Tilt vs. Trim

Ok, I had glossed over this little distinction until I came accross zonaman's TT thread from yesterday. It appears that there may actually be a distinction. My only experience with PTT was on my BIL's boat i used to bower. Had a 40 force on it and you could trim it while underway to get your best operating angle. When you got the boat out of the water, you would use the same switch to tilt the OB up to it's travel position. So I'm obviously missing something about PTT. Could someone help me fill in the blanks.

Re: Tilt vs. Trim

there is a limit switch. while at low angles, you are triming the boat (Power Trim). for trailering, etc. you are above the limit switch and tilting the motor. (power tilt). to tilt the motor, you usually have to depress another switch, or like my mercruiser, pull the switch up harder (2nd step in switch)

Re: Tilt vs. Trim

TRIM is the range of motion while operating the boat. There is usually trim limit switches that prevent the motor from raising out of the water.

TILT is moving the motor beyond the trim range. Used for trailering the boat etc.

Re: Tilt vs. Trim

Tilt gets you on and off a trailer.
Trim adjusts the angle while engine is running.

Most tilt pistons are smaller in diameter than trim. if you tried to hold up too much horsepower there would be real risk of cracking them. most tilt rams have an internal bypass valve to prevent this. if you try to trim on a tilt cylinder it will usually slam down around 5-10HP.

Most engines are water cooled. If you lift the cooing intakes out of the water while running then the engine might overheat and die. Therefore most trim systems disable at 15 degrees. Some engines use short pushrod trim pistons that only extend a few inches. Some use electronic sensors and some others use hydraulic bypass circuits. Either way, factory trim should not lift past 15 degrees.

Duck and gator hunters with single ram trim systems often request trim bypass circuit disabled. This is possible to do by setting the trim bypass valve to infinity (it just never opens). They know the risk but want the ability to skim the prop at or just below surface of water to clear an obstruction.

Re: Tilt vs. Trim

Old systems used a 2 stage tilt OR trim control but on most systems made since the early 80's or so you are on your own for figuring out when to stop trimming the motor up when under way. Now they just come up slow until you are past the reasonable trim level and then they come up fast.

Re: Tilt vs. Trim

Thanks for the replies. As they say, you learn something new everyday. I'm heading over to his house in a few. I'll take a peek at it and see how it's set up.

Re: Tilt vs. Trim

mercurymang said:

Thanks for the replies. As they say, you learn something new everyday. I'm heading over to his house in a few. I'll take a peek at it and see how it's set up.

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lift the engine all the way and then count how many shiny little trim&tilt shafts there are. usually one or three. with three rams, the two outside shafts usually are not connected.

Re: Tilt vs. Trim

On my Merc engines if you try to trim under way higher than the trim piston allows you hit a bypass valve and the lifting stops. If no pressure is against the ram, like out of the water or in the water engine off, it will continue on up.

If you are in a trim position and apply power to the engine in the water underway, the bypass valve will open and the engine will come down to the top of the trim positon.

Per a '96 sales brochure, tilt is from about vertical to 75 degrees up. Trim is only the first 20 degrees of that. I think the OEM's deliberately did it this way as if you were to have the same trim capability as tilt, I wouldn't doubt that on some boats you could just rip the transom out with all the torque set at a high degree on the transom. Would be a pretty good lever.

Mark

Re: Tilt vs. Trim

There was a mercury switch on some motors with the 3 ram, one tilt/trim switch that would not let the motor start nor run unless the motor was in the trim down section of the system. The mercury switch would kill the motor if it was raised to the tilt section as the motor would not be in the water deep enought for the water pump to pump water and do damage to the motor. JMO
Oldman570

Re: Tilt vs. Trim

Texasmark said:

On my Merc engines if you try to trim under way higher than the trim piston allows you hit a bypass valve and the lifting stops. If no pressure is against the ram, like out of the water or in the water engine off, it will continue on up.

If you are in a trim position and apply power to the engine in the water underway, the bypass valve will open and the engine will come down to the top of the trim positon.

Per a '96 sales brochure, tilt is from about vertical to 75 degrees up. Trim is only the first 20 degrees of that. I think the OEM's deliberately did it this way as if you were to have the same trim capability as tilt, I wouldn't doubt that on some boats you could just rip the transom out with all the torque set at a high degree on the transom. Would be a pretty good lever.

Mark

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It amazes me sometimes that it doesn't rip it out anyway.

I took a look at my brother in laws yesterday and couldn't really tell. There was only one pump and one cylinder. The battery was dead so I couldn't fiddle with it. Bottom line is that it sounds like there are several different types of setups so it may be hard to answer the question.

Re: Tilt vs. Trim

mercurymang said:

It amazes me sometimes that it doesn't rip it out anyway.

I took a look at my brother in laws yesterday and couldn't really tell. There was only one pump and one cylinder. The battery was dead so I couldn't fiddle with it. Bottom line is that it sounds like there are several different types of setups so it may be hard to answer the question.

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1989-2008 35-115HP mercury, mariner, and force mostly used a single ram trim system built by the oildyne division of parker hannifin (out of MN).
http://www.parker.com/portal/site/P...&vgnextdiv=200311&productcategory=productline

The whole package including motor and hydraulic cylinder fit up underneath the engine. Looking at it from behind the boat, the motor and pump are on your right and the hydraulic actuator is on your left. They are bolted together at the base. Mercury used two bypass valve settings 30-60HP and 60-120HP. They distinguished the two system from each other by using a different diameter mounting shaft. 9/16" mounting shafts designated a system with 30-60HP internal valves. 5/8" designated systems that had 60-120HP valves installed.

some engines had an option for manual assist trim. The electric pump was replaced with a hydraulic Lift&Lock mechanism. This assembly used the 9/16" mounting base. The 3ram 70-175HP system used the same mounting dimensions as the 9/16" single ram. According to the mercury gospel, customers with larger engines needed to use a 3ram system in order to upgrade. This is because none of the narrower mounting base systems had 120HP valves installed. However, leaving the mercury bible, the manual trim can be upgraded by simply bolting on an electric pump in place of the lift & lock. the single ram system has a third hydraulic circuit to handle trim bypass. The working range can be changed by replacing the trim bypass spring. Within a range, it can be adjusted or disabled by shimming.

Re: Tilt vs. Trim

Yep. Looking at those pics, that's what his setup looked like. My setup will be for a '75 650. Are there major differences there?

Re: Tilt vs. Trim

mercurymang said:

Yep. Looking at those pics, that's what his setup looked like. My setup will be for a '75 650. Are there major differences there?

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if you want trim then you need to stick with factory original system. Otherwise there is no guarantee that the geometry and weight distribution are both correct for your hull. If you want tilt then you can make one out of anything - even leftover log splitter or snowplow parts. just be sure not to lift too far and crush something.

Re: Tilt vs. Trim

Ok, I see where you are going. Sorry, a little slow sometimes. Ya, i don't care about tilt, only trim.

Re: Tilt vs. Trim

mercurymang said:

Ok, I see where you are going. Sorry, a little slow sometimes. Ya, i don't care about tilt, only trim.

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Yes you do too. Trim is only about 20 degrees from vertical. There are a lot of things you can't clear with only 20 degrees of engine angle from vertical.

Mark