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Guest Ralf Gruenig

Mast Bay River Skiff

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Guest Ralf Gruenig

Hello,

I have just launched my new Bay River Skiff,

everthing works fine. Here my question:

I have build the masts hollow, in two parts, from the timber called fichte in Germany, diameter

63 milimeter. In gusts the main mast bend really strong, I like to aid the mast but I don't now how. Thanks for helping, Ralf

ralf.gruenig@t-systems.com

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Guest Brad Whitehurst

"Fichte" translates as "spruce" according to Google's translation. That said, I am sure there are many different species of spruce that could have different properties. I have a set of Bay River Skiff plans, but don't recall the mast design. If the standard is solid as I would bet, then a hollow spar should be a bit larger in diameter than the solid one to get the same stiffness.

1. Is the standard Skiff mast specified as solid?

2. If the standard is solid, what diameter hollow mast did you fabricate? Stiffness will vary as the difference of the fourth powers of the outer radius and inner radius, so it would not have to be much larger in diameter (assuming a fairly thick wall) to match the stiffness of the solid spar.

Graham or another Naval Architect can smack me if I got any of that wrong! :D

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Guest Brad Whitehurst

Duh. I should read my messages before sending them so fast. Ralf does give a diameter, which I assume is the outer. That works out to about 2.5 inches diameter. Graham, my memory now seems to say something about aluminum tubing for a mast?? If so, Ralf would probably need your input for a suitable wood spar design. Since it is already made, if it were my mast and it was bending too much, I would consider looking for a tight fitting smaller aluminum tube I could put inside the wood mast to stiffen it.

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Guest Graham Byrnes

Yes your 63mm or 2 1/2" diameter hollow spruce mast will be too soft. The plans call for 2 1/2" diameter x .065" aluminum which is perfect for that boat or 2 1/2" solid fir. As you already have the mast steps built, the simplest way would be to replace the lower 2 or 3 meters of your wood masts with aluminum. Another way would be to add carbon fiber to the outside until it became stiff enough, but it would probably cost more than the aluminum. The white Bay River Skiff on our web site has only 2 1/4" aluminum masts which I tried hard to brake but never could. The reason I moved up a size was that I felt that it depowered the sails just a little early as the breeze picked up. It sure won a lot of races though and it's still sailing. If you decide to go the carbon route I will give you the bending dimensions to measure your masts against.

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