89er

[JulianB]

Rob, it's 2 and a bit months to Airlie, I possibly have 1 or 2 AGM's in Europe that I may need to attend, and I have this yukky feeling in the back of my mind not to go too short with the fin. That comes from WING's and 49ers, though with the 18teens way back in 1987 we did go really short and really fine with huge wings with a professional crew and it worked exceptionally.

Plus I am very sure we will pass ISO relatively easily, so we may not need anymore weight.

Alex, Darcy and I will just do the ISO test one day next week, and I will do things like pull the fin up, until it dose not pass, so we will know what is needed.

Once we have that empirical knowledge, refine my thinking, finish the bulb off, may even shave some more lead off, then some time in July when GT is back, do the whole test again with John Sturrock in attendance, send it off to John Swarbrick for certification, probably get my Cat 5 re done then also so we should be sweet, when we get to Airlie.

The gizmo that I got sent from HK is a Insta360 X3, pretty cool bit of kit, basically it will take 360° imagery all the time if you want it. Just a very upmarket GoPro, which I am taking as their hint that they want more vision. Trying to get the footage out of Port Stephens, also the B2B but to no avail todate. But I will get Alex to video our un-offical ISO test when we do it for you all to see. And if we go sailing mid week, it will be on-board. Also I had some more professional still and video (both drone and hand-held) booked, I need to get back onto that.

Got people wanting to build the boat, and some interest out of Europe, and here for boats. That was not the idea, but it could well be fun.

 

[Eoin]

Julian thanks for all the work you've done documenting the build in this thread. As someone with a background in sailing and engineering this stuff is fascinating. I'm in awe of your level of expertise in both, as well as the craftsmanship going into DP.

I met a certain GT on his holidays yesterday, wandering the docks in Ireland looking at boats. As we all do when in a new place! We had a nice chat about what you're doing and he said to log in and say hi. Hope you guys have a tonne more fun racing and refining things!

 

[JulianB]

Typical GT, talk to anyone, anywhere, amazing he has not been reported.

 

[Sidecar]

FWIW, I finally managed after 4 tries to get some videos showing the sail head vortices of my sails:

https://1drv.ms/v/s!Aky-jW86UoQLg0c82KUYA2D7MC_G
https://1drv.ms/v/s!Aky-jW86UoQLg0hlNGk8Qg0VzdbZ

In a previous video attempt, I did it without the jib spreader spar and the gaff batten reinserted, and the jib head streamed just the same, which surprised me. Maybe it was the presence of the mainsail? The windex reference arms BTW are set at 22.5 degrees AWA.

in the second video, I also managed to trail a streamer in the water to get an idea of leeway/yaw angle. What’s your verdict Julian?

 

[JulianB]

My initial reaction is not much leeway, but I have no reference point to make that judgment.
Maybe add a wand aligned with the CL so you can make a judgment.

Need to stress, I have not done this for 20 years, I last did it with Dad with 49ers, because MIT (as in Harvard/Ivy league) had a really big go at 49ers early in the piece and sort of said they (49ers) where impossible. Dad had a feild day! One of the many things they said was the fin was patently to small, so we streamed a ribbon out of the c'case, sure do a bad tack, AoA was up around 4-5°, but as soon as you got to 5-6knts it sort of snapped in to 2 - 2.5° and by the time you got to 7knts BS it was close to 1°.

The big advantage of streaming it out of the c'case is you have a reference (the rudder) so you know exactly how far off CL it is. I now know what to look for, but I was going to do it for the fun of it, next mid-week/weekend race with DP. Very likely with the light bulb and the existing fin, maybe in 2 weeks time.

Also you have a bit of a vortex. (ribbon of the top corner of your sail) During PS, with Nicky steering I had a lot of time to look around.
The leach ribbon 300mm below the Winglet flew very steadily, no vortex, but the 2 small tuffs on the winglet had some rotation. Mine is now sewn on, angle may not be quite right.

Need to get off the boat and look at it from a distance, maybe play around with the attitude of that.

 

[Sidecar]

My initial reaction is not much leeway, but I have no reference point to make that judgment.
Maybe add a wand aligned with the CL so you can make a judgment.

I have no centrecase or centreboard. My back was against the other weather lower shroud, so I my guess was zero yaw. I also have zero yaw when I fly the ama, you can tell by the wake and the fact that the front rudder is feathering at 0 degrees. The wake trail is more defined on my boat because of the narrow hulls with canoe sterns.

Definitely have a vortex on the mainsail, interestingly, I can change its character with different leech tensions. The relative steadiness of the jib head streamer was a surprise though…… It all needs more work and study, but hard to do solo with no one else around. One of the “problems” of living in the wild….

 

[JulianB]

It certainly looks like very little yawl or yaw, think I will stick with my fathers spelling. Yawl!
You obviously set up a transit, a reference, so it would be interesting to hear how you think you have managed to get zero yawl??? Any AoA of the "rudders"???

I was watching flow off a jib today (Farr 40) and with very little ease, the top ribbon behaved faultlessly, slight over trim and you could see the start of "span-wise-drift" [SWD]. Maybe some SWD is a good thing, maybe the flow at the front of the main that far up is a low pressure so sucks it clean. Farr 40 jibs are pin heads, and maybe North have got the camber ratios right.

I would be interesting to get your feedback on speeds with different trim settings. I was asked today about why I like what seems aimless mid week racing/sailing, and it's because it when you learn the most, because the unexpected becomes the expected, and you need to work out the answers, so you're sailing in the wilds of Tasmaina, besides being cool-ish could infact net so real insights.

Over on "Magic 25 mast rams" I have been asked to embellish my rational around rig tension and maybe this setting of the jib and possible over sheeting is some of the reason why, and I say this very surrealistically or dare I say generalistically that the looser you can run your rig, the better particularly in the lower wind speed you are. In the B2B we had some real fore-stay sag which only came to light when we went a bit deeper (to stay in the channel), far more than I would have expected or was prepared for. I left it, and the mast did not fall down, but I was cautious! Then again, think about Stars, and the absurd levels of f-stay sag they have, obvioulsy fast, particularly downhill.
Maybe (and this is upwind) as you ease the main, if you have your jib sheet set correctly (what ever that is) and you get a bit more fore-stay sag that the jib ends up with a bit of SWD (not sure if its up or down, on a Farr it's up, DP, hmmm) need to sleep on that, it's a good thing.

Maybe I'm talking shit!

 

[Sidecar]

You obviously set up a transit, a reference, so it would be interesting to hear how you think you have managed to get zero yawl??? Any AoA of the "rudders"???

The aft rudder is usually at 5+degrees, and definitely carries sail load. The forward one feathers or is set at zero. There is a difference between port and starboard tack due to shaft/tillerhead misalignment on the port tack forward rudder, which I will fix next time the boat comes out of the water, I need to drop the rudders out. You can see it in the first video.

In smooth waters and steady breezes, I can get a little bit of windward yaw by also putting some AoA on the forward rudder And maxing out the aft rudder. I also often steer with both rudders coming alongside a pontoon to crab closer in and also kill speed. And using both also makes for tight turns especially into the wind, where ama drag assists.

Whilst I don’t have a centreboard (I could fit one) I do have a chine runner, which works by restricting cross flow under the hull, and channeling it aft Instead. Having straight sides 300mm down to a 500mm wide flat bottom with a hard chine helps as well. And being a proa, I only need one. More here:

Jim Michalak's Boat Designs/The Index

Plywood Boat Plans and Essays

www.jimsboats.com

You are right though, the more you sail, the more you notice things, either by testing or by pure fluke or mistake.

FWIW, my rig is pretty slack. The boat does really well in lighter winds and flat water. It is rough water which really knocks the speed off. SWD on the jib has to be up, because it is canted ~ 26 degrees to leeward. Trimwise through the speed range, the mainsail behave pretty well, until i am over powered. It is the jib, behind me , which needs constant trim in terms of AoA and twist. The stronger the breeze, the harder you have to trim in.

 

[JulianB]

Hi all, we did the "trial" stability test today with smaller bulb on a reduced length, and sure, tip load was not huge but still very positive, and it passed, relatively easily.
Had the fin up 320mm, (because that's was the spacer I had from the B2B race).

So there is no confusion, I am talking about ISO 12217-2 Stability Compliance test.

I was pretty sure it would pass, but the only time I could get people was on the weekend and John Sturrock was unavailable so I did this unwittnesed, except Andrew (Dolly) Divola happened to be walking by and observed the whole thing. Dolly knows his stuff, so I have little doubt he could certify it if needed. More likely he will come for a sail, as dose John (S) want to.

I used substitute weight, so I pumped 450kgs of water into the bilge, then sealed it all up, and did the test, by the book.

I expect that I will re-do it with Mr Sturrock in attendance, with the bulb finished off and a new fin, early July along with re-certifying my Cat 5 certificate.

So, now, a few decisions need to be made as to whether we reduce the weight of the bulb even further, how long to make the fin, yad yad yad.

Been speaking with the team, we have a plan, but no decision has been made yet.

The size difference of the 2 bulbs is dramatic.

if you want to look



jB

 

[Bill E Goat]

Is it nearly worth getting rid of the bulb completely and having the lead encased in the bottom part of the fin, CofG not as low down but lower drag

 

[JulianB]

Is it nearly worth getting rid of the bulb completely and having the lead encased in the bottom part of the fin, CofG not as low down but lower drag

It's times like these that I really miss Dad.

The Timpenny had weight in the hull, and no weight in the Fin nor a bulb, and passed these sorts of tests easily, and it did this back in the 70's.

So we as a team have decided that the boat is pretty quick, and that lets not go to crazy and only change one thing at a time. So we have dropped bulb weight by 60%. And yes it passes ISO 12217-2 with the board at 1100mm. Next thing is to go sailing with the bulb, and we can raise and lower the board simply. Once we have done that, then make some decisions.

Got to admit, when it passed so easily today, Darcy said drop the whole bulb off and do the test again. We didn't do that, but maybe we are closer to the Timpenny than I would like to admit. Colin Thorn, may you rest in peace but get a bit of a kick out of that.

We get one shot at setting the boat up for Airlie! Don't know, but don't think we can get enough lead into the fin, and pretty keen on end plates, especially with a fin so short so this is a wait and see decision, with a very definite "use by date".

A little surprised it passed so easily, thought it would be closer, but alas, I don't know the limit!

jB

 

[Sidecar]

Is it nearly worth getting rid of the bulb completely and having the lead encased in the bottom part of the fin, CofG not as low down but lower drag

Getting rid of the bulb doesn’t preclude having an endplate. It just means that the end plate can be designed to do just the one job.

If one was to go down the flexible trailing edge route, getting rid of the bulb may not be so easy, in terms of both stability and endplating.

FWIW a couple of photos below from near the end of this paper:

https://www.ikarus342000.com/Antivortexp.pdf

Claims of ~ 20% increased efficiency. And the endplated version is pretty much what Julian posted upthread.

 

[JulianB]

If you haven't seen Dollies posts on fB, this is his shot from yesterday

Bulb in back home, I guess I start getting creative shortly.

 

[206]

Wow - that view makes the fin look tiny! Looks very fast as long as the flow stays attached

 

[JulianB]

Wow - that view makes the fin look tiny! Looks very fast as long as the flow stays attached

There would be just over 1m of fin (effective length, so from bottom of the boat to the top of the bulb) showing. When the fin is fully down it's 1440mm effective length and it's more than big enough at 7 - 7.4 knts which is upwind operating speed. We are very confident it operates inside the "bucket" drag curve, at 1440mm/7.4knts, which means it's laminar flow, so 2 - 2.5° AoA/yawl.

Over the next few weeks the plan is to lift the board to see how small we can go, we have techniques to measure yawl (which = AoA) and as long as we don't go turbulent (flow) then the shorter the better.

Boat is sailed flat, so excess length is just that (plus drag).

 

[chris foiler]

Thanks for the ISO 12217-2 very useful .Glad you pass so easily .

 

[kprice]

JB, for the flexible TE fin, what is the mechanical arrangement to control the deflection of the trailing edge?
Thanks...
KP

 

[JulianB]

JB, for the flexible TE fin, what is the mechanical arrangement to control the deflection of the trailing edge?
Thanks...
KP

In the past they have mostly been connected to the jib-sheet via a ring. You only need 20-40mm of movement, but it needs to be automatic.

On DP we have a self-tacking jib, and we use the 49er track and car because it's a tighter radius which makes it easy to adjust under load, so the outward load from the jib is sort of balance by the inward load of the tighter radius of the track, so I don't think we can rely on that to crank the TE.

Other option is the main-sheet hawse, so the traveler control system and there's plenty of load in that to do the job, and the other option is one of the swing straps. We have rope lanyards for adjustment, so it would be very easy to get a line in there which gave us say 40mm of movement and also un-cleated the leeward side. Thinking of putting a cleat in there, bit like a diode, once it comes on, it stays on until after you tack.

Last thing you want is on again - off again depending on how hard the wind is blowing (mainsheet) or swinging. You want it cranked and stayed cranked.

And sure, WRT downwind, it's more than likely it will over-lift due to the increase in BS, so all that happens is you pull away another 2-3-4° which open's the slots, could be a win-win.

Start on the foil next week, it will be interesting!!

 

[maartenvr]

Refer Kevin Dibley on Linked-in for research into tubercles on humpback whale flippers; you can turn those into lead filled appendages on your centreboard? byebye keel.

 

[Sidecar]

^^^^Dibley is not the only one:

Rudder Tubercles - Bieker Boats

Paul has designed rudder tubercles to decrease the tendency for stalling in certain cases. Drag is increased somewhat, but stall angle is increased and in the case of rudder arrangements that are likely to ventilate easily, the tubercles act as fences, reducing ventilation and subsequent flow...

biekerboats.com

Not likely to be useful on a centreboard/keel?