OH MY a Multihull
owner who can be honest about his boats performance and Australian too with a Seawind 1160
We have found that with our engines on we do pretty well to windward, notwithstanding the reputation of catamarans going into the breeze. As we have mentioned before we generally use only one engine
in such conditions, as we rarely use both when under way. (We only gain 15% of speed, but use 100% more fuel
We can generally sail upwind at an angle of about 25° to the wind
when motor-sailing and we do about 5-6 knots to windward with any breeze above 10-15 knots. We have to add about another 7-10° for leeway (the amount that the boat slips sideways in the water) so when we tack from one tack to the other we usually turn about 65-70° which is about what the big super racing
yachts can manage for their tacking angle.
Of course without the engines we would have an angle to the wind
of about 35°, and our speed in 15 knots of wind would be around 4 knots (5 or more at 40°) and at this speed the mini-keels don’t grip as well and we slip sideways more which has the effect of increasing the overall angle we are really moving at when measured on the GPS
- so all up we would have a tacking angle of about 100° (50° each side made up of 40° of our heading, plus another 10° for leeway).
The net effect of this, if you apply that trigonometry you had to learn in high school
, the net useful speed made directly upwind (called the “Velocity Made Good” to the wind) is made up using the following equation:
- -VMG = cos(angle to the wind) x boat speed
- -Without the motor = cos(50°)x 5kt = 64% of 5kt = 3.2k
- -with the motor this = cos(35°) x 6kt = 82% of 6kt = 4.9kt or more than 50% faster getting to where we’re going, and the effect is even greater in light winds of course.
In fact, we noticed coming down the west coast
that we were more than competitive with the monohulls when going to windward, as many of the cruising monos also used an engine
going to windward, and even so we would usually beat them except for a couple of the larger boats which were significantly longer than us, who we would not expect to catch in any conditions.
The take home message is that when cruising to windward, there is more use of motors than we had originally thought - not because we can’t get there without it, but because it actually works quite well and is generally much more comfortable than banging straight into a headwind. When coupled with the need to make electricity and water
- this further justifies the use of motors in such conditions.
Day 289 - VMG upwind to the Tamar River