Dennis
Scaling is complex. More involved than just considering Re# for a hull. Michlet takes the complexity out of it because it relates all the significant hydrodynamic variables, at least for calm water. So really you are validating the design process and tools you are using.
A flat bottom on the lw hull will not slam irrespective of the speed you can attain. You might get a bit of slapping if there are ripples and you can somehow get the bow to lift.
If there is a flat section on the ww hull it will be small. I have drawings somewhere of what I arrived at by looking at different load conditions. It did have a small flat section on the bottom but quite long rocker in the ends with "V" entry. I did not spend enough time on it to work out if it would be anywhere close to optimum for a range of sailing conditions.
Rick
On 06/08/2010, at 12:08 AM, Dennis Cox wrote:
Rick,"As noted earlier I have found pilot scale..." Well... some times I just need more than one kick in the head. My contention has always been that I don't think I have more than one boat construction in me. But maybe a "slap together" won't count. If fact... if it delivers the fun and satisfaction that I miss from my current tuna boat, it might push me that much faster.I really like the idea of doing one of the optimized designs you (and Godzilla & Flotilla) came up with... ie the more flat bottom designs. The construction damn near builds itself. And from any point of view for a beach cat, I'm fine with that.My... only... reservations are that I would like to be able to scale up (with Reynolds number methods) for predicting the full scale's behavior. Having said that, I am not opposed to chucking the progress I've made on the leeward hull. Most of it, I could shift over to a completely new design... At the very most, I might have to get a couple more sheets of OSB to cut new forms. IOW... no big deal.... AND my only reservation about these high speed, flat bottom designs stem from comments made by Rob about the rough ride and possible damage that such sharp jolts might cause to the boat and passengers... that he is heading toward more rounded than in the past. For the beach cat... no big deal... for a long distance, world cruiser... is a BIG deal. I plan on being old on it. :) Dennis
From: Rick Willoughby <rickwill@bigpond.net.au>
To: harryproa@yahoogroups.com.au
Sent: Thu, August 5, 2010 9:33:14 AM
Subject: Re: [harryproa] Having too much fun...
Dennis
As noted earlier I have found pilot scale often leads to the fastest and cheapest way of arriving at the desired end result.Scaling from what you are planning now is probably not required. Part of the pilot exercise is to validate the design process. So you should consider what might be possible with a particular package. Basically start with a clean slate and set out what you want in a beach proa. For starters it will only need to cater for a narrow range of displacement. Ideally it can be transported with the hulls intact although you might have sliding or folding beams. You can probably power it much closer to its limits.Unless you are using Rob's folding technique it is tough to beat ply in flat panels for speed and ease of construction. I do not experience any of the problems with hard chines that others observe. I think the observed turbulence is due to leeway and this should be avoided by using properly sized and trimmed rudders. You can simplify the shape tremendously without losing much performance. Long, narrow and light are the primary factors. The rest is window dressing if you are just testing. Ultimately you want to validate that you can predict with some precision how the boat will perform and test the merit of various ideas. It may be a different matter if you want to test the proposed method of construction with some form of strip planking but a lot more work.RickOn 05/08/2010, at 10:50 PM, Dennis Cox wrote:
OK... Todd and Rick with his human powered boats are having way too much fun and I can't wait for years before I get mine in the water. I am dieing to play with these bi-direction rudders that Rick and Todd are discussing. Having never seen a Proa in the flesh... it might be prudent for me to sail one before I spend years building the big one.So I want to build a reduced size one simply, cheaply, but mainly... quickly. I've reduced my DelftShip drawings a few times and find that somewhere between a third and half scale version will support two people in a beach cat size. I happen to still have the mast, boom and worn out sails of a Hobie 14 Turbo (Main and Jib).It is intended to be a test bed, so cosmetics and long life robustness are not necessary. I am looking to use 5mm Luan (because its cheap and available) and I'll epoxy and possibly glass over that. I would like to try to model the curvature of my lee hull if possible.Any suggestions on......bending or developing the wood?...converting my Hobie mast to free standing or staying into an adequate Proa rig?
Rick Willoughby03 9796 24150419 104 821
Rick Willoughby
03 9796 2415
0419 104 821
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