Any outboard or prop gurus?

[RangerNation81]

Ok guys here's the scoop.. I've got a 2007 ranger 620 with a 225 ETEC HO.. I'm running a 14.5 x 22 raker II for a prop... My issue is I'm only getting roughly 5000rpm and 53mph GPS. I've been reading that I should be hitting 5800rpms and close to 60 for a top end. The motor is firing on all 6 cylinders. There are some nice dings on the prop but not sure If that's the issue or not! Any ideas or suggestions? Thanks in advance guys

 

[SDMF]

Dings induce cavitation, reducing lift and efficiency. Very crudely, dinging your prop is akin to cutting off your lever or moving the fulcrum closer to you thereby shortening it's mechanical advantage.

It'd not be unprecedented for a boat to lose 2-5MPH from virgin prop to just a little chewing due to power loading on a gravel ramp. Honest to goodness "dings" can cost you more.

 

[RangerNation81]

Dings induce cavitation, reducing lift and efficiency. Very crudely, dinging your prop is akin to cutting off your lever or moving the fulcrum closer to you thereby shortening it's mechanical advantage.

It'd not be unprecedented for a boat to lose 2-5MPH from virgin prop to just a little chewing due to power loading on a gravel ramp. Honest to goodness "dings" can cost you more.

lol speak English buddy I'm just an oil field hand!! So what i gathered is I could be losing top end speed and Rpms due to a dinged up prop?

 

[Davey Crockett]

Have you checked your throttle linkage to make sure your getting WOT ? Also will a 4 blade prop have more drag from friction than a 3 blade ? My Sea Ray is a mutt , Its I/O merc with a v-8 chev and with 3 or 4 in the boat and full fuel/water tanks it has a hard time getting up on plane. I have a 4 blade prop I could put on it but logic seems like it would have more drag ?? I'm thinking I should start shopping for a SS prop.


Update- From my experience a dinged up prop will gain RPM and lose top end because it doesn't "hook up" as good.

 

[SDMF]

Maybe this is a better analogy. Your dinged prop is like a wrinkled up car trying to keep up with the draft @ Daytona. Wrinkles whether it's your prop or the stock car, prevent the water/air from flowing smoothly over it. Think about how much harder those wrinkles are to push through the water/air. Knife edge vs. spoon edge.

The prop obviously is what pushes the boat through the water and the hull does provide some of it's own lift, but, the prop lifts the hull as well, especially as you're approaching WOT and don't have much boat left in the water anyways.

Your numbers pencil out pretty well. Your lower unit is 1.86 so: 1.86 x 5000 =2688 prop RPM x22"/rev (prop pitch) = 59136"/min. 59136/12= 4928'/min. 4928/5280' per mi=.93. 60MPH x .93=56MPHx10% slip =50.4MPH

Using the same formula, that same prop running 5800RPM should net you ~61MPH.

- - - Updated - - -

Have you checked your throttle linkage to make sure your getting WOT ? Also will a 4 blade prop have more drag from friction than a 3 blade ? My Sea Ray is a mutt , Its I/O merc with a v-8 chev and with 3 or 4 in the boat and full fuel/water tanks it has a hard time getting up on plane. I have a 4 blade prop I could put on it but logic seems like it would have more drag ?? I'm thinking I should start shopping for a SS prop.


Update- From my experience a dinged up prop will gain RPM and lose top end because it doesn't "hook up" as good.

Yes, a 4 blade prop has more drag as well as robs HP via extra weight. However, a 4 blade MIGHT also have more lift than a 3 blade as well as having greater "traction" due to the extra blade. It might plane out faster, it might allow the boat to carry plane at a lower speed and it might create more bow lift. More bow lift = more boat outta the water = maybe faster/smoother. An extra blade on the prop might be a worthwhile trade if you get enough extra boat outta the water. Bolting it on is the only way to compare.

 

[Davey Crockett]

SDMF s analogy sounds better than mine , Mine was on an older merc that wasn't much of a hot rod so I "sharpened " it back up with a file. It spun fast but would cavitate at WOT.

 

[RangerNation81]

So any ideas as to where I'm losing 800rpms from? I'm not real knowledgeable as far as outboard motor trouble shooting! I'm considering having brainerd props send me a demo raker II prop to see if that isn't my issue!

 

[SDMF]

SDMF s analogy sounds better than mine , Mine was on an older merc that wasn't much of a hot rod so I "sharpened " it back up with a file. It spun fast but would cavitate at WOT.

Props aren't just about the "edges". The leading edge takes a scoop, the blade face "pushes" and speeds up the water that rides the face and heads for the trailing edge, and assuming cupped, the trailing edge holds the "speeded up" water for all it's worth creating the lift.

GROSSLY oversimplified. A prop engineer would give me the eternal face-palm for the above explanation.

 

[RangerNation81]

 

[SDMF]

So any ideas as to where I'm losing 800rpms from?

You're pushing a dull edge instead of a sharp edge through the water. Fill your sink at home. Push a spoon through the water, then a knife.

You're dinged up leading edges are slowing down the whole works because the motor has to work harder to push them through the water. Then the flow and volume of water over the blade face is being disturbed by air bubbles and turbulence created by the "dings", Lastly, that turbulence and air is costing you lift, and, if you're trailing edges are dinged as well that also costs you lift and again increases resistance.

 

[shorthairsrus]

Ranger go to etec owners group they will help u out. I have a 150. I raised my engine all the way up and now it hits 5500 with it trimmed out and full load. The prop guy up in brainerd ricky can probably adjust the dings on the prop plus if your height is right he can adjust the prop so u get the rpms

 

[riverfisher]

this might be obvious but have you tried adjusting your trim and trimming up

 

[SDMF]

The above data is for a 250HP, not a 225.

 

[NodakBuckeye]

Riverfisher asked what I was a gonna ask....

 

[Zogman]

Ranger go to etec owners group they will help u out. I have a 150. I raised my engine all the way up and now it hits 5500 with it trimmed out and full load. The prop guy up in brainerd ricky can probably adjust the dings on the prop plus if your height is right he can adjust the prop so u get the rpms

I have dealt with Ricky the "prop guy" in Brainard. He is extremely knowledgeable. Also SDMF gave you great info.

 

[Crankn]

SDMF where did you get that chart do they have one for a 620 and a 250 Yamaha four stroke?

 

[SDMF]

SDMF where did you get that chart do they have one for a 620 and a 250 Yamaha four stroke?

I didn't post that, Rangernation81 did and it's from the E-Tec webpage.

That said, direct from the Yamaha Marine Owner Resources section of their webpage a 620/F250 spec sheet is available:

http://yamahaoutboards.com/sites/de...letin_4stroke_hpv6_vmax_rng-620vs-f250txr.pdf

 

[Fishmission]

So any ideas as to where I'm losing 800rpms from? I'm not real knowledgeable as far as outboard motor trouble shooting! I'm considering having brainerd props send me a demo raker II prop to see if that isn't my issue!

A call to Ricky at Brainerd props will more than likely fix your problem. He knows Rangers and he will guide you in the right direction. Might even suggest a different prop

 

[RangerNation81]

The above data is for a 250HP, not a 225.

The data in the review is a 2008 620 with a 225

 

[SDMF]

The data in the review is a 2008 620 with a 225

Oops!! I was reading max HP for the boat, not what was actually bolted to it. That doesn't change any of my ideas though. Now, if you're not trimming when running and have the motor pinned to the transom as NodakBuckeye and Riverfisher asked about, then none of what I said is going to make any difference.