Return to Hobie.com
Hobie Forums
It is currently Mon Mar 18, 2024 10:59 pm

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 12 posts ] 
Author Message
PostPosted: Fri Apr 16, 2010 12:35 pm 
Offline
Site Rank - Old Salt

Joined: Mon Oct 09, 2006 2:34 pm
Posts: 621
Location: NC
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?

_________________
James
86' Redline Hobie 16
Sail # 76909


Top
 Profile  
 
PostPosted: Fri Apr 16, 2010 1:11 pm 
Offline
Hobie Approved Guru

Joined: Mon Jul 14, 2003 7:11 pm
Posts: 5197
Location: Detroit, MI
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!


Top
 Profile  
 
PostPosted: Fri Apr 16, 2010 2:16 pm 
Offline
Site Rank - Old Salt

Joined: Mon Oct 09, 2006 2:34 pm
Posts: 621
Location: NC
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.

_________________
James
86' Redline Hobie 16
Sail # 76909


Top
 Profile  
 
PostPosted: Fri Apr 16, 2010 5:37 pm 
Offline
Site Rank - Admiral

Joined: Wed Aug 12, 2009 5:25 pm
Posts: 163
Location: New Port Richey Fl.
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!

_________________
ADDICTION
1989 HOBIE 18 SE/sx wings
HOBIE ALTER SIGNATURE MODEL


Top
 Profile  
 
PostPosted: Tue Apr 20, 2010 2:57 pm 
Offline
Site Rank - Old Salt

Joined: Fri Aug 03, 2007 10:46 am
Posts: 1054
Location: eureka,california
The Hobie hull cleaner is nice when followed up by the Hobie protectant. Nice slick shiney surface.

_________________
Rich Vilvens
F-18 5150
[email protected]
http://www.sailblogs.com/member/f-185150sailing/


Top
 Profile  
 
PostPosted: Tue Apr 20, 2010 4:51 pm 
Offline
Site Rank - Old Salt

Joined: Wed Oct 14, 2009 11:26 am
Posts: 317
Lots of shiney adds 3 HP! I have heard that waxing with a product that has teflon is better for under hull surfaces though.


Top
 Profile  
 
PostPosted: Wed Apr 21, 2010 6:03 am 
Offline
Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 4176
Location: Jersey Shore
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


Top
 Profile  
 
PostPosted: Wed Apr 21, 2010 6:19 am 
Offline
Hobie Approved Guru

Joined: Mon Jul 14, 2003 7:11 pm
Posts: 5197
Location: Detroit, MI
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.


Top
 Profile  
 
PostPosted: Wed Apr 21, 2010 10:49 am 
Offline
Site Rank - Old Salt

Joined: Wed Jul 21, 2004 7:46 pm
Posts: 1457
Location: Santa Cruz
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:
[youtube]http://www.youtube.com/watch?v=74sEyot5A_o[/youtube]

_________________
Sail Revolution
Join us on our new FB Page!


Top
 Profile  
 
PostPosted: Wed Apr 21, 2010 11:39 am 
Offline
Site Rank - Old Salt

Joined: Mon Oct 09, 2006 2:34 pm
Posts: 621
Location: NC
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?

_________________
James
86' Redline Hobie 16
Sail # 76909


Top
 Profile  
 
PostPosted: Wed Apr 21, 2010 12:19 pm 
Offline
Site Rank - Old Salt

Joined: Wed Jul 21, 2004 7:46 pm
Posts: 1457
Location: Santa Cruz
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!

_________________
Sail Revolution
Join us on our new FB Page!


Top
 Profile  
 
PostPosted: Thu Apr 22, 2010 10:05 am 
Offline
Site Rank - Old Salt

Joined: Wed May 17, 2006 7:49 am
Posts: 1053
Location: North Carolina
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.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ] 

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Jump to:  
© Hobie Cat Company. All rights reserved.
Powered by phpBB® Forum Software © phpBB Group