Need trim advice

[Marlie]

I am new to boating. Bought a 290 SLX with twin engines and love it. However, when I get up on plane and try to trim it even a little, it begins to cavitate. Also, it goes great at about 3000 rpm and 30 mph but if I try to go more slowly it will gradually lose speed and basically stop. How do I maintain it in the 20 to 25 mph range?

 

[kaz911]

to stay on the plane at < 3000 RPM you might need to use your trim tabs to keep the nose down.

You can also consider putting on bigger trim tabs - as SR is famous for putting on borderline small trimtabs. That will lower your plane speed if spec'ed correct. (Ask Tabman...)

 

[Marlie]

Thanks Kaz. Have not really used the trim tabs, have been trying to trim the engines but as I said, moving them much causes cavitation. Still trying to find the sweet spot for cruising. I am on the Lake of the Ozarks which gets pretty rough and I need to go more slowly to remain safe. Thanks for the advice.

 

[Lazy Daze]

Marlie, from what you've said, the first thing that comes to mind is something wrong with the running gear. What's the condition of the bottom of the boat (clean, algae, grass, etc). Also take a really good look at the props and see if there's anything hung up on them and if there are any chunks missing or bent blades. Also visually check that the drives are moving through their entire "up/down" range, especially the down part. When fully down, the props should be angled at a slight downward angle as compared the hull bottom/keel.

 

[src]

What drives do you have on your boat? I have Bravo 3's, and there is VERY little trim range available on plane - more than a light touch leads to cavitation. I've read that that isn't unusual with the B3 drives on larger boats.

 

[Marlie]

Thanks Guys. Dennis, the boat is clean, on a lift most of the time, and mechanically checks out. SRC, don't have a Bravo III but that is also what Capt Chad from the marina where I bought my boat said. He told me there is very little room to use the power trim on the 290s. Don't know why that would be. Anyway, from reading trimming 101, I think I need to play around with the trim tabs, and then with the power trim, to keep the boat on plane at slower speeds.

 

[Molson]

On my Doral with twins/alpha's I have very little trim to use, as it will also ventilate. I can usually only bump the trim buttons once.

 

[src]

SRC, don't have a Bravo III but that is also what Capt Chad from the marina where I bought my boat said. He told me there is very little room to use the power trim on the 290s. Don't know why that would be.

My guess, based on the differences between my 175 and my 310, is that there just isn't enough mechanical advantage available on a larger boat for the drive angle to really affect the attitude of the boat.

On my 175, if I adjust the drive trim I can make fairly drastic changes to how much bow rise it has. There's enough of a moment arm on drive vs. the shorter hull for the drive's angle to push the nose up or down.

On the 310, you just can't get enough leverage back there to push the nose more than a degree or so - that's what the trim tabs do by adding lift (or drag, if you prefer) to push the back end up and pull the nose down.

 

[Marlie]

Sounds like a good explanation. Will go for the trim tabs next time I am in the water.