Trim Tabs

Looks like the trim tabs may hit the rudder when tilted down on this Californian 34. Anyone seen this before? Mechanic recommending cutting the upper rear corner of rudder for clearance.

Picture?

Mad_viking3 said:

Looks like the trim tabs may hit the rudder when tilted down on this Californian 34. Anyone seen this before? Mechanic recommending cutting the upper rear corner of rudder for clearance.

Click to expand...

If that's the case then I would have other questions. Were they using it like that and having a problem? Or has something been changed since they last used it? I'd just need something to make sense out of it as I can't imagine someone using it with that issue.

Here's an old shot of my tabs and rudders. When mine worked, they seemed to make little difference at my speed of 7.5 Kts. Never had an interference issue that I knew of. Years ago they died but I don't miss them.

Trim tabs are useless on a trawler anyway.
Just take them off.
They are good at creating drag though. May need them on a breaking seas bar.

Nomad Willy said:

May need them on a breaking seas bar.

Click to expand...

I would think that is the last place you would want to use them.

See attached pictures.

I use our tabs all the time at fast cruise (15 knots) but haven't noticed that they do much at slow speeds.

I wish mine were a little bigger actually, I'd like them to bring my bow down a little more.

I'm comfortable with trim tabs, as I also have a flats skiff that I run a lot. I wouldn't own a small, fast boat without tabs.

What year is your 34, MV? Your rudders look much larger then mine. Were they modified?

Key word here:

"Looks like the trim tabs MAY hit the rudder"

As sister ship has posted same setup, these may be factory. If so, I doubt they touch the rudders, and I see no sign in either picture of the tabs doing that.

The standard Bennett Trim Tab actuator has 2.5" of travel, or you can just grab the tab and pull down on it, the return spring will let you do that with 40-50 lbs of pressure. See right away if it hits or not

KD, When I clicked on and then enlarged his first image, I can see where it appears the tab is rubbing on the rudder top, fwd corner. It looks like it's missing some paint there.

TrimT abs

FlyWright said:

What year is your 34, MV? Your rudders look much larger then mine. Were they modified?

Click to expand...

Its a 1980. I don't think it has been modified. All looks like factory new.

Capt.Bill11 said:

I would think that is the last place you would want to use them.

Click to expand...

Bill,
As a brake.
Running inlets w breaking seas a drouge is frequently used .. as a brake.
So I was thinking tabs would have a significant braking effect from all the drag. And the drag is all the way aft.

On second thought the dang tabs would likely pitch the bow down into the next sea and probably cause a broach. For that reason you're right .. bad idea. Did'nt think about that one enough. However you should have called me out as to why.

I have a 7K boat and I too have tabs. Mine are no where near the rudder though. My rudder is down much deeper, under the hull more, the tabs are not wide enough, and there is only one rudder, not the two as on the boat above.

1---They do help reduce turbulence when travelling. I cannot really detect any speed change but I can hear a change in the engine note so they do have an effect.
2---Another effect I noticed is between up and down the stern wave is noticeably reduced when the tabs are down, especially when the boat is heavily loaded at the start of a cruise. Enough so that when travelling and I look over the dinghy top I can see the wave when retracted. When the tabs are deployed then I cannot see the wave over top of the dinghy.
3---They can change a list once the boat is moving.

If the boat is a full displacement or close I would expect they would be of little use, maybe just a nuisance.

However, my boat and the one shown above are S.D. or more of a planing boat so trim tabs can have an effect. Good or bad, it is how they are used or misused.

In rough following seas I definitely retract them or they can help to force the bow to dig into the wave ahead maybe causing a broach, at least harder steering.

It does look like that one tab contacts the rudder top from the paint rubbed off. Maybe trimming the rudder a bit would get more down movement from the tab which , if the rudder contact is fact, could be worthwhile. If the tabs cannot go full down from rudder contact then they cannot do the job they were intended to do. It's not that they cannot help, they are prevented from helping.

If the rudder is trimmed to allow the tabs to work properly then the three effects I outlined above may come into play which will help the boat, mildly yes, but still help. Since the tabs are already installed, consider getting them to work properly.

BUT in rough following seas be sure they are retracted.

Mad,

I don't think your rudders are original (or at least, they are different than mine). I have a 1981 and mine look just like Al's.

Mine has trim tabs but, alas, they are inoperative so I can't tell you if they interfere or not. The pump is no longer working. Repair is somewhere on the list but hasn't risen to the top yet.

I think people look at trim tabs expecting a huge dramatic difference which on a planing boat you might get. There you'll trim to get on plane and then go the other way to gain speed. However, just because they don't accomplish that on semi-displacement or displacement boats doesn't mean they don't do anything. Here it's measured in just a degree or two. Still finding the right trim may help you balance the effect of your unbalanced loads. You have a lot of stern weight and trim to lower the bow. When cruising you might find even trimming to raise or lower the bow 1-2% changes the comfort. Certainly, if you have unbalanced loads side to side, trim can help. It beats telling people to change seats. I'd suggest anyone with tabs just try them enough to get the feel for what they might do. Even if they don't make a difference most of the time, that occasional time they do might surprise you.

Bustlebomb said:

Mad,

I don't think your rudders are original (or at least, they are different than mine). I have a 1981 and mine look just like Al's.

Click to expand...

Even the rudders on the 38's and 42's look like Al's. Never seen a Californian rudder with all the squared off angels those have. Must be replacements.

Whether you in general use your trim tabs or not for cruising trim purposes: If you want to help keep them actively available for use and in good mechanical condition. Hydraulic trim tabs need to be exercised "full throw" up and down at least three to four times per year. More so in saltwater than freshwater. This exercise program can be done at anchor or at the dock so you can actually watch them to see they go "full throw". I have wife throw both steering station toggles while swimming, for really close up inspection. Old adage of "use em or lose em" is in play here. Also, be sure to keep their fluid container up to full level.

In addition to hydraulic tabs on our planning hull Tolly... which we use to accomplish more than one trim purpose while on plane... we also have manually bolt adjustable tabs on our 40 mph top speed, 14'8" Crestliner runabout that has 50 hp Johnson o/b . With those tabs set at correct angle and with o/b motor's manually adjustable trim pin also set at correct level... well... our tow behind runabout is a screamer that hits plane in a couple seconds. Never needs trim angle readjustment on the tabs or the o/b. I set em in correct position when we bought the Crestliner; have never needed to readjust either trim setup.