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new to boating...some trim and trim tab questions

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Old 05-24-2011, 08:06 AM
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Default new to boating...some trim and trim tab questions

well I got my first big boat and was wondering if you guys might be able to give me some insight on the proper way of running the boat on the water. Its a 39' chris craft 390 with 2 465hp 502's, trs drives, and 4 blade propellers.

Should I keep the outdrives in all the way when driving? I know that they need to go up for shallow water but what about any other times?

What about the trim tabs? Right now they are all the way up on the boat.

If I just bring the engines up to 3k rpm it goes on plane just about instantly, so I dont think I have any problems there.

I've been cruising the boat at around 32-3300 rpm and it would go 35-36. I played with the trim tabs the other day and the boat got up to 40-41mph!

I guess the most important question I have at first is:

Is there anyway I can break something by messing with the trim and trim tabs?

Last edited by darkostoj; 05-24-2011 at 08:17 AM.
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Old 05-24-2011, 08:22 AM
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Start with the drives in. Once on plane you trim the drives up or out. It lifts the hull and reduces the wetted surface, decreasing friction and increasing speed. If you over trim you'll start to decrease speed. Find the sweet spot.

Some boats need tabs to plane quicker. Sounds like you don't. Tabs can be used to stay on plane a lower speeds, correct a list from uneven weight distribution, etc. Play with the tabs in small amounts to see how your boat reacts.
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Old 05-24-2011, 08:23 AM
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First off, I'm a newb to boating so I'm still learning the proper trim and tab settings. For the most part, I leave my tabs on 3 which sits them level with the rest of the hull. I only adjust them further if I have to balance the boat. The drive I start all the way in until on plane. When I get on plane, I start creeping the drive up until I see my RPM's start going up and the boat smooths out.. Again, I'm still learning because when I go faster its smooths out nice around trim setting 4 to 4.5 on the indicator,but when I slow down I start porpoising like a mo fo.. I'm getting better about adjusting the trim when I slow down.. Just like I've been told, takes a lot of playing with and learning the boat... I'm sure you'll get a lot of info from they guys that have been doing this for a long time too...
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Old 05-24-2011, 10:35 AM
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This may give you a better understanding of how the tabs / drives work in combination.

http://www.youtube.com/watch?v=M8Qzsf6aZpk
Fountain Powerboats - Secret to Speed
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Old 05-24-2011, 01:15 PM
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Quote:
Originally Posted by darkostoj View Post
well I got my first big boat and was wondering if you guys might be able to give me some insight on the proper way of running the boat on the water. Its a 39' chris craft 390 with 2 465hp 502's, trs drives, and 4 blade propellers.

Should I keep the outdrives in all the way when driving? I know that they need to go up for shallow water but what about any other times?

What about the trim tabs? Right now they are all the way up on the boat.

If I just bring the engines up to 3k rpm it goes on plane just about instantly, so I dont think I have any problems there.

I've been cruising the boat at around 32-3300 rpm and it would go 35-36. I played with the trim tabs the other day and the boat got up to 40-41mph!

I guess the most important question I have at first is:

Is there anyway I can break something by messing with the trim and trim tabs?

On any offshore boat, you should always start with the trim tabs set all the way down, and the drives all the way in. Using the trim tabs in this manner will reduce the amount of strain on your drives when you attempt to get on plane.


It really isn't necessary to bring the engines up to 3,000 RPM instantly. Increase the RPM gradually, this gives the props a chance to hook up and bite. As you ease your way up to 3,000 RPM, you will notice the boat pop on plane. You then raise the trim tabs to the neutral position (usually number 3 on your trim indicator). This allows the nose to come up out of the water. The RPM will increase slightly.

Now that the tabs are up, you want to start trimming your drives out. Do this in small increments, and take note of how the boat responds. If you over trim, the boat will start to porpoise, and your speed will decrease.

This is by far the best video I've come across that explains how to properly operate an offshore boat.
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Old 05-24-2011, 02:11 PM
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I primarily use my tabs to level the boat and I use them to drop the nose and "lenghten" the boat in rougher water.

My cafe likes to start with the drives all the way in, and then trim them up once I get on plane. I don't see much benefit in my hull from having the Tabs down when I get up on plane.
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Old 05-24-2011, 02:56 PM
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Keep in mind that any trim and tab "number" mentioned here are all relative to that particular boat and whatever type of indicators they have. You will have to learn the numbers relative to your boat. I have Mercury mechanical indicators and at "3" I am over trimmed.

I would mark my indicator panel where the propshaft and tabs are level with the bottom of the boat for a reference point. That is usually a pretty safe setting when cruising. From there you can make adjustments.

My last boat was 24' w/280 K-planes, if you lowered the tabs all the way down the transom would lift enough to blow out the prop and the boat would bow steer.
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Old 05-24-2011, 06:46 PM
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Quote:
Originally Posted by darkostoj View Post
well I got my first big boat and was wondering if you guys might be able to give me some insight on the proper way of running the boat on the water. Its a 39' chris craft 390 with 2 465hp 502's, trs drives, and 4 blade propellers.

Should I keep the outdrives in all the way when driving? I know that they need to go up for shallow water but what about any other times?

What about the trim tabs? Right now they are all the way up on the boat.

If I just bring the engines up to 3k rpm it goes on plane just about instantly, so I dont think I have any problems there.

I've been cruising the boat at around 32-3300 rpm and it would go 35-36. I played with the trim tabs the other day and the boat got up to 40-41mph!

I guess the most important question I have at first is:

Is there anyway I can break something by messing with the trim and trim tabs?
I took the Tres Martin class a month ago at Lake Havasu. I was the most vocal person about the cost.... Yet, it was worth every penny and more. You will learn how to adjust your tabs and drives. Call them.
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