Proper Trim for Inboard / Outboard - 1991 Bayliner Capri Merc

[malibu3105]

In reading these posts, I am seeing people state that they Trim Up to get better speed. I am new to boating so am just trying to learn.
Don't I want to trim (lower the prop) down so that the boat planes flat on the water for best speed? And if I trim Up, doesn't that point the nose of the boat up, and push the bottom of the boat down? Seems that would slow my boat down.

Please advise, as I want to do it correct. I was out last weekend and had it trimmed all the way down (I think). the boat ran good, almost 40mph.
It has a 4.3L V6 Mercury engine.

Frank

 

[tpenfield]

Initially when you start off from a stand-still trimmed down will help the boat rise up out of the water. But . . . once you gain speed, the boat can hold itself up, so you can get a little less drag by trimming up a bit. there is a lot of 'feel' to it and no right or wrong. It is just that the boat will gain a few more mph when trimmed correctly for a given load and sea condition.

 

[thumpar]

Trimmed up does raise the bow but leaves less hull in the water for less drag. If you are trimmed down at speed you just plow through the water.

 

[H20Rat]

Too much of a good thing is never good also. When you are trimming up, there is a certain point where the prop will ventilate. Also, depending on the hull, you might actually lose speed before the prop ventilates. Need to watch GPS and tach while trimming if you want the optimal spot. Handling is also impacted by trim... Too much up trim and a hull will often ventilate on a turn. Too much down trim at speed during a turn and you get bow steer, which can be violent and dangerous. (again, all depending on the hull)

 

[tpenfield]

My boat only like a little bit of up trim. If I go even into a moderate range, well before ventilation, the boat looses 1-2 mph.

 

[smokeonthewater]

Yep it's all relative to the boat in question...

Most boats will handle odd at high speed trimmed all the way down and many will even be unsafe... Others might run the best there...

You need some way to measure speed water pressure speedo works but it is hard to see small speed changes.... GPS, be it high dollar marine, the dash mount from your car, or an app on your smart phone or tablet is much easier to use...

You generally start trimmed all the way down and gradually keep bumping it up a little as you accelerate... At top speed you want to keep making SLIGHT adjustments untill you find the most speed.... We may be talking about 8 mph difference or 1/2 mph...

Also you will adjust for handling and ride... If steering gets twitchy or the boat starts to porpoise you wanna back off a little...

Again very small adjustments... Often you will press the button for only a fraction of a second.

 

[Blind Date]

Yep little adjustments. Water conditions and how the boat is loaded at the time will determine best trim angle once upon plane. I don't look at speed & I don't look at engine RPMs. I trim my boat completely by feel given load, speed, water conditions.

 

[thumpar]

My last boat would porpoise if I went out more than about 1/4. With the current boat I just go full out as soon as I start getting out of the hole.

 

[southkogs]

I've got a Capri/Classic 1950 with the 3.0 ... It comes out of the water best trimmed all the way down, but it cruises best (and tops out best) with some trim UP. Maybe 1/8th by my gauge.

 

[smokeonthewater]

To make things as clear as mud I'll add that prop selection can have a huge effect on trim setting as well.

 

[Silvertip]

The seat of your pants, your ears, and your eyes are the best indicators of when trim is correct. Be aware that "one trim setting" is not best for all load conditions. You can practice setting trim by getting on-plane and then tickle the trim switch a bit at a time while watching the tach and speedometer. Your ears and butt can hear and feel subtle changes in speed. The rush of the water at the side of the boat will suddenly quiet substantially when good trim is reached. To get on-plane practice with various trim settings and don't rely on the trim gauge (if you have one).

 

[thumpar]

I might glance at the trim gauge but I normally only run by it when I am going to take off to make sure the drive is fully down/in. My old boat didn't even have one so it was completely seat of the pants.

 

[malibu3105]

I was out this last Saturday, and Monday (yesterday) and practiced trimming the boat. Now I understand. If I trim up the boat rises up and goes faster. If I trim to high, it bounces and sounds like the prop is slipping (forget what that is called), so I was able to find the sweet spot. And now I know where the bow should be, slightly up and not down. She glides very well. Got up to 41mph at WOT with good trim. Thanks for all the advise. I am learning Love having a boat !!!

 

[thumpar]

The bouncing is called porpoising. My old boat would do it very easily just not even half trimmed up.

 

[WIMUSKY]

Trimming up will also give you a smoother ride in choppy water......