Zincs for Trim Tabs -- Top or Bottom or Just the Top?

[rpasquarello]

I looked through the old posts and could not find a clear opinion on whether or not to replace the zincs on my tabs with ones on the top and underside of the tabs or just the topside of them.

I can't remember if the boat originally had them from the dealer on just the top, but I've been replacing them with ones that go on both sides of the tabs. -- which may affect the flow. I can't, offhand, remember the size I used on the stock tabs, either.

I am thinking that I should only put them on the top of the tab as to make the flow smoother on the underside of the tab next season. I am also adding DF12 drop fins to the stock tabs then, too.

Opinions?

 

[Tabman]

Just the top, that's what we supply to SeaRay when they are new. Normally it's an R-3 zinc. And yes, we do that so that the flow is smoother.

Tom McGow
Bennett Marine

 

[rpasquarello]

Thanks, Tom, for the info.

Have a happy and healthy New Years to you and your family!

-Rocco-

 

[Henry Boyd]

Tom,

I'm not so sure the flow is all that smooth with a lone bolt head on the bottom face of the trim tab. If I recall my flow dynamics correctly as the radius of an object decreases its influence (disruption) on laminar flow increases. IN other words a sharp small point will cause more disruption to laminar flow over a surface. It is the reason rivets on aircraft are recessed and have no exposed head. Added to that given the corrosion problems associated with the Bravo sterndrive, the additional anodes protection probably more than makes up for the difference in flow over the tab surface.

Personally, I'll go with corrosion protection every time.

Henry

 

[Air O'Nautical]

I have one on top and one on the bottom...wonder, if I'd go faster with only one on top and a smooth-ish pan head screw alone on the bottom. LOL!
They do make a small rectangle shaped zinc that attaches to the aft trailing edge of the tab if your really worried about it.


Henry, keep in mind the Bravo III won't use the zinc on the tab because, there not bonded together. My slip neighbor used to toss his old zincs into the water at his slip, thinking he was helping his boat somehow.... I never said anything to him..

I noticed on a Formula 41PC there are no zincs on the trim tabs.
Formula through bolted one of the trim tab mounting screws and attached a green bonding wire inside the hull to the big zinc bolted to the transom.

 

[Tabman]

Also keep in mind that as they "waste away" the zinc anodes become very "unsmooth". The amount of zinc in 1/2 of an R-3 has proven to be the right amount to protect all of the Trim Tabs we have supplied SeaRay for many years. Mark is also on target stating the that the zincs on the Tabs will not protect the outdrive.

Tom
Bennett Marine

 

[bmac]

Rocco

I'm sure Tom from Bennett is right, however, if you think the small protrusion of the lower half of two zincs is going to increase drag to any measurable level, you must be only using the boat for wind tunnel testing. Where we boat, barnacle build up will quickly mask any drag difference the two lower halves will ever contribute. Bennett may deliver tabs to Sea Ray with only the top half zinc, but I can tell you when my 40 Sundancer was delivered new it had both halves on. And, fwiw, I still install both halves on my boats. I don't think there's anything wrong with Tom's advice but when it comes to zincs in salt water I tend to take the more conservative approach.

 

[Henry Boyd]

My point was that either way, water flow is not improved by the presence, or absence, of a bottom zinc.

I also don't buy the argument that a lack connection to the bonding circuit negates the benefit of attaching a zinc. The stainless trim tabs will still create a galvanic cell with aluminum when immersed in water.

Henry


Sent from my iPad using Tapatalk HD

 

[Capt. Rusty Higgins]

I will follow Tom's professional advice each and every time, period.......I have dragged Bennett products behind me for more years than most have owned their boats. Bennett Tabs NOR Tom have failed me yet. And here he is answering your questions to the OEM standard, please do not banter???? Feel free to add as many as you wish is my advice so Tabman does not have to respond.

Thank you Tom, so very glad to see you back. Your health is more important than all the boats with 2 tabs each, that float on all the waters of the world.

All the Best,

Capt. Rusty Higgins
1-tab zinc kind'a guy!

 

[AFD]

Just an FYI. I had damage to one of my tabs from a dry dock accident that bent one of my tabs and the only way to repair it was to grind off the rivets and bend the tab back into shape on a bench vise with a mallet. i then counter sunk stainless screws and nuts with lock washers to have a smooth surface again.

I will follow Toms advice and only use 1/2 of an R-3 on the top of each tab and countersink the head of a stainless screw to keep it flush. It may not do anything but it will work in my head and be on par with Tom's advice who has helped me in the past as far as sending me (free of charge) a tab removal tool. although it may have only cost them shipping + $1 or $2, it was a huge gesture that goes a long way in securing my future business as well as trust.

Thanks Tom.

 

[Brian 59]

Mine had a pair of them (top and bottom) when I bought it. I have continued to do the same. Should I only be using one each ?