speed question

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Re: speed question

Postby iammarcuse » Sat Jul 25, 2015 8:50 am

Don't worry about your tach setting. It would be reading high not low. What you need to figure out is GPS speed relative to rpm. GPS speed at 3000 rpm, speed at 3500, speed at 40000, speed at wot. Then we can tell you what is going on. Everything else is just guessing.
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Re: speed question

Postby UT.EAR.DOC » Sun Jul 26, 2015 9:30 pm

Ok Friends,
I checked the speed with a GPS and I hit 38 mph at full throttle and 4200 rpms. I checked the setting on the tach and the black arrow is pointed to the 8c setting. If this is the normal operation for the boat that is fine, we love it. It just seems based on this site that the boat is under speed and it also guzzles gas. Thanks again for all the insight, I have learned quite a bit about the boat from this!
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Re: speed question

Postby iammarcuse » Sun Jul 26, 2015 10:57 pm

Glad you are loving the boat and keep enjoying it while you sort things out. But something is not quite right. You are looking at 32% slip instead of more like 12%. http://www.go-fast.com/Prop_Slip_Calculator.htm Which is about 10 mph slower than you should be running (and the commensurate poor fuel economy that reflects that as well).
The logical suspect at this point would be a bad prop... unless you are dragging your anchor lol Before I did another thing I would start by trying any 21p prop you can borrow and see if that makes a difference.
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Re: speed question

Postby UT.EAR.DOC » Mon Jul 27, 2015 7:18 am

Sounds like a new prop is worth a try. Two quick questions: 1--do I just get any 21p prop? 2--is this something pretty easy to change myself or should a professional install this?
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Re: speed question

Postby iammarcuse » Mon Jul 27, 2015 9:47 am

You said you had 3 props. Try the other two. Simple to change. Look it up on Youtube.
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Re: speed question

Postby UT.EAR.DOC » Mon Jul 27, 2015 10:08 am

Yeah I meant 3 blades, still learning the lingo and showing my ignorance!
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Re: speed question

Postby iammarcuse » Mon Jul 27, 2015 10:34 am

Try before you buy!
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Re: speed question

Postby UT.EAR.DOC » Mon Jul 27, 2015 11:30 am

Yes, for sure. Another thought, I put the boat in the water in late April and take it out after Labor Day. So, the boat has some "slime" on it by this time of the season. I suspect this could slow her down some as well but could it cause that big of a speed drop? Maybe I should pull the boat out and clean the slime every month or so.
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Re: speed question

Postby iammarcuse » Mon Jul 27, 2015 2:50 pm

Yup and it will run slower in heat and humidity as well
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Re: speed question

Postby foyboy062 » Wed Jul 29, 2015 4:47 pm

Lots of good thoughts but nobody has mentioned the trim, with the outdrive all the way down you will loose a great deal of speed, pull that drive up about 25% on the gauge and hang on! You'll know if you go to far !
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Re: speed question

Postby UT.EAR.DOC » Wed Aug 05, 2015 9:32 am

UPDATE: I pulled the boat out and cleaned off the "slime" and gave her a good shining. Put her back in the water and hit 41 mph (GPS) at 4200 rpm at full throttle and trimmed up to maximize the speed. I also inspected the prop and it looks good but is seriously coated in grime. The pressure washer knocked some off where I could see "shiny prop" but not much. Thanks!
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Re: speed question

Postby buyfire » Wed Aug 05, 2015 10:34 am

Any little bit of buildup on the prop will greatly increase slip and decrease top end/fuel efficiency. Pick up a $10 prop tool, take that puppy off, and give it a thorough cleaning. You'll probably make up that $10 in your first few outings. If it's stainless steel, it should shine!
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Re: speed question

Postby UT.EAR.DOC » Wed Aug 05, 2015 10:57 am

Thanks, will do that soon. What suggestions do you all have for cleaning a prop? Do you use any specific cleaner, soak it, etc? Never done this before and learning so much through this forum.
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Re: speed question

Postby UT.EAR.DOC » Wed Aug 05, 2015 5:37 pm

Buyfire, is there a specific wrench or are these sort of generic, one size fits all types of tools?
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Re: speed question

Postby buyfire » Thu Aug 06, 2015 10:34 am

I'd ask the folks at the marine dealer what to use on the prop, they should have some recommendations. I never left my boat in the water & never had the buildup problem. The prop wrench should be a standard size. I believe both Merc and Volvo drives use the same size.
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