

The clew attachments on Frog are very basic, just a couple of lines around the thin section of the boom. There is enough slackness to allow enough push/pull movement between the two sails. Works okay.

New wing mast, new beam.

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7 hours ago, neuronz said:

On the topic of foils, inside facing foils will cavitate earlier than outside facing foils because of the superposition of low pressure areas from the vertical and horizontal parts. This can be mitigated to some degree by increasing the transition radius between the horizontal and vertical parts.

Can you explain? I do not understand how you come to that conclusion.

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2 hours ago, Laurent said:

Can you explain? I do not understand how you come to that conclusion.

Assuming a foil designed to produce both sideforce and vertical lift, it needs to have two parts. One part approximately vertical for the sideforce and the other one somewhat horizontal. For simplicity let's assume it is an L-shape.

With both parts creating lift they both have a low pressure area associated with them. The vertical part on the windward side and the horizontal part on the upper side towards the water surface. For an inward facing foil the horizontal part extends from the vertical part to windward. This means that the two low pressure areas meet at the intersection between both parts of the foil which creates an area of very low pressure where cavitation will start. This is why foils usually have a radius where the two parts transition into each other.

If you had the horizontal part attached on the outside you would superimpose a low and a high pressure area. This may decrease the efficiency of the foils, but it helps with avoiding cavitation in this area.

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Almost finished the after and larger section of the above water central pod. When I finish the forward central hull part, will be able to assemble the tri/catamaran. Which will be named Frog 2. The main beam is finished. Have shortened it by a metre and a half because original tri platform was excessively wide for a cat. Am thinking of 5 metre length fine floats with braces fore and aft at the beam/float connection. To stiffen the area. Because there is only one beam. Will post images tomorrow.

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The long triangular shape on floor is the area aft of the main beam. Cockpit shell is nearest camera. The angled forward main beam lies on its side to the right. The thing above beam is the forward hull skeleton. Have been using thin ply that has been lying around in shed.  Because up until the last few days it has been impossible to buy materials in Auckland because of the dreaded Covid 19.

 

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Failed to mention that the central hull is above water surface, nor a conventional hull. Has shallow depth, as you can see in above photographs. Today I set up one of the cat hulls in tensioned ply. Was hoping to get two hulls out of my large ply sheets but too stiff to bend into a tight cross section circle.

 

 

 

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