Ultimate Trim Tab position

[Dignity]

Previously on my Allison 195 Vision the amount of room under the duckboard meant that I had to use short actuators and the trim tabs ended up around 170 mm from the chine. With the replacement pod there is an increase in height below the duckboard and I now realise that I can move the tabs 70 mm to where the hull flattens 100mm before the chine so that it is still in line with the hull bottom but further outwards.

I'm thinking of moving the tabs for 2 reasons:
1 - all my crew weigh twice my weight and generally the ice and fish are on the same side of the boat so I do have to deploy the tabs quite considerably on that side due to lean. and
2 - when the tabs are deployed they are within 50 mm of the transducer and therefore the reading is sketchy at speed due to turbulence from the tabs

There is some work involved as on the port side there is the live bait pump which will need to be moved and on the starboard side the pick up for the deck wash may have to be moved although I may just get away with some bending of the bracket it self.

What I'm looking for, will a 70 mm outwards movement of the trim tabs give me more control and also less turbulence to the transducer given the amount of repair work needed to the duckboard plugging old screw holes, shifting the bolts/screws holding the duckboards (5 mm left or right and I wouldn't have had to shift these) and plugging the old holes on the transom and repairing the gelcoat.

Or is it a lot of work for little return?

[scottar]

What is the distance from the keel to the centre of the tab now Sam?

Applying a bit of bush logic (correct or otherwise)

You can run some numbers through a torque calculator to see what sort of change the extra 70mm will make percentage wise given a fixed amount of applied force. To my way of thinking, as an example - if the distance was 100cm's and you increase it to 107cm's, you will see a 7% increase in rotational torque applied making the assumption that for any given boat speed the water flow to the tab remains the same thus the amount of force applied is the same.

Calculate Torque from Force & Lever Arm Length (sensorsone.com)

[Dignity]

Scott, it is 710 mm from the centre of the hull to the centre of the tab, there is a narrow planing plank which is 120 mm wide which means from the edge of that plank to the centre of the tab is 650 mm. I'll play with the figures as it seems there will be an improvement, even more so with the transducer.

[stue2]

Definitely give you more from the tabs by moving them outboard.
Be a bit of work but you might like the results more

Sent from my SM-G780F using Tapatalk

[scottar]

Assuming my theory holds water Sam you will see close enough to a 10% difference in torque applied to the hull for any given tab position. Hopefully someone around these parts with a bit more engineering nouse can confirm whether this is correct ........or I'm barking up the wrong tree. Whether that's worth it is a decision only you can make mate. What size are your planes?

[Dignity]

Assuming my theory holds water Sam you will see close enough to a 10% difference in torque applied to the hull for any given tab position. Hopefully someone around these parts with a bit more engineering nouse can confirm whether this is correct ........or I'm barking up the wrong tree. Whether that's worth it is a decision only you can make mate. What size are your planes?

Scott, they are 12" x 12", I think I will go ahead, if I can get a better sounder reading it will be a bonus.

[Dignity]

Definitely give you more from the tabs by moving them outboard.
Be a bit of work but you might like the results more

Sent from my SM-G780F using Tapatalk

Thanks Stue although maybe I should get skinnier crew.

[Noelm]

Might pay to have a look over the back at planing speed to make sure there is a clean flow of water further out (there probably will be) but, better to be sure.

[The Mad Cat]

I know the actuator is just sitting on your transducer, but that could be one of those brilliant idea's (the ones you get when the wind is up) to adjust transducer height at different speeds till you get it reading correctly.
Ahh well back to watching the weather report again.

TMC

[Getout]

I think that I would try adjusting the moveable ballast first. Prop torque will always cause heel to port and its worse with trim in. They are big tabs. They should work well enough where they are.

[inveratta]

I have no doubt in principle it will work "better"...the rest is just time and effort!

As far as the transducer goes...I followed a post in here some time ago and mounted the transducer in a wet box inside the transom...as far astern as possible...although I believe there is some loss of signal strength for deep water use ...otherwise its been brilliant..transducer protected ..less clutter on the transom to be damaged etc...less holes on the outside...just a thought...

[Dignity]

I know the actuator is just sitting on your transducer, but that could be one of those brilliant idea's (the ones you get when the wind is up) to adjust transducer height at different speeds till you get it reading correctly.
Ahh well back to watching the weather report again.

TMC

Now that's an interesting idea.

[Dignity]

I think that I would try adjusting the moveable ballast first. Prop torque will always cause heel to port and its worse with trim in. They are big tabs. They should work well enough where they are.

My mate will get of his seat and stand in the centre but on longer trips no such a good for his knees. He's been told by his docs he needs to lose a fair bit of weight but he just keeps putting it on. I don't help with having the pie warmer on board.

[Dignity]

I have no doubt in principle it will work "better"...the rest is just time and effort!

As far as the transducer goes...I followed a post in here some time ago and mounted the transducer in a wet box inside the transom...as far astern as possible...although I believe there is some loss of signal strength for deep water use ...otherwise its been brilliant..transducer protected ..less clutter on the transom to be damaged etc...less holes on the outside...just a thought...

I have thought of a wet box but limited space easily accessible and don't want to put a spin out in the floor at this stage although with the wind coming up it might be another project I could do.

[Dignity]

Project is on hold unfortunately as put a dingle in the bosses car today and she is not happy. Have to repair that first.