How much does the smoothness of the antifouling paint effect speed? Our choices are: 1- glass like smooth 2 - not so smooth , but uniform coating 3 - three coats in some areas ,flaked off areas painted over with single coat making for an overall rough coat Ablative paint in all cases and not a full keel. Might the difference be in the range of 1/4 knot or 1 knot?
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Drag = profile drag and parasitic drag
The smoother the hull finish will produce the least parasitic drag, hence the least amount of 'work' that the sails will have to overcome to get the boat moving at a certain speed. Rough pipe walls, rough river bottoms, rough boat hulls all impede the velocity of the water flowing past it --- all by increased friction. The smoother the surface against which a fluid is moving, the least amount of parasitic drag hence the more energy available to 'drive' the boat (to overcome the 'viscosity' of the water). The smoother the surface the greater chance of developing a stable 'boundary layer of fluid' that will vastly decrease the parasitic drag. The high end racing boats develop hull surfaces that are in the 'micro-inches' roughness (much smoother than glass). A detailed (complex) explanation of the effects of hull roughness versus parasitic drag can be found in such works as: "Sailing Theory and Practice" and "Sail Performance", by C. J. Marchaj. So, to answer your question a VERY smooth hull will be several/many percent faster than one that had its bottom paint applied with a 'paint roller' or has a lot of 'flaking paint' .... because it has LESS WORK to do to get to the SAME speed. A boat with a super smooth bottom will also have less heel, etc. ... alll relative and based on percentages. Such consideration are not only for high-end racers; but also, long distance passagemakers as it 'decreases the time' one is on passage (safety) and enables one to move more quickly away from storms, etc. Burnished Interlux VC17 or "BaltoPlate" are commmercially available hull finishes that can be radically flattened down to INCREASE SPEED. Such validation of results are typically done via 'tank testing'. Most navies of the world allocate a lot of $$$$ to evaluate bottom coatings to increase speed and reduce fuel consumption; many forms of marine life have evolved to do the same thing. The easiest way to get a FLAT layer on your bottom is to 'forget about using a paint roller'.
The smoother the hull finish will produce the least parasitic drag, hence the least amount of 'work' that the sails will have to overcome to get the boat moving at a certain speed. Rough pipe walls, rough river bottoms, rough boat hulls all impede the velocity of the water flowing past it --- all by increased friction. The smoother the surface against which a fluid is moving, the least amount of parasitic drag hence the more energy available to 'drive' the boat (to overcome the 'viscosity' of the water). The smoother the surface the greater chance of developing a stable 'boundary layer of fluid' that will vastly decrease the parasitic drag. The high end racing boats develop hull surfaces that are in the 'micro-inches' roughness (much smoother than glass). A detailed (complex) explanation of the effects of hull roughness versus parasitic drag can be found in such works as: "Sailing Theory and Practice" and "Sail Performance", by C. J. Marchaj. So, to answer your question a VERY smooth hull will be several/many percent faster than one that had its bottom paint applied with a 'paint roller' or has a lot of 'flaking paint' .... because it has LESS WORK to do to get to the SAME speed. A boat with a super smooth bottom will also have less heel, etc. ... alll relative and based on percentages. Such consideration are not only for high-end racers; but also, long distance passagemakers as it 'decreases the time' one is on passage (safety) and enables one to move more quickly away from storms, etc. Burnished Interlux VC17 or "BaltoPlate" are commmercially available hull finishes that can be radically flattened down to INCREASE SPEED. Such validation of results are typically done via 'tank testing'. Most navies of the world allocate a lot of $$$$ to evaluate bottom coatings to increase speed and reduce fuel consumption; many forms of marine life have evolved to do the same thing. The easiest way to get a FLAT layer on your bottom is to 'forget about using a paint roller'.
Not sure you have three choices
as you listed Hal. There are realities not mentioned over which you have more control than trying in vain to achive laminar flow theory across the hull form. You can't burnish ablative to make it "glass like smooth" as you describe in #1. If you really want to strive for a perfect bottom, you'll need to reconsider what paint you choose.
as you listed Hal. There are realities not mentioned over which you have more control than trying in vain to achive laminar flow theory across the hull form. You can't burnish ablative to make it "glass like smooth" as you describe in #1. If you really want to strive for a perfect bottom, you'll need to reconsider what paint you choose.
I disagree with Don .....
I apply my ablative bottom paint to my big 'crab crusher' with a plastic trowel in the same manner in which one applies epoxy/polyester to a male plug mold when building a boat. Such produces a FLAT layer of bottom paint that requires the very least amount of wet sanding and still gives a extremely FLAT finish. Also, ablative paint will eventually become roughened and 'cratered' (on a macroscopic level) so subsequent 'troweling' in future applications will quickly reestablish a FLAT bottom. In moderate wind ranges I probably (guess) get an extra ~1/2 knot out of my crab crusher .... but the hull is also faired and most of the 'protusions' are 'smoothed'. An extra ~1/2 knot over 24 hours is an extra 12 nMi travelled. which I think is reasonable for the minimal amount of work. My 'guess' is derived from sailing against identical boats on the same course, etc. ... (and with my sails 'mishaped' to match the other boat).
I apply my ablative bottom paint to my big 'crab crusher' with a plastic trowel in the same manner in which one applies epoxy/polyester to a male plug mold when building a boat. Such produces a FLAT layer of bottom paint that requires the very least amount of wet sanding and still gives a extremely FLAT finish. Also, ablative paint will eventually become roughened and 'cratered' (on a macroscopic level) so subsequent 'troweling' in future applications will quickly reestablish a FLAT bottom. In moderate wind ranges I probably (guess) get an extra ~1/2 knot out of my crab crusher .... but the hull is also faired and most of the 'protusions' are 'smoothed'. An extra ~1/2 knot over 24 hours is an extra 12 nMi travelled. which I think is reasonable for the minimal amount of work. My 'guess' is derived from sailing against identical boats on the same course, etc. ... (and with my sails 'mishaped' to match the other boat).
At 6 knots the drag coefficients hardly fall off the scale.
Just paint the bottom for protection and keep it clean. We'll usually kill more speed by leisure attention to the wheel than by paint drag on the bottom.
Just paint the bottom for protection and keep it clean. We'll usually kill more speed by leisure attention to the wheel than by paint drag on the bottom.
Not sure we disagree Rich
It is the "glass like smooth" descriptor that I referred to as a practical impossibility with any ablative. If it were possible to burnish the finish, the act of doing so would remove a lot of the paint.
It is the "glass like smooth" descriptor that I referred to as a practical impossibility with any ablative. If it were possible to burnish the finish, the act of doing so would remove a lot of the paint.
Don
It's a water based ablative called Aquagard. I also like it because it comes in white. That makes diving and cleaning very easy. I clean with a natural sponge and it cleans up with very little loss of paint. When I used to use Micron CSC the water around the boat would be white from the paint. http://www.aquagard-boatpaint.com/
It's a water based ablative called Aquagard. I also like it because it comes in white. That makes diving and cleaning very easy. I clean with a natural sponge and it cleans up with very little loss of paint. When I used to use Micron CSC the water around the boat would be white from the paint. http://www.aquagard-boatpaint.com/
thanls Alan
I've been considering using that very paint but never heard any first-hand experience about it's efficacy compared with CSC. If it's a relatively long-lived antifouling which also keeps the critters away and can be polished too, it soulds like a no-brainer.
I've been considering using that very paint but never heard any first-hand experience about it's efficacy compared with CSC. If it's a relatively long-lived antifouling which also keeps the critters away and can be polished too, it soulds like a no-brainer.
paint
Thanks. It looks like paying some attention to how smooth and unfouled it is can make a noticeable difference. To bad ,boats already in the water and it could have been smoother. Next year.
Thanks. It looks like paying some attention to how smooth and unfouled it is can make a noticeable difference. To bad ,boats already in the water and it could have been smoother. Next year.
Water- based
Oh ,by the way, last year we switched to, and find it works well, Pettit Hydrocoat, a water- based paint. It's potentially less damaging to the environment and the workers applying it (that would be me).Much easier to handle than oil based. Aquagard also sounds interesting .
Oh ,by the way, last year we switched to, and find it works well, Pettit Hydrocoat, a water- based paint. It's potentially less damaging to the environment and the workers applying it (that would be me).Much easier to handle than oil based. Aquagard also sounds interesting .
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