Just one quick note on swinging leeboard.
If you want it to be effective it has to be pretty long so even when swung back you still have a fair amount of board in the water; I built the one for Kevin’s schooner green proa and if I remember well, it was around 5 ft long; Kevin could give actual dimensions.

That creates a little problem (but not unsurmountable), which is when you want to shunt in shallow waters… and there is less water than the length of the leeboard when it is vertical, in the middle of the swing from one end to the other…
That is why Kevin got his board with the pivot point, itselt attached on a fore-and-aft tube on the lee gunwale of the main hull; you can swing the board horizontal to the lee side of the boat if need be.

Since he sails in warm waters (and you do too, I guess…), a shunt in very shallow waters does involve getting wet by standing in the water on the leeside of the boat, and lift the board to the leeside of the boat, and swing it while it is horizontal, to the other end of the boat and put it back in the water along the main hull.

Obviously, when you need to do this, that means you can stand on the water (4 feet or less of water); in deeper water, you swing the board in the water, sliding along the leeside of the hull.

One more thing, if you like to get technical, since you have to make a foil with leading edge and trailing edge which will be reversed at each shunt, conventional profiles do not work. A true Fluid Dynamics engineer fond of proas (Tom Speer) worked on this and published a series of profiles that he simulated in CFD (Computational Fluid Dynamics) to compare to conventional profile and found out that their performace is very close.

If interested, you can find much more information, including profile coordinates (for free) here:
http://www.basiliscus.com/ProaSections/ProaIndex.html

The proa 3 series is according to Tom the best one.

Cheers,

Laurent

When I give up on proas I going to build a duck punt, they weight steer and someone has just added chine runners

http://www.keepturningleft.co.uk/blogs/a-duckpunt-with-wings/

Says extra five degrees

Tink

Are you concerned about what the chine runners would get up to when the hull is severely bow down or bow up? Seems like they might ad a lot of drag in these situations.

With regards to the lee board, in your case you could just retract it completely when in shallow water, since your boat sails really well without it anyway. You still get that bit of extra pointing when you need it or want it in deeper water.

You could also try a “vertical chine runner” or tiny keel. Consider this: If you want to steer the boat in shallow water and move your weight all the way forward or back, draft increases. If you don’t go any deeper than this with the keel you don’t loose any shallow water sailing ability. Of course, you may not be able to get it all the way up on the beach like in that great picture earlier in the thread.

-Thomas

Thanks for all your comments.

You all seem to think that it’s not performing that bad, without boards and with such shallow draft. I haven’t got any other experience in proas, so can’t really tell how well or not I’m doing most of the time. As I mention before it is perfectly ok for me, as long as I have plenty of fun with it and I still go upwind. (but would be great to improve it!)

As mean of comparison, does anyone know what sort of upwind performance a proa similar to PM but more traditional with deep hull or boards? Something like Gary Dierking T2 or so?

Tink,

Looking at your settup you could use a hook on leeboard which could be moved and placed forward of the mast. On the shunt it would have to be moved over to the new bow. A big hassle but good for a quick dirty experiment. Alternatively you could attach a strut between the two leeward ends the aka and mount a movable board on that. In that way the mast would not be in the way.

This is why I have been so interested in your proa! I’ll avoid any boards wile I can, but I find your solution very nice. As curiosity, how do you deal with the shunts in shallow water? (see Laurent’s comment)

http://www.keepturningleft.co.uk/blogs/a-duckpunt-with-wings/

Says extra five degrees

That’s something… it doesn’t look like chine runners as I have in my mind (Matt Layden ones). Have to look more into it.

Thanks Tink

Laurent,

That creates a little problem (but not unsurmountable), which is when you want to shunt in shallow waters… and there is less water than the length of the leeboard when it is vertical, in the middle of the swing from one end to the other…
That is why Kevin got his board with the pivot point, itselt attached on a fore-and-aft tube on the lee gunwale of the main hull; you can swing the board horizontal to the lee side of the boat if need be.

Since he sails in warm waters (and you do too, I guess…), a shunt in very shallow waters does involve getting wet by standing in the water on the leeside of the boat, and lift the board to the leeside of the boat, and swing it while it is horizontal, to the other end of the boat and put it back in the water along the main hull.

That’s a very valid point that I never even considered! It got me thinking, but i think Thomas came up with a solution that would avoid having to get wet on every shunt.

With regards to the lee board, in your case you could just retract it completely when in shallow water, since your boat sails really well without it anyway. You still get that bit of extra pointing when you need it or want it in deeper water.

If getting stuck in shallow water unexpectedly, then I can use your method and get wet.

One more thing, if you like to get technical, since you have to make a foil with leading edge and trailing edge which will be reversed at each shunt, conventional profiles do not work. A true Fluid Dynamics engineer fond of proas (Tom Speer) worked on this and published a series of profiles that he simulated in CFD (Computational Fluid Dynamics) to compare to conventional profile and found out that their performace is very close.

I’ve been admiring his work for a wile, and although I can’t follow it all, it seems very interesting and Tom gives the profiles ready and easy to apply, witch I find great! I will go that road if board are to be made…

Thanks for the valuable information Laurent. oh, and yes, very warm water all year around here!... jealous? 😉

Skip,

I’ll be interested in results of chine runner trials, also think there’s some goodness in better aero.

More work than a leeboard but a narrower hull would give you more lateral area.

I’m at the moment making a new sail, so we’ll see how well that works.
Narrower hull also means more draft… Maybe something to consider in a next project, but on this one I’d like to keep the shallow draft on this one.

Thanks Skip, will keep posting my results (or lack of them…)

Since your hull is the only foil, I think a small (1/3 hull length) chinerunner could do the trick with upwind performance. I don´t think a 1/3 length chinerunner will add much drag, but it will probably make the but-steering more efficient. It will help damp some pitching motion to.

Have you tried a crab claw sail?

You all seem to think that it’s not performing that bad, without boards and with such shallow draft. I haven’t got any other experience in proas, so can’t really tell how well or not I’m doing most of the time. As I mention before it is perfectly ok for me, as long as I have plenty of fun with it and I still go upwind

I think your proa has really good performance. It seems so easy to steer with only weight-shift. That is a very desirable quality for a simple and fun proa.

Cheers,
Johannes

Thomas,

Are you concerned about what the chine runners would get up to when the hull is severely bow down or bow up? Seems like they might ad a lot of drag in these situations.
(...)
You could also try a “vertical chine runner” or tiny keel. Consider this: If you want to steer the boat in shallow water and move your weight all the way forward or back, draft increases. If you don’t go any deeper than this with the keel you don’t loose any shallow water sailing ability. Of course, you may not be able to get it all the way up on the beach like in that great picture earlier in the thread.

That’s might be a concern, but I’ll test it anyway, maybe not a full size chine, but only on the central part won’t affect it that much?
It’s annoying because everything is a compromise!
The keel/skeg idea crossed my mind, but will avoid it as it makes it also harder and more fragile to move it in dry land (maybe not that bad, but still not that keen on the idea!)

Cheers Thomas!

Johannes,

Since your hull is the only foil, I think a small (1/3 hull length) chinerunner could do the trick with upwind performance. I don´t think a 1/3 length chinerunner will add much drag, but it will probably make the but-steering more efficient. It will help damp some pitching motion to.

We were typing about the same thing at the same time! I agree and it is what I’ll try first.
Also came to mind that a small chine runner in the lee side of the ama might help wile the ama is not flying?.
My concern on the efficiency of chine runners in this boat is that they are usually used in a semi-heavy displacement boat (Matt’s paradox and so have much more draft than my 4in…). We’ll see how it works, if nothing else it will make a nice track for a board to lean against!

Have you tried a crab claw sail?

No, I feel like I should, but seems like so much more sticks and harder shunts… (obviously I have no experience at all with it though!)
I’m in the process of making one similar sail to the one I have but in pollytarp, a bit bigger and with reefing points.

Thanks Johannes!

gearbox - 23 June 2013 09:55 AM

Laurent,

Thanks for the valuable information Laurent. oh, and yes, very warm water all year around here!... jealous? 😉

I live now in Singapore, 140 kilometers North of the Equator… So no, not jealous about the warm waters!
Jealous about the sailing, though, I am in repair mode right now, and it seems to never end…

So not much sailing..

Laurent

Not sure why I didn’t think of this before but you should have a look at the catamaran roonio. There are a few articles about it on duckworks magazine. It has a very similar hull shape to your boat, and uses an interesting device called an “anti-vortex panel”.

They are used on some of Bernd Kohlers designs, and he has a pdf file which you can check out here:
http://www.google.co.nz/url?sa=t&rct=j&q=anti+vortex+panel&source=web&cd=1&ved=0CCkQFjAA&url=http://www.ikarus342000.com/Antivortexp.pdf&ei=BkDiUbH3NaetiAer4IDYCA&usg=AFQjCNHA35Kz_MbQGiR0meKxXM_aHFsLiQ&bvm=bv.48705608,d.aGc

Basically it is like a chine runner, but on the windward side of the hull! They are used on catamarans, and therefore do not rely on the boat to heel. Also they work best with hard chine hulls like yours.

People seem to doubt they work (not Bernd). I think your boat would be the ideal test case, lets see some GPS tracks before / after!

If they do work it would be pretty much ideal I think.

-Thomas

(PS, what app did you use to produce your GPS track?)

tdem - 13 July 2013 11:05 PM

(PS, what app did you use to produce your GPS track?)

If you did your GPS track from an iPhone, I am interested as well on the app…

Cheers,

Laurent

Not sure why I didn’t think of this before but you should have a look at the catamaran roonio. There are a few articles about it on duckworks magazine. It has a very similar hull shape to your boat, and uses an interesting device called an “anti-vortex panel”.

Thanks Thomas, I remember having a look at this ages ago, and not really knowing what to think about it… Just went back and read the pdf file, and it seems more interesting this time, although my brain still complains when I make it think of vortexes!

I haven’t had the chance to do any of the tests proposed in above posts (sorry Chris), but have been trying to get my head around the chine runners and how they could work.

I did check Steve Lewis’s “Duck Punt with wings”, mentioned by Think on a previous post. Duck Punts are really cool!
Steve says the chine runners make it point about 5 closer to the wind, being the normal on the DP about 75 to 78.
He also says that it only works well when the boat is quite heeled. This is also how Matt Layden’s designs work, and with much more draft, big rudder and sail quite aft…
I’m not sure if they would be effective at all in Proud Mary, unless maybe when flying the ama…

I think I’ll try the chines runners, then “anti-vortex panel” as they seem easy enough, and maybe i’ll be pleasantly surprised with either of them… fingers crossed!

(PS, what app did you use to produce your GPS track?)

For GPS tracking I’m using “GPSlogger II” on a blackberry bold (http://www.emacberry.com/gpslogger.html). It’s a simple app anklets you export tracks in lots of formats.
Sorry Laurent, only have a Blackberry phone.

have been trying to get my head around the chine runners and how they could work.

If you push your hull sideways through the water, the water will be pushed down from the high pressure on the lee side - down under the hull where there is less pressure. The chinerunner acts like an hydrodynamic “fence” creating a longer path with much more resistance for the water trying to flow down under the hull. It is all about keeping the high pressure “chock-wave” pushing back on the lee side instead of just flowing down under the hull.

If you “expand” the difference between a soft chine and a hard chine and make it more “hard” then just a sharp 90 degree angle, you effectivly get something similar to a chinerunner.

The chinerunners work best when deep down and angled slightly downward, but they are effective over a wide range of circumstances. The add a lot of damping for any non-forward unwanted motion too.

Cheers,
Johannes