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re: Any boat propeller experts on here? [update #3 Pg4]
Posted on 4/27/17 at 10:55 am to DeoreDX
Posted on 4/27/17 at 10:55 am to DeoreDX
An easy check is whether or not the cavitation plate is above the water line. If it is, you probably got a short shaft engine on a boat that needs a long shaft, or something along those lines. Got a slime line on it from yesterday you can check?
0
Posted on 4/27/17 at 11:00 am to DeoreDX
quote:
Going to suck to have to drive all the way out to the lake house, grab the trailer, drive out to the launch, pull the boat out, then drive all the way out to the dealer. Reason to buy a new one was to put the boat in the water and just ride it and not ever have to pull it out. Guess that ain't happening.
You need to rip the guy a new one.....maybe get some free shite like extended, free service or something out of this.
Posted on 4/27/17 at 11:54 am to DeoreDX
4 blade brah
Posted on 4/27/17 at 12:15 pm to Wtodd
I'd give them a chance to make it right, but if they didn't immediately start making it right I'd go postal.
Posted on 4/27/17 at 12:22 pm to DownshiftAndFloorIt
quote:
I'd give them a chance to make it right, but if they didn't immediately start making it right I'd go postal
I get being a nice guy but sometimes you need to let them know who the boss is. Get some extended warranty at minimum.
Posted on 4/27/17 at 12:33 pm to Wtodd
I would have had them come pick it up and bring it back fixed.
Of course if OP is just operating the boat incorrectly, the dealership doesn't really owe him anything.
Of course if OP is just operating the boat incorrectly, the dealership doesn't really owe him anything.
Posted on 4/27/17 at 2:46 pm to DownshiftAndFloorIt
If I had to guess they somehow put the wrong prop on there and its way too small, that would make the most sense. I don't think pontoons use long shafts so they wouldn't have put a short shaft on by accident?
Spun hub doesn't make sense unless it was a manufacturers defect.
How fast did the boat get up to OP?
As said, take notes when you take the boat out. Better yet, take pictures with your phone of the different RPM levels, trim levels, and the speed. This should help them out tremendously.
You also should run it around a little if that was only your first day, you could easily find an "im a dumbass" mistake that you forgot about being the first time you used it.
Spun hub doesn't make sense unless it was a manufacturers defect.
How fast did the boat get up to OP?
As said, take notes when you take the boat out. Better yet, take pictures with your phone of the different RPM levels, trim levels, and the speed. This should help them out tremendously.
You also should run it around a little if that was only your first day, you could easily find an "im a dumbass" mistake that you forgot about being the first time you used it.
Posted on 4/28/17 at 4:57 am to DeoreDX
I don't have all the facts for your situation to properly troubleshoot. 60% throttle at 5,500 rpm! During launch? During cruise? ?? At first glance, yes - you are significantly under-propped. Still, I'm a retired engineer & past 60 MPH+ bass boats' person with prop experience. I will add my 2 cents.
1. Prop (specifically, anti cavitation plate) must be totally below water level during and slightly after "launch or takeoff". If not, your stock engine will over-rev and SD to protect itself (like revving in air). See DownshiftAndFloorit post. Verify that plate & prop are well below water at rest. If not, address this issue.
2. If you checked off on #1 above, you are then significantly under-propped (by at least 2" pitch, IMO). Black painted per you means you have a black painted aluminum prop, not SS regular cupped or cleaver type prop (regardless if 3 or 4 blade). Aluminum props are relatively cheap to obtain. I am like others and more or less dismiss hub slippage as your problem (I may be wrong). Regardless, get a similar (3 blade per your posts) prop 2" to 3" higher pitch to fit your motor/lower unit and put this prop on. Pitch of your existing prop should be pretty prominently engraved on hub of your existing black painted aluminum prop. Purchase new size accordingly. Cost of new prop is pretty insignificant (IMO) compared to overall cost of your rig. I mean, you are not trying to buy a $500+ SS prop or props. Run your boat. RPMs now? Should be in range of 5,000 to 5,500 rpm (5,500 - 6,000 rpm max.).
If you could get propped to put your engine rpm in the (non cutout) range, you could actually calculate pretty much the pitch of your new required prop to achieve about 5,500 or so max. rpm. Would be simply a ratio of (actual experienced engine rpm/desired engine rpm x the " pitch of existing prop).
For example, if your existing prop is 21" and your max. speed is 6,800 rpm: get a 5,500 rpm/6,800 rpm x 21" = about a 17" pitch prop (in your case 3 blade aluminum prop).
Edited next day. I am so sorry to OP if I misled with the example in the above paragraph. Why did anyone not correct me? I got (only) above paragraph bass ackwards. The paragraph above beginning "If you could..." is totally correct.
My actual recommendation should read: "For example, if your existing prop is only 17" pitch (and over revving): get a 6,800 rpm/5500 rpm x 17" pitch prop = about a 21" pitch prop. Higher pitch new choice actually slows down (bogs down) the engine rpm. Understanding this is important. Again, sorry to wrongly mislead. I feel so bad about this wrong example. Not trying to "bump" this thread.
Hope I helped.
1. Prop (specifically, anti cavitation plate) must be totally below water level during and slightly after "launch or takeoff". If not, your stock engine will over-rev and SD to protect itself (like revving in air). See DownshiftAndFloorit post. Verify that plate & prop are well below water at rest. If not, address this issue.
2. If you checked off on #1 above, you are then significantly under-propped (by at least 2" pitch, IMO). Black painted per you means you have a black painted aluminum prop, not SS regular cupped or cleaver type prop (regardless if 3 or 4 blade). Aluminum props are relatively cheap to obtain. I am like others and more or less dismiss hub slippage as your problem (I may be wrong). Regardless, get a similar (3 blade per your posts) prop 2" to 3" higher pitch to fit your motor/lower unit and put this prop on. Pitch of your existing prop should be pretty prominently engraved on hub of your existing black painted aluminum prop. Purchase new size accordingly. Cost of new prop is pretty insignificant (IMO) compared to overall cost of your rig. I mean, you are not trying to buy a $500+ SS prop or props. Run your boat. RPMs now? Should be in range of 5,000 to 5,500 rpm (5,500 - 6,000 rpm max.).
If you could get propped to put your engine rpm in the (non cutout) range, you could actually calculate pretty much the pitch of your new required prop to achieve about 5,500 or so max. rpm. Would be simply a ratio of (actual experienced engine rpm/desired engine rpm x the " pitch of existing prop).
For example, if your existing prop is 21" and your max. speed is 6,800 rpm: get a 5,500 rpm/6,800 rpm x 21" = about a 17" pitch prop (in your case 3 blade aluminum prop).
Edited next day. I am so sorry to OP if I misled with the example in the above paragraph. Why did anyone not correct me? I got (only) above paragraph bass ackwards. The paragraph above beginning "If you could..." is totally correct.
My actual recommendation should read: "For example, if your existing prop is only 17" pitch (and over revving): get a 6,800 rpm/5500 rpm x 17" pitch prop = about a 21" pitch prop. Higher pitch new choice actually slows down (bogs down) the engine rpm. Understanding this is important. Again, sorry to wrongly mislead. I feel so bad about this wrong example. Not trying to "bump" this thread.
Hope I helped.
This post was edited on 4/29/17 at 3:03 am
Posted on 5/3/17 at 3:16 pm to DeoreDX
Pulled her out of the water today to take back to the dealer. I didn't get a chance to drive it at speed as I was was in charge of pulling the trailer. Trim all the way down doesn't help any. Did snap this picture as it was moving slowly from the slough.
Propeller with respect to the transom. You can make ou tthe scum line as it sits in the water empty. Less than two hours on it, is it normal to have that much paint worn off the prop already?
I did do the Mercury Prop selector from their web page. They suggest a 16" diameter prop with 12-14 pitch in the "Black Max" aluminum propeller family.
Running these numbers on the internet and it says I have a Black Max aluminum 14" Dia x 13P propeller.
Propeller with respect to the transom. You can make ou tthe scum line as it sits in the water empty. Less than two hours on it, is it normal to have that much paint worn off the prop already?
I did do the Mercury Prop selector from their web page. They suggest a 16" diameter prop with 12-14 pitch in the "Black Max" aluminum propeller family.
Running these numbers on the internet and it says I have a Black Max aluminum 14" Dia x 13P propeller.
Posted on 5/3/17 at 3:42 pm to DeoreDX
Sounds like a trim issue. Leave it down most of the time. I mean all the way down. Only trim up as needed for speed or otherwise.
Posted on 5/3/17 at 3:53 pm to AlxTgr
quote:
Sounds like a trim issue. Leave it down most of the time. I mean all the way down. Only trim up as needed for speed or otherwise.
Trimmed all the way down and it made zero difference. ETA the trim is up in this picture as the FiL was raising the motor at the time I snapped the picture.
This post was edited on 5/3/17 at 3:54 pm
Posted on 5/3/17 at 3:54 pm to DeoreDX
quote:Dang.
Sounds like a trim issue. Leave it down most of the time. I mean all the way down. Only trim up as needed for speed or otherwise.
Trimmed all the way down and it made zero difference.
Posted on 5/3/17 at 3:57 pm to Wtodd
quote:Terrible advice. Always best to try to settle amicably, first. Also, getting what he paid for, definitely; getting something extra should not be expected.
You need to rip the guy a new one.....maybe get some free shite like extended, free service or something out of this.
quote:lol. THEY hold the cards. They can turn a nice investment into a nightmare. Not to mention the fact that he could very likely need them down the road.
I get being a nice guy but sometimes you need to let them know who the boss is. Get some extended warranty at minimum.
Posted on 5/3/17 at 4:06 pm to DeoreDX
your motor height doesn't look too off.
with a 13P prop, and 2.38:1 ratio, you're only going to see about 21mph at 5k rpm, and 25mph at 6k rpm. i'm assuming 20% slip because:
1) aluminum props generally suck
2) 3-blade, which won't carry the load of a pontoon like a 4-blade
3) no cup
don't know what you're expecting top end to be. what is the fastest you've ever gotten it up to?
i'd go to propgods.com and find ken's email and ask him about this.
with a 13P prop, and 2.38:1 ratio, you're only going to see about 21mph at 5k rpm, and 25mph at 6k rpm. i'm assuming 20% slip because:
1) aluminum props generally suck
2) 3-blade, which won't carry the load of a pontoon like a 4-blade
3) no cup
don't know what you're expecting top end to be. what is the fastest you've ever gotten it up to?
i'd go to propgods.com and find ken's email and ask him about this.
Posted on 5/3/17 at 4:38 pm to G2160
quote:
don't know what you're expecting top end to be. what is the fastest you've ever gotten it up to?
Maybe 17-18mph. I'm not worried about top end as much as being able to give it full throttle without the prop losing it's bite and getting thrown forward like I shut the engine off.
Posted on 5/3/17 at 4:42 pm to DeoreDX
Knowing your top end and rpm is the first step to knowing whether you're propped right.
You're at about 42% slip if your prop is secured to the prop shaft. Probably want to be somewhere around 20%(?) with that boat. More efficient hulls are around 10%.
You're at about 42% slip if your prop is secured to the prop shaft. Probably want to be somewhere around 20%(?) with that boat. More efficient hulls are around 10%.
This post was edited on 5/3/17 at 4:46 pm
Posted on 5/3/17 at 5:22 pm to DeoreDX
quote:
I did do the Mercury Prop selector from their web page. They suggest a 16" diameter prop with 12-14 pitch in the "Black Max" aluminum propeller family.
quote:
Running these numbers on the internet and it says I have a Black Max aluminum 14" Dia x 13P propeller.
Seems you found your problem. The hub diameter of that prop is too small. I would guess you are getting exhaust ventilation coming around the prop instead of through it. They make ventilation rings for that issue. I don't know much about Merc 90s but generally speaking you want the prop and lower unit to be near the same size like in this picture.
Posted on 5/3/17 at 5:38 pm to DeoreDX
Sounds like you're just way under wheeled. What's the dealer got to say about it? You should not be cavitating with the motor trimmed down at that height especially at 18ish mph, unless it's cavitating from being spun too fast, which is very possible and would explain all the paint being gone off the trailing edge of the blades.
I'd think the dealer would make right on this if it's the case. Mercury knows how much power you need to turn that wheel and the boat manufacturer knows how much power the hull needs to make speed. It's pretty straight forward for them to select the right wheel. Give them a call and let them know that according to mercury's calculator you're wayyyyy underwheeled, and you'd just like to try a different one.
I'd think the dealer would make right on this if it's the case. Mercury knows how much power you need to turn that wheel and the boat manufacturer knows how much power the hull needs to make speed. It's pretty straight forward for them to select the right wheel. Give them a call and let them know that according to mercury's calculator you're wayyyyy underwheeled, and you'd just like to try a different one.
Posted on 5/3/17 at 5:41 pm to TheLSUriot
You're right about that part. Look closely at the picture he took of the part number on the hub. The hub is 1/4" smaller than the cone.
Posted on 5/3/17 at 5:41 pm to TheLSUriot
Lsuriot is right. You need a cavitation ring. Look up Mark Croxton on the Google and he should be able to get you one.
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