Trim Tabs

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ontheplane

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Hi there,

My boat is a bit underpowered (many posts on this) and I think i am gonna have to fit trim tabs.

Have seen Lancings "Size guide" for bennett tabs - and note that they vary in width (i.e. across transom) but are always 20cm in depth (how far they stick out from stern).

Bearing in mind that what I want is maximum lift with minimum drag, I would have thought that a deeper tab (40 or 50cm out from the stern) would mean that I could apply less angle of tab (less drag) and get more lift?

Am I wrong, or do I need to look around for a different tab maker (Lancing do Bennett).

Does anyone know people who do other makes (preferably cheaper than bennett)?

Thanks
 
Bennett did a racing version with a different profile - very long & relatively thin with twin pistons - but specifically for 28'+ 'Formula' types maxxing at 70 mph if I recall right.

Wouldn't think that would be any good for you, if your short of power tabs will help a bit but not that much ...
 
I don't think your logic is right. If you apply less angle on longer tabs to get the same trim position for the boat, then the drag is the same. VP sell trim tabs that operate vertically, so a 90 deg angle with very small tabs, and they don't create extra drag.

What longer tabs would allow you to do is to apply more trim to your boat, which may help the boat to get on the plane more easily, but that is a slightly different question.
 
Our boat has trim tabs, but the manual claims these are not needed! Well actually just for trimming against the wind, we've never needed to do that though and i doubt we ever will.

I did once take it from Poole to Briham with the tabs down, then the next time with them up. Not the slightest difference in fuel consumption or speed.

Never worth fitting as an extra I'm sure
 
My problem is getting on the plane with an underpowered overweight old boat.

So the next question is - are there any decent, cheaper versions of the trim tab other than Bennett, and who supplies in the UK?

Money's tight at the moment so looking for a good deal
 
Fairline Weekend 21 with volvo AQ145 and 280 leg.

The leg isn't power trim so I've set it at the lowest trim setting

The engine produced 145hp when new - bet that's dropped in the 20 years since she was built!

And weight wise, when new, dry with no kit it weighed 1800kg - with all kit on its probably more like 2000kg or even a bit higher now.
 
Maybe try one of those dolphin attachments for your leg.

I'm not sure trim tabs are going to be the cure you may be hoping for. They will certainly be a costly addition though.

Just another possible. Try trimming the leg up a little, I doubt if fully down is going to be helping if you are already struggling to get on the plane.
 
Sadly I can only get the Hydrofoils for the Mercruiser leg not the Volvo as the exhaust comes down the cavitation plate.

I also never had the best results with the hydrofoils.

I will try trimming the leg out a notch or two, however I have moved it in from 2 notches out as it wouldnt get on the plane at all, it is better, but not cured.
 
Theres other factors that come into play. How is weight distributed about the boat, is it stern heavy. Is the prop the right pitch for the boat/engine set up. Are you getting max revs etc.

I have the same engine/drive as you on my Tremlett. I found that setting the cav plate/exhaust level with the keel is the ideal set up. On a boat of around 21ft I'd say the issue is not power but the excess weight and the way its loaded. Mine hits high 20's easily and on a good day see's 30 knots and its around the same size weight as yours.
 
Hi - I have seen hydrofoils fitted to a Volvo leg with the through cavitation plate exhaust, it used a made up adaptor plate and from what I hear it worked very well - it was a similar size and type of boat to yours also. I'm sorry but I can't get you any more info as the chap who did the work (he did the modification to his fathers boat) has sadly passed away.

Although I have trim tabs I am still thinking of doing the same modification to my Sea Ray to get out of the hole faster when we do our winter lift out in February, i also seem to recall seeing detials of an purpose made adaptor plate when I googled hydrofoil volvo penta.

Best of luck with it.

Mike
 
have you looked into the Volvo set up? Always struck me as a bit counterintuitive that a blade going vertical into the water works well, but apparently it does. MAybe it causes less drag, if thats what your are worried about (No idea myslef!)
 
That setup is always going to struggle, most Weekenders were sold with larger V6's or V8's because of the marginal performance, its a common problem with many boats of that size and age. I used to have a Cruisers 224 with 190hp and that was the same you had to send the crew forwards to get it up then they could return to the cockpit once on the plane. To be honest I don't think the tabs are really going to help it as much as you think, would be cheaper to say buy some more anchor chain and make sure all your kit is stowed in the bow.
 
I've got a decent dinghy that I intend to tie onto the bow when underway, and asking crew to head for the cabin will be an option - however it's far from ideal.

I will look into the fitting of a Hydrofoil to the outdrive leg though as that may work.

Does anyone know what the main differences were on the AQ151 engine - as I suspect it may just have been larger carb jets or something so I wonder if there are any mods to bring the power up a bit - even 10-20hp may make all the difference!

As to prop pitch, I could perhaps go down an inch, but I fear I'd lose all top end and the engine would always be revving quite high then. Again it's something else to try.
 
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