Trimming out a dual Stern Drive

[Uplate]

A discussion for you dual sterdrive owners.

I am new to dual drives as well as Trim Tab controls.

Much simplier in my runabout with a single sterndrive, no tabs.

My manual states that a boat at cruising speed needs no trim. I do adjust them to counter balance weight loads. I leave them all the way down at idle speeds.

So my manual states that about a 5 degree up on the bow is ideal. No idea how you can judge this from the cockpit!

So this is what I do. Trim tabs full down, Outboard trims full down, WOT until on plane, then trim the Outboards up a little (about 1/4 up trim), adjust Trim tabs to make boat level.

I am sure this is a unique to every I/0 setup and am curious as to how the rest of you trim yours.

Thanks

 

[Carpedmman]

Mike- As you mention it depends a lot on your load. I use your method if I'm full of fuel and have a few passengers, although, typically with just the GF and I, 1/4-1/2 tank of fuel I just keep the outdrives trimmed down and slowly apply the juice. You are right, this will depend on the boat, weight, etc. Play with it in different scenarios and you'll find the right combo.

Enjoy!
Stuart

 

[Uplate]

Thanks for the input Stuart. what do you do with your trim tabs at slow and higher speeds?

 

[tdappleman]

I typically use my trim tabs only to balance out the load. I will use them to help plane if I'm running with more than just my family on board but it isn't really required. It really seems to depend on sea conditions for my 270 - it will take a little getting used to for you. I went from a single engine outboard and it took me a few trips to really get a good feel for it. For the drives - I typically have them full down all of the time - when I get to speed and know I'm going to cruise for a while then I'll trim them up slightly which allows me to throttle back slightly and maintain the speed. My tilt sending units are both out so it ends up being a guessing game anyway. Go and practice - it's a good excuse to get out and play on the boat! :grin:

 

[Uplate]

Both of my tilt sending units are out as well. Even the one on our Chapparal bowrider.
My mechanic said Merc could never get a dependable design for these units in the many years of making them.

Certainly tilting the outdrives up a little allows more RPM at the same throttle setting.

I go out and practice whenever I can. I hope by summer when the lake gets busy again I will have figured many things out!

Thanks.

 

[Bridog]

On my current boat I never needed to use the trim tabs at all. Never needed them. I trim the drives all the way down and bring them up a bit after coming up on plane. The 300DA doesn't like to be trimmed up very much at all. Just very slightly. The 260DA was a different story.

 

[douglee25]

Do you need tabs to get on plane? When you do in fact use tabs to get on plane, how much do you pull the tabs back off? If you don't need the tabs to get on plane, don't bother using them. Typically I use tabs just to balance the weight distribution. When on plane, I usually trim the drive up just to get the nose out of the water (2 - 3 quick bursts of the trim). When I see the rpms climb another 200 rpm or so, I'm usually at the ideal trim/tab points.

Doug

 

[Redhook98]

I use the tabs a little to get on a quick plane (or not at all if not in a hurry). After I am on a plane, I take the tabs all the way back up to the home position and use the drives to adjust the angle of the boat. While on a plane, the tabs are only used to level the load port and starboard. Tabs make alot more of a difference on inboards. They are a necessity on inboards.

Typical scenario: Start out with the drives all the way down and slight downward angle on the tabs. Accelerate to where your on plane and quickly put the tabs back to home position. Trim the drives up until you reach max rpms/speed for that throttle setting. Lower the tabs only to balance port and starboard. Works well and is the best method for conserving gas. The more you have in the down position (tabs and/or drives), the more gas you use. Even if incrementally.

 

[Stray Cat]

So my manual states that about a 5 degree up on the bow is ideal. No idea how you can judge this from the cockpit!

If you are about 5'6" and your butt is on the seat, and you can easily see over the helm while at cruising speed with no trim tabs, and ever so slight amount of drive trim to both units....that's close to a 5 degree bow rise. As you get used to running your boat, you will get a feel to where the sweet spot is.

I use my trim tabs on occasion in a cross wind, load imbalance, and when full of fuel. Generally, they are up.

 

[Kameroo]

I had a 1991 280 WE, same hull as the 92-95 300 WE and DA, so should be similar in size. We had twin 5.7Ls with Alpha Ones. Not sure of your setup (you can add it to your profile), but in our case, there was a sweet spot on the drive trim for any rpm on plane. At 2800 RPM, it was full down. At 3200, it was about 1/8-1/4 up, going to 1/2 up at WOT. The boat really seemed to plow if you left the drives down over 3000 RPM, and the engines would noticeably unload as you ran the trims up a little.

The bow would come up and the speed would pick up as you raised the trim (to a point). Unlike a bowrider, the bow wouldn't come up to far and porpoise if you ran them too high, but it just didn't sound right and the props were probably cavitating some.

Regarding trim tabs, I generally left them fully retracted (up), and only used a little here and there to compensate for an unbalanced load or big crosswind.

 

[Sundancer]

Tabs and trim full down until up on plane. I pull the tabs all the way out and then adjust the tabs to balance the load. Then I move the drive out a smidge while watching the GPS to determine the best speed for a particular throttle setting. You can watch your speed change slightly on the GPS while making adjustments to maximize your speed. IT gives me something to tinker with while I'm cruising. There are some conditions where slowing down with tabs all the way down make sense too. There are a lot of variables.

 

[MExcelsior]

Hi Mike, I went from a single engine 350 EFI Crownline 262 to a 280 with Twin 4.3. The first weekend, I handled my drive trim the same as with the single engine. (This is obviously wrong and I thought that something was wrong with the motors). The trim of the engines on a larger boat hardly need any adjustment. Just as an example, on my Smartcraft gauges, the drive trim has indicators of 1 through 20. (1-10 for normal running and 10-20 for trailer position). While running at cruising speed, I only set the drive trim at 3 (maximum). This will give you an idea of how little trim they need. You'll be able to hear and feel when they are too far up.

As far as trim tabs, I only use them while getting on plane with a boatload of people or running at cruise speed with a crosswind to level the ride. I suppose you could also use them to lower your cruising speed at a level where you would normal come off plane.

As far as coordinating the use of trim and tabs in a certain order to get on plane with a lot of people aboard.

1. Tabs down full
2. Drive trim down full
3. Hit gas
4. Set speed a hair above cruising to not come off plane
5. Adjust drive trim
6. Bring tabs full up if not needed

When I'm feeling in the zone, I just adjust drive tabs, speed and tabs all at the same time while steering with my belly.

 

[Air O'Nautical]

Generally speaking you should be able to get up on plane without tabs.
Normal take-off is tabs up, drives full down, power up until on plane. Now, trim drives out until RPM bumps up 2-3 hundred. Too much out/up drive trim and the props will loose there bite in the water and sound terrible. Bump drives down until it sounds better.. you are now trimmed for best mpg and speed for THAT throttle setting. Trimming the drives is mostly done be ear, you will get used to it.

The Tabs can assist attaining plane IF the boat is very heavy or underpowered.
Once onplane the tabs are used for side to side balance. The drives can be used to adjust running angle if necessary...eg. big water bow down for a better ride. Tab the bow down only if needed.
Tabs are also used to plane at a very slow cruise...eg. very big water.
Ever one should know the minimum planning speed with full down tabs and drives.
Check this by starting on plane and slowing down slowly..reduce throttle a hundred RPM at a time. Ensure drives and tabs are down full. Now watch the speed and RPM setting when the boat falls off plane. Use the min plane speed when the water is soo rough you kind of wish you were back at the dock enjoying a cold one.
Hope this helps,
Mark.

 

[Kameroo]

Ever one should know the minimum planning speed with full down tabs and drives....

Use the min plane speed when the water is soo rough you kind of wish you were back at the dock enjoying a cold one.
Hope this helps,
Mark.

Air,

We're speaking the same language. I agree on min planing speed--around my house we call it "V-mp".

 

[Carpedmman]

Thanks for the input Stuart. what do you do with your trim tabs at slow and higher speeds?

Mike- I always keep my tabs up out of the way unless I use them to plane with a heavy load or, as mentioned below, use to adjust the port/starboard tilt of, say, a strong wind on the port side.

I do trim up the outdrives anytime I plane-out as the boat gets more bow lift it will increase speed. There is a special spot between too much lift and just the right amount. If the bow starts to go up and down (Porpoising) then trim down just a tad. I cruise comfortably at 3000 RPM, 32-33mph. This is with 1/8-1/4 trim up on my outdrives. One last thing, if the water is rough then keep then don't trim the outdrives this will leave the bow in the water to "slice' the waves.

Sorry if this is boating 101...not quite sure of your skills....
Enjoy.

 

[Uplate]

Sorry if this is boating 101...not quite sure of your skills....
Enjoy.

Well this is the largest boat I have owned, the first with trim tabs, and the first with dual engines. So in that repect it is Boating 101 for me with a cruiser.

I learned a long time ago in boating that the only stupid question is the one you do not ask. I have also found that boaters are some of the most helpful people I know as we all share the same passion, no matter what kind you own.

Thanks to all that have responded with helpful advice!

So here are a few more:

1. Someone mentioned "home" position of the trim tabs. Is this up or down? My default is full down when not on plane (Have I been plowing around?)

2. It is also my understanding that "Down" means bow down and "up means bow up. This makes sense knowing how the tabs move.

3. PO told me to push tabs in Up position for 7 seconds. I think this is the time it takes to fully retract to Up position, drives trimmed up slightly, then WOT until on plane, then fine tune from there.

It also sounds from some of these messages that Full up Tabs should be the defualt and then use down as needed for leveling.

Thanks again for all the great advice.

 

[douglee25]

Some boats tabs operate differently from others depending on who did the wiring. The next information may/may not apply. You will have to figure out if this information applies to your boat or not.

Typically though -

1. When you want the bow to go down, the tabs should go down.
2. The port tab button should operate the starboard tab.
3. The starboard button should operate the port tab.
4. Usually the home position refers to the fully up or retracted position.

Doug

 

[Redhook98]

Well this is the largest boat I have owned, the first with trim tabs, and the first with dual engines. So in that repect it is Boating 101 for me with a cruiser.

I learned a long time ago in boating that the only stupid question is the one you do not ask. I have also found that boaters are some of the most helpful people I know as we all share the same passion, no matter what kind you own.

Thanks to all that have responded with helpful advice!

So here are a few more:

1. Someone mentioned "home" position of the trim tabs. Is this up or down? My default is full down when not on plane (Have I been plowing around?)

2. It is also my understanding that "Down" means bow down and "up means bow up. This makes sense knowing how the tabs move.

3. PO told me to push tabs in Up position for 7 seconds. I think this is the time it takes to fully retract to Up position, drives trimmed up slightly, then WOT until on plane, then fine tune from there.

It also sounds from some of these messages that Full up Tabs should be the defualt and then use down as needed for leveling.

Thanks again for all the great advice.

"Home" position is with the tabs in the all the way up position. If you have been cruising with them all the way down, you have been plowing a bit. But of course, the lower the speed, the less the plowing.

As for when I was talking about up or down, I was referring to the tabs. When the tabs are all the way up and the drives are trimmed properly, you are in a "neutral" state. I.E bow up slightly, boat more or less level. Tabs go down, bow goes down. Unless of course you are only tapping on one, then it could merely level you out.

Best way is to get out there and experiment. Just remember that tabs are there to primarily keep you level first, up on a slow plane second, and to assist with getting on a plane third. My philosophy.

and my .02 cents

 

[Carpedmman]

Well this is the largest boat I have owned, the first with trim tabs, and the first with dual engines. So in that repect it is Boating 101 for me with a cruiser.

I learned a long time ago in boating that the only stupid question is the one you do not ask. I have also found that boaters are some of the most helpful people I know as we all share the same passion, no matter what kind you own.

Thanks to all that have responded with helpful advice!

So here are a few more:

1. Someone mentioned "home" position of the trim tabs. Is this up or down? My default is full down when not on plane (Have I been plowing around?)

2. It is also my understanding that "Down" means bow down and "up means bow up. This makes sense knowing how the tabs move.

3. PO told me to push tabs in Up position for 7 seconds. I think this is the time it takes to fully retract to Up position, drives trimmed up slightly, then WOT until on plane, then fine tune from there.

It also sounds from some of these messages that Full up Tabs should be the defualt and then use down as needed for leveling.

Thanks again for all the great advice.

Hello Mike-
I agree completely that the question NOT asked is the worst thing someone can do, especially on a board full of boaters who love to share their knowledge. I did not mean to offend you by stating my boating 101 statement.

My opinion on your other questions:
1) Yes, Home Position is the Tabs completely UP.
2) Correct, DOWN on tabs equates to Bow down.
3) When going on plane I never adjust the trim up slightly prior to apply power. If you think about the forces against the rams of the outdrives, that is a lot of force. I start with the drives completely down and apply power slowly but firmly. I don't "punch it" becuse there will be prop slip. Once I get to around 3000 rpms I trim up slightly and then throttle back slightly to my sweetspot. *3000rpm. I say 3000rpm because with twin 454's this is where they seem to just hum. Your sweetspot will be different and after more time behind the wheel this will all make sense. Enjoy the ride!
Stuart

 

[Uplate]

Hello Mike-
I agree completely that the question NOT asked is the worst thing someone can do, especially on a board full of boaters who love to share their knowledge. I did not mean to offend you by stating my boating 101 statement.

My opinion on your other questions:
1) Yes, Home Position is the Tabs completely UP.
2) Correct, DOWN on tabs equates to Bow down.
3) When going on plane I never adjust the trim up slightly prior to apply power. If you think about the forces against the rams of the outdrives, that is a lot of force. I start with the drives completely down and apply power slowly but firmly. I don't "punch it" becuse there will be prop slip. Once I get to around 3000 rpms I trim up slightly and then throttle back slightly to my sweetspot. *3000rpm. I say 3000rpm because with twin 454's this is where they seem to just hum. Your sweetspot will be different and after more time behind the wheel this will all make sense. Enjoy the ride!
Stuart

thanks Stuart-

_Certainly_ no offense taken and thanks for your input. Hope to go out and play a little over the holidays.

Worse part about boating right now is I need to remove most of my back canvas cover to see the dock when backing in...and that gets cold!