T&T: Blisters, sailboats and drag

[LRZeitlin at aol.com]

In a message dated 8/4/07 12:00:40 AM, Dave and Nancy write:


> I also think that propellers, drivelines, gearboxes and engine haven't
> really been looked at for giving top efficiency or the conversion of a
> gallon of fuel into the most thrust. Another interesting related topic
> 
> 
> 
> Comments?
> 

Three short comments.

Reasonable minds may disagree on the proper method of blister repair. Since 
the subject is mostly witchcraft, my incantation may be different from yours. 
However, I've worked with FRP for 45 years and haven't had any structural 
failures yet. So I think I'll stick with my spells and forget about the chisels. 
I'm sure Harry Potter would agree.

Except for severe barnacle fouling, the difference in propulsive force 
required to move rough and smoothly painted hulls is very small, probably on the 
order of 1 or 2%. The difference is most pronounced at very slow speeds where 
drag due to skin friction is much greater than form resistance drag. Sailboat 
races around the buoys are often decided in feet. In one design racing, where all 
boats have approximately the same form resistance, a super slick hull with a 
miniscule less frictional drag, has an advantage, especially in light air. For 
competitive sailers, who haul their boats after every race, it doesn't matter 
how much cash or time it takes to polish the hull to a mirror surface. Ego 
gratification has no price. But as far as most trawlers go, while a mirror 
smooth bottom is always nice, fuel , even at today's stratospheric prices, is still 
one of the lower cost items in a season of boating. Your point may have more 
merit when diesel fuel prices reach $10 a gallon, perhaps next year.

I fully agree with the point that propeller, gearbox, and driveline 
efficiency has been neglected. With powerful motors and cheap fuel, why bother? It is a 
lot easier to sell a beamy boat that has a spacious and comfortable appearing 
interior than it is to sell one on the basis of fuel economy and efficiency. 
But now that fuel prices have made efficiency appealing, we may expect a 
return to the design precepts of the 1920s, an era where engines were much less 
powerful and boat interiors looked more like a men's club and not like the bridal 
suite at the Plaza. Long, narrow hulls driven by small engines swinging 
large, slow turning propellers. That's the ticket. Go down to the local library and 
look at the bound editions of Motorboating from the 1930s to see what the 
future holds. I welcome the retro change.

Larry Z


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