How fast should my boat go?

[jamerson62]

I have a 16 foot Four Winns Freedom 160, mercruise 3.0l with the Alpha 1 drive, and a 19 pitch three blade prop. My engine RPM's at WOT at 4600 and I only got about 33MPH with just myself, less then half a tank of fuel, and no gear. Is this right or should I be getting more out of it? I also run with the engine trimmed up to the max performance (any lower and I plow, any higher and I over rev.) Thank is advance.

 

[ezmobee]

Re: How fast should my boat go?

You should be able to hit 40MPH with that rig. Agree that you may be waterlogged.

 

[QC]

Re: How fast should my boat go?

How old is this rig? How you getting your speed number? GPS?

 

[45Auto]

Re: How fast should my boat go?

4600 RPM on a 19" pitch prop with zero slip would give you 41 MPH. A realistic slip of 10% would give you 37 MPH.

Only thing you could do for a noticeable increase in speed would be to increase your prop pitch and hope that your engine's power band delivers more power at a slightly lower RPM than it does at 4600 RPM.

On the other hand, if it is delivering max power at 4600 RPM, you just wasted several hundred dollars on a prop ......

 

[zagger]

Re: How fast should my boat go?

At 1960 lbs.(boat/engine) 10% slip is pretty optimistic. I think he will be in the 25/35% slip and 33 to 36 is probably the top speed.

 

[QC]

Re: How fast should my boat go?

I think that was 45's point . . . 0% not gonna happen, so 36 - 37 may be all she will ever do

 

[ezmobee]

Re: How fast should my boat go?

I hope you guys mean that's all it should ever do, with THAT prop. Cuz a 3.0 in a little 16' should be easily hitting 40+ unless it's too heavy.

 

[steelespike]

Re: How fast should my boat go?

I think it should be over reving with a 19" prop. Should be running a 21 or 23".
Motor may need a major tune up with a compression check,be sure the throttle opens all the way,timing set right and advancing as it should.Bottom clean and smooth.No hydrofoil
fin on the outdrive.Does the boat respond well to up trim?Prop in excellent condition?

 

[QC]

Re: How fast should my boat go?

Yes, with that prop and 4600 RPM. If ss and ez are on to something then the engine is sucking . . . as is indicated by ss's post.

I just want accurate data to start, GPS speed, accurate tach, correct ratio and correct pitch (assumes good prop condition). With that we can determine if there is something wrong with the numbers prior to trying to nail down what may be right or wrong with the combination. I agree that it should be low 40s if all is right.

 

[Philster]

Re: How fast should my boat go?

No one has responded to the outdrive trim notes: 'Any higher and I over rev'

So, the OP gets more RPM by trimming out more to the point he over revs... but no speed is returned? Is this what we are saying? Maybe engine has the power but prop is losing bite when trimmed out. Thus, at the point it loses bite he doesn't get the last few MPH. Bigger prop worth a shot, or different type of prop....

 

[QC]

Re: How fast should my boat go?

Agree ^^^^^ but the point that a few of us are making is that he is close to maxed with the existing prop if the data is right. Personally I'd try shifting some weight aft to see if we can get the bow (trim) higher before she begins to blow out. 33 MPH is pretty slow to get a really high bow anyway though, but a little more positive trim may get him to the 36ish that we should see with reasonable slip

 

[Philster]

Re: How fast should my boat go?

More variables: Clean or dirty hull, prop material, prop maker/model, how speed is measured (GPS, GPS two-way run, etc)

 

[45Auto]

Re: How fast should my boat go?

I hope you guys mean that's all it should ever do, with THAT prop. Cuz a 3.0 in a little 16' should be easily hitting 40+ unless it's too heavy.

Brand new 3.0's top speed will barely break 40 in most brand new boats. Go to Boattest.com, take your pick of 16-20 foot bowriders with 3.0's.

Last year Four Winns made the Freedom 160 was what, 1990?

It's at least a 20 year old boat. Typical wear and tear on the engine and outdrive will probably easily knock 10% off it's top speed from brand new (what were the compression readings last time - if ever - that they were checked?). I doubt he'll see 40 MPH without putting more into the boat than it's worth.

If everything is in good shape, a fresh tune-up and optimizing the prop would possibly get him into the high 30's.

EDIT: Couldn't find any tests on a Freedom 160, but according to the Stingray Performance archives a brand new 1997 Four Winns Horizon 160 with a 3.0 had a top speed of 38.3 MPH.

 

[Scott Danforth]

Re: How fast should my boat go?

my 84 Avanti 17' with a 3.0 and stringer 400 spinning a 19p prop would get 40mph per the GPS. that was topped out at about 4500rpm.

so 30 mph indicates that you may be water logged, not trimmed right, or have a damaged prop.

 

[zagger]

Re: How fast should my boat go?

If your drive gear ratio is 1.65 and the speed, rpm and prop pitch are correct than your slip calculates to 34% which is pretty high but not unreasonable for 20 year old boat especially with an aluminum prop. That also assumes your engine is really putting out 130 prop HP. You would have to be well under 20% slip to get up to 40 mph. Your boat weights in at 1960# dry which makes it on the heavy side for a 16 but probably rides better than lighter hulls. Switching to a vented SS prop might lower your slip and up the speed. As others have mentioned waterlogged hull will have an affect on overall performance, if feasible weigh your boat to see if that may be the case.

 

[45Auto]

Re: How fast should my boat go?

If your drive gear ratio is 1.65 and the speed, rpm and prop pitch are correct than your slip calculates to 34%

If you use the 2.0 ratio that comes with a 4 cylinder, his slip works out to 20% at 33 MPH. New props, etc, might possibly gain him 2 or 3 MPH depending on what kind of shape his drivetrain and hull are in. Up to him to decide how much that's worth to him.

 

[jamerson62]

Re: How fast should my boat go?

Thank you everyone for the information and ideas. I bought this boat begining of July from an older family that bought it new in 1987. Well maintained, they had maintence logs dating back to the date of purchase. I have since done a carb re-build, replaced the belt, and did a tune up. The prop on it is aluminum with some minor flaws, and a hydrofin is already on the outdrive. As keeping with my wife and I's tradition my christmas present in October is a new prop. I'm going to a four blade SS 21 pitch. I will take the boat to the scales here this weekend and find out how much she weighs. Some of you were concerned about waterlogged foam, is there anyway to check the foam or doing anything about it? Or is just the misfortune of owning a 24 year old boat? Also the hull was completely re-done a neighbor and myself completely re-sanded, buffed, and waxed the hull. Any more ideas are greatly appreciated, I know it won't be the fastest on the lake but when I have to try to keep up with a 22 foot deck boat, with a 150 outboard.... I KNOW something isn't right.

 

[John_S]

Re: How fast should my boat go?

I'd go with an aluminum prop and use the savings on other "boat" stuff. SS is not going to buy you much performance in that boat.

 

[jamerson62]

Re: How fast should my boat go?

Ok smart call if it's not going to do me much good then I'll go with aluminum.

 

[H20Rat]

Re: How fast should my boat go?

and a hydrofin is already on the outdrive.
...

Any more ideas are greatly appreciated,

One suggestion right there... remove the fin and see how it does.