Doug,
I hope it is noted that I came back to the standard :) HarryProa configuration. My original ww masts design was a mental exploration. As many of us want to do, I wanted to birth something into the world that is "mine". As such, I looked at the things in all Proa's and multihulls and picked points that I didn't like or that I thought I could do better.
Here are the points I wanted to address and following that are the points that drove me back to the fold...
1) I liked the idea that having the rudder/leeway prevention in the windward hull.
a) As the ww hull lifts, leeway prevention is reduced and the hulls skid. Sort of a self regulating safety valve.
b) Aesthetics. Some would discount this entirely. They drive Ford Pintos. Others would drive Ferrari's all the time if they could. Both will get you to a destination. Or... another metaphor... how many would prefer an ugly woman? I say... to each his own. In my case, I like fine lines. Imagining myself on the windward hull surveying my world... I didn't really like all the spray and the "contraptions" hanging on the inside of the leeward hull I see in videos. So... for my lady, I'd prefer a J boat to a Tug boat. Putting the rudders on the ww hull puts them and the spray under the bridge-deck out of view.
2) I wanted to minimize the amount of structure under high stress. This drove to the schooner design as having the wind loads directly transmitted to the leeway prevention only inches away seemed like a good idea.
3) It also aided in the supposed rigging to/from the transportable cases.
4) Basically the crossbeams strongest/stiffest/thickest point needs to be wherever the masts are. I liked the idea of having a nice tapered beam with say a 4" height going into the lw hull. This also required the ww placement of the masts.
5) Reduced linkages - Having all the rudder controls and sheets at hand instead of having to cross the beams to the lw hull. Being able to stay on the ww hull while dowsing the sails in a blow.
Back to the fold
These all seemed like good ideas... at the time. However, standing back and divorcing it as being "my" baby, I looked at it as if it was someone else's design... and started throwing darts.
1) Racking loads - Having a structural analysis background, I initially thought this was surmountable and still do... HOWEVER, as I started determining the magnitudes of these loads I realized I was adding far more complexity and weight... for what?... making a simple container into a stressed member.
2) I hate to admit it... but aesthetics came back into it. Rob casually pointed out the view from the cockpit with two masts mere feet away and ALWAYS over my head.
Basically... I've come to believe... Rob has described the simplest and most efficient configuration for the cheapest, strongest, lightest, fastest, real-world boat possible. The only things faster will involve wings and I just can't resolve those as being usable on a boat that has to cruise thousands of miles in light conditions also.
So... my differences from a HarryProa are subtle...
1) I've settled on a schooner.
a) Structurally... it places the main loads directly over the beams and rudders versus having to torque and bend the lw hull to trasmit the primary load from a central mast out to the beams and rudders.
b) I recognize it being less aerodynamically efficient. However, that means I just have to carry more sail to be as fast. This is no big deal. The schooner with its lower COE can do that easily.
c) Makes it easier to balance
d) Makes the individual sails more manageable
2) I'm still haven't settled on rudder placement. I still like the idea of having them tucked under the bridgedeck on the ww side. But as you see with MLM, I'm going to experiment with cassette style rudders. Maybe again I'm adding more structure to take rudder strikes, but there are many cats and tri's with daggerboard trunks. I'll let you know if I talk myself into or out of something.
Dennis
From: John <jrwells2007@yahoo.com.au>
To: harryproa@yahoogroups.com.au
Sent: Tue, December 28, 2010 5:15:21 AM
Subject: [harryproa] Re: Dennis's Design
With the rig in the ww hull you have the type of stresses that are found with a trimaran.
With a Harryproa the beams take the stress of the leverage of the mass of the ww hull plus the drag of the windward through the water and air.
A pacific proa setup has the leverage of the ww hull plus the drag of the lw hull that becomes greater as the ww hull lifts. Eventually as the ww hull comes out of the water the full drive pushing the proa along goes via the beams whereas with a Harryproa this drive does not stress the beams.
I would have thought that the pacific proa has to be able to cope with greater stress in the beams than the Harryproa.
--- In harryproa@yahoogroups.com.au, Doug Haines <doha720@...> wrote:
>
> Hi Dennis and Rob and all,
>
> I am looking at Dennis's Maxi trailer
60'er a bit more and see how this could be a better design with the rig in the ww hull.
> Secondly I am not sure, but it seems that there is going to be less stress on the beams if you have the sails on the hull that is getting lifted up. Instead of the sails over on lw hull.
> This is intuitive - I have to mull over a bit on that, but i think the hull and beams will see less loadwhen the wind starts to push the ww hull up out of the waater. It seems an even simpler way of sailing than standard HP - if that was possible.
>
> The down side is having to look up at your sails. I don't know what other changes it would mean.
>
> Doug
>
> --- On Tue, 28/12/10, Dennis Cox <dec720@...> wrote:
>