Trim tabs on the rudder

[jeanette]

Does anyone have any experience about the usefulness of such a thing?

The helm is very heavy on my boat when motoring, mostly due to the proximity of the rudder to the prop. Someone suggested a trimtab would make it a lot lighter and therefore easier to steer.

Does anyone have any comments?

It's a steel boat with a steel rudder. I am assuming a trim tab of some sort would be cheaper and easier to make-up and trial than a new rudder.

Thanks in anticipation.

<hr width=100% size=1>Jeanette

 

[boatless]

First thoughts..

If the prop wash is permanently trying to turn the rudder, a trim tab would be very effective if large enough and in the right place. Empirical testing would be the best way to design it! I wouldn't put it downstream of the prop though, better in clear water, because the prop wash is spiralling.

If it's just heavy, then I think the only solution is to get the area downstream of the prop further away or smaller.

<hr width=100% size=1>my opinion is complete rubbish, probably.

 

[jeanette]

The boat has a long keel, the only place to put it is on the back of the rudder. The rudder hangs off the transom.... mmmm.

<hr width=100% size=1>Jeanette

 

[boatless]

Jeanette, sorry.

Didn't make myself clear, meant open water but at the bottom of the rudder. So not open water at all, but clear of prop wash!

If that's not possible, then the majority of the area needs to be in either the top or bottom half of the prop wash.

If the tab was centred in the helical path it could mean that the helpful half of the tab was opposed by the other half.

<hr width=100% size=1>my opinion is complete rubbish, probably.

 

[maxi]

Having read an item (probably PBO) regarding propeller induced helm problems, we put a small fillet on the trailing edge of one side of the rudder of a Mirage 37, where the propshaft is slightly offset.

The effect was immediate and considerable in that it completely reversed the helm required. Subsequent paring down, of what was already a small fillet, quickly produced neutral helm under motor. No perceptible impairment under sail.

The only thing I cannot remember is which side of the rudder we put it, high pressure or low pressure, a little experimentation with a sliver of timber would soon show you where the fillet needs to be - and very worthwhile.

<hr width=100% size=1>

 

[jeanette]

Thanks for you comments - they give me more options that I had originally thought.


<hr width=100% size=1>Jeanette