Fairing perfection Vs performance

Yes, this could be another “I hate fairing” rant/thread but maybe there is some glimmer of information to be gathered here.

For fishing boats that aren’t 60+mph boats, more like 20 cruising - 40 wot, how much do surface imperfections actually affect performance? I’m referring to fairing imperfections in the hundredths of and inch range, visible, but are they hydrodynamically meaningful?

I can be a perfectionist sometime but when it comes to fine detail sanding my big dopy hands often aren’t up to the job. I struggle getting the corners of the strakes to the hull perfect. Some of those areas were damage where I had to do some grinding and glassing and some is the new strake extension but I’m essentially carving the shape from scratch. it’s smooth but not necessarily laser straight, maybe a little wavy.

the other issue is it’s an old imperfect hull. I don’t know how wavy it was to start but after 40 years of hard spots from internal structures and who know what else it’s not really flat anymore. I need to get some primer on it to have a better view but when it gets wet I can see high and low spots that are hard to feel with your hand.

At some point I have to stop. I know that’s often a personal decision, I’m sure I’ve made this one of the nicer old hulls out there, and I don’t think it could ever look like new again or if that is even something worth trying to achieve but I don’t want to not fix things that will meaningfully effect performance or mileage.

 

The biggest thing to do is sharpen the transom edge, not to a razor sharp, but one only round enough to take paint.

 

The other big thing is bottom paint. A burnished hard bottom paint is optimum, but a lot depends on how the boat is used and stored. All the work to smooth the hull can be totally wasted by the wrong choice of bottom paint.

Edit to add.

To answer the question, imperfections that small are basically in the noise after the first 6 inches at those speeds. Basically it will all be in the turbulent boundary layer. What really matters is the slope relative to flow of the humps, hollows, and blivets.

 

Thanks guys. The back edge is sharp, razor sharp for the moment. The bumps and things I was talking about are all smooth, no sharp edges (except where desired).

I was planning on VC performance epoxy. It’s a trailer boat so no growth resistant bottom paint but I wanted something totally waterproof if I did spend two weeks in the water.

 

Well I needed to see it looking different/better. More fairing to do but easier to see the issues now.

 

Sometimes; you really need a dustcoat to see what is happening after lotsa layers. I tried carbon black, but hate it.

 

Only the fish will notice. However, once you hook them, even the fish won't care. Launch the boat and enjoy the ride.

 

Changing topics a little. Anyone familiar with Interlux Interprotect HS? There is a (good) chance I goofed and only added half the amount of the part B activator. I was using the 2:1 scales on the cup and possibly (probably?) used the 3:1 scale for the activator (sigh). Anybody have any idea if it will still cure eventually? It’s been a week and it’s still rolling and pilling instead of sanding to dust. It’s baking in the sun now and I will be away from it for a bunch of days so I guess finger crossed. I’m waiting to hear back from their tech support next week now that I think (pretty sure) I’m missing the part B, see what they say.

 

Undercatalyzed epoxies do not cure. They will dry to a soft gooey stage, but it ain't a cure.

It would have been much easier to remove an errant mix earlier. Now, you will have to get the solvents required to clean it off.

I hate the bucket ratios and almost never trust them. I always use 1:1 and change it or jist the ounces. For paint, I generally switch to grams to control use down and get an idea on coverage. The stuff is too expensive to throw much away.

 

Yeah I kind of figured that’s where I was heading. I dont usually use them either, it’s easier to just used the fl ounce marks but i guess a mixing mistake eventually happens to everyone. I started off indoors and it was only in the 50s-60s so I assume an extra day or two wouldn’t be unreasonable. Then I moved it outside and started looking for alternative ideas for what I could have messed up. Unfortunately I’ll be away for a few days so we’ll see what it looks like when I get back. It’s hard enough that sandpaper does work. It’s probably a good couple hours of work. Bummer.

 

Just find out whether a solvent should or should not solve the cured finish. Most cured epoxies cannot be solved easily by acetone; so you ought to be able to see if acetone removes it, but the best bet for a chem test is to find out from Interlux how to chemically test for cure.

 

All un-cured epoxy can be dissolved in vinegar.

I've occasionally had to sand off soft paint. Frequent dusting with flour extends the useful life of sandpaper.

Good luck

 

Vinegar might be a good, safe way to test, but it would be pretty slow for removal of the layer.

 

There is no good way to remove a layer of uncured epoxy.

Vinegar will be one of the least bad options.

Be sure to rinse with a slightly basic solution such a baking soda/ water. Any acid left on the surface will prevent the next coat from curing.

 

I emailed with the tech support for Interlux. They told me it would cure even after I told them I had only put half the part B in. I rolled it out into the California sun and left it for two weeks, it cured. It’s sands nicely and is impervious to any solvents. I did end up sanding most of it off but that was the plan, it filled the multitudes of fine scratches and imperfections.