Skiff vs Canoe

Maybe this should go under the thread Hull Design yet I got lost in the technical aspects. I’m open for on-the-water tests and aesthetic replies.

Got the new Sailing World magazine (11-12/06) with an Open 60 on the cover. What a wide stern! I guess 60s have been that way for awhile.

In the rc world, the F100 yacht is flared back there…

…as are many IOMs.

I seem to be heading that way in design but wondered what others are doing? Are sterns getting wider in most cases (classes) and/or is it a “trade off” situation of performance gained in one condition/tack and lost in another?

As always, thanks from an eager learner.


Greg Vasiliff was a former poster here - and great builder racer - especially in Soling 1 Meter and US1M classes. I provided him with a set of lines for a model of a 110 Class boat (double ender) and it was going to be very light weight. Some other personal priorities came up and I don’t think he ever finished it. It looked from photos and displacement weight like it might have been a “killer” boat. Too bad it never hit the water to race against “normal” US 1 Meter boats.

EDIT: Added the following …

Greg’s comments

Here it is with the keel trunk/mast step in location, but not yet fixed
Well, she’ll be a lightweight! The total weight of the boat will be 4lbs, 4oz, ready to sail. That’s light! My ORCO is one of the lightest US1Ms around and it’s just over a pound more.
As far as floating on the original water lines, it’s not. I have the bow just breaking the water as is the transom. If I floated it on the original waterlines, then we are really talking light. I see the optional 1.5 lb keel coming into thinking here…(G)

So, can this boat carry enough ballast? Well, as you described the characteristics of the ‘flat’ bottom, it might. By the time it’s ready to sail, this particular boat will only carry about 2.5 lbs of bulb. My lightweight ORCO keel is 3lbs, 5oz.
So, if the boat can actually sail, then we just might have a light air killer as you thought we might.

Interesting question, Yar…the skiff-style stern was popularized, I think, by the success of the IOM TS2. They seem to excel on courses that favor the run, and in relatively stiff-wind conditions (I think that’s fair to say for the big boats, too.) For courses that favor the beat, or for light-wind conditions, it looks like IOMs are returning to more moderate beams and narrower sterns. Marbleheads and 10 Raters never seemed to favor wide sterns.

So as usual when it comes to hull design, there’s no right or wrong answer…it’s all about tradeoffs.

I suspect I’ve expressed opinions that won’t be shared by all…so flame away, guys. Maybe I’ll learn from the debate! :zbeer:

Bill H

From a former designer of offshore racing boats getting into models.

The most basic principle of yacht design is that you cannot use an elastic tape measure. Different functions of the boats are subject to square, cube or higher power (wave form analysis) functions as they scale. The classic example is stabilty. Statically this is a matter of volume and mass (same thig if densities of materials do not change). Hence it scales as the cube of the size. In other words, if we make the boat twice as big, we have 2^3 times the stabilty = 8 times. If we apply the simple elastic tape measure to the same scaling operation, we find that the sail area increases 2^2 times. - so it is quadrupled.

This whole scenario means that we now have four times the original sail area trying to drive eight times the original weight. The result is an undercanvassed, over-stable brute.

The maths that govern the waveforms generated by the hull are infinitely more complicated. Elastic tape measures do not work in any manner suceptible to normal non-mathematial comprehension.

You should also bear in mind that almost all fast boats are built to more or less artificial ‘rules’. In assessing any design it is necessary to look not only at the scale factors but at the underlying rule or constraints.

Skiffs come from the world of full-size dinghies. These rely on shifting ballast (the crew) to keep the boat reasonably upright. The lack of shifting ballast makes them less attractive as models, but since their stability relies largely on beam (^1) they retain sail-carrying power surprisingly well when scaled down. However, their relationship between wetted area and displacement goes very much in favour of wetted area: halve the size and you have 1/4 the wetted surface but 1/8 the displacement. Since skin friction makes up a higher proprtion of drag at small sizes (another scale effect), the tendency is for skiffs to be as dead as dogs in light weather.

I could go on almost indefinitely, and I am aware that this has not directly addressed your question in any way. However, it may provide food for thought.

For litterature I suggest anything by Marchaj (the older ones are better) and Larsson & Eliasson.

I hope this helps

I have edited my earlier post about the 110 Class flat bottom sloop that was a “terror” on Lake Huron and elsewhere on the Great Lakes and along the east coast of the US by adding a couple of “build” photos and some comments Greg provided at the time of keel bulb development.

Greg did the math from the original lines that I provided. I only wish he would have been able to sail it to see if it’s performance was all we hoped it would be. The philosophy was to use an ultralight weight hull, pointed at both ends. The hull on original and model is flat to promote a down-wind plane, and sail area for the model was based on the US1M rules. Greg decided to use a high aspect ratio keel and spade type rudder to improve the foil shapes from the older original design. As noted with the photos, he found that to float her off her lines would require a keel weight of nearly a pound less than his current ultralight weight ORCO and to let her float higher and “ON” her lines he could reduce keel weight even more. The question was would she sail … and unfortunately, I don’t have an answer. In the last photo, he has his keel and mast located, but not fixed. Add in a winch and rudder servo, receiver and put some light film for a deck, and it really would have been lighter than anything else on his local waters.

One reason we both worked on this design update, is the potential for a flat bottom, hard chine boat to have greater initial stability - and that coupled with a deeper keel than original, along with the additional effort required to make her heel significantly, our feeling was in light air, it would be an optimal shape.

Dang, I wish he would have finished her up.