Trim Tab Operation

J

journey on

New member
Well, here's a topic that'll either die quickly or get a few answers. I'm hoping for the latter.

The question is "how do YOU use trim tabs on YOUR C-Dory"?

All C-Dory 25's and Ventures come standard with trim tabs. I hope to find out how C-Brats use their trim tabs: when, how much and any other comment.

I come from the sailing world, where there are no trim tabs and I've been trying to figure them out ever since. First, note that the C-Dory is a flat bottom boat, not a v-hull. So, I'll put the tabs down to get up on plane and leave then down to ~15 (or more) knts. Then I'll pull them up a little unless I'm trying to go really fast, when they come up all the way. So, I try to keep the bow down. I also use them to balance the boat side-to-side, depending on how it's loaded (and how much Judy yells.)

I watched the BoatUS videos on trimming a boat, then search for "trim". A video on engine trim and one on trim tab operation. Both done using a center console, v-hull with 400 hp, 2 ea Yamahas. The message was that you could get your boat up on trim with the motor trimmed in and then adjust the pitch up of the boat so that most of it was out of the water using motor trim out. Trim the engine in until the boat is stable. The trim tab video explained how to trim the boat side-to-side, no mention on getting the boat up on plane. So, those videos didn't seem to apply to a C-Dory.

Well, a C-Dory 25 doesn't have that hull or that horsepower, so I was wondering how to trim a C-Dory with tabs. Do you trim up as soon as the boat is on plane? Do you let the bow come up for easier riding and more mileage?

Post how you operate the tabs on your boat and let all of us learn.

Boris[/b]
 
We have trim tabs and Permatrims (twin Honda's) on our CD22. The only time we use the trim tabs is if the water is very bumpy. But we trim the boat with the Permatrims. I continually trim as I can do it with my hand on the throttle. As I'm coming up on plane I'll trim the motors just by feel and then once on plane I'll find the balance between the nice smooth ride and the best speed/gph. Most of the time I use the Permatrims to balance the boat side to side.

This probably doesn't answer your question - but when we are on plane I find that I'm continually trimming the boat based on conditions - trying to maximize speed to comfort. The trim tabs are much harder to get the boat trimmed - along with the fact that the trim tab control is not on the throttle.
 
Hi Journey on

I use my motor trim to bring bow down or up and my tabs to remove list when
running.

Since I prefer to have a balanced load, I will move passengers around if they are the problem. I also mostly boat in the ocean where nothing is level anyway for long. There I make sure my tabs and motor trim are up when short steep following sea state to keep from bow steering and when really ugly not much way.

When I ran a white water racer jet boat the nozzle would raise and lower the hull. With the high horsepower you needed to hold the bow down until you got up and planing then raise the hull until it got squirrelly. Bow down for control when rough and bow up for speed.

You might look into an auto leveling tab setup and let it do the work for you.

Just be sure you know how to raise and lower them as the controls are reflecting
bow position wanted and not tab position. You really do not want the tabs down on a steep following sea.

I really don't use the tabs much. I use my motor trim the most for raising and lowering bow. I prefer to balance my load on the boat and not have the tabs compensate for an out of balance condition.

Hope this helps or opens discussion.
 
Hey Boris
We do exactly what you described - engine down, trim tabs 100%, then after we are planning bring the trim tabs up for best boat speed at chosen RPM.
Typically we will still be running with tabs at 60% and 40% up to 20 knots, then less as speed goes up.
Trimming the engine up past 50% usually results in a loss of hull speed.
In the chop we are usually all in on the trim to keep the bow in and minimize pounding.
Saying that we are raising our engine next week one notch and considering a four blade prop for stern lift as we are stern heavy with our DF 200, a kcker, water tank and 3 batteries all aft. Hopefully those changes would allow us to use less trim and increase fuel economy.
Best
Eric
 
We are on our 3rd year with our 22 and just starting to get the hang of the trim tabs and feeling like we have it figured out.

Our boat has twin Hondas and no permatrims, and bennet trim tabs. For the first 2 years, we would get the bow down by trimming the motors up, and always had the trim tabs down all the way. Our boat runs smoothest through the chop with the tabs pushing the bow all the way down. To adjust from side to side, I would make the dog (175 lb mastiff) move from one side of the boat or the other! :twisted:

Well finally this season I have these trim tabs figured out. It's still rare that I don't have them trimmed all the way down, unless were in ocean swells in a following sea when they are trimmed all the way up. Now I'm not concerned about balancing the weight in the boat and am using them to correct a list at speed. Also, I adjust the trim to compensate when we are taking waves at an angle or from the side. The trimming the boat as we travel with a beam sea really seems to smooth out the ride. I'm pretty sold on these tabs now that I've had some time to figure them out. And our dog is much happier as well!
 
There is a difference between how I used the tabs on the 25 and 22. The 25 was underpowered with the 130 Honda, so I had to keep a fair amount of trim tab down, except when in following seas. The motor was usually trimmed in and then leveled as we got on a plane.

With the 22, we leave the tabs about level with the bottom of the boat, and the motor trimmed slightly one, until the boat is on a plane. Then we adjust the boat side to side with the trim tabs, and trim for sea state with the outboard. If it is extreme chop, then we trim the dow down, with both the motor (came with a Doel Fin), and the trim tabs.
 
On my 22' I run the motor most of the way in and about 60-80% tab to get the ride where I want it.

Depending on the load I usually have one tab out more than the other to get the lateral trim right.

I adjust the trim with the tabs and not much with the motor. The tabs seem to have a much bigger effect on the trim than the motor position. I don't have a Permatrim.
 
On my CD-22, (and also an earlier Searay 268 Sundancer), I use the trim tabs to "level" or "balance" the list of the boat. With the small beam of the boats, it doesn't take much to cause a list. Even the wind has some effect. I'll also use the trim tabs to help get the boat up on plane faster, especially with a lot of weight in the cockpit, or if I want to cruise a little slower. I use the single outboard trim more to get the best speed for rpm (fuel flow) and depending upon chop of the water. More nose down to provide a little smoother ride. Also to lower the bow for better visibility. When using the trim tabs just for list correction, I tend to not use any more than necessary to level the boat's list. (Otherwise, more drag in the water.) Under normal conditions, I tend to run my engine trim just below the half way point. (Probably means nothing, other than a mark on my trim gauge.) Choppier water might require a little more down trim on the engine. Thinking about it, basically I have the engine trimmed down just a bit past cavitation/slippage. I should also note, at slower speeds, coming into a dock, etc, I have a lot more control of the boat, particularly going into reverse, with the engine in the lower half of it's trim, and with water depth available, will leave it down. Colby
 
Do a search. There is lots of info here already.

Use trim tabs to adjust your bow trim. trim the bow up in a following sea, and down into waves. If you are riding swells where you will have a bit of a run down the back of the wave, keep the bow up even though you ma be going into them,

Use trim tabs to accommodate any list, however first try to balance your load, as you will always be adjusting this as you change speeds, turn, etc.
 
I usually travel with a large 150 lt cooler full of ice when fishing on the west coast with down riggers, cannon balls, 55gal of fuel etc. All the stuff required for a weekend for two. On my old Honda I use to apply the trim tabs and the motor all the way down to get on plane and then raise the tabs to about half way, and the motor up a bit to find the best milage at about 16 kn.s The cooler was moved to one side to balance the weight of water and fuel as required and worked great, no fuss. On good trips the cooler never got lighter. The only issue I had was on a following sea remembering to raise the tabs and a swim grid up, they would get shoved and kick you sideways a bit under big swells. Very unnerving

Jim.
 
If you need trim tabs down to get your boat on plane, you are
underpowered. Some tab down can help getting on plane.

The primary purposes of trim tabs are to lower the bow and adjust
lateral roll.

BOTH TRIM TABS DOWN: (once on plane)
1. raises the stern, lowers the bow
2. the amount of 'down' on the tabs depends on
a. how your boat is loaded; stern or bow heavy, even load?
b. the ride; adjust to comfort
1) bow digging in; too much trim tab down
2) excess vertical bow movement (:oops:); too little trim tab
c. your course and sea state;
1) heading into larger seas; adjust bow (trim tabs) down to comfort
2) heading down larger seas; keep trim tabs up
d. engine tilt
1) efficient running w/engine tilted up but bow flopping; tabs down
to comfort and steady ride
2) this requires experimentation for a specific boat
e. how much fuel you want to burn
1) anytime you have trim tabs down too much, you burn Xtra fuel (drag)
2) best efficiency is to adjust ride with engine tilt and trim tabs

ONE TRIM TAB DOWN
a. stbd trim tab down raises stbd stern to correct
1) heavy stbd boat loading
2) port roll (digging) from heavy port side cross wind
b. port trim tab down raises port stern to correct reverse of above

NEUTRAL TRIM TABS
a. hard to determine w/o a trim tab indicator at helm
b. may be determined by getting engine tilt and trim tabs 'balanced'

TRIM TABS UP
a. when in heavy following seas
b. when hauling your boat

I always cringe when I see a boat underway bow digging, bow flopping, or
rolled to one side. But maybe it's just me.

Aye.
 
A lot of info already. Everyone seem to have their own procedure. For myself, the most efficient way to run the engine is with the prop shaft parallel to the surface of the water, thereby thrust straight back with no drag on the motor fins. So I trim the motor so that the top of the hood is parallel to the surface of the water.

The tabs, I use to take the list out of the boat, left to right. Then with the tabs I trim the bow up or down depending on chop or waves. You can over trim the bow down and cause the boat to "waller" or dig in in the turns, so be cautious.

I go back and forth with motor trim, as a change in the trim tabs will affect the attack angle of the prop. The end results, for me, is to have the motor level.
 
Trimming your boat out means two things, one, the least amount of drag in the water so you get the most out of your fuel, and two, a smooth or stand able ride. Bring your boat up on plane, set the throttle, wait a bit till your boat is up to speed. Now watch both your speed and engine rpm. Your prop should be running parallel to the bottom of your boat, and in best conditions your trim tabs will be all the way up. By making tiny adjustments to your trim tabs and power trim you should see an increase or decrease in either or both rpm and speed. You want the increase without touching your throttle. You can level the boat out using the trim tabs, by watching your speed and rpm, you will see if your loosing speed, you can also shuffle some weight around. This take a bit of practice.......but once mastered for your boat you do it with out much thought This also has a bit of listen and feel when your trimming it out.
 
With your trim tabs down, drag increases and your mileage will also decrease. In some sea conditions this is unavoidable if you wish to make reasonable headway. I use my "move-able ballast" such as coolers, tools, and spouse to load so that no trim tabs are needed, assuming no sea conditions which would necessitate their use, and the engines can remain in their neutral positions. I use the engine tilt/trim to trim out once on plane, and try to keep this as close to neutral as possible. Initially with full fuel I have to keep some down trim on the engines to keep an ideal planing position, but after about half the fuel is used I can generally move the engines to their neutral positions.
 
We run slowly with tabs neutral and motor trim from 0-25% (from bottom) then throttle up and get on plane. Once planning, we use the tabs to bring the bow down to the level we like and then adjust the motor trim a bit up or down for efficiency. We don't generally need to trim laterally but when that is needed I do it last. Using the tabs to help achieve a plane never really occurred to me but it does seem like that need would indicate another issue with power or balance.

I love the tabs and use them whenever we are doing over 10 knots.

Greg
 
Being new, I have a couple of questions:

1. I'm a little confused about "trimming up" and "trimming in" and all other combinations. Am I correct that with trim tabs, down means adjusting them so they are at an angle with the trailing edge lower than the leading edge; also that all the way up means the tabs are back parallel to the surface of the water (clam, not moving). I assume that trimming in relates only to the motor. When someone like thataway says he trims the motor in, does he mean that the bottom of the motor is moved closer to the transom (even past vertical). Motor trim out would mean that the gap btwn the bottom of the motor and the transom gets bigger.

2. In my CD25 with the Honda BF150, there is a motor trim gauge. I have never really known what the position of the needle means. Obviously, as the motor goes up, the needle goes up; but what do the markings on the gauge represent? My gauge has 3 marks: some sort of upper limit that is at approx 1 o'clock; a longer middle mark at 3 o'clock; and a down mark at approx 5 o'clock. On my boat to have the motor vane (or whatever that plate just above the prop is called) parallel to the water, I need to have the motor trim gauge very close to the 5 o'clock mark (say at 4:30).
 
Trimming up or down usually refers to the bow angle relative to the water. Bow down will require the tabs to be deflected trailing edge downward (might also be called extended). Trim tabs cannot usually tilt the bow up, they can only counteract the bow up tilt from the engine trim or water forces on the hull.

A lot of trim gauges actually have icons that indicate which directions on the indicator are bow up and bow down. You might have to look closely.

On the motor, trimming in will give you bow down. Trimming out will give bow up. These can also be referred to as trimming up and down and refers to what happens to the bow.

The trim indicator is not generally indicating any particular amount of trim (like degrees). It is just a pointer so you can set it to the same place when you want. Once you get the trim where you want it, you can note the indicator position so you can set it there again.
 
smckean, To me trimming the motor in, or down, means toward the boat. Trimming out or up, means to the surface of the water. Each manufacturer may vary, but, generally the top hash mark at the topis when the outboard is trimmed all of the way up, the next one, is when the second ram, or trailering ram engages. Generally at this level, the engine intake will be out of the water, or out of the water shortly, and it is not advisable to run the engine with the intake out of the water (burns up impellers and engine blocks!)

At times I have to run the boat in skinny water, during winter low tides, I may only have 15" of water in the channel to my bayou. Then I will watch the engine water telltale, to be sure that it always has a good stream, as I trim the motor up, so the prop is partly out of the water.

Not all trim tabs are set up the same way--but many will have labels, such as port bow down, Stb Bow down, Port Bow up, Stb Bow up. If there is confusion, best to label. Almost all of the manufactures have indicators, most are LED lights which are available as an extra, to mark where the trim tab is located. Some of these also have a "auto retract feature" so that the tab is not left down when the boat is beached, or put on a trailer, potentially damaging the tab.

The tab going down, depresses the bow, and raises the stern. The starboard tab also tilts the boat to the port, and visa versa. So you have to remember which way it will react.

Often the tabs will be above level with the bottom of the boat when trimmed all of the way "up" .

I would make one slight correction to Leon's excellent post. That is I prefer that the prop be parallel to the surface of the water, and that may or may not be parallel to the bottom of the boat. (Remember the wedge we have on the Radar to get the beam down, because on a plane, there is often some bow rise.) Also different boats have various amounts of "rocker" this is curve to the bottom of the boat. This may also affect at what attitude the bow is, as well as if the bottom of the boat is parallel to the surface of the water. Generally there is less wasted energy, if the boat is driven straight, thru the water, not pushing up, or down….But the ride depends on the amount of trim also. There are times when the bow is trimmed up, or down, when the best ride may be with the prop in its most effective position, for that state of trim, and yet not be parallel to the bottom of the boat. I do agree that a great way to see your most efficient setting is to leave the throttle alone, and slightly vary the trim, to get the highest RPM, and and speed. As he says, this is by hearing and feeling the boat, as well as watching the tachometer or a fuel flow gauge.
 
Sorry Bob ....the prop runs parallel to the bottom of the boat, it is a constant. On a perfect plane, on smooth water the bow will be slightly higher, and the motor with be a bit forward to the water. if you make the motor parallel to the water, you will be moving it back and a up, it will bring the bow up even higher.
 
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