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Old 10-11-2020, 08:21 PM   #1
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Trim tabs

I have a 1983 Nova Marine 42 Sundeck. when I purchased it, the 4' trim tabs were pinned in the fully down position. The hydraulics to operate them have been removed. question is, are they even needed on a boat that does no more than 12 knots? if I take these trim tabs off since they are in the down position, will I noticed a change in how the boat rides? The boat has a 14-ft beam.

Thanks for any advice you may have.
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Old 10-11-2020, 08:36 PM   #2
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Honestly, the only way to find out if they benefit your boat at the speeds it can run would be to get them working and find out. At low speeds, they're probably better off fully retracted. At semi-planing or planing speeds, they're likely beneficial either partially or all the way down.
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Old 10-11-2020, 09:28 PM   #3
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Welcome aboard. We have a 41’ sundeck. Our tabs are maybe down a bit but we never use them. We don’t run fast enough to make them effective. I would not run with them even half way down much less all the way down. You are just creating a lot of drag unnecessarily.
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Old 10-11-2020, 09:33 PM   #4
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While I can't comment on your specific boat, some boats lack the ability to climb over the bow wave and get up on plane or semi plane. You may find without them that 9 to 10 knots with a huge bow wave is all you can achieve. If you remove the arm that holds them in the down position and fasten them temporarily in the up position, that you can do some test runs. Having the boat full of fuel and water would be a good idea as that's the hardest situation to get over the bow wave.

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Old 10-11-2020, 09:39 PM   #5
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On our sea trial we hit 17 knots, if I ran up on plane I would use the tabs. But since we routinely run about 9 knots the tabs are pretty useless. I would do what Ted suggested and see how it runs with them up. I suspect you will gain some bit of efficiency.
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Old 10-11-2020, 10:54 PM   #6
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I agree that you will need to try to get them working to find out if they help.

My boat has them although MUCH smaller. I find they do make a difference even at my typical 6 -7 knots. They can affect a list to one side, they help lift the stern when I am fully loaded for a long trip.
I can hear the engine unload when the boat is heavily loaded, not much but it is definite. I can also see the large stern wave drop under the heavily loaded conditions.
Of course in a large following sea they are fully retracted.

I simply disagree with those who say that on our trawlers they are useless.
ALmost all of out boats are semi displacement hulls so tabs can often help even if not a lot.
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Old 10-11-2020, 11:47 PM   #7
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We have tabs on our Tolly.

When we cruise at 6.5 to 7 knots [calced hull speed is 7.58 kts] I keep then full up.

Being as our boat has full plane hull: While on plane at 16 to 17 knot cruise speed I adjust the tabs as necessary for fuel, water, black tank and persons aboard weights.

They work well.
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Old 10-12-2020, 04:51 AM   #8
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48" Tabs are substantial and should have some effect even at slower speeds. Assuming they are Bennett there should be a pin that attaches the actuator to the tab, or 2 screws that can be removed to release the lower hings and free the tab to do the experiment described above

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Old 10-12-2020, 05:32 AM   #9
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Trim tabs

Thank you everyone for the replies. I may very well try adjusting them in a different position to see what happens. For some reason, the hydraulic pump has been removed and they are manually pinned in the down position. I don't like having things attached to my boat that isn't used anymore so I was just going to remove them if it didn't make a difference.
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Old 10-12-2020, 05:36 AM   #10
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If they still are whole you might consider obtaining an air tank and a couple of valves.


It might be interesting to use one at a time , to see if dingle operation would reduce vessel rolling .
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Old 10-12-2020, 07:12 AM   #11
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On our 34 ft 14ft beam Mainship I retract tabs at low speed say below 10 mph. If I am going faster say 12-14 mph which is my fast cruise the tabs help push the bow down. Having tabs deployed can create problems in following seas.
You indicated they are "pinned" down. Not sure where the pins would be but can they be removed to try fully retracted which will mimic being removed?
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Old 10-17-2020, 06:49 AM   #12
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I dont want to hijack the thread. Let me know if this sounds like hijacking. I've been labeled a hijacker in the past.
Question 1. Has anyone had trim tabs on a non planning hull trawler and had the tabs removed? If yes, what was the difference? For that matter has anyone ever removed trim tabs on any type trawler or does everyone just leave em on?
Question 2. If tabs left on, in the up position, on a 7 knot displacement speed hull ballenced and riding level boat do they offer any benefits?
I ask because my boat is getting hauled on Monday and I'm considering removing them. Mine are in the up position and don't seem to make any difference at wot. They seem to create more drag and barnacle habitat. Id like to remove them but are not sure if they are helping in the retracted postion.
I'll copy the to a new post if this is not the place to ask.
Thanks
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Old 10-17-2020, 11:59 AM   #13
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So I have HUGH tabs (2 actuators per tab) on 48ft ASD. They do move the bow down and helps trimming the boat. But I also use them as a cheap man's stabilizers. When we have beam seas, I run the tabs to full down and it seems to "dampen" the roll.

I would agree with others to test them out in full down and full up. There is a reason why the tabs are in full down. Can you talk to the previous owner?
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Old 10-17-2020, 01:09 PM   #14
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Quote:
Originally Posted by John Vergis View Post
Thank you everyone for the replies. I may very well try adjusting them in a different position to see what happens. For some reason, the hydraulic pump has been removed and they are manually pinned in the down position. I don't like having things attached to my boat that isn't used anymore so I was just going to remove them if it didn't make a difference.
Having them full down at trawler speeds will add quite a bit of unnecessary drag. I would definitely pin them up and see what happens. With both of them down they are not helping in side to side trim, but maybe your boat goes way bow high even at slow speeds so try them up and see what happens. You can always pin them back full down if you donít like the ride with them up. We never have put ours down in the 5 years we have owned this boat. Good luck.
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Old 10-17-2020, 01:21 PM   #15
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Get tabs into working order. Then play with your tabs... it may feel good - LOL
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Old 10-17-2020, 04:21 PM   #16
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Quote:
Originally Posted by Alaskan Sea-Duction View Post
So I have HUGH tabs (2 actuators per tab) on 48ft ASD. They do move the bow down and helps trimming the boat. But I also use them as a cheap man's stabilizers. When we have beam seas, I run the tabs to full down and it seems to "dampen" the roll.

I would agree with others to test them out in full down and full up. There is a reason why the tabs are in full down. Can you talk to the previous owner?
I would never have thought of using them in beam seas. Will put that in memory bank and try sometime.
I know Mainship added " stops" to prevent full extension as some folks had issues with poor handling in following seas. When I had work done on mine I had them remove the stops and it helped in normal operation and I'm careful using them in following seas.
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Old 10-17-2020, 04:31 PM   #17
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I absolutely love and use my trim tabs but also have a mod planing hull. With wind-driven waves, bringing the bow up 3 feet helps me to cut through the waves.
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Old 10-17-2020, 05:25 PM   #18
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It was only mentioned in passing above, so I want to emphasize that you definitely do not want the tabs down in a following sea, especially coming into an inlet in a wind-against-ebb situation.

You can use one to mitigate any listing issue you may have, by the way.
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Old 10-17-2020, 06:13 PM   #19
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Tabs definitely require care in a following sea. They're not a hard no, depending on the hull and conditions. The concern is around pushing the bow down too much and stuffing it into a wave, causing bow steer and a possible broach.

On my boat, I typically keep a little tab in when on plane in following seas. I bring the bow up enough to prevent bow steer, but retracting the tabs all the way just reduces speed, wastes fuel and makes it harder to see over the bow. The boat also doesn't surf down waves as well with the bow too high. At lower speeds, tabs are all the way up, as the bow won't get too high.
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Old 10-17-2020, 08:01 PM   #20
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With my ~ 7K boat in following seas they are fully retracted. My bow is a little fine so I don't want to push the bow down in a rough following sea.
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