Gardner,

Don't forget to address what parts have to rotate. The load is split between the top and bottom bearing in your hull (most on the top bearing). When loads get high, plastic bearings are not recommended as they will stick due to coefficient of friction. Delrin rollers will deform and make flat spots. I have checked on all those and am now stuck with only cylindrical steel roller bearings for top and multiple ball type for bottom, all really expensive. PLastic can work for a while or well enough if not pushed to limit.

What cannot be easily modeled is the true load on the rig, since it is always in motion. Static loads give you one limit while dynamic loads are more while the spec for dynamic capability is less. THe spec limit is downrated due to acceleration/deceleration factors.

Just something to plan in your design. I know Rob has plastic stuff but no long tern experience, or extreme condition measures. I have double capability limit spec, not quite as high as normal 2.5 times cruise, but sufficient room for exceeding load limits. And have it engineered to match. Rob is correct in the extra mass and carbon needed for the base. But it does taper from top bearing to bottom.

I have not fully looked at the rudders but they too have problems with bearing load limits, especially as the boat speed increases on larger mass proas.

JT

--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
>
> 4'/1.2m on 40,000 'lbs/5.5 tonne metres is doable. Harry is 5 tonne metres
> and 1.7m, so you are going to need a heavier mast and more beefing up of the
> lee hull.
>
> Need to talk to the engineer, but for estimating purposes add 10% to the
> mast weight/cost and an extra layer of 600 db to the lee hull between the
> beams. Given that harry/Aroha is pretty stable, you could also look at
> reducing the beam or the weight in the ww hull.
>
> rob
>
> On Wed, Dec 30, 2009 at 9:03 AM, Gardner Pomper <gardner@...>wrote:
>
> >
> >
> > Hi,
> >
> > In a fairly recent posting, Rob mentioned that the amount of bury you
> > need for the mast isn't really related to the height of the mast, but
> > to the righting moment. Is there a rule of thumb that I can use for
> > checking the feasability of my layout? Current, I am looking at a
> > righting moment of about 40,000 ft-lbs to lift the ww hull. If
> > possible, I would like to do this with a mast bury of only 4'. Is that
> > reasonable?
> >
> > Thanks,
> > - Gardner
> > York, PA
> >
> >
>

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