How much should rpms change from no trim to full trim
 

How much should my rpms change from no trim to full trim at wot. Aceellerate to full throttle no trim and then go to full trim. What would be a normal rpm amount change to see or range...

What are you defining as these trim limits/levels? This is a bit of an odd question as it really doesn't work that way.

If you are at WOT and "full trim"; chances are you are on the rev limiter mimicking the fountains at the Bellagio, and about to blow your U-joints into the next county.
(assuming we are talking about an I/O setup)

My twin TRS lower units where recently setup with trim limit switches and it stops them from giving me much trim. They only move up a little bit and and I only gain 300.rpms from no trim to full trim now

My twin TRS lower units where recently setup with trim limit switches and it stops them from giving me much trim. They only move up a little bit and I only gain 300.rpms from no trim to full trim now. So my question is shouldn't I get more than 300 rpms from no trim to full trim. What is a normal range to expect in added rpms from no trim to full trim. 600, 800 or 1000 rpm increase? is 300 enough? or a normal increase in rpms?...NOTE: IF properly propped.and.I am not near the rev limiter because I am 700 rpms from it.) I recently purchased boat and trim pumps weren't working correctly now they are fixed but with the limit switches set the way they are why have trim. I think they are improperly set and need to be relaxed so I can actually trim the boat....Just looking for a realistic rpm change that I should expect....

More trim only helps if it helps top speed. Raising the drive without increasing speed serves no purpose. I usually only gain about 300 to 400 RPM with my Scarab. The Daytona is a totally different boat as far as trim is concerned.
The deeper your props are the more trim you will need. TOO much trim can make the bow too light and can be dangerous.

Need your info!! We are blind right now.

Boat, power, prop.. Then gps speeds and rpm at cruise and wot.
Trim should start out at neutral. Cav plate even with the plane of hull. Depending on several factors and hull running characteristics, ie. my Baja w/ no steps needs bow lift crated by positive trim, it depends how your boat typically runs.


You could possibly see 1-300 rpm increase by trimming up from neutral. Trimming down plows bow so that's pointless to discuss as your adding resistance.

Why did you add trim limit switches? IMO they are for drives without indicators, or novice boaters. When they fail (which they will) you will have no trim control at all.

I wouldn't be using using RPMs as the yardstick here to measure the effectiveness of trim. A few hundred RPMs would be the range, BUT the most important factor of trim range/setting is how it makes changes the attitude of the boat.

Why now the trim limits? Did over-trimming contribute to a failure?

You need to find neutral. (Mark neutral on your indicators.) Then the most you want to trim is maybe 3 ticks above neutral; give or take.

cant you adjust the limiters? to get the drives out more.

Yes.. And thats the info I am trying to figure out..... What is the measurement for the outdrives... How far should they extend... What is too much to where they are being damaged so to speak...I know that they aren't extending enough now.. Whether the measurement is in rpms or from bottom of hull out in inches.. What ever is the proper why to make sure they are correct and not over or under extended...

What sydways and4bus eluded to was that it's really point less. While running, too much will loose speed and eventually blow out.

I found this if you can't eyeball a good limit distance. You should know where your drive is per indicator regardless of trim limit.

http://www.mercstuff.com/trim_limit.htm

two things don't run WOT fully trimmed down that is dangerous, not every boat will do it but it can bow steer and spinout, and you will be starting a rooster tail past the highest trim you should be running at for best speed, unless you are really trimmed up and throwing a big rooster tail you shouldn't be hurting the u-joints.

Trim her till she losses speed.... Then knock back a bump or till it picks back up.... If you feel safe like that... Mark you indicators. Next time the boat is out st them on the mark to be sure it's acceptable..

I will make a note of this also.. But I did just find a site that said the limit should be set with the total measurement of the trim ram extended to 21 3/4 inches...This is a good starting point for me.. I will reset the limit switches to this measurement and see what happens. Then I will use your method to mark the indicators when I get them repaired to see the difference....its a start....

Every boat is different.... Ask a friend that has had lot if wheel time in a similar setup. To take your boat fir a ride. Watch him closely!!! Remember how the boat feels when he is driving. Hen it comes to trim you will learn how to feel it.

This is a good advice. In many larger sport boats, you will vent the propellers before a dangerous boat attitude will occur. The point in which the venting begins is a touch beyond your best max trim position.
In smaller lighter applications you might be able to trim beyond a comfort zone. In other word the boat can get to loose in the bow and become dangerous.
Besides marking the indicators at the full trim sweet spot, I usually put the drives at neutral while on the trailer and mark this spot as well.
Also, don't use the full trim best speed mark for every boat load and water condition. You need to adjust the trim to fit each rpm and water condition. Seat time will help you a bunch.
Take your time and enjoy the learning curve.
The 21.75" number is a max extension limit not what any particular boat might need.

Brett

Do you have a "trailer" button that overrides the limit switch? If so trim up with that until the boat loses speed. There's a lot more to it as Brett wrote about.

Yes great advise Brett .... When I first got my boat I marked neutral too. In time it will become natural.... As Brett said ...I use marks as advise not rule. Different conditions will warrant different settings. Once you feel the boat run good and fast.... You will remember the feeling. Soon you will be hardly looking to your indicators I normal conditions.