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Trim Tabs


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Hi all

At the weekend we took Osprey out on braydon for a blast and to get some photo's of her and freinds on the move (luke and annie I think you have some good pics of her. if you could send those to me please).

To my suprise she sat a lot flatter on the water than I was expecting as the pics of turbo's on the plane are always bow up a little.

What I have been doing is running full tab all the time and achive stanstill to planing in about 8 secounds and onto a top speed of 22.8 knots one way and 19.6 knots the other on braydon at nearly low tide.

The fairline had full tanks of fuel full tank of water, tender etc so was fully loaded up so I would guess about 11 - 12 tonnes. She has a pair of tamd 60b's 235hp each.

My question is should i have used full flap all the time or not? and would it have gone faster/slower or the same speed (yes luke I know I need another 400 hp and trust me i would love it lol)

cheersbar Barry

There is some pics of her on the plane in another thread posted the other day, see what you think to the trim andle :Stinky

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Hi Baz,

Using full tab will get you up faster and will allow you to stay up at lower speeds as most planing boats will drop by the stern as they slow, once you are up you are doing the equivelant of an airplane running full flaps.

Some boats benifit from a touch of tab when running just to pull the bow down a touch but a planing hull should clear its bow and sit on the planing sections aft reducing the amount of hull in the water and so creating less drag.

It is what seperates us from the less technicaly advanced semi displacement type :naughty:

If you are running into a decent head sea it can be good to apply some tab to bring the bow down and introduce the finer sections of the bow to the wave, breaking through it instead of slamming over it. If you are running with the sea then normally no tab is best, get the bow up and go.

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It’s something to experiment with Baz as they will have a different effect with each combination of conditions and loading. Personally I never (well, hardly ever) use mine as they make so little difference on a Semi Displacement even in a cross wind. I would certainly think that full down would have a detrimental effect on both fuel consumption and top end speed as too much bow down increases the wetted area and thereby increases drag. Try setting the throttles and then have a play to see what effect it has on revs. They are most useful in a side wind especially on a deep V where they can assist in preventing leaning into the wind and also in a head sea where a little bow down can help to make things a bit more comfy. One point though (sorry if this is teaching granny to suck eggs) Never, Ever use them in anything other than fully retracted in a following sea of any size or you risk driving deep into the back of a wave and having your **** end skewed around by the one you just overtook.

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I think it is inadvisable to run full tabs once on the plane due to; (a) making her bow-down and therefore increasing drag and so being less efficient, and (B) stress on the tab rams. I'm pretty sure that the Eltrim system I have on Serenity is not meant to be used with full tab in excess of 20 kts due to the potential for damage to the rams.

I use full tab to get her up, then quickly reduce to little or no tab once there. Last time out at sea, a large following swell meant I couldn't go much faster than 16kts, so lots of tab were used there to keep her planing, but on Breydon I wouldn't have thought you'd need much at all. (It seems I may suffer Davids wrath for this, but it was the most comfortable set up that still allowed us to plane and keep on top of the waves).

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I think it is inadvisable to run full tabs once on the plane due to; (a) making her bow-down and therefore increasing drag and so being less efficient, and (B) stress on the tab rams. I'm pretty sure that the Eltrim system I have on Serenity is not meant to be used with full tab in excess of 20 kts due to the potential for damage to the rams.

I use full tab to get her up, then quickly reduce to little or no tab once there. Last time out at sea, a large following swell meant I couldn't go much faster than 16kts, so lots of tab were used there to keep her planing, but on Breydon I wouldn't have thought you'd need much at all. (It seems I may suffer Davids wrath for this, but it was the most comfortable set up that still allowed us to plane and keep on top of the waves).

You could not do more than 16 knts Mark? :grin:

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It’s something to experiment with Baz as they will have a different effect with each combination of conditions and loading. Personally I never (well, hardly ever) use mine as they make so little difference on a Semi Displacement even in a cross wind. I would certainly think that full down would have a detrimental effect on both fuel consumption and top end speed as too much bow down increases the wetted area and thereby increases drag. Try setting the throttles and then have a play to see what effect it has on revs. They are most useful in a side wind especially on a deep V where they can assist in preventing leaning into the wind and also in a head sea where a little bow down can help to make things a bit more comfy. One point though (sorry if this is teaching granny to suck eggs) Never, Ever use them in anything other than fully retracted in a following sea of any size or you risk driving deep into the back of a wave and having your **** end skewed around by the one you just overtook.

This is very interesting as i used full flap last time out at sea and there was a big swell about 2+ mtr waves and when they were coming from the rear quater, I did suffer a lot of slewing which suprised me a bit as I have read a lot about the turbo's superb sea keeping abilities, they used to deliver them in anything upto 7s/8s.

what speed increase do people think i may achive and please look at the pic on the other thread and give me your apinions on the way she is sitting on yhe water.

cheersbar Barry

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I would be very supprised if you don't gain a couple of knots Baz,

As David said the easiest way to find the best trim is to set the throttles and then without touching them move the tabs a bit at a time until you get maximum speed. you will probably find it is +/- 1degree or a bit different to the 45 degrees you are running.

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Who has Trim Tab Guages, as i don't on mine. If you operate them without the engine running, you can tell when they have reached their full travel by the sound of the pump. However, when you have the engine running, you can't hear a thing and are never sure when they have reached the end of their travel.

Mind you, i haven't got a guage for the leg either, but i'm looking into that one and it only goes one way at the moment anyway - UP !

Grant :grin:

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Who has Trim Tab Guages, as i don't on mine. If you operate them without the engine running, you can tell when they have reached their full travel by the sound of the pump. However, when you have the engine running, you can't hear a thing and are never sure when they have reached the end of their travel.

Mind you, i haven't got a guage for the leg either, but i'm looking into that one and it only goes one way at the moment anyway - UP !

Grant :grin:

Hi grant I dont have gauges so I called bennets who made my tabs and they said I cannot fit gauges to my year of tabs .

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I bet you could knock something up with a couple of 0-180 or 240-30 ohm gauges and a couple of matching pots, if you really wanted to. I have them but even on the rare occasions I use the tabs I feel what the boat is doing rather than look at them. They are handy for a quick glance to see that they are retracted before leaving the boat so the rams don't get fouled but that could be achieved with a couple of LEDs.

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I bet you could knock something up with a couple of 0-180 or 240-30 ohm gauges and a couple of matching pots, if you really wanted to. I have them but even on the rare occasions I use the tabs I feel what the boat is doing rather than look at them. They are handy for a quick glance to see that they are retracted before leaving the boat so the rams don't get fouled but that could be achieved with a couple of LEDs.

My problem is when I am on the fly bridge I cannot feel the trim angle very well, down bellow I can but I only use the downstairs helm in horrible weather. But like what was said in this thread I should not need them to much so next time out I will play with them.

On another note when I was flat out I only reached 2600rpm the max on my engine is 2800rpm (would not having trim tabs all the way down increase the revs by that much. just to say I get no black smoke on the plane cheersbar

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The max revs given is usually not a finite number lke 2800 but more like 2600 to 2800 and if you are in that range then the motor is neither overloaded, overproped or underproped . As you had max trim down then you might get another couple of hundred revs but more likely another 100 to 150.

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The max revs given is usually not a finite number lke 2800 but more like 2600 to 2800 and if you are in that range then the motor is neither overloaded, overproped or underproped . As you had max trim down then you might get another couple of hundred revs but more likely another 100 to 150.

thanks for all the advice, it is nice to know people are there to help

cheerscheers

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