I’m aware that there has been numerous threads on hull design in this forum, but they appear to be several years ago. There seems to be a massive shift to chine hull shapes and combination’s of chines/round sectional shapes on almost every modern performance sail boat, including r/c designs.
To my way of thinking the only benefit seems to be achieving more surface area in the aft sections to encourage a boat to plane. On the r/c scene about the only class that I’m aware of that should plane off wind would be the Ten Rater. However I believe that almost every International One Metre Class yacht designed over the past couple of years has a chine in the aft quarters.
I’m not convinced that IOM’s plane frequently enough to use the chine, surely chines just increase wetted surface/drag. In the IOM class where wetted surface is king this just seems wrong.
My question is why has this massive shift in design occured and what other than giving a hull more surface area to plane on happened? Or have I alredy answered my own question?
In my opinion. wide flat stern sections, whether hard chine or not, are questionable in R/C yachts… Virtually all planing dinghys have the abililty to move the weight aft (ie crew)… and/or use a spinnaker to lift the bow… and get the flat aft sections to have a positive angle of attack relative to the surface of the water… Model yachts “plane” (more properly exceed hull speed) on the forward sections of the hull, so that is where the lift is needed… Unless you can move weight aft and/or alter the trim of the yacht I don’t think you will ever see an R/C yacht plane in the same manner as an Aussie 18…
Ten Raters (and Marbleheads) “plane” in the same manner as a multihull… They simply outrun the stern wave…
I can’t say that I’m a fan of the aft chine fad. In a sense this started with Bantock’s Paradox and has snowballed from there. On the paradox I believe that the reasoning was that it would help the boat track when heeled and reduce side-slipping, so it had nothing to do with inducing a plane on a run. Bantock has a lot of influence so the herd naturally follows.
I will say that I moved toward more volume aft as I developed my boats, not to get them up on a plane but to keep them from squatting downwind and dragging their sterns. Like you Bob I used U shapes aft.
I did design one Marblehead, I think it was my third maybe, that had aft chines extending from between sections 7 and 8 to the transom. The boat was my Cakewalk design which debuted in the 1980 Worlds in Ottawa. Did really well but it was more do to the faired in trim tab on the keel fin that the boat I’m afraid. The boat never finished the race. Squall winds ripped through the fleet and tore the rig off Cakewalk and split the upper half of the deck back to midships effectively ending my campaign. At the time I was in a three way tie for the lead.
they are more commonly used on full size boats like the VOR70, Open60 and even smaller ones like the mini transat 6.50m. Whilst I can understand to have them going from the bow to to roughly mid-ship not sure about the actual advantage or purpose in the aft sections. I’m sure there is a specific purpose but not sure. Talking to some of the IOM sailors who have GB’s design they claim to have more power after a tack than a U shape hull. Not sure about the actual benefit of these in 1m hulls !!!
I find myself quite competitive with Ian Vicker’s design V6 - though I struggle a bit in the light stuff - bizarre cos the boat is supposed to do well in the light conditions. yet I get better results in the medium to heavy wind. Love a bit of a chop as the boat powers through. did 2 races in winds over 34 knots last month - though it was a bit survival as a lot of the boats had to retire for one reason or another due to breakage. I stayed out and had a blast. was surfing down the waves and made really quick times on the run. Though the beat was a bit of a struggle. In particular to tack as I almost had to counter steer to get the boat to reverse to complete the tack.
did have much experience sailing against designs like the paradox but will soon as one of the skipper here ordered the brand new design replacing the Isis2 which I believe has shines in her aft sections.
Anyone who has a clear understanding of these chines in the aft section I’d love to hear as I genuinely don’t know their purpose/benefits.
I have several thoughts on the subject as it applies to the IOM class.
My cynical side says it is the latest fad designed to get you to buy the new latest go-fast hull and make you think that you could go faster if you had one too.
The comedic view . . . the aft chine has the effect of cutting off bits that don’t touch the water. . .reduces weight a bit.
The sailing dynamics view. . . Think of a wide stern boat as it heels sailing to weather. The stern and mid section support the hull and the bow goes down and the angle of attack of the fin is down and to leeward. Now cut away the stern bit (leaving a chine), now the stern has to sink in a bit. Now the bow lifts and so does the fin angle.
not sure you’re too cynical - I think there is a lot of “fashion” elements in IOM or from what I remember of M class too. all it takes is one brilliant sailor to win a major international event to have a order book of his boat builder full ! Guys like craig Smith, Brad Gibson just to name a few are simply excellent sailors who will most likely win sailing a tub of tuperware with a rig on it !!! ok a bit too much but you get my point. Actually brad used a production IOM boat the windstar from Robbe and used his magic on it and went on to win an event … so there point made ! ok I heard he modified the keel position, used his rig and sails and probably changed a few other bits but still the hull is still the same.
so if I understand you correctly what you’re saying that the chine should in theory provide you that extra lift getting you to point that little bit higher ?
That’s is my best thought on the reason. It looks to me like it changes the angle of attack of the fin compared to a similar hull without the aft chine.
That’s, finally, something that make sense.
But the question now is by how much does the chine change the angle … enogh to make a difference, especially in a “smaler” boat sailing in rel;ativly rough water?
it is fine to have the latest design that may give you that little bit extra speed or pointing but the real question is is the tuning optimum to the wind and sea conditions, have I opted for the best tactical options, am I handling the boat to the best of its potential ? is my boat handling ability up to it ? so many questions, so many elements that will influence to a greater extend the over performance over having the latest design.
I used to sail a TS2 designed by Craig Smith and it is a dated design today - mine was built in 1998. yet I was still giving a good run for their money to a lot of other skippers who have much more newer designs. I knew my boat very well and I was able to tune it quite well to the conditions.Still today her new owner is not far behind and get in the fight at the top from time to time and this is a perfect example that design matter but it’s not everything.