Sterndrive ratio causing low speed/low rpm?

[Andler]

Good Afternoon!

I bought a 1996 Maxum 2100 SR a couple months ago for my first boat.

I took my wife, 8yo son and 3yo daughter for the first ride/shakedown with a bunch of friends from our campground to make sure all is well. Well, it floats and runs, so that's all good lol

Only issue I'm having is it seems to be a little down on power/speed. Based on other maxum owners, they're seeing 50+ at 4600 rpms with a 15x19. Right now, my top speed is 40 at 4200 rpms. We used a few phone gps apps to gauge accuracy across apps.

I look a little deeper into the prop, it's a quicksilver 16x19, but the sterndrive is showing 1.79 or 1.78 gearing. I've seen quite a few people say that gearing is more for a v6, so I'm wondering if that could be why I'm not seeing the same speed as others.

[Phillbo]

What motor do you have?

[donald]

How many bodies did you have on board?
More bodies the lower the speed.
Don

[Andler]

I have the 5.7 with myself, my wife and my 3 year old and 8 year old. Full tank of gas.

[Phillbo]

Merc?

If so, you should also see 4600-4800rpm. You may be over propped.

[mmwjr]

At 4600 rpm the engine is right in its sweet spot. Are you sure the tach is correct? You can get a phototach from an auto store to verify. BTY an engine is not ment to run at WOT for long periods of time.

[Andler]

Yet it’s a mercruiser. I don’t expect to be running at top speed 100% of the time, it just didn’t seem to get on plane quickly and seemed to be slow at the top end.

[MoonRiver]

Sometimes moving the weight (passengers) around and playing with the trim will help achieve top speed and optimum performance.

Do you have trim tabs on that boat?

[mmwjr]

Is the prop in good shape? Do you know the health of the engine, compression good?

[jrsick]

+1 on comments made so far.
You are over-propped. 16x19 is a huge prop. You will see better performance with a 15x19 or even 15x17.
My guess, and only a guess, is that your boat came with a 1.47 drive. Along the line it was replaced with a 1.78, and a larger prop was added to compensate for the increased gear reduction.
Nothing to be concerned about though, you will have a nice performing boat with the right prop. The 5.7 is a monster engine.

[Andler]

Haven’t checked compression, but it’s on the list of things to check, along with throttle cable.

No trim tabs, but I’m about to pull the trigger on the Bennett tabs with the trim indicator. Those were planned if I got a boat without them. Kids sit in the front and me and my wife sit in the middle. No extra luggage in the back other than a tank of gas.