I was out sailing my IOM this afternoon, had everything from difting to top of A rig. I was having a great time and started to notice the wake behind the boat at different angles of heel. So I was wondering if the more wake is slow or does it matter? The boat some times had it bow in the water a little more then other times depending on wind strenght?
Come on with all you smart sailors no reply yet I am shocked???
Well, the easy part is that the bigger wake definitely means more drag. A wave contains energy, and in a wake, that energy has to be pumped in by the boat making the wake. My memory is that the amount of energy varies with the cube of the height, and if so, a wave twice as high would therefore have eight times the energy. If we assume the boat speed did not vary, which is to say that it was at hull speed in each case and so little faster while making the higher wake that we can ignore the difference, then the drag would be eight times higher with the higher wake.
The tough part is doing anything about the wake. On a full plane, the wake would be much smaller, but many model boat classes don’t plane much. The more lift you can get from the planing effect, generally, the less drag there’d be and the smaller the wake would be. One goal of model sailboat hull design is to produce a hull that has low drag even when heeled modestly, maybe 30 deg., say. You might find you can get your boat to travel a little faster by easing the sails out, thereby reducing the heeling angle.
Mike Biggs
Mike thank you for that explanation. Have you noticed a differance when sailing in afleet of RC boats that the faster boats generate less wake?
Hi Andrew,
I have not noticed such an effect. There are too many variables, and besides, I am concentrating on sailing my boat.
I have noticed a different stern wave on hulls of different shapes, but no speed difference. My Widget (relatively narrow with a square transom) pulls a larger stern wave than my FH (similar to a TS2 -very wide and with a sharp edged transom). Yet, overall I am sailing the Widget much faster- is it me or the boat???
There is a wide range of hull shapes in the IOM class, yet they can all very close in performance. It seems to come down to the sailor as the major factor in boat speed.
John,
Just the answer I was looking for. Thank you
I would respectfully disagree with this summation. :devil3:
The major factor in boat speed is “waterline length”
Provided the breeze is enough to get the hull up to maximum hull speed then pretty much all boats of the same length will go the same speed.
However that is NOT what wins races.
Winning races, does come down to the sailor.
Winning races is such a combination of so many factors that you could even write a book on the subject. :graduate:
Drag will make a difference, as will all of the following;
Sails, appendages, tuning, weight, hull finish, hull design and optimisation, helmsmanship, timing, cunning, gamesmanship and so much other stuff that I am beginning to bore you dear reader.
Suffice to say, unless everything comes together for you, it is difficult to win. That`s what makes it such a thrill when we do, RIGHT? :jump4:
Hi Ian.
while your comments are unquestionably correct, we are talking about a narrow field where most of the variables are negligible.
We are talking IOMs, so length, displacement, sail area are all very similar within a narrow range. Within those parameters, we are talking about the wave making potential of the hull form and the ability of the skipper.
John
Long answer short. You hit the nail on the head.
Rule of thumb saying “20% hardware & 80% brainware” 
Although I haven’t sailed on in several years, it was obviouis with US1M that some boats could exceed hull speed by quite a bit. Generally, as I recall, the skinny ones that were also harder to handle.
I don’t know if this applies in IOM, but if the DL isn’t too high, it’s likely that exceeding hull speed is not unusual, and in that case I’d guess details of hull design might become important. Unfortunately the AMYA site is down so I can’t go check what the difference is.
Of course, in my experience, the good skippers will win. And I’m not one. As long as my boat was away from the others, I could go fast. But I hadn’t learned to deal with the traffic, right of way, covering, etc.