T&T: Drag

[Dave Cooper]

Its funny that trawler owners don't feel that a very smooth bottom is worth
the effort but a racing sailboat owner will spend tens of thousands of $$
for a mirror smooth bottom. Are one or both of these folks wrong?

Drag is drag whether you are using sail or engine to push a hull thru the
water. Both sail and our trawlers work in similar speed ranges. So if the
difference in a sailboat hull is 10% or better speed with a slick faired
bottom vs. an unfaired average bottom then why isn't it the same for a
trawler? If it is then how much fuel is being used to make for the drag
caused by the "average" bottom? At $2, $3 or $4/gal it will become an issue
if it is not already.



The bottom paint we generally use are not the ones that are designed to be
"slick" but ones designed to last. We see the new silicon based very slick
paints that are now the norm for the merchant marine fleet.some are designed
to go 5 years without hauling!! Super slick and claim to save thousand of
gallons of fuel during the lifetime of the paint.



What I don't see is any of the recreational paint manufactures/suppliers
repackaging this product to sell into this market. Guess the boat yard lobby
and the paint lobby wouldn't like such a product as it would certainly trim
revenues.



OTOH, we see a move to limit copper in bottom paints. When this takes
effect, not if, I think we'll suddenly see all of the big bottom paint
manufactures start hyping this new silicon based product to us. New?? Heck
it's been around for at least 5 years, if not 7, for the merchant fleet.
International Paint is on its 3rd generation of it.



Hull drag hasn't been a concern for trawler owners in the past but with fuel
cost continuing to rise it certainly will be. Flush thru hull, faired
rudders, ..wow just like the race boats ;-)



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?



As always YMMV..





Dave & Nancy

Swan Song

Roughwater 58

Caribbean Cruise '07