Running surfaces... How rough is too rough?

[SeanKewley]

I know many people rough'en up their running surfaces... I usually do as well by using 400grit paper to reduce stiction (sp). BUT... I'm fiberglassing a tunnel hull right now and I use peel ply on top of the curing glass to soak up the excess epoxy and to avoid sanding between plys.

When you peel the peel ply off of the cured glass it leaves an evenly spread "rough" texture behind. I'm considering leaving this texture on the running surfaces and just painting/clearing over it with out sanding it smooth to get the same effect. I'm really tempted to experiment by leaving the texture in place to see what happens.

Anyone have some thoughts on this before I commit?

 

[Jeremy Linney]

I wish I could figure out a way to dimple running surfaces like a golf ball cover. I bet that would be great for freeing up the hull.

 

[John Knight]

If you want a faster and more predictable boat, do not leave it rough. Do this test - wet the surfaces and run your hand/fingers over the area. See how much resistance is there. Then test your area that has the 400 treatment done. See any difference? Wet sand it using 220, 400, 800, 1500 and finally 2000 grit sandpaper. You WILL see a significant difference in the water shedding and less resistance.

 

[Ted buckley]

This might sound really stupid to alot of boaters out there, :huh: but I've incorporated this into my running surfaces to my front sponson's on my .21 Hydro with improved results. I went to Home Depot and picked-up a few samples(Free) of linoleum counter-top peices and attached them to the bottoms of my sponsons. I know what your thinking, but they work!! Some of the samples have a unique texture on them, that simulate what your looking for. Smooth paint coatings don't work, but these do. I've had them on for over a year now - and they haven't come off..

Just a thought. B)

 

[Paul Traufler]

Hey Jeremy the golf ball dimple would work in air, in water not so much. On the full sized stuff (at one time) the running surfaces were primer, the thinking was the "rough" surface would hold water and make a bearing of sorts. (Very much like the golf ball dimple you asked about.) Now with the model boats the interface between boat and water is a good bit different than the full size stuff so I doubt you can make the same comparisons. I would also say the boat type would make a big difference here, I mean a rigger only has a VERY small contact surface and it is not the same as a deep vee or a tunnel boat.

Paul

 

[SeanKewley]

I'm pretty sure that the fluid dynamics of drag hold the same characteristics with water as it does with air. Obviously water is denser, but it should have the same physics... Correct?

 

[John Knight]

Hey Jeremy the golf ball dimple would work in air, in water not so much. On the full sized stuff (at one time) the running surfaces were primer, the thinking was the "rough" surface would hold water and make a bearing of sorts. (Very much like the golf ball dimple you asked about.) Now with the model boats the interface between boat and water is a good bit different than the full size stuff so I doubt you can make the same comparisons. I would also say the boat type would make a big difference here, I mean a rigger only has a VERY small contact surface and it is not the same as a deep vee or a tunnel boat.

Paul

Paul,

I have used this method on riggers, tunnels and a mono with equal and successful results. You are removing a lot of drag and that is always good. I also wax the boats with several coats and it helps even more.

 

[Paul Traufler]

Well sort of, water does not act like air due to its properties, there is more "stickyness" to the water and at the speeds the boats go we are in an area where inertial vs viscous forces start to really change how they interact with the surface. We also have to deal with surface tension that is far greater on water than air, so it is really pretty different. Sure that water is 700+ times more dense than air is the big step but all the other differences can not be ignored either.

Paul

 

[Paul Traufler]

John,

What kind of improvement did you see from rough to smooth surface? I would be interested in the tests done in this area, I would put the changes on a rigger surface drag change at very small if any improvement. (Again a very small wetted surface area here.) Now rudder and turn fin thickness, shape, depth that is a completely different area that could make for some real improvements in speeds.

 

[Ted buckley]

John,

What kind of improvement did you see from rough to smooth surface? I would be interested in the tests done in this area, I would put the changes on a rigger surface drag change at very small if any improvement. (Again a very small wetted surface area here.) Now rudder and turn fin thickness, shape, depth that is a completely different area that could make for some real improvements in speeds.

Seems to me that not too long ago there was a Thread that covered this subject in Detail. Not just the thread, but countless articles also(That i've read). The conclusion that appeared to come out of it was that a smooth surface didn't hold-up to the slightly Textured surface as far as Drag/cohesion. I'm not talking about a roughly sanded surface, but a textured surface - much like an orange-peel surface that produced the optimum results.

Actually, I read a big article discussing the dynamics of water and the material they used on the World Cup Sail Boats. Surface wasn't smooth, but a textured surface which broke up cohesion.

 

[Daniel's Racing]

I think what makes the textured possibly do better is the lift they might create in addition to just allowing the surface to break free. They are like a bunch of tiny overlapping shingles. Larger overlapping shingles on running surfaces many have tried with success with that type running surface mod.

 

[Grimracer]

Hey Jeremy the golf ball dimple would work in air, in water not so much. On the full sized stuff (at one time) the running surfaces were primer, the thinking was the "rough" surface would hold water and make a bearing of sorts. (Very much like the golf ball dimple you asked about.) Now with the model boats the interface between boat and water is a good bit different than the full size stuff so I doubt you can make the same comparisons. I would also say the boat type would make a big difference here, I mean a rigger only has a VERY small contact surface and it is not the same as a deep vee or a tunnel boat.

Paul

Paul,

I have used this method on riggers, tunnels and a mono with equal and successful results. You are removing a lot of drag and that is always good. I also wax the boats with several coats and it helps even more.

really.. do tell more...

Grim

 

[Paul Traufler]

Guys I agree that large hulls with a great deal of hull surface in the water will have a greater affect from the surface rough/smooth stuff, but in our smaller world (ie outriggers) we have such a small wetted area that this surface stuff just is not a big deal. In general whan you bring the scale down things do not stay linear when it comes to performance stuff. Or in other words our model boats perform WAY better than the full size scale boats do.

 

[Charles Perdue]

Just my humble opinion, BUTTTTtttttt..... I think what this calls for is a day at the lake, sandpaper of different grits, wax, radar gun, a cooler of refreshments of your choice and WITNESSES.

I have already done this but I am not telling....... That would spoil the fun.

 

[Ted buckley]

Guys I agree that large hulls with a great deal of hull surface in the water will have a greater affect from the surface rough/smooth stuff, but in our smaller world (ie outriggers) we have such a small wetted area that this surface stuff just is not a big deal. In general whan you bring the scale down things do not stay linear when it comes to performance stuff. Or in other words our model boats perform WAY better than the full size scale boats do.

Sorry, but tell Zip-Kits that.. They have already hit on it(Good job by the way). My advise would be to NOT stop testing!!

Test different configurations and maybe you'll be the next that they're all talking about.

 

[SeanKewley]

I've decided to leave the Peel Ply texture as is and test. It leaves a really neat diamond like texture on the glass. I can always block sand it smooth later if the hull performs poorly.

 

[Paul Traufler]

Charles my vote would be for the Hooter's girls to come out and witness the testing. You know how they love to hang out with us racers and all.

 

[tnrcboatracer]

All fluids scale, it is called Reynolds number. BAsed on velocity, density, viscosity, and chord length. IIRC

3M makes a film that was applied to the Americas Cup yachts to reduce drag. It was slightly textured like shark skin or tiny

fish scales. But again the reynolds numbers between the flow on a yacht and our hydros are MUCH different.......

 

[Jeremy Leaf]

I have always had the best results wet sanding flat ride surfaces with 320. I think the peel ply texture will be too rough if you are using the white economy ply. The light green stuff has a much tighter weave and may work better.

 

[Mark Poole ModVP]

I have taken a boat to the lake that was painted on the bottom and has a slight orange peel texture. Ran the boat like this and then brought it in and wet sanded the ride surfaces with 400 grit. I changed nothing else betwwen runs. The boat ran faster and was riding more freely also. 400 or 600 grit is better than a heavier texture.