Understanding my outdrive trim synching

[Cincy Aquaholic]

Having twins as well as Mercs is all brand new to me so here is something I'm not familar with. Since my manual is an hour away I thought the quickest answer would come from the board.

When I trim my outdrives either way I notice my smartcraft displays changes to "sync" view. The left shows the numerical trim of the port drive and the right shows the starboard drive. The center shows redundant numbers but also a little bar graph.

Question, why do my drives trim to different numbers? Sometimes I'll tap while on plan and one side will go to 7 and the other to 4. Sometimes they fluctuate and maybe sync up while just cruising.

Can anyone explain how this system is designed to work?

 

[Cincy Aquaholic]

I think I can trim my drives independently with the buttons on the controls or use the one on the throttle to trim them together. I guess I'm not so concerned with the numbers matching perfectly (which it seems to do anyway but not immediately) but more so as to why they seem to change positions occassionaly when the water conditions change during cruising.

Is this some feature to help keep the boat stable?

 

[Stray Cat]

Each drive has its own hydraulic pump. When you nudge the trim switch, you are initiating each hydraulic pump to either extend or retract your trim cylinders. Since the pumps are independant, the response time of each pump to react is different hence the difference in the trim positions. One of my trim indicators used to bounce around alot, and lag behind the other indicator. I could reset them according to the manual's procedure, but it would return to bouncing around. The trim sensor on the drive was replaced while under warranty. Now it doesn't vary a few tenths while on plane.

I use the engine sync screen (the ball floating to center when in sync) as my primary screen when cruising. When the trim switch is activated, the two small screens on the top left and right of the screen will indicate the trim position briefly then change back to their original status for water depth and clock time.

As Scott mentions, don't get hung up on them being dead nuts.

 

[boughtabouy]

Hi Cindy,

I have the same issue, although not as severe. Not sure what the deal is.

Notice my boat model and year...

 

[Half Off]

Don't know if this is advisable but it works for me. I just bump my single trailer trim switch and both drives trim at the same time. I don't have to give them much, maybe about 1 second. I try to get around 3600-3800 rpm's and 28-30 mph for optimum performance.

 

[Groucho]

I do not have this problem...:smt089

 

[gnealon]

Don't know if this is advisable but it works for me. I just bump my single trailer trim switch and both drives trim at the same time. I don't have to give them much, maybe about 1 second. I try to get around 3600-3800 rpm's and 28-30 mph for optimum performance.

I would like to hear what others have to say about this... i have done this as well in the past. Its nice and easy and you know both drives are going up the same amount (at least my smartcraft says it is).

 

[Half Off]

I agree, it could cause damage if trimmed too far for too long. One question, wouldn't you fall off of plane if trimmed past the safe limit? Not to mention the obvious lose of power and sound differance of over trimmed outdrives. That is why I check my rpm to mph ratio when doing it this way.

By the way Scott, the outdrive stand I got from you worked great.

 

[Stray Cat]

One question, wouldn't you fall off of plane if trimmed past the safe limit? Not to mention the obvious lose of power and sound differance of over trimmed outdrives.

If I over trim, my props lose their bite, the rpm climbs, the boat squats in the rear, and begins to slow down. I don't know if this is the correct term, I call it prop blow out....

Trimming back to get the props to hook up again really places a strain on the drive line in my opinion. Especially if the rpm climbs up to 3800 + It took me a couple times to realize on a 300, you don't trim much.

 

[Jerroz]

Is there a thread on this forum for the best way to trim your drives? I have been using my hydraulic tabs to level out the boat but read an article yesterday that said you should trim the outdrives instead, saying its a better way. When they say "better" I assume more fuel efficient.... not sure.

I typically cruise from spot to spot at 3700 RPM, about 30 knots depending on conditions, and I use the tabs when the wind changes or the crew moves around to level the boat, drive trim always set to Zero.... is that not the way to do it? Am I wasting gas doing it this way?

Any advice would be appreciated as to how you guys do it.

 

[terminaldegree]

On our 340 with stern drives, I would keep everything fully down/in until the boat has settled on plane. If going at minimum planing speed, as if you were going into chop, I kept the drives fully down and adjusted tabs to taste. I usually cruised 200-400 rpm above the minimum planing speed on a normal day, and would trim both drives up for about a full second. You can feel and hear the difference as the boat seems to strain less. If you do this correctly you will pick up a little speed and rpm without touching the throttle. Again, adjust the tabs to your liking.

At higher cruising speeds (above 3500) I was able to trim the drives up another second, and significantly higher if running at/near full speed.

If in doubt, experiment with trim and tabs while watching your gps at a fixed throttle setting. In calm water, always shoot for the setting that affords the best speed for a given rpm. Getting this right will result in better efficiency and lower noise as you may be able to run a lower cruising rpm to get the same speed.

Hope this helps.