Anyone remember the Britton Chance designed 12 metre Mariner - with two immersed transoms. She was a crashing failure but some of the ideas behind her stern could be applicable at Footy sizes/speeds.
Anyone know where there are any pictures of her afterbody?
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Mariner’s second immersed transom was called a “burble crease” if I recall correctly. I built an M class hull with one back then, inspired by the photos and the explanation of its purported gains in efficiency. My effort was an embarrassing failure (like Mariner’s) and taught me the valuable lesson not to put too much trust in the theoretical without ample physical proof to back the assertions.
Conceptually, the burble crease was supposed to induce the separation of a vortex to increase the lift effect of fluid flowing over the hull, much the way lift works on a boat’s sails. For more info on sails and airflow read “The Art and Science of Sails” by Tom Whidden, published by St. Martin’s Press.
I think that the Footy, because of the extreme curves along the hull to incorporate its relatively large displacement for its length, could not really take advantage of the theoretical efficiency gains. The way that a burble crease might help a Footy would be to stall the stern as the boat started to nose dive, the increased drag pulling the boat back to horizontal trim. But this would come at the price of speed. Quite a trade-off. Also, since I’ve tried a T-foil rudder to control the nose down attitude offwind to little effect I can’t say that a contrivance in the stern would induce enough drag to evoke horizontal trim, what with the forces involved.
Of course, as I stated before, I am only theorizing based on my bad experience with the idea. Anyone else out there who wants to build a mini Mariner and manages to wallop all comers is certainly welcome to do so and will impress us all.
OK - so what I would call a waterfall effect. Intuitively witrh water much ‘stickier’ at Footy speeds, sizes, a waterfall might be more stable.
As with anything with a 12m there was a rule tradeoff - it was a means of reducuing girth differences at a given displacement and hence increasing the prismatic coefficient - result Mariner had more sail than any other contemporary 12. In Footy terms this means putting volume into the stern and hence reducing the pot belly and associated extreme curvature.
However, from what I remember at the time there were, as you say, advertised to be positive hydrodynamic benefits - and there was a huge tank programme to back it up. Most of the wise opinion I have heard is that the thing failed because it was not possible to model the stability of the waterfall when pitching. With much less energy/momentum churning round the system, is this true with a Footy?
The other related discontinuity was the ‘Davidson crease’ invented by Lawrie Davidson and used by him, Ed Dubois and others to cheat the IOR rule. It consisted of an acute S-bend in the buttocks between the inner and outer after girth stations. I have never heard anyone suggest that it had any benefit other then reduucing rating more than speed.
Any futher wise thoughts?
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Angus, you are more versed than I in the intricacies of rule bending in the big boats. I would imagine that the hydrodynamics that act on a Footy hull, what with hobby-horsing, nose diving, and adverse reactions to broadside waves would be very hard to model on a computer. I think the best way to ascertain any performance benefits to be gained is to build a boat and test it. Of course you would need a benchmark to test against, currently my achilles heel, and I think probably the same for many people trying to design these boats from intuition rather than experience. Like they say, we’ll know more later.
When I said model, I meant model in the tank! This was in 1973-74!
A chopped of stern boat is two steps down my develpment path. Your opinions are highly appreciated (and that’s not simple brown-nosing) - but what I was largely looking for was some pictures of Mariner’s tail end to refresh my memory.
Yes, it’s all intuitive, but a little basic mechanics might push us in the right direction faster than none.
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Here you find a pic of Mariners transom: http://www.12mrclass.com/cms/index.php?option=com_zoom&Itemid=444&catid=106
I cannot see more than one underwater transom on the pic?
Does anyone out there know where to find the measurment certificate for Mariner.
I was told by a designer who was involved in 12mR design at the time of Mariners apperance, that though the transom was not a succes it is difficult to judge because there where other serious problems with the boat. Poor RM should be one of them.
Thank you. If you look closely, the aft/upper immersed transom is where the white-painted bottom ends.
It is interesting what you say about low RM. From Chancegger, his first 12 for Baron Bich, Chance always seemed to be ignoring gravity!. The fact that there was outright war between Ted Turner and Chance cannot have helped either.
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The upper small transom is then placed at the position of the aft girth station in order to reduce measured length/increase sailarea.
I have used this trick with positive result on a 2,4mR I built some years ago.
The big one is there to increase volume/bustle aft in order to fool the waterflow that the boat is longer than it actually is. I read in an article that the the testing done in tank showed positive effect. Models probably 1/3 of full size (6-7m). Scale effect might have tricked the designer.
I have rebuilt my 2,4mR to a similar shape but not yet fully evaluated the boat. The purpose is double, fooling water/increasing volume - more lead in the keel for better RM
Hopefully next spring will let me get on testing this design.
I have always suspected that the flow that was suposed to build up round the lower transom could not do so in the rather confused seas off Newport - overall flow direction over the hull changing too rapidly. This might be less of a problem at low Reynolds numbers: less inertia.
The Davidson crease, which looked rather like crease under the tail of the 12 m Sverige but more concentrated gore and aft (it was basically athwartships), was certianly a race winner under the IOR although I suspect that its only virtue was to fool the rule into believing it was much shorter than it actually was.
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I actually did a short test on my Marineration of my 2,4 in 6-8 knots/flat water just to check if it was way out before completing a rather radical rework of the entire structure of the boat.
During this test there was no sign of turbulens behind the boat and compared to bench mark boats I was doing ok.
This was the second version. The first was more like an IOR bustle but that did not look good in light conditions. You could see a lot of turbulence in the track of the boat, though driving hard down wind in 20-24 knots was pretty thrilling as the lead sled was surfing a lot easier than before. This led to the desicion to go all the way and marinerize the boat.
In my mind its more like the bigger the transom gets the faster you need to go to take advatage of it and a 2,4 is a lot faster than a 12 relative to the area of the transom.
If I recollect it right the IOR kind of bustle used to be a lot more developed on the smaller boats like the 1/4 tonners than on a 2 tonner, probably because the price to pay was higher on the bigger boats.
HM.
What was Turners famous quote? “Even a turd is pointed at both ends”
Seriously though…in the full size yachts I race (trailable sportsboats) ther are many fast boats with well immersed transoms at rest.
I also know of an IOM which finnished 2nd at an IOM world championship with the transom immersed 1cm at rest( a windy championship)
all powerboats ( planing types) have immesred transoms.
Footys are perhaps quite fast for their size,perhaps a higher prismatic and immersed ends would not be so slow?
I must come clean and tell of an experiment…you will all laugh , its sounds worse than it is.
I built a Footy from a plastic soda bottle.I won’t go into the actual details but it involves another plastic container on the front as well,kind like the stollery bottle yachts.
Truth be told a nearly half immersed drinking bottle was not so slow…my first attempt was rather crude ( I had a 10 year old helper!!) and was suffering from a leaky fin/bottle join,but never the less showed a fair turn of speed and some nice habits.I will revisit this again at some point with a better attempt.
Position of bustles on smaller IOR boats is very equivocal - I think mostly because it was appreciated much earlier at say 1/4 Ton size that the IOR did not really favour steamrollers. The SHE 31 (I think S.31 in Sweden) had virtually no bustle, but it was originally designed to the RORC rule. I know for a fact that the David Thomas Elizabethan 9 m had the bustle eliminated during tank testing over David Thomas’s dead body. The last production S&S half tonner, which was heavily bustloid, was a disaster - but the one tonners of the same period (Columbine, America Jane) weren’t much better! The only unequivocally successful small bustloid IOR boats I can think of are the Stehen Jones ones such as Odd Job and Supernova.
However, everything you say confirms that the waterfall effect does work at small sizes, at least in some circumstances.
On ends Brett, the fist fight between Ted Turner and Britton Chance allegedly started rather like this.
'Say, Britty, do you know why there ain’t no fishes with square asses? It’s ‘cos all the fishes with pointy asses swam faster and ate the fishes with square asses’. ZAP
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A feature of Mariner that I never knew about if it’s correct.
In the picture on the link you refer to she appears to have a chine rather like a Scampi or Norln 41 (artually I think I may remember it - but it might be my imagination!). Is this an artifact of the light or is it true?
I think we are probably agreed that in order of cleverness Mariner was in the same class as Constellation, Intrepid, Australia II and Stars & Stripes 87. A very clever boat in which things did not pan out properly.
Where in Sweden are you? I go to Stockholm on business from time to time and it might be interesting to have a beer or two.
Angus
Angus Im living in Gothenburg so if you pass by maybe I could get you a ride in my 2,4mR with Mariner transom.
To be honest I was not aware of the chine either. I have been trying to find more pictures and preferably the lines plan for Mariner on the net but it doesnt come easy.
This is the trend of the day so in that sence the designer was well ahead.
If you look at the 5,5 the hottest boats of the day they could just as well have been fully chined, built in plywood.
The new Victory challenge AC boat looks almost like a huge Starboat.
It seems to me that as the building tech gets better and better, increasing stability for same displacement, volume is taken off in the middel part more straight lines and higher cp.
Maybe I am wrong but did not Ron Hollands successful Mazanita 1/4 ton feature a pretty nasty stern?
I used to sail Elvström/Kjaerulfs 1/4 ton and 1/2 ton and they where just about the worst of them all in excessive IOR rule cheating.
HM
If it’s easier, write in Swedish.
Yes, many of the best 5.5s (which at the time were mostly desiged by Chance) had some very angular hulls. I think that the 1968 Olympics were won in the 5.5s by a Chance designed Swedish boat called Luv with what was virtually a chine hull in its afterbody.
In principle Mariner’s rating certificate should be available from whatever the IYRU now calls itself.
Higher CP is obvious: the more efficient the boat, the higher its average speed/length ratio round the course -> higher CP. I’m curreently interested in Footies (heavy, non-planing boats - look at metre-boat exoerience). The problem is to stuff quite a lot of displacement into a shape that does not look like an over-fed pig - hence my interest in merchanisms for moving displacement out of the ends.
I do think I remember Mariner having a chine. Look up some old magazines!
Get to go to bed.
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If it’s easier, write in Swedish.
Yes, many of the best 5.5s (which at the time were mostly desiged by Chance) had some very angular hulls. I think that the 1968 Olympics were won in the 5.5s by a Chance designed Swedish boat called Luv with what was virtually a chine hull in its afterbody.
In principle Mariner’s rating certificate should be available from whatever the IYRU now calls itself.
Higher CP is obvious: the more efficient the boat, the higher its average speed/length ratio round the course -> higher CP. I’m curreently interested in Footies (heavy, non-planing boats - look at metre-boat experience). The problem is to stuff quite a lot of displacement into a shape that does not look like an over-fed pig - hence my interest in merchanisms for moving displacement out to the ends.
I do think I remember Mariner having a chine. Look up some old magazines!
Get to go to bed.
A./
turner didn’t say that about mariner, it was said about the '95 us defender stars and stripes. i’m not even sure it was turner who said it, but whatever. anyway, Mariner was a DOG like none other! Brit may still have nightmares about that one… lol. if you what to know every last reason why us 25 never had a chance of winning the trials let alone the cup, or you want pics of the thing read/find “the grand gesture” its about the mariner fiasco. if you want to look at pretty 12s then look at the freedom’s [us 30] intrepids [us 27] vims, weatherlys, even the plastic fantastics and aussieII were better looking! [and II had the big hump under the water line]
but that is just my humble opinion… lol:devil3:
Got the book. It’s fascinating. Did poor old Mariner have problems! Don’t write off the funny stern just like that.
I had a conversation with David Pedrick who has been deeply involved in 12mR developement during this era and since. He was working for S&S at the time and did much work at the Davidsons test facility. His comment on Mariner is summed up in the following statement.
“It may well be that the flat-cut stern of Mariner was effective on a model with a 1m waterline passing through still water in the model tank. In real life, however, Mariner’s stern was worse than towing a bucket – more like an oil barrel”.
His own testing with big bustles with the 1m long models that was the standard of the time is said to have shown erratic and unpredictable results and his conclusion is that those tests where not useful for any trustworthy results.
Hence the testing indicating benefits for the Mariner shape was misleading because of poor quality of tests.