Proud Mary
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
Thanks Johannes, this is the simplest and most concise explanation I found so far, very refreshing after all the very involved theory I’ve been finding around the internet! I’ll try them with some extra optimism now!
Chris,
Here’s a totally self interested suggestion. Screw a piece of plywood that to the lee side that “looks” like 8 (ish?) more inches of rocker. You loose your shallow draft temporarily. But you test the theory behind SRIR!
Took me a wile, but did it yesterday. Unfortunately I didn’t have enough ply to make a full lenght rocker, but did do a 8ft kind of rocker shaped board, adding 7 inch to the draft (see pic under).
The wind was from non existent to about 3 or 4knots and changing direction, so hard to give accurate numbers.
From GPS track my best estimate is that the best windward performance was around 40degrees , but hard to say really. Fastest speed was 4.2kt. Huge and very noticeable improvement anyway!
Steering was normal, and it tracked quite well considering the lack of wind/speed.
Hope this is helpful… will try to get more precise data when possible.
Hey Hugo,
SUPER COOL! Are you saying it seemed like you were tacking through 80 degrees!?!? That’s pretty impressive.
I wonder if the combination of lateral area AND low frontal area (since there’s no hull volume between your floor and lee-keel).
Totally awesome experiment. Can’t wait to hear more.
Are you saying it seemed like you were tacking through 80 degrees!?!?
From GPS track it was tacking through from just under 80 degrees to 150ish degrees. I don’t think this is very conclusive, as the wind was very irregular and shifty and there was a fair current, so that might be what it reflects.
It is a very confusing track as i got caught a-back a few times when wind died and came back from different direction.
In any case it was a big improvement on the tracking, didn’t feel much leeway at all. Because it was just a ply board with no shaping there was lots of drag, water splashing from the front of it and all, so with a well shaped board or keel it should work very well.
Will have to try it with better wind and will let you know then. Will try to do that before I finally bring it home and make the chine runners.
And once you have some conclusive data, you could go out on a nice breezy day. Sail it, cut a bit off. Sail it, cut a bit off. That way you could find out the minimum size required.
-Thomas
...or just unscrew it and scooch it up….
I tried to sail PM with the lee keel again.
Still very light winds, 2 or 3 knots but at least more constant and not shifty.
I did use my first kite sail, but made a yard and battens of PVC, and it works nicely in light winds, but the yard is too flexible and flimsy.
My GPS track shows the first shunts were not to close winded, as I was trying to get used to the sail, but then it came to closer to 90degrees between tacks.
Maybe with more wind and better sail it would get better, but now PM is coming home for a round of repairs and improvements.
Down is my track, and and a link to a video of it.
How’s steering with the new keel—any difference?
Steering seemed to be about the same. had very little wind, but it all seemed to work fine.
Hey Hugo,
How are things? Any Proud Mary news? Any more days trying the keel?
I’ve been working on Red and have a new platform design. I have a question. How far does weight have to shift forward of the center point (middle station) sailing upwind and how far aft do you have to go before it wants to gybe?
I am trying to figure out if I can get away with an 8’ long platform on a 22.5’ waterline. There’s a lot of machining, so it would be nice to make it in one piece, but I’m wondering if going 4’ forward and 4’ aft of the center of the waterline is enough.
Does that make sense?
Hope you’re well,
chris
Hi Chris,
Sorry for the late reply.
I didn’t try the keel anymore, as a couple of the screw holes started to let water in, so I brought it back home and started working on it, but then my baby girl was born, so not much time spent on boats anymore…
How far does weight have to shift forward of the center point (middle station) sailing upwind and how far aft do you have to go before it wants to gybe?
My platform boards are just under 6ft.
If you look at the butt steering video ( https://www.youtube.com/watch?v=eKuecjDqAL8 ), you’ll see that I move as far forwards as the board goes to go upwind, but to go downwind to the point of risking a jibe I go further then the board, maybe 4 or 5 ft from the center point. This is about as extreme steering as I ever do, and any of the this positions would result in going aback if kept for a longer time.
After having a approximate good heading it takes probably no more than 2, max 3 ft of the center to keep a course in calm water.
As part of the work in course I’m considering extending the first deck board to allow me more room for maneuver, but this is to try faster turns, not needed to keep a good track.
If you are still thinking about rudders/paddles (Have to revisit your thread…) I think 8ft will be plenty, If not, in a very unscientific way, I’d give it more…
PM is very slowly getting some modifications and improvements, and I’ll post some pics soon. (chine runners, glassed bottom, rigging simplification, set for alternative sail plan, etc)
Hope this helps and is not too late Chris!
Hi Hugo,
Congrats on your baby girl!
That was very helpful info! Thanks.
My next step is to build a model to see how well my Marshallese hull shape does, and I wanted some ballpark weight shift parameters.
Good luck with your mods. I’m looking forward to hearing how they work.
chris
Hello to all,
It has been a long time since anything worth mentioning happened to “Proud Mary”, but now things are gaining form, so though I’d let you know PM is slowly coming back.
Main changes are a chine runner, folding akas and lighter platform (idea taken from Chris). Also new is a layer of FG on the bottom, self draining well and some hopefully dry storage in the vaka.
Still working on it, and need to also sort out the rig, but hopefully not to long before it is sailing again, and it should look like music on the water!
Cheers
Very nice, Hugo! The perforated deck is looking sweet.
Did you add to the beam with your folding akas? What is the BOA? What is the distance between your akas? How long is your platform? What adjustments are you making to the rig?
I love the musical paint job.
Looking forward to more sailing video!
Chris
Hi All
I’m chiming in late on this thread - as a newbie I just read through it (when I should be doing other things :(
Its such a pleasure to read the contributions of such a knowledgable and generous group of people.
One comment by Johannes : “What is not there - can not break or give any trouble, it does not cost anything and will never need any repair or rebuild” (!) This is not just good advice for boatbuilding, its good advice for life! In the same vein but so much more than ‘if irt ain’t broke don’t fix it’. Yr a philosopher dude!
Having been thinking about vortices and sail tip end plates lately, the chine runner/anti-vortex panel conversion really hit a chord. And the K-designs pdf was very interesting - thanks Thomas. I understand how a chine-runner/anti vortex plate will reduce drag, I’m trying to work through how does that transforms into pointing better - the overtax induces leeway I assume?
quoting Johannes again -
“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 chine runner.”
The anti vortex panels in the K design are short, but relatively wide, likewise the plates on the duck punt. As per the K designs discussion, chine runners won’t work on a U hull. But on a deep V with, perhaps a narrow flat bottom, (trapezoid then, strictly I guess) why not project the flat bottom out horizontally - on the lee side or both sides, for,say, for the full length of the full depth of the hull ? - Say for sake of argument 35% of the LWL. But project it only very short, 1” or 2” ? What would the optimum width of the antivortex plate be? Is lee side only the best choice? What edge profile, K…? (I’d go back to check the name but not sure I won’t lose my notes here).
I’m liking this idea very much as a way of improving the efficiency of a foil less deep V hull. Reducing leeway and draft!
“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.”
nice point!
best to all
and especially to Hugo and Proud Mary 😊
Simon