trim tabs

[ma glastron]

Got my new amita 3 prop today for my 3.0 mercruiser alpha 1. Went to put it on and it hits the trim tab. called solas up and he told me to cut the tab or buy a different style tab is this true?

 

[Brewman61]

Re: trim tabs

Well, yes. You certainly can't leave it as is. So you have to either grind it enough for correct clearance from your prop, or put on a special tab that is made for this purpose. Your boat, your choice.

 

[robjen1019]

Re: trim tabs

He is right, just mark how much you need to remove and take it over to the grinder. Ive done a few myself.

 

[Tail_Gunner]

Re: trim tabs

http://www.iboats.com/Mercury-Marin...19838457--**********.736297373--view_id.39250

Theres the real thing you can see the fin is offset

 

[tri-5-ron]

Re: trim tabs

I'm not trying to ask a different question, or highjack the OP's thread, if that is the case, I will gladly start a different thread.

I too have replaced the prop today with a Solas prop, and am hitting the trim tab.
I just came back fron the parts store, where I had seen the offset tab, shown in the picture above.
What I had noticed about that trim tab, was that the radius of the casting, (where the tab/fin meets the base plate, was a MUCH larger radius, and resulted in a larger area of "blockage" in the thrust stream.

Also, the Trailing Edge, of that tab was huge.
It was litterally flat/squared off., about 1/2" to 3/4" wide !

Being 26 years in aircraft, having some knowledge of aerodynamics, and knowing that Hydrodynamics are roughly 8x viscus,(if I am recalling that correctly).
I opted to try trimming my existing trim tab first, as was previously suggested in this thread.

So with that, (and I hope this is still directly related to the OP's question),...

When trimming the tab, how much clearance should there be, between the trailing edge of the prop, and the leading edge of the trim tab ?

I have heard that it needs to have more clearance, than just a minimal trim "trim to clear", to reduce any cavatation, aft of the trim tab fin.

 

[Tail_Gunner]

Re: trim tabs

Thats a merc trim tab made for high rake props..Likem or not merc does have a handle on such things..

 

[tri-5-ron]

Re: trim tabs

Tailgunner,
Honestly, I wasn't trying to be a smart-***, or anything like that.
And I realize that merc has a much better handle on what they are doing than I do. I wasn't trying to star a arguement, and I hope it wasn't taken that way.
I apoligize if it came off that way.

so as far as the question reguarding trimming of the tab,
Is there a preferred amount of clearance between prop and tab?

 

[Bifflefan]

Re: trim tabs

I have that exact tab on mine and it works great. The extra thickness is just more anode in my opinion.

 

[Tail_Gunner]

Re: trim tabs

Tailgunner,
Honestly, I wasn't trying to be a smart-***, or anything like that.
And I realize that merc has a much better handle on what they are doing than I do. I wasn't trying to star a arguement, and I hope it wasn't taken that way.
I apoligize if it came off that way.

so as far as the question reguarding trimming of the tab,
Is there a preferred amount of clearance between prop and tab?

Hey calm down your observation was well said...I just pointed out it was a merc tab that does not take away anything away from your statement i was just pointing out something easy...Good to see the input though...Watch for 45 or hiswii to get on a tech roll..Now those guys get it going..

 

[ma glastron]

Re: trim tabs

Thanks tail gunner, I ordered one of those trim tabs