William_H
Well-Known Member
Hull speed
Calm down. It's not your integrity but your arithmetic that's at issue. A 26 ft displacement boat won't sail through the water at eight knots. The formula (from Hiscock) for a good hull shape is sq rt of waterline x 1.4. Let's allow the MacG has a well designed underwater shape and say a 22 ft waterline. That gives 5.55 knots. QUOTE
The hull speed as given by Hiscock and others as 1.4 times sqare root of waterline length in feet is a fair formular. However it was never meant as a definitive max speed. It in fact gives a point on a steeply rising graph of driving force versus speed. The point (1.4) decided by Hiscock was like a "thats about it" point for his kind of boat. ie heavy with limited sail area. Confining our discussion to normal sailing boat displacement hulls I think his formular has become out dated in terms of absolute max speed. Modern hull shapes coupled with large sail areas mean that even without "planing" the speed can be pushed well beyond Hiscocks 1.4 limit.
My own 21ft trailer sailer can achieve 9 knots with plenty of breeze on the quarter and small spinnacker up. I keep hoping for the magic 10 knots. This always on GPS with no tidal influence. I didn't say easily achieve because it is a bit hairy at that speed and degree of overpowering. But it happens at least several times per season.
Of course a McGreggor will achieve 8 knots with a favourable wind direction. In my one sail on a Mcgreggor it would not sail to windward in a stiff breeze. It is a motor boat with some sail pretentions.
As a motor boat I would regard it as quite seaworthy. More so for having the sailing ability.
My friend who owned one (and sold it) did have trouble with the steering which seized up with corrosion.
I think if I owned one I would convert to tiller steering for the rudders as that little wheel is contributory to it not sailing well to windward. olewill