Subject: Re: [harryproa] Godzilla... how'd you do it? |
From: Rick Willoughby |
Date: 8/6/2010, 6:56 PM |
To: harryproa@yahoogroups.com.au |
Reply-to: harryproa@yahoogroups.com.au |
Dennis
Rick,I've been using Godzilla most of the afternoon. I've re-read the section on Shape Series over and over. Besides, Series 1, I don't see how you achieved the Godzilla optimization in your picture below. Even the in.mlt file you sent me some time ago does not enforce symmetry... and as far as I can see, I haven't found any way to get the prismatic station plan your flat bottom version exhibits. Square yes, but not strait sides that are flared out.Are you saying... that you take this rounded, 0.2 optimization into DelftShip and flatten out the sides and bottom till its develop-able and then export that back into Godzilla as a designed hull and then let it optimize on that?Dennis
From: Rick Willoughby <rickwill@bigpond.net.au>
To: harryproa@yahoogroups.com.au
Sent: Sat, July 17, 2010 5:22:59 AM
Subject: Re: [harryproa] construction
Dennis
The result I arrived at has surprised me but that is nothing new when using these tools. The linesplan for the round section and flat bottoms hulls I compared can be seen on this link:I had to constrain the minimum length to avoid getting planing hulls even with 4.5t hence the 18.3m.Making an estimate that the sail CoP is 10m above the centre of hull resistance, the round section hull actually trims 98mm bow up on net lift of 123mm at 15m/s while the flat section has a slight bow down trim of 30mm on a net lift of 217mm.I expect the drag I get from Flotilla is lower than you have seen with Michlet because both hulls exhibit lift at 15m/s. The round section shows drag of 5.02kN while flat bottom has drag of 5.34kN.Unlike the lighter hulls I have looked at before the round hull exhibits higher bow up moment than the flat bottom hull throughout the speed range to 30 kts.As noted in previous posts the flat bottom may get some benefit from dynamic lift if it actually trimmed bow up but that would require a lower CoP than 10m.Either hull works reasonably well and should be capable of 30kts with an efficient rig and rudders. The round section hull shows a slight advantage from drag perspective but then when you look at simplicity of building consistent quality with a flat panel hull it is likely it would have better performance.RickOn 16/07/2010, at 11:49 PM, Dennis Cox wrote:
Rick,I was just trying some things with the Godzilla after you sent it to me and I put it through an optimization that ended in a flat bottom hull. It did have very high speed potential, but if I remember correctly when I spit out its resistance curve, that it had a very high spike down around 10 knots... (far higher than the peak resistance at 30 knots). At first, this seemed reasonable to me... that the high surface area would be still in displacement mode and thus making a lot of drag. That once above that speed it would start planing and loose friction. Then... I recalled you said that Godzilla doesn't do lift... so my massive rationalization went out the window. So, I just assumed gigo happened.If your offering... what about a lee hull for a Harry...Length <= 18.3 mDisplacement when flying windward hull = 4500 kgBeing optimistic.. . shooting for 30+ knots.Dennis
From: Rick Willoughby <rickwill@bigpond. net.au>
To: harryproa@yahoogrou ps.com.au
Sent: Fri, July 16, 2010 12:48:47 AM
Subject: Re: [harryproa] construction
Your thoughts are similar to where I was 2 years ago. My flat panelled hull was aimed at easy building. I could not muster the will to carve another plug out of foam. I was prepared to give a little in performance with something easier to build.
I was very pleased and a little surprised when the end result actually performed better. So the flat panels was not a performance compromise. This was not quite what Michlet had predicted. The Flotilla software goes some way in providing the theoretical understanding of why it is better.It would be reasonably simple to make a long slender lw hull for a proa using ply that has very good performance. AND likely better performance than could be achieved with a round section hull. It could be designed to trim flat or slightly bow up through a wide speed range.If you want to have a go I can provide input on the shape that should perform best.
Rick
On 16/07/2010, at 2:21 PM, Doug Haines wrote:
Hello,considering how preferable the actual workmanship of wood (plywood mostly) is over meswsy glass/foam skins and cores etc. Then How about a flat bottomed, straight sided plywood shape?This is not used much normally, but harryproas need no rocker etc.Doug
--- On Fri, 16/7/10, tsstproa <bitme1234@yahoo. com> wrote:
From: tsstproa <bitme1234@yahoo. com>
Subject: [harryproa] Re: Rudder lift?
To: harryproa@yahoogrou ps.com.au
Date: Friday, 16 July, 2010, 13:25
What if the same 12m. hull was only 1/2 tonne displacement?
Todd
--- In harryproa@yahoogrou ps.com.au, Rick Willoughby <rickwill@...> wrote:
>
> The length constraint or non-constraint is a function of design speed
> and weight.
>
> As an example a 1 tonne hull with a flat bottom designed for minimum
> drag at 25 knots results in a length of 12m. However this hull will
> not generate enough bow up moment through wave making to counter the
> moment from the rig to drive it at that speed. Extending the length
> to 15m will get close.
>
Rick Willoughby03 9796 24150419 104 821
Rick Willoughby03 9796 24150419 104 821