Trying again: What's to fear about an unfair hull?

[The_Cunning_Ham]

I read the below excerpt from a web archive search of the Waterline Systems website. Does anyone have these in-warer test results available from the magazine or similar publication? I wish there were some open-acess journal for such sailing knowledge (it's quite possible there is), rather than Google Scholar we need Google Sail!

In the absence of other factors a 14% difference is huge (unknown at what speed, sea state, etc.).

"Julian Bethwaite, designer of the 49er, ran full-size, in-the-water tests between a faired 49er and a 49er fresh from the mold. Incredible as it seems, he found a 14% speed difference between the faired and as-molded hulls. He published his findings in Seahorse Magazine in 2007."

What spurred this thought: We're helping out a buddy who's hull is far from smooth or fair, started out like a large golf ball, soda blasted, knocked down many of the highs with 60 grit to glass in some spots, many pits still remain and undulations beyond this, one coat of epoxy barrier (current stage, see attached photo) and plan to fill with epoxy filler/fairing compound.

Best,
 CH

 

[See Level]

Turbulence matters.
Choose the amount your willing to put up with.

 

[SloopJonB]

Turbulence matters.
Choose the amount your willing to put up with.

That's the second corollary of the rule Speed costs money, how fast do you want to go?

 

[Kurtz]

In all fairness, pun intended - is this a turbulence issue or a laminar flow changing direction issue.

Can you have laminar flow changing direction without turbulence?

 

[Rushman]

@JulianB might be willing to share more if you ask him nicely

 

[JulianB]

14% is a lot.

Without going up into the attic and digging out notes, sub 80g was notably draggier than was 120g, something like double.

As you get closer and closer to a "mirror" surface the reduction gets less and less so the difference between say a 1200g and a 1600g/cut/polish is still real but its 0.5 - 1%.

WRT anti foul and boats that are wet-sailed, once you get past 240-320g your starting to hit diminishing returns.

My boat is presently "off the gun" I am yet to do the cut and polish, but I certainly will prior to the traveling season.

The other biggy is road grim, we found out about this in probably late 70's. Road grim is very draggy, the simplest of wash down nets huge benefits, far more that getting anal about 1200g.

 

[Grrr...]

14% is a lot.

Without going up into the attic and digging out notes, sub 80g was notably draggier than was 120g, something like double.

As you get closer and closer to a "mirror" surface the reduction gets less and less so the difference between say a 1200g and a 1600g/cut/polish is still real but its 0.5 - 1%.

WRT anti foul and boats that are wet-sailed, once you get past 240-320g your starting to hit diminishing returns.

My boat is presently "off the gun" I am yet to do the cut and polish, but I certainly will prior to the traveling season.

The other biggy is road grim, we found out about this in probably late 70's. Road grim is very draggy, the simplest of wash down nets huge benefits, far more that getting anal about 1200g.

1. The day before you leave, wax the living hell out of the hull.
2. Look up on the internet and you will find truck stops with washes where they wash it FOR you manually.
3. Go to the truck stop nearest your venue, pull in, they will wash and scrub your hull (after giving you some funny looks).
4. Drive to the venue and embarrass the other boats.

I learned that one the first time I trailed my 7.9 behind a diesel. Black soot stripes are not fast.