What's new

Fast Bottoms??

Ticktack

Member
Hello all, just looking for some feedback on the best finish to the bottom for racing.
I have been filling some small scratches in the fiberglass with marine Tex. I have sanded lengthwise until flush & fair With 600 grit & water.
I am tempted to buff out with electric buffer & compound but was concerned that the small swirls left in the surface might not be as fast even though it would look shinier.
which finish would create less drag, polished or sanded in the direction of water flow? Am I over thinking this?!!
 

mixmkr

Well-Known Member
If you're over 160lb, any manual sanding to help get you down to that weight "might" be beneficial.
 

AQBill

Member
You can "step down" in grit much further now than in the past and even get 3000 grit wet/dry sandpaper. The amount of benefit, however, would be minimal in a Sunfish. And, don't forget, you need to do the foils (daggerboard & rudder), too. Just get it clean and keep it that way and spend your time on the boat sailing...that's when you get real benefits.
 

Alan Glos

Active Member
In my humble opinion, bottom prep on a small sailboat is about half physics and about half mental. The physics part entails filling dings and scratches
as described above and then wet sanding with progressively higher grits of wet-n-dry sandpaper used wet. I like to use warm, soapy water with the
paper held in a quarter sheet rubber block. Yes, also wet sand the blades. Yes, sand fore and aft with the finer grits of sandpaper. The conventional wisdom is not to use wax as wax is supposed to slow the flow of water over the bottom and many classes prohibit the use of go-fast goop on hulls.,

The mental part is not insignificant. When you race, you want your boat to be well preped and tuned so you can concentrate on trim, tactics and
maintaining boatspeed rather than being distracted by any real or imagined flaws in the hull or rig. The truth is that missing a windshift will usually hurt you more than a few scratches in the hull, but a nice, smooth bottom will help you a little, and the cleaning and sanding is all part of the Zen of a fast boat.

Alan Glos
 
I would work up sanding from 600 - 800 - 1200 - 1600/2000 grit before polishing. After about the 1200/1600 grit region I think you're wasting your time. The Lightning Class did a fairly scientific study on this topic a long time ago, and it was discovered that a hull wet-sanded with 500 grit (no polish) had the least resistance, but that went away after about 2 sails as dirt became attached to the unwaxed hull. The hull that was progressively sanded up to 2000 grit, and then treated with polishing compound had the next lowest resistance, but it remained so for the duration of their study without further treatment. In one sentence, sand it up to 2000, and then buff the bottom with a proper marine wax.
 

beldar boathead

Well-Known Member
then treated with polishing compound had the next lowest resistance, but it remained so for the duration of their study without further treatment. In one sentence, sand it up to 2000, and then buff the bottom with a proper marine wax.
Polishing compound and wax are two different things. Did the Lightning get polished with compound or waxed?

My vote would be to sand to 2000 grit (or possible only 1000) and then coat with Hullcoat from McLube. That stuff is slippery!
 
Who remembers waxing the runners on your sled, with used, leftover candles?
I remember going out with my friends who I sailed with collecting candle stubs from the neighbors to wax my wooden Comet. Mrs Bradley who lived down in the hollow made her own candles and mixed cow fat into the wax. Her candles were absolutely the best for boatspeed.

The young ‘uns today don’t get to have that kind of experience. They just slop on the Hullcoat stuff and call it a day. It’s a real shame.
 
Polishing compound and wax are two different things. Did the Lightning get polished with compound or waxed?

My vote would be to sand to 2000 grit (or possible only 1000) and then coat with Hullcoat from McLube. That stuff is slippery!
I meant to write polishing treatment (PTFE/McLube or a similar treatment compound) -- it was not wax. I remember reading in a 1970s edition of "New Laser Sailing" that wax looks good, but can actually slow down the boat. Whatever you use, make sure it's made for boat bottoms. I like to use Eelsnot Boat Therapy, it's thick enough that it can actually help fill in the smaller scratches in the hull.
 

mixmkr

Well-Known Member
I have no idea, but I paint a lot of boats with VC17 bottom paint. Very low copper content but relies on the smooth, Teflon based paint to keep away any bottom growth. It can be "burnished" with a Scotchbright pad, yielding a very smooth surface for the racers. It's too thin to even fill in 200 grit sanding marks, but wonder if compared to the same [smooth] hull unpainted, if that helps. I kinda doubt it, but on paper, seems it might.
That said, some of my J22 buddies just keep it clean with no paint or sand with a very fine grit, as I stated in the other thread.
 

Ticktack

Member
In my humble opinion, bottom prep on a small sailboat is about half physics and about half mental. The physics part entails filling dings and scratches
as described above and then wet sanding with progressively higher grits of wet-n-dry sandpaper used wet. I like to use warm, soapy water with the
paper held in a quarter sheet rubber block. Yes, also wet sand the blades. Yes, sand fore and aft with the finer grits of sandpaper. The conventional wisdom is not to use wax as wax is supposed to slow the flow of water over the bottom and many classes prohibit the use of go-fast goop on hulls.,

The mental part is not insignificant. When you race, you want your boat to be well preped and tuned so you can concentrate on trim, tactics and
maintaining boatspeed rather than being distracted by any real or imagined flaws in the hull or rig. The truth is that missing a windshift will usually hurt you more than a few scratches in the hull, but a nice, smooth bottom will help you a little, and the cleaning and sanding is all part of the Zen of a fast boat.

Alan Glos
Thanks so much for this & everyone’s input, I’m looking forward to the upcoming racing season!!
 

odegaard

cAPTN oDIE
Hello all, just looking for some feedback on the best finish to the bottom for racing.
I have been filling some small scratches in the fiberglass with marine Tex. I have sanded lengthwise until flush & fair With 600 grit & water.
I am tempted to buff out with electric buffer & compound but was concerned that the small swirls left in the surface might not be as fast even though it would look shinier.
which finish would create less drag, polished or sanded in the direction of water flow? Am I over thinking this?!!
FYI Any work aft of mid ship is probaby a waste. The issue is turbulent flow replaises laminar flow after some point. Read up on books by Marchaj. Don't waste time on "INNIES"/small gouges--only the "OUTIES" matter. The water flow just goes over gouges and does not effect speed much. I do realize that your head game is important--i.e. U think you are fast with a smooth hull and could psyche yourself out with a rough hull.Spend time on good starts rather than hull issues.
 
Top