Trim Tabs

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whisper

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New boat has these along with normal powertrim on outdrive leg.
We've never previously employed the former protuberances so can those of you with experience thereof please give us some advice as to their efficient utilisation. OR for the less literate - what's the best way to use them? Also, are there any articles we could read on the subject?
I apologise in advance to anyone who thinks this question is "rude".
 
I apologise in advance to anyone who thinks this question is "rude".
RUDE! I think its disgusting, such slightly veiled allusions to deviant sex should be banned from the forum. You realise children come here as well as well brunged up ladies.

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Cribbed from "how to drive a power boat" by TCM (aged 13 1/2)

Re: trim tabs [re: JeremyF] Post Reply




at the backof a powerboat if you look into the water are 2 sort of flap things about 6- 8inches sqaure each with a little hydraulic ram. The ram can extend to push down the flap. This wd make the nose go down if u think abt it. Or, if just use one you can straighten up a unbalanced boat or trim for beam sea.

Often, trim tabs simply make the boat go slower. But mine a little teensy bit BUT not too much make it do 1 knot more! No trim tabs on a sail boat. Don't even say "trim tabs" or they'll know yerv been here.






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Now are you sitting comfortable. Then I'll begin. Sit up straight and pay attention cos its all been said a million times before and I'm fed up!! Besides some one will only contridict me. Or rephrase the same bloody thing.

So. Trim tabs can be used
1/ For better speed/economy.
2/ More comfort/saftey.

On flatish seas you maybe want best economic speed. So trim till the best is obtained at desired throttle settings. Maybe gain a few knots if you get it right.

The other reason for them is this. When going into the waves, it's better to have as much boat in the water as possible. So put the bows down.

With the sea behind you, the oposite is true. You need the bows up. Or might cart wheel at the bottom of the wave, when stuffing nose into the one in front.

You can use them independently if going side on to seas, to keep the boat level. But this is not recomended by some cos if things change suddenly you could be in the shit!!

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Haydn
 
I quote from my Fairline owners handbook -

Trim tabs are useful for the following purposes

1. To help the boat get up onto the plane when there are a large number of people in the cockpit or when for any reason the boat is very heavily loaded.

2.To push the bow of the boat down when running into a head sea so as to present a deeper "V" to the sea and have a softer ride.

3. To correct any tendancy of the boat to lean into the windwhen operated at planing speeds in a cross wind; and to correct any tendancy to lean as a result of the disposition of the crew or stores within the boat.

WARNING: Do not use trim tab controls in the opposite sense at the same time as this can over load the electrical circuit. Use both bow down, or both bow up, but do not use port bow down , starboard bow up at the same time.

I hope this helps you

Nick

My boat is here in time for winter....
 
For ref some Eltrim tabs fitted to Sealines actually operate contra for Port/Starboard triming, port tab up/starboard tab down, port tab down/starboard tab up.


Brian
 
Re: Ouch!

well, at least you kept the posting!

For whisper...

In flatish sea you adjust these for maximum speed at same revs, obviously gives max efficiency. Yeah, just fiddle with them a teensy bit. Can't imagine why you'd need the last 50% except to er make it look as though you were going downhill.

With radar, you can point the nose down to ensure the radar can "see" forwards, better than with the boat leaning back.

*make sure* that the things are all the way in every time you return to port, otherwise

a) you may rip them off if reversing hard against lowered trim tabs (aka flaps) or

b) the small hydraulic rams will get barnacles onnem and bugger up the seals, at which point you have the turned them into automatic hydraulic-fluid exhalers, and i never found a useful purpose for this feature...
 
Re: Ouch!

Na ! Just did a search .

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Re: Ouch!

Thanks tcm that's the sort of info I was after.
I knew what they were, what they were for and how they worked, but wondered if there were any tricks involved in using them properly.
Presumably different boats will react in slightly different ways to the same trim input, so we probably just need to experiment with it.
I get the impression from your comments that a heavy handed approach is unwise.
With apologies to Byron for the use of "tricks".
 
You can even use flaps...

...to test the hull design.
Though it is true (as mentioned in other posts below) that flaps can improve top speeds in some specific conditions, generally they shouldn't.
In ideal conditions (normal load, calm sea, no wind/current, correctly aligned legs - if any), a well designed hull should achieve both:
1) better fuel economy at cruising speed, and
2) maximum top speed
without trim tabs (i.e. trim tabs fully up).
If in those conditions you get any benefit from playing with the flaps, you'd better worry about the hull in the first place.
For high performance boats (where integral trim tabs are part of the hull design), this may not be true, but that's another story.
 
Morning gang.....

....work gets in the way of real life does'nt it!!

I agree with Nick2, I've got the same fairline info on tabs. I'm fairly new to all this and I'm sure its obvious stuff to all you experienced folk- but I have been amazed by the amount of fine tuning you can acheive by using tabs. I've got a 21' Fairline and noticed at the end of this season when playing about, carefull use of them made the difference between staying on the plane down to about 13/14 knots or falling off altogether!- not sure about fuel consumption when doing this, not measured it yet. I suppose this could mean the difference between being able to push on, or having to reduce to displacement speed if needed?

Like everybody else has said, can make considerable difference to comfort according to conditions. My only problem is knowing where the damm things are set- normally bring them both fully up before starting so I have a reference!
 
Yes. I have the same trouble. No indicators. I count up to six when pressing trim tab button. Which is fine the first time round. But then if need to adjust more, it's easy to lose track of where they are. Specialy cos one works faster than tother. So then have to go back to zero and start again.

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Haydn
 
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