IF it is a quick and dirty job to test proas, then don't mess about too much with hull shapes. Make a plywood box, flat on the top, bottom and sides, tapered towards the ends with as much reverse sheer as you like. If Rick's shape fits in this general configuration (pretty sure it will), then include it. Otherwise, wait until you know how to sail it, what bits can be lighter and build an optimal hull, using the technique you will use for the big one.
Use butt blocks or uni glass for the lengthwise joins, stringers (cut the butt blocks so the stringers can be full length) for the chines and sheer. Glass the ply (200 gsm) inside before you start. The mast should have 10% bury, as should the beams. This will be more than big enough to carry the weight. The windward hull should carry it's own weight, and the crew and still have 50% freeboard and 10:1 or better l/b.
Put bulkheads where the mast(s) and beams go and some reinforcement in the floor around the lower bearing which should go in before you close the box. The top bearing can be towed in place, as can the beams.
My El weighs 140 kgs complete and is 7.5m long x 4m wide. It has 11 sqm of sail which is not enough for one 90 kg crew. I have added 2m to the mast 5 sq m of sail. It used to be a 22 sqm schooner which was plenty for 2 people, hard work solo.
Forget the hobie rig and build a carbon unstayed mast or two, ideally wing section. Dimensions and instructions when I have some time.
Box or round beams towed onto the decks, with rudders mounted on them for ease of altering them. Definitely try bidirectional rudders, but allow for the possibility that they won't work safely on the big boat, which remains my fear.
Gardner Pomper is just up the road from you and is doing a similar boat. Suggest you drop him a line to compare notes.
rob
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 Willoughby03 9796 24150419 104 821