trimming motor without hydraulic trim

[richardlee]

I have an 1979 18 ft Starcraft Supersport that I have rebuilt from scratch. It has a 115 Merc without power trim. How do you know what hole to place the pin in to properly trim? Right now the motor is trimmed up and held by a transom saver for towing. The boat would cavitate when I tried increasing speed too much. The previous owner said something about pulling the pin and letting the motor swing freely. Since this is my first boat, I am trying to experiment. Any advice? thanks.

 

[tjatech]

Placing the trim pin is really based on the performance you are looking for. As you may know, trimming the motor up will raise the bow out of the water. This will typically give you a higher top speed, but not as good of hole shot. Trimming up too far with cause the motor to cavitate. Trimming down will give you a little more stable ride and hole shot.

On my boat (1974 Reiell Tri-Hull with a Johnson 115), I have to place the trim pin in the last hole (motor trimmed all the way down) in order to get a reasonable ride. Every boat is different, but I'd stay start at the bottom hole and work your way up until you experience too much bow rise or cavitation, then back it down 1 hole. I'm fairly new to this as well though, so maybe one of the more experienced folks can give you a better method.

 

[metriccrescentwrench]

Wow, I haven't had to deal with an outboard without power trim in years. It's purely a matter of trial and error to see what works best, and the optimum trim position could well change as your load varies.

IMO it would be a worthy upgrade to find an engine with power trim.

 

[GA_Boater]

I have an 1979 18 ft Starcraft Supersport that I have rebuilt from scratch. It has a 115 Merc without power trim. How do you know what hole to place the pin in to properly trim? Right now the motor is trimmed up and held by a transom saver for towing. The boat would cavitate when I tried increasing speed too much. The previous owner said something about pulling the pin and letting the motor swing freely. Since this is my first boat, I am trying to experiment. Any advice? thanks.

I don't think letting the motor swing freely is a very good idea for two reasons. First, you won't have reverse lock because the lock hooks don't have the pin to lock onto. Second, without a pin for the motor to rest against, there is nothing stop the motor from slamming into the clamp assembly or transom if you advance the throttle quickly. Think of the motor swinging like a pendulum. Leave the pin in place and experiment until you find the hole giving the best overall performance - It won't be a perfect hole shot, cruise and getting on plane, so you have to pick which is most important to you.

 

[Texasmark]

+1 on GA boater's comment. YOU DO NOT WANT TO LET YOUR ENGINE FLOP AROUND. Reason is, among other things, in reverse the lower unit/prop will propel itself to the surface and the minute you put it in F gear, it will come slamming down and can do a tremendous amount of damage to your transom and engine mounting brackets.

Back in 1972, before OMC had power trim and even tilt, and when the engines were power head rated (10-15% lower power than stated compared to todays prop rated engines) I had a 125 on an 18' Caravelle tri hull. I had a wife and 4 kids and we had a ton of fun with this boat cruising, water skiing and all. One time, at a company 4th of July party, I (alone in the boat) was able to get 5 skiers up, not for long.....hard to keep 5 up without one falling down....novices, but none the less I got them up "with a fixed engine angle (trim) position.

Since I had no way to remotely change the thrust angle of the engine, I just moved it from notch to notch till I got what worked. That is just what you have to do.

Mark

 

[Chris1956]

Normally the 2nd hole from the transom is the starting point. Most boat's performance will be best in that position. However, you need to try the first an third holes using a speedometer to see what is fastest. Also test for driveability.

 

[Stumpalump]

You want it as high as you can stand. You can't stand the cavitation so go down one hole. That's one hole closer to the transom.

 

[richardlee]

Thanks for all you suggestions. I have been out-of-town a lot and also spending time working at our son's house and have not had time to get the boat back on the water. Hopefully I can in a couple of weeks. Right now the motor is resting on the pin and lower unit is supported by a transom saver. My understanding of the posts is that I need to place the pin through the hole in the motor mount plus through the motor as well to keep it stable.

 

[Maclin]

If the motor has no provision for power tilt or trim then there should be a latching mechanism when the motor is down to grab the pin. That doubles as a breakaway if you hit something hard, to let the motor move up and not tear itself off the transom. Then there is a lever or other mechanism to undo that latch to be able to manually tilt it all the way up. There should also be a mechanism to flip down and keep it in the full up position without needing the transom saver. You can still use the transom saver by holding the motor as you undo the full-tilt mechanism then set it into the saver.

 

[Maclin]

Oh, and trial and error is how to set the pin. On one older boat I had that was manual like that, I tied a heavy string to the pin so I would not drop it into the water when I tried different settings in the water, sometimes I would switch it down one for skiing then put it back to higher trim for the trip back to the ramp if we had gone out a ways..

 

[richardlee]

Maclin, thanks for the info. Yesterday was a rain day and I didn't get a chance to work on the boat. Hopefully today will be better. I will at the motor to see how that latch works. I really appreciate the help.

 

[NSBCraig]

Buy yourself some smart tabs.

The best spot for your trim is gonna be slightly higher then level and the automatic tabs will push your boat up on plane. $100 well spent.