89er

[JulianB]

BTW guys, really love this banter, many heads are better than one, as long as we don't start designing by committee, and this boat is for Me, Myself and I so that ain't going to happen!

neuronz, if I can just negate yaw drag this will all be worth it!

Attach a rope to the front of a 49er weighted up to sailing weight (approx 310kgs) and pull it through the water at 7.5 knts will take about 18kgs of load.

DP has about double the SCP of a 49er so I'm guessing to pull it through the water at 7.5knts will take double if not a bit more force. But DP's mixture of drags, I'm guessing that the hull component will be up around 50% (up from 44% for a 49er) of the total and that the yaw component will be up.

Starting to get uncomfortable with shooting off at the mouth without back up data, so I did go hunting and I found this.

So this was done in October 2008. It's a 49er loaded to 310kgs and it's nose down, what my father would have called 4th mode.
Green is towed straight.
Magenta is towed with a yawl (my fathers spelling) of approx 3°.
I went even further hunting and got the numbers at 6knts, 8.23kgs and 10.8kgs respectively.
10.8-8.23 = 2.57/8.23 = 30% increase in drag due to yawl drag of a 49er in 4th mode.

If, and I accept it's a very big if, you carry those 49er drag curves fwd to 7.5knts which appears to be DP's sweet spot, then that 2.57kgs extra to drag it sideways at Yawl° would probably grow to 4kgs.

If I now go to the composite drag curve of a 49er and at 7.5knts add another 4kgs of grunt it's the best part of 3/4's of a knts in extra BS.

Ok in the case of 49er, they would more than likely take that in BS.
In the case of DP, we would most likely take that in the form of increase pointing angle.
Matters not, you in for a pretty big increase in VMG.
And DP's Yawl Drag signature/% is likely to be bigger than a 49er.

I'm not reducing the area of the fin, this is just negating the Yawl Drag component.

Other interesting tid-bit is jib-sheeting angle. If you look at jib-sheeting angle as the angle between the Yawl Angle and the jib-sheet to the CL then if you think your sheeting at say 6°, your really sheeting at 6° + 2.5° = 8.5°.
Zero Yawl due to asymmetric fin, you have to step your jib out 2.5° which frees up the slot, etc etc.

Sidecar, yep tapering fins works, mine at the keel is 12%, and the top of the bulb is less, I don't have my file infront of me, but guessing it's 8.5-9%.

Need to go capsize a boat, see if 74kgs is enough at 1.4m fin span.

jB

​

 

[Bill E Goat]

Would having a trim tab on the foil be worth looking at ?

 

[JulianB]

Would having a trim tab on the foil be worth looking at ?

Quick answer is hinge drag.
My belief is that hydrodynamicaly hinges and inconsistent surfaces (as in not fair), cruel any benefit.
Aerodynamic is far more forgiving.

 

[neuronz]

BTW guys, really love this banter, many heads are better than one, as long as we don't start designing by committee, and this boat is for Me, Myself and I so that ain't going to happen!

neuronz, if I can just negate yaw drag this will all be worth it!

Attach a rope to the front of a 49er weighted up to sailing weight (approx 310kgs) and pull it through the water at 7.5 knts will take about 18kgs of load.

DP has about double the SCP of a 49er so I'm guessing to pull it through the water at 7.5knts will take double if not a bit more force. But DP's mixture of drags, I'm guessing that the hull component will be up around 50% (up from 44% for a 49er) of the total and that the yaw component will be up.

Starting to get uncomfortable with shooting off at the mouth without back up data, so I did go hunting and I found this.

View attachment 581155

So this was done in October 2008. It's a 49er loaded to 310kgs and it's nose down, what my father would have called 4th mode.
Green is towed straight.
Magenta is towed with a yawl (my fathers spelling) of approx 3°.
I went even further hunting and got the numbers at 6knts, 8.23kgs and 10.8kgs respectively.
10.8-8.23 = 2.57/8.23 = 30% increase in drag due to yawl drag of a 49er in 4th mode.

If, and I accept it's a very big if, you carry those 49er drag curves fwd to 7.5knts which appears to be DP's sweet spot, then that 2.57kgs extra to drag it sideways at Yawl° would probably grow to 4kgs.

View attachment 581156

If I now go to the composite drag curve of a 49er and at 7.5knts add another 4kgs of grunt it's the best part of 3/4's of a knts in extra BS.

Ok in the case of 49er, they would more than likely take that in BS.
In the case of DP, we would most likely take that in the form of increase pointing angle.
Matters not, you in for a pretty big increase in VMG.
And DP's Yawl Drag signature/% is likely to be bigger than a 49er.

I'm not reducing the area of the fin, this is just negating the Yawl Drag component.

Other interesting tid-bit is jib-sheeting angle. If you look at jib-sheeting angle as the angle between the Yawl Angle and the jib-sheet to the CL then if you think your sheeting at say 6°, your really sheeting at 6° + 2.5° = 8.5°.
Zero Yawl due to asymmetric fin, you have to step your jib out 2.5° which frees up the slot, etc etc.

Sidecar, yep tapering fins works, mine at the keel is 12%, and the top of the bulb is less, I don't have my file infront of me, but guessing it's 8.5-9%.

Need to go capsize a boat, see if 74kgs is enough at 1.4m fin span.

jB

​

I looked into rotating keels in the past which is basically the same thing, taken to the extreme for the case of very wide hulls. You have a very small yaw angle already, so it might be borderline, but what I found was that the real benefits were in the aerodynamics. As you said your sheeting angle increases as you are rotating the hull away from the wind, orientating the lift vector more favorably. Now with added speed the apparent wind angle gets smaller again and you need to be able to make use of the power from a righting moment perspective but this is were I found the gains. The problem is that there are so many factors involved that only a VPP will give you an exact answer.

 

[JulianB]

The problem is that there are so many factors involved that only a VPP will give you an exact answer.

Hi neuronz, firstly can't say I agree with you above comment, I have never had a VPP give an exact number, in-fact, most VPP have so much fudge factor built in, they can only be called a in-exact science, but I get where you are coming from.

To that effect, Rob (Sidecar) has a mate Rick who has done a whole Java Foil predict program for which I an exceedingly grateful.

Again, absolutely love this stuff and the insight that comes from others taking a slightly differently slant on the same problem. Rick did that, introduced AR to the equation, and modeled the actual section and also added some thoughts on his POV and possible tweaks.

Both of us believe that the really big advantage comes from negating Yaw Drag.
The 2nd highly probably significant advantage will come form a reduction in the size if the fin due to a substantially increase in CoL. (almost double)
3rd is what we already spoke of, being a increase of AoA on all the sails off approx 2-3°, so this is the jib-sheeting angle, but also carries across to the main. Spinnaker down wind, interesting possibilities, the boat will crab to windward, so do you zero the TE or do you simply pull-away another 2-3-4° lower.

Time will tell.

4th that I had not thought about is you can dramatically sharpen the LE of your fin, lowering induced drag. That's a new bit of understanding. May be building a few fins, but this is what this boat is all about.

Certainly Rick has given me a lot of confidence to reduce foil length by at-least 200mm. I'm very sure Punisher will even be more happy as if he can cut 300mm off, where he sails (mouth of the Murray River) he won't have an issue, won't have to lift at all. Need to start on Rudder length, that may become the issue.

Next step, capsize test with 74kgs bulb weight, I can hang a bucket with 10kgs on the bulb if it marginal, or 2 buckets, we will get real empirical info I'm sure that Tubby and Brian (Punisher) will be ecstatic for.

Happy to share this with all of you, inc the video, so there are no innuendo's!

Great few days, Rick, plus we won (Wednesday beer can race) last night, really relaxed plesant sail and got fastest time over all the boats by 3+mins. Really good day at the office.

 

[neuronz]

Hi neuronz, firstly can't say I agree with you above comment, I have never had a VPP give an exact number, in-fact, most VPP have so much fudge factor built in, they can only be called a in-exact science, but I get where you are coming from.

To that effect, Rob (Sidecar) has a mate Rick who has done a whole Java Foil predict program for which I an exceedingly grateful.

Again, absolutely love this stuff and the insight that comes from others taking a slightly differently slant on the same problem. Rick did that, introduced AR to the equation, and modeled the actual section and also added some thoughts on his POV and possible tweaks.

Both of us believe that the really big advantage comes from negating Yaw Drag.
The 2nd highly probably significant advantage will come form a reduction in the size if the fin due to a substantially increase in CoL. (almost double)
3rd is what we already spoke of, being a increase of AoA on all the sails off approx 2-3°, so this is the jib-sheeting angle, but also carries across to the main. Spinnaker down wind, interesting possibilities, the boat will crab to windward, so do you zero the TE or do you simply pull-away another 2-3-4° lower.

Time will tell.

4th that I had not thought about is you can dramatically sharpen the LE of your fin, lowering induced drag. That's a new bit of understanding. May be building a few fins, but this is what this boat is all about.

Certainly Rick has given me a lot of confidence to reduce foil length by at-least 200mm. I'm very sure Punisher will even be more happy as if he can cut 300mm off, where he sails (mouth of the Murray River) he won't have an issue, won't have to lift at all. Need to start on Rudder length, that may become the issue.

Next step, capsize test with 74kgs bulb weight, I can hang a bucket with 10kgs on the bulb if it marginal, or 2 buckets, we will get real empirical info I'm sure that Tubby and Brian (Punisher) will be ecstatic for.

Happy to share this with all of you, inc the video, so there are no innuendo's!

Great few days, Rick, plus we won (Wednesday beer can race) last night, really relaxed plesant sail and got fastest time over all the boats by 3+mins. Really good day at the office.

Hi Julian,
I guess it depends on the VPP. A 'normal' VPP based on regression formulas will not give a very precise answer and mostly show trends. However, you can also use a VPP to postprocess your empirical and measurement and CFD data and then things really start to get interesting. It obviously requires modelling/supplying the data of the effects you want to exploit. For example I doubt a normal VPP will correctly capture the effects of windward heel or a twisting keel fin. But with a boat specific VPP I think you can do a lot.

 

[JulianB]

OK, neuronz, what Rick has done is amazing.
What it will allow me to do is take what I have got, and attach a value.
Then alter that sum with a different value assuming that BS in = BS out (and I mean that in a very respectful and grateful way) What I am trying to say is that Rick has generated CoL and AR's for the existing fin, using a process. If he now uses the same process and generates new CoL's for a different section, then I should have I hi degree of confidence that I am comparing apples with apples.
Even if Rick's numbers are windily fanciful, and I have to say, his symmetrical numbers appear that, but when I plug them in to my 30 year old foil size program, it works, so maybe I am just way to pessimistic.
Then if he then dose his calculation/process on the new section, the flexible TE one, using the same process, even if it seems implausible, then the results, even if I discount them say 20% have a hi degree of credibility.

Maybe I'm just out of sorts here and maybe I am just getting overwhelmed with data/ideas, but I have always thought these sorts of foils operated at 1/2 - 1m RN. Looking at data with the RN just shy of 2m, so double, and a AR of 7 - 7.5 is a bit confronting. Getting a increase in CoL of 2 1/2 times the SYM foil, sure a drag increase, but not a lot and a sweet spot (in CoD) at 0.25° so that means virtually no yaw drag.

I can't punch holes in the data, and I assure you I am trying.

BTW, had a great day, we had all but canned the Bay to Bay Race. I really wanted to do this but logistically, it was getting way to hard. Chance Fb encounter last night, we are now booked in for dinners, breakfasts & beds (on a house boat) and I have just entered the B->B race.

These guys helping us, are all 30-40. I'm the youngest on my boat at 66, may have to teach them how to drink, (that way we may stand a chance, get them pissed, better still on Negroni's). But that's what this boat is about and this sort of playing around with foils, that I have wanted to do for so many years.

It's a month away, we won't have new a new flex TE fin by then, we may have a 74kg bulb.

Those who don't know Australia or Queensland, who's abbreviation is QLD which also stand for Quite Little Drink, the Bay to Bay is from Tin Can Bay to Hervey Bay, it's over night up the Sth West Passage inside Fraser Island, you over night on Sat night on Houseboats and it's mandatory that you start sailing the next day with a hangover! After-all your in QLD!

 

[Kenny Dumas]

I’m surprised it works at 0.25 degrees, as I visualize pretty symmetric flow (no lift) from the fixed part of the keel and the flex section does all the work. I guess that means all the forces are in the flex as well?

 

[Sidecar]

One thing is pretty certain, the more asymmetry in the foil, the more lift produced. So the bigger the flexible TE (as a proportion of chord length) the more lift is likely to be produced. If you look at the various nearest applicable foil sections on line, most have a max chord at ~ 30% which also means a blunter leading edge. Julian’s foils (possibly out of structural necessity) have a max chord of ~ 40%. If you add a finer leading edge to that you may well have a superior foil on paper, but one which is less forgiving or performant in the water?

I referred to Tom Speer upthread. If you look at his data on 2 way proa foils, because the max thickness chord %age is fixed, it is maybe easier to see the %age differences for symmetric vs asymmetric sections, and fine leading edges vs fuller leading edges and perhaps can draw conclusions. Speer used Rn 1,000,000 for the calculations BTW….

APPENDIX A, PROA 1 DATA

There are 3 sets of data, with the third set being his conclusions for the optimum. The link is for the first set, the others you can get from his home page.

 

[JulianB]

Rob/Sidecar, thankyou, 100% agree with your comments.

To embellish that further, go back to Tuesdays post (by me) look at the graphs of the red foil section, and at 0° AoA it's still generating 0.5 CoL which is more than my existing sym foil generates at 2.5° AoA.

Now that I am doing the Bay -> Bay, I have a month. Not a lot of time so looking at computer time at nights on Flexiable TE's but need to get a 74kg bulb organised and a ISO reg 3 test, among a plethora of other bits and pieces.

 

[Sidecar]

In your shoes, once you know what bulb weight you need, I would make and adapt a Bulb C to match. The lower CoG will be a safety margin. Filleted as suggested if you decide to stay with fixed TE.

 

[Rantifarian]

A forward scanning sonar module might be more appropriate at bay to bay, what's your draft again? Sometimes it's nice to have another boat leading the way in a place like that, not an option for your rocket ship though
I recall watching the ultimate 30 having all sorts of fun trying to get through the flats one year. Half the crew on the wing, the rest sitting in the tender off the houseboat, pulling on a masthead halyard.

 

[he b gb]

^^ so true. The dogleg to Ungowa/ South White Cliffs is forever changing and the beacons are untrustworthy at times. Sure helps to have local knowledge on board though!

 

[JulianB]

It's about 240mm form the WL to the keel at the fin, another 1440mm to the top of the bulb, and the bulb is 160mm in dia.
Think the official draft is hi 1700s.
We have the capacity to lift it simply while sailing, 300 - 400mm, and sail with it raised.
May have only a 75kg bulb by then also.
Plus 2 of the guys onboard have done it 6-7-8 times, so we should be 👍

 

[Berndty]

It's about 240mm form the WL to the keel at the fin, another 1440mm to the top of the bulb, and the bulb is 160mm in dia.
Think the official draft is hi 1700s.
We have the capacity to lift it simply while sailing, 300 - 400mm, and sail with it raised.
May have only a 75kg bulb by then also.
Plus 2 of the guys onboard have done it 6-7-8 times, so we should be 👍

Jb the Shaw touches bang on 1.7 on the sounder and we get through most years without issue. If we do touch its only sand, and it's a touch if you stay in channel. I think they are moving sports boats to the 1st start Sunday at 7am to get the best out of the tide. They are also laying marks as gates at the narrow part of the channel to keep you off the banks.

 

[JulianB]

I did it many years ago on Trilogy, we also did the City to Surf (on Trilogy) and I have wanted to do it (B-B) on a SportsBoat for many years, few false starts with Perire, anyway, they have my entry, think we will be 5 up, But that's Shane's bag, I'm just supplying me and the boat. Slightly under cooked on crew, all mature, so that could be a issue, but looking fwd to some sailing and lots of camaraderie! It's what I built the boat for!

 

[he b gb]

I did it many years ago on Trilogy, we also did the City to Surf (on Trilogy) and I have wanted to do it (B-B) on a SportsBoat for many years, few false starts with Perire, anyway, they have my entry, think we will be 5 up, But that's Shane's bag, I'm just supplying me and the boat. Slightly under cooked on crew, all mature, so that could be a issue, but looking fwd to some sailing and lots of camaraderie! It's what I built the boat for!

Ha,Was that the B2B where Keith did the big handstand on the tight leg just before Gary’s anchorage and then parked on a sandbar and was late for the start on the second day and said he would never do a B2B again?
Vivace is an awesome boat and always seemed to be way ahead in the monos!
Followed the race last year as a spectator on a mates cat, will try to talk him into it again so I can see DP in action. Last year’s race was mellow with not much breeze and both down on fast boats in both the sports boats and multihulls.

 

[JulianB]

I can't remember doing a hand stand, but I can remember ploughing the bottom, a bit, both on the B2B and also C2S. Maybe I went a more genteel year!,

The big foil on Trilogy was deep, well over 2m and it started 400-500mm below WL.

 

[he b gb]

I thought Trilogy had only done the one B2B? Could be wrong though. Do you remember if Stewart Bloomfield (engineer/designer for Crowther) was on board as he was aboard for the big handstand.

 

[Bill E Goat]

B2B is a great race, we had 8 E7's one year and all stayed on a houseboat. Only problem is its a lot of mucking around to get in 6-8 hours of sailing over 2 days. Less for the faster boats, but when it started the boats weren't fast enough to do the whole trip in one day