Textured surface's affect on drag?

[atimm693]

I've been getting a little 14' Aluminum Ouachita V-bottom sea-worthy again, after I purchased it from a Scrapyard. I had to patch a stump-hole and a couple cracks, but it's starting to look like it'll hold water.

Anyway, I was wondering about the affect a textured surface has on the boat's hydrodynamics. The reason being because I have pondered the idea of coating the bottom of the boat (the inside has stringers that would prevent good surface prep) with flex-seal or a rubberized undercoating to ensure a 100% good seal. I am very confident in my repairs, however being an old boat I'm sure it will have leaky rivets here and there.

What I am worried about is the textured surface creating excess drag on the boat. It's no speed machine, but I will be powering it with a 5.5hp Evinrude so I will take all the help I can get to make it move faster. I would find a bigger motor, but I already have this one and a good title for it, so I want to use it. Plus it runs good. I don't have a big distance to cover, but at the same time I would like to be able to move from spot to spot somewhat efficiently. This is a light rig, the boat weighs probably 150, the motor around 60-70, fuel and gear maybe another 100. With me (260lbs) for sure and maybe another passenger. On rare occasions I may have 3 people with me, but I have a bigger boat for that.

Thanks

 

[Georgesalmon]

Re: Textured surface's affect on drag?

On a boat that small and slow I doubt a rough bottom surface would make much difference. However, most sealing attempts are usually done on the inside, not the outside. Part of the reason is that its hard to get something to stick on the outside when running in the water. Any little protrusion will catch the moving water and eventually rip it all off. Never used it but seems a lot of people use something called Gluvit on the INSIDE.

 

[spdracr39]

Re: Textured surface's affect on drag?

I was under the impression that a slightly textured surface runs with less resistance in the water due to air pockets being formed. The slowest boat bottom is a very slick and flat one.

 

[smokeonthewater]

Re: Textured surface's affect on drag?

At under 70 mph it isn't going to make ANY difference
You alone will be lucky to hit 10 mph and my bet is 6 and 5 with a friend.

 

[atimm693]

Re: Textured surface's affect on drag?

Thank you for the input.

I was thinking that it wouldn't make much of a difference but I read otherwise when researching the stuff. I was hoping that the Flex-seal would increase durability, and also deaden the hull. This boat will probably see some rivers and might need to be slid over rocks. The two major seams on this boat are welded, but there are still a good amount of rivets under the water line.

I have heard of Gluvit, but the cost is too high for this little project. That and this boat has V-shaped stringers in the bottom that would prevent me from applying anything where it matters from the inside, at least in the middle half of the boat.

I will hopefully be able to float the hull this weekend. If it doesn't take on much water, I won't mess with it.

 

[Frank Acampora]

Re: Textured surface's affect on drag?

"Wait---But that aint all!" And Flex Seal at 19.95 for two rattle cans is not expensive? How much area do you think they will cover?

Ditch that and get a better product. You can probably find it in the big home improvement stores.

 

[Bob_VT]

Re: Textured surface's affect on drag?

I advise HIGHLY against any undercoating or flex seal. Gluvit is worth every penny and was designed for aluminum boats. I have seen people try and regret using other products which included undercoating and bed-liner.

 

[atimm693]

Re: Textured surface's affect on drag?

I was using Flex-Seal more as an example; I hadn't decided on one or the other. My biggest question was regarding the texture.

But if it does leak substantially, I will go with Gluvit.

Thanks.

 

[Campylobacter]

Re: Textured surface's affect on drag?

The texture will not have a negative effect. The extra weight will.

 

[cpubud]

Re: Textured surface's affect on drag?

there is never enough time to do it right. but there is always time to do it again and again.

 

[Splat]

Re: Textured surface's affect on drag?

Your small motor aside, yes generally a textured surface is faster. Likewise a rippled lake is faster than a glass smooth one. Sane concept.

 

[64osby]

Re: Textured surface's affect on drag?

I advise HIGHLY against any undercoating or flex seal. Gluvit is worth every penny and was designed for aluminum boats. I have seen people try and regret using other products which included undercoating and bed-liner.

+1 on what Bob said.

Patches are best when rivets (solid or closed end) are used and 3M 5200 is used to seal the patch to the hull.

Gluvit works great, it sealed up my old Lone Star. It's now leak free.

A 5.5 on a 14'er will not be effected by any minor hull patches or "textured surfaces". You'll be lucky to hit 10mph. Start looking for a bigger motor if you need more speed.

Mine does 15mph with a 10hp and 23mph with an 18hp.

Lets see some pictures.

 

[atimm693]

Re: Textured surface's affect on drag?

+1 on what Bob said.

Patches are best when rivets (solid or closed end) are used and 3M 5200 is used to seal the patch to the hull.

Gluvit works great, it sealed up my old Lone Star. It's now leak free.

A 5.5 on a 14'er will not be effected by any minor hull patches or "textured surfaces". You'll be lucky to hit 10mph. Start looking for a bigger motor if you need more speed.

Mine does 15mph with a 10hp and 23mph with an 18hp.

Lets see some pictures.

The coating or paint is sounding more and more unlikely the more I think about it.

Like I said I'm not wanting a speed boat; that being said if I see a good deal on a 10 or 15hp motor I might jump on it. However finding one that's affordable, has the right shaft length, and has a title is unlikely. I will use the 16' Lund with a 35hp Mercury, if I have more people or need to go a long distance.

When I did the patch I sealed it to the hull with 5200, and used 1/4-20 machine screws sealed with 5200 to hold the inner and outer patches together. I am confident that it will hold water just fine. The hole was pretty significant, about 3" wide and 12" long. Looks like it had been run hard onto a stump or something. The PO patched it with tin, pop rivets, resin, and roofing tar over that. I figure if that job worked for them, then I did it a whole lot better and won't have a problem with it. There was a also a crack in the bottom because of poorly designed bunks. I patched it the same way. The big hole is right underneath the rear bench, so you can only see a little bit of the it from the inside.

The boat isn't at home now, I have it in a heated building so the 5200 will cure. When I get it back and start on the transom I will get some pictures up.

I will also be starting on the trailer pretty soon, and will have a build thread on that. It is a homemade deal (inspected and has a title.) The framework is done well, however the bunks are inadequate and the axle (from some sort of steerable wagon) needs to be swapped. The 13" wheels do have the common 4 lug pattern so I'm going to the scrapyard tomorrow to find a suitable axle.

I appreciate the input. This forum has been invaluable for this little "adventure." And I'm hoping for some Crappie and Walleye as a reward this spring.

 

[SigSaurP229]

Re: Textured surface's affect on drag?

Did you drill the end of the cracks? Honestly the machine screws MAY be ok I hope you used self locking nuts and loctite. I probably would have used Closed end blind rivets to make the patch. Gluvit Or Coat It will be a much better choice for leaking rivets.

 

[smokeonthewater]

Re: Textured surface's affect on drag?

or re set the rivets so the don't leak any more

 

[crabby captain john]

Re: Textured surface's affect on drag?

This is the part that bothers me with a 14' boat: "This is a light rig, the boat weighs probably 150, the motor around 60-70, fuel and gear maybe another 100. With me (260lbs) for sure and maybe another passenger. On rare occasions I may have 3 people with me, but I have a bigger boat for that.". What are 4 people going to do in a 14' leaky boat except be prepared to swim at any wave or wake?

 

[mrdancer]

Re: Textured surface's affect on drag?

You might try some of the hull coatings they put on airboats, such as Wetlander - The Ultimate Slick Bottom | The Best Boat Slick Bottom Coating, combining Ultra-Slippery with Rugged Durability or Wearlon Industrial Coatings - Wearlon Water-Based Industrial Coatings ...

As for smooth vs. textured in regards to efficiency...the Science journal "Nature" had a series of articles throughout the 1990s that discuss this very phenomenon. In one study, reflected by other studies, researchers determined that random protrusions on a surface increased hydrodynamic efficiency up to 17%, whereas uniform protrusions or slick bottoms decreased efficiency (as measured by water running through a pipe with different surface coatings). The idea is that, on a smooth surface, friction along the surface causes vortices to form and roll along the surface, like rolling up a rug or carpet across a room. This "snowball effect" continues until the vortice is large enough to break away from the surface, thus disturbing the adjacent laminar flow of water. However, with random protrusions, those vortices get broken up before they get very large, thus reducing disturbance to the nearby adjacent laminar flow, and enhancing overall efficiency.

 

[gm280]

Re: Textured surface's affect on drag?

Just for comparison issues, my neighbor owns a pontoon with a 25HP Mercury on it. The last time I was out with him, we used a GPS and clocked (could have used a calendar as well) his speed at 9 to 11 MPH wide open... So I don't think there is much he could do to increase speed. However, I do remember my 15' Hydro-Bass boat with a 115HP Mercury on it and any time I waxed the hull and O/B, it would give me around 3MPH faster speed. So reducing drag will increase speed, but the wax assistance would fade in less then three outings...

 

[atimm693]

Re: Textured surface's affect on drag?

Did you drill the end of the cracks? Honestly the machine screws MAY be ok I hope you used self locking nuts and loctite. I probably would have used Closed end blind rivets to make the patch. Gluvit Or Coat It will be a much better choice for leaking rivets.

Yes I drilled the ends of the crack. I figured that since the screws have 5200 on the threads that it would work as some sort of loc-tite. With as hard as it's supposed to bond aluminum I would think it would lock a nut pretty good too.

This is the part that bothers me with a 14' boat: "This is a light rig, the boat weighs probably 150, the motor around 60-70, fuel and gear maybe another 100. With me (260lbs) for sure and maybe another passenger. On rare occasions I may have 3 people with me, but I have a bigger boat for that.". What are 4 people going to do in a 14' leaky boat except be prepared to swim at any wave or wake?

That was a typo. I meant to say 3 people total in the boat. There's no way I could fit 4 total comfortably, this boat only has 2 benches and a small seat up front. I think the weight tag says 740lbs (it's hard to read) which comes out at about 3 people.

You might try some of the hull coatings they put on airboats, such as Wetlander - The Ultimate Slick Bottom | The Best Boat Slick Bottom Coating, combining Ultra-Slippery with Rugged Durability or Wearlon Industrial Coatings - Wearlon Water-Based Industrial Coatings ...

As for smooth vs. textured in regards to efficiency...the Science journal "Nature" had a series of articles throughout the 1990s that discuss this very phenomenon. In one study, reflected by other studies, researchers determined that random protrusions on a surface increased hydrodynamic efficiency up to 17%, whereas uniform protrusions or slick bottoms decreased efficiency (as measured by water running through a pipe with different surface coatings). The idea is that, on a smooth surface, friction along the surface causes vortices to form and roll along the surface, like rolling up a rug or carpet across a room. This "snowball effect" continues until the vortice is large enough to break away from the surface, thus disturbing the adjacent laminar flow of water. However, with random protrusions, those vortices get broken up before they get very large, thus reducing disturbance to the nearby adjacent laminar flow, and enhancing overall efficiency.

Well in a way my patchwork might increase the efficiency, although it probably won't be enough to matter.

Just for comparison issues, my neighbor owns a pontoon with a 25HP Mercury on it. The last time I was out with him, we used a GPS and clocked (could have used a calendar as well) his speed at 9 to 11 MPH wide open... So I don't think there is much he could do to increase speed. However, I do remember my 15' Hydro-Bass boat with a 115HP Mercury on it and any time I waxed the hull and O/B, it would give me around 3MPH faster speed. So reducing drag will increase speed, but the wax assistance would fade in less then three outings...

Either way I don't think I'll be adding any sort of coating to the bottom. If I did I'm sure it would be scraped off on the keel, and then the moving water would finish peeling the rest.

Like I said if it has any leaks when I float it (the weather isn't looking favorable this weekend) I will find out what else needs to be done.

 

[spdracr39]

Re: Textured surface's affect on drag?

Not really directly related to the question but how much can a 14' aluminum v bottom boat cost with no motor? Can't you just replace it with a decent used one that doesn't leak and save the time, money, and risk ?