trim tabs

niels · 05 February 2003, 09:33

Is there someone who has experience with trim tabs?
I'm thinking of bying them for my rib, but I don't have any knowledge about that subject. Manufacterers(?), size, do they realy work? And what about powerlift, does someone know a good site on the net or something?

thanks
Niels

Alan Priddy · 05 February 2003, 09:51

If your boat is under 7 metres forget it they will not do anything.

Alan P

Julian · 05 February 2003, 10:35

Hi

As Alan said you need a boat over 8 meters really and one that is quite heavy to get the benefit from them. We use them on our boat and they are great to help with the balance etc.

Julian

Manos · 05 February 2003, 12:47

I had made similar inquiry a few months back and I got the same aswer as you got from AP and Julian from the boat and trip tab manufacturers.
That is to get any benefit out of them you need a long heavy boat.

seafariskye · 05 February 2003, 19:09

Have just fitted them to my 7m.

I think the difference is very big, can now control the front lift on the boat, and can even it up with a load on.

Most difference i noticed, and is why i put them on, is going into a head on sea, the 'slamming' is greatly reduced, and so am pleased with the result - Taking into account my 7m is fairly heavy with the volvo in it (prob More than Average) on the stern.

By chance (and have not been in it) a couple here put fixed tabs on their 5.5m with a 50 hp yam 4 stroke on it - they said it made a big difference, again, in a head on sea.

My overall - wish i had fitted them last year.

Pete F

Dirk Diggler · 05 February 2003, 19:16

I'm a little confused by the replies to Niels question regarding trim tabs. Surely, if my understanding of the purpose of tabs is correct, they can only enhance the charecteristics of his hull.
To say that they won't work on a sub 7 metre boat is incorrect. Why do you think they wouldn't work?

Infact, take a look at www.bennettrimtabs.com , they have sizing guidlines for boats from 15' upwards.

As for powerlifts, I can recommend both Stainless Marine and Bobs Machine shop. Both excellent products, although I prefer the Stainless Marine version.

crazyhorse · 05 February 2003, 19:38

Im in agreement here with Seafriskye and Dirk.

They should help in trimming the boat and maybe keeping the nose down or up when needed.They will pay for themselves in fuel economy over a number of months.

Im also running with Bennet trim tabs they are available at most marine stockists.

matiboy · 05 February 2003, 19:44

good link to trim tab explanation

http://www.boatshop.com.au/Publish/index.html ( I like the bit about the auto trim tab which is supposed to adjust itself according to the attitude of the boat )

For a smaller boat wouldnt a hydrofoil do the same sort of job ?

The one main adv I can think of with trim tabs is that they would reduce chine walking & give a more stable ride, but ribs with low sponsons dont suffer the same as a glass deep vees as much anyway

Neils

What benefit are you hoping to get from fitting these ?

Dirk Diggler · 05 February 2003, 19:45

Blimey Crazyhorse, we actually agree on something, have a virtual pint on me my old mate.

crazyhorse · 05 February 2003, 19:48

Down Tiger

seahound · 05 February 2003, 21:44

I fined the trim tams good for a beam sea. If the swell is hitting you on the Stbd side, then drop the Stbd tab. This will level the boat out and give a smoother more efficient ride.

John Kennett · 06 February 2003, 08:23

Quote:

Originally posted by niels
I'm thinking of bying them for my rib, but I don't have any knowledge about that subject.

Why are you thinking of fitting trim tabs? Is it for a specific reason? If you, there may be other solutions as well as trim tabs.

If your RIB is set up correctly with a reasonable weight distribution then you shouldn't really need trim tabs, although there's no reason why you can't fit them if you want to!

John

Julian · 06 February 2003, 08:39

A good boat will ride level without trim tabs if set up correctly, they are usefull in a beam see as you can level the boat. We fitted them to our boat because of the weight in running a diesel , ie the stern is very heavy and with a full load it makes life easier if you can angle the boat according to the sea. With an out board you shoudl be able to set trim using the engine and steering correction when hitting a beam sea. Trim tabs also increase the fuel consumption and they increase drag on the boat. They are good on ours though.

Julian

Charles · 06 February 2003, 09:46

Bear in mind, trim tabs are like huge spades in the water and will slow you down -ie drag! Don't fit them if you don't need them.

Alan · 06 February 2003, 09:56

Confession time here. I went halfway around Britain in 2001 on Cyanide completely misunderstanding how to use tabs and getting frustrated. My logic was that to counteract a lean to port (caused by cross wind say) you would tab down on the opposite side. This of course is complete rowlocks as the tab gives you lift (think about it as a jack) so if you are listing to port you put port tab down. Life was much more comfortable once I had realised this!!

Tabs are useful to put the bow down in a head sea - moreso on a diesel boat than an outboard IMHO. As others have said, if the balance of the boat is right then less need for tabs. I don't feel any great need for them on my Scorpion although I do have a doelfin hydrofoil on the outboard which in theory gives me the for/aft trim ability. Clearly doesn't do anything for port/starboard.

Engine lifts as fas as I know are for the performance concious. Recommend Niels that you check out some of the US bulletin boards & websites as they are much more prevalent over there.

Dirk Diggler · 06 February 2003, 10:13

Quote:

Originally posted by Charles
Bear in mind, trim tabs are like huge spades in the water and will slow you down -ie drag! Don't fit them if you don't need them.

That is quite true, but they do go up as well as down. I think that the statement that a "A good boat will ride level without trim tabs if set up correctly" is a view held by many, but is sadly incorrect. Julian if you truly believe this, and you admit to having them on your boat, are you saying that your Scorpion is a Bad Boat or that it is Set up incorrectly.

A single engined sports boat or rib will in certain conditions lean to one side, and in these conditions a couple of degrees of tab will correct this. Surely there can't be any one here that at some time hasn't been in a beam sea, with the boat leaning into the wind, who hasn't changed course by a couple of degrees to try and level the boat up a bit and make it more comfortable. If so, surely you must appreciate what a set of trim tabs would do.

Julian · 06 February 2003, 10:23

Dirk

On the contrary the scorpion is a fantastic sea boat and the set up is very good. When you have an extra tonn of engine sitting on the back of a boat it changes the handling charateristics of the boat. We dont use trim tabs unless in a heavy beam sea, there is allways drag with the tabs and by raising them you can only go so far as when they are abouve the bottom of the hull they will not lift the bow an inch. they are purley used to balance the boat when needed and not to be used to trim the bow up etc.

Julian

Manos · 06 February 2003, 11:04

Quote:

Originally posted by Dirk Diggler
A single engined sports boat or rib will in certain conditions lean to one side, and in these conditions a couple of degrees of tab will correct this.

Correct (I would also say a twinn engine sports boat or RIB too) but this is factor between the boat's free-board distance and length.
I believe that for a small RIB and up to 7/8 mtrs with small free board there is no need to have trim tabs. However, for a larger RIB like the 10mtr Scorpion with high free board you need to have them to correct trim and balamce.

Dirk Diggler · 06 February 2003, 11:20

Manos,

What on earth are you talking about? Why do you think you only need to correct trim & balance on a 10 metre boat?

You also said in an earlier post that you had spoken to Tab Manufacturers and they told you that they wouldn't work on a 7 metre boat, who were they and why do they think that?

Manos · 06 February 2003, 11:55

If you have bothered to look at my post you see that I said that on a small boat with low free board you do not have a problem of trim and balance (meaning that you can corect the trim with the engine if you need to and the balance you can distribute the weight round so that it does not lean on one side. - since I thought you are an expert in boats you will understand that but.........

)
Now on a bigger boat is much more difficult to adjust all that (I expect that you will agree) and therefore you need trim tabs.
Cabin RIBS have high free board (and also speed is a factor but we will leave this out as we assume that the boats we are talking about do over 15 knots). Free board distance plays an important role in the boat leaning over in high winds and triming is of importance (triming means bow triming i.e. bow going up or down and balancing i.e. not leaning on either side - hope that I made this clear

).
What all means (what did you say your degree was on?? By the way for lessons on basic naval architecture and engineering try an HND course), is that the higher the boat the more exposed to the beam wind is and the more is pushed down on one side and the more uncomfortable the ride becomes so you need the trim tab to correct this as well as the bow ride.
Boat manufactures who said this are too many to list (also it will help you to know that you should have a look in basic naval architecture and engineering books). I have also asked some UK boat manufactures too and trim tab manufactures.
You will be supprised to know that they all said that these are TOYZS FOR THE BOYZS (I think the expression fits the description of someone I have never met doesn't it DIRK??

)
On a small RIB (up to 7/8 mtrs) trim tabs are not of much use (no that high free board, low boat weight, easy to move things on the boat to correct trim (i.e. leaning left or right

), engine trim use etc etc

)!!!

Now can we have a serious discussion in this forum??