Here’s F C Tansley’s “Skylark” from the 30’s, a very successful 36R with an immersed transom.
Cheers,
Earl
Hi Earl -
a the risk of being tried for heresy, what are your thoughts (and experiences) on taking a older set of lines, and updating them with a fin keel, bulb and spade type rudder? How would they fare?
In looking at your post and hull lines, it would seem you would be keeping the above water lines (looks), but (perhaps) improving performance with an updated set of foils. Any thoughts? Anyone done this in the past and what was outcome if you know?
Thanks, Dick
Dick - it’s been done full-size on at least 3 occasions to my knowledge - 2 of them successfully.
The S&S 43 footer Clarion of Wight (Fastnet winner 1963) went up the Goodwin sands some time in the late 1960s. She was rebuilt with the contemporary S&S stern with bustle and trim tab. She was far more competitive than she was immediately before her adventure.
The Holman & Pye Half-Tonner Sootica had similar treatment and went from being a total dog to being good enough to win the EAORA championship (albeit in very talented hands).
The final example was the Parker designed Half Tonner Norsue V. She was a dog before and a dog after. The same could be said for most boats designed by The Abominable Fred.
Note that one of the reasons for success was undoubtedly a substantial reduction in displacement without any increase in rating.
A.
It works. Thom McGlaughlin (who teaches the plank on frame course at WoodenBoat School) has done it with a couple of designs. There is at least one successful free-sailing upgraded Skylark at San Francisco and I believe several in the UK.
Cheers,
Earl
Thank you both. This seems to open the door for some beautiful looking yachts to be updated to more modern foils. Especially for those looking toward on-water performance. With so many oder designs, the idea of taking the hull and making the change is something to contemplate.
I realize some would consider an older 12 Meter design with modern keel, bulb and rudder to be unacceptable. On the other hand, when sailing, does authenticiy really matter below the surface?
Many thanks for your thoughts.
It also occure to me that one of the nicest fin jobs was Tre Sang - an ex-30 Square Metre designed by Knud Reimers in about 1938. In her old age her sternpost went rotten and was cut out. She was then given a new spade rudder placed well aft. In this configuration she was quite cetainly the most exciting and responsive boat I have ever sailed despite being somewhat ‘parish rigged’- essentially a 45 foot 10R.
Go for it!
A.
as mentioned earlier,
I will have another go at this as the first one wasn’t bad.
Very well balanced circular hull form I would have to say!!
Immersed back end did not seem to show to much of a fuss,powerfull bow resisted diving very well…
Pretty silly…but hey,why not? cheap and hi tech.
Looks that the Cunning Kiwi and the Running Fat Man might be moving in the same direction!
I have got one with a much more estreme immersed transom, but by man with the rapid protyping machine, CNC miller, etc. is retiring on ill health very soon - so we’ll not stick our necks out.
Angus… as one cartoon character to another I cannot resist…
“All aboard the Skylark!”
http://www.thechestnut.com/noah-nelly.htm if you don’t remember, or didn’t watch kids tv in the 70’s in Blighty.
Back to our serious progamming…
Capt’n Pugwash
It appears from a lot of research that the Stevens Institute tank (then claimed to be the best in the world) got results from Chance’s fastback hulls that were consistent but totally at variance with reality - and was quite unable to explain why. Best theories at the time were that the beneficial effects were destroyed at larger sizes by ‘higher eddy energies’.
We’ll continue (cautiously) down the immersed transom route in Footy designs.
An intersting fact that I came across last night.
The original wooden prototype of the highly successful C.R.Holman designed Twister (approx. 28 feet) of about 1960 had a substantially immersed transom. Later production boats in GRP did not and were nothing like as effective in competition.
The plot thickens. I should have an immersed transom Footy sailing soon - I hope.
Question… should a substantially immersed transom be more or less vertical? I am imagining that a forward raked immersed transom would more likely create eddy currents along it’s immersed edge… or am I imagining things?
Dunno. Very good question indeed. Successful examples include vertical (Skylark) and swept back (Twister). Mariner’s was vertical.
Anyone got any good theories?
Having thought about it at some length, I guess (and I mean guess) that the ideal -or at least the safe route - is to have a constant change in pressure all round the discontunuity. Unfortunately the velocity/pressure distribution at the perimeter will almost certainly vary with speed. Further, if the discontinuity is an immersed transom, the shape of the immersed discontinuity will vasty with heel.
I think this may leave us with slightly greater theoretical understanding but little closer to a ‘cook-book’ ready use solution.
close to a test sail of my Bottle footy.
displacment is 600g,certainly has an immersed transom Mariner style.
Beam is 80mm and lcb will not shift on heeling(its a cylinder after all)
rudder is 2 layers of balsa glued with epoxy,light and stiff enough.
Fin is the bottom half of an IOM mould I had,it is moulded in “Microlight” filler,no glass or carbon reinforcment at all,is quite light and stiff enough.
Ballast is longer than my “normal” shape and comes in at 250g.
Rig will be my balanced Una type.Boom is 2mm ply epoxy saturated,mast is western red cedar,oval shape.about 6 x 4mm at the bottom and 2x 2 mm at the top.
General construction is very easy,a 6mm dowel runs through the centre of the bottle.a tube is mounted through the dowel at the stern for the overhanging rudder.The fin is siliconed into a slot in the bottle and glues to the dowel.The servos are fastened to the fin sides,the mast tube glues to the central dowel as well.Alignment of all the parts is very easy with this central dowel.
a Plastic pet food container is taped onto tthe front to form the bow
Any reports on how the immersed transom works Brett?
Its not been wet yet and won’t be this weekend either,A full weekend of “Bigboat” sailing coming up.
Very interesting thing. I came across a video of an American Footy sailing the other day. Ehen heeled its transom is quite extensively immersed. Most of the time the wake looks beautiful and the stern wave is being druiven unnaturally far back - but not always. This suggests that a narrower stern with more constant peripheal pressure differences is probably better.
The other thing that has emerged from recent correspondence in other forums is that the cut-off point of the emerge sterm must be a knife edge. We are modiifying the Dingo mould to fit a 2 mm scoop stern with near razor edges
Interestingly enough my current boat has a 6mm immersed transom,this boat has the best internet course time yet posted.
Is the current boat really faster than boats of the same design without the transom immersed?
Andrew Cook in AUS has a nice example of a footy using lines from Angus with quite a deep immersed transom,The wave train is very flat.
Times under 6 minutes on the internet course equate to froude numbers above 0.4…this is well into “forced mode” showing that these boats are very fast indeed for leadmines.
Food for thought.
It’s not really THAT surprising - the Stephens onstitute tank was probably the best instrumented ijn the world at the time Mariner was tested - and the absolute mesurements from the tank showed the fastest 12 m model ever tested. The problem only arose when trying to scale it up from 1 m waterline to about 43 m.
I seem to remember Barrett saying a long way back down this thread that his father drinks with Britton Chance. It would be interesting to know what Chance thinks was going on at model level.