Proa Proasis sailing downwind in 20 kn

Cruising downwind on our proa Proasis. Wind was between 18-20 kn from behind, speed was between 7 and 9.5 kn, averaging at 8.something. Dry and relaxed sailing!
Visit www.proas.is for more information about the Proasis-Project!

[@zacharycawthorne-nugent4988]

I'm in love with your boat. I did have a small question regarding the sail size. How did you pick the sail area considering it won't be reefed? In all your videos so far you seem to have everything well in hand and are moving along nicely so you've obviously got the right size. Is there a particular sa/displacement rationality were aiming for?

[@proasisproject]

Thanks! Sail size depends on many factors. I dont think there is a simple rule for this kind of vessel. On a proa with traditional sail your quite limited with the size. If the length of the booms is increased the area adds up in the back resulting in weatherhelm, especially downwind. On the other hand longer spars are heavy and make the sail difficult to handle. For safe singlehanded operation I wouldnt go beyond 6.5m spars. We've tested the entire design with a 1 to 5 scaled model (video on youtube too) to determine a sail size that gives us good speed but proper balance and stability at the same time. The current system is designed to lift the windward hull at 30kn if sheeted in tightly and going upwind. So far, the ww hull never left the water but I think it would do somewhere around 30 kn. This winter we plan to make a slightly larger sail (16 sqm) for better low wind performance and add 2 reef lines for stronger winds. Sometimes its just more comfortable to sail with a reef in.

[@pakde8002]

Moving along nicely. How many square meters is your sail? It looks like she could handle more sail. Edit: I see the question has already been answered:)

[@proasisproject]

Back then we only had 15sqm. Our new sail got 19 sqm, much better!

[@georg8624]

Segelst du jetzt gerade vor Strande/Schilksee mit Kurs Süd?

[@proasisproject]

Gut beobachtet, haben grade von Bülk nach Falkenstein verholt :D

[@lucdekeyser]

It is difficult to tell but does the lee hull pitch down some? GPS trace or it did not happen;-)

[@proasisproject]

Not much. Sometimes gets stuck in the back of steep swell. We have tracked it but not imported the data from the device yet. You have to believe me ;)

[@lucdekeyser]

@@proasisproject In any case this looks quite promising with such a relatively small sail. The boat seems to be still quite high on its lines. Interesting to learn what loading up the lee hull would do.

[@proasisproject]

@@lucdekeyser We have been out with 8 or 9 people a few times. The boat reacts noticeably slower, especially during shunts. Aside of that its not much of a difference.

[@dimitricherny]

What was your speed? What is that silver disk on the ama? What are your length to width ratios at the waterline? What's your draft on both hulls?

[@proasisproject]

Topspeed that day was 9.5 kn, averaging around 8kn. I think what you mean is a ventilator. Can be opened and closed from inside. Ratios are 1:21 for the leeward hull and 1:18 for the windward hull. Draft without leeboard and rudder is about 20 cm. More information, drawings, pictures, numbers etc. available on www.proas.is. We will upload more videos (a boat tour i. eg.). Make sure you subscribe if your interested :)

[@lucdekeyser]

@@proasisproject from the numbers in the table on the web site the ratio for the lw hull would be at least 1:24, right? OK it is explained in more details in the text as the lw hull is wider at the water line than listed in the table. The shape of the lw hull is quite more complex than I thought. Has anybody else built this way before?

[@proasisproject]

@@lucdekeyser yeah that depends a bit how deep she's loaded. She gets wider to the top. Difficult to measure too. Can't tell you exactly but it's ranging somewhere between 20 and 24 :D

[@lucdekeyser]

@@proasisproject mathematically you could calculate it exactly but in this case this complexity is not worth the difference to be relevant enough in the discussion.