Elevation change on prop selection?
 

Hi,

I have an 04 SC21 with a Merc 4.3 and Alpha 1 1:81 that is running a 17P 4 blade at the moment. It came from CO and was running at around 4700' elevation. This set up worked fine for the PO (Motto on here) and ran low 40s at recommended rev ranges with a good hole shot. He had problems with the 17P 3 blade that came with the boat when he got it and the change to the 4 blade sorted that for him. He gave me both props but I expect to have to change them due to my lower elevation.

I will be using the boat at between 1200 and 1500' elevation in southern NV in a mix of river and lake. My question is what is a good starting point to jump to? A search seems to suggest that most here go with a 19P 3 or a 20P 4 on this engine set up but I don't know if that is the best for my elevation? Would a 19P 4 be a good start maybe or should i just go for the 20P 4 and not worry about the elevation? The 20 seems a big jump from the 17 with its known good performance only a couple of thousand feet higher up? Not looking for the flat out best top end but good mid range cruising and reasonable hole shot for tubing and so on.

Thanks

Ian


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Re: Elevation change on prop selection?
 

Need to run her when you get a chance and see what the WOT is at 1500ft.
Need 4400-4800 rpm for optimum running.
I would bet on the 20P 4 blade , but don't hold it to me.:yes_grin:
For what your after , no matter what I'd stay with a 4 blade prop. You only loose a couple mph compared to a 3 blade , with a lot better characteristics for play / cruise mode.

Re: Elevation change on prop selection?
 

I'm gonna go with the 19" - 4 blade and would suggest an aluminum Mercury Spitfire prop. The reason i'm suggesting the 19" is because that 4.3 is going to have to work a bit to push that 21' boat and i think the 20" might be just a bit much for it. I also suggest the Spitfire prop design cuz it is a bit on the aggressive side so it should help in the performance.

You might also want to consider installing a set of Smart Tabs!

Re: Elevation change on prop selection?
 

+1 on smart tabs!
If you end up buying from a local shop lots of them will let you try the prop so you can get it dialed in. I'm curious to see what she ends up running down there!

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Re: Elevation change on prop selection?
 

Thanks Guys. Smart Tabs are high on the list but I want to get a feel for the boat before I put them on so I can compare.

I am looking to stay with a 4 blade probably to get the low end and mid range, just wasn't sure if I should get a 19 or the recommended 20 to start with and see how it handled. Think I will go with the 19. I am sure I will need to dial it in a little and maybe play around with a couple of different props but it sounds like the 19 is a good starting point.

Will keep the 17s as I plan to go play in Lake Powel now and again and that's closer to the elevation Moto was running at.

Thx

Ian

Re: Elevation change on prop selection?
 

There are some pretty reasonable props out there. I think that Solas 4 blade was under the 150$ mark from the boat shop.
I bet the 19p 4 will get you around pretty good.

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Re: Elevation change on prop selection?
 

Thanks Moto. Will get one, see what it does and let you know.

Re: Elevation change on prop selection?
 

Just ordered a set of Smart Tabs. SX10512-70 are what they recommended. Lake was a bit rough and had a lot of porpoising the other day, we'll see if they calm it down a little.

Having some welding done to the lower unit at the moment after finding the sandbar right opposite the boat ramp that everybody but me apparently knew about and taking a chunk out of it.... :(

Will have a 19P 4 Solas on it when I get it back as well.

Re: Elevation change on prop selection?
 

Good to hear you have her out on the water! You'll love those tabs. As for the skeg... Its only aluminum. Its fixable!

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Re: Elevation change on prop selection?
 

Skeg wasn't the main issue it was the large chunk missing off the cavitation plate.... :eek_animated:

Was just moving out from the ramp towards the entrance to the lake with the drive fully down and hit a sandbar. No warning buoys or markers!! Lakes so low they have given up trying to mark them apparently. Picked up a rock or something and it took out a pretty big chunk of the plate and half the brand new anode... Skeg was just nicked a bit. :(

Found a local Mom and Pop prop shop and he's welding it up and putting on the new prop I wanted. Hoping to get it back tomorrow so I can go get it wet over the holiday weekend.

He agreed the 19P 4 was a good choice for the new elevation. I'll just get the solas for now whilst I am still 'mapping' sandbars.... :yes_grin:

Re: Elevation change on prop selection?
 

That kinda stuff happens! Its boating! We have logs that come down the river here. They suspend under the surface. I've heard they can take an outdrive clean off.
Glad you weren't injured!

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Re: Elevation change on prop selection?
 

Yup, just one of those things I guess. Was worried I would need a new lower unit but the prop shop guy said he could fix it, we'll see when I get it back.

Re: Elevation change on prop selection?
 

Ouch!:eek_animated:
Glad you are OK.

All I run is Solas Titan SS 4 blade props(19P , 17P , 15P).
I am very pleased with their performance and quality.:wink_thumbup:

Shoot us some pics of the repair when you get her back.

Re: Elevation change on prop selection?
 

Thanks guys. Was just embarrassing more than anything being right opposite the ramp.... Then annoying trying to get off it. At least it never touched the hull.

Will grab some after pics once its back together.

Re: Elevation change on prop selection?
 

Sh-- happens!
Anyone that says they haven't had their moment , or moments for some of us , is lying through their teeth.
Bet you learned a little something from it , huh.
Hopefully your on the water for the 4th! :wink_thumbup:

Re: Elevation change on prop selection?
 

Reminds me of a quote from a safety course. "There are two types of boaters, those who will admit they have run aground and those who wont".... :wink_thumbup:

I learned where the shallow spot is opposite my local ramp, I know that. :yes_grin:

Re: Elevation change on prop selection?
 

Topomaps and GPS only go so far!
Don't sweat it, it will be back on the water soon!

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Re: Elevation change on prop selection?
 

Looking at the photo I'm thinking the advantage of an aluminum prop may have been utilized here. They give when a SS won't. May have saved the prop shaft.

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Re: Elevation change on prop selection?
 

I think this is one of those situations where the OP should stick with an aluminum prop, particularly if there are sand bars, rock shelves and semi-floating objects where you boat. You will lose very little in performance using an aluminum vs a SS prop.

Re: Elevation change on prop selection?
 

Yep, i did it once. Hit a rock shelf that i knew was there alongside a route that i've taken the boat thru at least 100 times. Got distracted picking up some M&M's that i dropped and let the boat wander. Sure made a mess of the 90 hp Evinrude that was on my Stingray at the time. From now on i'll get the wife to pick them up for me..... :yes_grin:

Re: Elevation change on prop selection?
 

I think you guys may be right, and sticking with an aluminum for a while at least is a good idea. Planning to do quite a bit of exploring and cove hunting so probably not the last sandbar I will 'discover'. Lake Mead is really low right now and a lot of the stuff is not really shown on the maps at the moment as the 'low' lake levels on even the digital maps look to be higher than where it seems to be at the moment.

Better pic of the prop below. Looks like 1 of the blades dug out a rock or something with the tip and the next one got a good hit on it. That's probably what took the lump off the cavitation plate.

Look at my avatar. That's the cove where the ramp is. Pic is taken from the ramp just after backing off the trailer. The sandbar is directly in the background about 100yds or so to my starboard in that shot. right in the middle of the cove just about.

Re: Elevation change on prop selection?
 

Lower unit is done and back on the boat. Guy did a great job and the cost was pretty reasonable!!

Got a new 19P 4 blade on there now as well.

Now to take her out and get wet over the weekend... :wink_thumbup:

Re: Elevation change on prop selection?
 

Like new!!

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Re: Elevation change on prop selection?
 

Awesome! :wink_thumbup:
Glad you are ready for the weekend. Enjoy!

Re: Elevation change on prop selection?
 

Attachment 5607Now she's right where she should be ready to go for the weekend!!

Have a great holiday weekend guys.


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Re: Elevation change on prop selection?
 

I got a chance to open her up last night on calm(ish) water. She topped out around 42mph on the GPS but at only about 3100rpm. That seems way, way low to me? Was looking to get her in the 4400-4800 range but couldn't get her up there.

I am thinking I might try a 18P 4 and see what that does? Its a brand new tach.

Had her out every day over the holiday weekend but the lake was choppy so couldn't really open her up. Hole shot is about 2-3 seconds or so and she will hold plane down to just under 20mph. Cruising at 25-30 at between 2 and 2.5k revs she seemed quite happy and was using about 5gph.

This is without trim tabs yet.

Re: Elevation change on prop selection?
 

3100 does sound low. Im pretty sure that motor is suppose to be 4400-4800 like you said. Going down one pitch should gain you a few hundred RPM (around 200?).
How did you manage to figure your GPH?

Re: Elevation change on prop selection?
 

The speed is probably reasonably good for that boat/motor but the rpms are way low and i'm still convinced that the 19" 4 blade is the way to go with that boat. Something tells me your tach isn't reading or set correctly. Access the backside of that tach and you will find a small wheel marked '2-4-6-8'. Give the wheel a spin there Vanna and then re-set it to 6 Cyl. See if that helps.

Re: Elevation change on prop selection?
 

+1 What Mikey said.
If that boat is getting up in 2-3 seconds that is prob a great prop for it. I went from a 19 to a 21 Mirage on the Shabah 250 and it dogged out of the hole plus only did about 3800RPM down from the mid 4000s like it does with the 19p.

Something is not adding up there with the RPM, WOT speed, time out of the hole...

Re: Elevation change on prop selection?
 

Hi Motto, the new tach I got has an hour meter built in. I use an app to record costs, fill ups, expiry dates and stuff. Enter in the fill up amount and the hours and it calculates the GPH for you. I use that to keep a rough idea in my head of how much fuel I have used and to double check the fuel gauge.

I didn't fit the new tach. I bought it but had no time so I put the boat in to a service place to do a full annual service with impeller, etc. and they fitted the tach and the new depth finder for me at the same time. Wondering if they didn't set the # cyls like you suggested Mikey? If its set to 8 cyl that would probably mean its reading pretty low and might explain the low rpms I guess? When I get chance I will pull it and make sure its set correctly.

Re: Elevation change on prop selection?
 

Nice!! Glad the tach was an easy fix. I never got around to messing with it, obviously.
Have to admit, I'm envious of your GPH. I really don't know what I get but I can assure you going 25-30 (typically 2800 rpm range) I'm not getting anything close to 5! Something like 24GPH at WOT... Cruising is more enjoyable. Can't be in a hurry at the lake- there to relax!


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Re: Elevation change on prop selection?
 

Ouch!! 24GPH, I would be sucking fumes in less than a couple of hours.... :)

Mead is a big lake and our current favorite cove is about 20 miles from the ramps so cruising and a little towing/play is mostly what she does.

Yes I am very happy with her, you looked after her very well and she's a great boat. The shop said the engine was 'Sweet' after servicing her. Just have some little odds and ends to do as she's a 10yr old boat obviously. Tach and Depth Gauge were easy fixes. Had a new horn put in and an iffy breaker on the nav lights replaced.