Top speed only 28mph...Is this right?

[imported_Captain Morgan]

I recently bought an 88 Wellcraft Classic 17' open bow ski boat with a Mercruiser 3.0L engine. It doesn't register over 28 mph on the speedometer with 3 200lb. guys onboard. is this normal or do I have a problem?

 

[QC]

Re: Top speed only 28mph...Is this right?

Seems slow to me, I would guess at least 35 and maybe 40+ MPH from that package. 3 - 200 pounders is a pretty good load though . . .

First, you need to verify the speed number with a GPS. Boat speedos are notoriously inaccurate.

Second, you need to post your wide open throttle RPM which should also be from an accurate tach and be with an average load and trimmed to reach the max possible speed. This will determine if it is propped properly.

Third, there may in fact be something wrong with the engine and/or drive and/or hull that are limiting your speed. Ya know stuff like a tune up, good drive maintenance and a clean bottom can make a difference.

Fourth, your boat may be waterlogged and could be heavier than she should be. That will also have a dramatic impact on top speed. Good luck and welcome to iboats!!

 

[Boatist]

Re: Top speed only 28mph...Is this right?

All I can tell you is my 3.0L OMC on a 21 foot Aluminum V hull weighs 2800 pounds dry and with 4 people on board it reaches 38 MPH on the speedo and GPS.

More weight or a deeper V will reduce the speed. Wrong prop or marine growth will reduce the speed.

Engine down on power will reduce the speed.

Tell us the weight of your boat the WOT RPMS and number of blades, Prop Diameter, and prop pitch.

I would do a compresion check first and look at the plugs.

 

[cobra 3.0]

Re: Top speed only 28mph...Is this right?

It could be a tad slow, but that needs to be verified with a GPS as mentionned earlier. Also, as asked above, knowing your prop's pitch and your top rpm would certainly help.

My 16 foot 3.0 OMC Cobra isn't much faster as it tops off at about 34 mph with two people on board at about 4600 rpm and a 17" pitch prop, but it doesn't have a stepped hull design like the newer models often do, the motor is probably a little tired (lower compression), and the foam is probably waterlogged because I had some soft spots in the floor(extra weight).

With a 19" pitch prop it gains about 2 mph at about 4200 rpm. A 21" pitch could maybe fair better, but I suspect the rpm's will be too low and out of the specified operating rpm range.

However, it will pull up two adult skiers with ease. When tubing, it'll throw around a three person tube and get lot's of air off a wake for a really wild ride. So, I live with it's limits for now as it hasn't cramped my style at all.

 

[Bondo]

Re: Top speed only 28mph...Is this right?

What are the RPMs at that speed,..??...

 

[bomar76]

Re: Top speed only 28mph...Is this right?

I am more worried as to why you would have 3 200 lbs GUYS on a boat .... need to swap out the guys for gals....

 

[Bondo]

Re: Top speed only 28mph...Is this right?

Ayuh,........ It's a Fishing Thing Bomar............

 

[imported_Captain Morgan]

Re: Top speed only 28mph...Is this right?

Thanks for the replies. I don't have a gps. I did buy a new pitot tube speedometer sensor. Maybe that will make a difference. I don't trust the RPM gauge since it was reading 3000rpm at near idle. After we got out on the water, it seemed to "unstick" and read a realistic figure, but I don't remember what it was. I'll have to take it out and gather some more information such as prop size, rpm, load, etc. Thanks again so far. I'll be back with more questions I'm sure.

 

[calwldlif]

Re: Top speed only 28mph...Is this right?

:=

 

[Don S]

Re: Top speed only 28mph...Is this right?

:=

My thoughts exactly.

 

[imported_Captain Morgan]

Re: Top speed only 28mph...Is this right?

Looks like I won't be able to get it on the water this weekend, but I did get a little more info if this helps. The prop is a 3 blade with a 13.5 inch diameter. The motor says it's wot rpm is 4200-4600. The rpm gauge seemed to not be accurate during our test drive. Would replacing the gauge correct the problem or is there more to it than that?

 

[cobra 3.0]

Re: Top speed only 28mph...Is this right?

Without the accurate info requested, the answer is "who knows?"

If you can borrow a GPS and an rpm gauge from a mechanic/shop and find the pitch of the prop, then get accurate readings from your boat, we can take you a step further in your puzzle.

So is it just your gauges? Maybe and maybe not.