Oversize Trim Tabs

ontheplane

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Had a lengthy chat with Magic Marine about the problems with getting the Fairline Weekender up on the plane.

After a while we've come up with what we hope is a good solution - oversize trim tabs.

Basically for a 21' boat they would usually reccommend a 12" span x 9" chord (how far they stretch back from the transom). I will be fitting a 24" x 12" tab!

Theoretically, a tab twice the chord will provide four times the lift at full application, and one twice the width (span) will give twice the lift - therefore, these tabs will provide around four times the lift compared with a standard size tab for this boat.

The logic is, that to get the boat up on the plane, the tabs will need to be reasonably deployed, but hopefully they won't need to be anywhere near fully down - this should provide considerably less drag than deploying a smaller tab fully down.

I'll post back once they are fitted to let everyone know if the theory is borne out in practice!!!

Has anyone fitted Bennett Trim Tabs with the Electronic switches that also have the indicator lights on them?? If so, are there any major worries or pitfalls to watch out for? Reading the Instructions they look pretty complex, however hopefully as long as we follow them step by step we should be ok???
 

ontheplane

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..forgot to ask - what size trim tab anodes do I need on these, and should I antifoul them or not.

If I should antifoul them then do I paint them before or after fitting the anodes and should I paint the anodes or leave them unpainted.

Also where on the tab should the anode be fitted, or doesn't it really matter?


Thanks
 

Kawasaki

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Crikey!
That seems one heck of a Trimtab.
Some years ago, maybe 15, so the mememory dims.
I fitted some leccy bits, radio and stuff to a 21.

Didn,t have tabs but She planed ok with 4 peeps aboard.
What engine does She have?

As hlb says don't paint the anodes.

The size.
The smallest you think will last between lift outs.
IE the anode should 'rot' if it is doing it's job.
This is a mute point however.
It depends on how electrolysis is active where you berth etc.
 

hlb

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Yep, you need the smallest that will last between lift outs. or ones that will last for two. REcon I could put my old anodes back on again. But a bit of a balls up, if It dont reach next lifting date.
 

hlb

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I'd be a bit worried about to big a tab. Tabs are amazingly effective. MF is 8 tons, yet quite small tabs, have a big effect. Can make the boat heal like crasy if press the right one. or wrong one as the case mght be.
 

AndieMac

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What is the power plant of the boat? Assuming it is an outdrive, have you thought about a Stingray foil that bolts on the top of the cavitation plate, above the prop?

It makes a massive difference to my boat, of course assuming yours is inboard/sterndrive.

A cheap investment for a lot of result, and Bennent gear is good, as long as properly installed.
 

AndieMac

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Do the outdrive foils rate in Britain?

They certainly do in my books, original Stingray brand anyway. There appears no noticeable difference in fuel consumption, and they bring the bow nicely.

The application does lend itself to heavy sterned inboards, particuarly in the 21 to 25 foot range.
I have heard of go fast outboard powered boats at high speed in a following sea have had "situations" occur. That of course could have been operator issues!


idomeneus5... G'day.. the cruisecraft are a great boat, is yours on a trailer?

jkay.. are you saying the 21 footer in question has a 145 h.p. outdrive? is that petrol or diesel?
 

Kawasaki

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[ QUOTE ]
145hp,I,ll help his thread along /forums/images/graemlins/grin.gif

[/ QUOTE ]

Good help jkay.
Lots were fitted with 200hp.
The boat is designed to go fast.
It is a Planing hull.
With 145hp, lots of people and a dirty bottom it will struggle.

on the plane.
Look at the Fairline owners club web sight.

/forums/images/graemlins/wink.gif
 

ontheplane

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Yes they were fitted with up to the 200hp V8

This one only has the 145 4cyl and she will plane, however she needs full throttle, and all the crew to move forward to the cabin, the leg trimmed right in (not power trim so adjustment by the bar on the sterndrive), a PERFECT clean bottom etc etc....

I looked at the doelfin type things but there are two probs with those -

1) It's the old fashioned Volvo sterndrive with the exhaust running through the cavitation plate so no-one makes a foil to fit
2) I don't like the idea of that much load going in a vertical plane - the drive wasn't designed strong in that direction.


You are right it's over tabbed. I will never use full tab I don't think - certainly not to correct heel - possibly will only need 10-20% of tab but the idea is to be able to create a huge amount of lift at the back without having a steep tab angle - this SHOULD (and the proof of the pudding will be in the eating) allow me to get her to pop up onto the plane at a very low speed, then ease out the tab until she'll cruise at an economical 15kts or so staying up on the plane not dropping off.

We'll have to see.

To fit the anodes, do I just drill a hole thru the tab, a bolt and a nut and the anode??

I'm surprised they don't supply a stud or something on the tab to help with this - won't a bolt-head on the underside of the tab create drag?

Thanks
 
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