Trim tabs - very slow up and down

[Lshulan]

During this last season, I noticed that the trim tabs didn’t seem to be working in that at any speed, I saw no difference in heel or angle of bow. I hadn’t really ever tried them before. Now on land, I tried them and my wife said that while they moved, movement was extremely slow. It took about 30 seconds to move down only about an inch. So when on the water, clearly I wasn’t engaging them long enough. But that time seems way too long, is that normal? So does anyone know approx time to engage fully up or down? If tabs are dying, can they be replaced from bottom of platform or do they need to be loosened from within the swim platform?

 

[rslifkin]

That sounds a bit slower than they should be. But if they're Bennett tabs, they don't exactly move quickly. Setups with 2 actuators per tab move half as fast, although mine are still faster than 30 seconds per inch.

 

[Duetto]

i have not timed out of water, i will in spring, but i've used counting to 30 to make sure fully down.

 

[Shrew]

Whether they are fast or slow should not impact their effectiveness. They either do or don't move the full length of their travel. One they are are fully in(down), their either are or are not changing the heal and/or pitch.

tabs are effective on planing hulls. At 8 -10 knots, I don't see a perceivable difference. The drag decreases fuel efficiency. I don't use them.

 

[rslifkin]

Whether they are fast or slow should not impact their effectiveness. They either do or don't move the full length of their travel. One they are are fully in(down), their either are or are not changing the heal and/or pitch.

tabs are effective on planing hulls. At 8 -10 knots, I don't see a perceivable difference. The drag decreases fuel efficiency. I don't use them.

It depends on the hull and the size of the tabs. Even at 6.5 kts, on my hull there is some effect from deploying the tabs a bit. Not all the way down (mine are big and don't need to be anywhere near fully deployed even at planing speeds), but deployed enough to bring them from a little above flush with the hull to a little below it.

There's no noticeable change in speed from that amount of deployment, but the ride changes noticeably. Pitching motion is much better damped and is a little smaller in amplitude. Roll motion gains a similar effect, although not as much. The boat almost starts to feel heavier in how it responds to waves, but depending on the sea state, it can be a noticeable (although not huge) improvement in ride comfort.

 

[Comodave]

I attached a Bennet trim tab troubleshooting guide. Maybe it will help.

 

[Lshulan]

Comodave - very helpful, clearly mine are way way too slow. I wonder if the fluid may be low? On the MS390, anyone know where the reservoir is?

 

[BBS]

On my 2004 390, the reservoir is in the starboard aft corner of the lazarette.

 

[Lshulan]

BBS - thanks, will check it out in spring when boat is unshrunked

 

[Shrew]

It depends on the hull and the size of the tabs. Even at 6.5 kts, on my hull there is some effect from deploying the tabs a bit. Not all the way down (mine are big and don't need to be anywhere near fully deployed even at planing speeds), but deployed enough to bring them from a little above flush with the hull to a little below it.

There's no noticeable change in speed from that amount of deployment, but the ride changes noticeably. Pitching motion is much better damped and is a little smaller in amplitude. Roll motion gains a similar effect, although not as much. The boat almost starts to feel heavier in how it responds to waves, but depending on the sea state, it can be a noticeable (although not huge) improvement in ride comfort.

I'm not sure if we're comparing apples here. The Mainship tabs aren't oversized. Since they are mounted flush in the hull, there is no way to oversize them.

In your case, I'm sure they work, though I'm amazed that they do so at such a slow speed. However, I can tell you that at 8-10 knots they are not perceivable on my mainship.

 

[rslifkin]

I'm not sure if we're comparing apples here. The Mainship tabs aren't oversized. Since they are mounted flush in the hull, there is no way to oversize them.

In your case, I'm sure they work, though I'm amazed that they do so at such a slow speed. However, I can tell you that at 8-10 knots they are not perceivable on my mainship.

I was equally surprised the first time I deployed them a bit at that speed (on a whim). Interestingly, even when deployed enough to change the ride noticeably, at low speeds it's not enough to make for a detectable change in deck angle (or to lift the stern enough to visibly change the wake). It's possible further deployment would start to have some effect there, but it would also likely add enough drag to start showing as reduced speed.

Even with the smaller Mainship tabs it may be worth trying deploying them just a little bit on a snotty day to see if it does anything to the ride. It's possible that some of the effect on mine is due to the tabs extending aft of the transom, so the fully retracted position is above flush (where the tabs have very little effect on water flowing off the hull). Once they're deployed slightly, they start to function as more of an extension of the hull bottom.

 

[skipper724]

trim tabs

I have twin yanmars. I see the tabs actually working, but the speed needs to be over 14 knots.

 

[SteveK]

I have to agree the tabs are noticed well above trawler speeds.

I have wondered whether having four of them acts like an extended hull.

 

[Bacchus]

I'm not sure if we're comparing apples here. The Mainship tabs aren't oversized. Since they are mounted flush in the hull, there is no way to oversize them.

In your case, I'm sure they work, though I'm amazed that they do so at such a slow speed. However, I can tell you that at 8-10 knots they are not perceivable on my mainship.

That's the case on the 390's but very different for those with a 34 T/HT.
Their tabs are large but I understand MS installed stops to prevent them from being fully deployed due to some handling problems when operators had them deployed in following seas.
I had one actuator replaced and told the yard to remove the stop on the existing actuator so they were both the same. Mine provide a noticeable affect at higher cruise speeds (2700 RPM / 13 MPH) but little at slow cruise.

 

[Keysdisease]

Some good observations above. Tabs effectiveness is based of tab size and waterflow (speed.) At slow speeds larger tabs are called for, at higher speeds, smaller tabs will have the same effect.
The tabs on the 390 are flush in the hull extension (technically a "Bustle") and as a result are what would be considered "undersized" at 12" x 26". There really wasn't a lot of room for bigger tabs. For example the MS400 has 12" x 48" tabs.
As Bacchus said, Mainship specified reduced travel actuators for their Bennett Trim Tabs, 1.75" vs 2.5" standard travel. When on the hard this is an easy 10 minute fix per side to get to 2.5" if you wish to go there.
As for the speed of deployment, one side w single actuator will go full travel in about 6 seconds, both sides at the same time about 12 seconds. If this slow response is on both sides it has to be the pump. It could be something as simple as corrosion at a wire connection reducing voltage to the pump making it anemic. If only 1 side it could be a variety of things.

 

[jleonard]

It could also be bad solenoid valves or bad conn cations. The valves can get corrosion inside or get “gummed up” and not open all the way. They should be replaceable, they thread in as I recall. ( I worked for a company that used to make the valves)
Keys disease could verify or refute that if they are available as a separate part.

 

[rslifkin]

Some good observations above. Tabs effectiveness is based of tab size and waterflow (speed.) At slow speeds larger tabs are called for, at higher speeds, smaller tabs will have the same effect.
The tabs on the 390 are flush in the hull extension (technically a "Bustle") and as a result are what would be considered "undersized" at 12" x 26". There really wasn't a lot of room for bigger tabs. For example the MS400 has 12" x 48" tabs.
As Bacchus said, Mainship specified reduced travel actuators for their Bennett Trim Tabs, 1.75" vs 2.5" standard travel. When on the hard this is an easy 10 minute fix per side to get to 2.5" if you wish to go there.
As for the speed of deployment, one side w single actuator will go full travel in about 6 seconds, both sides at the same time about 12 seconds. If this slow response is on both sides it has to be the pump. It could be something as simple as corrosion at a wire connection reducing voltage to the pump making it anemic. If only 1 side it could be a variety of things.

Agreed on tab size having a huge impact on how noticeable their affects are (especially at low speeds). My boat is very close in size to an MS400 and also has 48x12 tabs.

 

[Pete Meisinger]

In my experience the trim tabs should move faster than that. But of more concern is their limited range of motion, you definately need more than an inch of travel.

pete

 

[Keysdisease]

The solenoid valves are indeed available as a separate part.
If the issue was limited to just 1 side they might be the issue, if both sides still possible but doubtful. The solenoids will not work at all if voltage drops below a certain point.
If the issue is both sides I would suggest checking every wire connection from the power supply to the control to the pump
Issues as you describe are rarely plumbing and almost always electrical

 

[SteveK]

There is a wire connection 6 inches from the pump. Continuity of all wires need to be checked. High resitance there may provide the low speed.

 

[Lshulan]

Pete - the 1” travel I referred to isn’t the total travel, it’s all that I timed, was using that as an example of how slow it was.

To you guys with the. Immenrs about the electric connections, thanks, that’s a great idea. But since she’s shrink wrapped, will have to wait until spring. Will also check the hydraulic fluid as well at same time

Thanks to all and hope you all have a great Thanksgiving and happy holiday season

 

[Comodave]

They put zipper doors in the shrink wrap here so you can get inside the boat. If the sun is out the boat usually warms up inside the shrink.

 

[C lectric]

#1 ensure the oil is filled to an adequate level. Check at full retraction. Change the oil if over 10 yrs.

#2 check for voltage problems , LOW, between both the pos. and the neg. wiring. Go from the pos. and a good ground. Check resistance from the neg. and a good ground. Should be virtually zero for both
.
If voltage is lost then the motor will be slow but also won't produce the power needed to overcome the pressure pushing up from the water as you travel. Test with a DMM at the connections and see what the voltage is.

#3 check the connections. Like all wiring if poorly done then the power cannot get to the motor. They MUST be clean, tight , no corrosion and well made and then the gap between the insulation and the connector sealed with glue lined heat shrink tubing. Use NoAlox or a DIELECTRIC grease, not just grease, and swipe the wires with it before inserting into the connector. Keeps/stops corrosion of wiring.

My boat is on the borderline whether my tabs are worthwhile or not. I run by boat at about 8knots. However it does compensate for the list, I can see the wash from my wake reduced over my dingbat mounted on the swimgrid
and there is a slight difference in the engine drone so they are staying.