G'day,
I was not referring top a similar weight or size mono or it's rudder.
Picture a monohull (or a multi) with a rudder the same depth below
the lower bearing as a harry. If that doesn't do it, picture one
twice as deep. The advantage that harrys have is the rudder shaft
can be beefed up above the waterline as it does not have to fit inside
the blade.
The loads are large, but they can be determined relatively easily, and
the rudders designed and built to resist them. To overbuild a carbon
shaft is easy, and not expensive. I doubt any of these will be
broken. The kick up mechanism and the support for the shaft on the
beams are more complex (same loads, just more complexity in the paths)
so need more attention to detail.
Or, they can be made simpler. For example: 1) Building the beams so
the rudder can be mounted through them rather than hanging off the
back with all the funny angles and peeling loads (the weak point of
composites) this entails. The sideways load bearing structure is
reduced to compression/ tension along the beam. It also makes the
beams lighter as there is no carbon required on the vertical faces.
2) Using the beam the rudder is mounted on to resist the fore and aft
loads is very difficult as the beam is relatively small in cross
section. Better is to tie the rudder to the other beam, or, in the
case of the front rudder, to the bow. As these loads are always
tension, and this is the direction they kick up in a collision, the
structure can be reduced to a piece of rope with a fuse in it.
Having the structure hanging off the beam makes it much easier to
overbuild it. For example, adding more glass or carbon, using thicker
struts, and spreading the loads over a larger area of beam. As the
actual structure is quite small, this beefing up does not add much
weight or cost. It does make it messier, but it is very easy to
cover.
regards,
Rob
On Tue, Dec 2, 2008 at 7:20 AM, Gardner Pomper <gardner@networknow. org> wrote:
> Rob,
>
> I am not clear on how the loads can be the same as on a monohull in
> that there is an extra 2 to 3 feet of leverage working against the
> harry rudders If they are not supported below the beam. Monohull
> rudders are supported where they enter the hull, below the waterline.
>
> If I am wrong about this I would be really interested in a better
> description of how the rudders work. They are a continuing area of
> concern for me.
>
> Gardner
>
> On 12/1/08, Rob Denney <harryproa@gmail. com> wrote:
>>>
>>> --- In harryproa@yahoogrou ps.com.au, "Robert" <cateran1949@ ...> wrote:
>>>>
>>>> Proasailor has just been bagging Harryproas on the multihull forum.
>>>> Usual bit about how having the wtw doesn't work and Harryproas haven't
>>>> proved themselves crossing oceans. Nothing specific. It does become a
>>>> bore. Still it gives an excuse to reply and highlight the advantages
>>>> of a Harry
>>>>
>>
>> G'day,
>>
>> Sure does, and you are doing an excellent job, thanks. Proasailor is
>> Joe Oster, who was thrown off the proa group for abusive language.
>> Should be amusing to see what he comes up with on the free for all
>> Sailing Anarchy site if he is pushed hard enough.
>>
>> As for the rudders, the loads are no higher than they are on many
>> monos, and just as easily, (or as difficultly) engineered and built to
>> take those loads.
>>
>> Regards,
>>
>> Rob
>>
>
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