Trim Tabs

[ED66677]

Can someone explain in detail why one would use trim tabs on a mono, what they are supposed to do and how to set them up?
I'm just wondering if I need some on my 29" DF copy, as I've only used some once on a cruiser that was overpowered and was running with a 15° angle and it did help a lot!

[andym]

This has been talked about alot on all the forums, some say they are nothing but a crutch for a poor set up. I personaly think they can take a hull to performance levels that far exceed the standard hull. My Delta Force 33 has 2" two piece tabs and I ran this boat first with out them upto about 45mph no problems after that in less than ideal conditions no way. With the inside tabs set 1.5mm up and the outside tabs at 4mm the boat has been transformed. No chine walk, No tendancy to flip in race conditions at speeds upto 55mph. I was racin a 42" gas Cat on Saturday and ran over its wake flat out no worries! This hull will not handle like that without them. Just my 2 cents worth. All hulls are different and what works with my build mite work on yours but if you are having trouble with stability at high speed then I say try them they have worked for me and alot of the guys on here.

[deestingray]

I know that on my boat without trim tabs, it was a dog to drive. It hopped, skipped and porpoised. That is with a non adjustable strut and probably around 1 or 2 degrees down. My strut sticks out about 80mm on a 26 inch boat, what the trim tabs did was extend the planing surface towards my prop which I believe in theory moves the COG forward a bit without actually moving it. All I used was a piece of 40mm angle at zero degrees and it now rides very nicely and turns well without so much as a hop. There are a lot of things that adjustable trim tabs can do to settle an unstable boat, I just know that they work in some situations.

From what I have seen of the 25" DF copy, it comes with just a strut and a rudder, no trim tabs or turn fins and is one of the stablest boats I have seen. That was being powered by a SV27 motor and a 45mm prop too on 4S!!!!

[ED66677]

Tanks for these input guys! that's very valuable!
My problem as per as today is :
the boat runs very well (you can take a look at my web page and see 4 vids) on rough water, really stable and cornering is just awesome (I have to confess that the rudder is home made and certainly oversized), I did the first runs with 3 or 4" waves and it was fantastic!
the boat seems to be running wet on flat water and speed is ridiculous compared to the previous situation, I tryed everything from positif to negative strut angle, COG from 35 to 25%, nothing has improved at all!
I'm currently running under 3S, I know it's just enough and will soon test 4S, but I'm wondering if before this next test, I should prepare some tabs, it seems yes!
Andym, your explanation make me feel like the tabs are pulling the transom down, correct?
Deestingray, your point is interresting because my home made strut is a bit too long, I originaly planed to buy a 33" mono and ended with a 29", so the prop might be too far from the transom!

[properchopper]

This has been talked about alot on all the forums, some say they are nothing but a crutch for a poor set up. I personaly think they can take a hull to performance levels that far exceed the standard hull. My Delta Force 33 has 2" two piece tabs and I ran this boat first with out them upto about 45mph no problems after that in less than ideal conditions no way. With the inside tabs set 1.5mm up and the outside tabs at 4mm the boat has been transformed. No chine walk, No tendancy to flip in race conditions at speeds upto 55mph. I was racin a 42" gas Cat on Saturday and ran over its wake flat out no worries! This hull will not handle like that without them. Just my 2 cents worth. All hulls are different and what works with my build mite work on yours but if you are having trouble with stability at high speed then I say try them they have worked for me and alot of the guys on here.

Well said !! My experience exactly.

[Spot Me 2]

Tanks for these input guys! that's very valuable!
My problem as per as today is :
the boat runs very well (you can take a look at my web page and see 4 vids) on rough water, really stable and cornering is just awesome (I have to confess that the rudder is home made and certainly oversized), I did the first runs with 3 or 4" waves and it was fantastic!
the boat seems to be running wet on flat water and speed is ridiculous compared to the previous situation, I tryed everything from positif to negative strut angle, COG from 35 to 25%, nothing has improved at all!

Every V hulled boat runs slower and more wet on smooth water. The smooth surface has more drag and acts like a suction cup pulling the hull down. A deep V runs a lot better and faster on a little bit of chop. Less of the hull is in the water creating drag. Trim tab wont help you there.

[ED66677]

that's something I noticed when I drove my boat where she previously generated waves, the acceleration was sudden and awesome!