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Old 25 June 2001, 05:03   #1
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Trim Tabs

Hi,

I have a 5 meter RIB. After fitting recently
an aux engine and a second fuel tank, I feel that the balance of the boat changed and it is harder to get the boat into plane........

I am thinking of fitting trim tabs.
Will this resolve the problem, are there any side effects ?

Should the boat be specially designed in order to fit trimming tabs or is it something that you can fit on any rib ?

Thank's in advance.

Dimitris
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Old 26 June 2001, 02:55   #2
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Dimitris

You really shouldn't need trim tabs on a RIB this size, but if all else fails they might help.

Where are the aux engine and extra fuel tank fitted? Are they right at the back of the boat? If so, relocating them forward would be the best option -- trim tabs are a poor second best to balancing the boat properly.

If that's not possible, then trim tabs are relatively easy to fit. You may find that a pair of simple fixed trim tabs would be good enough, which would save the expense and extra installation work involved with hydraulic tabs.

The drawback will be a reduction in efficiency as you will be using some of your power to dynamically balance the boat rather than push it forward.

John

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Old 26 June 2001, 05:55   #3
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Thanks for the advice.

Yes, they are both fitted at the back of the boat.

I will try to rellocate the fuel tank.

Is there a limitation in the distance between the fuel tank and the aux. engine ?

Can I use a fuel pipe bigger than the one provided with the aux engine ?

Thanks again

Dimitris
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Old 26 June 2001, 10:49   #4
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Quote:
Is there a limitation in the distance between the fuel tank and the aux. engine ?
Probably. But you're unlikely to reach the limit in a 5 metre RIB!
Quote:
Can I use a fuel pipe bigger than the one provided with the aux engine ?
Can't think of any reason why not . . .

John

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Old 27 June 2001, 21:54   #5
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i own a zodiac pro 550 (5.5 meter) and researched trim tabs on the bennet trim tab web site. i built a set of fixed tabs and i notice that the boat lands softer when coming off a wave. i also found that i can plane at a lower speed however my top speed remained the same. chris
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Old 28 June 2001, 04:04   #6
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Dimitris

I would agree with John, You shouldn’t need trim tabs on a boat this size. Better weight distribution is the key to trimming a smaller boat.

Try fitting a pair of Outboard Hydrofoils to your engine; these are plastic wings that bolt on to the outboard cavitation plate. Not needed to use them myself but people who I’ve talked to that have fitted these reckon there very good. Better pull out/Lift and more stability. Might be worth trying, cheaper and easier to fit than trim tabs.
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Old 28 June 2001, 09:11   #7
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Thank's again all of you, especially to John for maintaining such a site.

I think I've got the message "Weight Distribution".

If that fails on my boat, I'll try the Outboard Hydrofoils .

As a final option I'll try fixed tabs.

Dimitris

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Old 01 July 2001, 23:15   #8
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try raising your motor so that the prop is at least level with the bottom of your hull. this will increase the trim a bit as well as your top speed. for every inch in height you gain about 500 rpm. you will need to try different props. some props like mercs laser will help keep the back end down where as the mirage prop will add lift.
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Old 09 August 2001, 03:10   #9
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Dimitris, I suppose you are Greek too. Try to put some heavy loads at the bow. I own a Bat 9 Falcon X and the first thing I did was to put an inox fuel tank as near as possible to the front. That gave me the result by two ways. First I unloaded the stern by 110 kg and secondly I loaded the bow with the same weight. I carry an auxiliarry engine as you do at the back of the boat, but since the "better weight distribution" everything seams to be normal. I also suggest that you might build an adaptor from your main fuel tank to the second engine. That will give you the advantage NOT to carry the extra tank.
Michael
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Old 09 August 2001, 18:49   #10
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It might not take very much weight removed from the sternto help your problem. We recently did RB4 and suffered the whole time from exactly the same problem simply because the console & seats were a few inches too far back. Adding weight at the front was only marginal help as it became even harder to get on the plane because of the marginal engine size (50HP). When we got back home I emptied out the back locker (about 80kg) and the boat was so much better. When I removed the spare fuel load at the bow (about 80kg) the problem was back, albeit less severe. I then moved the console and seats 9 inches forward and it is now like driving a different boat.
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