ekkau
New Member
When do I use Engine Trim, and when do I use the Trim Tabs?
Is it good practise to start the boat with Engine Trimmed in?
KK
Is it good practise to start the boat with Engine Trimmed in?
KK
How to use Engine Trim & Trim Tabs on Stern Drive
- Thread starter ekkau
- Start date
AndieMac
Well-Known Member
G'day and welcome....
Start off with the drive/s trimmed in until she is up on the plane, then lift the leg/s slowly until the bow gives a slight rise. You can feel the boat running a lot easier, the later model Mercs and VP's have drive position indicators, but you can feel the easy running attitude with a bit of practice.
Some boaters with lower power options or a heavily laden vessel will use the trim tabs down to assist the boat up onto the plane as well. Once again, as soon as she is up, back off the tabs to a 'free' run, better fuel economy will be achieved.
Use the drive trimmed in also when taking on a choppy head sea, as with the tabs, only use what you need, and as the conditions/directions change, adjust back to normal running.
Following sea, let the drive out slightly (too much and prop will cavitate) to keep the bow up (and stops tracking down the wave front), just keep practicing until you know by the feel and sound of engine and drive. Your only going to be adjusting within the 'trim' range anyway, which isn't very far but makes quite a difference.
Good luck
Start off with the drive/s trimmed in until she is up on the plane, then lift the leg/s slowly until the bow gives a slight rise. You can feel the boat running a lot easier, the later model Mercs and VP's have drive position indicators, but you can feel the easy running attitude with a bit of practice.
Some boaters with lower power options or a heavily laden vessel will use the trim tabs down to assist the boat up onto the plane as well. Once again, as soon as she is up, back off the tabs to a 'free' run, better fuel economy will be achieved.
Use the drive trimmed in also when taking on a choppy head sea, as with the tabs, only use what you need, and as the conditions/directions change, adjust back to normal running.
Following sea, let the drive out slightly (too much and prop will cavitate) to keep the bow up (and stops tracking down the wave front), just keep practicing until you know by the feel and sound of engine and drive. Your only going to be adjusting within the 'trim' range anyway, which isn't very far but makes quite a difference.
Good luck
Last edited:
gjgm
Well-Known Member
pretty fair answer there!
Id just add that you might find it simpler to think of the tabs as balancing the boat port/starboard due to uneven weight or wind, and the drive trim to angle the boat bow/stern.
With the drive trim, in good seas,keeping the throttle at half, say, the speed is a good indicator of the trim being correct.
As you move from too far in to too far out, the speed will increase and then decrease again. Top speed is when the trim is correct at that speed. Generally, the faster the speed, the more you can lift the leg out, but depending on the boat, it can start to get a bit twitchy if you lift too much.
Id just add that you might find it simpler to think of the tabs as balancing the boat port/starboard due to uneven weight or wind, and the drive trim to angle the boat bow/stern.
With the drive trim, in good seas,keeping the throttle at half, say, the speed is a good indicator of the trim being correct.
As you move from too far in to too far out, the speed will increase and then decrease again. Top speed is when the trim is correct at that speed. Generally, the faster the speed, the more you can lift the leg out, but depending on the boat, it can start to get a bit twitchy if you lift too much.
tico
Well-Known Member
When you say 'trimmed in' , how much?
Is it OK (for the drive and UJs) to run at -5 for any length of time? especially when accelerating (max torque) onto the plane?
Is it OK (for the drive and UJs) to run at -5 for any length of time? especially when accelerating (max torque) onto the plane?
gjgm
Well-Known Member
well I m no engineer... you should be on the plane in some seconds (10/20?).. dont think its going to do any damage then ! And it would have to be a very unbalanced boat to need to run at -5?
tico
Well-Known Member
Getting on the plane isnt really a problem 
(pocket rocket)
i'm more interested in running in rough water (pretty much normal here), with my engineering head on , prefer to run as close as poss to 0 trim for the sake of the UJs, but wondering if its OK to run at -3 or -2 for any length of time to keep the bows down in a chop rather than at 0 with the consequent slamming
(pocket rocket)i'm more interested in running in rough water (pretty much normal here), with my engineering head on , prefer to run as close as poss to 0 trim for the sake of the UJs, but wondering if its OK to run at -3 or -2 for any length of time to keep the bows down in a chop rather than at 0 with the consequent slamming
gjgm
Well-Known Member
I would say that is fine.. I ve done several hours at a time in rough weather
spannerman
Well-Known Member
It will be no problem to run with negative trim of -2 -3 as the U/J's drive through 5 degrees and more when you apply steering.
If you think about there are thousands of trucks hammering up and down motorways for hours on end and their drive lines aren't exctly in line i.e. 0 degrees as a look under any long box truck will show.
The max torque isn't an issue with the U/J as the prop slips somewhat and its the gears that work hardest as they slide in and out of mesh.
I have only seen a couple of worn out U/J's in 15 yrs, the reason most are damaged are rust from water in the bellows.
Volvo specify that the U/J's should be overhauled at 500 hrs on boats that work for a living, I think I have done about 10-12 boats for this reason out of the 50 odd I have changed, and they weren't always worn out at 500 hrs!.
If you think about there are thousands of trucks hammering up and down motorways for hours on end and their drive lines aren't exctly in line i.e. 0 degrees as a look under any long box truck will show.
The max torque isn't an issue with the U/J as the prop slips somewhat and its the gears that work hardest as they slide in and out of mesh.
I have only seen a couple of worn out U/J's in 15 yrs, the reason most are damaged are rust from water in the bellows.
Volvo specify that the U/J's should be overhauled at 500 hrs on boats that work for a living, I think I have done about 10-12 boats for this reason out of the 50 odd I have changed, and they weren't always worn out at 500 hrs!.
