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PostPosted: Fri Apr 16, 2010 12:35 pm 
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What's the best for racing, ie. faster? I know polish and wax will likely look much nicer, but I remember being told by someone or reading somewhere that wax is slow. What do most of you do to prep your hull surface before a race?

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PostPosted: Fri Apr 16, 2010 1:11 pm 
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If the surface is in good shape, polish with 3M Finesse-It II, followed by McLube HullKote.

Now, the technical discussion:
The drag on a boat has 3 components: Skin Friction, Wave Making Resistance and Form Drag.

At very low speeds, Skin Friction predominates. As speed increases, the other two components ramp up quickly and dominate.

Surface preparation only affects skin friction. The difference between a finely sanded surface and a waxed surface is very slight. At low speeds, the sanded surface will preserve the laminar boundary layer (less drag) longer before it transitions to a turbulent boundary layer (more drag).

Bottom line - the difference is extremely small, and only at low speeds (3 kts or less)

You would more than offset the gain by not washing the boat after a long trailer ride, having your weight too far back on the boat or being slow in a single tack.

Waxing gives the gel coat UV protection and keeps it from absorbing tannins (the brown grunge) from water. Besides, you gotta look good to go fast!


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PostPosted: Fri Apr 16, 2010 2:16 pm 
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Thanks Matt, that is exactly what I was looking for. I guess I will opt to look good. The surface is alright, just slightly oxidized. Great info.

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PostPosted: Fri Apr 16, 2010 5:37 pm 
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I sanded my 18. Started with 220, 320, 400, 600, 800, 1000, 1200, 1500. All sanded by hand with a sanding block! Finished off with 3M Super Duty Rubbing Compound. 3 coats of Liquid Glass ultimate polish/finish over 3 days to allow for curing between coats. I agree with Matt, you gotta look fast to be fast!

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PostPosted: Tue Apr 20, 2010 2:57 pm 
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The Hobie hull cleaner is nice when followed up by the Hobie protectant. Nice slick shiney surface.

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PostPosted: Tue Apr 20, 2010 4:51 pm 
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Lots of shiney adds 3 HP! I have heard that waxing with a product that has teflon is better for under hull surfaces though.


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PostPosted: Wed Apr 21, 2010 6:03 am 
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From the Hobie Class Rules..

9.2 No friction-reducing agents may be employed
on the hulls, rudders or boards.


Probably one of the more ambiguous rules in the book. I suppose that it could be argued that even soap is a friction-reducing agent. I wonder if anyone's ever been protested under this rule.

In any case, it's something to keep in mind.

sm


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PostPosted: Wed Apr 21, 2010 6:19 am 
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You left out what comes before that:
Quote:
9.1 Hulls may be rubbed, waxed, sanded or buffed in the normal process of maintenance.


Putting on my judge's hat, I would interpret "friction reducing agent" in 9.2 (in the context of 9.1) as an ablative compound. Any hydrophobic coating (like wax) actually increases skin friction.

I also look at it in the context of RRS 53:
Quote:
53 SKIN FRICTION
A boat shall not eject or release a substance, such as a polymer, or
have specially textured surfaces that could improve the character of
the flow of water inside the boundary layer.


Leaving a layer of soap on the boat would technically violate the rules, since it does reduce friction and is an ablative (it wears off). It wouldn't last very long, though.


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PostPosted: Wed Apr 21, 2010 10:49 am 
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HOBIE 911 wrote:
I sanded my 18. Started with 220, 320, 400, 600, 800, 1000, 1200, 1500.


Do yourself a huge favor and don't touch it with anything less than 600. You'll make HUGE scratches in the gel and will probably remove too much of the surface. And on the other end, there's no need to hit it with 1500. The label of the Perfectit states that it will remove 1200 G scratches and I've successfully removed 800 g scratches no problem. Honestly, unless it's really bad, I wouldn't even hit it with sand paper what so ever. That's pretty extreme, just buff it with Perfectit III Extra Cut.

Here's how I do it, even on really bad hulls.
1) Wash to remove sand/other contaminates
2) Buff
3) wax with HullKote

Like this:

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PostPosted: Wed Apr 21, 2010 11:39 am 
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Thanks guys. Jeremy, your video is what I was basing this question on, given the results looked so great.

I had a buddy re-do my bottoms for me, so I definately have to sand all that back down.

My plan is to sand down the bottoms, re-gel with a more matched color (I have and 86 yellow boat and the newer gel is a little too light) I know It likely won't be perfect, but hopefully better. I have a buddy that is a professional auto painter that I hope will help out.

Then, I will do the above steps (wash, polish, wax)

Does this sound about right?

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PostPosted: Wed Apr 21, 2010 12:19 pm 
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Sounds good to me. My video shows the results, and I would only wetsand under very extreme circumstance. This particular hull sat on its side in the sun for 20 years...and I mean direct, beating sun. I'd try he minimum and work back from there, you'll save a ton of time, money and effort.

The Perfectit III starts out as a heavy cut rubbing compound and breaks down into a polish. Gone are the multiple steps and using different products. It's pricey, but works the best out of any I've used...and it saves a ton of time for the production work that we do here. Like I said, I wouldn't even touch it with sand paper unless it was really scratched up or you got some overspray from the bottom job. Most people would do more damage, say, wetsanding it with 320. And use a soft pad if wetsanding around a bend, not a stiff one. On the curved bottoms I usually just use the paper on my hand and mimic the curves of the boat. On the flat surfaces, sure, use a block.

Have fun! Good polishing!

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PostPosted: Thu Apr 22, 2010 10:05 am 
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This question is a long time argument amongst surfers, is a rough out faster than a glossed board. Based on the concept of adhesion a rough out is faster. I have raced boats both ways and can't begin to notice any speed difference. I did notice the effect of water on the hull, roughed out the water seems to just slide along when glossed the water seems to be drawn up on the hull and creates small wavelets along the hull surface. Its got to be like the golf ball dimples, a dimpled ball will travel further than a smooth ball will. So, a roughed out hull should in theory have less resistance than a glossed hull.


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