Forums > Sailing General

Trim tab design and construction

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Created by garymalmgren > 9 months ago, 10 Mar 2020
garymalmgren
1172 posts
10 Mar 2020 7:08AM
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On another post Cisco expressed interest in a trim tab system for a stern hung rudder.
In this video Kevin goes through his unit in pretty good detail.

Gary

cisco
QLD, 12337 posts
10 Mar 2020 10:56AM
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Thanks Gary.

stray
SA, 323 posts
10 Mar 2020 8:05PM
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Here's my DIY vane gear set up.
I took it off my previous boat to use on the next.











Things to note are -
the 20ish degree angle of the pivot is needed to self dampen the vane. When it lays over it gets to a point where its forced back toward centre.

Adjustable counter weight can be used for damping.

wind blade is as light as possible.
I made a hollow air foil balsa one, with epoxy dynel layer.

link rods are adjustable with fork turnbuckles welded to rod.

Trim tab cant be balanced at all because it needs to force the whole system back to a nuetral position whenever the boat comes back on course. If its balanced it will wander either side of a course. You may also have problems if the rudder is over balanced.

The counter weight on the right angle lever is to counter the weight of the top link rod.

the trim tab was just a steel flatbar welded to 12mm stainless round bar.

this set up should work on most transom hung rudders as long as the helm always tends to centre itself when left free.
Mine was on an auxiliary rudder and designed to allow the use of dinghy davits.

hope this inspires some of you DIY types out there.

cisco
QLD, 12337 posts
10 Mar 2020 9:39PM
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It will take me a bit to nut that one out but it looks good.
Thanks for the post.

boty
QLD, 685 posts
11 Mar 2020 7:25AM
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Select to expand quote
stray said..
Here's my DIY vane gear set up.
I took it off my previous boat to use on the next.











Things to note are -
the 20ish degree angle of the pivot is needed to self dampen the vane. When it lays over it gets to a point where its forced back toward centre.

Adjustable counter weight can be used for damping.

wind blade is as light as possible.
I made a hollow air foil balsa one, with epoxy dynel layer.

link rods are adjustable with fork turnbuckles welded to rod.

Trim tab cant be balanced at all because it needs to force the whole system back to a nuetral position whenever the boat comes back on course. If its balanced it will wander either side of a course. You may also have problems if the rudder is over balanced.

The counter weight on the right angle lever is to counter the weight of the top link rod.

the trim tab was just a steel flatbar welded to 12mm stainless round bar.

this set up should work on most transom hung rudders as long as the helm always tends to centre itself when left free.
Mine was on an auxiliary rudder and designed to allow the use of dinghy davits.

hope this inspires some of you DIY types out there.


wow nice work

Ramona
NSW, 7584 posts
11 Mar 2020 8:33AM
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I would suggest going straight to a servo system. Trim tab systems work OK up wind and reaching but will not be satisfactory sailing dead down wind in light conditions.
My replica Monitor in SS probably cost about $200 in materials, a fair bit of this was in the bevel gears. But the labour was extensive. I paid $700 for my secondhand Aries. The Aries steers exceptionally well, especially downwind. The course adjusting levers make it a better unit to use than the real Monitors or Flemings.
My SS unit is installed on my fence as a garden ornament at the moment. The video shows the unit in it's earlier guise. Now has brass gears and a stronger tiller.

stray
SA, 323 posts
11 Mar 2020 10:17AM
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Ramona said..
I would suggest going straight to a servo system. Trim tab systems work OK up wind and reaching but will not be satisfactory sailing dead down wind in light conditions.
My replica Monitor in SS probably cost about $200 in materials, a fair bit of this was in the bevel gears. But the labour was extensive. I paid $700 for my secondhand Aries. The Aries steers exceptionally well, especially downwind. The course adjusting levers make it a better unit to use than the real Monitors or Flemings.
My SS unit is installed on my fence as a garden ornament at the moment. The video shows the unit in it's earlier guise. Now has brass gears and a stronger tiller.



Why go to a servo if you have a transom hung rudder ?
My auxiliary transom hung rudder steered fine on a run.
It seems like a lot of extra gear to do the job of a trim tab.



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"Trim tab design and construction" started by garymalmgren