Subject: Re: [harryproa] Wave Interference
From: Rick Willoughby
Date: 8/6/2010, 9:01 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Dennis

With the bigger hull we have shown the trim is like wave interference.  It is essentially second order from a drag perspective.  It will pay to confirm though and that is where Flotilla is used.  It would not be used in the first iteration.

I agree with what you have started with.  The missing bit is the design speed.  For an initial stab I suggest you use loaded windward hull of 300kg and design speed of 7m/s.

Since you are aiming to use flat panel construction I suggest you set the 2nd shape factor to a maximum of 0.2 and the seed lower than this.  The seed can be zero.  Get the hull shape from this into Delftship and save the ship-outpu-by-speed.mlt.  Just for the sake of it do a run with the shape factor set to 3.  It should produce close to semi-circular section.  Compare the drag results at 7m/s.  This is the approximate cost of using flat panel.

I have already done the exercise for the 300kg 7m/s and section constraint so let me know and I can compare with my result.

Rather than forcing the hard chine in GODZILLA I form it in Delftship.  This only takes a few minutes. It means you can put some flare in the mid section.  For the proa you only work with the bow section imported from Michlet and then mirror to get the other bow. 

You then need to think about the strategy for determining the ww hull shape.  I have some thoughts on this and have done a few checks.

As far as sails and the like go it is a bit early to get into that yet.

Rick

On 06/08/2010, at 10:17 PM, Dennis Cox wrote:

 

Rick,
 
For a two person, high speed Proa...
 
I've re-read through the steps you suggested on Aug-3 email.  I want to start with a clean sheet of paper.  I haven't run Flotilla yet... If I understand correctly... its functionality adds (to Godzilla) the ability to trim based on the wave pattern, but not dynamic lift.  Is that correct?  So for the first step of the first iteration, I would need to design the leeward hull for maximum speed with the windward flying????
 
So if you would be willing to give a first stab, here's some criterion...

Hull Shape - whatever is fastest. 
Length - hopefully something else restricts, but 30' (9.1 m)
Weight with crew and all - Conservative 800 lbs (360 kg) Optimistic 450 lbs (200 kg)
Sails - 150 sq-ft (14 sq-m)  COE above mast step - 8 ft (2.4 m)
 
Dennis

From: Rick Willoughby <rickwill@bigpond.net.au>
To: harryproa@yahoogroups.com.au
Sent: Thu, August 5, 2010 5:58:01 PM
Subject: Re: [harryproa] Wave Interference

 

JIB

Scaling is complex.  It is easier to let Michlet determine the interplay of all the variables.  The viscous drag and wave drag scale differently so I could not even be certain that wave interference would not be more significant at some scale. 

It only takes a few minutes to do the analysis.  If you have some hull displacements and target speed I can do it.

Rick  
On 05/08/2010, at 7:45 PM, jhargrovewright2@ juno.com wrote:

 

Rick or all,
Would these dimensions scale down and still be "correct"?  If yes..... would the scale speed also be "correct?
Thanks!
JIB

---------- Original Message ----------
From: "willoughby_ rick" <rickwill@bigpond. net.au>
 
Curiosity got the better of me.

I have looked at the lowest drag hulls for 4t combined; with 3t on the lw and 1t on the ww. The hulls just happen to end up 21m and 13m long and total drag at 15.9kts is 2360N. The individual hulls have a drag of 1577N for the lw and 779N for the ww. So the interference is detrimental even at the optimised speed although I did have a max beam constraint of 8m and settled at 7m WOA.

There is detrimental interference maximising at 37N at 11.8kts when total drag is 1196N. Above 17kts the interference is mostly beneficial but too small to worry about. - always well under 1% of total.

This initial look suggests wave interference is a second order factor. It would pay to do a check with the ww hull more heavily loaded.

Putting time into the rudders is going to be much more rewarding in terms of performance than playing with wave interference. Likewise the selection and placement of the rig has big potential.

Rick



Rick Willoughby
03 9796 2415
0419 104 821




Rick Willoughby
03 9796 2415
0419 104 821

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