Too Slow?

[Swivelhart]

Just took my 1966 Larson All American 16ft out on the lake for first time. Runs great and purrs like a kitten. It has an OMC 120hp 4cylinder inboard outboard and when up on plane it doesnt seem that fast. It doesnt miss or bog or anything just doesnt seem fast. My guess is its doing about 25mph. It's hard to tell though because it has an RPM guage but no speedo. It redlines at 4500 but I only brought it up to 3500 to be easy on it. Should this boat be fast or what? The outdrive has new electric coils in it and seems to shift perffect. Any thoughts?

 

[steelespike]

Re: Too Slow?

Thats a nice old timer.
Just guessing but at 3500 it wouldn't likely seem fast.3500 is cruising speed some boats won't stay on plane at 3500.I would say in good health at max rpm it would approach 40.Not fast by todays standards but typical of the setup.
On the water with the top down would seem fast.
Maybe you can borrow a gps or take a friend with one for a ride.

 

[Bifflefan]

Re: Too Slow?

I agree with all stated above.
What is the prop pitch?
17 to 19 Should be about right i would think. 120 is not a ton of power so the 17 may be a good choice, depending what is on it now.
Without a good GPS speed tho you can guess all day long. Even a car gps or a phone with GPS mph on it will do fine.
3500 to 4500 is also a good difference in speed.
But to me it sounds like you are right on the money with what you have.
You know the old saying, "if you want a faster boat, Buy a faster boat."

 

[Swivelhart]

Re: Too Slow?

I appreciate the feedback. So is the redline on the rpm guage a true warning area? I mean can I bring it up to say 4300 rpms even though the little red line starts at 4500? Maybe it's different than a car. In a car if I had it at the beginning of the redline I would be expecting something to go wrong. Am I correct? Just want to be safe. I have no idea what pitch prop is on there.

 

[steelespike]

Re: Too Slow?

That motor in a car would probably redlined at 5,000 or more because it is usually only a momentary peak just before you or it shifts.In a boat yopu might run at thje red line for any length of time routinely,
thus the lower limit.If a person were to run a boat routinely at the redline
repairs/rebuilds would be more frequent. If a motor was weakoned with age/wear it would be more likely to fail near the redline than cruising speed.
That said I had a boat that was 70 yeares old and had never been rebuilt
I would run it full throttle 3,200 regulartly but for probably a minute or two at most.

 

[Swivelhart]

Re: Too Slow?

That makes sense. I'll bring up the rpms next time on the water being carefull not to push it. Is there stamp somewhere on the prop that indicates what pitch it is. If not how in the world do I figure out which one I have. As far as a prop is concerned I would imagine a prop designed for greater speed would add aditional stress on the sterndrive correct? Is the extra stress insignificant?