Subject: Re: [harryproa] Proa Phoenix (was Tacking a Harry)
From: Rob Denney
Date: 7/29/2012, 10:06 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 



On Sat, Jul 28, 2012 at 3:40 AM, Dennis <spidennis@gmail.com> wrote:
 

Rob,
so far this is just a concept model,
all the technical details have yet to be worked out.


Goodo.  Just letting you know some things to watch for. 


In my neck of the woods shallow water is a huge concern,
and also for the Ultimate Florida Challenge.

Too true.  My point was to make sure you can lift the boards while sailing fast, without putting yourself in danger. 

I should be able to lower the masts with the sails and boom still attached.
they will also be removable for the portage,
or on the skinny and narrow upper reaches of the rivers
where I will basically have to cut a trail thru the downed trees and blowdown.
 Yup, the drag of the mounting of the swinging stub masts are a concern.
If I can keep it out of the water I should be good.
The lower stub mast section will be faired to reduce catching any waves.

Suspect it will be easier (and lighter), to mount them inside the hull, with a semi circular trough for the foot. 

What's next?
I have to come up with a sail plan, and boat length.
>From there I can figure out the CE and CLR and such
and can figure in just where those rudders are going.

If you have two rudders and two sails, the theoretical clr and coe will both be just aft of the middle,  regardless of where they are mounted.   The actual clr will be a lot further forward upwind, the actual clr, a little.  When you start sailing, the relationship gets screwed up due to the drag of the ww hull, so designing this properly is key.

I would make the first "known variables" the length and the weight.  Lee hull as long and low as possible within all your unique constraints, ww hull as short as possible and still able to carry the gear that will be permanently in it, both with L/W of 11/1 or better).  The first weight iteration is a wild guess (Elementarry is 120 kgs/264 lbs), but every time you calculate something, update the weight.  Then choose a suitable Bruce number (Tornado cats without crew etc are 2.2, higher downwind with the spinnaker) to get a sail area.     As this is mostly a function of mast height and boom length, there is no need to decide exact numbers until the hulls are finished and the weight verified.

rob



Right now I'm working on another boat project
which must be finished first before I move on with building the Proa Phoenix.
that doesn't stop me from doing all the design work though!
can't build it until I know what I'm going to build, right?

When the time comes I'll be getting help from someone to design the hulls .....
different build methods are being considered.
when I start flying the ww hull it's got to be strong!


Only has to be strong enough.  Any stronger is just excess weight. 


--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
>
>
>
> Dennis,
> Looks good. When are you starting to build?
> Couple of details:
> 1) rudders a long way back are hard to access to lift them. I find weed
> and reducing wetted surface for reaching/running are the cause more often
> than shallow water.
> 2) Outboard masts solve the dropping problem, but the drag will be huge.
> Will you have to remove the sail and boom each time you drop the mast?
> 3) What is the purpose of the platform? If the boat has enough sail area
> to be fast, you will be sitting on the ww hull most of the time, and on the
> lw one the rest of it. There is not much middle ground as, once you start
> moving, the apparent goes up very quickly. Clambering over the platform
> to balance the boat, and to reach the sails and rudders will be harder work
> than necessary.
> 4) Folding looks good, just make sure all the overlaps are big enough to
> support the righting moment and that it all locks into place, rather than
> relying on lines.
>
> rob
>
>


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