Trim Tabs????

[Getout]

Chimo, I'm surprised to see foils on the cav plates. Are they for trim control or to reduce cavitation because you have a high motor position?

[jimbo59]

Yes the tabs will fix the problem but a set of wedges is all that might be required,your motor might not have enough negetive trim.When you fit tabs on some hulls to fix this problem it lifts the bum and makes the nose smash down when it gets lifted up over a swell becuase they are fighting against each other;motor v tabs. Its your call $750 v $60. ... jim

[Chimo]

Hi Getout

I fitted the foils first as I always like to be able to plane slower and also get the bum up quicker which foils always do. I've had foils on all but the first 12ft ply boat I've had including small tinnies with 9.9 HP.

I always try to get my motors as high as I can without getting cavitation etc.

There is no cavitation occuring and at medium to high cruise the foils sit either on or above the water surface which means drag is minimized and speed economy are optimized.

The Lenco trim tabs do deal with side to side trim but even when in their fully up position they do effectively add to the boat hull length which further aids rapid bum lifting.

The in / down trim on the outboards when first starting to move up to slow or med cruise is far less critical with the tabs and the foils fitted. Also note I have 13.25 d and 20 pitch Rakers fitted and these are a prop capable of running high ie almost as a surface piercing prop. From what I've been told Vipers and similar props need to run deeper in the water to give their best performance. At WOT (approx 5200 or 5300 rpm) speed is around 42 or 3 kn from memory.

As said in previous posts when Lindsay Fry fitted the Lencos and was asked why they are not on all the bigger Seafarers it just comes down to what people wish or are able to spend. Those who have them would not be with out them. In my case I have set the boat up (motor height etc) to benefit from both foils and tabs.

Hope this answers your question and that I have not rambled too much.

Cheers
Chimo

[Mad one.]

Thanks Guys,

If I were to fit tabs would there be any down side, I currently have a foil and the boat has the old sport fish transom (open)

What would be the best tabs to fit?


Please find attached a pic of the moter in full down trim,

Mad One

[Smithy]

The Volvos you have to gain direct access to only a couple of inches up from the bottom of the hull. On my boat that didn't suit as I had a welded in chequerplate floor. My Bennett rams are therefore above deck level on my boat as you need access to them to run the hydraulic lines. I have not fitted Lencos, only used them but they rely on an electric screw drive instead of a hydraulic ram. They are the 3 main players in the game. If you can gain access directly behind them the Volvos have all the kudos at the moment. Bennetts had the best reputation for reliability till the Volvos came along and of all the electric brands Lencos have the best reputatation for reliability.

PS

Couldn't see your picture.

[Chimo]

Madone

Smithy is correct about the need to get low access with the Volvos

The Bennett rams are oil filled and powered so you need electric and also have to have oil lines etc. Had oil ones before and dont want any more oil other than the hyd steering anymore thanks.

The Lencos only need a elec feed and the screw set up is fool proof as you cannot over do adjuatment up or down. You can get an adjustment button with LEDs that shows their positions. I dont have that bit just the normal ones. would be nice but you can tell / feel where things are with a bit of experience.

If you like simple as I do then think about Lenco or similar,

Pics of set up thru transom on the Vag fyi.

Cheers
Chimo

[Mad one.]

Attachment 23210

Photo of motor with full down trim,

[Chimo]

Mad One

be easier to see if you set pic size to 600 by 400ish and took pic with motor level Ie half trim

Also need a pic from rear, level with tabs to see motor height relative to boat bottom / keel

Do you use http://www.irfanview.com/ to resize pics for AF?

Cheers
Chimo

[gofishin]

A lot of people think that tabs are only for lateral trim (side/side), and that motor trim is best for longitudinal trim.

Wedges are really only of benefit to correct an inappropriate transom angle (transom has been made too upright). There are some minor differences between motor manufacturers, but generally 15 degrees is about right (from memory) to allow the motor trim ‘sweet spot’ to be approx in the middle of the trim range. If your transom angle is OK (for make of your donk), and you use wedges to gain –ve trim (nose down) then you are loosing +ve trim (trim out). Like robbing Peter to pay Paul…

Smithy, you couldn’t have said it better, especially this part.

...allowing you to run the prop at a neutral angle for more efficiency...

The following has probably been written often, but it is a very important statement “Motor trim is for trimming the prop, trim tabs are for trimming the boat”.

Using the motor for –ve trim has a big effect on propulsion efficiency, that’s why shaft drives are quite inefficient when compared to outboards, sterndrives and the new IPS type systems. Think about the line of thrust compared to the movement of the boat through/over the water, the larger the angle between these, the less efficient the propulsion system will be, and that’s a FACT.

With conventional transoms I have not previously heard of the need to drop the donk, however it may obviously be required in some cases. Mirage, was the outboard(s) on a pod in your case?

Dropping the motor down (if required) will have the negative effect of increasing bow lift due to the line of thrust being further away from the friction force on the hull (force at a distance creates a twisting motion). However, this ‘negative’ is only small when compared to the large ‘positive’ you will gain from installing tabs.

The only downsides that come to mind are that conventional tabs create a bit of drag when reversing hard, and that the hinges on some conventional tabs ‘as supplied’ can create a lot of spray at lower speeds. The former is not really that much of a problem with trailer boats as it is easy enough to spin the boat & chase the fish down etc. Obviously the QL tabs don’t have this problem.

The latter can be solved with a strip of ~1mm plastic sheet and a heat gun by making up an ‘angle’ the width of your tabs and securing between tab and transom. This covers the hinges and prevents any spray coming through the hinges. Obviously flexible material would work too.
cheers
Brendon