Trim Tab Removal, Yes or No

Our 42 Classic has a massive pair of ironing board size trim tabs. The actuator pump failed long ago and they are stuck in the up (flush with hull bottom) position. We find them seriously hazardous when boarding the swim platform. Is there any benefit to having them on the boat in this position? Does this 'extension' of the bottom accomplish anything? I would really like to remove them if they serve no purpose.

Yes, I do understand how they work. We have over 2,000nm on Shangri-La both offshore and in the ditch - haven't seen a need for them yet. Thoughts?

If it were me and I weren't going to replace the pump to see if it improved the ride, I would remove them. I assume that you realize that the cylinders have large coiled springs in them that hold the tabs up until pump pressure forces them down. If they are Bennett trim tabs, I'd probably buy a replacement pump and see if they made a difference. The slower you cruise, the less effective they will be.

Ted

Do they give you any issues in a heavy following sea?

OC Diver - good point. Getting this gurl up and running at speeds where the tabs may help is outside of our budget. We cruise at 8K and run the engines up now and then to exercise them but really don't plan to run at those speeds. My question is about the extension of the hull bottom with those huge boards and if they would make any difference in our ride/performance once gone. Seems like they add length in some fashion, but I'm not a nautical engineer.
As to the question on following seas, I find there is usually a sweet spot in our speed that will mitigate the pushing and wallowing. We don't have a lot of offshore time, maybe 350 miles but have so far been able to manage quarter and full stern seas without much discomfort. Beam seas - we won't go there.

The reason they are "massive" is that the slower you go, the more tab you need to be effective. These large tabs, even at 8knts are probably enough to straighten you up with wind on the beam for example.

To answer your question, given that they would be the typical 12" chord Bennett Tabs and were almost full transom (massive) the theoretical hull speed from 40' water line to 41' water line would be 8.54knts to 8.64knts, maybe.

On the other hand, the KISS principle would dictate removal. They seem to be a boarding hazard, they are inoperable, and you don't seem to believe you need them. On the other hand a replacement pump would probably cost less than to have them removed.


$0.02

Don’t think it will apply to you but I installed fixed tabs on a small skiff. I was having trouble getting it on a plane. I had to move forward to get it over the hump. The fixed tabs, which were flush with the bottom, added lift aft as it was trying to get on plane.

You might find that removing them allows the stern to squat at certain speeds.

NightCrawler said:

Our 42 Classic has a massive pair of ironing board size trim tabs. The actuator pump failed long ago and they are stuck in the up (flush with hull bottom) position. We find them seriously hazardous when boarding the swim platform. Is there any benefit to having them on the boat in this position? Does this 'extension' of the bottom accomplish anything? I would really like to remove them if they serve no purpose.

Yes, I do understand how they work. We have over 2,000nm on Shangri-La both offshore and in the ditch - haven't seen a need for them yet. Thoughts?

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So have they ever worked in the time you have owned the boat?

I have big tabs on my Ocean Alexander and I find that at the upper end of our normal cruise rpm they do drop the bow and correct side to side trim if I get lazy on fuel balancing.. that is at around 7.5-8kts. You must have the stock worthless width GB swim platform.. our tabs are tucked under our by over a foot, so no boarding issues.

I recall that our GB 36 really started to squat when pushed to the upper end and was even more trim sensitive than our O.A.

On the negative side of tabs .. I do hate to clean the things.
HOLLYWOOD

Now y'all have me thinking (a good thing) the pump is less than 300 bucks and can be replaced without hauling. . .question remains, will our ride change if they come off?

hollywood8118 said:

So have they ever worked in the time you have owned the boat?

I have big tabs on my Ocean Alexander and I find that at the upper end of our normal cruise rpm they do drop the bow and correct side to side trim if I get lazy on fuel balancing.. that is at around 7.5-8kts. You must have the stock worthless width GB swim platform.. our tabs are tucked under our by over a foot, so no boarding issues.

I recall that our GB 36 really started to squat when pushed to the upper end and was even more trim sensitive than our O.A.

On the negative side of tabs .. I do hate to clean the things.
HOLLYWOOD

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No, they've obviously been DOA for some time. In sea trials, empty of gear most fuel and no water, she hit 17K with the tabs up where they are now (the engine surveyor was floored.) We've hit 15 fully tanked and we live aboard - lots of gear. So to make a bridge or get back into an inlet we have enough to satisfy that need. But will it 'squat' more with the tabs off, I don't know. . .and yeah, shopping for a new swim platform now

Since the tabs are in the fully retracted position I doubt there will be an appreciable effect by removal.
However from my own experience you may be removing a good tool for running. Even though you will not plane the boat they can still help when used.
--Remove side to side list when running
--lift the stern even at lower speeds which will lower the engine loading at the same speed without them.

I have them on my much smaller boat [32'] and questioned the same thing. My tabs are really too small to help a lot BUT I can hear the engine unload, I can see the large stern wave reduce and they do help with running list removal.

You may find them worthwhile if reactivated.

Greetings,
Mr. NC. How about this...Replace the motor and try them out for a while. IF they are not to your expectations, remove the whole works and sell them. At least you may recoup some of your $$. Just a thought...

My North Pacific 43 has large Bennet trim tabs. The original owner said that he noticed no effect with the tabs, but this is the same very nice gentleman that ran the boat up on a rock.

I have found that I can adjust the tabs to get maybe a .1 or .2 additional knots at a typical 7-8 knot cruise. On the very rare occasions that we run faster, the tabs really help raise the stern, reduce the wake, and make the boat ride a bit more comfortably.

If you didn’t have the tabs I wouldn’t recommend installing them. Since you do have them, I would suggest you replace the pump and see how you like it.

If you elect to replace pump, the cylinder seals may be your next project.

A different boat...and we run pretty often at around 15 knots...but I would never consider removing our trim tabs. They are a huge help in keeping the bow down. I deploy them all the time at anything over about 1800 rpm.

I doubt they do anything at all if they are in the up position though.

Trim tabs are for planing boats IMO

Too much drag on slower boats and not enough (if any) gain in any situation.

Also if you have a trim problem it should be fixed by adjusting the CG. Many boats have a CG problem even when new so you may be out of best trim especially if your boat has received considerable weight since new (most have)... and not be aware of it. Many boats have their engines ahead of CG and come in single and twin configurations and it’s obvious one or both is not ideal. But a running CG is a range of fairly small variations so few boats are perfect. And there are different owner preferences like level running, efficiency or bow level of a “wet boat”. But safety would probably prefer a slightly aft CG to one too far fwd. I don’t recall seeing any trawlers w an obvious aft CG problem but I’ve seen many bow down trawlers mostly by pics on TF.

I am not much help but I did have a 42' Ocean Alexander and removed the same trim tabs when they stopped working. Did not seem to make any difference at all at lower speeds.

Mike Lowthian said:

I am not much help but I did have a 42' Ocean Alexander and removed the same trim tabs when they stopped working. Did not seem to make any difference at all at lower speeds.

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Not much help? That's exactly what I needed to know. Thank you!!

Call Bennett 954 427-1400 and ask if they have any rebuilt pumps available.

NightCrawler said:

Now y'all have me thinking (a good thing) the pump is less than 300 bucks and can be replaced without hauling. . .question remains, will our ride change if they come off?

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I am thinking of removing mine, never turn them on, have tried and notice no difference. They are a pain to paint, barnacles love them. If they will slide out of mount, I will remove, but, if not they will stay, don’t want to mess with all those screw holes. Hauling in 10 days, if I remove, will review results after this cruising season.

Food for thought: At some point a past owner had operating tabs....and then they died. He or she was familiar with both tabbed and untabbed operation, and opted not to fix them.

The builder apparently believed that operational tabs were useful for the boat's operations. So, on first thought, get them operational and work with them. You might be pleasantly surprised. Nevertheless, if you're satisfied with the boat's operation, either forget about or remove them. ... Fortunately, my slow boat has no need for the complication.

If the tabs are underwater at your normal cruise speed, I would guess that the turbulence they create is more of a hindrance than a help. The huge negative pressure area created above them is a braking force.
Removing them just might result in improved speed and economy!

One final thought, you might post on the GB forum whether any one with your model boat has trim tabs and at what speeds and conditions they make a difference. Having someone on this forum tell you it doesn't make a difference on their (different manufacturers) boat, so it won't make a difference on yours, seems not very valid. I would be very surprised if someone on the GB forum hasn't got the answers you want.

Ted

The GB was designed as a semi-displacement hull and then they installed engines insufficient to plane. Then, as sales fell, they put large engines in the same hull and used trim tabs and strakes on the bow so they could "plane." A modern (10 year-old) GB 42 Europa will do about 25 knots but its wake is only unimpressive to a tsunami survivor. If you can do the 17 knots you suggest, I would definitely fix them. My friend's Symbol does 18 knots and he uses his tabs then but he doesn't bother with them when cruising alonside me at 7.5 - 8 knots. I doubt if you would even notice them at 8 knots.

I don't have trim tabs.

I have cruised extensively with a GB 36. My boat is 44. The 36 had no trouble keeping up and did so on less fuel burn than mine. No trim tabs. You be the judge.

Adios Trim Tabs. After more conversation with the folks here where we are at Atlantic Yacht Basin in VA, we were more convinced to remove the tabs. They do excellent work, fiber glassing the holes and mounts, rather than just pumping 5200 into the transom. Got her a new bottom coat and we're good to go!!!

Oh, and many thanks for the thoughtful responses here on TF. Very much appreciate that.

I have a new 45 ft. (SD/FD hull; Cruise 6-8K) boat arriving in a few weeks and it won't have tabs.

Thank you for keeping us informed. She looks darn good. Good work!

Xsbank said:

Thank you for keeping us informed. She looks darn good. Good work!

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+1 on both counts.

Update on Tabs Removal

The trim tabs were removed in Chesapeake, VA. We're now in Toledo, OH. After running slow via the Erie Canal, and having some fun across Lake Erie, I'm convinced removing them was a good call. We've tracked fuel burn for the entire two years we've lived aboard Shangri-La, over 3,000nm. Removing the tabs made no difference at all. We do not notice any change in ride. (Keeping in mind, they were not functioning, just dragging along behind)

Thanks again to the group for thoughtful feedback.