I am having my engineer do the FEA on the rudder shaft, pivots and
such. Rob has more confidence than I do on carbon rudders/ shafts.
Rob plans to profile the shaft so that it gets wider toward the
beam/bearings to spread the load, cause it isn't the carbon failing
but epoxy resins which have a more limited tolerance for compression
situations. Also that helps the bearings set as they can't take
execssive loads without deformation. Thus need more bearings/
rollers to help. Cannot use plastic bearings as side loads will more
drastically change the force required to overcome friction at higher
load situations. Better to stay with roller bearing types. THose
too can't handle really high loads without making flat spots, unless
they have enough roller content.
Will have a complete analysis hopefully soon, so the forum can
discuss options further. I will be using aluminum 6082 shafting
profiled from 1 inch dia at tip to 4 inches at the lower bearing.
That is enough for a reasonable safety factor but no guarantee the
shaft won't bend. I make all these assumptions with the fact my
rudder will only be 1 meter deep and 0.5 meter chord. Shoaling in my
normal sailing region of Pamlico Sound dictates a shallow draft for
most areas. Rare Bird rudders are 1.5 meters deep, with the same
chord.
All understood the rudders are an engineering challenge. Cruising
forum has a recent posting regarding multihull rudders caught in a
grounding situation. Lateral loads are bad news !
JT
--- In harryproa@yahoogrou
>
> Hi ya,
>
> I'm not really weighing into any arguement here, but I managed to
break the carbon shafted blade back when still on first versions of
rudders.
> It was a very windy day 30/40 on the river and taking a short cut
through a sand sspit. The kick up would have been OK but I turned
fairly hard because of looking for the channel when the rudder hit
the sand. The desin was raked a little forward and it just stiuck
hard and the strong wind just pushed the boat against it side on and
snapped up at the bearing.
> Still was more of an accident than normal loads, but the rudders
are going to be prone to this in and unpotected position.
> See it as somewhere than just needs a lot mpre thought than the
rest of the simple design of the Hp's.
>
> Doug
>
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